CD4 T-cell help is required during the generation and maintenance of effective antitumor CD8 T cell-mediated immunity. The goal of this study was to determine whether HER-2/neu-specific CD8 T-cell immunity could be elicited using HER-2/neu-derived MHC class II "helper" peptides, which contain encompassed HLA-A2-binding motifs. Nineteen HLA-A2 patients with HER-2/neu-overexpressing cancers received a vaccine preparation consisting of putative HER-2/neu helper peptides p369-384, p688-703, and p971-984. Contained within these sequences are the HLA-A2-binding motifs p369-377, p689-697, and p971-979. After vaccination, the mean peptide-specific T-cell precursor frequency to the HLA-A2 peptides increased in the majority of patients. In addition, the peptide-specific T cells were able to lyse tumors. The responses were long-lived and detectable for more than 1 year after the final vaccination in select patients. These results demonstrate that HER-2/neu MHC class II epitopes containing encompassed MHC class I epitopes are able to induce long-lasting HER-2-specific IFN-γ-producing CD8 T cells.
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