PDCD1 and cancer: Monoclonal antibodies (mAbs) directed against co-inhibitory molecules involved in T cell exhaustion or Treg cell function such as CTLA-4 (cytotoxic T-lymphocyte-associated antigen 4) and the PD-1/PD-L1 axes (programmed cell death 1/programmed death-ligand 1) have revolutionized the treatment of an increasing number of cancers, including melanoma, lung cancer, renal cancer, bladder cancer, and Hodgkin's lymphoma (60).