PDCD1 and hepatocellular carcinoma: Previous studies have demonstrated that elevated expression of PD-1 in lymphocytes within the liver, especially exhausted T cells and Tregs, are closely associated with a dysfunction of the immune response in chronic HBV infection and HBV-related HCC (Boni et al., 2007; Fisicaro et al., 2010; Hsu et al., 2010; Wang et al., 2011).