A phase I/II study of OTSGC-A24 combined peptide vaccine in advanced gastric cancer.

65 Background: The aim of this study was to evaluate the safety and optimal dosing schedule of a HLA-restricted cancer vaccine cocktail, OTSGC-A24 targeting novel specific tumor antigens FOXM1, DEPDC1, KIF20A, URLC10 and VEGFR1 in advanced gastric cancer patients with HLA-2402 haplotype. Methods: The vaccine was administered subcutaneously at 3-weekly, 2-weekly and weekly interval. In the first phase, 3 evaluable patients were treated in each dose cohort. The decision to expand the 2-weekly and weekly cohort to 10 patients per cohort was based on specific cytotoxic T-lymphocyte (CTL) induction rate using ELISPOT assay 4 weeks after vaccination. Results: The vaccine was well tolerated at all dose cohorts. The most common toxicity seen was skin induration at the injection sites. No DLT was observed. One patient developed G2 interstitial pneumonitis, 6 months after initiation of treatment. Stable disease was seen in 4 of 9 evaluable patients. The specific CTL induction can be observed at 4 weeks post vaccination with the highest (>2 of 3) observed in the weekly and 2-weekly cohorts. One of 3 patients in the 3-weekly cohort achieved specific CTL response at 4 weeks post vaccination, although all patients attained specific CTL response by 12 weeks after vaccination. Conclusions: OTSGC-A24 combined peptide vaccine was well tolerated. At 4 weeks post vaccination, the CTL induction rate is superior in the weekly and 2-weekly cohort. Efficacy data of the expanded cohorts will be presented. Clinical trial information: NCT01227772.