Interrogation of a live-attenuated enterotoxigenic Escherichia coli vaccine highlights features unique to wild-type infection

Subhra Chakraborty,David A Rasko,Philip L Felgner,Barbara Denearing,Arlo Randall,James M Fleckenstein,Petra E Gilmore,Doug Molina,A Louis Bourgeois,Jessica Brubaker,Sachin Mani,Tim J Vickers,Heather Wenzel,Clayton D Harro,David A Sack,Michael J Darsley,Xiaowu Liang,R Reid Townsend

doi:10.1038/s41541-019-0131-7

Abstract

Enterotoxigenic Escherichia coli (ETEC) infections are a common cause of severe diarrheal illness in low- and middle-income countries. The live-attenuated ACE527 ETEC vaccine, adjuvanted with double mutant heat-labile toxin (dmLT), affords clear but partial protection against ETEC challenge in human volunteers. Comparatively, initial wild-type ETEC challenge completely protects against severe diarrhea on homologous re-challenge. To investigate determinants of protection, vaccine antigen content was compared to wild-type ETEC, and proteome microarrays were used to assess immune responses following vaccination and ETEC challenge. Although molecular interrogation of the vaccine confirmed expression of targeted canonical antigens, relative to wild-type ETEC, vaccine strains were deficient in production of flagellar antigens, immotile, and lacked production of the EtpA adhesin. Similarly, vaccination ± dmLT elicited responses to targeted canonical antigens, but relative to wild-type challenge, vaccine responses to some potentially protective non-canonical antigens including EtpA and the YghJ metalloprotease were diminished or absent. These studies highlight important differences in vaccine and wild-type ETEC antigen content and call attention to distinct immunologic signatures that could inform investigation of correlates of protection, and guide vaccine antigen selection for these pathogens of global importance.

Highlights

Enterotoxigenic Escherichia coli (ETEC) cause substantial morbidity due to diarrheal illness in resource-poor areas of the world where young children are disproportionately affected
We combined genomic and proteomic interrogation of a live-attenuated vaccine with immunoproteomic analysis following vaccination and experimental human challenge with ETEC H10407, an extensively characterized strain originally obtained from a patient with severe choleralike diarrheal illness.[32]
Previous studies demonstrating that challenge with wild-type ETEC H10407 bacteria affords virtually complete protection against severe diarrhea on subsequent rechallenge[10] provide important benchmarks for comparison of candidate vaccines

Summary

Introduction

Enterotoxigenic Escherichia coli (ETEC) cause substantial morbidity due to diarrheal illness in resource-poor areas of the world where young children are disproportionately affected. In children under five years of age, these pathogens are among the leading causes of moderate-to-severe diarrhea and deaths due to acute diarrheal illness.[1,2] ETEC causes severe illness, clinically indistinguishable from cholera,[3,4,5] and death in older individuals[6] and remains the most common cause of travelers’ diarrhea. The ETEC pathovar is defined by the production and effective delivery of heat-stable (ST) and/or heat-labile (LT) enterotoxins to epithelial receptors in the small intestine. In the classical ETEC pathogenesis paradigm, plasmid-encoded colonization factor (CF) or coli surface (CS) antigens facilitate small intestinal colonization.[8]

Methods

Results

Conclusion