PDCD1 and neoplasm: In 1999, Chen’s team discovered a B7 homologous transmembrane protein, B7-H1 (now known as PD-L1).55 Later, it was found that PD-L1 is a ligand of PD-1, which clarified the negative immune regulation function of PD-L1 and highlighted its potential for application in tumor treatment.56 In 2002, PD-L1 was demonstrated to promote T cell apoptosis, and a B7-H1 antibody was applied to inhibit tumor growth, which demonstrated that PD-L1 functions in tumor immune escape for the first time.57,58 Since then, the effectiveness of PD-L1 antibody therapy has been witnessed by successive clinical trials.