Peptide-pulsed dendritic cells induce tumoricidal cytotoxic T lymphocytes from healthy donors against stably HLA-A*0201-binding peptides from the Melan-A/MART-1 self antigen

The melanoma antigen Melan-A/MART-1 was screened for the presence of potential HLA-A*0201-binding cytotoxic T lymphocytes (CTL) epitopes. The immunodominant nonamer epitope AAGIGILTV demonstrated weak binding to T2 but a significant half-life of binding to HLA-A*0201 in contrast to the decamer EAAGIGILTV. In addition to the immunodominant CTL epitope, we describe two peptides, GILTVILGV and ALMDKSLHV, that display stable binding to HLA-A*0201. Using cultured autologous dendritic cells pulsed with these peptides, CTL lines were induced from peripheral blood lymphocytes that displayed reactivity with HLA-A2⁺, Melan-A/MART-1⁺ melanoma cells. CTL reactivity against the immunodominant epitope could be induced with the nonamer epitope alone, but not with the decamer variant. CTL clones generated from an (EAAGIGILTV + AAGIGILTV)-induced CTL line recognize the appropriate melanoma cells and normal melanocytes. Upon further characterization of one of these CTL clones, it was found to be of surprisingly high affinity considering that it is directed against a self antigen. This study demonstrates that immunogenic peptides can be selected based on stability (half-life) of peptide/HLA binding. In addition, cultured DC were found to efficiently induce CTL responses in vitro against such selected peptides, and some of these CTL were capable of recognizing endogenously processed antigen.