METHODS AND SYSTEMS FOR PROCESSING POLYNUCLEOTIDES
The present disclosure provides methods, compositions and systems for processing polynucleotides from or within individual cells or cell populations. The processing of polynucleotides from or within individual cells or cell populations may be performed by partitioning the individual cells or cell populations with processing reagents for accessing cellular contents, and for uniquely identifying the polynucleotides of a given cell or cell population.
This application is a Continuation Application of U.S. patent application Ser. No. 15/825,740, filed Nov. 29, 2017, which is a Continuation Application of International patent Application PCT/US2017/057269, filed Oct. 18, 2017, which claims the benefit of U.S. Provisional Patent Application No. 62/410,326, filed Oct. 19, 2016, and U.S. Provisional Patent Application No. 62/490,546, filed Apr. 26, 2017, each of which is incorporated herein by reference in its entirety for all purposes.
SEQUENCE LISTINGThe instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 19, 2021, is named 43487-745.601 SL and is 44,144 bytes in size.
BACKGROUNDSignificant advances in analyzing and characterizing biological and biochemical materials and systems have led to unprecedented advances in understanding the mechanisms of life, health, disease and treatment. Among these advances, technologies that target and characterize the genomic make up of biological systems have yielded some of the most groundbreaking results, including advances in the use and exploitation of genetic amplification technologies, and nucleic acid sequencing technologies.
Nucleic acid sequencing can be used to obtain information in a wide variety of biomedical contexts, including diagnostics, prognostics, biotechnology, and forensic biology. Sequencing may involve methods including Maxam-Gilbert sequencing and chain-termination methods, or de novo sequencing methods including shotgun sequencing and bridge PCR, or next-generation methods including polony sequencing, 454 pyrosequencing, Illumina sequencing, SOLiD sequencing, Ion Torrent semiconductor sequencing, HeliScope single molecule sequencing, SMRT® sequencing, and others. Nucleic acid sequencing technologies, including next-generation DNA sequencing, have been useful for genomic and proteomic analysis of cell populations.
SUMMARYRecognized herein is the need for methods, compositions and systems for analyzing genomic and proteomic information from individual cells or a small population of cells. Such cells include, but are not limited to, cancer cells, fetal cells, and immune cells involved in immune responses. Provided herein are methods, compositions and systems for analyzing individual cells or a small population of cells, including the analysis and attribution of nucleic acids from and to these individual cells or cell populations.
In an aspect, the present disclosure provides a method for nucleic acid sequencing, comprising (a) providing a plurality of droplets, wherein a droplet of the plurality of droplets comprises (i) a ribonucleic acid (RNA) molecule comprising a nucleic acid sequence, and (ii) a bead comprising a nucleic acid barcode molecule coupled thereto, wherein the nucleic acid barcode molecule comprises a barcode sequence; (b) using the RNA molecule and the nucleic acid barcode molecule to generate a barcoded nucleic acid molecule comprising, from a 5′ end to a 3′ end, a sequence corresponding to the nucleic acid sequence of the RNA molecule and a complement of the barcode sequence; and (c) sequencing the barcoded nucleic acid molecule or a derivative thereof.
In some embodiments, the RNA molecule is from a cell. In some embodiments, the droplet comprises the cell. In some embodiments, the method further comprises releasing the RNA molecule from the cell prior to (b).
In some embodiments, the bead comprises a plurality of nucleic acid molecules coupled thereto, wherein the plurality of nucleic acid molecules comprises the nucleic acid barcode molecule.
In some embodiments, each of the plurality of nucleic acid molecules comprises the barcode sequence. In some embodiments, each of the plurality of nucleic acid molecules comprises an additional barcode sequence that varies across the plurality of nucleic acid molecules.
In some embodiments, the nucleic acid barcode molecule comprises a template switching sequence.
In some embodiments, the method further comprises, prior to (c), subjecting the barcoded nucleic acid molecule or derivative thereof to nucleic acid amplification. In some embodiments, the nucleic acid amplification is performed subsequent to releasing the barcoded nucleic acid molecule or derivative thereof from the droplet. In some embodiments, the nucleic acid amplification is polymerase chain reaction. In some embodiments, the RNA molecule is a messenger ribonucleic acid (mRNA) molecule.
In some embodiments, in (a) the droplet comprises (i) an additional nucleic acid molecule comprising an additional nucleic acid sequence, and (ii) an additional nucleic acid barcode molecule comprising an additional barcode sequence, and wherein in (b) the additional nucleic acid molecule and the additional nucleic acid barcode molecule are used to generate an additional barcoded nucleic acid molecule comprising, from a 5′ end to a 3′ end, the additional barcode sequence and an additional sequence corresponding to the additional nucleic acid sequence. In some embodiments, the additional nucleic acid barcode molecule is coupled to the bead. In some embodiments, the additional nucleic acid barcode molecule is coupled to an additional bead.
In some embodiments, (b) is performed in the droplet.
In some embodiments, the method further comprises releasing the barcoded nucleic acid molecule or a derivative thereof from the droplet.
In some embodiments, the barcoded nucleic acid molecule further comprises, towards a 3′ end, a functional sequence for permitting the barcoded nucleic acid molecule or a derivative thereof to couple to a flow cell of a sequencer.
In some embodiments, the sequence is a reverse complement of the nucleic acid sequence.
In some embodiments, the method further comprises, prior to (c), using the barcoded nucleic acid molecule or a derivative thereof and a pair of primers to generate a subset of nucleic acids having a target nucleic acid sequence. In some embodiments, the target nucleic acid sequence comprises a T cell receptor variable region sequence, a B cell receptor variable region sequence, or an immunoglobulin variable region sequence. In some embodiments, the at least one of the pair of primers hybridizes to a constant region of a T cell receptor nucleic acid sequence, a constant region of a B cell receptor nucleic acid sequence, or a constant region of an immunoglobulin nucleic acid sequence. In some embodiments, the subset of nucleic acids or derivatives thereof are sequenced in (c).
In some embodiments, the method further comprises releasing the nucleic acid barcode molecule from the bead. In some embodiments, the nucleic acid barcode molecule is released from the bead before the barcoded nucleic acid molecule is generated. In some embodiments, the nucleic acid barcode molecule is released from the bead while the barcoded nucleic acid molecule is generated. In some embodiments, the nucleic acid barcode molecule is released from the bead after the barcoded nucleic acid molecule is generated. In some embodiments, the bead is a gel bead.
In some embodiments, the barcode sequence is a combinatorial assembly of a plurality of barcode segments. In some embodiments, the plurality of barcode segments comprises at least three segments.
In an aspect, the present disclosure provides a method for generating a labeled polynucleotide. The method comprises (a) subjecting a reaction mixture to a first amplification reaction under conditions sufficient to generate a first amplification product, wherein the reaction mixture comprises a template polynucleotide and (i) a primer having a sequence towards a 3′ end that hybridizes to the template polynucleotide, and (ii) a template switching oligonucleotide that comprises a first predefined sequence towards a 5′ end; and (b) subjecting the first amplification product to a second amplification reaction in the presence of a barcoded oligonucleotide under conditions sufficient to generate a second amplification product, wherein the barcoded oligonucleotide comprises a sequence of at least a segment of the template switching oligonucleotide and at least a second predefined sequence, wherein (i) the second amplification reaction uses the first amplification product as a template and the barcoded oligonucleotide as a primer, or (ii) the second amplification reaction uses the barcoded oligonucleotide as a template and at least a portion of the first amplification product as a primer, to generate the second amplification product, wherein the first amplification reaction and the second amplification reaction are performed within a same reaction volume. In some embodiments, the second amplification reaction uses the first amplification product as a template and the barcoded oligonucleotide as a primer. In some embodiments, the second amplification reaction uses the barcoded oligonucleotide as a template and at least a portion of the first amplification product as a primer.
In an aspect, the present disclosure provides a method for generating a labeled polynucleotide comprising (a) providing a reaction mixture in a reaction volume, wherein the reaction mixture comprises (i) a template polynucleotide, (ii) a primer comprising a sequence towards a 3′ end of the primer that hybridizes to the template polynucleotide, and (iii) a template switching oligonucleotide; (b) in the reaction volume, subjecting the reaction mixture to a first reaction under conditions sufficient to generate a first nucleic acid product comprising the primer, a reverse complement of a sequence of the template polynucleotide, and a sequence complementary to at least a portion of the template switch oligonucleotide; and (c) subjecting the first nucleic acid product to a second reaction in the reaction volume, which second reaction comprises using (i) the first nucleic acid product as a template and a barcoded oligonucleotide as a primer, which barcoded oligonucleotide comprises a sequence of at least a segment of the template switching oligonucleotide, or (ii) the barcoded oligonucleotide as a template and at least a portion of the first nucleic acid as a primer, to generate a second nucleic acid product.
In some embodiments, the template polynucleotide is obtained from a single cell. In some embodiments, the single cell is an immune cell. In some embodiments, the immune cell is a T-cell. In some embodiments, the immune cell is a B-cell. In some embodiments, the method further comprises lysing the single cell in the same reaction volume to obtain the template polynucleotide prior to generating the first amplification product in the first amplification reaction.
In some embodiments, the template polynucleotide comprises a T-cell receptor gene or gene product. In some embodiments, the template polynucleotide comprises a B-cell receptor gene or gene product. In some embodiments, the template polynucleotide is among a plurality of template polynucleotides.
In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least two times that of a concentration of the barcoded oligonucleotide in the same reaction volume. In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least five times that of a concentration of the barcoded oligonucleotide in the same reaction volume. In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least ten times that of a concentration of the barcoded oligonucleotide in the same reaction volume. In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least twenty times that of a concentration of the barcoded oligonucleotide in the same reaction volume. In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least fifty times that of a concentration of the barcoded oligonucleotide in the same reaction volume. In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least one hundred times that of a concentration of the barcoded oligonucleotide in the same reaction volume. In some embodiments, a concentration of the template switching oligonucleotide in the same reaction volume is at least two hundred times that of a concentration of the barcoded oligonucleotide in the same reaction volume.
In some embodiments, the primer comprises a sequence towards a 5′ end that does not specifically hybridize to the template polynucleotide.
In some embodiments, the first amplification reaction is facilitated using an enzyme comprising polymerase activity. In some embodiments, the enzyme is a DNA-dependent polymerase. In some embodiments, the enzyme is a reverse transcriptase.
In some embodiments, the second amplification reaction is facilitated using an enzyme comprising polymerase activity. In some embodiments, the enzyme is a DNA-dependent polymerase.
In some embodiments, the first amplification reaction comprises polymerase chain reaction. In some embodiments, the first amplification reaction comprises reverse transcription. In some embodiments, the second amplification reaction comprises polymerase chain reaction.
In some embodiments, the first amplification reaction and the second amplification reaction are performed sequentially in the absence of an intervening purification step.
In some embodiments, the template switching oligonucleotide is not available for primer extension during the second amplification reaction.
In some embodiments, the method further comprises degrading the template switching oligonucleotide prior to the second amplification reaction. In some embodiments, the template switching oligonucleotide comprises ribonucleic acids (RNA). In some embodiments, the template switching oligonucleotide comprises at least 10% ribonucleic acids (RNA).
In some embodiments, the method further comprises degrading the template switching oligonucleotide during the second amplification reaction. In some embodiments, the template switching oligonucleotide comprises ribonucleic acids (RNA). In some embodiments, the template switching oligonucleotide comprises at least 10% ribonucleic acids (RNA).
In some embodiments, a first reaction rate of the second amplification reaction using the barcoded oligonucleotide is greater than a second reaction rate of the second amplification using the template switching oligonucleotide.
In some embodiments, the first amplification product and the barcoded oligonucleotide has a higher melting temperature as compared to a melting temperature of the first amplification product and the template switching oligonucleotide. In some embodiments, a primer annealing temperature of the second amplification reaction is at least 0.5° C. greater than a primer annealing temperature of the first amplification reaction.
In some embodiments, the template switching oligonucleotide comprises modified nucleotides. In some embodiments, the template switching oligonucleotide comprises at least 10% modified nucleotides. In some embodiments, the template switching oligonucleotide comprises modified nucleotides selected from unlocked nucleic acids (UNAs), locked nucleic acids (LNAs), and 5-hydroxybutynl-2′-deoxyuridine.
In some embodiments, the barcoded oligonucleotide comprises modified nucleotides. In some embodiments, the barcoded oligonucleotide comprises at least 10% modified nucleotides. In some embodiments, the barcoded oligonucleotide comprises modified nucleotides selected from locked nucleic acids (LNAs), unlocked nucleic acids (UNAs), and 5-hydroxybutynl-2′-deoxyuridine.
In some embodiments, the same reaction volume comprises an emulsion, a droplet, or a microwell.
In some embodiments, the first defined sequence comprises at least one of an adaptor sequence, a barcode sequence, a unique molecular identifier sequence, a primer binding site, and a sequencing primer binding site. In some embodiments, the second defined sequence comprises at least one of an adaptor sequence, a barcode sequence, a unique molecular identifier sequence, a primer binding site, and a sequencing primer binding site.
In some embodiments, the primer is among a plurality of primers. In some embodiments, the sequence towards the 3′ end of the primer comprises a random sequence. In some embodiments, the sequence towards the 3′ end of the primer comprises a gene specific sequence. In some embodiments, the sequence towards the 3′ end of the primer comprises a polyA sequence.
In some embodiments, the template switching oligonucleotide is among a plurality of template switching oligonucleotides. In some embodiments, the barcoded oligonucleotide is among a plurality of barcoded oligonucleotides.
In some embodiments, the method further comprises subjecting the second amplification product to sequencing.
In some embodiments, the barcoded oligonucleotide is releasably coupled to a microcapsule. In some embodiments, the method further comprises releasing the barcoded oligonucleotide from the microcapsule. In some embodiments, the barcoded oligonucleotide is released from the microcapsule upon application of a stimulus. In some embodiments, the stimulus is at least one of a biological stimulus, a chemical stimulus, a thermal stimulus, an electrical stimulus, a magnetic stimulus, a photo stimulus, or any combination thereof. In some embodiments, the microcapsule is a degradable microcapsule and releasing the barcoded oligonucleotide comprises degrading the microcapsule. In some embodiments, the microcapsule comprises a polymer gel. In some embodiments, the polymer gel is a polyacrylamide. In some embodiments, the microcapsule comprises a bead. In some embodiments, the bead is a gel bead. In some embodiments, the microcapsule comprises a chemical cross-linker. In some embodiments, the chemical cross-linker is a disulfide bond.
In an aspect, the present disclosure provides a method comprising (a) providing a reaction volume comprising (i) a cell or cell derivative, and (ii) a bead comprising a barcoded oligonucleotide releasably coupled thereto, wherein the barcoded oligonucleotide is a template switching oligonucleotide; and (b) releasing the barcoded oligonucleotide from the bead to provide the barcoded oligonucleotide in the reaction volume at a concentration of at least about 0.20 μM; and (c) subjecting the reaction volume to an amplification reaction to generate an amplification product, wherein during the amplification reaction, the reaction volume comprises a template polynucleotide from the cell or cell derivative, the barcoded oligonucleotide and a primer having a sequence towards a 3′ end that hybridizes to the template polynucleotide, and wherein the amplification product has sequence complementarity with the template polynucleotide and the barcoded oligonucleotide.
In an aspect, the present disclosure provides a method comprising (a) providing a reaction volume comprising a cell and a microcapsule comprising a barcoded oligonucleotide releasably coupled thereto, wherein the barcoded oligonucleotide is a template switching oligonucleotide; and (b) subjecting the reaction volume to dissociation conditions sufficient to release the barcoded oligonucleotide from the microcapsule, thereby providing the barcoded oligonucleotide in the reaction volume at a concentration of at least about 0.20 uM; and (c) subjecting the reaction volume to an amplification reaction to generate an amplification product, wherein during the amplification reaction, the reaction volume comprises a template polynucleotide from the cell, the barcoded oligonucleotide and a primer having a sequence towards a 3′ end that hybridizes to the template polynucleotide, and wherein the amplification product has sequence complementarity with the template polynucleotide and the barcoded oligonucleotide.
In some embodiments, the method further comprises subjecting the amplification product to sequencing. In some embodiments, the barcoded oligonucleotide does not hybridize to the template polynucleotide. In some embodiments, the template polynucleotide is an mRNA molecule. In some embodiments, the method further comprises subjecting the reaction volume to a second amplification reaction to generate an additional amplification product using the amplification product as a template.
In some embodiments, the method further comprises subjecting the additional amplification product to sequencing.
In some embodiments, the cell is a mammalian cell. In some embodiments, the cell is an immune cell. In some embodiments, the immune cell is a B-cell. In some embodiments, the immune cell is a T-cell. In some embodiments, the cell is cancer cell. In some embodiments, the cancer cell is obtained from a tissue sample. In some embodiments, the cancer cell is obtained from a biological fluid. In some embodiments, the biological fluid comprises blood. In some embodiments, the biological fluid comprises lymph fluid.
In some embodiments, the template polynucleotide comprises a T cell receptor gene sequence, a B cell receptor gene sequence, or an immunoglobulin gene sequence. In some embodiments, the template polynucleotide is a T cell receptor mRNA molecule, a B cell receptor mRNA molecule, or an immunoglobulin mRNA molecule.
In some embodiments, the reaction volume further comprises an enzyme. In some embodiments, the enzyme is a DNA polymerase. In some embodiments, the enzyme is a reverse transcriptase.
In some embodiments, the reaction volume further comprises at least one reagent for nucleic acid amplification. In some embodiments, the at least one reagent comprises dNTPs. In some embodiments, the at least one reagent comprises oligonucleotide primers.
In some embodiments, the microcapsule comprises a polymer gel. In some embodiments, the polymer gel is a polyacrylamide. In some embodiments, the microcapsule comprises a bead. In some embodiments, the bead is a gel bead. In some embodiments, the microcapsule comprises a chemical cross-linker. In some embodiments, the chemical cross-linker is a disulfide bond. In some embodiments, the dissociation condition is at least one of a biological stimulus, a chemical stimulus, a thermal stimulus, an electrical stimulus, a magnetic stimulus, a photo stimulus, or any combination thereof.
In some embodiments, the barcoded oligonucleotide comprises at least one of an adaptor sequence, a barcode sequence, unique molecular identifier sequence, a primer binding site, and a sequencing primer binding site.
In some embodiments, the same reaction volume comprises an emulsion, a droplet, or a microwell.
In some embodiments, the method further comprises performing a third reaction, wherein the third reaction specifically amplifies variable region cDNAs, wherein the variable region cDNA are derived from a T cell receptor cDNA, a B cell receptor cDNA, or an immunoglobulin cDNA. In some embodiments, the third reaction comprises use of a primer that specifically binds in the constant region of the T cell receptor cDNA, B cell receptor cDNA, or immunoglobulin cDNA, and extends through the variable region of the T cell receptor cDNA, B cell receptor cDNA, or immunoglobulin cDNA. In some embodiments, the third reaction results in an enrichment product that comprises at (a) least one of a T cell receptor variable region sequence, a B cell receptor variable region sequence, and an immunoglobulin variable region sequence, and (b) at least one of an adaptor sequence, a barcode sequence, a unique molecular identifier sequence, a primer binding site, and a sequencing primer binding site. In some embodiments, greater than about 25% of reads in a subsequent short-read sequencing reaction map to a T cell receptor, a B cell receptor, or an immunoglobulin gene.
In an aspect, the present disclosure provides a non-transitory computer-readable medium comprising machine-executable code that, upon execution by one of more computer processors, implements a method for nucleic acid sequencing, comprising (a) providing a plurality of droplets, wherein a droplet of the plurality of droplets comprises (i) a ribonucleic acid (RNA) molecule comprising a nucleic acid sequence, and (ii) a bead comprising a nucleic acid barcode molecule coupled thereto, wherein the nucleic acid barcode molecule comprises a barcode sequence; (b) using the RNA molecule and the nucleic acid barcode molecule to generate a barcoded nucleic acid molecule comprising, from a 5′ end to a 3′ end, a sequence corresponding to the nucleic acid sequence of the RNA molecule and a complement of the barcode sequence; and (c) sequencing the barcoded nucleic acid molecule or a derivative thereof.
In an aspect, the present disclosure provides a non-transitory computer-readable medium comprising machine-executable code that, upon execution by one of more computer processors, implements a method for generating a labeled polynucleotide, the method comprising (a) subjecting a reaction mixture to a first reaction under conditions sufficient to generate a first nucleic acid product, wherein the reaction mixture comprises (i) a template polynucleotide, (ii) a primer having a sequence towards a 3′ end that hybridizes to the template polynucleotide, and (iii) a template switching oligonucleotide, wherein the first nucleic acid product comprises the primer, a reverse complement of a sequence of the template polynucleotide, and a sequence complementary to at least a portion of the template switch oligonucleotide; and (b) subjecting the first nucleic acid product to a second reaction in the presence of a barcoded oligonucleotide under conditions sufficient to generate a second nucleic acid product, wherein the barcoded oligonucleotide comprises a sequence of at least a segment of the template switching oligonucleotide, wherein (i) the second reaction uses the first nucleic acid as a template and the barcoded oligonucleotide as a primer, or (ii) the second reaction uses the barcoded oligonucleotide as a template and at least a portion of the first nucleic acid as a primer, to generate the second nucleic acid product, wherein the first reaction and the second reaction are performed within a same reaction volume.
In an aspect, the present disclosure provides a non-transitory computer-readable medium comprising machine-executable code that, upon execution by one of more computer processors, implements a method for generating a labeled polynucleotide. The method comprises (a) subjecting a reaction mixture to a first amplification reaction under conditions sufficient to generate a first amplification product, wherein the reaction mixture comprises a template polynucleotide and (i) a primer having a sequence towards a 3′ end that hybridizes to the template polynucleotide, and (ii) a template switching oligonucleotide that comprises a first predefined sequence towards a 5′ end; and (b) subjecting the first amplification product to a second amplification reaction in the presence of a barcoded oligonucleotide under conditions sufficient to generate a second amplification product, wherein the barcoded oligonucleotide comprises a sequence of at least a segment of the template switching oligonucleotide and at least a second predefined sequence, wherein (i) the second amplification reaction uses the first amplification product as a template and the barcoded oligonucleotide as a primer, or (ii) the second amplification reaction uses the barcoded oligonucleotide as a template and at least a portion of the first amplification product as a primer, to generate the second amplification product, wherein the first amplification reaction and the second amplification reaction are performed within a same reaction volume.
Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only illustrative embodiments of the present disclosure are shown and described. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
INCORPORATION BY REFERENCEAll publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.
The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings (also “Figure” and “FIG.” herein), of which:
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- (B) after enrichment, and (C) after sequencing library preparation.
While various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.
Where values are described as ranges, it will be understood that such disclosure includes the disclosure of all possible sub-ranges within such ranges, as well as specific numerical values that fall within such ranges irrespective of whether a specific numerical value or specific sub-range is expressly stated.
