Development and Comparison of a Panel of Modified CS17 Fimbrial Tip Adhesin Proteins as Components for an Adhesin-Based Vaccine against Enterotoxigenic Escherichia coli.

Yang Liu,Stephen J Savarino,Milton Maciel,Aisling O’Dowd,Julianne E Rollenhagen,Irina V Etobayeva,Steven T Poole

doi:10.3390/microorganisms9081646

Abstract

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrhea in travelers and children in resource-limited countries. ETEC colonization factors, fimbrial tip adhesins and enterotoxins are key virulence factors, and thus have been studied as vaccine candidates. Some prevalent colonization factors, including CFA/I and CS17, belong to the class 5 family. We previously found that passive oral administration of hyperimmune bovine colostral IgG (bIgG) raised against dscCfaE (donor strand complemented CFA/I tip adhesin) protected volunteers against CFA/I+ ETEC challenge, while anti-dscCsbD bIgG (CS17 tip adhesin) did not confer protection. These findings led us to develop and optimize a panel of alternative CsbD-based vaccine candidates based on allele matching and in silico protein engineering. Physicochemical characterizations revealed that an optimized vaccine candidate dscCsbDLSN139(P218A/G3) had the greatest thermal stability among the six tested dscCsbD adhesins, whereas the overall secondary structures and solubility of these adhesins had no obvious differences. Importantly, dscCsbDLSN139(P218A/G3) elicited significantly higher CS17+ ETEC hemagglutination inhibition titers in sera from mice intranasally immunized with the panel of dscCsbD adhesins, while no significant difference was observed among heterologous neutralizing titers. Our results strongly advocate for the incorporation of these modifications into a new generation of CsbD-based ETEC vaccine candidates.

Highlights

Enterotoxigenic Escherichia coli (ETEC) has been identified as one of the top five pathogens causing diarrhea among children under age five in regions such as South Asia and Sub-Saharan Africa [1]
The CS17 adhesin CsbD has been reported to have seven allelic variants in amino acid sequences [19], and allele matching of vaccine antigens plays a significant role in eliciting protective responses [23,24]
ETEC is a major etiology of morbidity and mortality caused by bacterial diarrhea in travelers and pediatric population in endemic regions [1,3]

Summary

Introduction

Enterotoxigenic Escherichia coli (ETEC) has been identified as one of the top five pathogens causing diarrhea among children under age five in regions such as South Asia and Sub-Saharan Africa [1]. ETEC is estimated to cause over 50,000 deaths and several hundred million of diarrheal cases per year [4]; the dismal situation is exacerbated by rising antibiotic resistance [5] and no licensed ETEC vaccine. A few current ETEC vaccine candidates in clinical trials pivot on ETEC colonization factors, fimbrial tip adhesins and enterotoxin toxoids, as they are recognized as protective antigens. More than 25 ETEC colonization factors displaying distinct serotype diversity have been identified on the surface of clinical ETEC isolates, which complicates the vaccine development. Class 5 fimbriae, CS3, CS6, and CS21 are predominant ETEC colonization factors significantly associated with moderate to severe diarrhea [3,6]

Methods

Results

Conclusion