Nondividing but Metabolically Active Gamma-IrradiatedBrucella melitensisIs Protective against VirulentB. melitensisChallenge in Mice

Abstract

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 gammairradiation 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.

Immunization of mice with gamma-irradiated Brucella neotomae and its recombinant strains induces protection against virulent B. abortus, B. melitensis, and B. suis challenge

“…Therefore, we used exposure to a minimum dose of gamma radiation as a means to abolish the ability of B. neotomae to replicate. The use of ionizing radiation has been used in the development of vaccines for preventing infectious diseases of animals and humans that are caused by different viruses, bacteria, and parasites [13, 25-29]. However, a recently developed strategy specifically uses exposure to a minimum dose of radiation, which is sufficient to abolish replication of the organism, for developing safer vaccines for diseases caused by intracellular pathogens [13, 28-29].…”

Humoral Immunity and CD4+ Th1 Cells Are Both Necessary for a Fully Protective Immune Response upon Secondary Infection with Brucella melitensis

“…However, live-attenuated strains retain generally unacceptable levels of virulence for human vaccination. The g-irradiated Brucella do not divide but conserve metabolic activity and protect mice against virulent bacterial challenge without signs of residual virulence (94). Thus, inactivated, yet metabolically active, microbes could represent a promising strategy for safe vaccination against B. melitensis.…”

DiscordantBrucella melitensisAntigens Yield Cognate CD8+T Cells In Vivo

“…In addition, our group and others are looking further into Brucella attenuation as an effective vaccine development strategy (5,29). Identifying and dissecting B. melitensis CD8 ϩ T-cell epitopes that trigger host immunity in vivo are critical to assembling future Brucella vaccines, and we will be able to investigate the effectiveness of a multivalent peptide vaccine that includes multiple Brucella epitopes.…”

“…For the antigen processing studies, groups of 12 mice were immunized intraperitoneally (i.p.) with 10 8 replication-deficient, but metabolically active B. melitensis-green fluorescent protein (GFP) in 0.1 ml of PBS previously irradiated with 350 kilorads as described previously (29). Briefly, log phase bacteria were collected, pelleted, and resuspended in fresh brucella broth.…”