Particularly, checkpoint blockade immunotherapy that interferes inhibitory pathways in adaptive immunity has improved patient survival across a variety of cancer types4, as exemplified by the clinical practice of the U.S. Food and Drug Administration (FDA)-approved antibodies that antagonize cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1)/programmed death-ligand 1 (PD-L1)5,6. Here, PDCD1 is linked to cancer.