PDCD1 and cancer: However, when administered alone, ICB approaches, such as anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), anti-programmed cell death protein 1 (PD-1), and/or anti-programmed death-ligand 1 (PD-L1) antibodies, generally elicit low objective response rates (ORRs), ranging from 0 to 33%, which are durable only in a minority of cancer patients [1–3].