Improving Mucosal Immunity of TeeVax for the Protection Against Streptococcus pyogenes Infections

Abstract

Background: Infections caused by the human pathogen Streptococcus pyogenes (strep A) are often instigated on the mucosal surfaces through adhesion and colonisation by the pilus. The pilus structure consists mainly of backbone protein, also known as the T-antigen. Targeting the pilus for a vaccine is an advantage due to the lower antigenic variation of T serotypes compared to the M proteins, which presumably could provide broader protection against strep A strains. The multivalent vaccine called TeeVax, composed of multiple T-antigens from various strep A strains was previously constructed. This study focuses on comparing the novel vaccine TeeVax formulated with different mucosal adjuvants (CTB, curdlan and CAF01) and clinically approved adjuvant, alum. Methods: FVB/n mice (n=5 per group) were immunised using the 'prime' and 'pull' vaccination strategy with different vaccine formulations. Serum and mucosal samples were collected post immunisations and analysed by ELISA. Cytokine levels from mouse splenocytes were analysed using a Luminex multiplex immunoassay. Results: This study showed that significant elevation of vaccine-specific IgG antibody in mouse sera from CTB and CAF01 was observed after the first immunisation. All adjuvanted groups produced high IgG titres by day 28, with the domination of IgG1 subclass. Meanwhile, all of the IgG subclasses in the CTB and CAF01 groups were relatively high, suggesting a mixed Th1/Th2 response. In comparison, due to the low development of IgG3, alum and curdlan groups were more biased toward Th2-like response. However, mucosal IgA secretion was barely detectable across all adjuvanted groups. Re-stimulation of splenocytes with TeeVax show significant increase of IL-4, IL-6 and IL-10 in CTB group, while CAF01 group had high IL-2 and IL-4 production suggesting that CTB produced a strong Th2-like response while Th1/Th2 immune responses were produced by the CAF01 group. Conclusion: These findings indicated that CAF01 and CTB produced superior immunological responses to alum, and represent improved adjuvant formulation with TeeVax. However, failure to detect mucosal immune responses suggests further improvements are needed.