PDCD1 and neoplasm: Its anti-tumor mechanism is mainly to block PD-1/PD-L1 signaling pathway, improve T cell response activity in vitro and in vivo, and achieve T cell proliferation and anti-tumor effect (Greenwald, 2008); In addition, it mediates the endocytosis of PD-1, reduces the expression of PD-1 membrane, and relieves T cell immunosuppression.