[Immunogenicity of DNA vaccine prime-BCG boost against Mycobacterium tuberculosis]

To compare the immunogenicity of vaccine strategies about combined DNA prime-BCG boost and DNA or BCG vaccination only.

BALB/c mice were divided into four groups each containing 6 mice, and all mice received three immunizations at 2 weeks interval. One group of mice was vaccinated with PBS (PBS group); one group was vaccinated twice at 0 week and 2 weeks with combined DNA expressing two mycobacterial antigens, ESAT-6 and antigen 85A respectively; and then boosted with BCG at 4 weeks (DNA/BCG group); another group was vaccinated twice with combined DNA at 0 week, 2 weeks and 4 weeks(DNA/DNA group); and the final group received PBS twice at 0 week and 2 weeks and then vaccinated with BCG at 4 weeks(BCG group). Specific IgG antibody in serum of mice was determined with indirect ELISA in 4 weeks, 6 weeks, 8 weeks respectively after final vaccination.The splenic lymphocytes of mice were separated and stimulated with PPD to measure their proliferation by XTT, and to evaluate the production of interferon-r(IFN-gamma) and IL-4 in cell suspensions of spleen cells by ELISA.

PPD could stimulate specific IgG responses in DNA/BCG, DNA/DNA and BCG groups (DNA/DNA group>DNA/BCG group and BCG group), and the most significant response occurred in 12 weeks; the splenic lymphocyte proliferation reactions and IFN-gamma and IL-4 production was detectable in DNA/BCG, DNA/DNA and BCG groups and DNA/BCG group induced significant higher production, especially in 12 weeks.

Priming with the combined DNA vaccines and boost with attenuated M. bovis vaccine (BCG) could enhance specific cell reactions and high level IFN-gamma compared with DNA or attenuated M. bovis vaccine alone.