A pantothenate auxotroph of Mycobacterium tuberculosis is highly attenuated and protects mice against tuberculosis

Abstract

With the advent of HIV and the widespread emergence of drug-resistant strains of Mycobacterium tuberculosis, newer control strategies in the form of a better vaccine could decrease the global incidence of tuberculosis. A desirable trait in an effective live attenuated vaccine strain is an ability to persist within the host in a limited fashion in order to produce important protective antigens in vivo. Attenuated M. tuberculosis vaccine candidates have been constructed by deleting genes required for growth in mice. These candidate vaccines did not elicit adequate protective immunity in animal models, due to their inability to persist sufficiently long within the host tissues. Here we report that an auxotrophic mutant of M. tuberculosis defective in the de novo biosynthesis of pantothenic acid (vitamin B5) is highly attenuated in immunocompromised SCID mice and in immunocompetent BALB/c mice. SCID mice infected with the pantothenate auxotroph survived significantly longer (250 days) than mice infected with either bacille Calmette-Guerin (BCG) vaccine or virulent M. tuberculosis (77 and 35 days, respectively). Subcutaneous immunization with this auxotroph conferred protection in C57BL/6J mice against an aerosol challenge with virulent M. tuberculosis, which was comparable with that afforded by BCG vaccination. Our findings highlight the importance of de novo pantothenate biosynthesis in limiting the intracellular survival and pathogenesis of M. tuberculosis without reducing its immunogenicity in vaccinated mice.

Mycobacterial persistence requires the utilization of host cholesterol

“…However, the antimicrobial effect of IFN-␥ cannot be solely attributed to these responses (9), and activated macrophages also restrict the growth of intracellular bacteria by depriving them of essential nutrients (10). The inability of many different auxotrophic mutants to replicate in vivo attests to the scarcity of nutrients in this environment (11)(12)(13)(14)(15). Although the mechanisms by which M. tuberculosis resists host-derived oxidative and nitrosative stresses have been intensively studied (16,17), it is entirely unclear how this pathogen acquires the nutrients necessary for replication in this isolated compartment.…”

Essential roles of methionine and S -adenosylmethionine in the autarkic lifestyle of Mycobacterium tuberculosis

“…Subverting nutritional restrictions by the host (9, 35) via an autarkic metabolic lifestyle is likely an evolutionary advantage that contributes greatly to Mtb's unmatched persistence in humans. It turns out that this important feature of Mtb's metabolism also is a substantial vulnerability, because several auxotrophic strains of Mtb show significant levels of attenuation in mice (8,16,17,26,(36)(37)(38)(39)(40)(41)(42). However, most of these auxotrophies are less bactericidal than Fig.…”

Next generation: tuberculosis vaccines that elicit protective CD8+T cells

“…Thus, a leucine auxotroph requires growth media that is supplemented with leucine. Auxotrophs of M. tuberculosis and other well-defined mutants such as the phoP deletion, potentially have even a better safety profile than BCG, which may be advantageous for use in HIV-infected individuals; yet, except for the defined defects, they express a full complement of antigens comparable to pathogenic M. tuberculosis [52][53][54][55]. Nevertheless, safety concerns over using attenuated M. tuberculosis in people, particularly in those that may be immunocompromised because of HIV infection, has led investigators to develop strains with a least two independent mutations.…”