Cross-reactive monoclonal and polyclonal antibodies which recognize surface proteins from coagulase-negative staphylococci and staphylococcus aureus
Polyclonal and monoclonal antibodies which are cross-reactive to both coagulase-positive staphylococcus bacteria, such as S. aureus and to coagulase-negative bacteria, such as S. epidermidis and S. hemolyticus, are provided which can recognize surface proteins from both coagulase-positive and coagulase negative staph bacteria. The antibodies may be generated from surface proteins that have been isolated on the basis of characteristics that may be common between S. aureus and coagulase-negative staphylococci, and these recombinant surface proteins are used to generate the antibodies of the invention. There is also provided vaccines and methods which utilize these proteins and antibodies for the treatment or protection against a wide variety of staphylococcal infections.
The present application claims the benefit of U.S. provisional application Ser. No. 60/298,098 filed Jun. 15, 2001.
FIELD OF THE INVENTIONThe present invention relates in general to surface proteins from Staphylococcus aureus and their active regions such as their A domains which have homologue proteins on coagulase-negative Staphylococci such as S. epidermidis and S. hemolyticus as well as antibodies which recognize said proteins, and in particular to isolated monoclonal and polyclonal antibodies which recognize specific proteins from Staphylococcus aureus and coagulase-negative Staphylococci and which are cross-reactive against S. aureus and coagulase-negative Staphylococci and can thus be utilized in vaccines and methods useful for preventing or treating a wide variety of infections caused by staphylococcal bacteria.
BACKGROUND OF THE INVENTIONThe successful colonization of the host is a process required for most microorganisms to cause infections in animals and humans. Microbial adhesion is the first crucial step in a series of events that can eventually lead to disease. Pathogenic microorganisms colonize the host by attaching to host tissues or serum conditioned implanted biomaterials, such as catheters, artificial joints, and vascular grafts, through specific adhesins present on the surface of the bacteria. MSCRAMM®s (Microbial Surface Components Recognizing Adhesive Matrix Molecules) are a family of cell surface adhesins that recognize and specifically bind to distinct components in the host's extracellular matrix. Once the bacteria have successfully adhered and colonized host tissues, their physiology is dramatically altered and damaging components such as toxins and proteolytic enzymes are secreted. Moreover, adherent bacteria often produce a biofilm and quickly become more resistant to the killing effect of most antibiotics.
S. aureus causes a spectrum of infections that range from cutaneous lesions such as wound infections, impetigo, and furuncles to life-threatening conditions that include pneumonia, septic arthritis, sepsis, endocarditis, and biomaterial related infections. S. aureus is known to express a repertoire of different MSCRAMMs that can act individually or in concert to facilitate microbial adhesion to specific host tissue components. In addition, another type of staphylococcus bacteria is identified as the coagulase-negative bacteria, including such species as S. epidermidis and S. hemolyticus which are also have been known to express MSCRAMMs, and which also are responsible for a wide range of bacterial infections and related diseases. In this regard, MSCRAMMs generally provide an excellent target for immunological attack by antibodies, both polyclonal and monoclonal antibodies.
However, because antibodies by nature are very specific and in the case of different types of Staphylococci, such as S. aureus on one hand (coagulase-positive) and S. epidermidis and S. hemolyticus on the other (coagulase-negative), it has still remained a significant problem to develop antibodies that exhibit cross-reactivity across the different types of bacteria. Such cross-reactive antibodies are particularly desirable because of their potential in immunizing human and animal patients and providing protection against infections caused by both types of Staphylococcal bacteria, namely coagulase-positive bacteria such as S. aureus and the coagulase-negative bacteria, such as S. epidermidis and S. hemolyticus. Such antibodies would thus be extremely useful in preventing or treating a wide variety of the infections caused by staphylococcal bacteria.
SUMMARY OF THE INVENTIONAccordingly, it is an object of the present invention to provide monoclonal antibodies that recognize MSCRAMM®'s from both coagulase-positive bacteria such as S. aureus as well as MSCRAMM®'s from coagulase-negative bacteria, such as S. epidermidis and S. hemolyticus.
It is also an object of the present invention to identify and isolate MSCRAMM®'s from staphylococcal bacteria, as well as their active regions such as the A domain, which can be used to generate monoclonal and polyclonal antibodies that will be cross-reactive against both coagulase-positive and coagulase-negative staphylococci.
It is still further an object of the present invention to provide isolated antibodies that can recognize the A domain of surface proteins such as the DgsK protein from coagulase-negative staphylococci and at the same time recognize surface proteins such as the SasA protein from Staphylococcus aureus.
It is yet another object of the present invention to utilize the isolated proteins, A domains and antibodies of the invention to produce vaccines useful in the treatment or prevention of staphylococcal infections, and to provide methods wherein the vaccines and antibodies of the invention are used to prevent or treat a staphylococcal infection.
These and other objects are provided by virtue of the present invention which comprises the identification and isolation of surface proteins from one type of staphylococcal bacteria, such as coagulase-negative or coagulase-positive staph, which can give rise to cross-reactive antibodies which can recognize surface proteins of both types of staph and which can thus be utilized in vaccines and methods of treating or preventing a wide range of staphylococcal infections. The present invention also relates to the generation of both polyclonal and monoclonal antibodies from these surface proteins and their use in preventing or treating staphylococcal infections.
These embodiments and other alternatives and modifications within the spirit and scope of the disclosed invention will become readily apparent to those skilled in the art from reading the present specification and/or the references cited herein, all of which are incorporated by reference.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
In accordance with the present invention, there are provided specific surface proteins from coagulase-positive staphylococcal bacteria, such as S. aureus as well as from coagulase-negative staph such as S. epidermidis and S. hemolyticus, including active fragments thereof such -as the A domains of these proteins or other epitotic regions which can generate antibodies that recognize the whole protein. In accordance with the invention, the identification and isolation of candidate peptide sequences and proteins was carried out based on some of the common features of the MSCRAMM®s ((Microbial Surface Components Recognizing Adhesive Matrix Molecules) which are in most cases are covalently anchored to the cell wall peptidoglycan. These surface proteins had the following common features which were utilized in identifying and isolated the sequences of the present invention, namely: (i) an N-terminal signal peptide (approximately 40 residues in length) required for Sec-dependent secretion, (ii) a wall spanning domain either rich in proline and glycine residues or composed of serine and aspartate dipeptide repeats, (iii) an LPXTG motif required for covalent anchoring of the protein to the pentaglycine crossbridge in peptidoglycan, (iv) a hydrophobic membrane-spanning domain followed by (v) several positively charged residues.
