In this study, we demonstrated that calves vaccinated with a combined
DNA vaccine encoding Ag85B, MPT- 64, and MPT-83
antigens from the Mycobacterium tuberculosis for the priming and subsequently boosting with BCG prior to experimental challenge with virulent Mycobacterium bovis (M. bovis) resulted in improved immune responses over immunizing. Vaccination with the combined
DNA/BCG induced higher levels of
antigen- specific
gamma interferon (IFN-gamma) in whole-blood cultures 4 weeks after final vaccination and the level of
antigen-specific IFN-gamma in response to
Ag85, MPT-64, and MPT-83 were still higher 4 weeks after challenge when compared to the combined
DNA group. There was a significant bias toward induction of CD4+ T cells rather than CD8+ T cells responses, and the mean percentage of CD4+ T cells was increased about 2.6-fold in peripheral blood mononuclear cells (PBMC) cultures in
DNA prime-BCG boost vaccination when compared to the nonvaccinated group. In addition,
DNA prime-BCG boost vaccination resulted in stronger humoral immune responses, and the levels of the specific
antibodies to three
antigens were increased two- to 32- fold when compared to the combined
DNA group. Vaccination with the combined
DNA/BCG induced a high level of protection against an intratracheal challenge with virulent M. bovis, based on a significant enhancement of six pathological and microbiological parameters of protection compared to the nonvaccinated group. Finally, the combined
DNA/BCG increased the protective efficacy by more than 10-100-fold as measured by reduced CFU counts in the lungs from calves challenged with M. bovis compared to the combined
DNA and BCG groups. These results suggest that use of the prime-boost strategy offers better protection against
bovine tuberculosis than does the combined
DNA vaccines and BCG.