CD8+ T-Cell Responses in Hepatitis B and C: The (HLA-) A, B, and C of Hepatitis B and C.

Approximately 500 million people are chronically infected with the hepatitis B virus (HBV) or hepatitis C virus (HCV) worldwide and are thus at high risk of progressive liver disease, leading to liver fibrosis, cirrhosis and ultimately hepatocellular cancer. Virus-specific CD8+ T-cells play a major role in viral clearance in >90% of adult patients who clear HBV and in approximately 30% of patients who clear HCV in acute infection. However, several mechanisms contribute to the failure of the adaptive CD8+ T-cell response in those patients who progress to chronic infection. These include viral mutations leading to escape from the CD8+ T-cell response as well as exhaustion and dysfunction of virus-specific CD8+ T-cells. Antiviral efficacy of the virus-specific CD8+ T-cell response also strongly depends on its restriction by specific human leukocyte antigens (HLA) class I alleles. Our review will summarize the role of HLA-A, B and C-restricted CD8+ T-cells in HBV and HCV infection. Due to the current lack of a comprehensive database of HBV- and HCV-specific CD8+ T-cell epitopes, we also provide a summary of the repertoire of currently well-described HBV- and HCV-specific CD8+ T-cell epitopes. A better understanding of the factors that contribute to the success or failure of virus-specific CD8+ T-cells may help to develop new therapeutic options for HBV eradication in patients with chronic HBV infection (therapeutic vaccination and/or immunomodulation) as well as a prophylactic vaccine against HCV infection.