PDCD1 and neoplasm: While an in-depth analysis of CD4+ T helper cells lies outside the scope of this study, Jin et al have previously shown that CD4+ T cell depletion prior to CT26 tumor installation has very little effect on tumor growth, and does not affect anti-PD-1 efficacy, in contrast to CD8+ T cell depletion.16 This suggests that the role of T helper cells in tumor control both naturally and in the context of anti-PD-1 may be difficult to define.