Peptide-Human Leukocyte Antigen complex (pHLA) (pHLA complex)

The Peptide-Human Leukocyte Antigen (pHLA) complex is a molecular assembly consisting of a short peptide fragment, derived from intracellular or exogenous proteins, bound within the groove of an HLA molecule on the cell surface. This complex serves as the primary ligand for T-cell receptors (TCRs), acting as a critical signal that allows the adaptive immune system to monitor cellular health and detect foreign or mutated proteins (Nature Reviews Immunology, 2019). In oncology, pHLA complexes containing tumor-associated antigens or neoantigens are targeted by advanced immunotherapies, including TCR-engineered T-cells (TCR-T) and Immune-Mobilizing Monoclonal TCRs Against Cancer (ImmTACs). For example, Tebentafusp targets a gp100 peptide presented by HLA-A*02:01 to treat uveal melanoma (NEJM, 2021), while Afamitresgene autoleucel targets the MAGE-A4/HLA-A*02:01 complex in synovial sarcoma (FDA, 2024). Because these complexes represent intracellular targets, they expand the range of druggable antigens beyond surface proteins. However, the high degree of specificity required for pHLA recognition presents significant safety challenges, as cross-reactivity with similar peptides in healthy tissues can lead to severe, potentially fatal, off-target toxicities (Journal of Clinical Oncology, 2013).

Other names

Peptide-MHC complexpMHCAntigen-HLA complexHLA-peptide complexMHC-peptide complex

Therapeutic agents such as TCR-engineered T-cells or bispecific T-cell engagers bind specifically to the peptide-HLA complex, triggering T-cell activation, cytokine release, and directed cytotoxicity against the target cell.