The term “barcode,” as used herein, generally refers to a label, or identifier, that can be part of an analyte to convey information about the analyte. A barcode can be a tag attached to an analyte (e.g., nucleic acid molecule) or a combination of the tag in addition to an endogenous characteristic of the analyte (e.g., size of the analyte or end sequence(s)). The barcode may be unique. Barcodes can have a variety of different formats, for example, barcodes can include: polynucleotide barcodes; random nucleic acid and/or amino acid sequences; and synthetic nucleic acid and/or amino acid sequences. A barcode can be attached to an analyte in a reversible or irreversible manner. The barcode can be added to, for example, a fragment of a deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) sample before, during, and/or after sequencing of the sample. Barcodes can allow for identification and/or quantification of individual sequencing-reads in real time. In some examples, the barcode is generated in a combinatorial manner. Barcodes that may be used with methods, devices and systems of the present disclosure, including methods for forming such barcodes, are described in, for example, U.S. Patent Pub. No. 2014/0378350, which is entirely incorporated herein by reference.
The term “subject,” as used herein, generally refers to an animal, such as a mammalian species (e.g., human) or avian (e.g., bird) species, or other organism, such as a plant. The subject can be a vertebrate, a mammal, a mouse, a primate, a simian or a human. Animals may include, but are not limited to, farm animals, sport animals, and pets. A subject can be a healthy individual, an individual that has or is suspected of having a disease or a pre-disposition to the disease, or an individual that is in need of therapy or suspected of needing therapy. A subject can be a patient.
The term “genome,” as used herein, generally refers to an entirety of a subject's hereditary information. A genome can be encoded either in DNA or in RNA. A genome can comprise coding regions that code for proteins as well as non-coding regions. A genome can include the sequence of all chromosomes together in an organism. For example, the human genome has a total of 46 chromosomes. The sequence of all of these together may constitute a human genome.
The terms “adaptor(s)”, “adapter(s)” and “tag(s)” may be used synonymously. An adaptor or tag can be coupled to a polynucleotide sequence to be “tagged” by any approach including ligation, hybridization, or other approaches.
The term “sequencing,” as used herein, generally refers to methods and technologies for determining the sequence of nucleotide bases in one or more polynucleotides. The polynucleotides can be, for example, deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), including variants or derivatives thereof (e.g., single stranded DNA). Sequencing can be performed by various systems currently available, such as, with limitation, a sequencing system by Illumina, Pacific Biosciences, Oxford Nanopore, or Life Technologies (Ion Torrent). Such devices may provide a plurality of raw genetic data corresponding to the genetic information of a subject (e.g., human), as generated by the device from a sample provided by the subject. In some situations, systems and methods provided herein may be used with proteomic information.
The term “variant,” as used herein, generally refers to a genetic variant, such as a nucleic acid molecule comprising a polymorphism. A variant can be a structural variant or copy number variant, which can be genomic variants that are larger than single nucleotide variants or short indels. A variant can be an alteration or polymorphism in a nucleic acid sample or genome of a subject. Single nucleotide polymorphisms (SNPs) are a form of polymorphisms. Polymorphisms can include single nucleotide variations (SNVs), insertions, deletions, repeats, small insertions, small deletions, small repeats, structural variant junctions, variable length tandem repeats, and/or flanking sequences. Copy number variants (CNVs), transversions and other rearrangements are also forms of genetic variation. A genomic alternation may be a base change, insertion, deletion, repeat, copy number variation, or transversion.
The term “bead,” as used herein, generally refers to a particle. The bead may be a solid or semi-solid particle. The bead may be a gel. The bead may be formed of a polymeric material. The bead may be magnetic or non-magnetic.
The term “sample,” as used herein, generally refers to a biological sample of a subject. The sample may be a tissue sample, such as a biopsy, core biopsy, needle aspirate, or fine needle aspirate. The sample may be a fluid sample, such as a blood sample, urine sample, or saliva sample. The sample may be a skin sample. The sample may be a cheek swap. The sample may be a plasma or serum sample. The sample may be a cell-free or cell free sample. A cell-free sample may include extracellular polynucleotides. Extracellular polynucleotides may be isolated from a bodily sample that may be selected from a group consisting of blood, plasma, serum, urine, saliva, mucosal excretions, sputum, stool and tears.
The term “primer,” as used herein generally refers to a strand of RNA or DNA that serves as a starting point for nucleic acid (e.g., DNA) synthesis. A primer may be used in a primer extension reaction, which may be a nucleic acid amplification reaction, such as, for example, polymerase chain reaction (PCR) or reverse transcription PCR (RT-PCR). The primer may have a sequence that is capable of coupling to a nucleic acid molecule. Such sequence may be complementary to the nucleic acid molecule, such as a poly-T sequence or a predetermined sequence, or a sequence that is otherwise capable of coupling (e.g., hybridizing) to the nucleic acid molecule, such as a universal primer.
Nucleic acid sequencing technologies have yielded substantial results in sequencing biological materials, including providing substantial sequence information on individual organisms, and relatively pure biological samples. However, these systems have traditionally not been effective at being able to identify and characterize cells at the single cell level.
Many nucleic acid sequencing technologies derive the nucleic acids that they sequence from collections of cells obtained from tissue or other samples, such as biological fluids (e.g., blood, plasma, etc). The cells can be processed (e.g., all together) to extract the genetic material that represents an average of the population of cells, which can then be processed into sequencing ready DNA libraries that are configured for a given sequencing technology. Although often discussed in terms of DNA or nucleic acids, the nucleic acids derived from the cells may include DNA, or RNA, including, e.g., mRNA, total RNA, or the like, that may be processed to produce complementary DNA (cDNA) for sequencing. Following processing, absent a cell specific marker, attribution of genetic material as being contributed by a subset of cells or an individual cell may not be possible in such an ensemble approach.
In addition to the inability to attribute characteristics to particular subsets of cells or individual cells, such ensemble sample preparation methods can be, from the outset, predisposed to primarily identifying and characterizing the majority constituents in the sample of cells, and may not be designed to pick out the minority constituents, e.g., genetic material contributed by one cell, a few cells, or a small percentage of total cells in the sample. Likewise, where analyzing expression levels, e.g., of mRNA, an ensemble approach can be predisposed to presenting potentially inaccurate data from cell populations that are non-homogeneous in terms of expression levels. In some cases, where expression is high in a small minority of the cells in an analyzed population, and absent in the majority of the cells of the population, an ensemble method may indicate low level expression for the entire population.
These inaccuracies can be further magnified through processing operations used in generating the sequencing libraries from these samples. In particular, many next generation sequencing technologies (e.g., massively parallel sequencing) may rely upon the geometric amplification of nucleic acid fragments, such as via polymerase chain reaction, in order to produce sufficient DNA for the sequencing library. However, such amplification can be biased toward amplification of majority constituents in a sample, and may not preserve the starting ratios of such minority and majority components. While some of these difficulties may be addressed by utilizing different sequencing systems, such as single molecule systems that do not require amplification, the single molecule systems, as well as the ensemble sequencing methods of other next generation sequencing systems, can also have large input DNA requirements. Some single molecule sequencing systems, for example, can have sample input DNA requirements of from 500 nanograms (ng) to upwards of 10 micrograms (μg), which may not be obtainable from individual cells or even small subpopulations of cells. Likewise, other NGS systems can be optimized for starting amounts of sample DNA in the sample of from approximately 50 ng to about 1 μg.
Disclosed herein are methods and systems for characterizing nucleic acids from small populations of cells, and in some cases, for characterizing nucleic acids from individual cells. The methods described herein may compartmentalize the analysis of individual cells or small populations of cells, including e.g., nucleic acids from individual cells or small groups of cells, and then allow that analysis to be attributed back to the individual cell or small group of cells from which the nucleic acids were derived. This can be accomplished regardless of whether the cell population represents a 50/50 mix of cell types, a 90/10 mix of cell types, or virtually any ratio of cell types, as well as a complete heterogeneous mix of different cell types, or any mixture between these. Differing cell types may include cells from different tissue types of an individual or the same tissue type from different individuals, or biological organisms such as microorganisms from differing genera, species, strains, variants, or any combination of any or all of the foregoing. For example, differing cell types may include normal and tumor tissue from an individual, various cell types obtained from a human subject such as a variety of immune cells (e.g., B cells, T cells, and the like), multiple different bacterial species, strains and/or variants from environmental, forensic, microbiome or other samples, or any of a variety of other mixtures of cell types.
Methods and systems described herein may provide for the compartmentalization, depositing or partitioning of the nucleic acid contents of individual cells from a sample material containing cells, into discrete compartments or partitions (referred to interchangeably herein as partitions), where each partition maintains separation of its own contents from the contents of other partitions. In some examples, a partition is a droplet or well. Unique identifiers, e.g., barcodes, may be previously, subsequently or concurrently delivered to the partitions that hold the compartmentalized or partitioned cells or cellular derivatives, in order to allow for the later attribution of the characteristics of the individual cells to the particular compartment. Barcodes may be delivered, for example in an oligonucleotide to a partition via any suitable mechanism, such as using beads (e.g., gel beads). In some examples, cellular derivatives, such as cells or constituents of such cells in matrix (e.g., gel or polymeric matrix), are compartmentalized or partitioned in partitions (e.g., droplets or wells).
In some embodiments, barcoded oligonucleotides are delivered to a partition via a microcapsule. In some cases, barcoded oligonucleotides are initially associated with the microcapsule and then released from the microcapsule upon application of a stimulus which allows the oligonucleotides to dissociate or to be released from the microcapsule.
A microcapsule, in some embodiments, comprises a bead. In some embodiments, a bead may be porous, non-porous, solid, semi-solid, semi-fluidic, or fluidic. In some embodiments, a bead may be dissolvable, disruptable, or degradable. In some cases, a bead may not be degradable. In some embodiments, the bead may be a gel bead. A gel bead may be a hydrogel bead. A gel bead may be formed from molecular precursors, such as a polymeric or monomeric species. A semi-solid bead may be a liposomal bead. Solid beads may comprise metals including iron oxide, gold, and silver. In some cases, the beads are silica beads. In some cases, the beads are rigid. In some cases, the beads may be flexible and/or compressible.
In some embodiments, the bead may contain molecular precursors (e.g., monomers or polymers), which may form a polymer network via polymerization of the precursors. In some cases, a precursor may be an already polymerized species capable of undergoing further polymerization via, for example, a chemical cross-linkage. In some cases, a precursor comprises one or more of an acrylamide or a methacrylamide monomer, oligomer, or polymer. In some cases, the bead may comprise prepolymers, which are oligomers capable of further polymerization. For example, polyurethane beads may be prepared using prepolymers. In some cases, the bead may contain individual polymers that may be further polymerized together. In some cases, beads may be generated via polymerization of different precursors, such that they comprise mixed polymers, co-polymers, and/or block co-polymers.
A bead may comprise natural and/or synthetic materials. For example, a polymer can be a natural polymer or a synthetic polymer. In some cases, a bead comprises both natural and synthetic polymers. Examples of natural polymers include proteins and sugars such as deoxyribonucleic acid, rubber, cellulose, starch (e.g., amylose, amylopectin), proteins, enzymes, polysaccharides, silks, polyhydroxyalkanoates, chitosan, dextran, collagen, carrageenan, ispaghula, acacia, agar, gelatin, shellac, sterculia gum, xanthan gum, Corn sugar gum, guar gum, gum karaya, agarose, alginic acid, alginate, or natural polymers thereof. Examples of synthetic polymers include acrylics, nylons, silicones, spandex, viscose rayon, polycarboxylic acids, polyvinyl acetate, polyacrylamide, polyacrylate, polyethylene glycol, polyurethanes, polylactic acid, silica, polystyrene, polyacrylonitrile, polybutadiene, polycarbonate, polyethylene, polyethylene terephthalate, poly(chlorotrifluoroethylene), poly(ethylene oxide), poly(ethylene terephthalate), polyethylene, polyisobutylene, poly(methyl methacrylate), poly(oxymethylene), polyformaldehyde, polypropylene, polystyrene, poly(tetrafluoroethylene), poly(vinyl acetate), poly(vinyl alcohol), poly(vinyl chloride), poly(vinylidene dichloride), poly(vinylidene difluoride), poly(vinyl fluoride) and combinations (e.g., co-polymers) thereof. Beads may also be formed from materials other than polymers, including lipids, micelles, ceramics, glass-ceramics, material composites, metals, other inorganic materials, and others.
In some cases, a chemical cross-linker may be a precursor used to cross-link monomers during polymerization of the monomers and/or may be used to attach oligonucleotides (e.g., barcoded oligonucleotides) to the bead. In some cases, polymers may be further polymerized with a cross-linker species or other type of monomer to generate a further polymeric network. Non-limiting examples of chemical cross-linkers (also referred to as a “crosslinker” or a “crosslinker agent” herein) include cystamine, gluteraldehyde, dimethyl suberimidate, N-Hydroxysuccinimide crosslinker BS3, formaldehyde, carbodiimide (EDC), SMCC, Sulfo-SMCC, vinylsilane, N,N′diallyltartardiamide (DATD), N,N′-Bis(acryloyl)cystamine (BAC), or homologs thereof. In some cases, the crosslinker used in the present disclosure contains cystamine.
Crosslinking may be permanent or reversible, depending upon the particular crosslinker used. Reversible crosslinking may allow for the polymer to linearize or dissociate under appropriate conditions. In some cases, reversible cross-linking may also allow for reversible attachment of a material bound to the surface of a bead. In some cases, a cross-linker may form disulfide linkages. In some cases, the chemical cross-linker forming disulfide linkages may be cystamine or a modified cystamine.
In some embodiments, disulfide linkages can be formed between molecular precursor units (e.g., monomers, oligomers, or linear polymers) or precursors incorporated into a bead and oligonucleotides. Cystamine (including modified cystamines), for example, is an organic agent comprising a disulfide bond that may be used as a crosslinker agent between individual monomeric or polymeric precursors of a bead. Polyacrylamide may be polymerized in the presence of cystamine or a species comprising cystamine (e.g., a modified cystamine) to generate polyacrylamide gel beads comprising disulfide linkages (e.g., chemically degradable beads comprising chemically-reducible cross-linkers). The disulfide linkages may permit the bead to be degraded (or dissolved) upon exposure of the bead to a reducing agent.
In some embodiments, chitosan, a linear polysaccharide polymer, may be crosslinked with glutaraldehyde via hydrophilic chains to form a bead. Crosslinking of chitosan polymers may be achieved by chemical reactions that are initiated by heat, pressure, change in pH, and/or radiation.
In some embodiments, the bead may comprise covalent or ionic bonds between polymeric precursors (e.g., monomers, oligomers, linear polymers), oligonucleotides, primers, and other entities. In some cases, the covalent bonds comprise carbon-carbon bonds or thioether bonds.
In some cases, a bead may comprise an acrydite moiety, which in certain aspects may be used to attach one or more oligonucleotides (e.g., barcode sequence, barcoded oligonucleotide, primer, or other oligonucleotide) to the bead. In some cases, an acrydite moiety can refer to an acrydite analogue generated from the reaction of acrydite with one or more species, such as, the reaction of acrydite with other monomers and cross-linkers during a polymerization reaction. Acrydite moieties may be modified to form chemical bonds with a species to be attached, such as an oligonucleotide (e.g., barcode sequence, barcoded oligonucleotide, primer, or other oligonucleotide). Acrydite moieties may be modified with thiol groups capable of forming a disulfide bond or may be modified with groups already comprising a disulfide bond. The thiol or disulfide (via disulfide exchange) may be used as an anchor point for a species to be attached or another part of the acrydite moiety may be used for attachment. In some cases, attachment is reversible, such that when the disulfide bond is broken (e.g., in the presence of a reducing agent), the attached species is released from the bead. In other cases, an acrydite moiety comprises a reactive hydroxyl group that may be used for attachment.
Functionalization of beads for attachment of oligonucleotides may be achieved through a wide range of different approaches, including activation of chemical groups within a polymer, incorporation of active or activatable functional groups in the polymer structure, or attachment at the pre-polymer or monomer stage in bead production.
For example, precursors (e.g., monomers, cross-linkers) that are polymerized to form a bead may comprise acrydite moieties, such that when a bead is generated, the bead also comprises acrydite moieties. The acrydite moieties can be attached to an oligonucleotide, such as a primer (e.g., a primer for amplifying target nucleic acids, barcoded oligonucleotide, etc) that is desired to be incorporated into the bead. In some cases, the primer comprises a P5 sequence for attachment to a sequencing flow cell for Illumina sequencing. In some cases, the primer comprises a P7 sequence for attachment to a sequencing flow cell for Illumina sequencing. In some cases, the primer comprises a barcode sequence. In some cases, the primer further comprises a unique molecular identifier (UMI). In some cases, the primer comprises an R1 primer sequence for Illumina sequencing. In some cases, the primer comprises an R2 primer sequence for Illumina sequencing.
In some cases, precursors comprising a functional group that is reactive or capable of being activated such that it becomes reactive can be polymerized with other precursors to generate gel beads comprising the activated or activatable functional group. The functional group may then be used to attach additional species (e.g., disulfide linkers, primers, other oligonucleotides, etc.) to the gel beads. For example, some precursors comprising a carboxylic acid (COOH) group can co-polymerize with other precursors to form a gel bead that also comprises a COOH functional group. In some cases, acrylic acid (a species comprising free COOH groups), acrylamide, and bis(acryloyl)cystamine can be co-polymerized together to generate a gel bead comprising free COOH groups. The COOH groups of the gel bead can be activated (e.g., via 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-Hydroxysuccinimide (NHS) or 4-(4,6-Dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM)) such that they are reactive (e.g., reactive to amine functional groups where EDC/NHS or DMTMM are used for activation). The activated COOH groups can then react with an appropriate species (e.g., a species comprising an amine functional group where the carboxylic acid groups are activated to be reactive with an amine functional group) comprising a moiety to be linked to the bead.
Beads comprising disulfide linkages in their polymeric network may be functionalized with additional species via reduction of some of the disulfide linkages to free thiols. The disulfide linkages may be reduced via, for example, the action of a reducing agent (e.g., DTT, TCEP, etc.) to generate free thiol groups, without dissolution of the bead. Free thiols of the beads can then react with free thiols of a species or a species comprising another disulfide bond (e.g., via thiol-disulfide exchange) such that the species can be linked to the beads (e.g., via a generated disulfide bond). In some cases, free thiols of the beads may react with any other suitable group. For example, free thiols of the beads may react with species comprising an acrydite moiety. The free thiol groups of the beads can react with the acrydite via Michael addition chemistry, such that the species comprising the acrydite is linked to the bead. In some cases, uncontrolled reactions can be prevented by inclusion of a thiol capping agent such as N-ethylmalieamide or iodoacetate.
Activation of disulfide linkages within a bead can be controlled such that only a small number of disulfide linkages are activated. Control may be exerted, for example, by controlling the concentration of a reducing agent used to generate free thiol groups and/or concentration of reagents used to form disulfide bonds in bead polymerization. In some cases, a low concentration (e.g., molecules of reducing agent: gel bead ratios of less than about 10,000; 100,000; 1,000,000; 10,000,000; 100,000,000; 1,000,000,000; 10,000,000,000; or 100,000,000,000) of reducing agent may be used for reduction. Controlling the number of disulfide linkages that are reduced to free thiols may be useful in ensuring bead structural integrity during functionalization. In some cases, optically-active agents, such as fluorescent dyes may be may be coupled to beads via free thiol groups of the beads and used to quantify the number of free thiols present in a bead and/or track a bead.
In some cases, addition of moieties to a gel bead after gel bead formation may be advantageous. For example, addition of an oligonucleotide (e.g., barcoded oligonucleotide) after gel bead formation may avoid loss of the species during chain transfer termination that can occur during polymerization. Moreover, smaller precursors (e.g., monomers or cross linkers that do not comprise side chain groups and linked moieties) may be used for polymerization and can be minimally hindered from growing chain ends due to viscous effects. In some cases, functionalization after gel bead synthesis can minimize exposure of species (e.g., oligonucleotides) to be loaded with potentially damaging agents (e.g., free radicals) and/or chemical environments. In some cases, the generated gel may possess an upper critical solution temperature (UCST) that can permit temperature driven swelling and collapse of a bead. Such functionality may aid in oligonucleotide (e.g., a primer) infiltration into the bead during subsequent functionalization of the bead with the oligonucleotide. Post-production functionalization may also be useful in controlling loading ratios of species in beads, such that, for example, the variability in loading ratio is minimized. Species loading may also be performed in a batch process such that a plurality of beads can be functionalized with the species in a single batch.
In some cases, an acrydite moiety linked to precursor, another species linked to a precursor, or a precursor itself comprises a labile bond, such as chemically, thermally, or photo-sensitive bonds e.g., disulfide bonds, UV sensitive bonds, or the like. Once acrydite moieties or other moieties comprising a labile bond are incorporated into a bead, the bead may also comprise the labile bond. The labile bond may be, for example, useful in reversibly linking (e.g., covalently linking) species (e.g., barcodes, primers, etc.) to a bead. In some cases, a thermally labile bond may include a nucleic acid hybridization based attachment, e.g., where an oligonucleotide is hybridized to a complementary sequence that is attached to the bead, such that thermal melting of the hybrid releases the oligonucleotide, e.g., a barcode containing sequence, from the bead or microcapsule.
The addition of multiple types of labile bonds to a gel bead may result in the generation of a bead capable of responding to varied stimuli. Each type of labile bond may be sensitive to an associated stimulus (e.g., chemical stimulus, light, temperature, etc.) such that release of species attached to a bead via each labile bond may be controlled by the application of the appropriate stimulus. Such functionality may be useful in controlled release of species from a gel bead. In some cases, another species comprising a labile bond may be linked to a gel bead after gel bead formation via, for example, an activated functional group of the gel bead as described above. As will be appreciated, barcodes that are releasably, cleavably or reversibly attached to the beads described herein include barcodes that are released or releasable through cleavage of a linkage between the barcode molecule and the bead, or that are released through degradation of the underlying bead itself, allowing the barcodes to be accessed or accessible by other reagents, or both.
The barcodes that are releasable as described herein may sometimes be referred to as being activatable, in that they are available for reaction once released. Thus, for example, an activatable barcode may be activated by releasing the barcode from a bead (or other suitable type of partition described herein). Other activatable configurations are also envisioned in the context of the described methods and systems.
In addition to thermally cleavable bonds, disulfide bonds and UV sensitive bonds, other non-limiting examples of labile bonds that may be coupled to a precursor or bead include an ester linkage (e.g., cleavable with an acid, a base, or hydroxylamine), a vicinal diol linkage (e.g., cleavable via sodium periodate), a Diels-Alder linkage (e.g., cleavable via heat), a sulfone linkage (e.g., cleavable via a base), a silyl ether linkage (e.g., cleavable via an acid), a glycosidic linkage (e.g., cleavable via an amylase), a peptide linkage (e.g., cleavable via a protease), or a phosphodiester linkage (e.g., cleavable via a nuclease (e.g., DNAase)).
