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

Abstract

BackgroundGroup 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.MethodsOMVs 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.ResultsOur 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.ConclusionWe 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.TopicStreptococcus pyogenes, immunoglobulins, polysaccharides, opsonophagocytosis, acute rheumatic fever, M protein, invasive Group A Streptococcus, hyaluronic acid

A platform for the recombinant production of Group A Streptococcus glycoconjugate vaccines

“…The Lancefield Group A carbohydrate (GAC) is a conserved, abundant, and immunogenic surface structure that has been shown to be an excellent glycoconjugate vaccine candidate [6,9,19]. However, there is concern that the GlcNAc side chain may elicit unwanted immune complications [15].…”

“…We have previously cloned the requisite genes for Strep A RhaPS and demonstrated its heterologous production in E. coli [13]. RhaPS is synthesised by the enzymes GacB-G on the inner membrane as lipid-linked carbohydrate [9]. Production of RhaPS in an O-antigen ligase (waaL) positive strain of E. coli results in its deposition on the cell surface, which can serve as a platform for production of Outer Membrane Vesicle (OMV) vaccines [9].…”

“…RhaPS is synthesised by the enzymes GacB-G on the inner membrane as lipid-linked carbohydrate [9]. Production of RhaPS in an O-antigen ligase (waaL) positive strain of E. coli results in its deposition on the cell surface, which can serve as a platform for production of Outer Membrane Vesicle (OMV) vaccines [9]. The native GAC structure contains a rhamnose residue that is β-(1→4)-linked to GlcNAc at its reducing end (Fig.…”

“…We have previously shown that deletion of gacB abrogates production of RhaPS [13,51]. We now assessed the ability of the Shi1 and Shi2a repeating unit pathways to complement this gacB deletion (Fig.…”

“…All Strep A serotypes display the Lancefield Group A Carbohydrate (GAC) on the surface, which is conserved and immunogenic and therefore an excellent vaccine candidate [4][5][6][7][8][9][10]. GAC is a peptidoglycan-anchored surface structure consisting of a polyrhamnose backbone with N-acetylglucosamine (GlcNAc) side chains (Fig.…”