Identification of novel Lck-derived T helper epitope long peptides applicable for HLA-A2(+) cancer patients as cancer vaccine.

The present study attempted to identify T helper epitope long peptides capable of inducing cytotoxic T lymphocytes (CTL) from Lck antigen (p56(Lck) ), the src family tyrosine kinase, which is known to be aberrantly expressed in metastatic cancers cells, in order to develop a long peptide-based cancer vaccine for HLA-A2(+) cancer patients. Based on the biding motif to the HLA-DR and HLA-A2 alleles, 94 peptides were prepared from the Lck antigen. These peptides were screened for their reactivity to immunoglobulin G (IgG) from plasma of cancer patients, followed by testing of their ability to induce both CD4(+) and CD8(+) T lymphocytes showing not only peptide-specific IFN-γ production but cytotoxicity against HLA-A2(+) cancer cells from peripheral blood mononuclear cells (PBMC) of HLA-A2(+) cancer patients. Among 94 peptides tested, the three T helper epitope long peptides and their inner CTL epitope short peptides with HLA-A2 binding motifs were frequently recognized by IgG of cancer patients, and efficiently induced both CD4(+) IFN-γ(+) and CD8(+) IFN-γ(+) T lymphocytes. Patients' PBMC stimulated with these long peptides showed cytotoxicity against HLA-A2(+) Lck(+) cancer cells in HLA-class I and HLA-class II dependent manners. These three peptides might be useful for long peptide-based vaccines for HLA-A2(+) cancer patients with Lck(+) tumor cells.