Evaluation of two different vaccine platforms for immunization against melioidosis and glanders

Abstract

Burkholderia pseudomallei and the closely related species, Burkholderia mallei, produce similar multifaceted diseases which range from rapidly fatal to protracted and chronic, and are a major cause of mortality in endemic regions. Besides causing natural infections, both microbes are Tier 1 potential biothreat agents. Antibiotic treatment is prolonged with variable results, hence effective vaccines are urgently needed. The purpose of our studies was to compare candidate vaccines that target both melioidosis and glanders to identify the most efficacious one(s) and define residual requirements for their transition to the non-human primate aerosol model. Studies were conducted in the C57BL/6 mouse model to evaluate the humoral and cell-mediated immune response and protective efficacy of three Burkholderia vaccine candidates against lethal aerosol challenges with B. pseudomallei K96243, B. pseudomallei MSHR5855, and B. mallei FMH. The recombinant vaccines generated significant immune responses to the vaccine antigens, and the live attenuated vaccine generated a greater immune response to OPS and the whole bacterial cells. Regardless of the candidate vaccine evaluated, the protection of mice was associated with a dampened cytokine response within the lungs after exposure to aerosolized bacteria. Despite being delivered by two different platforms and generating distinct immune responses, two experimental vaccines, a capsule conjugate + Hcp1 subunit vaccine and the live B. pseudomallei 668 ΔilvI strain, provided significant protection and were down-selected for further investigation and advanced development.

Layered and integrated medical countermeasures against Burkholderia pseudomallei infections in C57BL/6 mice

“…Significant effort has been spent on the identification, characterization, and optimization of protective vaccine antigens that will prevent or ameliorate B. pseudomallei infections and melioidosis disease. Various vaccine strategies including live attenuated vaccine strains, OMVs, and protein subunit/polysaccharide conjugate combinations have produced robust immune responses that have been protective in both mouse and non-human primate models of melioidosis ( Atkins et al, 2002 ; Nieves et al, 2011 , 2014 ; Burtnick et al, 2012 , 2018 ; Petersen et al, 2014 ; Scott et al, 2014 ; Titball et al, 2017 ; Amemiya et al, 2019 ; Khakhum et al, 2019a ; Biryukov et al, 2022 ). Even with these successes in vaccine strategies, there remains the possibility that survivors of the acute phase of the infection could continue to harbor the bacteria that could reemerge later.…”

“…Vaccinations were carried out as previously described ( Burtnick et al, 2012 , 2018 ; Amemiya et al, 2019 ; Biryukov et al, 2022 ). Briefly, mice receiving the live attenuated vaccine 668 Δ ilvI were vaccinated on day 0 and day 21 or 24 with a target dose of approximately 1.0 × 10 7 CFU delivered in 200 μl injections subcutaneously.…”

“…Here we report the improvement of disease outcome observed when suboptimal antibiotic regimens were used in combination with current experimental vaccines. A detailed description of the vaccine candidates used in this report and their resulting immune responses is described by Biryukov et al (2022) within this special issue of Frontiers in Microbiology.…”

Efficacy of Treatment with the Antibiotic Novobiocin against Infection with Bacillus anthracis or Burkholderia pseudomallei

“…Future efforts will focus on optimizing the Novo treatment regimen (number and timing of doses) and expanding on the strategy of combining vaccine pre-exposure prophylaxis and post-exposure antibiotic treatment. This layered strategy has the potential to enhance efficacy of medical countermeasures against bacterial pathogens refractory to antibiotic treatment and/or vaccine prophylaxis [ 8 , 40 , 41 ]. The significantly extended survival time after aerosol challenge with B. pseudomallei obtained by post-exposure treatment of mice vaccinated with a live vaccine strain provided further support of this approach ( Figure 4 ).…”

“…Strain B. thailandensis E555 Δ ilvI was derived from B. thailandensis E555, a natural isolate that had genetically acquired the genes encoding the capsular polysaccharide expressed by the pathogenic Burkholderia species [ 42 , 43 ]. The deletion of the gene which encodes a subunit of an acetolactate synthase ( ilvI ) that is required for the synthesis of the branched chain amino acids isoleucine, leucine, and valine has been shown to greatly attenuate bacterial virulence, e.g., this deletion in B. pseudomallei produced a mutant strain that was greatly weakened yet that effectively protected against lethal infection with B. pseudomallei [ 31 , 40 , 44 ]. The detailed DNA manipulation and cloning steps involved in creating B. thailandensis E555 Δ ilvI are described in Table S1 [ 42 , 43 , 45 , 46 , 47 ].…”