PDCD1 and neoplasm: However, due to the immunosuppressive nature of tumor microenvironments, tumor‐infiltrating T cells become “exhausted” or otherwise suppressed, severely impairing their proliferative capacity and effector function.[1, 2] Recent efforts to reactivate immune responses by blocking T cell coinhibitory receptors such as programmed death 1 (PD‐1) or cytotoxic T‐lymphocyte antigen 4 (CTLA‐4) have shown clinical promise.[3, 4] Meanwhile, pathogens such as bacteria, viruses, fungi, or protozoa can cause acute and chronic infections in their hosts.