Sterilization by Adaptive Immunity of a Conditionally Persistent Mutant of Mycobacterium tuberculosis.

(), the causative agent of tuberculosis, can enter into a persistent state that confers resistance to antibacterial agents. Many observations suggest that persistent cells also evade the antimycobacterial immune mechanisms, thereby reducing the effectiveness of the current tuberculosis vaccine. Understanding the factors that contribute to persistence may enable the rational design of vaccines that stimulate effective immune killing mechanisms against persister cells. Independent mutations targeting the methionine and arginine biosynthetic pathways are bactericidal for in mice. However, in this study, we discovered that the addition of leucine and pantothenate auxotrophy altered the bactericidality of methionine auxotrophy. Whereas the leucine/pantothenate/methionine auxotrophic strain H37Rv Δ Δ Δ was eliminated in immunocompetent mice, this strain persisted in multiple organs of immunodeficient mice for at least a year. In contrast, the leucine/pantothenate/arginine auxotroph H37Rv Δ Δ Δ was eliminated in both immunocompetent and immunodeficient mice. Our results showed that leucine and pantothenate starvation metabolically blocked the sterilization mechanisms of methionine starvation but not those of arginine starvation. These triple-auxotrophic strains should be invaluable tools for unravelling the bacterial and host factors that enable persistence and for vaccine development studies to assess the efficacy of vaccines that boost immune recognition of in the persistent state. The sterilization of the Δ Δ Δ auxotroph in immunocompetent mice, but not in mice lacking an adaptive immune response, could provide a new system for studying the antimycobacterial killing mechanisms of adaptive immunity. The bacterial pathogen can enter into a persistent state in which can evade host immunity, thereby reducing the effectiveness of current tuberculosis vaccines. Understanding the factors that contribute to persistence would enable the rational design of vaccines effective against persisters. We previously generated two attenuated, triple-auxotrophic strains that are safe to use in a biosafety level 2 laboratory. Herein, we discovered that the triple-auxotrophic strain H37Rv Δ Δ Δ persisted in immunodeficient mice, which lack adaptive immunity, but not in immunocompetent mice. The conditional persistence of this auxotrophic mutant, which is susceptible to the sterilizing effect of the adaptive immune response over time, provides an important tool to dissect the mycobactericidal effector mechanisms mediated by adaptive immunity. Furthermore, because of its remarkable safety attributes, this auxotrophic mutant can potentially be used to develop a practical human challenge model to facilitate vaccine development.