Antigen-specific peptide-Major Histocompatibility Complex

The antigen-specific peptide-MHC (pMHC) complex is a molecular structure formed when a peptide fragment, typically derived from an intracellular or extracellular protein antigen, binds to a major histocompatibility complex (MHC) molecule. This complex is then displayed on the surface of cells and specifically recognized by T cell receptors (TCRs), including those introduced through genetic engineering in adoptive cell therapies such as TCR-T. It plays a crucial role in immune surveillance and activation of T cells. The specific combination of the presented peptide and the particular MHC allele determines recognition specificity for each unique TCR. In engineered cellular therapies like adoptive transfer of transgenic or cloned TCRs (TCR-T therapy), patient-derived lymphocytes are modified ex vivo with genes encoding tumor-antigen-specific receptors that recognize target pMHC complexes on cancerous or infected cells with high specificity, enabling targeted immune responses against disease while sparing normal tissues lacking that specific pMHC combination.

Recognition by the appropriate introduced or native TCR triggers downstream signaling events leading to activation, proliferation, cytokine production, or cytotoxic activity in the responding T cell. The function of MHC molecules is to bind peptide fragments derived from pathogens [or other sources] and display them on the cell surface for recognition by appropriate T cells...the specificity of a [introduced] T-cell receptor is defined both by the peptide it recognizes and by the MHC molecule bound to it.