Development of a Group B Streptococcus bioconjugate vaccine

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PROJECT SUMMARY Streptococcus agalactiae, commonly referred to as Group B Streptococcus (GBS), is a leading cause of neonatal meningitis and sepsis worldwide. GBS neonatal disease manifests as early onset invasive disease, defined as disease between birth and 6 days of life, or late onset invasive disease, defined as disease occurring between 7 and 89 days. In some instances, early onset disease is preventable with intrapartum antibiotic prophylaxis; however, this treatment strategy is not practical for low- and middle-income countries, which account for 95% of all neonatal GBS infections, nor does it prevent late onset disease. Three GBS serotypes (type Ia, Ib, and III) account for >60% of all early-onset and >90% of all late-onset invasive GBS infections. As such, a low-cost vaccine strategy to prevent the majority of invasive GBS neonatal disease associated with these three serotypes would be a valuable therapeutic intervention option. Conjugate vaccines, composed of polysaccharides covalently linked to carrier proteins, are life-saving vaccines used to prevent disease from multiple bacterial pathogens. Conjugate vaccines are conventionally manufactured using chemical conjugation, which is notoriously complex, labor intensive, and costly, hindering the development of new conjugate vaccines. Aware of these drawbacks, VaxNewMo has been advancing an alternative method for manufacturing conjugate vaccines that utilizes prokaryotic glycosylation systems in a process termed bioconjugation. VaxNewMo’s proprietary bioconjugation platform relies on a conjugating enzyme to transfer bacterial polysaccharides to engineered carrier proteins using E. coli as a host. Moreover, since bioconjugation is an enzymatic process, the conjugates produced are non-derivatized and the polysaccharides are structurally identical to those presented to immune cells by the pathogen itself. In Phase I, we developed a prototype trivalent (serotypes Ia, Ib, and III) bioconjugate vaccine and demonstrated that it was immunogenic, elicited functional antibody responses towards all three GBS serotypes, and protected newborn mouse pups from invasive serotype III GBS disease. In Phase II, we will produce type Ia-, Ib-, III-bioconjugates using an improved, di-glycosylated carrier protein design that mimics the final formulation, establish bioprocessing capabilities and downstream purification processes, as well as perform pre-IND enabling studies in mice. In Aim 1, we will optimize production of the GBS Ia, Ib and III bioconjugate vaccines, moving from shake flasks to more industrial fed-batch bioreactor systems, remove histidine tags from the bioconjugates (which are not acceptable in marketed vaccines for human use), and establish downstream purification processes as well as characterize vaccine quality attributes. In Aim 2, we will perform dose-escalation studies in mice using monovalent and trivalent formulations of GBS bioconjugate vaccines produced on the improved, di-glycosylated carrier protein to assess immunogenicity via ELISA and functional antibody responses using an opsonophagocytic killing assay (OPKA). Additionally, we will evaluate vaccine efficacy by evaluating survival of newborn mouse pups challenged with a GBS strain (either type Ia, Ib, or III) born to trivalent bioconjugate vaccinated mothers.