Inhibitory receptor molecules in chronic hepatitis B and C infections: novel targets for immunotherapy?

Chronic HBV and HCV infections are the leading cause of liver-related morbidity and mortality. For effective antiviral immunity, virus-specific T cells are required, but these cells have been shown to be weak or absent in chronic HBV and HCV patients. One of the mechanisms that underlies the impaired T-cell response is the result of the continuously high viral load that causes HBV-specific and HCV-specific T cells to become exhausted, which is characterized by impaired proliferation, cytokine production and cytotoxic activity of T cells as well as high susceptibility to apoptosis. In vitro studies from chronic HBV and HCV patients as well as in vivo studies in animal models demonstrated a reversible state of T-cell exhaustion, which can be manipulated to reinvigorate the specific antiviral immune responses. In chronic HCV infection, this concept has been explored in clinical trials by administration of specific antibody to block the inhibitory pathways. The manipulation of inhibitory receptors is a promising and potential strategy for immunotherapeutic interventions in chronic HBV and HCV patients to facilitate complete elimination of the viruses or sustained viral control.