PDCD1 and hepatocellular carcinoma: Alteration in the expression and regulation of PD-1 has been demonstrated to be closely associated with T cell dysfunction in chronic HBV infection [8, 16–21] and HBV-related HCC [17, 19, 22–26], and blockade of PD-1 pathway has been shown to be able to restore T-cell responses in chronic HBV infection [8, 16, 20, 27].