Virological footprint of CD4+ T-cell responses during chronic hepatitis C virus infection.

Human and animal model evidence suggests that CD4+ T cells play a critical role in the control of chronic hepatitis C virus (HCV) infection. However, despite their importance, the mechanism behind the failure of such populations in chronic disease is not understood and the contribution of viral mutation is not known. To address this, this study defined the specificity and virological footprint of CD4+ T cells in chronic infection. CD8+ T-cell-depleted peripheral blood mononuclear cells from 61 HCV genotype 1-infected patients were analysed against a panel of peptides covering the HCV genotype 1 core--a region where CD4+ T-cell responses may be reproducibly obtained. In parallel, the core region and E2 protein were sequenced. Gamma interferon-secreting CD4+ T-cell responses directed against multiple epitopes were detected in 53% of individuals, targeting between one and four peptides in the HCV core. Viral sequence evaluation revealed that these CD4+ T-cell responses were associated with mutants in 2/21 individuals. In these two cases, the circulating sequence variant was poorly recognized by host CD4+ T cells. Bioinformatics analyses revealed no overall evidence of selection in the target epitopes and no differences between the groups with and without detectable CD4+ T-cell responses. It was concluded that sustained core peptide-specific CD4+ T-cell responses may be reproducibly measured during chronic HCV infection and that immune escape may occur in specific instances. However, overall the virological impact of such responses is limited and other causes for CD4+ T-cell failure in HCV must be sought.