Dietary Pyridoxine Controls Efficacy of Vitamin B(6)-Auxotrophic Tuberculosis Vaccine Bacillus Calmette-Guérin ΔureC::hly Δpdx1 in Mice

The only tuberculosis (TB) vaccine in use today, bacillus Calmette-Guérin (BCG), provides insufficient protection and can cause adverse events in immunocompromised individuals, such as BCGosis in HIV(+) newborns. We previously reported improved preclinical efficacy and safety of the recombinant vaccine candidate BCG ΔureC::hly, which secretes the pore-forming listeriolysin O of Listeria monocytogenes. Here, we evaluate a second-generation construct, BCG ΔureC::hly Δpdx1, which is deficient in pyridoxine synthase, an enzyme that is required for biosynthesis of the essential cofactor vitamin B(6). This candidate was auxotrophic for vitamin B(6) in a concentration-dependent manner, as was its survival in vivo. BCG ΔureC::hly Δpdx1 showed markedly restricted dissemination in subcutaneously vaccinated mice, which was ameliorated by dietary supplementation with vitamin B(6). The construct was safer in severe combined immunodeficiency mice than the parental BCG ΔureC::hly. A prompt innate immune response to vaccination, measured by secretion of interleukin-6, granulocyte colony-stimulating factor, keratinocyte cytokine, and macrophage inflammatory protein-1α, remained independent of vitamin B(6) administration, while acquired immunity, notably stimulation of antigen-specific CD4 T cells, B cells, and memory T cells, was contingent on vitamin B(6) administration. The early protection provided by BCG ΔureC::hly Δpdx1 in a murine Mycobacterium tuberculosis aerosol challenge model consistently depended on vitamin B(6) supplementation. Prime-boost vaccination increased protection against the canonical M. tuberculosis H37Rv laboratory strain and a clinical isolate of the Beijing/W lineage. We demonstrate that the efficacy of a profoundly attenuated recombinant BCG vaccine construct can be modulated by external administration of a small molecule. This principle fosters the development of safer vaccines required for immunocompromised individuals, notably HIV(+) infants.