Immunogenicity and protective efficacy of a tuberculosis DNA vaccine expressing a fusion protein of Ag85B-Esat6-HspX in mice

Tuberculosis remains a major infectious disease worldwide due to the low efficacy of available vaccine of the Mycobacterium bovis Bacillus Calmette–Guérin (BCG). DNA vaccines are especially promising candidates; however, the efficacy of DNA vaccine expressing single antigen of Mycobacterium tuberculosis (MTb) is limited. In this study, a plasmid DNA vaccine, pAEH, was constructed and designed to express a fusion protein of the Ag85B, Esat6, and HspX of MTb. Its immunogenicity and protective efficacy as well as therapeutic effect were assessed in a mouse model of tuberculosis. Vaccination with the pAEH significantly increased the frequency of peripheral blood CD4+ and CD8+ T cells, but not γδT cells, similar to that of vaccination with the BCG, and induced significantly higher levels of HspX-specific T cell proliferation, as compared with vaccination with BCG or the pHspX. Furthermore, vaccination with the pAEH increased the frequency of Ag85B, Esat6 and HspX-specific IFNγ-secreting T cells, accompanied by significantly higher levels of IFN-γ and IL-2 production ex vivo, as compared with that of the BCG or pHspX-vaccinated mice. Apparently, vaccination with the pAEH induced potent Th1 responses in mice. More importantly, vaccination with the pAEH inhibited the replication of virulent MTb in the lungs and spleens, even after MTb infection, and related lung inflammation in mice. Potentially, the newly developed pAEH vaccine may be used for the prevention and therapeutic intervention of MTb infection.