Proline substitution independently enhances H-2D^b complex stabilization and TCR recognition of melanoma-associated peptides

The immunogenicity of H-2D^b (D^b) restricted epitopes can be significantly increased by substituting peptide position 3 to a proline (p3P). The p3P modification enhances MHC stability without altering the conformation of the modified epitope allowing for T-cell cross-reactivity with the native peptide. The present study reveals how specific interactions between p3P and the highly conserved MHC heavy chain residue Y159 increase the stability of D^b in complex with an optimized version of the melanoma-associated epitope gp100_25-33. Furthermore, the p3P modification directly increased the affinity of the D^b/gp100_25-33-specific T-cell receptor (TCR) pMel. Surprisingly, the enhanced TCR binding was independent from the observed increased stability of the optimized D^b/gp100_25-33 complex and from the interactions formed between p3P and Y159, indicating a direct effect of the p3P modification on TCR recognition.