Characterization and immunogenicity of a Shigella flexneri 2a O-antigen bioconjugate vaccine candidate.

Neil Ravenscroft,Martin Braun,Michael Kowarik,Paula Carranza,Claire Jones,Dominique Sirena,Micha A Haeuptle,Stefan Herwig,Michael Wetter,Joerg Schneider,Anita M Dreyer,Andrew J Pollard,Stefan Kemmler,Michael Wacker,Michael Steffen

doi:10.1093/glycob/cwz044

Neil Ravenscroft, Martin Braun + Show 13 more

Open Access

https://doi.org/10.1093/glycob/cwz044

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Abstract

Shigellosis remains a major cause of diarrheal disease in developing countries and causes substantial morbidity and mortality in children. Vaccination represents a promising preventive measure to fight the burden of the disease, but despite enormous efforts, an efficacious vaccine is not available to date. The use of an innovative biosynthetic Escherichia coli glycosylation system substantially simplifies the production of a multivalent conjugate vaccine to prevent shigellosis. This bioconjugation approach has been used to produce the Shigella dysenteriae type O1 conjugate that has been successfully tested in a phase I clinical study in humans. In this report, we describe a similar approach for the production of an additional serotype required for a broadly protective shigellosis vaccine candidate. The Shigella flexneri 2a O-polysaccharide is conjugated to introduced asparagine residues of the carrier protein exotoxin A (EPA) from Pseudomonas aeruginosa by co-expression with the PglB oligosaccharyltransferase. The bioconjugate was purified, characterized using physicochemical methods and subjected to preclinical evaluation in rats. The bioconjugate elicited functional antibodies as shown by a bactericidal assay for S. flexneri 2a. This study confirms the applicability of bioconjugation for the S. flexneri 2a O-antigen, which provides an intrinsic advantage over chemical conjugates due to the simplicity of a single production step and ease of characterization of the homogenous monomeric conjugate formed. In addition, it shows that bioconjugates are able to raise functional antibodies against the polysaccharide antigen.

Highlights

Shigella is one of the five main pathogens causing diarrheal disease, resulting in 1 in 10 child deaths during their first 5 years of life (Kotloff et al 2013; Platts-Mills et al 2015)
The use of an innovative biosynthetic Escherichia coli glycosylation system substantially simplifies the production of a multivalent conjugate vaccine to prevent shigellosis
We show the construction of a modified E. coli strain functionally expressing the lipid-linked S. flexneri type 2a PS, which serves as a substrate for the oligosaccharyltransferase PglB

Summary

Introduction

Shigella is one of the five main pathogens causing diarrheal disease, resulting in 1 in 10 child deaths during their first 5 years of life (Kotloff et al 2013; Platts-Mills et al 2015). This results in about 800,000 fatalities annually, mainly in sub-Saharan Africa and South Asia (Liu et al 2012). Shigella flexneri is the major cause of shigellosis in endemic countries, accounting for up to 60% cases of shigellosis mainly in developing countries (Livio et al 2014). S. dysenteriae O1 caused epidemics and pandemics during times of population upheaval; few cases have been reported since 1990 (Kotloff et al 2017)

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