PDCD1 and cancer: Therapeutic antibodies against immune checkpoint proteins such as anticytotoxic T lymphocyte–associated antigen 4 (CTLA-4), anti-programmed cell death 1 (PD-1), or anti-programmed death ligand-1 (PD-L1) have emerged as promising therapies for several types of cancers, including melanoma, non-small cell lung cancer (NSCLC), renal cancer, endometrial cancer, and other cancers9–11.