In accordance with the invention, by exploiting the whole genome of S. aureus in light of the properties as set forth above, at least eight novel open reading frames encoding proteins with secretion and anchorage motifs indicative of MSCRAMMs were identified (i.e. bearing an N-terminal signal peptide and a C-terminal LPXTG motif followed by a hydrophobic domain and a positively charged tail). Table 1 illustrates the list of proteins identified including their distribution among S. aureus genomes, their protein size and C-terminal cell wall sorting sequence.
Abbreviations: eMRSA-16; N, 8325; C, COL; S, MSSA; J, N315, M, Mu50. Six out of eight are conserved in all of the six staphylococcal genomes currently sequenced and the remaining two are present in 5/6 of these genomes.
In accordance with the invention, amino acid and nucleic acid sequences coding for the above proteins were obtained, and these were as follows: Ekes MRSA—SEQ ID NO:1 (DNA sequence); EkeS_MRSA—SEQ ID NO:2 (Protein sequence); DsqA (8325)—SEQ ID NO:3 (DNA sequence); DsqA (8325)—SEQ ID NO:4 (Protein sequence); KesK1 (8325)—SEQ ID NO:5 (DNA sequence); KesK1 (8325)—SEQ ID NO:6 (Protein sequence); KrkN2 (8325)—SEQ ID NO:7 (DNA sequence); KrkN2 (8325)—SEQ ID NO:8 (Protein sequence); KrkN (8325)—SEQ ID NO:9 (DNA sequence); KrkN (8325)—SEQ ID NO:10 (Protein sequence); RkaS (COL)—SEQ ID NO:11 (DNA sequence); RkaS (COL)—SEQ ID NO:12 (Protein sequence); RrkN (8325)—SEQ ID NO:13 (DNA sequence); RrkN (8325)—SEQ ID NO:14 (Protein sequence); KnkA (8325)—SEQ ID NO:15 (DNA sequence); KnkA (8325)—SEQ ID NO:16 (Protein sequence).
In accordance with the present invention, isolated antibodies may be generated from the above proteins or their active regions such as the A domain so as to be able to recognize said proteins and/or said domains. These antibodies may be either monoclonal or polyclonal. If polyclonal antibodies are desired, these may be generated in any of a number of conventional ways well known in the art. In a typical process, the desired surface protein or active region thereof may be injected into a suitable host animal, e.g., a mouse or rabbit, and after a suitable time period, antibodies may be isolated and recovered from the host animal. With regard to monoclonal antibodies, in accordance with the present invention, these may be produced in any number of suitable ways including, e.g., the well known method of Kohler and Milstein, Nature 256:495-497 (1975), or other suitable ways known in the field, such as those methods disclosed in U.S. Pat. Nos. 6,331,415; 5,981,216; 5,807,715; and 4,816,567; Eur. Pat. App. 519,596; and PCT publication WO 00/71585, all of these patent publications incorporated herein by reference. These methods include their preparation as chimeric, humanized, or human monoclonal antibodies in ways that would be well known in this field. Still further, monoclonal antibodies may be prepared from a single chain, such as the light or heavy chains, and in addition may be prepared from active fragments of an antibody which retain the binding characteristics (e.g., specificity and/or affinity) of the whole antibody. By active fragments is meant an antibody fragment which has the same binding specificity as a complete antibody which binds to the particular surface protein or its homologue from the different type of staph bacteria (i.e., coagulase negative or coagulase-positive), and the term “antibody” as used herein is meant to include said fragments. Additionally, antisera prepared using monoclonal or polyclonal antibodies in accordance with the invention are also contemplated and may be prepared in a number of suitable ways as would be recognized by one skilled in the art.
As indicated above, antibodies to the isolated surface proteins and/or their active regions in accordance with the invention may be prepared in a number of suitable ways that would be well known in the art, such as the well-established Kohler and Milstein method described above which can be utilized to generate monoclonal antibodies. For example, in preliminary steps utilized in such a process, mice may be injected intraperitoneally once a week for a prolonged period with a purified recombinant MSCRAMM® in accordance with the invention or an active portion thereof, followed by a test of blood obtained from the immunized mice to determine reactivity to the purified protein. Following identification of mice reactive to the proteins, lymphocytes isolated from mouse spleens are fused to mouse myeloma cells to produce hybridomas positive for the antibodies against the surface proteins of the invention which are then isolated and cultured, following by purification and isotyping.
In order to generate monoclonal antibodies in accordance with the invention, it is preferred that these be generated using recombinantly prepared MSCRAMM®'s in accordance with the invention, and these recombinants may be generated and isolated using a number of standard methods well known in the art. For example, one such method employs the use of E. coli expression vector pQE-30 as an expression vector for cloning and expressing recombinant proteins and peptides. In one preferred method, using PCR, the A domain of the surface protein identified as DgsK or SasA was amplified from the sequences described above and subcloned into the E. coli expression vector PQE-30 (Qiagen), which allows for the expression of a recombinant fusion protein containing six histidine residues. This vector was subsequently transformed into E. coli strain ATCC 55151, grown in a 15-liter fermentor to an optical density (OD600) of 0.7 and induced with 0.2 mM isopropyl-1-beta-D galactoside (IPTG) for 4 hours. The cells were harvested using an AG Technologies hollow-fiber assembly (pore size 0.45 μm) and the cell paste frozen at −80° C. Cells were lysed in 1×PBS (10 mL buffer/1 g of cell paste) using 2 passes through the French Press @ 1100 psi. Lysed cells were spun down at 17,000 rpm for 30 minutes to remove cell debris. Supernatant was passed over a 5-mL HiTrap Chelating (Pharmacia) column charged with 0.1M NiCl2. After loading, the column was washed with 5 column volumes of 10 mM Tris, pH 8.0, 100 mM NaCl (Buffer A). Protein was eluted using a 0-100% gradient of 10 mM Tris, pH 8.0, 100 mM NaCl, 200 mM imidazole (Buffer B) over 30 column volumes. SdrGNlN2N3 or SdrGN2N3 eluted at ˜13% Buffer B (˜26mM imidazole). Absorbance at 280nm was monitored. Fractions containing SdrGN1N2N3 or SdrGN2N3 were dialyzed in 1×PBS.
