PDCD1 and cancer: Physiologically, these immunosuppressive signaling pathways play important roles in maintaining self-tolerance to prevent autoimmunity, limit immune-mediated tissue damage, and control the resolution of inflammation.332,333 Cancer cells may take advantage of these immune checkpoints to disguise themselves from body immune system.334,335 Among these immune checkpoints, cytotoxic T-lymphocyte antigen 4 (CTLA-4) and PD-1/PD-L1 axis are the most potent examples of T-cell immune-checkpoint molecules.