PDCD1 and neoplasm: Monoclonal antibodies that bind to PD-1 or PD-L1 are immune checkpoint inhibitors that prevent this receptor-ligand interaction and consequently allow CTLs to limit tumor growth and improve prognosis in multiple T cell-responsive cancers including renal adenocarcinoma by enhancing the cytotoxic, antitumor activity of CD8+ tumor infiltrating lymphocytes (TILs) (2–6).