Characterization of HCV-specific Patr class II restricted CD4+ T cell responses in an acutely infected chimpanzee.

Resolution of hepatitis C virus (HCV) infection is associated with strong and sustained virus-specific CD4+ T cell responses. In this study, we investigated the evolution of functional T cell responses during acute infection of a chimpanzee and the longevity of these lymphocytes in blood and liver after resolution of infection. Viremia increased through the first 3 weeks of infection and then remained stable until the onset of T cell responses at weeks 6 and 8 postinfection. CD4+ T cells targeting nonstructural HCV proteins were detected in proliferation assays by week 6 postinfection, but they failed to produce interferon gamma (IFN-gamma). HCV-specific CD4+ and CD8+ T cells with the ability to produce IFN-gamma appeared at week 8 when a rapid 10-fold reduction in plasma viremia was first observed. This cytokine response persisted through to week 24 when infection apparently resolved. T cell lines targeting 3 CD4+ T cell epitopes and 1 CD8+ T cell epitope were derived from liver and their Patr major histocompatibility complex (MHC) restriction elements were identified. In retrospective studies performed on cryopreserved peripheral blood mononuclear cells (PBMCs) collected at various timepoints after infection, the onset of an IFN-gamma response measured against the class II restricted epitopes correlated with viral clearance. In conclusion, the characterization of the HCV epitopes and MHC class II restriction elements described here will facilitate a detailed comparison of CD4+ T cell function in animals with resolved and persistent infections.