Immunogenicity and Protective Efficacy Conferred by a Novel Recombinant Mycobacterium bovis Bacillus Calmette‐Guérin Strain Expressing Interleukin‐12p70 of Human Cytokine and Ag85A of Mycobacterium tuberculosis Fusion Protein

Abstract

Mycobacterium bovis bacillus Calmette-Gu erin (BCG) immunization provides protection against tuberculosis (TB) in infants, but the antituberculosis protective immunity wanes gradually after initial immunization and lasts less than 15 years. Therefore, more efficacious vaccines are urgently needed. In this study, we constructed a new tuberculosis vaccine of recombinant BCG strain (rBCG-IA), which could express IL-12p70 of human cytokine and Ag85A of M. tuberculosis fusion protein, and investigated its immunogenicity in BALB/c mice by measuring antibody titres, proliferation rate of splenocytes, ratios of CD4 + T and CD8 + T cells stimulated by specific antigens and levels of IFN-c production in antigen-stimulated splenocyte cultures. Meanwhile, we evaluated its protective efficacy against M. tuberculosis H37Rv infection through detecting lung histopathology, organ bacterial loads and lung acid-fast stain. Immunogenicity experiments illustrated that from 2nd to 8th week after immunization, the rBCG-IA vaccine was able to induce the highest level of antibody titres, proliferation rate of splenocytes and IFN-c production among groups and gained improved ratio of CD4 + T and CD8 + T cells from 6th to 8th week after vaccination. And from 2nd to 8th week after M. tuberculosis H37Rv infection, the score of pathology and bacterial loads in the rBCG-IA group were obviously lower than that in rBCG-I group, rBCG-A group or control group (PBST group), but similar to that in BCG group. This study suggested that rBCG-IA was able to elicit stronger humoral and cellular immune responses, but could only confer similar protective efficacy compared with its parental BCG vaccine.

Immunogenicity and protective efficacy of recombinant Bacille Calmette-Guerin strains expressing mycobacterium antigens Ag85A, CFP10, ESAT-6, GM-CSF and IL-12p70

“…It has been reported, vaccination with rBCG over-expressing ESAT-6 could induce stronger IFN-g response than BCG, but exhibited no significant improvement in protective efficacy against M. tuberculosis infection over BCG vaccine 30 ; rBCG-IA was able to elicit stronger humoral and cellular immune responses, while similar protective efficacy with parental BCG was revealed. 31 In this study, the bacterial load in spleen and lung was significantly reduced by immunization of various rBCGs, but the protective degree of diverse rBCGs varied from their immune response. In the short term, significantly lower bacterial load in spleen than parental BCG was exhibited on rBCG-1173s, which indicated that these rBCGs could obviously decrease the infection of M. tuberculosis.…”

Recombinant BCG to Enhance Its Immunomodulatory Activities

“…In another study, in which IL-12 was co-expressed with Ag85A in rBCG::IL-12-Ag85A, the recombinant strain also induced stronger T cell proliferation and IFN-γ responses than pBCG, rBCG::Ag85A or rBCG::IL-12 [ 62 ]. In this case, rBCG::IL-12-Ag85A induced similar levels of protection as pBCG against M. tuberculosis challenge, but curiously, rBCG::IL-12 and rBCG::Ag85A provided less protection than pBCG with respect to bacterial counts in the lungs and spleen.…”