CD8+ T-cell response against hepatitis C virus.

CD8+ T-cell response is thought to be important for the control of hepatitis C virus (HCV) as well as for the liver cell injury caused by HCV infection. Studies on antigen-specific CD8+ T cells had long been hampered by lack of suitable techniques. Recently developed single-cell based assays, including peptide major histocompatibility complex (MHC) tetramer staining and intracellular cytokine staining, have greatly enhanced the opportunities for directly studying HCV-specific CD8+ T cells. Thanks to these novel assays the quantitative and qualitative nature of HCV-specific CD8+ T cells, including their number, phenotype, and effector functions, are starting to be revealed. However, much important information remains missing, including the signals for differentiation and migration of HCV-specific CD8+ T cells and the precise functions of antigen-specific effector cells in the virus-infected liver. The urgent need for effective immunotherapy and vaccines can not be met without a better understanding of the CD8+ T-cell response in HCV infection, which calls for a comprehensive strategy to study such cells directly using sensitive and quantitative assays.