Chemical and enzymatic syntheses working in synergy toward broad coverage carbohydrate-based vaccines – CarbUniVax

At the forefront of the rising fields of Chemical and Synthetic Biology, CarbUniVax is a multidisciplinary project sitting at the frontier between Glycosciences and Vaccinology. The ambition of the project is to propose new highly convergent chemical and chemo-enzymatic routes to deliver fine-tuned modular glyco-bricks, easy-to-assemble into biologically active pharmaceuticals. It aims at promoting and valorizing the possible synergy between chemical synthesis and enzymatic synthesis using computer-aided engineered biocatalysts able to act on complex synthetic substrates, to produce a portfolio of well-defined modular antigenic components. These glyco-bricks will be combined to build an audacious and innovative glycoconjugate prototype of vaccinal interest.

The chemo-enzymatic route starts with the chemical synthesis of carbohydrate motifs that will be subjected to the action of glycoenzymes purposely engineered to produce a set of glycoconjugates varying in their glucosylation pattern and their antigenic profile. The construction is such that the various molecules produced by enzymes can be evolved by chemical means into modular synthetic intermediates, glycobricks, that can next be combined into homo- or hetero-oligomers.

Haptens resulting from glycobrick combinations and offering the largest antigenic diversity will be identified by physico-chemical and/or structural studies, on the basis of their recognition by serotype-specific or cross-reactive protective monoclonal antibodies. The best antigenic glycobrick assemblies – universal antigens – will be evolved into original unimolecular synthetic carbohydrate-based vaccine candidates, which will be representative of at least three serotypes of medical interest. The immunogenic properties of these unimolecular constructions and their ability to confer a multi-serotype protection will be evaluated in mice. A similar strategy will be followed by chemical routes using a fully orthogonally protected precursor, compatible with on demand site-selective chemical modifications, including 1,2-cis glucosylation. This latter approach can be pursued independently of the identification of the required biocatalysts. In combination with in vivo assays, it will ensure proof-of-concept demonstration of the potential of the unimolecular hapten concept towards innovative vaccinal prototypes.

These original vaccinal prototypes, derived from rationally designed synthetic carbohydrates, aim at overcoming limitations of current polysaccharide conjugate vaccines, in particular the need for multivalency. The proposed synthetic routes to access glycovaccine candidates will tend to obey Sustainable Chemistry criteria. The main challenge addressed here is the development of a broad serotype-coverage vaccine against endemic bacillary dysentery, one of the four most prevalent enteric diseases in children under 5 living in developing countries. While the concept is tackled for bacillary dysentery, its versatility ensures broader applications in biomedical and sustainable chemistry fields.

The achievement of CarbUniVax relies on the synergistic interactions between the four partners composing the consortium, located at two different sites, who will share their expertise and skills in enzyme design and engineering, glycochemistry and vaccinology, physico-chemistry of biomolecular interactions and immune response to carbohydrate antigens.