PDCD1 and neoplasm: Tumor growth inhibition of anti–PD-1 therapy was almost completely reversed in the CD8+ T cell depletion group (P < 0.001), while depletion of NK cells did not affect the therapeutic antitumor effect of anti–PD-1; this indicated that CD8+ T cells had a more critical role than NK cells in directing anti–PD-1 immunotherapy and that CD8+ T cells contributed more to the secretion of granzyme B in tumors treated with anti–PD-1 antibody.