Deciphering the amine/acetylation code of PNAG through comprehensive libraries of synthetic oligosaccharides for effective anti-microbial vaccines

Project summary With the prevalence and challenges of antimicrobial resistant microbes, there is an urgent need to develop novel vaccines to prevent these infections. Poly-β-(1−6)-N-acetylglucosamine (PNAG) is an attractive target for vaccine development as it is a key virulence factor present on the surface of many species of non-viral pathogens. Since naturally existing PNAG can bear a varying number of free amines rather than N-acetamides on its glucosamine units, it is not known how the numbers and the positions of amines vs N-acetamides of PNAG (amine/acetylation code) can impact the antigenicity and protective efficacy generated by PNAG-targeting vaccines. Fur- thermore, PNAG antigens require a carrier system to elicit an anti-PNAG antibody response for protective immunity. To thoroughly probe the key structural features of PNAG for effective vac- cines, an interdisciplinary team has been formed to integrate expertise in carbohydrate chemistry, microbiology and vaccinology. In aim 1, new methodologies will be established to expedite the synthesis of a comprehensive library of PNAG pentasaccharides with systematically varied amine/acetylation patterns, as well as longer PNAG glycans with well-defined sequences. The library of PNAG glycans will be covalently linked with a powerful immunogenic carrier, i.e., mutant bacteriophage Qβ, in aim 2. The immunogenicity of the conjugates in both mice and rabbits will be investigated with the optimal linker, antigen density and adjuvant established to elicit high- titered, and long-lasting protective antibodies to PNAG. Subsequently, the effectiveness of the optimal vaccine candidates and adjuvant will be evaluated against Staphylococcus aureus includ- ing methicillin resistant Staphylococcus aureus (MRSA) strains. In aim 3, as currently there are no approved vaccines available to protect against Neisseria gonorrhoeae, to fill this critical clinical need, mQβ-PNAG based vaccine will be tested against Neisseria gonorrhoeae experimental in- fections. The efficacy of the vaccine will be established in multiple challenge models to lay the groundwork for future translation. This project highlights the exciting potential of synthetic PNAG glycan aided epitope discovery for next generation vaccine design.