Next, each protein was then put through an endotoxin removal protocol. Buffers used during this protocol were made endotoxin free by passing over a 5-mL Mono-Q sepharose (Pharmacia) column. Protein was divided evenly between 4×15 mL tubes. The volume of each tube was brought to 9 mL with Buffer A. 1 mL of 10% Triton X-114 was added to each tube and incubated with rotation for 1 hour at 4° C. Tubes were placed in a 37° C. water bath to separate phases. Tubes were spun down at 2,000 rpm for 10 minutes and the upper aqueous phase from each tube was collected and the detergent extraction repeated. Aqueous phases from the 2nd extraction were combined and passed over a 5-mL IDA chelating (Sigma) column, charged with 0.1M NiCl2 to remove remaining detergent. The column was washed with 9 column volumes of Buffer A before the protein was eluted with 3 column volumes of Buffer B. The eluant was passed over a 5-mL Detoxigel (Sigma) column and the flow-through collected and reapplied to the column. The flow-through from the second pass was collected and dialyzed in 1×PBS. The purified product was analyzed for concentration, purity and endotoxin level before administration into the mice.
In the preferred process, monoclonal antibodies in accordance with the present invention may be prepared from the recombinant proteins identified above in the following manner. In this process, E. coli expressed and purified recombinant SasA and DsgK proteins were used to generate a panel of murine monoclonal antibodies while the mouse sera was used as a source of polyclonal antibodies. Briefly, a group of Balb/C or SJL mice received a series of subcutaneous immunizations of 1-10 mg of protein in solution or mixed with adjuvant as described below in Table 2.
At the time of sacrifice (RIMMS) or seven days after a boost (conventional) serum was collected and titered in ELISA assays against MSCRAMM® proteins or on whole cells (S. epidermidis and S. aureus). Three days after the final boost, the spleens or lymph nodes were removed, teased into a single cell suspension and the lymphocytes harvested. Lymphocytes were then fused to a P3X63Ag8.653 myeloma cell line (ATCC #CRL-1580). Cell fusion, subsequent plating and feeding were performed according to the Production of Monoclonal Antibodies protocol from Current Protocols in Immunology (Chapter 2, Unit 2.), incorporated herein by reference.
Any clones that were generated from the fusion were then screened for specific anti-SasA antibody production using a standard ELISA assay. Positive clones were expanded and tested further for activity in a whole bacterial cell binding assay by flow cytometry and SasA binding by Biacore analysis. Throughout the Biacore analysis, the flow rate remained constant at 10 ml/min. Prior to the SasA or DgsK injection, test antibody was adsorbed to the chip via RAM-Fc binding. At time 0, SasA or DgsK at a concentration of 30 mg/ml was injected over the chip for 3 min followed by 2 minutes of dissociation. This phase of the analysis measured the relative association and disassociation kinetics of the Mab/SasA or DgsK interaction.
Next, the antibodies prepared as set forth above were tested for binding to whole bacteria. In these tests, bacterial samples S. aureus Newman, S. aureus 67-0, S. aureus 397 (Sal6), S. aureus Wood, S. aureus 8325-4, methicillin resistant S. aureus MRSA 16, S. epidermidis ATCC 35984, S. epidermidis HB, S. epidermidis CN-899 and S. haemolyticus ATCC 43253 were collected, washed and incubated with Mab or PBS alone (control) at a concentration of 2 μg/ml after blocking with rabbit IgG (50 mg/ml). Following incubation with antibody, bacterial cells were incubated with Goat-F(ab′)2-Anti-Mouse-F(ab′)2-FITC which served as the detection antibody. After antibody labeling, bacterial cells were aspirated through the FACScaliber flow cytometer to analyze fluorescence emissipon (excitation: 488, emission: 570). For each bacterial strain, 10,000 events were collected and measured. These data indicate that antibodies against S. aureus SasA were able to recognize a homologous protein on the surface of coagulase-negative staphylococci. The data support Western blot analysis demonstrating that rabbit polyclonal antibodies against S. aureus SasA cross-react with a protein released from the cell surface of S. epidermidis HB as well as the recombinant A-region from DsgK cloned from S. epidermidis (see
Although production of antibodies using recombinant forms of the surface proteins of the present invention is preferred, antibodies may be generated from natural isolated and purified versions of these proteins or their active regions such as the A domain, and monoclonal or polyclonal antibodies can be generated using these proteins or active regions in the same manner as described above to obtain such antibodies. Still other conventional ways are available to generate the antibodies of the present invention using recombinant or natural purified proteins or their active regions, as would be recognized by one skilled in the art.
As would be recognized by one skilled in the art, the antibodies of the present invention may also be formed into suitable pharmaceutical compositions for administration to a human or animal patient in order to treat or prevent an infection caused by staphylococcal bacteria. Pharmaceutical compositions containing the antibodies of the present invention, or effective fragments thereof, may be formulated in combination with any suitable pharmaceutical vehicle, excipient or carrier that would commonly be used in this art, including such as saline, dextrose, water, glycerol, ethanol, other therapeutic compounds, and combinations thereof. As one skilled in this art would recognize, the particular vehicle, excipient or carrier used will vary depending on the patient and the patient's condition, and a variety of modes of administration would be suitable for the compositions of the invention, as would be recognized by one of ordinary skill in this art. Suitable methods of administering any pharmaceutical composition disclosed in this application include, but are not limited to, topical, oral, anal, vaginal, intravenous, intraperitoneal, intramuscular, subcutaneous, intranasal and intradermal administration.
