Deletion of nuoG from the Vaccine Candidate Mycobacterium bovis BCG ΔureC::hly Improves Protection against Tuberculosis

The current tuberculosis (TB) vaccine, Mycobacterium bovis Bacillus Calmette-Guérin (BCG), provides insufficient protection against pulmonary TB. Previously, we generated a listeriolysin-expressing recombinant BCG strain, which to date has successfully completed phase I and phase IIa clinical trials. In an attempt to further improve efficacy, we deleted the antiapoptotic virulence gene nuoG, encoding NADH dehydrogenase 1 subunit G, from BCG ΔureC::hly. In vitro, deletion of nuoG unexpectedly led to strongly increased recruitment of the autophagosome marker LC3 to the engulfed vaccine, suggesting that nuoG also affects xenophagic pathways. In mice, BCG ΔureC::hly ΔnuoG vaccination was safer than BCG and improved protection over that of parental BCG ΔureC::hly, significantly reducing TB load in murine lungs, ameliorating pulmonary pathology, and enhancing immune responses. Transcriptome analysis of draining lymph nodes after vaccination with either BCG ΔureC::hly or BCG ΔureC::hly ΔnuoG demonstrated earlier and stronger induction of immune responses than that with BCG SSI and suggested upregulation of inflammasome activation and interferon-induced GTPases. In summary, BCG ΔureC::hly ΔnuoG is a promising next-generation TB vaccine candidate with excellent efficacy and safety.