Immune checkpoint blockade (ICB) immunotherapy targeting intrinsic downregulators of immunity, such as cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), programmed cell death protein 1 (PD-1), and programmed cell death ligand 1 (PD-L1) has shown durable clinical responses and recently been a source of promising new cancer treatments (1, 2). Here, PDCD1 is linked to cancer.