The hepatitis C virus (HCV)-specific CD8؉ -T-cell response is thought to play a critical role in HCV infection. Studies of these responses have largely relied on the analysis of a small number of previously described or predicted HCV epitopes, mostly restricted by HLA A2. In order to determine the actual breadth and magnitude of CD8؉ -T-cell responses in the context of diverse HLA class I alleles, we performed a comprehensive analysis of responses to all expressed HCV proteins. By using a panel of 301 overlapping peptides, we analyzed peripheral blood mononuclear cells (PBMC) from a cohort of 14 anti-HCV-positive, HLA A2-positive individuals in an enzyme-linked immunospot assay. Only four subjects had detectable HLA A2-restricted responses in PBMC, and only 3 of 19 predicted A2 epitopes were targeted, all of which were confirmed by tetramer analysis. In contrast, 9 of 14 persons showed responses with more comprehensive analyses, with many responses directed against previously unreported epitopes. These results indicate that circulating HCV-specific CD8؉ -T-cell responses can be detected in PBMC in the majority of infected persons and that these responses are heterogeneous with no immunodominant epitopes consistently recognized. Since responses to epitopes restricted by single HLA alleles such as HLA A2 do not predict the overall response in an individual, more comprehensive approaches, as shown here, should facilitate definition of the role of the CD8 ؉ -T-cell response in HCV infection. Moreover, the low level or absence of responses to many predicted epitopes provides a rationale for immunotherapeutic interventions to broaden cytotoxic-T-lymphocyte recognition.
The CD8ϩ T-cell response is thought to play a crucial role in the course of hepatitis C virus (HCV) infection. In humans and in chimpanzees, a strong and broadly directed HCV-specific cytoxoxic-T-lymphocyte (CTL) response has been associated with viral clearance during acute HCV infection (7,29). In contrast, individuals with chronic infection are often found to have a relatively weak and narrowly directed CD8 ϩ -T-cell response against HCV (reviewed in reference 27). Whether these responses in chronic disease are still beneficial in containing viral replication or whether they are mediators of hepatic injury and disease is unclear. In several studies, the magnitude of the HCV-specific CD8 ϩ -T-cell response has been correlated to HCV viral load and to liver histology, but the results of these studies have been mixed (17,31,33,34,41). Overall, the levels of responses detected by most investigators, using a variety of methods, have been fairly low compared to those found in many other viral infections.Thus far, most studies of the HCV-specific CD8 ϩ -T-cell response have been undertaken in HLA A2-positive individuals, and the analysis usually has been restricted to a set of previously described HLA A2-restricted HCV epitopes or to HCV peptides shown to bind strongly to HLA A2 and therefore predicted to elicit responses (2,4,5,14,15,28,30,33,34,(37)(38)(3...
