PDCD1 and neoplasm: First, in MC38 tumor, proteins in MHC class I antigen presentation pathways and cytotoxicity were enhanced upon anti-PD-1 treatment, and the additional CD4+-TIL depletion further boosted these pathway changes (Table 2 and Supplemental Fig. 3), suggesting that anti-PD-1 caused tumor death due to increased anti-tumor immunity, which is boosted by the CD4+ depletion (CD4+ suppresses anti-tumor activity in MC38, consistent with hypothesis MOA per above observations).