Notably, the recognition that the PD-1/PD-L1/PD-L2 immunomodulatory axis was involved in tumor progression provided scientific rationale for the development of drugs, namely monoclonal antibodies, which specifically target the PD-1/PD-L1/PD-L2 axis and are capable of significantly regenerating the antitumor functions of T cells [18,19]. Here, PDCD1 is linked to neoplasm.