PDCD1 and neoplasm: The blockade of the coinhibitory cytotoxic T-lymphocyte–associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1) allows the activation of T cell stimulatory signaling, thereby enhancing antitumor T cell cytotoxicity, proinflammatory cytokine production, and proliferation and promoting tumor destruction (21–24).