Evaluation of Burkholderia mallei ΔtonB Δhcp1 (CLH001) as a live attenuated vaccine in murine models of glanders and melioidosis

Abstract

Background Glanders caused by Burkholderia mallei is a re-emerging zoonotic disease affecting solipeds and humans. Furthermore, B . mallei is genetically related to B . pseudomallei , which is the causative agent of melioidosis. Both facultative intracellular bacteria are classified as tier 1 select biothreat agents. Our previous study with a B . mallei Δ tonB Δ hcp1 (CLH001) live-attenuated vaccine demonstrated that it is attenuated, safe and protective against B . mallei wild-type strain in the susceptible BALB/c mouse model. Methodology/Principal finding In our current work, we evaluated the protective efficacy of CLH001 against glanders and melioidosis in the more disease-resistant C57BL/6 mouse strain. The humoral as well as cellular immune responses were also examined. We found that CLH001-immunized mice showed 100% survival against intranasal and aerosol challenge with B . mallei ATCC 23344. Moreover, this vaccine also afforded significant cross-protection against B . pseudomallei K96243, with low level bacterial burden detected in organs. Immunization with a prime and boost regimen of CLH001 induced significantly greater levels of total and subclasses of IgG, and generated antigen-specific splenocyte production of IFN-γ and IL-17A. Interestingly, protection induced by CLH001 is primarily dependent on humoral immunity, while CD4 + and CD8 + T cells played a less critical protective role. Conclusions/Significance Our data indicate that CLH001 serves as an effective live attenuated vaccine to prevent glanders and melioidosis. The quantity and quality of antibody responses as well as improving cell-mediated immune responses following vaccination need to be further investigated prior to advancement to preclinical studies.

The Peptidoglycan-associated lipoprotein Pal contributes to the virulence of Burkholderia mallei and provides protection against lethal aerosol challenge

“…Fortunately, the genetic, virulence, and disease similarities between B. mallei and B. pseudomallei suggest the feasibility of devising medical countermeasures that protect against both organisms. This premise is supported by studies showing that antibodies against in vivo expressed Burkholderia antigens [ 19 ], vaccination with Burkholderia live attenuated strains [ 19 , 20 ] and outer membrane vesicles [ 21 , 22 ], and polysaccharide-based vaccines [ 23 , 24 ] provide cross-species protection in animal models of melioidosis and glanders.…”

Burkholderia pseudomallei OMVs derived from infection mimicking conditions elicit similar protection to a live-attenuated vaccine

“…The ability of the OMV vaccine to drive both helper and cytotoxic T cells is significant because although T cells appear dispensable in mouse models, it is likely that cellular immunity will be important for complete vaccine efficacy against melioidosis in humans 35 , 36 . Both live and non-replicating vaccine candidates for B. pseudomallei have been shown to induce Th1 immune responses, as evidenced by CD4 T-cell IFN-γ production, in mouse models 32 , 37 . It is well established that vaccine-elicited IFN-γ-producing CD4 T cells drive the antibacterial effector functions of macrophages to control or eliminate facultative intracellular bacteria.…”

Current Advances in Burkholderia Vaccines Development

“…However, this mutant may not have been fully attenuated, as the immunized mice developed splenomegaly and multiple splenic abscesses [ 49 ]. The Δ tonB Δ hcp1 double mutant appears to be the safest and most effective B. mallei and B. pseudomallei attenuated vaccine tested so far ( Table 2 ); complete protection was observed in immunized mice with no pathological lesions and minimal residual bacterial numbers in organs after infection challenge [ 50 , 51 ]. Vaccination of mice generated robust humoral and cellular immune responses; however, CD4 + and CD8 + T cells did not appear to be critical for protection [ 50 , 51 ].…”

“…The Δ tonB Δ hcp1 double mutant appears to be the safest and most effective B. mallei and B. pseudomallei attenuated vaccine tested so far ( Table 2 ); complete protection was observed in immunized mice with no pathological lesions and minimal residual bacterial numbers in organs after infection challenge [ 50 , 51 ]. Vaccination of mice generated robust humoral and cellular immune responses; however, CD4 + and CD8 + T cells did not appear to be critical for protection [ 50 , 51 ]. Zimmerman et al [ 52 ] investigated the protective effect of another attenuated mutant, Δ batA , against B. mallei infection in mice.…”