Species that do not participate in polymerization may also be encapsulated in beads during bead generation (e.g., during polymerization of precursors). Such species may be entered into polymerization reaction mixtures such that generated beads comprise the species upon bead formation. In some cases, such species may be added to the gel beads after formation. Such species may include, for example, oligonucleotides, reagents for a nucleic acid amplification reaction (e.g., primers, polymerases, dNTPs, co-factors (e.g., ionic co-factors)) including those described herein, reagents for enzymatic reactions (e.g., enzymes, co-factors, substrates), or reagents for a nucleic acid modification reactions such as polymerization, ligation, or digestion. Trapping of such species may be controlled by the polymer network density generated during polymerization of precursors, control of ionic charge within the gel bead (e.g., via ionic species linked to polymerized species), or by the release of other species. Encapsulated species may be released from a bead upon bead degradation and/or by application of a stimulus capable of releasing the species from the bead.
Beads may be of uniform size or heterogeneous size. In some cases, the diameter of a bead may be about 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 250 μm, 500 μm, or 1 mm. In some cases, a bead may have a diameter of at least about 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 250 μm, 500 μm, 1 mm, or more. In some cases, a bead may have a diameter of less than about 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 250 μm, 500 μm, or 1 mm. In some cases, a bead may have a diameter in the range of about 40-75 μm, 30-75 μm, 20-75 μm, 40-85 μm, 40-95 μm, 20-100 μm, 10-100 μm, 1-100 μm, 20-250 μm, or 20-500 μm.
In certain aspects, beads are provided as a population or plurality of beads having a relatively monodisperse size distribution. Where it may be desirable to provide relatively consistent amounts of reagents within partitions, maintaining relatively consistent bead characteristics, such as size, can contribute to the overall consistency. In particular, the beads described herein may have size distributions that have a coefficient of variation in their cross-sectional dimensions of less than 50%, less than 40%, less than 30%, less than 20%, and in some cases less than 15%, less than 10%, or even less than 5%.
Beads may be of any suitable shape. Examples of bead shapes include, but are not limited to, spherical, non-spherical, oval, oblong, amorphous, circular, cylindrical, and variations thereof.
In addition to, or as an alternative to the cleavable linkages between the beads and the associated molecules, e.g., barcode containing oligonucleotides, described above, the beads may be degradable, disruptable, or dissolvable spontaneously or upon exposure to one or more stimuli (e.g., temperature changes, pH changes, exposure to particular chemical species or phase, exposure to light, reducing agent, etc.). In some cases, a bead may be dissolvable, such that material components of the beads are solubilized when exposed to a particular chemical species or an environmental change, such as a change temperature or a change in pH. In some cases, a gel bead is degraded or dissolved at elevated temperature and/or in basic conditions. In some cases, a bead may be thermally degradable such that when the bead is exposed to an appropriate change in temperature (e.g., heat), the bead degrades. Degradation or dissolution of a bead bound to a species (e.g., an oligonucleotide, e.g., barcoded oligonucleotide) may result in release of the species from the bead.
A degradable bead may comprise one or more species with a labile bond such that, when the bead/species is exposed to the appropriate stimuli, the bond is broken and the bead degrades. The labile bond may be a chemical bond (e.g., covalent bond, ionic bond) or may be another type of physical interaction (e.g., van der Waals interactions, dipole-dipole interactions, etc.). In some cases, a crosslinker used to generate a bead may comprise a labile bond. Upon exposure to the appropriate conditions, the labile bond can be broken and the bead degraded. For example, upon exposure of a polyacrylamide gel bead comprising cystamine crosslinkers to a reducing agent, the disulfide bonds of the cystamine can be broken and the bead degraded.
A degradable bead may be useful in more quickly releasing an attached species (e.g., an oligonucleotide, a barcode sequence, a primer, etc) from the bead when the appropriate stimulus is applied to the bead as compared to a bead that does not degrade. For example, for a species bound to an inner surface of a porous bead or in the case of an encapsulated species, the species may have greater mobility and accessibility to other species in solution upon degradation of the bead. In some cases, a species may also be attached to a degradable bead via a degradable linker (e.g., disulfide linker). The degradable linker may respond to the same stimuli as the degradable bead or the two degradable species may respond to different stimuli. For example, a barcode sequence may be attached, via a disulfide bond, to a polyacrylamide bead comprising cystamine. Upon exposure of the barcoded-bead to a reducing agent, the bead degrades and the barcode sequence is released upon breakage of both the disulfide linkage between the barcode sequence and the bead and the disulfide linkages of the cystamine in the bead.
A degradable bead may be introduced into a partition, such as a droplet of an emulsion or a well, such that the bead degrades within the partition and any associated species (e.g., oligonucleotides) are released within the droplet when the appropriate stimulus is applied. The free species (e.g., oligonucleotides) may interact with other reagents contained in the partition. For example, a polyacrylamide bead comprising cystamine and linked, via a disulfide bond, to a barcode sequence, may be combined with a reducing agent within a droplet of a water-in-oil emulsion. Within the droplet, the reducing agent breaks the various disulfide bonds resulting in bead degradation and release of the barcode sequence into the aqueous, inner environment of the droplet. In another example, heating of a droplet comprising a bead-bound barcode sequence in basic solution may also result in bead degradation and release of the attached barcode sequence into the aqueous, inner environment of the droplet.
As will be appreciated from the above disclosure, while referred to as degradation of a bead, in many instances as noted above, that degradation may refer to the disassociation of a bound or entrained species from a bead, both with and without structurally degrading the physical bead itself. For example, entrained species may be released from beads through osmotic pressure differences due to, for example, changing chemical environments. By way of example, alteration of bead pore sizes due to osmotic pressure differences can generally occur without structural degradation of the bead itself. In some cases, an increase in pore size due to osmotic swelling of a bead can permit the release of entrained species within the bead. In other cases, osmotic shrinking of a bead may cause a bead to better retain an entrained species due to pore size contraction.
Where degradable beads are provided, it may be desirable to avoid exposing such beads to the stimulus or stimuli that cause such degradation prior to the desired time, in order to avoid premature bead degradation and issues that arise from such degradation, including for example poor flow characteristics and aggregation. By way of example, where beads comprise reducible cross-linking groups, such as disulfide groups, it will be desirable to avoid contacting such beads with reducing agents, e.g., DTT or other disulfide cleaving reagents. In such cases, treatment to the beads described herein will, in some cases be provided free of reducing agents, such as DTT. Because reducing agents are often provided in commercial enzyme preparations, it may be desirable to provide reducing agent free (or DTT free) enzyme preparations in treating the beads described herein. Examples of such enzymes include, e.g., polymerase enzyme preparations, reverse transcriptase enzyme preparations, ligase enzyme preparations, as well as many other enzyme preparations that may be used to treat the beads described herein. The terms “reducing agent free” or “DTT free” preparations can refer to a preparation having less than 1/10th, less than 1/50th, and even less than 1/100th of the lower ranges for such materials used in degrading the beads. For example, for DTT, the reducing agent free preparation will typically have less than 0.01 mM, 0.005 mM, 0.001 mM DTT, 0.0005 mM DTT, or even less than 0.0001 mM DTT. In many cases, the amount of DTT will be undetectable.
In some cases, a stimulus may be used to trigger degradation of the bead, which may result in the release of contents from the bead. Generally, a stimulus may cause degradation of the bead structure, such as degradation of the covalent bonds or other types of physical interaction. These stimuli may be useful in inducing a bead to degrade and/or to release its contents. Examples of stimuli that may be used include chemical stimuli, thermal stimuli, optical stimuli (e.g., light) and any combination thereof, as described more fully below.
Numerous chemical triggers may be used to trigger the degradation of beads. Examples of these chemical changes may include, but are not limited to pH-mediated changes to the integrity of a component within the bead, degradation of a component of a bead via cleavage of cross-linked bonds, and depolymerization of a component of a bead.
In some embodiments, a bead may be formed from materials that comprise degradable chemical crosslinkers, such as BAC or cystamine. Degradation of such degradable crosslinkers may be accomplished through a number of mechanisms. In some examples, a bead may be contacted with a chemical degrading agent that may induce oxidation, reduction or other chemical changes. For example, a chemical degrading agent may be a reducing agent, such as dithiothreitol (DTT). Additional examples of reducing agents may include β-mercaptoethanol, (2S)-2-amino-1,4-dimercaptobutane (dithiobutylamine or DTBA), tris(2-carboxyethyl) phosphine (TCEP), or combinations thereof. A reducing agent may degrade the disulfide bonds formed between gel precursors forming the bead, and thus, degrade the bead. In other cases, a change in pH of a solution, such as an increase in pH, may trigger degradation of a bead. In other cases, exposure to an aqueous solution, such as water, may trigger hydrolytic degradation, and thus degradation of the bead.
Beads may also be induced to release their contents upon the application of a thermal stimulus. A change in temperature can cause a variety of changes to a bead. For example, heat can cause a solid bead to liquefy. A change in heat may cause melting of a bead such that a portion of the bead degrades. In other cases, heat may increase the internal pressure of the bead components such that the bead ruptures or explodes. Heat may also act upon heat-sensitive polymers used as materials to construct beads.
The methods, compositions, devices, and kits of this disclosure may be used with any suitable agent to degrade beads. In some embodiments, changes in temperature or pH may be used to degrade thermo-sensitive or pH-sensitive bonds within beads. In some embodiments, chemical degrading agents may be used to degrade chemical bonds within beads by oxidation, reduction or other chemical changes. For example, a chemical degrading agent may be a reducing agent, such as DTT, wherein DTT may degrade the disulfide bonds formed between a crosslinker and gel precursors, thus degrading the bead. In some embodiments, a reducing agent may be added to degrade the bead, which may or may not cause the bead to release its contents. Examples of reducing agents may include dithiothreitol (DTT), β-mercaptoethanol, (2S)-2-amino-1,4-dimercaptobutane (dithiobutylamine or DTBA), tris(2-carboxyethyl) phosphine (TCEP), or combinations thereof. The reducing agent may be present at a concentration of about 0.1 mM, 0.5 mM, 1 mM, 5 mM, or 10 mM. The reducing agent may be present at a concentration of at least about 0.1 mM, 0.5 mM, 1 mM, 5 mM, 10 mM, or greater. The reducing agent may be present at concentration of at most about 0.1 mM, 0.5 mM, 1 mM, 5 mM, or 10 mM.
Any suitable number of nucleic acid molecules (e.g., primer, e.g., barcoded oligonucleotide) can be associated with a bead such that, upon release from the bead, the nucleic acid molecules (e.g., primer, e.g., barcoded oligonucleotide) are present in the partition at a pre-defined concentration. Such pre-defined concentration may be selected to facilitate certain reactions for generating a sequencing library, e.g., amplification, within the partition. In some cases, the pre-defined concentration of the primer is limited by the process of producing oligonucleotide bearing beads.
In some aspects, the partitions refer to containers or vessels (such as wells, microwells, tubes, vials, through ports in nanoarray substrates, e.g., BioTrove nanoarrays, or other containers). In some aspects, the compartments or partitions comprise partitions that are flowable within fluid streams. These partitions may comprise, e.g., micro-vesicles that have an outer barrier surrounding an inner fluid center or core, or, in some cases, they may comprise a porous matrix that is capable of entraining and/or retaining materials within its matrix. In some aspects, partitions comprise droplets of aqueous fluid within a non-aqueous continuous phase, e.g., an oil phase. A variety of different vessels are described in, for example, U.S. Patent Application Publication No. 20140155295, the full disclosure of which is incorporated herein by reference in its entirety for all purposes. Emulsion systems for creating stable droplets in non-aqueous or oil continuous phases are described in detail in, e.g., U.S. Patent Application Publication No. 20100105112, the full disclosure of which is incorporated herein by reference in its entirety for all purposes.
In the case of droplets in an emulsion, allocating individual cells to discrete partitions may generally be accomplished by introducing a flowing stream of cells in an aqueous fluid into a flowing stream of a non-aqueous fluid, such that droplets are generated at the junction of the two streams. By providing the aqueous cell-containing stream at a certain concentration of cells, the occupancy of the resulting partitions (e.g., number of cells per partition) can be controlled. Where single cell partitions are desired, the relative flow rates of the fluids can be selected such that, on average, the partitions contain less than one cell per partition, in order to ensure that those partitions that are occupied, are primarily singly occupied. In some embodiments, the relative flow rates of the fluids can be selected such that a majority of partitions are occupied, e.g., allowing for only a small percentage of unoccupied partitions. In some aspects, the flows and channel architectures are controlled as to ensure a desired number of singly occupied partitions, less than a certain level of unoccupied partitions and less than a certain level of multiply occupied partitions.
The systems and methods described herein can be operated such that a majority of occupied partitions include no more than one cell per occupied partition. In some cases, the partitioning process is conducted such that fewer than 25% of the occupied partitions contain more than one cell, and in many cases, fewer than 20% of the occupied partitions have more than one cell. In some cases, fewer than 10% or even fewer than 5% of the occupied partitions include more than one cell per partition.
In some cases, it is desirable to avoid the creation of excessive numbers of empty partitions. For example, from a cost perspective and/or efficiency perspective, it may desirable to minimize the number of empty partitions. While this may be accomplished by providing sufficient numbers of cells into the partitioning zone, the Poissonian distribution may expectedly increase the number of partitions that may include multiple cells. As such, in accordance with aspects described herein, the flow of one or more of the cells, or other fluids directed into the partitioning zone are conducted such that, in many cases, no more than 50% of the generated partitions, no more than 25% of the generated partitions, or no more than 10% of the generated partitions are unoccupied. Further, in some aspects, these flows are controlled so as to present non-Poissonian distribution of single occupied partitions while providing lower levels of unoccupied partitions. Restated, in some aspects, the above noted ranges of unoccupied partitions can be achieved while still providing any of the single occupancy rates described above. For example, in many cases, the use of the systems and methods described herein creates resulting partitions that have multiple occupancy rates of less than 25%, less than 20%, less than 15%, less than 10%, and in many cases, less than 5%, while having unoccupied partitions of less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, and in some cases, less than 5%.
As will be appreciated, the above-described occupancy rates are also applicable to partitions that include both cells and additional reagents, including, but not limited to, microcapsules carrying barcoded oligonucleotides. In some aspects, a substantial percentage of the overall occupied partitions can include both a microcapsule (e.g., bead) comprising barcoded oligonucleotides and a cell.
Although described in terms of providing substantially singly occupied partitions, above, in certain cases, it is desirable to provide multiply occupied partitions, e.g., containing two, three, four or more cells and/or microcapsules (e.g., beads) comprising barcoded oligonucleotides within a single partition. Accordingly, as noted above, the flow characteristics of the cell and/or bead containing fluids and partitioning fluids may be controlled to provide for such multiply occupied partitions. In particular, the flow parameters may be controlled to provide a desired occupancy rate at greater than 50% of the partitions, greater than 75%, and in some cases greater than 80%, 90%, 95%, or higher.
In some cases, additional microcapsules are used to deliver additional reagents to a partition. In such cases, it may be advantageous to introduce different beads into a common channel or droplet generation junction, from different bead sources, i.e., containing different associated reagents, through different channel inlets into such common channel or droplet generation junction. In such cases, the flow and frequency of the different beads into the channel or junction may be controlled to provide for the desired ratio of microcapsules from each source, while ensuring the desired pairing or combination of such beads into a partition with the desired number of cells.
The partitions described herein may comprise small volumes, e.g., less than 10 μL, less than 54, less than 14, less than 900 picoliters (pL), less than 800 pL, less than 700 pL, less than 600 pL, less than 500 pL, less than 400 pL, less than 300 pL, less than 200 pL, less than 100 pL, less than 50 pL, less than 20 pL, less than 10 pL, less than 1 pL, less than 500 nanoliters (nL), or even less than 100 nL, 50 nL, or even less.
For example, in the case of droplet based partitions, the droplets may have overall volumes that are less than 1000 pL, less than 900 pL, less than 800 pL, less than 700 pL, less than 600 pL, less than 500 pL, less than 400 pL, less than 300 pL, less than 200 pL, less than 100 pL, less than 50 pL, less than 20 pL, less than 10 pL, or even less than 1 pL. Where co-partitioned with microcapsules, it will be appreciated that the sample fluid volume, e.g., including co-partitioned cells, within the partitions may be less than 90% of the above described volumes, less than 80%, less than 70%, less than 60%, less than 50%, less than 40%, less than 30%, less than 20%, or even less than 10% the above described volumes.
As is described elsewhere herein, partitioning species may generate a population or plurality of partitions. In such cases, any suitable number of partitions can be generated to generate the plurality of partitions. For example, in a method described herein, a plurality of partitions may be generated that comprises at least about 1,000 partitions, at least about 5,000 partitions, at least about 10,000 partitions, at least about 50,000 partitions, at least about 100,000 partitions, at least about 500,000 partitions, at least about 1,000,000 partitions, at least about 5,000,000 partitions at least about 10,000,000 partitions, at least about 50,000,000 partitions, at least about 100,000,000 partitions, at least about 500,000,000 partitions or at least about 1,000,000,000 partitions. Moreover, the plurality of partitions may comprise both unoccupied partitions (e.g., empty partitions) and occupied partitions
Microfluidic channel networks can be utilized to generate partitions as described herein. Alternative mechanisms may also be employed in the partitioning of individual cells, including porous membranes through which aqueous mixtures of cells are extruded into non-aqueous fluids.
An example of a simplified microfluidic channel structure for partitioning individual cells is illustrated in
In some aspects, this second fluid 116 comprises an oil, such as a fluorinated oil, that includes a fluorosurfactant for stabilizing the resulting droplets, e.g., inhibiting subsequent coalescence of the resulting droplets. Examples of particularly useful partitioning fluids and fluorosurfactants are described for example, in U.S. Patent Application Publication No. 20100105112, the full disclosure of which is hereby incorporated herein by reference in its entirety for all purposes.
In other aspects, in addition to or as an alternative to droplet based partitioning, cells may be encapsulated within a microcapsule that comprises an outer shell or layer or porous matrix in which is entrained one or more individual cells or small groups of cells, and may include other reagents. Encapsulation of cells may be carried out by a variety of processes. Such processes combine an aqueous fluid containing the cells to be analyzed with a polymeric precursor material that may be capable of being formed into a gel or other solid or semi-solid matrix upon application of a particular stimulus to the polymer precursor. Such stimuli include, e.g., thermal stimuli (either heating or cooling), photo-stimuli (e.g., through photo-curing), chemical stimuli (e.g., through crosslinking, polymerization initiation of the precursor (e.g., through added initiators), or the like.
Preparation of microcapsules comprising cells may be carried out by a variety of methods. For example, air knife droplet or aerosol generators may be used to dispense droplets of precursor fluids into gelling solutions in order to form microcapsules that include individual cells or small groups of cells. Likewise, membrane based encapsulation systems may be used to generate microcapsules comprising encapsulated cells as described herein. In some aspects, microfluidic systems like that shown in
For example, in the case where the polymer precursor material comprises a linear polymer material, e.g., a linear polyacrylamide, PEG, or other linear polymeric material, the activation agent may comprise a cross-linking agent, or a chemical that activates a cross-linking agent within the formed droplets. Likewise, for polymer precursors that comprise polymerizable monomers, the activation agent may comprise a polymerization initiator. For example, in certain cases, where the polymer precursor comprises a mixture of acrylamide monomer with a N,N′-bis-(acryloyl)cystamine (BAC) comonomer, an agent such as tetraethylmethylenediamine (TEMED) may be provided within the second fluid streams in channel segments 104 and 106, which initiates the copolymerization of the acrylamide and BAC into a cross-linked polymer network or, hydrogel.
Upon contact of the second fluid stream 116 with the first fluid stream 112 at junction 110 in the formation of droplets, the TEMED may diffuse from the second fluid 116 into the aqueous first fluid 112 comprising the linear polyacrylamide, which will activate the crosslinking of the polyacrylamide within the droplets, resulting in the formation of the gel, e.g., hydrogel, microcapsules 118, as solid or semi-solid beads or particles entraining the cells 114. Although described in terms of polyacrylamide encapsulation, other ‘activatable’ encapsulation compositions may also be employed in the context of the methods and compositions described herein. For example, formation of alginate droplets followed by exposure to divalent metal ions, e.g., Ca2+, can be used as an encapsulation process using the described processes. Likewise, agarose droplets may also be transformed into capsules through temperature based gelling, e.g., upon cooling, or the like. In some cases, encapsulated cells can be selectively releasable from the microcapsule, e.g., through passage of time, or upon application of a particular stimulus, that degrades the microcapsule sufficiently to allow the cell, or its contents to be released from the microcapsule, e.g., into a partition, such as a droplet. For example, in the case of the polyacrylamide polymer described above, degradation of the microcapsule may be accomplished through the introduction of an appropriate reducing agent, such as DTT or the like, to cleave disulfide bonds that cross link the polymer matrix (See, e.g., U.S. Patent Application Publication No. 20140378345, the full disclosures of which are hereby incorporated herein by reference in their entirety for all purposes.
Encapsulated cells or cell populations provide certain potential advantages of being storable, and more portable than droplet based partitioned cells. Furthermore, in some cases, it may be desirable to allow cells to be analyzed to incubate for a select period of time, in order to characterize changes in such cells over time, either in the presence or absence of different stimuli. In such cases, encapsulation of individual cells may allow for longer incubation than partitioning in emulsion droplets, although in some cases, droplet partitioned cells may also be incubated for different periods of time, e.g., at least 10 seconds, at least 30 seconds, at least 1 minute, at least 5 minutes, at least 10 minutes, at least 30 minutes, at least 1 hour, at least 2 hours, at least 5 hours, or at least 10 hours or more. The encapsulation of cells may constitute the partitioning of the cells into which other reagents are co-partitioned. Alternatively, encapsulated cells may be readily deposited into other partitions, e.g., droplets, as described above.
In accordance with certain aspects, the cells may be partitioned along with lysis reagents in order to release the contents of the cells within the partition. In such cases, the lysis agents can be contacted with the cell suspension concurrently with, or immediately prior to the introduction of the cells into the partitioning junction/droplet generation zone, e.g., through an additional channel or channels upstream of channel junction 110. Examples of lysis agents include bioactive reagents, such as lysis enzymes that are used for lysis of different cell types, e.g., gram positive or negative bacteria, plants, yeast, mammalian, etc., such as lysozymes, achromopeptidase, lysostaphin, labiase, kitalase, lyticase, and a variety of other lysis enzymes available from, e.g., Sigma-Aldrich, Inc. (St Louis, Mo.), as well as other commercially available lysis enzymes. Other lysis agents may additionally or alternatively be co-partitioned with the cells to cause the release of the cell's contents into the partitions. For example, in some cases, surfactant based lysis solutions may be used to lyse cells, although these may be less desirable for emulsion based systems where the surfactants can interfere with stable emulsions. In some cases, lysis solutions may include non-ionic surfactants such as, for example, TritonX-100 and Tween 20. In some cases, lysis solutions may include ionic surfactants such as, for example, sarcosyl and sodium dodecyl sulfate (SDS). Electroporation, thermal, acoustic or mechanical cellular disruption may also be used in certain cases, e.g., non-emulsion based partitioning such as encapsulation of cells that may be in addition to or in place of droplet partitioning, where any pore size of the encapsulate is sufficiently small to retain nucleic acid fragments of a desired size, following cellular disruption.
