Diverse expansion potential and heterogeneous avidity in tumor‐associated antigen‐specific T lymphocytes from primary melanoma patients

While tumor‐associated antigen (TAA)‐specific CD8+ T lymphocytes have been detected in metastatic melanoma patients, immune response in early disease phases has not yet been carefully evaluated. We looked for circulating cytotoxic T lymphocytes (CTL) directed against Melan‐A / MART1, tyrosinase, gp100 and MAGE‐3 antigens in patients with a diagnosis of primary cutaneous melanoma by using fluorescent HLA‐A2 tetramers. In five out of six cases high numbers of CD8+ / tetramer+ cells could be detected by flow cytometry, and in four patients lymphocyte populations specific for two different melanoma antigens (Melan‐A / MART1 and tyrosinase) were contemporarily present. The TAA‐specific cells could represent as much as 1 / 220 T lymphocytes in the circulating CD8+ population. When tetramers were used to monitor the in vitro expansion of TAA‐specific CTL precursors upon antigen‐specific stimulation, a diverse expansion potential was evidenced in CTL from the different donors and, more strikingly, in CTL specific for the different TAA. Melan‐A / MART1‐specific CTL clones derived from two patients exhibited a broad range of avidity. Only the highest avidity clones, representing about 50 % of the cases analyzed, were tumor specific. By correlating tetramer staining with clone avidity, we found that tetramer fluorescence intensity could represent a good indicator of TCR affinity, but not of overall clone avidity.