Moreover, the study showed that when healthy donor PBMCs were co-cultured with human hepatoma cells HepG2.2.15 (transfected with HBV) and its parental cell line HepG2, the Treg population increased and upregulated the expression of CTLA-4 on HepG2.2.15 compared with the HepG2 cells [16]. Here, CTLA4 is linked to hepatocellular carcinoma.