PDCD1 and neoplasm: Checkpoint inhibitors, for example antibodies against programmed cell death protein 1 (PD-1) or its ligand PD-L1 as well as cytotoxic T lymphocyte-associated protein 4 (CTLA-4), may block the communication of T cells with their suppressive cognate ligands on tumor or stromal cells [47,213], to release an antitumor immune reaction.