Immunogenicity of interleukin 12 and DNA vaccine prime-BCG boost against Mycobacterium tuberculosis

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Background: BCG as an only effective vaccine to TB played variable efficacy. New vaccination strategies are required. We used interleukin 12 with the combined DNA prime- BCG boost strategies to observe whether the immunogenicity of vaccines against M.Tuberculosis would be improved.

Methods: Plasmid pcDNA- Ag85A and pc-Esat-6 were constructed for vaccination. The mice were divided into 4 immunity groups: BCG group(1), DNA/BCG group(2), DNA+IL- 12/BCG group(3) and DNA/BCG+IL-12 group(4). All mice received three immunizations at 2- week interval For prime-boost experiments, animals were twice vaccinated intramuscular injection with combined DNA (Ag85A and ESAT-6) or mixed DNA-IL-12 and combined DNA, then boosted with BCG or mixed with DNA-IL-12 and BCG. ELISA was used to determine IgG antibody specificity and the proliferative responses of lymphocytes and the phenotype was detected by flow cytometry. Production of INF-γ was detected at 4-week, 6-week, and 8-week after boost.

Results: The antibody titer of group 1, group 2, group 3 and group4 showed a positive reaction. Group3 and 4 compared with group2 and 1, induced high antibody titer. The antibody titer of all four groups increased gradually, and achieved a higher level at 8 week after booster. Group 1, group 2, group 3and group4 all showed significant difference of proliferative responses (P<0.05). Group 3and group 4 were much higher that group 2 and group1 (P<0.05).

The group 3 and the group 4 induced stronger antigen-specific IFN-γ. The mean IFN-γ responses of group 3and the group 4 were not only significantly higher than group PBS (P<0.01) but also higher than group 2and group 1 (P<0.05). The mean percentage of CD4+and CD8+ T cells vaccinated with DNA/BCG+IL-12, DNA+IL-12/BCG, DNA/BCG, or BCG were significantly higher compared to group PBS(P<0.05). A higher mean percentage of CD4+ and CD8+ T cells were observed in mice vaccinated with DNA+IL-12/BCG or DNA/BCG+IL-12 when compared to the DNA/BCG or BCG groups.

Conclusion: Our results showed that the strategy of using human interleukin 12(IL-12) associate DNA priming followed by BCG boosting is an effective way to increase the immunogenicity of tuberculosis, not only increasing cell immunity but also maintaining a stable humoral immunity.