Background: Strep A bacteria (Streptococcus pyogenes, Group A Streptococcus) cause over 500,000 deaths annually, underscoring the urgent need for a safe and effective vaccine. The World Health Organisation has prioritised Strep A vaccine development, but identifying conserved antigens across 250+ serotypes remains a challenge.
Methods: We developed RHAPSEDA, a recombinant glycoengineering platform in Escherichia coli, to produce carbohydrate-based glycoconjugate vaccines targeting all Strep A serotypes1. Using biochemical and immunological assays, we validated the platform by analysing antibodies and host cytokine profiles from mice and rabbit vaccination studies. To assess functional immunity, we developed a novel opsonophagocytic killing assay (OPKA) to measure immune-cell-mediated Strep A killing.
Results: We successfully produced multiple recombinant Strep A vaccine candidates composed of Group A Carbohydrate derivatives, conjugated to different Strep A proteins. Our dual-hit approach targets both the conserved surface carbohydrate and disease-specific proteins/toxins, overcoming the limitations of low serotype coverage in protein-based vaccines. Immunisation studies in mice and rabbits demonstrate the induction of cross-serotype reactive antibodies with potent opsonisation activity, facilitating monocyte- and macrophage-dependent killing across all tested Strep A serotypes. Importantly, our site-specific conjugation allows the production of protein specific antibodies that neutralise the toxin function.
Conclusions: Our recombinant carbohydrate-based vaccine platform is cost-effective, scalable, and suitable for low- and middle-income countries. This work represents a significant advancement in Strep A vaccine development, addressing global health priorities for Strep A. Beyond Strep A, the RHAPSEDA platform can be extended to target Group C and G streptococci, offering broad protection against high-burden human diseases.