Divergent T-cell receptor recognition modes of a HLA-I restricted extended tumour-associated peptide

Human leukocyte antigen (HLA)-I molecules generally bind short peptides (8-10 amino acids), although extended HLA-I restricted peptides (>10 amino acids) can be presented to T cells. However, the function of such extended HLA-I epitopes in tumour immunity, and how they would be recognised by T-cell receptors (TCR) remains unclear. Here we show that the structures of two distinct TCRs (TRAV4⁺TRAJ21⁺-TRBV28⁺TRBJ2-3⁺ and TRAV4 ⁺ TRAJ8⁺-TRBV9⁺TRBJ2-1⁺), originating from a polyclonal T-cell repertoire, bind to HLA-B∗07:02, presenting a 13-amino-acid-long tumour-associated peptide, NY-ESO-1_60-72. Comparison of the structures reveals that the two TCRs differentially binds NY-ESO-1_60-72-HLA-B∗07:02 complex, and induces differing extent of conformational change of the NY-ESO-1_60-72 epitope. Accordingly, polyclonal TCR usage towards an extended HLA-I restricted tumour epitope translates to differing TCR recognition modes, whereby extensive flexibility at the TCR-pHLA-I interface engenders recognition.