PDCD1 and neoplasm: In addition to regulating CD8 + T cell function to mediate resistance to anti-PD-1 therapy, several in vitro and in vivo experiments have indicated that exosomal circUHRF1 and circZNF451 induce immunosuppression in HCC and LUAD by impairing the activity of NK cells and macrophages, respectively, thereby promoting tumor immune evasion and resistance to anti-PD-1 immunotherapy [181–183].