Group B Streptococcus (GBS), a common commensal bacterium in adults, can cause severe invasive diseases in newborns. This affects approximately 0.5 per 1000 newborns globally, with mortality rates ranging from 19% to 5% in low- and high-income countries respectively. While some disease can be prevented and/or treated with antibiotics, a vaccine would reduce morbidity, provide preventative protection and reduce antibiotic use. GBS vaccines currently under development focus on conjugated capsular polysaccharide and protein vaccines designed for intramuscular delivery. In contrast, mucosal delivery of a universal protein vaccine could provide improved mucosal immunity in addition to systemic immunity. This could more effectively reduce carriage of GBS in pregnant women, which is the main risk factor for colonisation of newborns.
Our aim was therefore to evaluate the vaccine potential of two conserved GBS proteins: FbsC, a cell wall protein, and EsxA, a secreted toxin. Immunogenicity of the proteins and functionality of the antibody response were evaluated following parenteral and mucosal delivery of adjuvanted protein. Antibody responses were measured by ELISA and functionality evaluated through activity of serum mediating opsonophagocytosis and inhibition of GBS colonisation of epithelial cells.
Initial mouse studies using the two proteins in subcutaneous immunisation showed they elicit a strong antibody response. Functional assays showed that anti-FbsC immune serum is effective at mediating opsonophagocytosis of GBS serotypes.
Both proteins are also being formulated as mRNA vaccine candidates. Future work will evaluate their immunogenicity following subcutaneous and sublingual delivery, advancing efforts to develop a mucosal vaccine strategy against GBS.