Shi Chang-hong

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.

Immune Responses and Protective Efficacy of the Gene Vaccine Expressing Ag85B and ESAT6 Fusion Protein from Mycobacterium tuberculosis

Genetic immunity is a new promising approach for the development of novel tuberculosis vaccines. In this study, it is shown that DNA vaccines expressing the fusion protein of antigen 85B (Ag85B) and early secreted antigenic target 6-kDa antigen (ESAT6) can induce high levels of specific IgG2a antibody subtype in the mice. With the prolongation of postimmunization time, the levels of IgG2a antibody decrease gradually. Although a high-level specific IgG2a antibody subtype is also elicited by classical BCG, the ratio of antibody subtypes IgG2a to IgG1 changes 4 weeks after immunization, and IgG1 is gradually shifted to the main antibody subtype. DNA vaccines also elicit cellular immunity as shown by specific spleen lymphocytes proliferation to Ag85B or ESAT6 protein and the production of high levels of IFN-gamma and IL-2, which is similar to that elicited by BCG. Vaccination of mice with DNA vaccines expressing the fusion protein Ag85B-ESAT6 results in a significant level of protection against the subsequent high-dose challenge with virulent Mycobacterium tuberculosis (MTB) H37Rv. Dramatic reduction in the number of MTB colony-forming units in the spleens and lungs is observed. Pathological examination showed that recombinant plasmid and BCG groups have only minor damage and organizational structures that are kept relatively complete, while in the control group, spleens and lungs are damaged seriously. Therefore, although the reducing degree of mycobacterial loads in the organ of mice immunized with recombinant plasmid is not more than that of BCG, through the analysis of pathological changes, we may conclude that the protective effect provided by DNA vaccine expressing the Ag85B-ESAT6 fusion protein is equivalent to that afforded by the classical BCG.