Identification of human melanoma peptides recognized by class I restricted tumor infiltrating T lymphocytes

Using a newly described pH 3.3 acid elution technique, peptides were extracted by denaturation of class I molecules on the surface of human melanomas. HPLC fractionation of this material revealed six T cell epitopes (termed P1-P6) recognized by HLA-A2-restricted, melanoma-specific tumor infiltrating lymphocyte (TIL) lines. Three of these fractions (P1, P2, and P4) appeared to represent shared/immunodominant melanoma Ag recognized in the context of HLA-A2 because they were expressed by 4/4 HLA-A2⁺ melanoma cell lines and were each recognized by all four oligoclonal HLA-A2-restricted TIL lines examined. Interestingly, P1 and P2 (but not P3-P6) could also be recognized by these same TIL when presented by the HLA-Aw69 class I molecule, which is closely related to HLA-A2. P3, P5, and P6 displayed more restricted expression and were differentially recognized by the four oligoclonal TIL lines. These results suggest that synthetic peptide derived from P1, P2, and P4 sequences (when deduced) may form the basis of effective prophylactic or therapeutic melanoma vaccines by stimulating CD8⁺ CTL in HLA-A2⁺ individuals. This approach of identifying T cell epitopes presented by class I molecules should prove generally applicable to the study of other tumors recognized by class I-restricted CTL.