Among the strategies used to reverse immunosuppression, cancer immunotherapy that targets immune checkpoints such as cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), programmed cell death 1 (PD-1) or programmed cell death ligand 1 (PD-L1) of immune checkpoint has demonstrated remarkable efficacy in various cancers. Here, PDCD1 is linked to cancer.