In addition to the lysis agents co-partitioned with the cells described above, other reagents can also be co-partitioned with the cells, including, for example, DNase and RNase inactivating agents or inhibitors, such as proteinase K, chelating agents, such as EDTA, and other reagents employed in removing or otherwise reducing negative activity or impact of different cell lysate components on subsequent processing of nucleic acids. In addition, in the case of encapsulated cells, the cells may be exposed to an appropriate stimulus to release the cells or their contents from a co-partitioned microcapsule. For example, in some cases, a chemical stimulus may be co-partitioned along with an encapsulated cell to allow for the degradation of the microcapsule and release of the cell or its contents into the larger partition. In some cases, this stimulus may be the same as the stimulus described elsewhere herein for release of oligonucleotides from their respective microcapsule (e.g., bead). In alternative aspects, this may be a different and non-overlapping stimulus, in order to allow an encapsulated cell to be released into a partition at a different time from the release of oligonucleotides into the same partition.
Additional reagents may also be co-partitioned with the cells, such as endonucleases to fragment the cell's DNA, DNA polymerase enzymes and dNTPs used to amplify the cell's nucleic acid fragments and to attach the barcode oligonucleotides to the amplified fragments. Additional reagents may also include reverse transcriptase enzymes, including enzymes with terminal transferase activity, primers and oligonucleotides, and switch oligonucleotides (also referred to herein as “switch oligos” or “template switching oligonucleotides”) which can be used for template switching. In some cases, template switching can be used to increase the length of a cDNA. In some cases, template switching can be used to append a predefined nucleic acid sequence to the cDNA. In one example of template switching, cDNA can be generated from reverse transcription of a template, e.g., cellular mRNA, where a reverse transcriptase with terminal transferase activity can add additional nucleotides, e.g., polyC, to the cDNA in a template independent manner. Switch oligos can include sequences complementary to the additional nucleotides, e.g., polyG. The additional nucleotides (e.g., polyC) on the cDNA can hybridize to the additional nucleotides (e.g., polyG) on the switch oligo, whereby the switch oligo can be used by the reverse transcriptase as template to further extend the cDNA. Template switching oligonucleotides may comprise a hybridization region and a template region. The hybridization region can comprise any sequence capable of hybridizing to the target. In some cases, as previously described, the hybridization region comprises a series of G bases to complement the overhanging C bases at the 3′ end of a cDNA molecule. The series of G bases may comprise 1 G base, 2 G bases, 3 G bases, 4 G bases, 5 G bases or more than 5 G bases. The template sequence can comprise any sequence to be incorporated into the cDNA. In some cases, the template region comprises at least 1 (e.g., at least 2, 3, 4, 5 or more) tag sequences and/or functional sequences. Switch oligos may comprise deoxyribonucleic acids; ribonucleic acids; modified nucleic acids including 2-Aminopurine, 2,6-Diaminopurine (2-Amino-dA), inverted dT, 5-Methyl dC, 2′-deoxylnosine, Super T (5-hydroxybutynl-2′-deoxyuridine), Super G (8-aza-7-deazaguanosine), locked nucleic acids (LNAs), unlocked nucleic acids (UNAs, e.g., UNA-A, UNA-U, UNA-C, UNA-G), Iso-dG, Iso-dC, 2′ Fluoro bases (e.g., Fluoro C, Fluoro U, Fluoro A, and Fluoro G), or any combination.
In some cases, the length of a switch oligo may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250 nucleotides or longer.
In some cases, the length of a switch oligo may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249 or 250 nucleotides or longer.
In some cases, the length of a switch oligo may be at most 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249 or 250 nucleotides.
Once the contents of the cells are released into their respective partitions, the nucleic acids contained therein may be further processed within the partitions. In accordance with the methods and systems described herein, the nucleic acid contents of individual cells can be provided with unique identifiers such that, upon characterization of those nucleic acids they may be attributed as having been derived from the same cell or cells. The ability to attribute characteristics to individual cells or groups of cells is provided by the assignment of unique identifiers specifically to an individual cell or groups of cells. Unique identifiers, e.g., in the form of nucleic acid barcodes can be assigned or associated with individual cells or populations of cells, in order to tag or label the cell's components (and as a result, its characteristics) with the unique identifiers. These unique identifiers can then be used to attribute the cell's components and characteristics to an individual cell or group of cells. In some aspects, this is carried out by co-partitioning the individual cells or groups of cells with the unique identifiers. In some aspects, the unique identifiers are provided in the form of oligonucleotides that comprise nucleic acid barcode sequences that may be attached to or otherwise associated with the nucleic acid contents of individual cells, or to other components of the cells, and particularly to fragments of those nucleic acids. The oligonucleotides are partitioned such that as between oligonucleotides in a given partition, the nucleic acid barcode sequences contained therein are the same, but as between different partitions, the oligonucleotides can, and do have differing barcode sequences, or at least represent a large number of different barcode sequences across all of the partitions in a given analysis. In some aspects, only one nucleic acid barcode sequence can be associated with a given partition, although in some cases, two or more different barcode sequences may be present.
The nucleic acid barcode sequences can include from 6 to about 20 or more nucleotides within the sequence of the oligonucleotides. In some cases, the length of a barcode sequence may be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 nucleotides or longer. In some cases, the length of a barcode sequence may be at least 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 nucleotides or longer. In some cases, the length of a barcode sequence may be at most 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 nucleotides or shorter. These nucleotides may be completely contiguous, i.e., in a single stretch of adjacent nucleotides, or they may be separated into two or more separate subsequences that are separated by 1 or more nucleotides. In some cases, separated barcode subsequences can be from about 4 to about 16 nucleotides in length. In some cases, the barcode subsequence may be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 nucleotides or longer. In some cases, the barcode subsequence may be at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 nucleotides or longer. In some cases, the barcode subsequence may be at most 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 nucleotides or shorter.
The co-partitioned oligonucleotides can also comprise other functional sequences useful in the processing of the nucleic acids from the co-partitioned cells. These sequences include, e.g., targeted or random/universal amplification primer sequences for amplifying the genomic DNA from the individual cells within the partitions while attaching the associated barcode sequences, sequencing primers or primer recognition sites, hybridization or probing sequences, e.g., for identification of presence of the sequences or for pulling down barcoded nucleic acids, or any of a number of other potential functional sequences. Other mechanisms of co-partitioning oligonucleotides may also be employed, including, e.g., coalescence of two or more droplets, where one droplet contains oligonucleotides, or microdispensing of oligonucleotides into partitions, e.g., droplets within microfluidic systems.
Briefly, in one example, microcapsules, such as beads, are provided that each include large numbers of the above described barcoded oligonucleotides releasably attached to the beads, where all of the oligonucleotides attached to a particular bead will include the same nucleic acid barcode sequence, but where a large number of diverse barcode sequences are represented across the population of beads used. In some embodiments, hydrogel beads, e.g., comprising polyacrylamide polymer matrices, are used as a solid support and delivery vehicle for the oligonucleotides into the partitions, as they are capable of carrying large numbers of oligonucleotide molecules, and may be configured to release those oligonucleotides upon exposure to a particular stimulus, as described elsewhere herein. In some cases, the population of beads will provide a diverse barcode sequence library that includes at least 1,000 different barcode sequences, at least 5,000 different barcode sequences, at least 10,000 different barcode sequences, at least at least 50,000 different barcode sequences, at least 100,000 different barcode sequences, at least 1,000,000 different barcode sequences, at least 5,000,000 different barcode sequences, or at least 10,000,000 different barcode sequences. Additionally, each bead can be provided with large numbers of oligonucleotide molecules attached. In particular, the number of molecules of oligonucleotides including the barcode sequence on an individual bead can be at least 1,000 oligonucleotide molecules, at least 5,000 oligonucleotide molecules, at least 10,000 oligonucleotide molecules, at least 50,000 oligonucleotide molecules, at least 100,000 oligonucleotide molecules, at least 500,000 oligonucleotides, at least 1,000,000 oligonucleotide molecules, at least 5,000,000 oligonucleotide molecules, at least 10,000,000 oligonucleotide molecules, at least 50,000,000 oligonucleotide molecules, at least 100,000,000 oligonucleotide molecules, and in some cases at least 1 billion oligonucleotide molecules.
Moreover, when the population of beads is partitioned, the resulting population of partitions can also include a diverse barcode library that includes at least 1,000 different barcode sequences, at least 5,000 different barcode sequences, at least 10,000 different barcode sequences, at least at least 50,000 different barcode sequences, at least 100,000 different barcode sequences, at least 1,000,000 different barcode sequences, at least 5,000,000 different barcode sequences, or at least 10,000,000 different barcode sequences. Additionally, each partition of the population can include at least 1,000 oligonucleotide molecules, at least 5,000 oligonucleotide molecules, at least 10,000 oligonucleotide molecules, at least 50,000 oligonucleotide molecules, at least 100,000 oligonucleotide molecules, at least 500,000 oligonucleotides, at least 1,000,000 oligonucleotide molecules, at least 5,000,000 oligonucleotide molecules, at least 10,000,000 oligonucleotide molecules, at least 50,000,000 oligonucleotide molecules, at least 100,000,000 oligonucleotide molecules, and in some cases at least 1 billion oligonucleotide molecules.
In some cases, it may be desirable to incorporate multiple different barcodes within a given partition, either attached to a single or multiple beads within the partition. For example, in some cases, a mixed, but known barcode sequences set may provide greater assurance of identification in the subsequent processing, e.g., by providing a stronger address or attribution of the barcodes to a given partition, as a duplicate or independent confirmation of the output from a given partition.
The oligonucleotides are releasable from the beads upon the application of a particular stimulus to the beads. In some cases, the stimulus may be a photo-stimulus, e.g., through cleavage of a photo-labile linkage that releases the oligonucleotides. In other cases, a thermal stimulus may be used, where elevation of the temperature of the beads environment will result in cleavage of a linkage or other release of the oligonucleotides form the beads. In still other cases, a chemical stimulus is used that cleaves a linkage of the oligonucleotides to the beads, or otherwise results in release of the oligonucleotides from the beads. In one case, such compositions include the polyacrylamide matrices described above for encapsulation of cells, and may be degraded for release of the attached oligonucleotides through exposure to a reducing agent, such as DTT.
In accordance with the methods and systems described herein, the beads including the attached oligonucleotides are co-partitioned with the individual cells, such that a single bead and a single cell are contained within an individual partition. As noted above, while single cell/single bead occupancy is the most desired state, it will be appreciated that multiply occupied partitions (either in terms of cells, beads or both), or unoccupied partitions (either in terms of cells, beads or both) will often be present. An example of a microfluidic channel structure for co-partitioning cells and beads comprising barcode oligonucleotides is schematically illustrated in
Concurrently, an aqueous stream comprising the barcode carrying beads 216, is flowed through channel segment 204 toward channel junction 212. A non-aqueous partitioning fluid 216 is introduced into channel junction 212 from each of side channels 206 and 208, and the combined streams are flowed into outlet channel 210. Within channel junction 212, the two combined aqueous streams from channel segments 202 and 204 are combined, and partitioned into droplets 218, that include co-partitioned cells 214 and beads 216. As noted previously, by controlling the flow characteristics of each of the fluids combining at channel junction 212, as well as controlling the geometry of the channel junction, partitioning can be optimized to achieve a desired occupancy level of beads, cells or both, within the partitions 218 that are generated.
In some cases, lysis agents, e.g., cell lysis enzymes, may be introduced into the partition with the bead stream, e.g., flowing through channel segment 204, such that lysis of the cell only commences at or after the time of partitioning. Additional reagents may also be added to the partition in this configuration, such as endonucleases to fragment the cell's DNA, DNA polymerase enzyme and dNTPs used to amplify the cell's nucleic acid fragments and to attach the barcode oligonucleotides to the amplified fragments. As noted above, in many cases, a chemical stimulus, such as DTT, may be used to release the barcodes from their respective beads into the partition. In such cases, it may be particularly desirable to provide the chemical stimulus along with the cell-containing stream in channel segment 202, such that release of the barcodes only occurs after the two streams have been combined, e.g., within the partitions 218. Where the cells are encapsulated, however, introduction of a common chemical stimulus, e.g., that both releases the oligonucleotides form their beads, and releases cells from their microcapsules may generally be provided from a separate additional side channel (not shown) upstream of or connected to channel junction 212.
A number of other reagents may be co-partitioned along with the cells, beads, lysis agents and chemical stimuli, including, for example, protective reagents, like proteinase K, chelators, nucleic acid extension, replication, transcription or amplification reagents such as polymerases, reverse transcriptases, transposases which can be used for transposon based methods (e.g., Nextera), nucleoside triphosphates or NTP analogues, primer sequences and additional cofactors such as divalent metal ions used in such reactions, ligation reaction reagents, such as ligase enzymes and ligation sequences, dyes, labels, or other tagging reagents.
The channel networks, e.g., as described herein, can be fluidly coupled to appropriate fluidic components. For example, the inlet channel segments, e.g., channel segments 202, 204, 206 and 208 are fluidly coupled to appropriate sources of the materials they are to deliver to channel junction 212. For example, channel segment 202 will be fluidly coupled to a source of an aqueous suspension of cells 214 to be analyzed, while channel segment 204 may be fluidly coupled to a source of an aqueous suspension of beads 216. Channel segments 206 and 208 may then be fluidly connected to one or more sources of the non-aqueous fluid. These sources may include any of a variety of different fluidic components, from simple reservoirs defined in or connected to a body structure of a microfluidic device, to fluid conduits that deliver fluids from off-device sources, manifolds, or the like. Likewise, the outlet channel segment 210 may be fluidly coupled to a receiving vessel or conduit for the partitioned cells. Again, this may be a reservoir defined in the body of a microfluidic device, or it may be a fluidic conduit for delivering the partitioned cells to a subsequent process operation, instrument or component.
In operation, once lysed, the nucleic acid contents of the individual cells are then available for further processing within the partitions, including, e.g., fragmentation, amplification and barcoding, as well as attachment of other functional sequences. As noted above, fragmentation may be accomplished through the co-partitioning of shearing enzymes, such as endonucleases, in order to fragment the nucleic acids into smaller fragments. These endonucleases may include restriction endonucleases, including type II and type IIs restriction endonucleases as well as other nucleic acid cleaving enzymes, such as nicking endonucleases, and the like. In some cases, fragmentation may not be desired, and full length nucleic acids may be retained within the partitions, or in the case of encapsulated cells or cell contents, fragmentation may be carried out prior to partitioning, e.g., through enzymatic methods, e.g., those described herein, or through mechanical methods, e.g., mechanical, acoustic or other shearing.
Once co-partitioned, and the cells are lysed to release their nucleic acids, the oligonucleotides disposed upon the bead may be used to barcode and amplify fragments of those nucleic acids. Briefly, in one aspect, the oligonucleotides present on the beads that are co-partitioned with the cells, are released from their beads into the partition with the cell's nucleic acids. The oligonucleotides can include, along with the barcode sequence, a primer sequence at its 5′ end. This primer sequence may be a random oligonucleotide sequence intended to randomly prime numerous different regions on the cell's nucleic acids, or it may be a specific primer sequence targeted to prime upstream of a specific targeted region of the cell's genome.
Once released, the primer portion of the oligonucleotide can anneal to a complementary region of the cell's nucleic acid. Extension reaction reagents, e.g., DNA polymerase, nucleoside triphosphates, co-factors (e.g., Mg2+ or Mn2+), that are also co-partitioned with the cells and beads, then extend the primer sequence using the cell's nucleic acid as a template, to produce a complementary fragment to the strand of the cell's nucleic acid to which the primer annealed, which complementary fragment includes the oligonucleotide and its associated barcode sequence. Annealing and extension of multiple primers to different portions of the cell's nucleic acids will result in a large pool of overlapping complementary fragments of the nucleic acid, each possessing its own barcode sequence indicative of the partition in which it was created. In some cases, these complementary fragments may themselves be used as a template primed by the oligonucleotides present in the partition to produce a complement of the complement that again, includes the barcode sequence. In some cases, this replication process is configured such that when the first complement is duplicated, it produces two complementary sequences at or near its termini, to allow formation of a hairpin structure or partial hairpin structure, the reduces the ability of the molecule to be the basis for producing further iterative copies. As described herein, the cell's nucleic acids may include any desired nucleic acids within the cell including, for example, the cell's DNA, e.g., genomic DNA, RNA, e.g., messenger RNA, and the like. For example, in some cases, the methods and systems described herein are used in characterizing expressed mRNA, including, e.g., the presence and quantification of such mRNA, and may include RNA sequencing processes as the characterization process. Alternatively or additionally, the reagents partitioned along with the cells may include reagents for the conversion of mRNA into cDNA, e.g., reverse transcriptase enzymes and reagents, to facilitate sequencing processes where DNA sequencing is employed. In some cases, where the nucleic acids to be characterized comprise RNA, e.g., mRNA, schematic illustration of one example of this is shown in
As shown, oligonucleotides that include a barcode sequence are co-partitioned in, e.g., a droplet 302 in an emulsion, along with a sample nucleic acid 304. As noted elsewhere herein, the oligonucleotides 308 may be provided on a bead 306 that is co-partitioned with the sample nucleic acid 304, which oligonucleotides are releasable from the bead 306, as shown in panel A. The oligonucleotides 308 include a barcode sequence 312, in addition to one or more functional sequences, e.g., sequences 310, 314 and 316. For example, oligonucleotide 308 is shown as comprising barcode sequence 312, as well as sequence 310 that may function as an attachment or immobilization sequence for a given sequencing system, e.g., a P5 sequence used for attachment in flow cells of an Illumina Hiseq® or Miseq® system. As shown, the oligonucleotides also include a primer sequence 316, which may include a random or targeted N-mer for priming replication of portions of the sample nucleic acid 304. Also included within oligonucleotide 308 is a sequence 314 which may provide a sequencing priming region, such as a “read1” or R1 priming region, that is used to prime polymerase mediated, template directed sequencing by synthesis reactions in sequencing systems. As will be appreciated, the functional sequences may be selected to be compatible with a variety of different sequencing systems, e.g., 454 Sequencing, Ion Torrent Proton or PGM, Illumina X10, etc., and the requirements thereof. In many cases, the barcode sequence 312, immobilization sequence 310 and R1 sequence 314 may be common to all of the oligonucleotides attached to a given bead. The primer sequence 316 may vary for random N-mer primers, or may be common to the oligonucleotides on a given bead for certain targeted applications.
As will be appreciated, in some cases, the functional sequences may include primer sequences useful for RNA-seq applications. For example, in some cases, the oligonucleotides may include poly-T primers for priming reverse transcription of RNA for RNA-seq. In still other cases, oligonucleotides in a given partition, e.g., included on an individual bead, may include multiple types of primer sequences in addition to the common barcode sequences, such as both DNA-sequencing and RNA sequencing primers, e.g., poly-T primer sequences included within the oligonucleotides coupled to the bead. In such cases, a single partitioned cell may be both subjected to DNA and RNA sequencing processes.
Based upon the presence of primer sequence 316, the oligonucleotides can prime the sample nucleic acid as shown in panel B, which allows for extension of the oligonucleotides 308 and 308a using polymerase enzymes and other extension reagents also co-partitioned with the bead 306 and sample nucleic acid 304. As shown in panel C, following extension of the oligonucleotides that, for random N-mer primers, may anneal to multiple different regions of the sample nucleic acid 304; multiple overlapping complements or fragments of the nucleic acid are created, e.g., fragments 318 and 320. Although including sequence portions that are complementary to portions of sample nucleic acid, e.g., sequences 322 and 324, these constructs are generally referred to herein as comprising fragments of the sample nucleic acid 304, having the attached barcode sequences.
The barcoded nucleic acid fragments may then be subjected to characterization, e.g., through sequence analysis, or they may be further amplified in the process, as shown in panel D. For example, additional oligonucleotides, e.g., oligonucleotide 308b, also released from bead 306, may prime the fragments 318 and 320. This shown for fragment 318. In particular, again, based upon the presence of the random N-mer primer 316b in oligonucleotide 308b (which in many cases can be different from other random N-mers in a given partition, e.g., primer sequence 316), the oligonucleotide anneals with the fragment 318, and is extended to create a complement 326 to at least a portion of fragment 318 which includes sequence 328, that comprises a duplicate of a portion of the sample nucleic acid sequence. Extension of the oligonucleotide 308b continues until it has replicated through the oligonucleotide portion 308 of fragment 318. As noted elsewhere herein, and as illustrated in panel D, the oligonucleotides may be configured to prompt a stop in the replication by the polymerase at a desired point, e.g., after replicating through sequences 316 and 314 of oligonucleotide 308 that is included within fragment 318. As described herein, this may be accomplished by different methods, including, for example, the incorporation of different nucleotides and/or nucleotide analogues that are not capable of being processed by the polymerase enzyme used. For example, this may include the inclusion of uracil containing nucleotides within the sequence region 312 to prevent a non-uracil tolerant polymerase to cease replication of that region. As a result a fragment 326 is created that includes the full-length oligonucleotide 308b at one end, including the barcode sequence 312, the attachment sequence 310, the R1 primer region 314, and the random N-mer sequence 316b. At the other end of the sequence may be included the complement 316′ to the random N-mer of the first oligonucleotide 308, as well as a complement to all or a portion of the R1 sequence, shown as sequence 314′. The R1 sequence 314 and its complement 314′ are then able to hybridize together to form a partial hairpin structure 328. As will be appreciated because the random N-mers differ among different oligonucleotides, these sequences and their complements may not be expected to participate in hairpin formation, e.g., sequence 316′, which is the complement to random N-mer 316, may not be expected to be complementary to random N-mer sequence 316b. This may not be the case for other applications, e.g., targeted primers, where the N-mers may be common among oligonucleotides within a given partition.
By forming these partial hairpin structures, it allows for the removal of first level duplicates of the sample sequence from further replication, e.g., preventing iterative copying of copies. The partial hairpin structure also provides a useful structure for subsequent processing of the created fragments, e.g., fragment 326.
In general, the amplification of the cell's nucleic acids is carried out until the barcoded overlapping fragments within the partition constitute at least 1× coverage of the particular portion or all of the cell's genome, at least 2×, at least 3×, at least 4×, at least 5×, at least 10×, at least 20×, at least 40× or more coverage of the genome or its relevant portion of interest. Once the barcoded fragments are produced, they may be directly sequenced on an appropriate sequencing system, e.g., an Illumina Hiseq®, Miseq® or X10 system, or they may be subjected to additional processing, such as further amplification, attachment of other functional sequences, e.g., second sequencing primers, for reverse reads, sample index sequences, and the like.
