PDCD1 and cancer: While there was heterogeneity among the models they found, the strongest determinants of checkpoint inhibitor responses were the profiles of immune cells within the tumors, which broadly determined whether a model was “hot, cold, or immunosuppressive.” The “hot” cancer models (including, CT26 colorectal and RENCA kidney cancer models) were most responsive to anti-CTLA-4 and anti-PD-1 mAbs, a result that aligns with clinical evidence.