Vaccination against hepatitis delta virus infection: studies in the woodchuck (Marmota monax) model

Hepatitis delta virus (HDV) superinfection of hepatitis B virus carriers causes severe liver disease and results in a high rate of chronicity. So far, neither sufficient therapy nor vaccines to prevent HBV carriers from superinfection are available. A good model to test vaccine candidates is the woodchuck chronically infected with the woodchuck hepatitis virus (WHV); the woodchuck can be superinfected with HDV and shows a course of infection similar to that of patients. Different strategies have been investigated to establish a protective vaccine against HDV superinfection. Both proteins of HDV (HDAg p24 and p27), which differ only in the C-terminal amino acid sequence, have been used as vaccine candidates. Synthetic peptides derived from B cell epitopes of HDAg and HDAg p24 expressed in Escherichia coli, yeast, or baculovirus have been used to immunize woodchucks. The protein immunization induced a specific antibody response, however, no protection from HDV superinfection was achieved. Vaccinations with vaccinia virus expressing HDAg p24 or p27 and DNA immunization with vectors expressing p24 were also not able to induce a protective immune response, but seemed to modulate the course of HDV superinfection. Thus, new strategies to develop a vaccine to prevent HDV superinfection are needed.