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

Abstract

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 (DcydC, DcydD and DpurD single mutants, and DcydCDcydD and DcydCDpurD double mutants) of RB51 with the aim of increasing the safety of the possible use of these mutants as vaccine candidates. The RB51DcydC, RB51DcydD, RB51DpurD, RB51DcydCDcydD and RB51DcydCDpurD mutants exhibited significant attenuation of virulence when assayed in murine macrophages in vitro or in BALB/c mice. A single intraperitoneal immunization with RB51DcydC, RB51DcydD, RB51DcydCDcydD or RB51DcydCDpurD mutants was rapidly cleared from mice within 3 weeks, whereas the RB51DpurD 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.

Brucella ovis mutant in ABC transporter protects against Brucella canis infection in mice and it is safe for dogs

“…The vaccine strain BoΔabcBA, in contrast to the WT strain, is attenuated in ovine macrophage [24], and displays the same profile in canine primary macrophages. Attenuation in cells is a common feature of vaccine strains [43]. Therefore, these results support the notion that a B. ovis attenuated strain may be suitable as a vaccine candidate for B. canis infection in dogs.…”

“…The ability to invade macrophages, is important for exposing antigens, possibly inducing cross protection against other species of Brucella [43], due to the markedly high similarities among Brucella species [48]. Mice immunized with alginate-encapsulated BoΔabcBA responded with splenocyte proliferation and IFN-γ production in response to either B. ovis or B. canis, clearly indicating the potential of this vaccine strain to induce a cross-reactive protective response against B. canis.…”

“…Attenuated strains tend to confer the best protection against Brucella spp. [26], but this vaccine strategy has not been extensively studied for prevention of B. canis infection, with only one previous study evaluating a B. canis mutant strain in mice [42], and another study that assessed protection provided by the vaccine strain B. abortus RB51 against B. canis challenge in mice [43], although RB51 has zoonotic potential, which limits its suitability to dogs. This is the first study that demonstrated the capacity of Brucella spp.…”

Substantial Protective Immunity Conferred by a Combination of Brucella abortus Recombinant Proteins against Brucella abortus 544 Infection in BALB/c Mice

“…The search for the ideal vaccine will continue to be the primary goal in the effort to eradicate brucellosis as vaccination still remains the most efficient method in the control of this infectious agent. RB51, a widely used live attenuated vaccine, offers major advantages such as noninterference in the diagnosis of brucellosis, however it also causes residual virulence in both animals and humans [25]. Several antigenic proteins such as periplasmic, cytoplasmic, inner and outer membranes have been previously identified according to previous studies.…”

Development of new generation of vaccines for Brucella abortus

“…However, booster dose vaccination of these mutants induced both humoral and cellular immune responses with improved protection against a challenge with B. abortus 2308 compared with classical B. abortus RB51 vaccine. Further evaluations in bovine are needed to verify efficacy [84]. Also, same double deletion in B. abortus biovar 1 field isolate (BA15) provided similar protective results but without the need for further booster vaccination [85].…”