Vaccination with peptides derived from cancer-testis antigens in combination with CpG-7909 elicits strong specific CD8+ T cell response in patients with metastatic esophageal squamous cell carcinoma.

Potent helper action is necessary for peptide-based vaccines to efficiently induce antitumor immune responses against advanced cancer. A phase I trial for advanced esophageal squamous cell carcinoma was carried out for patients with HLA-A*2402 using epitope peptides derived from novel cancer-testis antigens, LY6K and TTK, in combination with CpG-7909 (NCT00669292). This study investigated the feasibility and the toxicity as well as induction of tumor antigen-specific immune responses. Nine patients were vaccinated on days 1, 8, 15, and 22 of each 28-day treatment cycle with peptide LY6K-177, peptide TTK-567, and CpG-7909 (level-1; 0, level-2; 0.02, level-3; 0.1 mg/kg) and all were tolerated by this treatment. LY6K-specific T cell responses in PBMCs were detected in two of the three patients in each level. In particular, two patients in level-2/3 showed potent LY6K-specific T cell responses. In contrast, only two patients in level-2/3 showed TTK-567-specific T cell responses. The frequency of LY6K-177 or TTK-567-specific CD8+ T cells increased in patients in level-2/3 (with CpG). The vaccination with peptides and CpG-7909 increased and activated both plasmacytoid dendritic cells and natural killer cells, and increased the serum level of α-interferon. There were no complete response (CR) and partial response (PR), however, one of three patients in level-1, and four of six patients in level-2/3 showed stable disease (SD). In conclusion, vaccination with LY6K-177 and TTK-567 in combination with CpG-7909 successfully elicited antigen-specific CD8+ T cell responses and enhanced the innate immunity of patients with advanced esophageal squamous cell carcinoma. This vaccine protocol is therefore recommended to undergo further phase II trials.