All of the fragments from multiple different partitions may then be pooled for sequencing on high throughput sequencers as described herein, where the pooled fragments comprise a large number of fragments derived from the nucleic acids of different cells or small cell populations, but where the fragments from the nucleic acids of a given cell will share the same barcode sequence. In particular, because each fragment is coded as to its partition of origin, and consequently its single cell or small population of cells, the sequence of that fragment may be attributed back to that cell or those cells based upon the presence of the barcode, which will also aid in applying the various sequence fragments from multiple partitions to assembly of individual genomes for different cells. This is schematically illustrated in
Within each partition, each cell's nucleic acids 404 and 406 is then processed to separately provide overlapping set of second fragments of the first fragment(s), e.g., second fragment sets 408 and 410. This processing also provides the second fragments with a barcode sequence that is the same for each of the second fragments derived from a particular first fragment. As shown, the barcode sequence for second fragment set 408 is denoted by “1” while the barcode sequence for fragment set 410 is denoted by “2”. A diverse library of barcodes may be used to differentially barcode large numbers of different fragment sets. However, it is not necessary for every second fragment set from a different first fragment to be barcoded with different barcode sequences. In fact, in many cases, multiple different first fragments may be processed concurrently to include the same barcode sequence. Diverse barcode libraries are described in detail elsewhere herein.
The barcoded fragments, e.g., from fragment sets 408 and 410, may then be pooled for sequencing using, for example, sequence by synthesis technologies available from Illumina or Ion Torrent division of Thermo-Fisher, Inc. Once sequenced, the sequence reads 412 can be attributed to their respective fragment set, e.g., as shown in aggregated reads 414 and 416, at least in part based upon the included barcodes, and in some cases, in part based upon the sequence of the fragment itself. The attributed sequence reads for each fragment set are then assembled to provide the assembled sequence for each cell's nucleic acids, e.g., sequences 418 and 420, which in turn, may be attributed to individual cells, e.g., cells 400 and 402.
While described in terms of analyzing the genetic material present within cells, the methods and systems described herein may have much broader applicability, including the ability to characterize other aspects of individual cells or cell populations, by allowing for the allocation of reagents to individual cells, and providing for the attributable analysis or characterization of those cells in response to those reagents. These methods and systems are particularly valuable in being able to characterize cells for, e.g., research, diagnostic, pathogen identification, and many other purposes. By way of example, a wide range of different cell surface features, e.g., cell surface proteins like cluster of differentiation or CD proteins, have significant diagnostic relevance in characterization of diseases like cancer.
In one particularly useful application, the methods and systems described herein may be used to characterize cell features, such as cell surface features, e.g., proteins, receptors, etc. In particular, the methods described herein may be used to attach reporter molecules to these cell features, that when partitioned as described above, may be barcoded and analyzed, e.g., using DNA sequencing technologies, to ascertain the presence, and in some cases, relative abundance or quantity of such cell features within an individual cell or population of cells.
In a particular example, a library of potential cell binding ligands, e.g., antibodies, antibody fragments, cell surface receptor binding molecules, or the like, may be provided associated with a first set of nucleic acid reporter molecules, e.g., where a different reporter oligonucleotide sequence is associated with a specific ligand, and therefore capable of binding to a specific cell surface feature. In some aspects, different members of the library may be characterized by the presence of a different oligonucleotide sequence label, e.g., an antibody to a first type of cell surface protein or receptor may have associated with it a first known reporter oligonucleotide sequence, while an antibody to a second receptor protein may have a different known reporter oligonucleotide sequence associated with it. Prior to co-partitioning, the cells may be incubated with the library of ligands, that may represent antibodies to a broad panel of different cell surface features, e.g., receptors, proteins, etc., and which include their associated reporter oligonucleotides. Unbound ligands are washed from the cells, and the cells are then co-partitioned along with the barcode oligonucleotides described above. As a result, the partitions will include the cell or cells, as well as the bound ligands and their known, associated reporter oligonucleotides.
Without the need for lysing the cells within the partitions, one may then subject the reporter oligonucleotides to the barcoding operations described above for cellular nucleic acids, to produce barcoded, reporter oligonucleotides, where the presence of the reporter oligonucleotides can be indicative of the presence of the particular cell surface feature, and the barcode sequence will allow the attribution of the range of different cell surface features to a given individual cell or population of cells based upon the barcode sequence that was co-partitioned with that cell or population of cells. As a result, one may generate a cell-by-cell profile of the cell surface features within a broader population of cells. This aspect of the methods and systems described herein, is described in greater detail below.
This example is schematically illustrated in
Single cell processing and analysis methods and systems described herein can be utilized for a wide variety of applications, including analysis of specific individual cells, analysis of different cell types within populations of differing cell types, analysis and characterization of large populations of cells for environmental, human health, epidemiological forensic, or any of a wide variety of different applications.
A particularly valuable application of the single cell analysis processes described herein is in the sequencing and characterization of a diseased cell. A diseased cell can have altered metabolic properties, gene expression, and/or morphologic features. Examples of diseases include inflammatory disorders, metabolic disorders, nervous system disorders, and cancer.
Of particular interest are cancer cells. In particular, conventional analytical techniques, including the ensemble sequencing processes alluded to above, are not highly adept at picking small variations in genomic make-up of cancer cells, particularly where those exist in a sea of normal tissue cells. Further, even as between tumor cells, wide variations can exist and can be masked by the ensemble approaches to sequencing (See, e.g., Patel, et al., Single-cell RNA-seq highlights intratumoral heterogeneity in primary glioblastoma, Science DOI: 10.1126/science.1254257 (Published online Jun. 12, 2014). Cancer cells may be derived from solid tumors, hematological malignancies, cell lines, or obtained as circulating tumor cells, and subjected to the partitioning processes described above. Upon analysis, one can identify individual cell sequences as deriving from a single cell or small group of cells, and distinguish those over normal tissue cell sequences.
Non-limiting examples of cancer cells include cells of cancers such as Acanthoma, Acinic cell carcinoma, Acoustic neuroma, Acral lentiginous melanoma, Acrospiroma, Acute eosinophilic leukemia, Acute lymphoblastic leukemia, Acute megakaryoblastic leukemia, Acute monocytic leukemia, Acute myeloblastic leukemia with maturation, Acute myeloid dendritic cell leukemia, Acute myeloid leukemia, Acute promyelocytic leukemia, Adamantinoma, Adenocarcinoma, Adenoid cystic carcinoma, Adenoma, Adenomatoid odontogenic tumor, Adrenocortical carcinoma, Adult T-cell leukemia, Aggressive NK-cell leukemia, AIDS-Related Cancers, AIDS-related lymphoma, Alveolar soft part sarcoma, Ameloblastic fibroma, Anal cancer, Anaplastic large cell lymphoma, Anaplastic thyroid cancer, Angioimmunoblastic T-cell lymphoma, Angiomyolipoma, Angiosarcoma, Appendix cancer, Astrocytoma, Atypical teratoid rhabdoid tumor, Basal cell carcinoma, Basal-like carcinoma, B-cell leukemia, B-cell lymphoma, Bellini duct carcinoma, Biliary tract cancer, Bladder cancer, Blastoma, Bone Cancer, Bone tumor, Brain Stem Glioma, Brain Tumor, Breast Cancer, Brenner tumor, Bronchial Tumor, Bronchioloalveolar carcinoma, Brown tumor, Burkitt's lymphoma, Cancer of Unknown Primary Site, Carcinoid Tumor, Carcinoma, Carcinoma in situ, Carcinoma of the penis, Carcinoma of Unknown Primary Site, Carcinosarcoma, Castleman's Disease, Central Nervous System Embryonal Tumor, Cerebellar Astrocytoma, Cerebral Astrocytoma, Cervical Cancer, Cholangiocarcinoma, Chondroma, Chondrosarcoma, Chordoma, Choriocarcinoma, Choroid plexus papilloma, Chronic Lymphocytic Leukemia, Chronic monocytic leukemia, Chronic myelogenous leukemia, Chronic Myeloproliferative Disorder, Chronic neutrophilic leukemia, Clear-cell tumor, Colon Cancer, Colorectal cancer, Craniopharyngioma, Cutaneous T-cell lymphoma, Degos disease, Dermatofibrosarcoma protuberans, Dermoid cyst, Desmoplastic small round cell tumor, Diffuse large B cell lymphoma, Dysembryoplastic neuroepithelial tumor, Embryonal carcinoma, Endodermal sinus tumor, Endometrial cancer, Endometrial Uterine Cancer, Endometrioid tumor, Enteropathy-associated T-cell lymphoma, Ependymoblastoma, Ependymoma, Epithelioid sarcoma, Erythroleukemia, Esophageal cancer, Esthesioneuroblastoma, Ewing Family of Tumor, Ewing Family Sarcoma, Ewing's sarcoma, Extracranial Germ Cell Tumor, Extragonadal Germ Cell Tumor, Extrahepatic Bile Duct Cancer, Extramammary Paget's disease, Fallopian tube cancer, Fetus in fetu, Fibroma, Fibrosarcoma, Follicular lymphoma, Follicular thyroid cancer, Gallbladder Cancer, Gallbladder cancer, Ganglioglioma, Ganglioneuroma, Gastric Cancer, Gastric lymphoma, Gastrointestinal cancer, Gastrointestinal Carcinoid Tumor, Gastrointestinal Stromal Tumor, Gastrointestinal stromal tumor, Germ cell tumor, Germinoma, Gestational choriocarcinoma, Gestational Trophoblastic Tumor, Giant cell tumor of bone, Glioblastoma multiforme, Glioma, Gliomatosis cerebri, Glomus tumor, Glucagonoma, Gonadoblastoma, Granulosa cell tumor, Hairy Cell Leukemia, Hairy cell leukemia, Head and Neck Cancer, Head and neck cancer, Heart cancer, Hemangioblastoma, Hemangiopericytoma, Hemangiosarcoma, Hematological malignancy, Hepatocellular carcinoma, Hepatosplenic T-cell lymphoma, Hereditary breast-ovarian cancer syndrome, Hodgkin Lymphoma, Hodgkin's lymphoma, Hypopharyngeal Cancer, Hypothalamic Glioma, Inflammatory breast cancer, Intraocular Melanoma, Islet cell carcinoma, Islet Cell Tumor, Juvenile myelomonocytic leukemia, Kaposi Sarcoma, Kaposi's sarcoma, Kidney Cancer, Klatskin tumor, Krukenberg tumor, Laryngeal Cancer, Laryngeal cancer, Lentigo maligna melanoma, Leukemia, Leukemia, Lip and Oral Cavity Cancer, Liposarcoma, Lung cancer, Luteoma, Lymphangioma, Lymphangiosarcoma, Lymphoepithelioma, Lymphoid leukemia, Lymphoma, Macroglobulinemia, Malignant Fibrous Histiocytoma, Malignant fibrous histiocytoma, Malignant Fibrous Histiocytoma of Bone, Malignant Glioma, Malignant Mesothelioma, Malignant peripheral nerve sheath tumor, Malignant rhabdoid tumor, Malignant triton tumor, MALT lymphoma, Mantle cell lymphoma, Mast cell leukemia, Mediastinal germ cell tumor, Mediastinal tumor, Medullary thyroid cancer, Medulloblastoma, Medulloblastoma, Medulloepithelioma, Melanoma, Melanoma, Meningioma, Merkel Cell Carcinoma, Mesothelioma, Mesothelioma, Metastatic Squamous Neck Cancer with Occult Primary, Metastatic urothelial carcinoma, Mixed Mullerian tumor, Monocytic leukemia, Mouth Cancer, Mucinous tumor, Multiple Endocrine Neoplasia Syndrome, Multiple Myeloma, Multiple myeloma, Mycosis Fungoides, Mycosis fungoides, Myelodysplastic Disease, Myelodysplastic Syndromes, Myeloid leukemia, Myeloid sarcoma, Myeloproliferative Disease, Myxoma, Nasal Cavity Cancer, Nasopharyngeal Cancer, Nasopharyngeal carcinoma, Neoplasm, Neurinoma, Neuroblastoma, Neuroblastoma, Neurofibroma, Neuroma, Nodular melanoma, Non-Hodgkin Lymphoma, Non-Hodgkin lymphoma, Nonmelanoma Skin Cancer, Non-Small Cell Lung Cancer, Ocular oncology, Oligoastrocytoma, Oligodendroglioma, Oncocytoma, Optic nerve sheath meningioma, Oral Cancer, Oral cancer, Oropharyngeal Cancer, Osteosarcoma, Osteosarcoma, Ovarian Cancer, Ovarian cancer, Ovarian Epithelial Cancer, Ovarian Germ Cell Tumor, Ovarian Low Malignant Potential Tumor, Paget's disease of the breast, Pancoast tumor, Pancreatic Cancer, Pancreatic cancer, Papillary thyroid cancer, Papillomatosis, Paraganglioma, Paranasal Sinus Cancer, Parathyroid Cancer, Penile Cancer, Perivascular epithelioid cell tumor, Pharyngeal Cancer, Pheochromocytoma, Pineal Parenchymal Tumor of Intermediate Differentiation, Pineoblastoma, Pituicytoma, Pituitary adenoma, Pituitary tumor, Plasma Cell Neoplasm, Pleuropulmonary blastoma, Polyembryoma, Precursor T-lymphoblastic lymphoma, Primary central nervous system lymphoma, Primary effusion lymphoma, Primary Hepatocellular Cancer, Primary Liver Cancer, Primary peritoneal cancer, Primitive neuroectodermal tumor, Prostate cancer, Pseudomyxoma peritonei, Rectal Cancer, Renal cell carcinoma, Respiratory Tract Carcinoma Involving the NUT Gene on Chromosome 15, Retinoblastoma, Rhabdomyoma, Rhabdomyosarcoma, Richter's transformation, Sacrococcygeal teratoma, Salivary Gland Cancer, Sarcoma, Schwannomatosis, Sebaceous gland carcinoma, Secondary neoplasm, Seminoma, Serous tumor, Sertoli-Leydig cell tumor, Sex cord-stromal tumor, Sezary Syndrome, Signet ring cell carcinoma, Skin Cancer, Small blue round cell tumor, Small cell carcinoma, Small Cell Lung Cancer, Small cell lymphoma, Small intestine cancer, Soft tissue sarcoma, Somatostatinoma, Soot wart, Spinal Cord Tumor, Spinal tumor, Splenic marginal zone lymphoma, Squamous cell carcinoma, Stomach cancer, Superficial spreading melanoma, Supratentorial Primitive Neuroectodermal Tumor, Surface epithelial-stromal tumor, Synovial sarcoma, T-cell acute lymphoblastic leukemia, T-cell large granular lymphocyte leukemia, T-cell leukemia, T-cell lymphoma, T-cell prolymphocytic leukemia, Teratoma, Terminal lymphatic cancer, Testicular cancer, Thecoma, Throat Cancer, Thymic Carcinoma, Thymoma, Thyroid cancer, Transitional Cell Cancer of Renal Pelvis and Ureter, Transitional cell carcinoma, Urachal cancer, Urethral cancer, Urogenital neoplasm, Uterine sarcoma, Uveal melanoma, Vaginal Cancer, Verner Morrison syndrome, Verrucous carcinoma, Visual Pathway Glioma, Vulvar Cancer, Waldenstrom's macroglobulinemia, Warthin's tumor, Wilms' tumor, and combinations thereof.
Where cancer cells are to be analyzed, primer sequences useful in any of the various operations for attaching barcode sequences and/or amplification reactions may comprise gene specific sequences which target genes or regions of genes associated with or suspected of being associated with cancer. For example, this can include genes or regions of genes where the presence of mutations (e.g., insertions, deletions, polymorphisms, copy number variations, and gene fusions) associated with a cancerous condition are suspected to be present in a cell population.
As with cancer cell analysis, the analysis and diagnosis of fetal health or abnormality through the analysis of fetal cells is a difficult task using conventional techniques. In particular, in the absence of relatively invasive procedures, such as amniocentesis obtaining fetal cell samples can employ harvesting those cells from the maternal circulation. As will be appreciated, such circulating fetal cells make up an extremely small fraction of the overall cellular population of that circulation. As a result complex analyses are performed in order to characterize what of the obtained data is likely derived from fetal cells as opposed to maternal cells. By employing the single cell characterization methods and systems described herein, however, one can attribute genetic make up to individual cells, and categorize those cells as maternal or fetal based upon their respective genetic make-up. Further, the genetic sequence of fetal cells may be used to identify any of a number of genetic disorders, including, e.g., aneuploidy such as Down syndrome, Edwards syndrome, and Patau syndrome.
Also of interest are immune cells. Methods and compositions disclosed herein can be utilized for sequence analysis of the immune repertoire. Analysis of sequence information underlying the immune repertoire can provide a significant improvement in understanding the status and function of the immune system.
Non-limiting examples of immune cells which can be analyzed utilizing the methods described herein include B cells, T cells (e.g., cytotoxic T cells, natural killer T cells, regulatory T cells, and T helper cells), natural killer cells, cytokine induced killer (CIK) cells; myeloid cells, such as granulocytes (basophil granulocytes, eosinophil granulocytes, neutrophil granulocytes/hypersegmented neutrophils), monocytes/macrophages, mast cell, thrombocytes/megakaryocytes, and dendritic cells. In some embodiments, individual T cells are analyzed using the methods disclosed herein. In some embodiments, individual B cells are analyzed using the methods disclosed herein.
Immune cells express various adaptive immunological receptors relating to immune function, such as T cell receptors and B cell receptors. T cell receptors and B cells receptors play a part in the immune response by specifically recognizing and binding to antigens and aiding in their destruction.
The T cell receptor, or TCR, is a molecule found on the surface of T cells that is generally responsible for recognizing fragments of antigen as peptides bound to major histocompatibility complex (MHC) molecules. The TCR is generally a heterodimer of two chains, each of which is a member of the immunoglobulin superfamily, possessing an N-terminal variable (V) domain, and a C terminal constant domain. In humans, in 95% of T cells the TCR consists of an alpha (α) and beta (β) chain, whereas in 5% of T cells the TCR consists of gamma and delta (γ/δ) chains. This ratio can change during ontogeny and in diseased states as well as in different species. When the TCR engages with antigenic peptide and MHC (peptide/MHC), the T lymphocyte is activated through signal transduction.
Each of the two chains of a TCR contains multiple copies of gene segments—a variable ‘V’ gene segment, a diversity ‘β’ gene segment, and a joining T gene segment. The TCR alpha chain is generated by recombination of V and J segments, while the beta chain is generated by recombination of V, D, and J segments. Similarly, generation of the TCR gamma chain involves recombination of V and J gene segments, while generation of the TCR delta chain occurs by recombination of V, D, and J gene segments. The intersection of these specific regions (V and J for the alpha or gamma chain, or V, D and J for the beta or delta chain) corresponds to the CDR3 region that is important for antigen-MHC recognition. Complementarity determining regions (e.g., CDR1, CDR2, and CDR3), or hypervariable regions, are sequences in the variable domains of antigen receptors (e.g., T cell receptor and immunoglobulin) that can complement an antigen. Most of the diversity of CDRs is found in CDR3, with the diversity being generated by somatic recombination events during the development of T lymphocytes. A unique nucleotide sequence that arises during the gene arrangement process can be referred to as a clonotype.
The B cell receptor, or BCR, is a molecule found on the surface of B cells. The antigen binding portion of a BCR is composed of a membrane-bound antibody that, like most antibodies (e.g., immunoglobulins), has a unique and randomly determined antigen-binding site. The antigen binding portion of a BCR includes membrane-bound immunoglobulin molecule of one isotype (e.g., IgD, IgM, IgA, IgG, or IgE). When a B cell is activated by its first encounter with a cognate antigen, the cell proliferates and differentiates to generate a population of antibody-secreting plasma B cells and memory B cells. The various immunoglobulin isotypes differ in their biological features, structure, target specificity and distribution. A variety of molecular mechanisms exist to generate initial diversity, including genetic recombination at multiple sites.
The BCR is composed of two genes IgH and IgK (or IgL) coding for antibody heavy and light chains. Immunoglobulins are formed by recombination among gene segments, sequence diversification at the junctions of these segments, and point mutations throughout the gene. Each heavy chain gene contains multiple copies of three different gene segments—a variable ‘V’ gene segment, a diversity ‘D’ gene segment, and a joining T gene segment. Each light chain gene contains multiple copies of two different gene segments for the variable region of the protein—a variable ‘V’ gene segment and a joining T gene segment. The recombination can generate a molecule with one of each of the V, D, and J segments. Furthermore, several bases may be deleted and others added (called N and P nucleotides) at each of the two junctions, thereby generating further diversity. After B cell activation, a process of affinity maturation through somatic hypermutation occurs. In this process progeny cells of the activated B cells accumulate distinct somatic mutations throughout the gene with higher mutation concentration in the CDR regions leading to the generation of antibodies with higher affinity to the antigens. In addition to somatic hypermutation activated B cells undergo the process of isotype switching. Antibodies with the same variable segments can have different forms (isotypes) depending on the constant segment. Whereas all naïve B cells express IgM (or IgD), activated B cells mostly express IgG but also IgM, IgA and IgE. This expression switching from IgM (and/or IgD) to IgG, IgA, or IgE occurs through a recombination event causing one cell to specialize in producing a specific isotype. A unique nucleotide sequence that arises during the gene arrangement process can similarly be referred to as a clonotype.
In some embodiments, the methods, compositions and systems disclosed herein are utilized to analyze the various sequences of TCRs and BCRs from immune cells, for example various clonotypes. In some embodiments, methods, compositions and systems disclosed herein are used to analyze the sequence of a TCR alpha chain, a TCR beta chain, a TCR delta chain, a TCR gamma chain, or any fragment thereof (e.g., variable regions including VDJ or VJ regions, constant regions, transmembrane regions, fragments thereof, combinations thereof, and combinations of fragments thereof). In some embodiments, methods, compositions and systems disclosed herein are used to analyze the sequence of a B cell receptor heavy chain, B cell receptor light chain, or any fragment thereof (e.g., variable regions including VDJ or VJ regions, constant regions, transmembrane regions, fragments thereof, combinations thereof, and combinations of fragments thereof).
Where immune cells are to be analyzed, primer sequences useful in any of the various operations for attaching barcode sequences and/or amplification reactions may comprise gene specific sequences which target genes or regions of genes of immune cell proteins, for example immune receptors. Such gene sequences include, but are not limited to, sequences of various T cell receptor alpha variable genes (TRAV genes), T cell receptor alpha joining genes (TRAJ genes), T cell receptor alpha constant genes (TRAC genes), T cell receptor beta variable genes (TRBV genes), T cell receptor beta diversity genes (TRBD genes), T cell receptor beta joining genes (TRBJ genes), T cell receptor beta constant genes (TRBC genes), T cell receptor gamma variable genes (TRGV genes), T cell receptor gamma joining genes (TRGJ genes), T cell receptor gamma constant genes (TRGC genes), T cell receptor delta variable genes (TRDV genes), T cell receptor delta diversity genes (TRDD genes), T cell receptor delta joining genes (TRDJ genes), and T cell receptor delta constant genes (TRDC genes).
