High frequency of T cell clonal expansions in primary human melanoma. Involvement of a dominant clonotype in autologous tumor recognition

It was previously found that primary melenomas from HLA-A2-matched patients display an increased expression of a few T cell receptor (TCR) variable-re gion beta-chain transcripts (BV) compared with autologous peripheral blood lymphocytes (PBL) and uninvolved skin. In order to see whether expansions o f clonal/oligoclonal subsets of T cells occurred, complementarity-determini ng region 3 (CDR3) of BV transcripts overexpressed in the neoplastic infilt rate were cloned and sequenced. Dominant rearrangements were found for BV14 , which were commonly increased in the neoplastic lesions of all analysed H LA-A2 melanoma patients, as well as for other overexpressed BV gene familie s, but none of them could be identified among autologous PBL. No identical CDR3 sequences could be detected in the dominant BV14 rearrangements obtain ed from the different patients. In one patient a single clonally expanded S LSGTGVNEQF CDR3 clonotype accounted for the entire BV14 relative frequency of expression (24%) in tumor-infiltrating lymphocytes (TIL). Two independen t mixed lymphocyte/tumor cultures (MLTC) could be successfully established from TIL of the patient and were found to exert HLA-class-I-restricted cyto toxicity for the autologous melanoma line. BV14 T cells that constituted fr om 22% to 32% of all T cells present in both MLTC lines, as assessed by flo w cytometry, all displayed the same CDR3 clonotype found in vivo and could be shown, by TCR downmodulation experiments, to be involved in autologous t umor recognition. These results support the hypothesis of a tumor-antigen-d riven origin of clonally amplified T cells present at high frequency in the in situ neoplastic infiltrate.