Immunogenicity and Protective Efficacy against Enterotoxigenic Escherichia coli Colonization following Intradermal, Sublingual, or Oral Vaccination with EtpA Adhesin

Abstract

c Enterotoxigenic Escherichia coli (ETEC) strains are a common cause of diarrhea. Extraordinary antigenic diversity has prompted a search for conserved antigens to complement canonical approaches to ETEC vaccine development. EtpA, an immunogenic extracellular ETEC adhesin relatively conserved in the ETEC pathovar, has previously been shown to be a protective antigen following intranasal immunization. These studies were undertaken to explore alternative routes of EtpA vaccination that would permit use of a double mutant (R192G L211A) heat-labile toxin (dmLT) adjuvant. Here, oral vaccination with EtpA adjuvanted with dmLT afforded significant protection against small intestinal colonization, and the degree of protection correlated with fecal IgG, IgA, or total fecal antibody responses to EtpA. Sublingual vaccination yielded compartmentalized mucosal immune responses with significant increases in anti-EtpA fecal IgG and IgA, and mice vaccinated via this route were also protected against colonization. In contrast, while intradermal (i.d.) vaccination achieved high levels of both serum and fecal antibodies against both EtpA and dmLT, mice vaccinated via the i.d. route were not protected against subsequent colonization and the avidity of serum IgG and IgA EtpA-specific antibodies was significantly lower after i.d. immunization compared to other routes. Finally, we demonstrate that antiserum from vaccinated mice significantly impairs binding of LT to cognate GM1 receptors and shows near complete neutralization of toxin delivery by ETEC in vitro. Collectively, these data provide further evidence that EtpA could complement future vaccine strategies but also suggest that additional effort will be required to optimize its use as a protective immunogen. Enterotoxigenic Escherichia coli (ETEC) strains are among the most common causes of diarrheal illness in developing countries, where young children are most susceptible (1, 2). In addition, these pathogens are also a common cause of diarrhea in immunologically naive travelers (3) who venture to areas of endemicity where sanitation and clean water remain limited.Given the significant impact of ETEC on global health, a vaccine to prevent these infections is a significant priority (4). However, despite decades of investigative efforts following the discovery of toxin-producing E. coli in patients with clinical illnesses indistinguishable from cholera (5), a vaccine that affords broadbased protection has yet to be developed.All of the ETEC-specific virulence genes described to date are encoded on plasmids. These include the heat-labile and/or heatstable enterotoxins that define this pathovar and the colonization factors (CFs). Most vaccines to date have primarily targeted these colonization factors, which include a broad array of fimbrial as well as afimbrial surface antigens thought to be essential for intestinal colonization and/or heat-labile toxin.Unfortunately, the heterogeneity of CF antigenic structures presents a challenge to development of a broadly protective vaccine. ...

Enterotoxigenic Escherichia coli–blood group A interactions intensify diarrheal severity

“…Among the more recently described putative virulence molecules not targeted in the current generation of ETEC vaccines is EtpA, a high-molecular weight secreted adhesin (25) bridge between ETEC and intestinal epithelia (26). EtpA appears to be conserved among a phylogenetically and geographically diverse population of ETEC strains (27)(28)(29) and has shown promise as a protective antigen in preclinical vaccine studies (30)(31)(32)(33). Nevertheless, many questions remain to be answered about the contribution of this antigen and other molecules to disease pathogenesis and their potential use in vaccines relative to canonical ETEC pathovar-specific adhesins.…”

A Self-Assembling Whole-Cell Vaccine Antigen Presentation Platform

“…Proteins and lectins, in particular, are a common, if not universal, component of bacterial biofilm matrices (6,(24)(25)(26). Furthermore, sublingual delivery of protein antigens has been shown to generate mucosal immune responses in the intestine, lungs, and female genital tract (23,27,28). Therefore, we propose that our technology may be generalizable to the biofilm matrices synthesized by pulmonary or sexually transmitted bacterial pathogens and that these biofilm matrix components may be similarly harnessed for the presentation of heterologous antigens relevant to these mucosal surfaces.…”

Maternal Vaccination. Immunization of Sows during Pregnancy against ETEC Infections

“…EatA and YghJ are mucin-degrading enzymes released by ETEC strains to reduce the viscosity of the mucus layer ( Figure 2 ). Studies performed in mice demonstrate that vaccination with EatA afforded significant protection against infection [ 45 , 46 ] Moreover, YghJ is recognized by convalescent antibody following ETEC infection [ 47 ].…”