Booster vaccination with safe, modified, live-attenuated mutants of Brucella abortus strain RB51 vaccine confers protective immunity against virulent strains of B. abortus and Brucella canis in BALB/c mice

초록

Brucella abortus attenuated strain RB51 vaccine (RB51) is widely used in prevention of bovine brucellosis. Although vaccination with this strain has been shown to be effective in conferring protection against bovine brucellosis, RB51 has several drawbacks, including residual virulence for animals and humans. Therefore, a safe and efficacious vaccine is needed to overcome these disadvantages. In this study, we constructed several gene deletion mutants (Delta cydC, Delta cydD and Delta purD single mutants, and Delta cydC Delta cydD and Delta cydC Delta purD double mutants) of RB51 with the aim of increasing the safety of the possible use of these mutants as vaccine candidates. The RB51 Delta cydC, RB51 Delta cydD, RB51 Delta purD, RB51 Delta cydC Delta cydD and RB51 Delta cydC Delta purD mutants exhibited significant attenuation of virulence when assayed in murine macrophages in vitro or in BALB/c mice. A single intraperitoneal immunization with RB51 Delta cydC, RB51 Delta cydD, RB51 Delta cydC Delta cydD or RB51 Delta cydC Delta purD mutants was rapidly cleared from mice within 3 weeks, whereas the RB51 Delta purD mutant and RB51 were detectable in spleens until 4 and 7 weeks, respectively. Vaccination with a single dose of RB51 mutants induced lower protective immunity in mice than did parental RB51. However, a booster dose of these mutants provided significant levels of protection in mice against challenge with either the virulent homologous B. abortus strain 2308 or the heterologous Brucella canis strain 26. In addition, these mutants were found to induce a mixed but T-helper-1-biased humoral and cellular immune response in immunized mice. These data suggest that immunization with a booster dose of attenuated RB51 mutants provides an attractive strategy to protect against either bovine or canine brucellosis.

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