PDCD1 and neoplasm: CD4+ cell-depletion, on the other hand, not only completely abolished the antitumor effect of anti-PD-1-antibody treatment, but also dramatically accelerated tumor growth (TGI -101%, Table 1 Experiment 2 and Fig. 3A,B), suggesting that CD4+-Teff mediated the MOA of anti-PD-1 antibody treatment in the Hepa 1–6 tumor, and consistent with above observation that CD4+-Teff was the main source of tumor immunity.