Human leukocyte antigen–peptide complex (HLA–peptide complex)

The HLA-peptide complex is a cell-surface molecular assembly where a polymorphic human leukocyte antigen (HLA, also known as MHC in non-human species) binds short antigenic peptides within a specialized groove formed by the α1 and α2 domains. The complexes are recognized by T cell receptors, enabling T lymphocytes to distinguish normal, infected, or malignant cells. The peptide-binding groove is defined by six key pockets (A–F), each conferring specificity for peptide residues; the B and F pockets typically anchor the key residues that determine stable complex formation and immune recognition. The diversity of HLA alleles and peptide repertoires facilitates wide antigen presentation but is also the basis for variable disease risk, immune surveillance against tumors, viral escape from immunity, and transplant rejection. In oncology, peptide–HLA complexes displaying mutated or tumor-specific peptides are central targets for novel immunotherapies, including engineered TCRs and peptide vaccines. Safety concerns stem from the potential for inappropriate or excessive immune activation, particularly when self-peptides are targeted.

Other names

Major histocompatibility complex (MHC) class I–peptide complexMHC–peptide complexHLA class I/II–peptide complexPeptide–MHC complex

Enhancement or inhibition of T cell recognition Induction of cytotoxic T cell responses (peptide vaccines, engineered TCRs) Modulation of immune checkpoint pathways (antibodies that enhance/reduce T cell activation via HLA-peptide recognition) Selective targeting of cancer-specific peptide–HLA complexes on tumor cells