Peptide vaccine as an adjuvant therapy for glypican-3-positive hepatocellular carcinoma induces peptide-specific CTLs and improves long prognosis

There is no established postoperative adjuvant therapy for hepatocellular carcinoma (HCC), and improvement of patient prognosis has been limited. We conducted long-term monitoring of patients within a phase II trial that targeted a cancer antigen, glypican-3 (GPC3), specifically expressed in HCC. We sought to determine if the GPC3 peptide vaccine was an effective adjuvant therapy by monitoring disease-free survival and overall survival. We also tracked GPC3 immunohistochemical (IHC) staining, CTL induction, and postoperative plasma GPC3 for a patient group that was administered the vaccine (n = 35) and an unvaccinated patient group that underwent surgery only (n = 33). The 1-y recurrence rate after surgery was reduced by approximately 15%, and the 5-y and 8-y survival rates were improved by approximately 10% and 30%, respectively, in the vaccinated group compared with the unvaccinated group. Patients who were positive for GPC3 IHC staining were more likely to have induced CTLs, and 60% survived beyond 5 y. Vaccine efficacy had a positive relationship with plasma concentration of GPC3; high concentrations increased the 5-y survival rate to 75%. We thus expect GPC3 vaccination in patients with HCC, who are positive for GPC3 IHC staining and/or plasma GPC3 to induce CTL and have significantly improved long-term prognosis.