A Replication-Limited Recombinant Mycobacterium bovis BCG Vaccine against Tuberculosis Designed for Human Immunodeficiency Virus-Positive Persons Is Safer and More Efficacious than BCG

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Abstract
Tuberculosis is the leading cause of death in AIDS patients, yet the current tuberculosis vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is contraindicated for immunocompromised individuals, including human immunodeficiency virus-positive persons, because it can cause disseminated disease; moreover, its efficacy is suboptimal. To address these problems, we have engineered BCG mutants that grow normally in vitro in the presence of a supplement, are preloadable with supplement to allow limited growth in vivo, and express the highly immunoprotective Mycobacterium tuberculosis 30-kDa major secretory protein. The limited replication in vivo renders these vaccines safer than BCG in SCID mice yet is sufficient to induce potent cell-mediated and protective immunity in the outbred guinea pig model of pulmonary tuberculosis. In the case of one vaccine, rBCG( mbtB )30, protection was superior to that with BCG (0.3-log fewer CFU of M. tuberculosis in the lung [ P < 0.04] and 0.6-log fewer CFU in the spleen [ P = 0.001] in aerosol-challenged animals [means for three experiments]); hence, rBCG( mbtB )30 is the first live mycobacterial vaccine that is both more attenuated than BCG in the SCID mouse and more potent than BCG in the guinea pig. Our study demonstrates the feasibility of developing safer and more potent vaccines against tuberculosis. The novel approach of engineering a replication-limited vaccine expressing a recombinant immunoprotective antigen and preloading it with a required nutrient, such as iron, that is capable of being stored should be generally applicable to other live vaccine vectors targeting intracellular pathogens.