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.