The ability to characterize individual cells from larger diverse populations of cells is also of significant value in both environmental testing as well as in forensic analysis, where samples may, by their nature, be made up of diverse populations of cells and other material that “contaminate” the sample, relative to the cells for which the sample is being tested, e.g., environmental indicator organisms, toxic organisms, and the like for, e.g., environmental and food safety testing, victim and/or perpetrator cells in forensic analysis for sexual assault, and other violent crimes, and the like.
Additionally the methods and compositions disclosed herein, allow the determination of not only the immune repertoire and different clonotypes, but the functional characteristics (e.g., the transcriptome) of the cells associated with a clonotype or plurality of clonotypes that bind to the same or similar antigen. These functional characteristics can comprise transcription of cytokine, chemokine, or cell-surface associated molecules, such as, costimulatory molecules, checkpoint inhibitors, cell surface maturation markers, or cell-adhesion molecules. Such analysis allows a cell or cell population expressing a particular T cell receptor, B cell receptor, or immunoglobulin to be associated with certain functional characteristics. For example, for any given antigen there will be multiple clonotypes of T cell receptor, B cell receptor, or immunoglobulin that specifically bind to that antigen. Multiple clonotypes that bind to the same antigen are known as the idiotype.
Additional useful applications of the above described single cell sequencing and characterization processes are in the field of neuroscience research and diagnosis. In particular, neural cells can include long interspersed nuclear elements (LINEs), or ‘jumping’ genes that can move around the genome, which cause each neuron to differ from its neighbor cells. Research has shown that the number of LINEs in human brain exceeds that of other tissues, e.g., heart and liver tissue, with between 80 and 300 unique insertions (See, e.g., Coufal, N. G. et al. Nature 460, 1127-1131 (2009)). These differences have been postulated as being related to a person's susceptibility to neuro-logical disorders (see, e.g., Muotri, A. R. et al. Nature 468, 443-446 (2010)), or provide the brain with a diversity with which to respond to challenges. As such, the methods described herein may be used in the sequencing and characterization of individual neural cells.
The single cell analysis methods described herein are also useful in the analysis of gene expression, as noted above, both in terms of identification of RNA transcripts and their quantitation. In particular, using the single cell level analysis methods described herein, one can isolate and analyze the RNA transcripts present in individual cells, populations of cells, or subsets of populations of cells. In particular, in some cases, the barcode oligonucleotides may be configured to prime, replicate and consequently yield barcoded fragments of RNA from individual cells. For example, in some cases, the barcode oligonucleotides may include mRNA specific priming sequences, e.g., poly-T primer segments that allow priming and replication of mRNA in a reverse transcription reaction or other targeted priming sequences. Alternatively or additionally, random RNA priming may be carried out using random N-mer primer segments of the barcode oligonucleotides.
As noted elsewhere herein, the structure of the barcode oligonucleotides may include a number of sequence elements in addition to the oligonucleotide barcode sequence. One example of a barcode oligonucleotide for use in RNA analysis as described above is shown in
In operation, and with reference to
As noted elsewhere herein, while a poly-T primer sequence is described, other targeted or random priming sequences may also be used in priming the reverse transcription reaction. In some cases, the primer sequence can be a gene specific primer sequence which targets specific genes for reverse transcription. In some examples, such target genes comprise T cell receptor genes, B cell receptor genes or immunoglobulin receptor genes. Likewise, although described as releasing the barcoded oligonucleotides into the partition along with the contents of the lysed cells, it will be appreciated that in some cases, the gel bead bound oligonucleotides may be used to hybridize and capture the mRNA on the solid phase of the gel beads, in order to facilitate the separation of the RNA from other cell contents.
An additional example of a barcode oligonucleotide for use in RNA analysis, including messenger RNA (mRNA, including mRNA obtained from a cell) analysis, is shown in
In an example method of cellular RNA (e.g., mRNA) analysis and in reference to
In an alternative example of a barcode oligonucleotide for use in RNA (e.g., cellular RNA) analysis as shown in
Shown in
Shown in
Shown in
Shown in
The approaches of
Another example of a barcode oligonucleotide for use in RNA analysis, including messenger RNA (mRNA, including mRNA obtained from a cell) analysis is shown in
In an example method of cellular RNA analysis and in reference to
In an alternative example of a barcode oligonucleotide for use in RNA (e.g., cellular RNA) analysis as shown in
An additional example of a barcode oligonucleotide for use in RNA analysis, including messenger RNA (mRNA, including mRNA obtained from a cell) analysis is shown in
In an example method of cellular mRNA analysis and in reference to
Subsequent to cell lysis and the release of barcoded oligonucleotides from the microcapsule, the reaction volume can be subjected to an amplification reaction to generate an amplification product. In an example amplification reaction, the polyT sequence hybridizes to the polyA tail of mRNA 1120 released from the cell as illustrated in operation 1150. Next, in operation 1152, the polyT sequence is then extended in a reverse transcription reaction using the mRNA as a template to produce a cDNA transcript 1122 complementary to the mRNA. Terminal transferase activity of the reverse transcriptase can add additional bases to the cDNA transcript (e.g., polyC) in a template independent manner. The additional bases added to the cDNA transcript, e.g., polyC, can then hybridize with 1114 of the barcoded oligonucleotide. This can facilitate template switching and a sequence complementary to the barcoded oligonucleotide can be incorporated into the cDNA transcript. In various embodiments, the barcoded oligonucleotide does not hybridize to the template polynucleotide.
The barcoded oligonucleotide, upon release from the microcapsule, can be present in the reaction volume at any suitable concentration. In some embodiments, the barcoded oligonucleotide is present in the reaction volume at a concentration of about 0.2 μM, 0.3 μM, 0.4 μM, 0.5 μM, 1 μM, 5 μM, 10 μM, 15 μM, 20 μM, 25 μM, 30 μM, 35 μM, 40 μM, 50 μM, 100 μM, 150 μM, 200 μM, 250 μM, 300 μM, 400 μM, or 500 μM. In some embodiments, the barcoded oligonucleotide is present in the reaction volume at a concentration of at least about 0.2 μM, 0.3 μM, 0.4 μM, 0.5 μM, 1 μM, 5 μM, 10 μM, 15 μM, 20 μM, 25 μM, 30 μM, 35 μM, 40 μM, 50 μM, 100 μM, 150 μM, 200 μM, 250 μM, 300 μM, 400 μM, 500 μM or greater. In some embodiments, the barcoded oligonucleotide is present in the reaction volume at a concentration of at most about 0.2 μM, 0.3 μM, 0.4 μM, 0.5 μM, 1 μM, 5 μM, 10 μM, 15 μM, 20 μM, 25 μM, 30 μM, 35 μM, 40 μM, 50 μM, 100 μM, 150 μM, 200 μM, 250 μM, 300 μM, 400 μM, or 500 μM.
The transcripts can be further processed (e.g., amplified, portions removed, additional sequences added, etc.) and characterized as described elsewhere herein. In some embodiments, the transcripts are sequenced directly. In some embodiments, the transcripts are further processed (e.g., portions removed, additional sequences added, etc) and then sequenced. In some embodiments, the reaction volume is subjected to a second amplification reaction to generate an additional amplification product. The transcripts or first amplification products can be used as the template for the second amplification reaction. In some embodiments, primers for the second amplification reaction comprise the barcoded oligonucleotide and polyT sequence. In some embodiments, primers for the second amplification reaction comprise additional primers co-partitioned with the cell. In some embodiments, these additional amplification products are sequenced directly. In some embodiments, these additional amplification products are further processed (e.g., portions removed, additional sequences added, etc) and then sequenced. The configuration of the amplification products (e.g., first amplification products and second amplification products) generated by such a method can help minimize (or avoid) sequencing of the poly-T sequence during sequencing.
An additional example of a barcode oligonucleotide for use in RNA analysis, including cellular RNA analysis is shown in
An additional example of a barcode oligonucleotide for use in RNA analysis, including cellular RNA analysis is shown in
The single cell analysis methods described herein may also be useful in the analysis of the whole transcriptome. Referring back to the barcode of
In some embodiments, the barcode sequence can be appended to the 3′ end of the template polynucleotide sequence (e.g., mRNA). Such configuration may be desired, for example, if the sequence at the 3′ end of the template polynucleotide is desired to be analyzed.
In some embodiments, the barcode sequence can be appended to the 5′ end of a template polynucleotide sequence (e.g., mRNA). Such configuration may be desired, for example, if the sequence at the 5′ end of the template polynucleotide is desired to be analyzed.
In some embodiments, a barcode sequence can be appended to the 3′ end of a first subset of the template polynucleotides, and a barcode sequence can be appended to the 5′ end of a second subset of the template polynucleotides. In some embodiments, the first subset of template polynucleotides and the second subset of template polynucleotides are appended to barcode sequences in the same partition. In some cases, the barcodes appended to the 3′ ends of template polynucleotides are different from the barcodes appended to the 5′ ends of template polynucleotides. For example, the barcodes appended to the 3′ ends may have a different barcode sequence compared to the barcodes appended to the 5′ end. In some cases, the barcodes appended to the 3′ ends of template polynucleotides have the same barcode sequence as the barcodes appended to the 5′ ends of template polynucleotides. In some cases, beads are used to deliver the barcode oligonucleotides to partitions. The different barcodes can be attached to the same or different bead.
A barcode sequence can be appended to the 5′ end of a template polynucleotide sequence by any suitable method. In some cases, the template polynucleotide is a messenger RNA, mRNA, molecule. The barcode sequence can be appended to the 5′ end of a template polynucleotide sequence by use of a primer comprising the barcode sequence in a primer extension reaction. For example, the barcode may be present in a primer used for a primer extension reaction in which the template polynucleotide or a derivative thereof, for example an amplification product, is used as the template for primer extension. In some cases, the barcode may be present on a template switching oligonucleotide participating in a primer extension reaction. As an alternative, the barcode sequence can be appended to the 5′ end of a template polynucleotide by ligating an oligonucleotide comprising the barcode sequence directly to the template polynucleotide.
In another aspect, the present disclosure provides a method of appending a barcode sequence to the 5′ end of a template polynucleotide sequence by a primer extension reaction using a primer comprising a barcode sequence and the template polynucleotide or a derivative thereof as the template for primer extension. The primer extension reaction may occur in a partition. In some embodiments, a cell, or a nucleic acid derivative thereof, is co-partitioned with a primer capable of primer extension and a template switching oligo comprising a barcode sequence. The primer capable of primer extension may hybridize to a nucleic acid of the cell or to a nucleic acid derivative. In some cases, the template switching oligo comprising the barcode sequence is releasably attached to a bead, e.g., a gel bead. In some embodiments, a cell, or a nucleic acid derivative thereof, is co-partitioned with a primer having a sequence towards a 3′ end that hybridizes to the template polynucleotide, a template switching oligonucleotide having a first predefined sequence towards a 5′ end, and a microcapsule, such as a bead, having barcoded oligonucleotides releasably coupled thereto. In some embodiments, the oligonucleotides coupled to the bead include barcode sequences that are identical (e.g., all oligonucleotides sharing the same barcode sequence). In some aspects, the oligonucleotides coupled to the beads additionally include unique molecular identifier (UMI) sequence segments (e.g., all oligonucleotides having different unique molecular identifier sequences).
In an example,
Although shown as a single oligonucleotide tethered to the surface of a bead, individual beads can include tens to hundreds of thousands or even millions of individual oligonucleotide molecules, where, as previously noted herein, the barcode sequence can be constant or relatively constant for a given bead.
In an example method of generating labeled polynucleotides using a barcode oligonucleotide, a cell or a nucleic acid derived therefrom is co-partitioned with a bead bearing a barcoded oligonucleotide and reagents such as reverse transcriptase, poly-T primers, dNTPs, and a chemical stimulus (e.g., reducing agent) into a partition. The barcoded oligonucleotide attached to the bead can comprise a sequence to facilitate template switching (e.g., polyG or riboG). The partition can be a droplet in an emulsion. In cases where a cell is provided in the partition, the partition can further comprise a lysis reagent to lyse the cell.
Where the bead is a degradable or disruptable bead, the barcoded oligonucleotide can be released from the bead when contacted with the chemical stimulus (e.g., reducing agent). Following release from the bead, the barcoded oligonucleotide can be present in the partition at any suitable concentration. In some embodiments, the barcoded oligonucleotide is present in the partition at a concentration that is suitable for generating a sufficient yield of amplification products for downstream processing and analysis, including, but not limited to, sequencing adaptor attachment and sequencing analysis.
With reference to
Subsequent to 1903A, the nucleic acid product (e.g., cDNA product) may be released from the partition and subject to further processing reactions such as additional amplification. In some cases, the nucleic acid product is pooled with products from other partitions for subsequent processing in bulk. In some cases, a portion of the amplified product can be subjected to enrichment to obtain a subset of nucleic acids corresponding to genes of interest.
In some cases, enrichment to obtain a subset of nucleic acids corresponding to genes of interest comprises one or more amplification reactions. One or more gene specific primers can be used for primer extension using the cDNA molecule as a template. Any of a variety of polymerases can be used in embodiments herein for primer extension, non-limiting examples of which include exonuclease minus DNA Polymerase I large (Klenow) Fragment, Phi29 DNA polymerase, Taq DNA Polymerase, T4 DNA polymerase, T7 DNA polymerase, and the like. Further examples of polymerase enzymes that can be used in embodiments herein include thermostable polymerases, including but not limited to, Thermus thermophilus HB8; Thermus oshimai; Thermus scotoductus; Thermus thermophilus 1B21; Thermus thermophilus GK24; Thermus aquaticus polymerase AmpliTaq® FS or Taq (G46D; F667Y), Taq (G46D; F667Y; E6811), and Taq (G46D; F667Y; T664N; R660G); Pyrococcus furiosus polymerase; Thermococcus gorgonarius polymerase; Pyrococcus species GB-D polymerase; Thermococcus sp. (strain 9deg. N-7) polymerase; Bacillus stearo thermophilus polymerase; Tsp polymerase; Thermus flavus polymerase; Thermus litoralis polymerase; Thermus Z05 polymerase; delta Z05 polymerase (e.g. delta Z05 Gold DNA polymerase); and mutants, variants, or derivatives thereof. In some embodiments, a hot start polymerase is used. A hot start polymerase is a modified form of a DNA polymerase that can be activated by incubation at elevated temperatures.
Additional functional sequences can be added to the nucleic acid product or an amplification product thereof. The additional functional sequences may allow for amplification or sample identification. This may occur in the partition or, alternatively, in bulk. In some cases, the amplification products can be sheared, ligated to adapters and amplified to add additional functional sequences. In some cases, both the enriched and unenriched amplification products are subject to analysis.
In an example method of cellular polynucleotide analysis using the barcode oligonucleotide of
Where the bead is a degradable or disruptable bead, the barcoded oligonucleotide can be released from the bead following the application of stimulus as previously described herein. Following release from the bead, the barcoded oligonucleotide can be present in the partition at any suitable concentration. In some embodiments, the barcoded oligonucleotide is present in the partition at a concentration that is suitable for generating a sufficient yield of amplification products for downstream processing and analysis, including, but not limited to, sequencing adaptor attachment and sequencing analysis. In some embodiments, the concentration of the barcoded oligonucleotide is limited by the loading capacity of the barcode bearing bead, or the amount of oligonucleotides deliverable by the bead.
The template switching oligonucleotide, which can be co-partitioned with the cell, bead bearing barcoded oligonucleotides, etc, can be present in the partition at any suitable concentration. In some embodiments, the template switching oligonucleotide is present in the partition at a concentration that is suitable for efficient template switching during an amplification reaction. The concentration of the template switching oligonucleotide can be dependent on the reagents used for droplet generation. In some embodiments, the template switching oligonucleotide is among a plurality of template switching oligonucleotides.
In some embodiments, the barcoded oligonucleotide and template switching oligonucleotide are present in the partition at similar concentrations. In some embodiments, the barcoded oligonucleotide and template switching oligonucleotides may be present in proportions reflective of the desired amount of amplification products to be generated using each oligonucleotide. In some embodiments, the template switching oligonucleotide is present in the partition at a greater concentration than the barcoded oligonucleotide. This difference in concentration can be due to limitations on the capacity of the barcode bearing bead. In some embodiments, the concentration of the template switching oligonucleotide in the reaction volume is at least 2, 5, 10, 20, 50, 100, 200 or more times that of the concentration of the barcoded oligonucleotide in the same reaction volume when the barcoded oligonucleotide is free in the partition (e.g., not attached to the bead).
As illustrated in
Among a plurality of partitions, the primer and template switching oligonucleotide may be universal to all partitions. The partitions may individually contain more than one cell, one cell, no cells, or nucleic acids derived from a cell. Where analysis of mRNA is desired, for example, the primer may comprise at least a polyT segment capable of hybridizing and priming an extension reaction from the polyA segment of an mRNA. Where analysis of a variety of polynucleotides is desired, the primer may comprise a random sequence capable of hybridizing to and priming extension reactions randomly on various polynucleotide templates. As template switching can occur with the use of an enzyme having terminal transferase activity, a template switching oligonucleotide having a sequence capable of hybridizing to the appended bases can be used for template switching in manner that is independent of the sequence of the polynucleotide templates to be analyzed. In some embodiments, the template switching oligonucleotide can comprise a first predefined sequence towards a 5′ end that does not specifically hybridize to the template. In some embodiments, analysis of particular genes is desired. In such cases, the primer may comprise a gene specific sequence capable of hybridizing to and priming extension reactions from templates comprising specific genes. In some embodiments, multiple genes are to be analyzed and a primer is among a plurality of primers. Individual primers of the plurality may target different genes. Each of the plurality of primers may have a sequence for a particular gene.
Subsequent to the first amplification reaction, the first amplification product or transcript can be subjected to a second amplification reaction to generate a second amplification product. In some cases, additional sequences (e.g., functional sequences such as flow cell attachment sequence, sequencing primer binding sequences, barcode sequences, etc) are to be attached. The first and second amplification reactions can be performed in the same volume, such as for example in a droplet or well. In some cases, the first amplification product is subjected to a second amplification reaction in the presence of a barcoded oligonucleotide to generate a second amplification product having a barcode sequence. The barcode sequence can be unique to a partition, that is, each partition has a unique barcode sequence. The barcoded oligonucleotide may comprise a sequence of at least a segment of the template switching oligonucleotide and at least a second predefined sequence. The segment of the template switching oligonucleotide on the barcoded oligonucleotide can facilitate hybridization of the barcoded oligonucleotide to the transcript, e.g., cDNA transcript, to facilitate the generation of a second amplification product. In addition to a barcode sequence, the barcoded oligonucleotide may comprise a second defined sequence such as at least one of an adaptor sequence, a unique molecular identifier (UMI) sequence, a primer binding site, and a sequencing primer binding site or any combination thereof.
In some embodiments, the second amplification reaction uses the first amplification product as a template and the barcoded oligonucleotide as a primer. As illustrated in operation 1954B, the segment of the template switching oligonucleotide on the barcoded oligonucleotide 1928B can hybridize to the portion of the cDNA transcript or complementary fragment 1922B having a sequence complementary to the template switching oligonucleotide or that which was copied from the template switching oligonucleotide. In the second amplification reaction, extension reaction reagents, e.g., polymerase, nucleoside triphosphates, co-factors (e.g., Mg2+ or Mn2+), that are also co-partitioned, can extend the primer sequence using the first amplification product as template as illustrated in operation 1956B. The second amplification product can comprise a second predefined sequence (e.g., 1808, 1812, and 1810), a sequence of a segment of the template polynucleotide (e.g., mRNA), and a sequence complementary to the primer (e.g., 1924B). In cases where the template polynucleotide is an mRNA molecule, amplification products derived therefrom can comprise the corresponding DNA sequence, for example thymine instead of uracil bases.
In some embodiments, the second amplification product uses the barcoded oligonucleotide as a template and at least a portion of the first amplification product as a primer. As illustrated in operation 1954B, the segment of the first amplification product (e.g., cDNA transcript) having a sequence complementary to the template switching oligonucleotide can hybridize to the segment of the barcoded oligonucleotide comprising a sequence of at least a segment of the template switching oligonucleotide. In the second amplification reaction, extension reaction reagents, e.g., polymerase, nucleoside triphosphates, co-factors (e.g., Mg2+ or Mn2+), that are also co-partitioned, can extend the primer sequence (e.g., first amplification product) using the barcoded oligonucleotide as template as illustrated in operation 1958B. The second amplification product may comprise the sequence of the primer (e.g., 1924B), a sequence which is complementary to the sequence of the template polynucleotide (e.g., mRNA), and a sequence complementary to the second predefined sequence (e.g., 1808, 1812, and 1810).
In some embodiments, the second amplification reaction is performed subsequent to the first amplification reaction in the presence of an intervening purification step. An intervening purification step can be used, for example, to purify the template (e.g., first amplification product) from excess reagents, including excess primers such as template switching oligonucleotides. In some embodiments, the amplification reaction is performed in the absence of an intervening purification step. In certain embodiments, an intervening purification step is not performed so that all sample preparation is performed in a same reaction volume. In the absence of an intervening purification step, the template switching oligonucleotide may compete with barcoded oligonucleotide in the second amplification reaction as the barcoded oligonucleotide comprises at least a segment of the template switching oligonucleotide. Competition between the template switching oligonucleotide and barcoded oligonucleotide in the second amplification reaction to generate additional amplification product may result in a second amplification product lacking a barcode sequence. Such amplification products lacking a barcode sequence may be undesirable as they lack a barcode sequence which can provide unique identifying information of the template. In some embodiments, the template switching oligonucleotide may out-compete the barcoded oligonucleotide in the second amplification reaction if the template switching oligonucleotide is present at a higher concentration in the reaction volume than the barcoded oligonucleotide. Various approaches can be utilized to favor the use of the barcoded oligonucleotide in the second amplification reaction to generate amplification products having a barcode sequence in situations where the barcoded oligonucleotide is present at a lower concentration than the template switching oligonucleotide in the reaction volume.
In some embodiments, the template switching oligonucleotide is not available for primer extension during the second amplification reaction. In some embodiments, the template switching oligonucleotide is degraded prior to the second amplification reaction. In some embodiments, the template switching oligonucleotide is degraded during the second amplification reaction. The template switching oligonucleotide may comprise ribonucleic acids (RNA). A template switching oligonucleotide comprising RNA can be degraded, for example, by elevated temperatures or alkaline conditions. In some embodiments, the template switching oligonucleotide comprises at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% RNA. In some embodiments, the template switching oligonucleotide comprises 100% RNA. In some embodiments, a first reaction rate of the second amplification reaction using the barcoded oligonucleotide is greater than a second reaction rate of the second amplification using the template switching oligonucleotide.
