Melioidosis is an infectious disease caused by Burkholderia pseudomallei and is associated with high morbidity and mortality rates in endemic areas. It is difficult to treat with antibiotics and there is no licensed vaccine. Capsular polysaccharides have historically made effective vaccine candidates and many capsule-based vaccines are currently licensed, including those against Neisseria meningitidis, Streptococcus pneumoniae and Haemophilus influenzae infection. B. pseudomallei expresses a capsular polysaccharide (CPS) consisting of a homopolymer of unbranched 1-3 linked 2-O-acetyl-6-deoxy-�-D-manno-heptopyranose. This polysaccharide is a major virulence determinant and is thought to be present in all examples of this species, offering the opportunity to develop a univalent vaccine protective against melioidosis.Access to CPS antigen is currently through a traditional bioprocessing route. This requires expensive containment facilities and yields a product with a naturally heterogeneous chain length containing some impurities, adding a considerable complicating factor to the manufacture of pharmaceutical grade vaccine. We have taken an entirely synthetic approach to access CPS antigen of defined chain length and purity well suited for development. The synthetic antigen was designed to incorporate all of the defining structural characteristics of natural CPS in addition to an amine-based linker to allow efficient conjugation to protein carriers. The choice of a hexasaccharide antigen provided a size likely to be immunologically relevant whilst retaining favorable handling characteristics.Antigen was synthesized using a modular assembly approach and coupled to the non-toxic Hc domain of tetanus toxin to promote recruitment of T-cell help for antigen display. Mice immunized with the glycoconjugate developed IgM and IgG responses capable of recognizing natural CPS, demonstrating the immunogenicity of the synthetic CPS and providing a basis for future efficacy studies. This work may lead to an effective licensed vaccine which will allow the warfighter to continue to operate independently of detection technologies in a potential BW environment.

De novo synthesis, conjugation, and immnunogenicity of the Burkholderia pseudomallei manno-heptose capsule

248th National Meeting (2014)

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