For topical administration, the composition is formulated in the form of an ointment, cream, gel, lotion, drops (such as eye drops and ear drops), or solution (such as mouthwash). Wound or surgical dressings, sutures and aerosols may be impregnated with the composition. The composition may contain conventional additives, such as preservatives, solvents to promote penetration, and emollients. Topical formulations may also contain conventional carriers such as cream or ointment bases, ethanol, or oleyl alcohol. Additional forms of antibody compositions, and other information concerning compositions, vaccines, methods and applications with regard to other MSCRAMM®s will generally also be applicable to the present invention involving the aforementioned MSCRAMM®s and their active regions and antibodies thereto, and these other MSCRAMM®s are disclosed, for example, in U.S. Pat. Nos. 5,175,096; 5,320,951; 5,416,021; 5,440,014; 5,571,514; 5,652,217; 5,707,702; 5,789,549; 5,840,846; 5,980,908; 6,086,895; 6,008,341; 6,177,084; 5,851,794 and 6,288,214; all of these patents incorporated herein by reference.
The antibody compositions of the present invention may also be administered with a suitable adjuvant in an amount effective to enhance the immunogenic response. For example, suitable adjuvants may include alum (aluminum phosphate or aluminum hydroxide), which is used widely in humans, and other adjuvants such as saponin and its purified component Quil A, Freund's complete adjuvant, RIBBI adjuvant, and other adjuvants used in research and veterinary applications. Still other chemically defined preparations such as muramyl dipeptide, monophosphoryl lipid A, phospholipid conjugates such as those described by Goodman-Snitkoff et al. J. Immunol. 147:410415 (1991) and incorporated by reference herein, encapsulation of the conjugate within a proteoliposome as described by Miller et al., J. Exp. Med. 176:1739-1744 (1992) and incorporated by reference herein, and encapsulation of the protein in lipid vesicles such as Novasome™ lipid vesicles (Micro Vescular Systems, Inc., Nashua, N.H.) may also be useful.
In any event, the antibody compositions of the present invention which recognize the proteins or their active regions as set forth above will be useful in methods of preventing or treating staphylococcal infection, and in inhibiting binding of staphylococcal bacteria to host tissue and/or cells. In accordance with the present invention, methods are provided for preventing or treating a staphylococcal infection which comprise administering an effective amount of an antibody to the surface proteins as set forth herein or their active subregions so as to treat or prevent a staphylococcal infection. In addition, these monoclonal antibodies will be useful in impairing the binding of staphylococcal bacteria to host cells
Accordingly, in accordance with the invention, administration of the antibodies of the present invention in any of the conventional ways described above (e.g., topical, parenteral, intramuscular, etc.), and will thus provide an extremely useful method of treating or preventing staphylococcal infections in human or animal patients when an effective amount of the antibody compositions are administered to a human or animal patient. By effective amount is meant that level of use, such as of an antibody titer, that will be sufficient to either prevent adherence of the bacteria, to inhibit binding of staph bacteria to host cells and thus be useful in the treatment or prevention of a staph infection. As would be recognized by one of ordinary skill in this art, the level of antibody titer needed to be effective in treating or preventing staphylococcal infection will vary depending on the nature and condition of the patient, and/or the severity of the pre-existing staphylococcal infection.
In addition to use in methods or treating or preventing a staphylococcal infection, the antibodies of the invention may also be used for the specific detection of staphylococcal proteins, or as research tools. The term “antibodies” as used herein includes monoclonal, polyclonal, chimeric, single chain, bispecific, simianized, and humanized or primatized antibodies as well as Fab fragments, such as those fragments which maintain the binding specificity of the antibodies to the surface proteins specified above, including the products of an Fab immunoglobulin expression library. Accordingly, the invention contemplates the use of single chains such as the variable heavy and light chains of the antibodies. Generation of any of these types of antibodies or antibody fragments is well known to those skilled in the art. In the present case, antibodies to the surface proteins or their active regions as referred to above can be generated, isolated and/or purified, and then used to treat or protect against staphylococcal infection.
Any of the above described antibodies may be labeled directly with a detectable label for identification and quantification of staph bacteria. Labels for use in immunoassays are generally known to those skilled in the art and include enzymes, radioisotopes, and fluorescent, luminescent and chromogenic substances, including colored particles such as colloidal gold or latex beads. Suitable immunoassays include enzyme-linked immunosorbent assays (ELISA).
Alternatively, the antibody may be labeled indirectly by reaction with labeled substances that have an affinity for immunoglobulin. The antibody may be conjugated with a second substance and detected with a labeled third substance having an affinity for the second substance conjugated to the antibody. For example, the antibody may be conjugated to biotin and the antibody-biotin conjugate detected using labeled avidin or streptavidin. Similarly, the antibody may be conjugated to a hapten and the antibody-hapten conjugate detected using labeled anti-hapten antibody. These and other methods of labeling antibodies and assay conjugates are well known to those skilled in the art.
In accordance with the present invention, there are also provided vaccines for either active or passive immunization designed to treat or protect against staphylococcal infections, and these vaccines may be prepared from the surface proteins or their active regions as set forth above using a number of the conventional vaccine preparation methods well known in this field. In the typical vaccine, an immunogenic amount of a suitable surface protein or active fragment thereof is combined with a suitable pharmaceutically acceptable vehicle, carrier or excipient, and an amount of this vaccine effective to immunize a human or animal patient may be administered as appropriate. By immunogenic amount it would be understood by one of ordinary skill in this art that this refers to any amount of the protein or active fragment or subregion thereof which is able to raise an immunogenic response in the human or animal patient.
In addition to active vaccines wherein antibodies are generated in the patient by virtue of the introduction or administration of an immunogenic amount of a protein or active fragment in accordance with the present invention, the isolated antibodies of the present invention, or active fragments thereof, may also be utilized in the development of vaccines for passive immunization against staph infections. In such a case, the antibody compositions as described above, namely an effective amount of the antibody and a pharmaceutically acceptable vehicle, carrier or excipient, may be administered as appropriate to a human or animal patient.
Accordingly, in accordance with the invention, the proteins or active fragments thereof may be utilized as active vaccines, and the antibodies of the invention may be used as a passive vaccine which will be useful in providing suitable antibodies to treat or prevent a staphylococcal infection. As would be recognized by one skilled in this art, a vaccine may be packaged for administration in a number of suitable ways, such as by parenteral (i.e., intramuscular, intradermal or subcutaneous) administration or nasopharyngeal (i.e., intranasal) administration. One such mode is where the vaccine is injected intramuscularly, e.g., into the deltoid muscle, however, the particular mode of administration will depend on the nature of the bacterial infection to be dealt with and the condition of the patient. The vaccine is preferably combined with a pharmaceutically acceptable vehicle, carrier or excipient to facilitate administration, and the carrier is usually water or a buffered saline, with or without a preservative. The vaccine may be lyophilized for resuspension at the time of administration or in solution.