In some embodiments, the barcoded oligonucleotide can hybridize to the first amplification product at a higher annealing temperature as compared to the template switching oligonucleotide. For example, the first amplification product and the barcoded oligonucleotide can have a higher melting temperature as compared to a melting temperature of the first amplification product and the template switching oligonucleotide. In such cases, the second amplification reaction may be performed with an annealing temperature at which the barcoded oligonucleotide is able to hybridize to the first amplification product and initiation primer extension and at which the template switching oligonucleotide is unable to hybridize to the first amplification product and initiate primer extension. In some embodiments, the primer annealing temperature of the second amplification reaction is at least about 0.5° C., 1° C., 2° C., 3° C., 4° C., 5° C., 6° C., 7° C., 8° C., 9° C., 10° C. or greater than a primer annealing temperature of the first amplification reaction. The difference in melting temperatures can result from the presence of modified nucleotides in the template switching oligonucleotide. In some embodiment, the template switching oligonucleotide comprises at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% modified nucleotides. In some embodiments, the template switching oligonucleotide comprises 100% modified oligonucleotides. In some embodiments, the difference in melting temperature can be the result of the presence of modified nucleotides in the barcoded oligonucleotide. In some embodiment, the barcoded oligonucleotide comprises at least 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% modified nucleotides. In some embodiments, the barcoded oligonucleotide comprises 100% modified oligonucleotides. Modified nucleotides include, but are not limited to, 2-Aminopurine, 2,6-Diaminopurine (2-Amino-dA), inverted dT, 5-Methyl dC, 2′-deoxylnosine, Super T (5-hydroxybutynl-2′-deoxyuridine), Super G (8-aza-7-deazaguanosine), locked nucleic acids (LNAs), unlocked nucleic acids (UNAs, e.g., UNA-A, UNA-U, UNA-C, UNA-G), Iso-dG, Iso-dC, and 2′ Fluoro bases (e.g., Fluoro C, Fluoro U, Fluoro A, and Fluoro G).
In various embodiments, the first amplification reaction is facilitated using an enzyme comprising polymerase activity. For example, the first amplification reaction can be facilitated by a DNA-dependent polymerase or a reverse-transcriptase (e.g., RNA dependent). In some embodiments, the first amplification reaction comprises polymerase chain reaction. In some embodiments, the first amplification reaction comprises reverse transcription. In various embodiments, the second amplification reaction is facilitated using an enzyme comprising polymerase activity. For example, the second amplification reaction can be facilitated by a DNA-dependent polymerase. In some embodiments, the second amplification reaction comprises polymerase chain reaction.
In another aspect, a template polynucleotide comprising mRNA may first be reverse transcribed to cDNA (e.g., an amplification product of the template polynucleotide). The mRNA molecule can be reverse transcribed to cDNA using a reverse transcriptase enzyme and a primer, such as a poly-T primer. Non-limiting examples of enzymes that can be used for reverse transcription in embodiments herein include HIV-1 reverse transcriptase, M-MLV reverse transcriptase, AMV reverse transcriptase, telomerase reverse transcriptase, and variants, modified products and derivatives thereof.
A gene specific primer having a barcode sequence can then be used for primer extension using the cDNA molecule (e.g., amplification product of the template polynucleotide) as a template. A primer comprising a barcode can hybridize to the cDNA molecule via sequence complementarity. Extension of the primer using the cDNA molecule as template may result in a polynucleotide product comprising the template polynucleotide sequence and the barcode sequence located at the 5′ end of the template polynucleotide sequence. Any of a variety of polymerases can be used in embodiments herein for primer extension, non-limiting examples of which include exonuclease minus DNA Polymerase I large (Klenow) Fragment, Phi29 DNA polymerase, Taq DNA Polymerase, T4 DNA polymerase, T7 DNA polymerase, and the like. Further examples of polymerase enzymes that can be used in embodiments herein include thermostable polymerases, including but not limited to, Thermus thermophilus HB8; Thermus oshimai; Thermus scotoductus; Thermus thermophilus 1B21; Thermus thermophilus GK24; Thermus aquaticus polymerase AmpliTaq® FS or Taq (G46D; F667Y), Taq (G46D; F667Y; E6811), and Taq (G46D; F667Y; T664N; R660G); Pyrococcus furiosus polymerase; Thermococcus gorgonarius polymerase; Pyrococcus species GB-D polymerase; Thermococcus sp. (strain 9deg. N-7) polymerase; Bacillus stearo thermophilus polymerase; Tsp polymerase; Thermus flavus polymerase; Thermus litoralis polymerase; Thermus Z05 polymerase; delta Z05 polymerase (e.g. delta Z05 Gold DNA polymerase); and mutants, variants, or derivatives thereof. In some embodiments, a hot start polymerase is used. A hot start polymerase is a modified form of a DNA polymerase that can be activated by incubation at elevated temperatures. Such a polymerase can be used, for example, to further increase sensitivity, specificity, and yield; and/or to further improve low copy target amplification.
In another aspect, a barcode sequence is appended to the 5′ end of a template polynucleotide sequence by ligating an oligonucleotide comprising a barcode sequence directly to the 5′ end of the template polynucleotide. Ligating an oligonucleotide comprising a barcode sequence to a template polynucleotide can be implemented by various methods. In some embodiments herein, ligating an oligonucleotide comprising a barcode sequence to a template polynucleotide involves an enzyme, such as a ligase (e.g., an RNA ligase or a DNA ligase). Non-limiting examples of enzymes that can be used for ligation in embodiments herein include ATP-dependent double-stranded polynucleotide ligases, NAD+ dependent DNA or RNA ligases, and single-strand polynucleotide ligases. Non-limiting examples of ligases which can be used in embodiments herein include CircLigase I and CircLigase II (Epicentre; Madison, Wis.), Escherichia coli DNA ligase, Thermus filiformis DNA ligase, Tth DNA ligase, Thermus scotoductus DNA ligase (I and II), T3 DNA ligase, T4 DNA ligase, T4 RNA ligase, T7 DNA ligase, Taq ligase, Ampligase (Epicentre® Technologies Corp.), VanC-type ligase, 9° N DNA Ligase, Tsp DNA ligase, DNA ligase I, DNA ligase III, DNA ligase IV, Sso7-T3 DNA ligase, Sso7-T4 DNA ligase, Sso7-T7 DNA ligase, Sso7-Taq DNA ligase, Sso7-E. coli DNA ligase, Sso7-Ampligase DNA ligase, and thermostable ligases. Ligase enzymes may be wild-type, mutant isoforms, and genetically engineered variants.
In some embodiments where a barcode oligonucleotide is ligated to a template polynucleotide comprising mRNA, the mRNA molecule can be treated to yield a 5′ monophosphate group prior to ligating. Any suitable reaction may be employed to yield a 5′ monophosphate group. For example, the mRNA molecule can be treated with an enzyme such as a pyrophosphohydrolase. An example of a pyrophosphohydrolase that can be used in embodiments herein is RNA 5′ phyrophosphohydrolase (RppH). In some cases, all of the phosphate groups at the 5′ end of the molecule are removed and a single phosphate groups is added back to the 5′ end. In some cases, two phosphate groups are removed from a triphosphate group to yield a monophosphate. In some cases, a single enzyme both removes the phosphate groups present on the mRNA molecule and adds the monophosphate group. In some cases, a first enzyme removes the phosphate groups present on the mRNA molecule and a second enzyme adds the monophosphate group. In some cases, the phosphate groups are removed from the 5′ end of the mRNA molecule and the 5′ end is adenylated. An enzyme which can be used for 5′ adenylation in embodiments herein includes Mth RNA ligase.
In some cases, the oligonucleotide comprising the barcode sequence is ligated to the template polynucleotide within a partition (e.g., droplet or well). A partition, in some cases, comprises a polynucleotide sample comprising the template polynucleotide, an oligonucleotide having the barcode sequence, a ligase enzyme, and any other suitable reagents for ligation. The ligase can implement the attachment of the oligonucleotide comprising the barcode sequence to the template polynucleotide within the partition. In some cases, the template polynucleotide is an mRNA molecule and the oligonucleotide ligated to it is a DNA molecule. In some cases, the oligonucleotide comprising the barcode sequence is ligated to the template polynucleotide outside of a partition.
Following the attachment of an oligonucleotide comprising a barcode sequence to the 5′ end of a template polynucleotide, for example an mRNA polynucleotide, the barcoded template can be subjected to further amplification. In some cases, one or more further amplification reactions are performed within the partition. In some cases, one or more further amplification reactions are performed outside of a partition. In some cases, a plurality of barcoded mRNA polynucleotides, for example from a plurality of partitions, is pooled and subjected to further processing in bulk. In some embodiments, the barcoded template polynucleotide is subjected to polymerase chain reaction. In some embodiments, the template polynucleotide comprises mRNA and the barcoded template polynucleotide is subjected to reverse transcription, yielding a cDNA transcript. In embodiments where reverse transcription is performed in a partition, the partitions can comprise primers having a poly-T region capable of hybridizing to the poly-A region of the barcoded mRNA. Within the partition, the primer having a poly-T region can hybridize to the barcoded template and initiate primer extension in reverse transcription. Non-limiting examples of enzymes that can be used for reverse transcription in embodiments herein include HIV-1 reverse transcriptase, M-MLV reverse transcriptase, AMV reverse transcriptase, telomerase reverse transcriptase, and variants, modified products and derivatives thereof. A partition can contain a reverse transcriptase enzyme capable of reverse transcribing a template polynucleotide that is attached at its 5′ end to a barcoded oligonucleotide. In embodiments where reverse transcription is performed in bulk, a plurality of barcoded mRNA polynucleotides from a plurality of partitions can be pooled for bulk processing. The reaction volume for performing reverse transcription can comprise primers having a poly-T region capable of hybridizing to the poly-A region of a barcoded mRNA. In some cases, the primers for reverse transcription further comprise additional elements, such as tags, which can be used, for example, for isolating cDNA transcripts. For example, cDNA transcripts comprising biotin tags can be isolated from components of the reaction volume (e.g., excess primers, reverse transcriptase enzyme, barcoded mRNA molecules) by performing a purification reaction with streptavidin or other molecule capable of binding biotin.
Following the generation of barcoded template polynucleotides or derivatives (e.g., amplification products) thereof, subsequent operations may be performed, including purification (e.g., via solid phase reversible immobilization (SPRI)) or further processing (e.g., shearing, addition of functional sequences, and subsequent amplification (e.g., via PCR)). Functional sequences, such as flow cell sequences, may be added by ligation. These operations may occur in bulk (e.g., outside the partition). In the case where a partition is a droplet in an emulsion, the emulsion can be broken and the contents of the droplet pooled for additional operations. Additional reagents that may be co-partitioned along with the barcode bearing bead may include oligonucleotides to block ribosomal RNA (rRNA) and nucleases to digest genomic DNA from cells. Alternatively, rRNA removal agents may be applied during additional processing operations. The configuration of the constructs generated by such a method can help minimize (or avoid) sequencing of the poly-T sequence during sequencing and/or sequence the 5′ end of a polynucleotide sequence. The amplification products, for example first amplification products and/or second amplification products, may be subject to sequencing for sequence analysis.
Although operations with various barcode designs have been discussed individually, individual beads can include barcode oligonucleotides of various designs for simultaneous use.
In addition to characterizing individual cells or cell sub-populations from larger populations, the processes and systems described herein may also be used to characterize individual cells as a way to provide an overall profile of a cellular, or other organismal population. A variety of applications require the evaluation of the presence and quantification of different cell or organism types within a population of cells, including, for example, microbiome analysis and characterization, environmental testing, food safety testing, epidemiological analysis, e.g., in tracing contamination or the like. In particular, the analysis processes described above may be used to individually characterize, sequence and/or identify large numbers of individual cells within a population. This characterization may then be used to assemble an overall profile of the originating population, which can provide important prognostic and diagnostic information.
For example, shifts in human microbiomes, including, e.g., gut, buccal, epidermal microbiomes, etc., have been identified as being both diagnostic and prognostic of different conditions or general states of health. Using the single cell analysis methods and systems described herein, one can again, characterize, sequence and identify individual cells in an overall population, and identify shifts within that population that may be indicative of diagnostic ally relevant factors. By way of example, sequencing of bacterial 16S ribosomal RNA genes has been used as a highly accurate method for taxonomic classification of bacteria. Using the targeted amplification and sequencing processes described above can provide identification of individual cells within a population of cells. One may further quantify the numbers of different cells within a population to identify current states or shifts in states over time. See, e.g., Morgan et al, PLoS Comput. Biol., Ch. 12, December 2012, 8(12):e1002808, and Ram et al., Syst. Biol. Reprod. Med., June 2011, 57(3):162-170, each of which is incorporated herein by reference in its entirety for all purposes. Likewise, identification and diagnosis of infection or potential infection may also benefit from the single cell analyses described herein, e.g., to identify microbial species present in large mixes of other cells or other biological material, cells and/or nucleic acids, including the environments described above, as well as any other diagnostically relevant environments, e.g., cerebrospinal fluid, blood, fecal or intestinal samples, or the like.
The foregoing analyses may also be particularly useful in the characterization of potential drug resistance of different cells or pathogens, e.g., cancer cells, bacterial pathogens, etc., through the analysis of distribution and profiling of different resistance markers/mutations across cell populations in a given sample. Additionally, characterization of shifts in these markers/mutations across populations of cells over time can provide valuable insight into the progression, alteration, prevention, and treatment of a variety of diseases characterized by such drug resistance issues.
Although described in terms of cells, it will be appreciated that any of a variety of individual biological organisms, or components of organisms are encompassed within this description, including, for example, cells, viruses, organelles, cellular inclusions, vesicles, or the like. Additionally, where referring to cells, it will be appreciated that such reference includes any type of cell, including without limitation prokaryotic cells, eukaryotic cells, bacterial, fungal, plant, mammalian, or other animal cell types, mycoplasmas, normal tissue cells, tumor cells, or any other cell type, whether derived from single cell or multicellular organisms.
Similarly, analysis of different environmental samples to profile the microbial organisms, viruses, or other biological contaminants that are present within such samples, can provide important information about disease epidemiology, and potentially aid in forecasting disease outbreaks, epidemics an pandemics.
As described above, the methods, systems and compositions described herein may also be used for analysis and characterization of other aspects of individual cells or populations of cells. In one example process, a sample is provided that contains cells that are to be analyzed and characterized as to their cell surface proteins. Also provided is a library of antibodies, antibody fragments, or other molecules having a binding affinity to the cell surface proteins or antigens (or other cell features) for which the cell is to be characterized (also referred to herein as cell surface feature binding groups). For ease of discussion, these affinity groups are referred to herein as binding groups. The binding groups can include a reporter molecule that is indicative of the cell surface feature to which the binding group binds. In particular, a binding group type that is specific to one type of cell surface feature will comprise a first reporter molecule, while a binding group type that is specific to a different cell surface feature will have a different reporter molecule associated with it. In some aspects, these reporter molecules will comprise oligonucleotide sequences. Oligonucleotide based reporter molecules provide advantages of being able to generate significant diversity in terms of sequence, while also being readily attachable to most biomolecules, e.g., antibodies, etc., as well as being readily detected, e.g., using sequencing or array technologies. In the example process, the binding groups include oligonucleotides attached to them. Thus, a first binding group type, e.g., antibodies to a first type of cell surface feature, will have associated with it a reporter oligonucleotide that has a first nucleotide sequence. Different binding group types, e.g., antibodies having binding affinity for other, different cell surface features, will have associated therewith reporter oligonucleotides that comprise different nucleotide sequences, e.g., having a partially or completely different nucleotide sequence. In some cases, for each type of cell surface feature binding group, e.g., antibody or antibody fragment, the reporter oligonucleotide sequence may be known and readily identifiable as being associated with the known cell surface feature binding group. These oligonucleotides may be directly coupled to the binding group, or they may be attached to a bead, molecular lattice, e.g., a linear, globular, cross-slinked, or other polymer, or other framework that is attached or otherwise associated with the binding group, which allows attachment of multiple reporter oligonucleotides to a single binding group.
In the case of multiple reporter molecules coupled to a single binding group, such reporter molecules can comprise the same sequence, or a particular binding group will include a known set of reporter oligonucleotide sequences. As between different binding groups, e.g., specific for different cell surface features, the reporter molecules can be different and attributable to the particular binding group.
Attachment of the reporter groups to the binding groups may be achieved through any of a variety of direct or indirect, covalent or non-covalent associations or attachments. For example, in the case of oligonucleotide reporter groups associated with antibody based binding groups, such oligonucleotides may be covalently attached to a portion of an antibody or antibody fragment using chemical conjugation techniques (e.g., Lightning-Link® antibody labeling kits available from Innova Biosciences), as well as other non-covalent attachment mechanisms, e.g., using biotinylated antibodies and oligonucleotides (or beads that include one or more biotinylated linker, coupled to oligonucleotides) with an avidin or streptavidin linker. Antibody and oligonucleotide biotinylation techniques are available (See, e.g., Fang, et al., Fluoride—Cleavable Biotinylation Phosphoramidite for 5′-end-Labeling and Affinity Purification of Synthetic Oligonucleotides, Nucleic Acids Res. Jan. 15, 2003; 31(2):708-715, DNA 3′ End Biotinylation Kit, available from Thermo Scientific, the full disclosures of which are incorporated herein by reference in their entirety for all purposes). Likewise, protein and peptide biotinylation techniques have been developed and are readily available (See, e.g., U.S. Pat. No. 6,265,552, the full disclosures of which are incorporated herein by reference in their entirety for all purposes).
The reporter oligonucleotides may be provided having any of a range of different lengths, depending upon the diversity of reporter molecules desired or a given analysis, the sequence detection scheme employed, and the like. In some cases, these reporter sequences can be greater than about 5 nucleotides in length, greater than about 10 nucleotides in length, greater than about 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 150 or even 200 nucleotides in length. In some cases, these reporter nucleotides may be less than about 250 nucleotides in length, less than about 200, 180, 150, 120 100, 90, 80, 70, 60, 50, 40, or even 30 nucleotides in length. In many cases, the reporter oligonucleotides may be selected to provide barcoded products that are already sized, and otherwise configured to be analyzed on a sequencing system. For example, these sequences may be provided at a length that ideally creates sequenceable products of a desired length for particular sequencing systems. Likewise, these reporter oligonucleotides may include additional sequence elements, in addition to the reporter sequence, such as sequencer attachment sequences, sequencing primer sequences, amplification primer sequences, or the complements to any of these.
In operation, a cell-containing sample is incubated with the binding molecules and their associated reporter oligonucleotides, for any of the cell surface features desired to be analyzed. Following incubation, the cells are washed to remove unbound binding groups. Following washing, the cells are partitioned into separate partitions, e.g., droplets, along with the barcode carrying beads described above, where each partition includes a limited number of cells, e.g., in some cases, a single cell. Upon releasing the barcodes from the beads, they will prime the amplification and barcoding of the reporter oligonucleotides. As noted above, the barcoded replicates of the reporter molecules may additionally include functional sequences, such as primer sequences, attachment sequences or the like.
The barcoded reporter oligonucleotides are then subjected to sequence analysis to identify which reporter oligonucleotides bound to the cells within the partitions. Further, by also sequencing the associated barcode sequence, one can identify that a given cell surface feature likely came from the same cell as other, different cell surface features, whose reporter sequences include the same barcode sequence, i.e., they were derived from the same partition.
Based upon the reporter molecules that emanate from an individual partition based upon the presence of the barcode sequence, one may then create a cell surface profile of individual cells from a population of cells. Profiles of individual cells or populations of cells may be compared to profiles from other cells, e.g., ‘normal’ cells, to identify variations in cell surface features, which may provide diagnostically relevant information. In particular, these profiles may be particularly useful in the diagnosis of a variety of disorders that are characterized by variations in cell surface receptors, such as cancer and other disorders.
The present disclosure also provides methods for reducing nonspecific priming in a single-cell 5′ gene expression assay. In generating an assay that allows measurement of 1) a cell barcode sequence (barcode), 2) a unique molecular identifier sequence (UMI) and 3) the 5′ sequence of an mRNA transcript simultaneously, one strategy is to place these sequences on a sequence that attaches to the 5′ end of an mRNA transcript—in the present disclosure, this may be accomplished by placing the barcode and UMI on a template switching oligonucleotide (TSO). This oligonucleotide may be attached to the first strand cDNA via a template switching reaction where the reverse transcription (RT) enzyme 1) reverse transcribes a messenger RNA (mRNA) sequence into first-strand complementary DNA (cDNA) from a primer targeting the 3′ end of the mRNA, 2) adds nontemplated cytidines to the 5′ end of the first-strand cDNA, 3) switches template to the TSO, which may contain 3′ guanidines or guanidine-derivatives that hybridize to the added cytidines. The result is a first-strand cDNA molecule that is complementary to the TSO sequence: cell-barcode, UMI, guanidines, and the 5′ end of the mRNA.
In some cases, the TSO may co-exist in solution with the RT enzyme and the total RNA contents of a cell. If the TSO is a single stranded DNA (ssDNA) molecule, it can participate as an RT primer rather than as a template-switching substrate. Given, for example, that the over 90% of the total RNA contents of a cell include noncoding ribosomal RNA (rRNA), this may produce barcoded off products that do not contribute to the 5′ gene expression or V(D)J sequencing assay but do consume sequencing reads, increasing the cost required to achieve the same sequencing depth. In addition, if the UMI is implemented as a randomer, the presence of this randomer at the 3′ end of the TSO greatly increases its ability to serve as a primer on rRNA template.
In some cases, a TSO that is less likely to serve as an RT primer via the introduction of a particular spacer sequence between the UMI and terminal riboGs may be used. Another approach is to design and include a set of auxiliary blocking oligonucleotides that may hybridize to rRNA and prevent binding of the TSO.
The spacer sequence can be optimized by selecting a sequence that minimizes the predicted melting temperature of the (spacer-GGG):rRNA duplex against all human ribosomal RNA molecules.
The blocker sequences can be optimized by selecting sequences that maximize the predicted melting temperature of the (blocker):rRNA duplex against all human ribosomal RNA molecules.
Provided herein are TSO that are less likely to serve as an RT primer via the introduction of a particular spacer sequence between the UMI and terminal riboGs. Additionally, described herein are auxiliary blocking oligonucleotides that hybridize to rRNA and prevent binding of the TSO.
Table 1 provides examples of spacer sequences that are optimized by selecting a sequence that minimizes the predicted melting temperature of the (spacer-GGG):rRNA duplex against all human ribosomal RNA molecules.
Table 2 provides examples of blocker sequences that are optimized by selecting sequences that maximize the predicted melting temperature of the (blocker):rRNA duplex against all human ribosomal RNA molecules.
Table 3 provides examples of full construct barcodes.
In some examples, a cell barcode may be a 16 base sequence that is a random choice from about 737,000 sequences. The length of the barcode (16) can be altered. The diversity of potential barcode sequences (737k) can be alterable. The defined nature of the barcode can be altered, for example, it may also be completely random (16 Ns) or semi-random (16 bases that come from a biased distribution of nucleotides).
The canonical UMI sequence may be a 10 nucleotide randomer. The length of the UMI can be altered. The random nature of the UMI can be altered, for example, it may be semi-random (bases that come from a biased distribution of nucleotides.) In a certain case, the distribution of UMI nucleotide(s) may be biased; for example, UMI sequences that do not contain Gs or Cs may be less likely to serve as primers.
