IL2 and cancer: Combination therapy with PD-1 blockade and IL-2 substantially improves anti-tumor efficacy compared with PD-1 blockade or IL-2 monotherapy, which has been extensively explored for immunotherapy of various cancers.15,21,26,47 The basic principle of combined immunotherapy with PD-1 blockade and IL-2 is to remove the PD-1 inhibitory brake and in the meantime provide a stimulatory signal for cytotoxic T lymphocytes with IL-2.