CD274 and cancer: In particular, the discovery of immune checkpoint molecules, co-inhibitory receptors expressed on the surface of T cells to negatively regulate T cell-mediated immune responses such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death-1 (PD-1) and its ligand programmed death-ligand 1 (PD-L1) have made a huge impact on the clinical use of cancer immunotherapy.