Abstract: The application relates to biological components, methods, systems, and kits for modulating immune responses. The disclosed biological components include genetically modified cells comprising an inserted exogenous sequence in a major histocompatibility complex (MHC)-associated gene. The inserted exogenous sequence encodes a peptide and the genetically modified cells express a fusion protein comprising the peptide and at least a portion of the polypeptide encoded by the MHC-associated gene to form a modified MHC complex. The genetically modified cells may present the peptide as an antigen associated with the MHC complex and may be utilized in methods for modulating T cell activity, inducing an immune response, and inducing a tolerogenic response. As such, the disclosed biological components, methods, systems, and kits may be utilized in order to treat and/or prevent a disease or disorder in a subject in need thereof and to screen and validate clinically relevant antigens.

Abstract: The present disclosure provides a method of regulating expression of a target polynucleotide in a cell. The method may comprise expressing a system in the cell, wherein the cell comprises a receptor having a ligand binding domain specific for a ligand. The method may comprise contacting the cell with the ligand that binds specifically the ligand binding domain. The system expressed in the cell may comprise a first chimeric polypeptide and a second chimeric polypeptide that are activatable upon the contacting. One of the first and second chimeric polypeptides may comprise a gene modulating polypeptide (GMP) comprising an actuator moiety linked to a cleavage recognition site. The actuator moiety may be capable of regulating the expression of the target polynucleotide in the cell. The other of the first and second chimeric polypeptides may comprise a cleavage moiety capable of cleaving the cleavage recognition site of the GMP.