In addition, in certain cases, the antibodies of the present invention may be modified as necessary so that, when necessary, they become less immunogenic in the patient to whom it is administered. For example, if the patient is a human, the antibody may be “humanized” by transplanting the complimentarity determining regions of the hybridoma-derived antibody into a human monoclonal antibody as described, e.g., by Jones et al., Nature 321:522-525 (1986) or Tempest et al. Biotechnology 9:266-273 (1991) or “veneered” by changing the surface exposed murine framework residues in the immunoglobulin variable regions to mimic a homologous human framework counterpart as described, e.g., by Padlan, Molecular Imm. 28:489-498 (1991), these references incorporated herein by reference. Even further, when so desired, the monoclonal antibodies of the present invention may be administered in conjunction with a suitable antibiotic to further enhance the ability of the present compositions to fight bacterial infections when necessary.
In addition to treating human or animal patients, the present compositions may also be used to halt or prevent infection of a medical device or other biomaterials such as an implant. Medical devices or polymeric biomaterials to be coated with the antibodies, proteins and active fragments described herein include, but are not limited to, staples, sutures, replacement heart valves, cardiac assist devices, hard and soft contact lenses, intraocular lens implants (anterior chamber or posterior chamber), other implants such as corneal inlays, kerato-prostheses, vascular stents, epikeratophalia devices, glaucoma shunts, retinal staples, scleral buckles, dental prostheses, thyroplastic devices, laryngoplastic devices, vascular grafts, soft and hard tissue prostheses including, but not limited to, pumps, electrical devices including stimulators and recorders, auditory prostheses, pacemakers, artificial larynx, dental implants, mammary implants, penile implants, cranio/facial tendons, artificial joints, tendons, ligaments, menisci, and disks, artificial bones, artificial organs including artificial pancreas, artificial hearts, artificial limbs, and heart valves; stents, wires, guide wires, intravenous and central venous catheters, laser and balloon angioplasty devices, vascular and heart devices (tubes, catheters, balloons), ventricular assists, blood dialysis components, blood oxygenators, urethral/ureteral/urinary devices (Foley catheters, stents, tubes and balloons), airway catheters (endotracheal and tracheostomy tubes and cuffs), enteral feeding tubes (including nasogastric, intragastric and jejunal tubes), wound drainage tubes, tubes used to drain the body cavities such as the pleural, peritoneal, cranial, and pericardial cavities, blood bags, test tubes, blood collection tubes, vacutainers, syringes, needles, pipettes, pipette tips, and blood tubing.
It will be understood by those skilled in the art that the term “coated” or “coating”, as used herein, means to apply the antibody or active fragment, or pharmaceutical composition derived therefrom, to a surface of the device, preferably an outer surface that would be exposed to streptococcal bacterial infection. The surface of the device need not be entirely covered by the protein, antibody or active fragment.
The preferred dose for administration of an antibody composition in accordance with the present invention is that amount will be effective in preventing of treating a staphylococcal infection, and one would readily recognize that this amount will vary greatly depending on the nature of the infection and the condition of a patient. As indicated above, an “effective amount” of antibody or pharmaceutical agent to be used in accordance with the invention is intended to mean a nontoxic but sufficient amount of the agent, such that the desired prophylactic or therapeutic effect is produced. As will be pointed out below, the exact amount of the antibody or a particular agent that is required will vary from subject to subject, depending on the species, age, and general condition of the subject, the severity of the condition being treated, the particular carrier or adjuvant being used and its mode of administration, and the like. Accordingly, the “effective amount” of any particular antibody composition will vary based on the particular circumstances, and an appropriate effective amount may be determined in each case of application by one of ordinary skill in the art using only routine experimentation. The dose should be adjusted to suit the individual to whom the composition is administered and will vary with age, weight and metabolism of the individual. The compositions may also contain stabilizers or pharmaceutically acceptable preservatives, such as thimerosal (ethyl(2-mercaptobenzoate-S)mercury sodium salt) (Sigma Chemical Company, St. Louis, Mo.).
When used with suitable labels or other appropriate detectable biomolecule or chemicals, the monoclonal antibodies described herein are useful for purposes such as in vivo and in vitro diagnosis of staphylococcal infections or detection of staphylococcal bacteria. Laboratory research may also be facilitated through use of such antibodies. Various types of labels and methods of conjugating the labels to the antibodies of the invention are well known to those skilled in the art, such as the ones set forth below.
For example, the antibody can be conjugated (directly or via chelation) to a radiolabel such as, but not restricted to, 32P, 3H, 14C, 35S, 125I, or 131I. Detection of a label can be by methods such as scintillation counting, gamma ray spectrometry or autoradiography. Bioluminescent labels, such as derivatives of firefly luciferin, are also useful. The bioluminescent substance is covalently bound to the protein by conventional methods, and the labeled protein is detected when an enzyme, such as luciferase, catalyzes a reaction with ATP causing the bioluminescent molecule to emit photons of light. Fluorogens may also be used to label proteins. Examples of fluorogens include fluorescein and derivatives, phycoerythrin, allo-phycocyanin, phycocyanin, rhodamine, and Texas Red. The fluorogens are generally detected by a fluorescence detector.
The location of a ligand in cells can be determined by labeling an antibody as described above and detecting the label in accordance with methods well known to one skilled in the art, such as immunofluorescence microscopy using procedures such as those described by Warren et al. (Mol. Cell. Biol., 7: 1326-1337, 1987).
As indicated above, the monoclonal antibodies of the present invention, or active portions or fragments thereof, are particularly useful for interfering with the initial physical interaction between a staphylococcal pathogen responsible for infection and a mammalian host, and this interference with the physical interaction may be useful both in treating patients and in preventing or reducing bacteria infection on in-dwelling medical devices to make them safer for use.
