Abstract
One approach for improving BCG efficacy is to utilize BCG as vehicle to develop recombinant BCG (rBCG) strains overexpressing Mycobacterium tuberculosis (M. tb) antigens. Also expression level of a candidate antigen should impact the final T cell responses conferred by rBCG. In this study, based on our previously constructed differential expression system, we developed two rBCG strains overexpressing M. tb chimeric antigen Ag856A2 (coding a recombinant ag85a with 2 copies of esat-6 inserted at Acc I site of ag85a) at differential levels under the control of the subtly modified furA promoters. These two rBCG strains were used to vaccinate C57BL/6 mice and exploit dose of incorporated antigen in rBCG to optimize immune response and protective efficiency against M. tb challenge in mouse model. The results showed that rBCG strains overexpressing Ag856A2 at differential levels induced different antigen-specific IFN-γ production and comparable number of M. tb-specific CD4 T cells expressing IL-2. M. tb challenge experiment showed that rBCG strains afforded enhanced but comparable immune protection characterized by reduced bacillary load, lung pathology, and inflammation. These results suggested that the dose of antigens incorporated in rBCG can impact T cell immune responses but imposed no significantly differential protective efficacies.
Highlights
Tuberculosis (TB) caused by Mycobacterium tuberculosis (M. tb) continues to be a significant global health problem, affecting millions of people worldwide [1, 2]
The global incidence of TB is raising due to coinfection with the human immunodeficiency virus (HIV) and the emergence of multidrug-resistant (MDR) M. tb strains [5, 6]
We have previously reported the construction of a M. tb furA gene operator/promoter-based differential expression system, from which it is feasible to express target antigens of interest in a modular fashion [4]
Summary
Tuberculosis (TB) caused by Mycobacterium tuberculosis (M. tb) continues to be a significant global health problem, affecting millions of people worldwide [1, 2]. We have previously reported the construction of a M. tb furA gene operator/promoter (pfurA)-based differential expression system, from which it is feasible to express target antigens of interest in a modular fashion [4] This system will facilitate the development of novel recombinant BCG vaccine candidates. We selected two rBCG strains overexpressing the same chimeric antigen Ag856A2 at the maximum difference: rBCG186 and rBCG486 overexpressing the fusion protein under control of the wild-type or the optimized double-mutated furA promoters, respectively [4]. We tested their efficacy as vaccines in C57BL/6 mice, comparing immune response and protection against M. tb challenge. The protective efficacies imposed by the two rBCG strains displayed no significant differences higher protection was observed in rBCG486 vaccinated mice than that in rBCG186 vaccinated mice
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