Longitudinal mapping of protective CD4+ T cell responses against HCV:: analysis of fluctuating dominant and subdominant HLA-DR11 restricted epitopes

Cellular immunity plays an important role in the control of persistent virus infections such as hepatitis C virus (HCV). Antiviral CD4(+) T cell responses have been shown to accompany resolution of acute disease and there is also a consistent association between HLA Class II genes, notably HLADRBI*1101 (and the closely linked HLADQBI*0301) and disease resolution. We initially mapped longitudinal CD4(+) T cell responses in an individual after spontaneous resolution of acute HCV, and identified three HLA-DR11-restricted responses which vary in immunodominance over time. Functional assays and HLA Class II1 tetramer staining revealed one to be a response to a commonly recognized epitope, NS3(1248-1261), although cytokine capture assays showed these specific cells to be at a very low frequency. In this patient, and in others reported, this most frequently recognized HLA-DR11 restricted epitope is not immunodominant. We analysed whether sequence variability within and between genotypes might account for differences in recognition of HLA-DR11 restricted epitopes. We found that a limited number, including NS3(1248-1261), showed extreme sequence conservation. Within NS3, the ability of peptides to accept amino acid substitutions was clearly related to the structure of the protein. Overall the data provide a deeper understanding of the relationship between protein structure and variability of HLA-DR11 restricted peptides and may explain the apparent dominance of responses to NS3(1248-1261) across studies but not within an individual immune response.