In another embodiment of the present invention, a kit which may be useful in isolating and identifying staphylococcal bacteria and infection is provided which comprises the antibodies of the present invention in a suitable form, such as lyophilized in a single vessel which then becomes active by addition of an aqueous sample suspected of containing the staphylococcal bacteria. Such a kit will typically include a suitable container for housing the antibodies in a suitable form along with a suitable immunodetection reagent which will allow identification of complexes binding to the surface proteins or the antibodies of the invention. In general, these kits may contain an antibody in accordance with the invention and means to identify binding of that antibody when a sample from a patient is introduced to the antibody. For example, a suitable immunodetection reagent may comprise an appropriate detectable signal or label, such as a biotin or enzyme that produces a detectable color, etc., which may be linked to the antibody or utilized in other suitable ways so as to provide a detectable result when the antibody binds to the antigen.
In short, the antibodies of the preset invention which recognize and bind to the surface proteins of the invention, or active fragments thereof, will thus be useful in treating a wide variety of staphylococcal infections in human and animal patients and in medical or other in-dwelling devices. In accordance with the invention, because of the nature of these proteins and the fact that they contain epitopes in common with proteins of the other type of staphylococcal bacteria, i.e., a protein from a coagulase-negative staph will raise antibodies that recognize a homologous protein from S. aureus and vice versa, the antibodies of the invention will exhibit cross-reactivity and should be effective against a broad range of staphylococcal infections. Accordingly, the present invention provides methods and compositions for improved methods of treating or protecting against a wide range of staphylococcal infections.
EXAMPLESThe following examples are provided which exemplify aspects of the preferred embodiments of the present invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
Example 1 Isolation and Sequencing of MSCRAMM's from S. AureusStaphylococcus aureus is known to express a class of surface-associated proteins which play important roles in pathogenicity by allowing bacteria to avoid host defenses and by acting as adhesins. These proteins are known as MSCRAMMs (Microbial Surface Components Recognizing Adhesive Matrix Molecules) and in most cases are covalently anchored to the cell wall peptidoglycan. They have several common features: (i) an N-terminal signal peptide (approximately 40 residues in length) required for Sec-dependent secretion, (ii) a wall spanning domain either rich in proline and glycine residues or composed of serine and aspartate dipeptide repeats, (iii) an LPXTG motif required for covalent anchoring of the protein to the pentaglycine crossbridge in peptidoglycan, (iv) a hydrophobic membrane-spanning domain followed by (v) several positively charged residues.
By exploiting the whole genome sequences of S. aureus, eight novel open reading frames encoding proteins with secretion and anchorage motifs indicative of MSCRAMMs were identified (i.e. bearing an N-terminal signal peptide and a C-terminal LPXTG motif followed by a hydrophobic domain and a positively charged tail). The following Table illustrates the list of proteins identified including their distribution among S. aureus genomes, their protein size and C-terminal cell wall sorting sequence.
Abbreviations: eMRSA-16; N, 8325; C, COL; S, MSSA; J, N315, M, Mu50. Six out of eight are conserved in all of the six staphylococcal genomes currently sequenced and the remaining two are present in 5/6 of these genomes.
The following is a list of the DNA and protein sequences:
Primary Structure Analysis:
A bioinformatic approach was used for primary structure and function prediction (
DsqA is similar in structural organization to the Sdr family of proteins. It contains a typical A domain followed by a TYYFTDVK motif which is similar to a conserved TYTFTVYVD motif found in all of the Sdr proteins. The function of this motif has yet to be determined. Two 88 residue repeat domains reside in the centre of the protein followed by a C-terminal SX-repeat motif similar to the SD-repeat motif found in the Sdr proteins. The size of this repeat varies from strain to strain. DsqA neighbors secY and secA on the genome. A DsqA homolog (>90% identical) is also found in S. epidermidis.
KnkA contains no repeat domains in its sequence. Secondary structure prediction analysis indicate that this protein is predominantly composed of alpha-helices.
RkaS contains no repeat domains in its sequence. BLAST analysis indicates that it is similar to a 5′ nucleotidase UDP-sugar hydrolase. The gene encoding RkaS lies directly upstream from orfX, the insertion site of the mec element.
KesK contains two 140 residue repeat domains at the N-terminus of the protein which are 38% identical. Hydropathy plot analysis (Kyte and Doolittle, 1982) indicates that there is a large hydrophilic domain in the center of the protein (residue 500-560).
EkeS contains two 300 residue repeat domains in the center of the protein which are 38% identical. Blast analysis indicates that the N-terminus of the protein (residues 1-1268, bearing both repeats) is 49% identical to FmtB, an LPXTG protein with 17 tandem repeats. FmtB is proposed to be involved indirectly in methicillin resistance as inactivation of fmtB abolishes methicillin resistance. This appears to be due to affecting cell wall composition as methicillin sensitivity can be relieved by increasing the production of the cell wall precursor glucosamine-1-phosphate (Komatsuzawa et al., 2000).
KrkN and KrkN2 neighbor each other on the genome.
Expression Analysis:
Due to lack of sequence homology with protein databases, a putative function for each of these proteins could not be predicted and hence a molecular approach was taken. Unique regions of four of the offs were expressed in E. coli as recombinant his-tagged fusion proteins using the Qiagen pQE-30 expression system.
Western immunoblotting of the cell wall fraction of strain 8325-4 using anti-KesK antibodies identified a 150 kDa immunoreactive band in both exponential and stationary phase cultures. A similar sized immunoreactive protein released from the cell wall fraction of Lactococcus lactis expressing full length KesK on an expression plasmid (pKS80) suggests that the 150 kDa band represents the kesK gene product (data not shown). A kesk knockout mutant in S. aureus would be required to confirm the size of the cell wall-released KesK protein.
Western immunoblotting of the cell wall fraction of S. aureus strain MSSA and eMRSA-16 using anti-DsqA antibodies identified a 130 kDa immunoreactive band. Expression levels are higher in stationary phase cells.
