Alloreactive and cross-reactive self peptide–HLA complexes (pHLA complexes)

Alloreactive and cross-reactive self peptide–HLA (pHLA) complexes are molecular assemblies on the surface of normal host cells that can trigger unintended and often harmful immune responses. These complexes consist of a Human Leukocyte Antigen (HLA) molecule—either Class I or Class II—presenting a self-peptide derived from the host's own proteome. In allogeneic hematopoietic stem cell transplantation, these complexes are recognized by donor-derived T-cells as foreign, a phenomenon known as alloreactivity, which is the primary driver of Graft-versus-Host Disease (GvHD) [PMID: 19285998]. Furthermore, in the development of engineered T-cell receptor (TCR) therapies, these complexes pose a significant risk of "off-target" toxicity if the therapeutic TCR cross-reacts with a self-peptide that resembles the intended tumor antigen [PMID: 23943601]. For instance, clinical trials have seen fatal cardiotoxicity when TCRs designed for MAGE-A3 cross-reacted with a Titin-derived peptide on heart tissue [PMID: 23943601]. Consequently, these complexes are critical targets for safety screening in immunotherapy and for the development of immunosuppressive agents that modulate T-cell activation [PMID: 17892810]. Understanding the structural basis of how T-cells distinguish between these self-complexes and foreign or tumor-specific antigens is essential for advancing precision medicine.

Other names

Alloreactive HLA-peptide complexesCross-reactive self-antigen HLA complexesOff-target pHLAAllo-HLAMHC-peptide complexesSelf-peptide MHC complexes

Inhibition of T-cell activation, costimulation blockade, or T-cell depletion to prevent immune attack against host tissues presenting these complexes.