PDCD1 and neoplasm: The awareness of this mechanism has sparked the use of antagonist mAbs (particularly involving cytotoxic T-lymphocyte-associated protein 4 (CTLA-4/CD152) and programmed cell death protein 1 (PD-1/CD279) or its ligand programmed death-ligand 1 (PD-L1/CD274) that prevents inhibitory receptor-counterreceptor bridging without triggering coinhibitory signals and thus, releases T cell inhibition and enhances anti-tumor immunity (62, 64).