Immunogenicity and Protection Induced by a Mycobacterium tuberculosis sigE Mutant in a BALB/c Mouse Model of Progressive Pulmonary Tuberculosis

Abstract

Tuberculosis is still one of the main challenges to human global health, leading to about two million deaths every year. One of the reasons for its success is the lack of efficacy of the widely used vaccine Mycobacterium bovis BCG. In this article, we analyze the potential use of an attenuated mutant of Mycobacterium tuberculosis H37Rv lacking the sigma factor E as a live vaccine. We have demonstrated that BALB/c mice infected by the intratracheal route with this mutant strain showed significantly higher survival rates and less tissue damage than animals infected with the parental or complemented mutant strain. Although animals infected with the sigE mutant had low bacillary loads, their lungs showed significantly higher production of the protective factors gamma interferon (IFN-␥), tumor necrosis factor alpha (TNF-␣), inducible nitric oxide synthase (iNOS), and ␤-defensins than those of animals infected with the parental or complemented mutant strain. Moreover, we demonstrate that the sigE mutant, when inoculated subcutaneously, was more attenuated than BCG in immunodeficient nude mice, thus representing a good candidate for a novel attenuated live vaccine strain. Finally, when we used the sigE mutant as a subcutaneous vaccine, it was able to induce a higher level of protection than did BCG with both H37Rv and a highly virulent strain of M. tuberculosis (Beijing code 9501000). Taken together, our findings suggest that the sigE mutant is a very promising strain for the development of a new vaccine against tuberculosis.

The Alternative Sigma Factors SigE and SigB Are Involved in Tolerance and Persistence to Antitubercular Drugs

“…Mice infected with the mutant strain cleared the infection at least 2 weeks before those infected with the wild-type strain, and bacterial clearance followed different kinetics in mice infected with the two strains: while the number of CFU of the wild-type strain dropped constantly during the whole course of the experiment, the number of CFU of the sigE mutant dropped at a higher rate than that of H37Rv during the first 7 days of treatment (10-fold for the wild type, 67-fold for the sigE mutant) and then remained stable for a week, finally dropping to below the detection limit after an additional 15 days. It has previously been proposed that immune activation induces drug tolerance in vivo (30): since the sigE mutant is able to induce a stronger immune response than its parental strain (12), it is possible to hypothesize that after mice acquired a complete immune response (between 21 and 28 days postinfection), this strain acquired a transient tolerance to isoniazid that delayed its clearance between day 21 and day 28. Whether these observations depend on a higher susceptibility of the mutant to isoniazid in vitro or on a lower burden of this mutant in infected animals at the time of treatment is still not known.…”

“…A sigE mutant was shown to be unable to block phagosome maturation and grow in macrophages (10), to be strongly attenuated in mice (11), and to elicit a protective immune response stronger than that elicited by its wild-type parental strain (12), and the mutation was shown to be essential for capsular polysaccharide production during prolonged exposure to phosphate starvation (13). Finally, SigE has recently been hypothesized to represent a bistable switch and to be involved in persistence following growth arrest due to hypoxia (14,15).…”

Virulence and Immunity Orchestrated by the Global Gene Regulator sigL in Mycobacterium avium subsp. paratuberculosis

“…The dotted line shows the limit of detection (2 pg/ml). *, P Ͻ 0.05; **, P Ͻ 0.01. cobacteria (50,51). In our study, observations gained from both in vitro and murine model experiments encouraged us to investigate the vaccine potential of M. avium subsp.…”

Current efforts and future prospects in the development of live mycobacteria as vaccines

“…The Mtb ΔsigE mutant show significant attenuation of virulence in BALB/c and nude mouse models. Immunogenicity of Mtb ΔsigE was superior to that of BCG, and in turn provided better protection after Mtb challenge (78). Further analysis shows that Mtb ΔsigE was not capable of arresting phagosome maturation as shown by an increase in phagosome-lysosome fusion (79).…”