Identification of helper T-cell epitopes that encompass or lie proximal to cytotoxic T-cell epitopes in the gp100 melanoma tumor antigen.

The melanocyte-associated antigen gp100 constitutes one of the most attractive targets for T-cell-based immunotherapy against malignant melanoma. Although several MHC class I-restricted epitopes have been identified for CTLs, thus far, only one MHC class II T helper epitope (restricted by HLA-DR4) has been described in the literature. Using an algorithm to identify promiscuous helper T-cell epitopes, here we describe three additional MHC class II-restricted epitopes from gp100. Whereas one T helper epitope, gp100(175-189), was restricted by the HLA-DR53 and DQw6 alleles, the T-cell responses to two other epitopes, gp100(74-89) and gp100(576-590), were restricted by HLA-DR7. Most interestingly, the newly identified helper T lymphocyte epitopes encompass or lie proximal to previously described CTL epitopes for this tumor-associated antigen. Together with the previously described HLA-DR4-restricted epitope, these T helper epitopes offer coverage for the majority of the human population. Moreover, the use of peptide vaccines containing both CTLs and T helper epitopes could offer therapeutic advantages over current approaches that focus solely on eliciting antitumor CTL responses.