PDCD1 and neoplasm: The major factors attributed to the resistance to anti-PD-1/PD-L1 therapy include the lack of infiltrating T lymphocytes in tumor tissues characterizing the so-called “cold tumor”6, and the presence of tumor immunosuppressive microenvironment, such as regulatory T (Treg) cells and myeloid-derived suppressor cells (MDSCs) to inhibit the anti-PD-1/PD-L1 antibody-regenerated anti-tumor cytotoxic T lymphocytes and Th1 cell response7,8.