Although antitumor immunity can employ diverse effector mechanisms, clinical cancer immunotherapy has become dominated by different immune checkpoint blockade (ICB) strategies, with programmed cell death 1/programmed cell death ligand 1 (PD-1/PD-L1) and cytotoxic T lymphocyte–associated protein 4 (CTLA-4) blocking antibodies (Ab) already approved for multiple indications (4). Here, PDCD1 is linked to cancer.