First‐in‐human study of the cancer peptide vaccine TAS0313 in patients with advanced solid tumors

TAS0313, a novel cancer vaccine cocktail, was developed to overcome the disadvantages of previously developed short and long peptide vaccines; it comprises several long peptides targeting multiple cancer antigens. We evaluated TAS0313 monotherapy in Japanese patients with advanced solid tumors for which no other therapies were available. In the dose‐finding cohort, patients received TAS0313 (9 or 27 mg) on days 1, 8, and 15 of cycles 1 and 2, and then on day 1 of each subsequent 21‐day cycle. The primary objective was the evaluation of safety and tolerability. Secondary objectives were evaluation of efficacy, tumor responses, and immune activation (CTL, IgG, and tumor‐infiltrating lymphocyte [TIL] levels). The full analysis set contained 10 patients in the 9‐mg group and seven in the 27‐mg group. No dose‐limiting toxicities were reported in cycle 1. All adverse drug reactions (ADRs) were grade 1 or 2; the most common ADRs were injection site‐related events. The best response was stable disease in four of 17 patients. The median progression‐free survival (PFS) duration was 2.2 (95% confidence interval, 1.0‐2.3) months overall; patients with baseline low lymphocyte counts (≤750/μL) had shorter PFS. Compared with baseline, TILs were increased in five patients. Although CTLs, IgG, and TILs were induced, no correlative pattern with clinical outcomes was observed. The safety, tolerability, and induction of immune responses in patients with advanced solid tumors receiving TAS0313 were confirmed. Further evaluation of TAS0313’s efficacy as monotherapy or in combination with pembrolizumab is underway. The study is registered at www.clinicaltrials.jp (JapicCTI‐183824).