Distinct but overlapping T helper epitopes in the 37–58 region of SSX-2

Because of their specific expression in tumors of different histological types, the products of the SSX genes are important candidate targets for development of cancer vaccines. We have previously identified two immunodominant SSX-2-derived T cell epitopes recognized by HLA-A2-restricted CD8+ T cells (SSX-2 41–49) and HLA-DR11-restricted CD4+ T cells (SSX-2 45–59), respectively. In this study, we report the identification of an HLA-DR3-restricted epitope mapping to the 37–51 region of SSX-2, overlapping both previously identified epitopes. As about one fifth of individuals from several major ethnic groups express HLA-DR3, the identification of this epitope significantly increases the percent of patients that are expected to mount specific CD4+ T cell responses following vaccination with peptides in this region of SSX-2. Retrieval of multiple overlapping epitopes in a defined region of SSX-2 protein suggests the presence of a “hot spot” for T cell recognition that may prove sufficient for the induction of immune responses.