PDCD1 and neoplasm: Moreover, with increasing understanding on the tumor microenvironment, reports to the primary and adaptive resistance to anti-PD-1/PD-L1 therapy, and in vitro/ex vivo research demonstrating the role of PD-1/PD-L1 pathway in chronic infection, there is a need to explore novel biomarkers, novel combinatorial strategies, and implement clinical trials evaluating the efficacy of PD-1/PD-L1 blockade on chronic infection, to broaden its clinical applicability in the future.