Virus-like particle-display of the enterotoxigenic Escherichia coli heat-stable toxoid STh-A14T elicits neutralizing antibodies in mice

Morten L Govasli,Yuleima Diaz,Pål Puntervoll

doi:10.1016/j.vaccine.2019.09.004

Morten L Govasli, Yuleima Diaz + Show 1 more

Open Access

https://doi.org/10.1016/j.vaccine.2019.09.004

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Journal: Vaccine	Publication Date: Sep 9, 2019
Citations: 20	License type: cc-by

Affiliation: NORCE Norwegian Research Centre, University of Bergen

Abstract

Enterotoxigenic Escherichia coli (ETEC) causes diarrhoea by secreting enterotoxins into the small intestine. Human ETEC strains may secrete any combination of three enterotoxins: the heat-labile toxin (LT) and the heat-stable toxins (ST), of which there are two variants, called human ST (STh) and porcine ST (STp). Strains expressing STh, either alone or in combination with LT and/or STp, are among the four most important diarrhoea-causing pathogens affecting children in low- and middle-income countries. ST is therefore an attractive target for ETEC vaccine development. To produce a safe ST-based vaccine, several challenges must be solved. ST must be rendered immunogenic and non-toxic, and antibodies elicited by an ST vaccine should neutralize ST but not cross-react with the endogenous ligands uroguanylin and guanylin. Virus-like particles (VLPs) tend to be highly immunogenic and are increasingly being used as carriers for presenting heterologous antigens in new vaccines. In this study, we have coupled native STh and the STh-A14T toxoid to the coat protein of Acinetobacter phage AP205 by using the SpyCatcher system and immunized mice with these VLPs without the use of adjuvants. We found that both STs were efficiently coupled to the VLP, that both the STh and STh-A14T VLPs were immunogenic in mice, and that the resulting serum antibodies could completely neutralize the toxic activities of native STh. The serum antibodies showed a high degree of immunological cross-reaction to STp, while there was little or no unwanted cross-reaction to uroguanylin and guanylin. Moreover, compared to native STh, the STh-A14T mutation did not seem to negatively impact the immunogenicity of the construct or the neutralizing ability of the resulting sera. Taken together, these findings demonstrate that VLPs are suitable carriers for making STs immunogenic, and that the STh-A14T-coupled AP205 VLP represents a promising ETEC vaccine candidate.

Highlights

Diarrheal diseases caused by infections with enterotoxigenic Escherichia coli (ETEC) is a major contributor to health problems among young children living in low- and middle-income countries (LMICs) [1,2,3,4,5] and for travellers visiting these countries [6]
We investigated the suitability of using the SpyCatcher-AP205 virus-like particle (VLP) system to render STh immunogenic, assessed the ability of the non-toxic STh-A14T mutant to elicit STh-neutralizing antibodies in mice, and we investigated the degree of cross-reactivity the serum antibodies had towards STp, guanylin, and uroguanylin
We have for the first time used VLPs to make both native STh and the non-toxic mutant STh-A14T immunogenic

Summary

Introduction

Diarrheal diseases caused by infections with enterotoxigenic Escherichia coli (ETEC) is a major contributor to health problems among young children living in low- and middle-income countries (LMICs) [1,2,3,4,5] and for travellers visiting these countries [6]. ETEC colonizes the small intestine, and diarrhoea is induced by the secretion of one, two, or all of three different enterotoxins: the heat-labile enterotoxin (LT), the human heat-stable enterotoxin (STh), and the porcine heat-stable enterotoxin (STp) [11]. ETEC strains secreting STh are among the four most important pathogens associated with moderate-tosevere diarrhoea in LMIC children [13], making STh one of the most attractive targets for ETEC vaccine development

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