Human Challenge Model Refinement With Enterotoxigenic Escherichia Coli Strain B7A

Enterotoxigenic Escherichia coli (ETEC) is the most common causes of infectious diarrhea in
children in resource limited countries, and is also a frequent cause of traveler's diarrhea
in civilian and military travelers to endemic countries. ETEC strains express one or both of
two enterotoxins (heat labile toxin (LT) and heat stable toxin (ST)) that cause help the
bacteria cause the main symptom of watery diarrhea. They also express a variety of
colonization factors (CF) that help them attach to the intestinal wall. Each colonization
factor has one or more surface antigens (CS).

Vaccines and treatments to prevent ETEC disease are under development. Some of these target
specific enterotoxins or colonization factors. For over 40 years, we have used ETEC human
challenge studies to understand the ETEC disease process, immune response, and more recently,
to determine whether treatments or vaccines are protective or effective in mitigating
disease. One concern about these challenge study is the use of high doses of bacteria given
may overwhelm the protective efficacy of the vaccine or treatment. Several strains of ETEC
have been used in these challenge studies; a frequently used strain is B7A (CS6+, LT+, ST+.
O148:H28).

This study will explore the optimal dosing strategy for B7A, in order to minimize the dose of
ETEC necessary to produce disease in healthy adult volunteers. There will be two inpatient
admissions. The first will examine 4 dosing and fasting regimens in healthy volunteers. The
second admission will include volunteers who became ill during the first admission, as well
as a new group of volunteers. This second admission will validate the optimal dose from the
first admission, as well as to determine if previous infection with B7A ETEC will protect
against a new infection. Trying to understand the immune response to this challenge organism
may help us optimize vaccine design and delivery to protect people from this infection.

Inclusion Criteria:

1. Male or female between 18 and 50 years of age, inclusive.

2. General good health, without clinically significant medical history, physical
examination findings or clinical laboratory abnormalities per clinical judgment of the
PI.

3. Completion of a training session and demonstration of comprehension of the protocol
procedures and knowledge of ETEC-associated illness by passing a written examination.

4. Willingness to participate after informed consent obtained.

5. Availability for the study duration, including all planned follow-up visits.

6. Negative pregnancy test with understanding to not become pregnant during the study or
within three months following last scheduled study visit.

Exclusion Criteria:

1. Presence of a significant medical condition which in the opinion of the investigator
precludes participation in the study.

2. Significant abnormalities in screening hematology or serum chemistry as determined by
PI or PI in consultation with the research monitor and sponsor.

3. Evidence of confirmed infection with HIV, Hepatitis B, or Hepatitis C.

4. Evidence of Immunoglobulin A (IgA) deficiency (serum IgA < 7 mg/dL or below the limit
of detection of assay).

5. Evidence of current excessive alcohol consumption or drug dependence (a targeted drug
screen may be used to evaluate at the clinician's discretion).

6. Evidence of impaired immune function.

7. Recent vaccination or receipt of an investigational product (within 30 days before
receipt of challenge).

8. Any other criteria which, in the investigator's opinion, would compromise the ability
of the subject to participate in the study, the safety of the study, or the results of
the study.

9. History of microbiologically confirmed ETEC or cholera infection in last 3 years.

10. Occupation involving handling of ETEC or Vibrio cholerae currently, or in the past 3
years.

11. Symptoms consistent with Travelers' Diarrhea concurrent with travel or planned travel
to countries where ETEC infection is endemic.

12. Vaccination for or ingestion of ETEC, cholera, or E coli heat labile toxin within 3
years prior to dosing.

13. Any prior experimental infection with ETEC strain B7A.

14. Abnormal stool pattern.

15. Regular use of laxatives, antacids, or other agents to lower stomach acidity.

16. Use of any medication known to affect the immune function.

17. Known allergy to two of the following antibiotics: ciprofloxacin,
trimethoprim-sulfamethoxazole, and amoxicillin.