Enterotoxigenic Escherichia coli (ETEC) strains are categorized as priority B pathogens by NIAID. ETEC-associated diarrhea is responsible for nearly one million deaths each year around the world in addition to causing of illness to immunocompromised individuals and travelers including deployed military personnel. The key virulence factors in ETEC- associated diarrhea are bacterial adhesins or colonization factor antigens (CFAs) and enterotoxins. CFAs mediate bacterial attachment to the host epithelium cells, but it is the enterotoxin, the heat-labile (LT) and heat-stable (STa), that stimulate fluid hyper-secretion and cause diarrhea. Early studies using LT and STa antigens for developing antitoxin vaccines had limited success because of the high toxicity of both toxins, non-immunogenicity of STa antigen, and lack of a suitable animal study model. Current advance in molecular biology makes it feasible to eliminate or reduce toxicity and to enhance STa immunogenicity. In this study, we will genetically mutate both LT and STa genes for expressing non- or low toxic LT and STa toxoids, and then genetically fuse these two mutated genes for LT and STa toxoid fusion antigens to enhance STa immunogenicity. These fusion antigens are expected to induce anti-LT and anti-STa antibodies, and those antibodies will neutralize native LT and STa toxins thus provide protection against ETEC infection. In our preliminary studies, we demonstrated that a genetic fusion of a porcine LT toxoid with a STa toxoid or STb (another non-immunogenic heat stable toxin) induced anti-LT and anti-ST antibodies, and these antibodies are protective against ETEC infection in a piglet challenge model. Piglet model, especially the system using piglets expressing K88ac receptors and ETEC strains expressing K88ac fimbriae, is perhaps the best model to study human ETEC associated diarrhea. K88ac receptor positive piglets are neutrally susceptible to ETEC strains expressing K88ac fimbriae, and develop identical clinical disease after infection of ETEC strains as human diarrheal patients. Furthermore, using pig model allows us to examine intestinal immunity, which is critical for providing protection against this disease. Our expertise in applying pig model in studying ETEC makes our research team the best candidate to conduct ETEC diarrhea research and prevention using the pig model. Determination vaccine candidacy of LT and STa toxoid fusions against ETEC diarrhea will provide essential information for antitoxin vaccine development, and will be very instructive in developing prevention and treatment strategies to protect humans and animals from diarrhea disease.

Public Health Relevance

Enterotoxigenic Escherichia coli (ETEC) are the primary cause of diarrheal disease. ETEC diarrhea is responsible for near one million deaths each year, and brings major health problems and economic consequences in immunocompromised individuals (especially children under age of five years), international travelers and military personnel. Heat labile (LT) and heat-stable (STa) enterotoxins produced by ETEC strains are the virulence determinants in diarrheal infection. LT and STa stimulate fluid hyper-secretion in guts that results in diarrhea. Yet, there are no vaccines available to control or prevent this disease. Development of antitoxin vaccines could be an effective strategy to prevent diarrhea. However, both LT and STa are sufficiently toxic, thereby they cannot be used directly as antigens for developing antitoxin vaccines. This proposed research is to construct LT and STa toxoids, and to determine vaccine candidacy of fusion antigens from a full-length LT toxoid and a full-length STa toxoid against ETEC infection in a piglet model. The determination of vaccine candidacy of LT and STa toxoid fusions against diarrheal disease will provide essential information for developing effective antitoxin vaccines to prevent or control this disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21AI083897-02
Application #
7860302
Study Section
Vaccines Against Microbial Diseases (VMD)
Program Officer
Baqar, Shahida
Project Start
2009-06-05
Project End
2012-05-31
Budget Start
2010-06-01
Budget End
2012-05-31
Support Year
2
Fiscal Year
2010
Total Cost
$206,632
Indirect Cost
Name
South Dakota State University
Department
Veterinary Sciences
Type
Schools of Earth Sciences/Natur
DUNS #
929929743
City
Brookings
State
SD
Country
United States
Zip Code
57007
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Ruan, Xiaosai; Knudsen, David E; Wollenberg, Katie M et al. (2014) Multiepitope fusion antigen induces broadly protective antibodies that prevent adherence of Escherichia coli strains expressing colonization factor antigen I (CFA/I), CFA/II, and CFA/IV. Clin Vaccine Immunol 21:243-9
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