Evaluation of Cholera Toxin B Subunit as a Novel Carrier Protein for Polysaccharide Conjugate Vaccines

Background: The immunogenicity of polysaccharide conjugate vaccines is critically influenced by the choice of carrier protein, which promotes a T-cell-dependent immune response mechanism leading to strong antibody production. In this study, the cholera toxin B subunit (CTB), a non-toxic pentameric protein, was evaluated as a novel carrier protein for pneumococcal polysaccharide antigens. Methods: Recombinant CTB was produced in Escherichia coli and purified using scalable chromatographic methods. Pneumococcal polysaccharides from serotypes 7F, 22F, and 33F were chemically activated with CDAP and conjugated to CTB. Results: The resulting glycoconjugates were characterized by SEC-MALS, confirming successful conjugation, high molecular weights, consistent polysaccharide-to-protein ratios, and acceptable endotoxin levels. Immunogenicity was assessed in rabbits following immunization with alum-adjuvanted formulations. Results: Robust IgG responses were elicited by all CTB-based conjugates, with antibody levels found to be comparable to those induced by CRM197 conjugates, demonstrating the potential of CTB as a promising alternative for the next generation of conjugate vaccines.