Semisynthetic glycoconjugates based on capsular polysaccharide fragments of Haemophilus influenzae type a as potential vaccine candidates

Glycoconjugate vaccines, which combine pathogen-associated carbohydrates with immunogenic carrier proteins, are a highly cost-effective strategy for preventing bacterial, viral, and fungal infections. While most licensed glycoconjugate vaccines currently derive their saccharide antigens from bacterial sources, synthetic oligosaccharide antigens offer a promising alternative1. These well-defined structures provide homogeneous constructs. Haemophilus influenzae (Hi), a significant cause of severe diseases like meningitis, sepsis, and otitis in young children, has recently seen an increased rate of invasive infections caused by Hi serotype a2,3. Unfortunately, no vaccine specifically targeting Hia is currently available. The capsular polysaccharide (CPS) of Hia consists of phosphodiester-linked repeating units of 4-β-D-Glucose-(1→4)-D-ribitol-5-(PO4→) and serves as the antigen for protein-conjugated polysaccharide vaccines4. To explore the potential of Hia CPS as an antigen, we synthesized well-defined oligosaccharides with varying chain lengths, containing up to five repeating units (Figure 1). After optimizing the required monosaccharide building blocks synthetically, we assembled them through fine-tuned glycosylation reactions and combined them using the phosphoramidite approach. The resulting CPS-based Hia oligomers were then conjugated to the CRM197 carrier protein and evaluated for their immunogenic potential in a rat animal model. The results demonstrated that all prepared glycoconjugates induced antibodies that bound to Hia oligosaccharides; hence, the well-defined synthetic oligosaccharides can potentially mimic Hia CPS and the obtained glycoconjugates could be employed for the development of anti-Hia glycoconjugate vaccines.