Therapeutic efficacy of a tuberculosis DNA vaccine encoding heat shock protein 65 of Mycobacterium tuberculosis and the human interleukin 2 fusion gene.

Use of therapeutic DNA vaccines is a promising strategy against tuberculosis (TB), however, their immunogenicity still needs to be improved. In this study, a plasmid DNA vaccine expressing heat shock protein 65 (HSP65) and the human interleukin 2 (IL-2) fusion gene was constructed. Immune responses induced by the vaccine in the mice and protection against Mycobacterium tuberculosis (MTB) were investigated, along with the therapeutic effect of the DNA vaccine on tuberculosis in mice. Administration of the HSP65-IL-2-DNA vaccine enhanced Th1-type cellular responses by producing greater amounts of interferon-gamma (IFN-gamma) and IL-2 with a higher titer of antigen-specific anti-Hsp65 IgG2a. Compared with the Bacille Calmette-Guérin (BCG) vaccine, the DNA vaccine was able to evoke both CD4 and CD8 T-cell responses, with an especially high percentage of CD8 T-cells. The DNA vaccine was also able to induce high antigen-specific cytotoxicity activity against target cells. When the mice were challenged with virulent MTB H37Rv, a dramatic decrease in the numbers of MTB colony forming units in the spleen and lungs was observed in the mice immunized with HSP65-IL-2-DNA (P<0.05). Meanwhile, the bacterial numbers in TB infected mice treated with the DNA vaccine were also significantly reduced. The protective and therapeutic effects of the HSP65-IL-2-DNA vaccine in the spleen and lungs were superior to that of the HSP65-DNA vaccine (P<0.05). These results suggest that the DNA vaccine expression of IL-2 and the HSP65 fusion gene enhances the immunogenicity and protective as well as therapeutic effects of the HSP65-DNA vaccine against TB in mice by improving the Th1-type response.