Identification of HER2/neu-derived peptide epitopes recognized by gastric cancer-specific cytotoxic T lymphocytes

We have derived HLA-A2.1-restricted, gastric cancer-specific cytotoxic T lymphocyte (CTL) lines by repetitive in vitro stimulation of tumor- associated lymphocytes (TAL) with autologous tumor cells. The HER2/neu specificity of these gastric cancer-specific CTLs was demonstrated using HER2/neu-transfected cell lines and HER2/neu-expressing tumors, and with a set of HER2/neu-derived peptide epitopes. Gastric cancer-specific CTLs specifically lysed autologous and allogeneic HLA-A2.1 +, HER2/neu⁺ gastric cancer cells, HER2/neu-transfected CIR/A2 cell lines (HLA-A2.1⁺, HER2⁺) and HLA-A2.1-transfected SW626 tumor cell lines (HLA-A2.1⁺, HER2⁺). This recognition could be inhibited by anti-HLA-A2 antibody or by cold target HER2/neu-transfected CIR/A2 cells. Our results demonstrate that the HER2/neu- encoded HLA-A2.1-associated epitopes recognized by CTLs are presented as naturally processed peptides on gastric cancer lines. Furthermore, 3 of 19 tested HER2/neu-derived peptide epitopes [HER2(9₁₀₆), HER2(9₃₆₉), HER2(9₆₈₉)], which all bound HLA-A2.1 with high (IC₅₀ < 50 nM) affinity, were able to sensitize HLA-A2⁺ CIR/A2 cells to be recognized by the gastric cancer-specific CTLs, demonstrating the immunodominance of these epitopes. In conclusion, our findings implicate HER2/neu-derived epitopes as potential candidates for novel immunotherapy and vaccine strategies against gastric cancer.