Heterologous Expression in Lactococcus lactis:
Heterologous expression of S. aureus surface proteins in Lactococcus lactis (L. lactis) has previously been used as a tool to study protein function (Sinha et al., 2000). In this study this surrogate system will be used to express each of the in silico-predicted MSCRAMMs on the surface of L. lactis to fish for a function. KesK and KnkA have been cloned into L. lactis and shown by dot blotting to be surface expressed (
KesK was detected in the cell wall fraction of L. lactis but migrated at a smaller molecular weight than the KesK protein released from the cell wall of S. aureus. The majority of MSCRAMMs expressed on the surface of L. lactis are prone to proteolysis during the cell wall extraction procedure (Louise O'Brien, personal communication). Therefore, it is possible that the KesK protein released from the surface of L. lactis represents a truncated form of KesK. Shorter digestion times with lysozyme and mutanolysin has been shown to limit the extent of proteolysis.
Expression of in Silico-Predicted MSCRAMMs In Vivo:
Convalescent-phase sera from 33 patients recovering from S. aureus infections were tested in their ability to recognize the purified N-terminal his-tag fusion proteins in an ELISA assay. Pooled sera from children and healthy blood donors were used as negative controls. A positive reaction was taken as a value equal to or greater than twice the value of the negative control.
References:
- Komatsuzawa, H., Ohta, K., Sugai, M., Fujiwara, T., Glanzmann, P., Berger-Bachi, B., Suginaka, H. (2000) Tn551-mediated insertional inactivation of the fmtB gene encoding a cell wall-associated protein abolishes methicillin resistance in Staphylococcus aureus. J. Antimicrob. Chemother. 45: 421-31.
- Sinha, B., Francois, P., Que, Y. A., Hussain, M., Heilmann, C., Moreillon, P., Lew, D., Krause, K. H., Peters, G., Herrmann, M. (2000) Heterologously expressed Staphylococcus aureus fibronectin-binding proteins are sufficient for invasion of host cells.
- Infect. Immun. 68: 6871-6878.
- Pallen, M. J., Lam, A. C., Antonio, M., Dunbar, K. (2000) An embarrassment of sortases—a richness of substrates? Trends. Microbiol. 9: 97-101
It has been recently shown that S. epidermidis contains surface proteins structurally related to S. aureus MSCRAMM® proteins (U.S. Ser. No. 09/386,962). One protein from S. aureus is of particular interest since it has a close homologue in S. epidermidis. The protein is called DsqA or SasA (S. aureus) and DgsK (S. epidermidis). They are characterized by a typical “A” domain of approximately 500 amino acid residues, followed by two B repeats of 88 residues that are ˜40% identical, and a unique SXSX dipeptide repeat that can vary in length depending on the strain. Contained within the A domain of the S. aureus DsqA/SasA is a 180 residue region that has ˜40% identity to a similar sized domain within region A of S. aureus proteins RrkN, Pls and S. epidermidis protein Aap The A regions of the DsqA/SasA and DgsK proteins are 46% identical at the amino acid level, the BB repeats are 50% identical. Active and passive immunization strategies that include; vaccines, polyclonal and monoclonal antibodies recognizing both S. aureus and coagulase-negative staphylococcal proteins are the subject of this invention.
Specific Examples of Antibodies that Cross-React with Coagulase-Negative Staphylococci and S. aureus.
The entire sequence of the Aap protein and the DNA coding therefor (with an indication of the presence of the A domain) is shown below:
Protein Production and Purification
Using PCR, the A domain of DgsK or SasA was amplified from the sequences described above and subcloned into the E. coli expression vector PQE-30 (Qiagen), which allows for the expression of a recombinant fusion protein containing six histidine residues. This vector was subsequently transformed into the E. coli strain ATCC 55151, grown in a 15-liter fermentor to an optical density (OD600) of 0.7 and induced with 0.2 mM isopropyl-1-beta-D galactoside (IPTG) for 4 hours. The cells were harvested using an AG Technologies hollow-fiber assembly (pore size of 0.45 Om) and the cell paste frozen at −80° C. Cells were lysed in 1×PBS (10 mL of buffer/1 g of cell paste) using 2 passes through the French Press @ 1100psi. Lysed cells were spun down at 17,000 rpm for 30 minutes to remove cell debris. Supernatant was passed over a 5-mL HiTrap Chelating (Pharmacia) column charged with 0.1M NiCl2. After loading, the column was washed with 5 column volumes of 10 mM Tris, pH 8.0, 100 mM NaCl (Buffer A). Protein was eluted using a 0-100% gradient of 10 mM Tris, pH 8.0, 100 mM NaCl, 200 mM imidazole (Buffer B) over 30 column volumes. SdrGN1N2N3 or SdrGN2N3 eluted at ˜13% Buffer B (26 mM imidazole). Absorbance at 280 nm was monitored. Fractions containing SdrGN1N2N3 or SdrGN2N3 were dialyzed in 1×PBS.
Each protein was then put through an endotoxin removal protocol. Buffers used during this protocol were made endotoxin free by passing over a 5-mL Mono-Q sepharose (Pharmacia) column. Protein was divided evenly between 4×15 mL tubes. The volume of each tube was brought to 9 mL with Buffer A. 1 mL of 10% Triton X-114 was added to each tube and incubated with rotation for 1 hour at 4° C. Tubes were placed in a 37° C. water bath to separate phases. Tubes were spun down at 2,000 rpm for 10 minutes and the upper aqueous phase from each tube was collected and the detergent extraction repeated. Aqueous phases from the 2nd extraction were combined and passed over a 5-mL IDA chelating (Sigma) column, charged with 0.1M NiCl2 to remove remaining detergent. The column was washed with 9 column volumes of Buffer A before the protein was eluted with 3 column volumes of Buffer B. The eluant was passed over a 5-mL Detoxigel (Sigma) column and the flow-through collected and reapplied to the column. The flow-through from the second pass was collected and dialyzed in 1×PBS. The purified product was analyzed for concentration, purity and endotoxin level before administration into the mice.
Monoclonal Antibody Production
E. coli expressed and purified recombinant SasA and DsgK proteins were used to generate a panel of murine monoclonal antibodies while the mouse sera was used as a source of polyclonal antibodies. Briefly, a group of Balb/C or SJL mice received a series of subcutaneous immunizations of 1-10 mg of protein in solution or mixed with adjuvant as described in the Table below.
