Immunization with Vaccinia Virus Expressing HDAg

Vaccination with recombinant vaccinia virus expressing viral antigens, e.g., antigens of the human or simian immunodeficiency viruses, is able to induce a specific CTL response (Allen et al. 2000; Dorrell et al. 2000).

Two groups tested the efficacy of immunization with vaccinia virus expressing either S- or L-HDAg (Eckart et al. 1993; Karayiannis et al. 1993a, 1993b). Altogether, six WHV carrier woodchucks were immunized. None of these animals produced a measurable humoral immune response after immunization; the cellular immune response was not measurable at this time in the woodchuck model. After challenge all animals developed chronic HDV infection. Karayiannis et al., however, described a modulation of the course of infection. Viremia was detected some weeks later and presented at lower levels in the immunized woodchucks in comparison to the control animals. Eckart et al. observed no differences in the course of infection between vaccinated and control woodchucks. It is difficult to discern the reasons for the different course of infection in these studies. The amount of the vaccinia virus given is comparable, but Karayiannis et al. immunized twice intradermally, whereas Eckart et al. immunized once intravenously. Probably, the intradermal protocol was more effective and was able to modulate the course of infection, however, all animals became chronically infected.

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