Nondividing but metabolically active gamma-irradiated Brucella melitensis is protective against virulent B. melitensis challenge in mice.
Brucella spp. are gram-negative bacteria that cause the most frequent zoonotic disease worldwide, with more than 500,000 human infections yearly; however, no human vaccine is currently available. As with other intracellular organisms, cytotoxic mechanisms against infected cells are thought to have an important role in controlling infection and mediating long-term immunity. Live attenuated strains developed for use in animals elicit protection but retain unacceptable levels of virulence. Thus, the optimal design for a brucellosis vaccine requires a nonliving vaccine that confers effective immunity. Historically, inactivation methods such as chemical or heat treatment successfully impair Brucella reproductive capacity; nevertheless, metabolically inactive vaccines (subunit or killed) present very limited efficacy. Hence, we hypothesized that bacterial metabolism plays a major role in creating the proper antigenic and adjuvant properties required for efficient triggering of protective responses. Here, we demonstrate that inactivation of Brucella melitensis by gamma-irradiation inhibited its replication capability and yet retained live-Brucella protective features. Irradiated Brucella possessed metabolic and transcriptional activity, persisted in macrophages, generated antigen-specific cytotoxic T cells, and protected mice against virulent bacterial challenge, without signs of residual virulence. In conclusion, pathogen metabolic activity has a positive role in shaping protective responses, and the generation of inactivated and yet metabolically active microbes is a promising strategy for safely vaccinating against intracellular organisms such as B. melitensis.
Magnani
D M
DM
Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, AHABS, 1656 Linden Drive, Madison, WI 53706, USA.
Harms
J S
JS
Durward
M A
MA
Splitter
G A
GA
D000818:Animals; D002004:Brucella Vaccine / Q000276:immunology / Q000627:therapeutic use*; D017347:Brucella melitensis / Q000502:physiology / Q000528:radiation effects*; D002006:Brucellosis / Q000517:prevention & control*; D003602:Cytotoxicity, Immunologic; D005720:Gamma Rays; D051379:Mice; D014613:Vaccines, Attenuated / Q000276:immunology / Q000627:therapeutic use; D037521:Virulence Factors / Q000096:biosynthesis / Q000528:radiation effects
D002004:Brucella Vaccine; D014613:Vaccines, Attenuated; D037521:Virulence Factors
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