Predictive and Experimental Immunogenicity of Burkholderia Collagen-like Protein 8-Derived Antigens

Abstract

Burkholderia pseudomallei is an infectious bacterium of clinical and biodefense concern, and is the causative agent of melioidosis. The mortality rate can reach up to 50% and affects 165,000 people per year; however, there is currently no vaccine available. In this study, we examine the antigen-specific immune response to a vaccine formulated with antigens derived from an outer membrane protein in B. pseudomallei, Bucl8. Here, we employed a number of bioinformatic tools to predict Bucl8-derived epitopes that are non-allergenic and non-toxic, but would elicit an immune response. From these data, we formulated a vaccine based on two extracellular components of Bucl8, the β-barrel loops and extended collagen and non-collagen domains. Outbred CD-1 mice were immunized with vaccine formulations—composed of recombinant proteins or conjugated synthetic peptides with adjuvant—to assess the antigen-specific immune responses in mouse sera and lymphoid organs. We found that mice vaccinated with either Bucl8-derived components generated a robust TH2-skewed antibody response when antigen was combined with the adjuvant AddaVax, while the TH1 response was limited. Mice immunized with synthetic loop peptides had a stronger, more consistent antibody response than recombinant protein antigens, based on higher IgG titers and recognition of bacteria. We then compared peptide-based vaccines in an established C57BL/6 inbred mouse model and observed a similar TH2-skewed response. The resulting formulations will be applied in future studies examining the protection of Bucl8-derived vaccines.

Burkholderia pseudomallei Complex Subunit and Glycoconjugate Vaccines and Their Potential to Elicit Cross-Protection to Burkholderia cepacia Complex

“…Likely recognizing the inherent difficulty of recombinantly expressing a multimeric integral membrane protein, the study instead opted to try a peptide-based vaccination strategy [ 182 ]. They first used ElliPro to bioinformatically predict that the Bucl8 extracellular β-barrel loops could serve as linear B cell epitopes for antibody binding.…”

“…Then, immunization studies were performed with each of Bucl8’s two extracellular loop peptides chemically conjugated to an inactivated diphtheria toxoid carrier protein and formulated in AddaVax. These vaccines, delivered subcutaneously, were capable of eliciting robust IgG1-skewed antibody titers that reacted to the respective peptide or an attenuated B. pseudomallei strain [ 182 ]. However, this subcutaneous immunization was not protective against a heterologous intranasal challenge of 8 × 10 6 CFU of B. thailandensis strain E264 [ 183 ].…”

Melioidosis and Burkholderia pseudomallei: progress in epidemiology, diagnosis, treatment and vaccination

“…Outer membrane vesicles (OMV) derived from B. pseudomallei are highly effective immunogens, and immunization of mice with enhanced OMV derived from infection-mimicking conditions provided significant protection against pulmonary infection [76 ▪ ]. Other OMV vaccine candidates are also being assessed [77–79]. Live attenuated vaccines show robust immune responses in a mouse model, eliciting both humoral and cellular immunity with the potential to protect against inhalational melioidosis [80 ▪ ].…”

Intranasal immunization with a Bucl8-based vaccine ameliorates bacterial burden and pathological inflammation, and promotes an IgG2a/b dominant response in an outbred mouse model of Burkholderia infection

“…The Bucl8 protein sequence includes two tandem outer-membrane efflux domains, as well as an extended extracellular collagen-like domain ( 20 ). The OMP portion forms a characteristic periplasmic α-barrel and outer membrane-spanning β-barrel with surface-exposed loops, designated L1 and L2 ( 21 , 22 ). Bucl8 is conserved across multiple Burkholderia species such as B. pseudomallei and B. mallei and has homologs without the extracellular collagen-like domain in B. thailandensis and majority of the BCC species ( 22 ).…”