The spacer may alterable within given or predetermined parameters. For example one method may give an optimal sequence of TTTCTTATAT (SEQ ID NO: 159), but using a slightly different optimization strategy results in a sequence that is likely just as or nearly as good.
The selected template switching region can comprise 3 consecutive riboGs or more. The selected template switching region can comprise 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 consecutive riboGs or more. Alternative nucleotide may be used such as deoxyribo Gs, LNA G's, and potentially any combination thereof.
The present disclosure also provides methods of enriching cDNA sequences. Enrichment may be useful for TCR, BCR, and immunoglobulin gene analysis since these genes may possess similar yet polymorphic variable region sequences. These sequences can be responsible for antigen binding and peptide-MHC interactions. For example, due to gene recombination events in individual developing T cells, a single human or mouse will naturally express many thousands of different TCR genes. This T cell repertoire can exceed 100,000 or more different TCR rearrangements occurring during T cell development, yielding a total T cell population that is highly polymorphic with respect to its TCR gene sequences especially for the variable region. For immunoglobulin genes, the same may apply, except even greater diversity may be present. As previously noted, each distinct sequence may correspond to a clonotype. In certain embodiments, enrichment increases accuracy and sensitivity of methods for sequencing TCR, BCR and immunoglobulin genes at a single cell level. In certain embodiments, enrichment increases the number of sequencing reads that map to a TCR, BCR, or immunoglobulin gene. In some embodiments, enrichment leads to greater than or equal to 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or more of total sequencing reads mapping to a TCR, BCR or immunoglobulin gene. In some embodiments, enrichment leads to greater than or equal to 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or more of total sequencing reads mapping to a variable region of a TCR, BCR or immunoglobulin gene.
In order to aide in sequencing, detection, and analysis of sequences of interest, an enrichment step can be employed. Enrichment may be useful for the sequencing and analysis of genes that may be related yet highly polymorphic. In some embodiments, an enriched gene comprises a TCR sequence, a BCR sequence, or an immunoglobulin sequence. In some embodiments, an enriched gene comprises a mitochondrial gene or a cytochrome family gene. In some embodiments, enrichment is employed after an initial round of reverse transcription (e.g., cDNA production). In some embodiments, enrichment is employed after an initial round of reverse transcription and cDNA amplification for at least 5, 10, 15, 20, 25, 30, 40 or more cycles. In some embodiments, enrichment is employed after a cDNA amplification. In some embodiments, the amplified cDNA can be subjected to a clean up step before the enrichment step using a column, gel extraction, or beads in order to remove unincorporated primers, unincorporated nucleotides, very short or very long nucleic acid fragments and enzymes. In some embodiments, enrichment is followed by a clean-up step before sequencing library preparation.
Enrichment of gene or cDNA sequences can be facilitated by a primer that anneals within a known sequence of the target gene. In some embodiments, for enrichment of a TCR, BCR, or immunoglobulin gene, a primer that anneals to a constant region of the gene or cDNA can be paired with a sequencing primer that anneals to a TSO functional sequence. In some embodiments, the enriched cDNA falls into a length range that approximately corresponds to that genes variable region. In some embodiments, greater than about 50%, 60%, 70%, 80%, 85%, 90%, 95% or more cDNA or cDNA fragments fall within a range of about 300 base pairs to about 900 base pairs, of about 400 base pairs to about 800 base pairs, of about 500 base pairs to about 700 base pairs, or of about 500 base pairs to about 600 base pairs.
Next, additional functional sequences can be added that allow for amplification or sample identification. This may occur in a partition or in bulk. This reaction yields amplified cDNA molecules as in 2003 which are mixed templates comprising a barcode and sequencing primers. In some cases, not all of these cDNA molecules will comprise a target variable region sequence. In one enrichment scheme, shown in operation 2004, a primer 2018 that anneals to a sequence 3′ of a TCR, BCR or immunoglobulin variable region 2020 specifically amplifies the variable region comprising cDNAs yielding products as shown in operation 2005. Such enrichment may be performed for various approaches described herein, such as, e.g., the approaches described above in the context of
In certain aspects, primer 2018 anneals in a constant region of a TCR (e.g., TCR-alpha or TCR-beta), BCR or immunoglobulin gene. After amplification the products are sheared, adaptors ligated and amplified a second time to add additional functional sequences 2007 and 2011 and a sample index 2009 as shown in operation 2006. The additional functional sequences can functionally complement the first pair 2008 and 2010 and comprise for example a P5 or R1 sequence.
In some embodiments, clonotype information derived from next-generation sequencing data of cDNA prepped from cellular RNA is combined with other targeted on non targeted cDNA enrichment to illuminate functional and ontological aspects of B-cell and T cells that express a given TCR, BCR, or immunoglobulin. In some embodiments, clonotype information is combined with analysis of expression of an immunologically relevant cDNA. In some embodiments, the cDNA encodes a cell lineage marker, a cell surface functional marker, immunoglobulin isotype, a cytokine and/or chemokine, an intracellular signaling polypeptide, a cell metabolism polypeptide, a cell-cycle polypeptide, an apoptosis polypeptide, a transcriptional activator/inhibitor, an miRNA or lncRNA.
Also disclosed herein are methods and systems for reference-free clonotype identification. Such methods may be implemented by way of software executing algorithms. Tools for assembling T-cell Receptor (TCR) sequences may use known sequences of V and C regions to “anchor” assemblies. This may make such tools only applicable to organisms with well characterized references (human and mouse). However, most mammalian T cell receptors have similar amino acid motifs and similar structure. In the absence of a reference, a method can scan assembled transcripts for regions that are diverse or semi-diverse, find the junction region which should be highly diverse, then scan for known amino acid motifs. In some cases, it may not be critical that the complementary CDRs, such as the CDR1, CDR2, or CDR3, region be accurately delimited, only that a diverse sequence is found that can uniquely identify the clonotype. One advantage of this method is that the software may not require a set of reference sequences and can operate fully de novo, thus this method can enable immune research in eukaryotes with poorly characterized genomes/transcriptomes.
The methods described herein allow simultaneously obtaining single-cell gene expression information with single-cell immune receptor sequences (TCRs/BCRs). This can be achieved using the methods described herein, such as by amplifying genes relevant to lymphocyte function and state (either in a targeted or unbiased way) while simultaneously amplifying the TCR/BCR sequences for clonotyping. This can allow such applications as 1) interrogating changes in lymphocyte activation/response to an antigen, at the single clonotype or single cell level; or 2) classifying lymphocytes into subtypes based on gene expression while simultaneously sequencing their TCR/BCRs. UMIs are typically ignored during TCR (or generally transcriptome) assembly.
Key analytical operations involved in clonotype sequencing according to the methods described herein include: 1) Assemble each UMI separately, then merge highly similar assembled sequences. High depth per molecule in TCR sequencing makes this feasible. This may result in a reduced chance of “chimeric” assemblies; 2) Assemble all UMIs from each cell together but use UMI information to choose paths in the assembly graph. This is analogous to using barcode and read-pair information to resolve “bubbles” in WGS assemblies; 3) Base quality estimation. UMI information and alignment of short reads may be used to assemble contigs to compute per-base quality scores. Base quality scoring may be important as a few base differences in a CDR sequence may differentiate one clonotype from another. This may be in contrast to other methods that rely on using long-read sequencing.
Thus, base quality estimates for assembled contigs can inform clonotype inference. Errors can make cells with the same (real) clonotype have mismatching assembled sequences. Further, combining base-quality estimates and clonotype abundances to correct clonotype assignments. For example, if 10 cells have clonotype X and one cell has a clonotype that differs by X in only a few bases and these bases have low quality, then this cell may be assigned to clonotype X. In some embodiments, clonotypes that differ by a single amino acid or nucleic acid may be discriminated. In some embodiments, clonotypes that differ by less than 50, 40, 30, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, or 2 amino acids or nucleic acids may be discriminated. An example, non limiting, base error calculation scheme is shown below in Example VII.
Also provided herein are the microfluidic devices used for partitioning the cells as described above. Such microfluidic devices can comprise channel networks for carrying out the partitioning process like those set forth in
Also provided are systems that control flow of these fluids through the channel networks e.g., through applied pressure differentials, centrifugal force, electrokinetic pumping, capillary or gravity flow, or the like.
Also provided herein are kits for analyzing individual cells or small populations of cells. The kits may include one, two, three, four, five or more, up to all of partitioning fluids, including both aqueous buffers and non-aqueous partitioning fluids or oils, nucleic acid barcode libraries that are releasably associated with beads, as described herein, microfluidic devices, reagents for disrupting cells amplifying nucleic acids, and providing additional functional sequences on fragments of cellular nucleic acids or replicates thereof, as well as instructions for using any of the foregoing in the methods described herein.
The present disclosure provides computer control systems that are programmed to implement methods of the disclosure.
The computer system 1701 includes a central processing unit (CPU, also “processor” and “computer processor” herein) 1705, which can be a single core or multi core processor, or a plurality of processors for parallel processing. The computer system 1701 also includes memory or memory location 1710 (e.g., random-access memory, read-only memory, flash memory), electronic storage unit 1715 (e.g., hard disk), communication interface 1720 (e.g., network adapter) for communicating with one or more other systems, and peripheral devices 1725, such as cache, other memory, data storage and/or electronic display adapters. The memory 1710, storage unit 1715, interface 1720 and peripheral devices 1725 are in communication with the CPU 1705 through a communication bus (solid lines), such as a motherboard. The storage unit 1715 can be a data storage unit (or data repository) for storing data. The computer system 1701 can be operatively coupled to a computer network (“network”) 1730 with the aid of the communication interface 1720. The network 1730 can be the Internet, an internet and/or extranet, or an intranet and/or extranet that is in communication with the Internet. The network 1730 in some cases is a telecommunication and/or data network. The network 1730 can include one or more computer servers, which can enable distributed computing, such as cloud computing. The network 1730, in some cases with the aid of the computer system 1701, can implement a peer-to-peer network, which may enable devices coupled to the computer system 1701 to behave as a client or a server.
The CPU 1705 can execute a sequence of machine-readable instructions, which can be embodied in a program or software. The instructions may be stored in a memory location, such as the memory 1710. The instructions can be directed to the CPU 1705, which can subsequently program or otherwise configure the CPU 1705 to implement methods of the present disclosure. Examples of operations performed by the CPU 1705 can include fetch, decode, execute, and writeback.
The CPU 1705 can be part of a circuit, such as an integrated circuit. One or more other components of the system 1701 can be included in the circuit. In some cases, the circuit is an application specific integrated circuit (ASIC).
The storage unit 1715 can store files, such as drivers, libraries and saved programs. The storage unit 1715 can store user data, e.g., user preferences and user programs. The computer system 1701 in some cases can include one or more additional data storage units that are external to the computer system 1701, such as located on a remote server that is in communication with the computer system 1701 through an intranet or the Internet.
The computer system 1701 can communicate with one or more remote computer systems through the network 1730. For instance, the computer system 1701 can communicate with a remote computer system of a user. Examples of remote computer systems include personal computers (e.g., portable PC), slate or tablet PC's (e.g., Apple® iPad, Samsung® Galaxy Tab), telephones, Smart phones (e.g., Apple® iPhone, Android-enabled device, Blackberry®), or personal digital assistants. The user can access the computer system 1701 via the network 1730.
Methods as described herein can be implemented by way of machine (e.g., computer processor) executable code stored on an electronic storage location of the computer system 1701, such as, for example, on the memory 1710 or electronic storage unit 1715. The machine executable or machine readable code can be provided in the form of software. During use, the code can be executed by the processor 1705. In some cases, the code can be retrieved from the storage unit 1715 and stored on the memory 1710 for ready access by the processor 1705. In some situations, the electronic storage unit 1715 can be precluded, and machine-executable instructions are stored on memory 1710.
The code can be pre-compiled and configured for use with a machine having a processer adapted to execute the code, or can be compiled during runtime. The code can be supplied in a programming language that can be selected to enable the code to execute in a pre-compiled or as-compiled fashion.
Aspects of the systems and methods provided herein, such as the computer system 1701, can be embodied in programming. Various aspects of the technology may be thought of as “products” or “articles of manufacture” typically in the form of machine (or processor) executable code and/or associated data that is carried on or embodied in a type of machine readable medium. Machine-executable code can be stored on an electronic storage unit, such as memory (e.g., read-only memory, random-access memory, flash memory) or a hard disk. “Storage” type media can include any or all of the tangible memory of the computers, processors or the like, or associated modules thereof, such as various semiconductor memories, tape drives, disk drives and the like, which may provide non-transitory storage at any time for the software programming. All or portions of the software may at times be communicated through the Internet or various other telecommunication networks. Such communications, for example, may enable loading of the software from one computer or processor into another, for example, from a management server or host computer into the computer platform of an application server. Thus, another type of media that may bear the software elements includes optical, electrical and electromagnetic waves, such as used across physical interfaces between local devices, through wired and optical landline networks and over various air-links. The physical elements that carry such waves, such as wired or wireless links, optical links or the like, also may be considered as media bearing the software. As used herein, unless restricted to non-transitory, tangible “storage” media, terms such as computer or machine “readable medium” refer to any medium that participates in providing instructions to a processor for execution.
Hence, a machine readable medium, such as computer-executable code, may take many forms, including but not limited to, a tangible storage medium, a carrier wave medium or physical transmission medium. Non-volatile storage media include, for example, optical or magnetic disks, such as any of the storage devices in any computer(s) or the like, such as may be used to implement the databases, etc. shown in the drawings. Volatile storage media include dynamic memory, such as main memory of such a computer platform. Tangible transmission media include coaxial cables; copper wire and fiber optics, including the wires that comprise a bus within a computer system. Carrier-wave transmission media may take the form of electric or electromagnetic signals, or acoustic or light waves such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media therefore include for example: a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD or DVD-ROM, any other optical medium, punch cards paper tape, any other physical storage medium with patterns of holes, a RAM, a ROM, a PROM and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave transporting data or instructions, cables or links transporting such a carrier wave, or any other medium from which a computer may read programming code and/or data. Many of these forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to a processor for execution.
The computer system 1701 can include or be in communication with an electronic display 1735 that comprises a user interface (UI) 1740 for providing, for example, results of nucleic acid sequencing, analysis of nucleic acid sequencing data, characterization of nucleic acid sequencing samples, cell characterizations, etc. Examples of UI's include, without limitation, a graphical user interface (GUI) and web-based user interface.
Methods and systems of the present disclosure can be implemented by way of one or more algorithms. An algorithm can be implemented by way of software upon execution by the central processing unit 1705. The algorithm can, for example, initiate nucleic acid sequencing, process nucleic acid sequencing data, interpret nucleic acid sequencing results, characterize nucleic acid samples, characterize cells, etc.
EXAMPLESThe following non-limiting examples are given for the purpose of illustrating various embodiments of present disclosure.
Example I: Cellular RNA Analysis Using EmulsionsIn an example, reverse transcription with template switching and cDNA amplification (via PCR) is performed in emulsion droplets with operations as shown in
The yield from template switch reverse transcription and PCR in emulsions is shown for 1,000 cells in
In another example, reverse transcription with template switching and cDNA amplification (via PCR) is performed in emulsion droplets with operations as shown in
In another example, reverse transcription is performed in emulsion droplets and cDNA amplification is performed in bulk in a manner similar to that as shown in
In another example, in vitro transcription by T7 polymerase is used to produce RNA transcripts as shown in
In this example, methods disclosed herein are used to assay T-cell receptors. To generate labeled polynucleotides comprising T-cell receptor gene sequences, T-cells are co-partitioned with gel beads comprising barcoded template switching oligonucleotides. Prior to partitioning, T-cells are optionally enriched from a cell sample, for example by fluorescence activated cell sorting (FACS) or other sorting technique. Additional reagents for generating labeled polynucleotides including, but not limited to, reverse transcriptase enzyme, poly(dT) primer, and dNTPs, are delivered to partitions as part of a master mix. Within partitions, cells are lysed, thereby yielding template polynucleotides comprising nucleic acids from T-cells. As illustrated schematically in
Using methods disclosed herein, reverse transcription performed within partitions generates unbiased cDNA comprising a sequencing adapter, a cell barcode and a unique molecular identifier (UMI) on the 5′ end of the transcript. To enrich for transcripts comprising TCR gene sequences, the first amplification reaction product or cDNA transcript is subjected to a second amplification reaction to generate a second amplification product. Polymerase chain reaction (PCR) is performed with one primer for the 5′ end of the transcript and one or more primers for the desired TCR/Ig constant region(s) (e.g., primers targeting TCR alpha (α) and/or beta (β) chain, and in some cases gamma and/or delta (γ/δ) chains). The contents of multiple partitions can be combined such that the second amplification reaction is performed in bulk.
Next, amplification products are subjected to enzymatic fragmentation and further processed to attach sequencing adaptors to generate a sequencing library. Additional sequences include functional sequences such as flow cell attachment sequences and sequencing primer binding sequences. The labeled polynucleotides are sequenced to yield sequencing reads, and sequencing reads are used to assemble full or partial TCR receptor gene sequences. Additional analysis includes transcript counting for which an analysis pipeline may include, for example, (i) barcode processing, (ii) read filtering, (iii) cell-by-cell consensus assembly, (iv) V(D)J annotation, and (v) clonotype inference and clustering.
Other receptors (e.g., B-cell receptors (BCRs) and Ig receptors) can be similarly analyzed using the methods described herein by partitioning the appropriate immune cell type for generating labeled polynucleotides and using receptor specific primers to generate amplification products.
Example VI: Enrichment of T-cell Receptor (TCR) transcriptsIn this example, cellular suspensions of 3,000; 6,000; or 12,000 primary human T cells were loaded on a GemCode Single Cell Instrument (10× Genomics, Pleasanton, Calif.) to generate single cell-gel bead emulsions (SC-GEMs). The gel beads were modified to carry a template switching oligonucleotide (TSO) as shown in
Indexed sequencing libraries were constructed using the GemCode Single Cell 3′ Library Kit, following these steps: 1) end repair and A-tailing; 2) adapter ligation; 3) post-ligation cleanup with SPRIselect; 4) sample index PCR and cleanup. These sequencing libraries were sequenced using an Illumina MiSeq sequencer. Sequencing performance of poly-T primed libraries was compared to libraries constructed from enriched cDNA libraries created by using an enriched priming method which substituted the poly-T primer with primers that bound the constant region of TCRα, TCRβ, or both.
In order to increase cDNA yields prior to sequencing library preparation, differing concentrations of TSO were tested. TSO were tested at concentrations of 32, 16, 8, 4, 2, 1, and 0.5 μM (which may correspond to 800, 400, 200, 100, 50, 25, and 12.5 μM immobilized to gel beads). Jurkat T cells were used for this experiment, and results are shown in
Differing enrichment schemes were tested to determine optimal enrichment methods. Using a non-GEM protocol, cDNA from 3,000 primary T cells was prepared using poly-T priming followed by enrichment using primers that anneal to TCR constant regions, yielding 38.5% VDJ mappable reads, quantitation of this enrichment is shown in
To further optimize enrichment, a comparison was conducted between using P7 primers and variable region specific primers in combination with the constant region primers for cDNA amplification. Primer sequences used are shown in Table 4.
GEM-RT was carried out using poly-T priming followed by a template switch using 8 μM TSO-GB, followed by clean up, 15 cycles of cDNA amplification and enrichment for 20 cycles. Results shown in
In this example, and with reference to
In some cases, a first subset of the polynucleotide products from cDNA amplification can be subjected to target enrichment (
The labeled polynucleotides can then be subjected to sequencing analysis. Sequencing reads of the enriched polynucleotides can yield sequence information about a particular population of the mRNA molecules in the cell whereas the enriched polynucleotides can yield sequence information about various mRNA molecules in the cell.
Example VIII: Base Error CalculationsAll calculations of this example are for a single base. The terms transcript and UMI will be used inter-changeably, assuming that there is a 1-1 relationship between transcripts and UMIs. Let D be all observed data (reads, qualities, UMIs) at a given base and Du, u=1, . . . , m be the data from UMI u. Let R be the real template base at the given position and Tu be the (unobserved) base at the given position on transcript/UMI u. Let Rui and Rui be the real (pre-sequencing errors) and observed (post-sequencing errors) bases on the ith read of UMI u and Qui be the corresponding base quality. Let prt be probability of an RT error, and ppcr be the probability of a PCR error. Let also ps(Q)=10−Q/10 be the probability of a sequencing error given a base quality of Q. Finally, let L={A, C, G, T}. Transcripts are conditionally independent given the real template base and reads from a transcript are conditionally independent given the base of the transcript (i.e. errors occur completely independently of one another). Below, Equation I can be derived by summing over the unobserved value c of transcript u at the given position and the (also unobserved) real value d of each read at this position.
If it is assumed that ppcr is negligible (compared to sequencing and RT errors), that is the sequenced base Rui always equals the transcript base Tu, the simplified form of Equation II can be derived below.
Devices, systems, compositions and methods of the present disclosure may be used for various applications, such as, for example, processing a single analyte (e.g., RNA, DNA, or protein) or multiple analytes (e.g., DNA and RNA, DNA and protein, RNA and protein, or RNA, DNA and protein) form a single cell. For example, a biological particle (e.g., a cell or cell bead) is partitioned in a partition (e.g., droplet), and multiple analytes from the biological particle are processed for subsequent processing. The multiple analytes may be from the single cell. This may enable, for example, simultaneous proteomic, transcriptomic and genomic analysis of the cell.
While some embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. It is not intended that the invention be limited by the specific examples provided within the specification. While the invention has been described with reference to the aforementioned specification, the descriptions and illustrations of the embodiments herein are not meant to be construed in a limiting sense. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Furthermore, it shall be understood that all aspects of the invention are not limited to the specific depictions, configurations or relative proportions set forth herein which depend upon a variety of conditions and variables. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is therefore contemplated that the invention shall also cover any such alternatives, modifications, variations or equivalents. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
Claims
1. A method, comprising:
- (a) providing a reaction volume comprising (i) a cell or cell derivative, and (ii) a bead comprising a barcoded oligonucleotide releasably coupled thereto, wherein said barcoded oligonucleotide is a template switching oligonucleotide; and
- (b) releasing said barcoded oligonucleotide from said bead to provide said barcoded oligonucleotide in said reaction volume; and
- (c) subjecting said reaction volume to an amplification reaction to generate an amplification product, wherein during said amplification reaction, said reaction volume comprises a template polynucleotide from said cell or cell derivative, said barcoded oligonucleotide and a primer having a sequence towards a 3′ end that hybridizes to said template polynucleotide, and wherein said amplification product has sequence complementarity with said template polynucleotide and said barcoded oligonucleotide.
Type: Application
Filed: Dec 22, 2020
Publication Date: Aug 5, 2021
Inventors: Tarjei Sigurd Mikkelsen (Dublin, CA), Phillip Belgrader (Livermore, CA), Xinying Zheng (San Jose, CA)
Application Number: 17/131,494
