Recombinant Group A Carbohydrate backbone embedded into Outer Membrane Vesicles is a potent vaccine candidate targeting Group A Streptococcus from Streptococcus pyogenes and Streptococcus dysgalactiae subsp. equisimilis

Background Group A Streptococcus (GAS) are responsible for a wide range of human-exclusive infections, annually killing more than 500,000 people. Antibiotic resistance incidence of invasive GAS tripled in the past decade and emphasises the need to develop a universal GAS vaccine. We have produced, for the first time, a recombinant polyrhamnose backbone (pRha), a validated universal GAS vaccine candidate. E. coli outer membrane vesicles (OMVs) carrying pRha were investigated for their immunogenicity and efficacy in an animal model. Methods OMVs decorated with pRha were administered to C57BL/6J mouse and rabbit models. Flow cytometry, ELISA, Luminex, immunofluorescence microscopy and serum bactericidal assay assays were conducted to investigate the ability of pRha-specific antibodies to recognise and kill clinical (hypervirulent) GAS strains. Results Our results suggest that pRha-OMVs induce specific antibodies which recognise Group A Carbohydrate (GAC) from S pyogenes and S. dysgalactiae subsp. equisimilis . Increased IgG levels correlate with increased bactericidal killing of the hypervirulent GAS M89 strain. Elevated IL-17a from pRha-OMV-immunised splenocytes indicates possible stimulation of long-term memory immune cells. Conclusion We are the first to report efficacy and potency of this unique, exogenously produced polysaccharide, pRha, in the induction of humoral-mediated immune responses to GAS. Topic Streptococcus pyogenes , immunoglobulins, polysaccharides, opsonophagocytosis, acute rheumatic fever, M protein, invasive Group A Streptococcus, hyaluronic acid