Despite the substantial burden of Streptococcus pyogenes infections and their associated sequalae, there is currently no Strep A vaccine. To address this global human health issue, we have developed a combination peptide-based vaccine that utilises conserved epitopes—p*17 from the M protein and K4S2 from SpyCEP, an anti-neutrophil protease—, each conjugated to diphtheria toxoid and adjuvanted with Alum. This vaccine is now in a phase 1 clinical trial.
Transgenic mice expressing human HLA-DR3-DQ2 (HLA-II) were intramuscularly immunised at days 0, 21, and 42, leading to the induction of p*17- and K4S2-specific serum IgG antibodies, which are capable of binding multiple clinical isolate strains of StrepA. However, following a 5-month resting period, a decline in antibody levels and S. pyogenes binding capabilities was observed. To investigate the efficacy of the vaccine in vivo, vaccinated HLA-II mice were challenged intranasally with the S. pyogenes M75 strain. Protection was assessed by measuring bacterial burden in the nasal-associated lymphoid tissue and lungs, as well as via throat swabs, at two time points post-final booster—2 weeks and 5 months. Notably, significant protection against S. pyogenes was maintained in all tissues analysed, regardless of the levels of antigen-specific antibody. Immunological analyses revealed increased systemic IL-1β levels in 5-month-rested vaccinated mice, suggesting a role for sustained innate and cytokine-mediated responses in long-term protection against infection. To further validate these findings, vaccination and challenge studies involving IL-1β knockout mice revealed a loss of vaccine efficacy compared to wild-type controls, despite comparable antibody levels, emphasising the role of IL-1β in mediating vaccine-induced immunity.
Author Contributions
Conceptualization, M.F.G., M.P. and A.L.; methodology and experiments, A.L., D.V., D.B., V.O., A.C. and S.R.; formal analysis, D.V., A.L. and D.B.; investigation, A.L., D.V., D.B., V.O., A.C. and S.R.; resources, M.F.G. and M.P.; data curation, A.L. and D.V.; writing—original draft preparation, D.V. and A.L.; writing—review and editing, D.V., A.L., M.F.G. and M.P.; visualization, D.V., A.L., M.P. and M.F.G.; supervision, A. L., M.F.G. and M.P.; project administration, M.F.G. and M.P.; funding acquisition, A.L., M.P. and M.F.G. All authors have read and agreed to the published version of the manuscript.
Funding
This work was supported by the National Health and Medical Research Council (NHMRC), Australia, Program Grant APP1083548 (M.F.G.) and NHMRC Australia, Investigator Fellowship APP1174091 (M.F.G.), NHMRC Project Grant APP1160379 (M.P.), Heart Foundation Vanguard Grant (108443-2024) and Griffith University internal grant to A.L.
Institutional Review Board Statement
All animal protocols were reviewed and approved by the Griffith University Animal Ethics Committee (GU-AEC) in accordance with the National Health and Medical Research Council (NHMRC) of Australia guidelines. All mice were housed. In a PC2-certified animal facility in individually ventilated cages (IVC) with a maximum of 5 mice/cage. The relative humidity ranged between 45–65% and temperature 20–24 °C. Mice were exposed to a 12-h light-dark cycle.
Informed Consent Statement
Not applicable.
Data Availability Statement
The data presented in this study are available upon request from the corresponding author.
Conflicts of Interest
The authors declare no conflict of interest.
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