Immunization Schemes
At the time of sacrifice (RIMMS) or seven days after a boost (conventional) serum was collected and titered in ELISA assays against MSCRAMM® proteins or on whole cells (S. epidermidis and S. aureus). Three days after the final boost, the spleens or lymph nodes were removed, teased into a single cell suspension and the lymphocytes harvested. The lymphocytes were then fused to a P3X63Ag8.653 myeloma cell line (ATCC #CRL-1580). Cell fusion, subsequent plating and feeding were performed according to the Production of Monoclonal Antibodies protocol from Current Protocols in Immunology (Chapter 2, Unit 2.).
Any clones that were generated from the fusion were then screened for specific anti-SasA antibody production using a standard ELISA assay. Positive clones were expanded and tested further for activity in a whole bacterial cell binding assay by flow cytometry and SasA binding by Biacore analysis.
Biacore Analysis
Throughout the analysis, the flow rate remained constant at 10 ml/min. Prior to the SasA or DgsK injection, test antibody was adsorbed to the chip via RAM-Fc binding. At time 0, SasA or DgsK at a concentration of 30 mg/ml was injected over the chip for 3 min followed by 2 minutes of dissociation. This phase of the analysis measured the relative association and disassociation kinetics of the Mab/SasA or DgsK interaction.
Binding to Whole Bacteria
Bacterial samples S. aureus Newman, S. aureus 67-0, S. aureus 397 (Sal6), S. aureus Wood, S. aureus 8325-4, methicillin resistant S. aureus MRSA 16, S. epidermidis ATCC 35984, S. epidermidis HB, S. epidermidis CN-899 and S. haemolyticus ATCC 43253 were collected, washed and incubated with Mab or PBS alone (control) at a concentration of 2 μg/ml after blocking with rabbit IgG (50 mg/ml). Following incubation with antibody, bacterial cells were incubated with Goat-F(ab′)2-Anti-Mouse-F(ab′)2-FITC which served as the detection antibody. After antibody labeling, bacterial cells were aspirated through the FACScaliber flow cytometer to analyze fluorescence emission (excitation: 488, emission: 570). For each bacterial strain, 10,000 events were collected and measured. These data indicate that antibodies against S. aureus SasA were able to recognize a homologous protein on the surface of coagulase-negative staphylococci. The data support Western blot analysis demonstrating that rabbit polyclonal antibodies against S. aureus SasA cross-react with a protein released from the cell surface of S. epidermidis HB as well as the recombinant A-region from DsgK cloned from S. epidermidis (see Table below and
Claims
1. An isolated antibody which is capable of binding to a staphylococcal surface protein selected from the group consisting of SEQ ID NOS. 2, 4, 6, 8, 10, 12, 14, 16, 17, 19 and 21.
2. The antibody according to claim 1 wherein the antibody is raised against the A domain of the surface protein.
3. The antibody according to claim 1, wherein the antibody is suitable for parenteral, oral, intranasal, subcutaneous, aerosolized or intravenous administration in a human or animal.
4. The antibody according to claim 1, wherein said antibody is a polyclonal antibody.
5. The antibody according to claim 1, wherein said antibody is a monoclonal antibody.
6. The antibody according to claim 5 wherein the monoclonal antibody is of a type selected from the group consisting of murine, chimeric, humanized and human monoclonal antibodies.
7. The antibody according to claim 5 wherein the antibody is a single chain monoclonal antibody.
8. The antibody according to claim 1 which comprises an antibody fragment having the same binding specificity of an antibody which is capable of biding to a staphylococcal surface protein having the sequence selected from the group consisting of SEQ ID NOS. 2, 4, 6, 8, 10, 12, 14, 16, 17, 19 and 21.
9. The antibody according to claim 1 that is raised against a protein having an amino acid sequence selected from the group consisting of SEQ ID NOS. 2, 4, 6, 8, 10, 12, 14, 16, 17, 19 and 21.
10. The antibody according to claim 1 wherein the surface protein has an amino acid sequence encoded by a nucleic acid sequence selected from the group consisting of nucleic acid sequences SEQ ID NOS. 1, 3, 5, 7, 9, 11, 13, 15, 20 and the nucleic acid sequences coding for the A domain of the Aap protein or degenerates thereof.
11. Isolated antisera containing an antibody according to claim 1.
12. A diagnostic kit comprising an antibody according to claim 1 and means for detecting binding by that antibody.
13. A diagnostic kit according to claim 12 wherein said means for detecting binding comprises a detectable label that is linked to said antibody.
14. A method of diagnosing an infection of S. aureus comprising adding an antibody according to claim 1 to a sample suspected of being infected with S. aureus, and determining if antibodies have bound to the sample.
15. A pharmaceutical composition for treating or preventing an infection of S. aureus comprising an effective amount of the antibody of claim 1 and a pharmaceutically acceptable vehicle, carrier or excipient.
16. A method of treating or preventing an infection of S. aureus comprising administering to a human or animal patient an effective amount of an antibody according to claim 1.
17. A method of inducing an immunological response comprising administering to a human or animal an immunogenic amount of an isolated protein selected from the group consisting of the amino acid sequences SEQ ID NOS. 2, 4, 6, 8, 10, 12, 14, 16, 17, 18, 19 and 21.
18. An isolated antibody according to claim 1 that has the ability to bind to an amino acid sequence coded by the nucleic acid sequence of SEQ ID NOS. 1, 3, 5, 7, 9, 11, 13, 15, 20 and the nucleic acid sequences coding for the A domain of the Aap protein or degenerates thereof.
19. An isolated active fragment from the A domain of the DsqA protein.
20. A composition comprising the isolated antibody according to claim 1 and a physiologically acceptable antibiotic.
21. A vaccine for treating or preventing an infection of S. aureus comprising an amount of a protein sequence selected from the group consisting of SEQ ID NOS. 2, 4, 6, 8, 10, 12, 14, 16, 17, 18, 19 and 21 in an amount effective to elicit an immune response, and a pharmaceutically acceptable vehicle, carrier or excipient.
Type: Application
Filed: Dec 27, 2004
Publication Date: May 19, 2005
Inventors: Timothy Foster (Dublin), Fiona Roche (Dublin), Mark Pallen (Malvern), Joseph Patti (Cumming, GA), Jeff Hutchins (Cumming, GA), Pietro Speziale (Pavia)
Application Number: 11/020,509
