PDCD1 and hepatocellular carcinoma: Analyses of Tregs in the HBV-associated HCC tumor microenvironment showed a more immunosuppressive and effective status [20], with increased expression levels of FOXP3 [20,26,37], PD-1 [20,25,37], CTLA-4 [20,25], ICOS [20], and LAG-3 [37] compared with non-HBV HCC.