Enhanced Immunogenicity of CD4+T-Cell Responses and Protective Efficacy of a DNA-Modified Vaccinia Virus Ankara Prime-Boost Vaccination Regimen for Murine Tuberculosis

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Abstract
DNA vaccines whose DNA encodes a variety of antigens fromMycobacterium tuberculosishave been evaluated for immunogenicity and protective efficacy. CD8+T-cell responses and protection achieved in other infectious disease models have been optimized by using a DNA immunization to prime the immune system and a recombinant virus encoding the same antigen(s) to boost the response. A DNA vaccine (D) and recombinant modified vaccinia virus Ankara (M) in which the DNA encodes early secreted antigenic target 6 and mycobacterial protein tuberculosis 63 synthesized, and each was found to generate specific gamma interferon (IFN-γ)-secreting CD4+T cells. Enhanced CD4+IFN-γ T-cell responses were produced by both D-M and M-D immunization regimens. Significantly higher levels of IFN-γ were seen with a D-D-D-M immunization regimen. The most immunogenic regimens were assessed in a challenge study and found to produce protection equivalent to that produced byMycobacterium bovisBCG. Thus, heterologous prime-boost regimens boost CD4+as well as CD8+T-cell responses, and the use of heterologous constructs encoding the same antigen(s) may improve the immunogenicity and protective efficacy of DNA vaccines against tuberculosis and other diseases.