Characterization of T-cell response to woodchuck hepatitis virus core protein and protection of woodchucks from infection by immunization with peptides containing a T-cell epitope.

Specific activation of T cells appears to be a prerequisite for viral clearance during hepatitis B virus (HBV) infection. The T-cell response to HBV core protein is essential in determining an acute or chronic outcome of HBV infection, but how this immune response contributes to the course of infection remains unclear. This is due to results obtained from humans, which are restricted to phenomenological observations occurring during the clinical onset after HBV infection. Thus, a useful animal model is needed. Characterization of the T-cell response to the core protein (WHcAg) of woodchuck hepatitis virus (WHV) in woodchucks contributes to the understanding of these mechanisms. Therefore, we investigated the response of woodchuck peripheral blood mononuclear cells (PBMCs) to WHcAg and WHcAg-derived peptides, using our 5-bromo-2'-deoxyuridine assay. We demonstrated WHcAg-specific proliferation of PBMCs and nylon wool-nonadherent cells from acutely WHV-infected woodchucks. Using a cross-reacting anti-human T-cell (CD3) antiserum, we identified nonadherent cells as woodchuck T cells. T-cell epitope mapping with overlapping peptides, covering the entire WHcAg, revealed T-cell responses of acutely WHV-infected woodchucks to peptide1-20, peptide100-119, and peptide112-131. Detailed epitope analysis in the WHcAg region from amino acids 97 to 140 showed that T cells especially recognized peptide97-110. Establishment of polyclonal T-cell lines with WHcAg or peptide97-110 revealed reciprocal stimulation by peptide97-110 or WHcAg, respectively. We vaccinated woodchucks with peptide97-110 or WHcAg to prove the importance of this immunodominant T-cell epitope. All woodchucks immunized with peptide97-110 or WHcAg were protected. Our results show that the cellular immune response to WHcAg or to one T-cell epitope protects woodchucks from WHV infection.