PDCD1 and neoplasm: For example, the stimulatory and coinhibitory interactions between lymphocytes infiltrating tumor stroma and tumor cells expressing receptor-ligands pairs, like immune check point inhibitors [cytotoxic T-lymphocyte antigen-4 (CTLA-4), programmed cell death-1 (PD-1), and its ligand (PD-L1)] correlates with T cell dysfunction [37].