Dose-Finding Study of CS19 Expressing ETEC Challenge Strains

This is a phase 1, open-label, strain and dose-finding study designed to establish a human
challenge modelfor CS19-ETEC that causes a > 80% attack rate without causing high output
diarrhea. This study design is identical to that of the CS17 challenge model recently
completed. Two strains of CS19-ETEC isolated from human diarrheal cases have been identified
and characterized. Each clinical isolate was used to generate a cGMP MCB and procedures were
established to create a fresh inoculum to administer orally in a sodium bicarbonate solution
for challenge. Refer to Section 8 for full details on the isolation and preparation of these
strains.

CS19-ETEC strain WS0115A (toxin phenotype of LT+ ST+ and serotype O114:H-) will be the lead
strain and will be administered orally to an initial cohort of 5 subjects. This strain was
isolated from the stool of a 12-month-old Egyptian girl suffering from watery diarrhea
identified during a surveillance study conducted in Abees, Egypt from 1993 to 1995 by
investigators at the Naval Medical Research Unit-3 (NAMRU-3), Cairo, Egypt. A negative
microbiologic work-up for copathogens (other bacterialenteropathogens, rotavirus, Giardia
lamblia, Entamoeba histolytica, and Cryptosporidium) supports that the isolated WS0115A
strain was pathogenic in this child. Since this strain has an LT+ST+ toxin phenotype, it is
the preferred strain to lead in testing the challenge model, since heterologous protection
by bovine milk IgG anti-CsbD against an LT+ST+ phenotype would offer a more robust test of
the protection afforded by anti-colonization. The alternate strain, CS-19 ETEC strain DS26-1
(toxin phenotype LT+ST-;serotype O8:H9) was isolated in 1990 at the U.S. Navy Forward
Laboratory from a U.S. soldier with diarrhea while on deployment to Saudi Arabia during
Operation Desert Shield. A negative microbiologic work-up for copathogens (Salmonella typhi,
Vibrio cholerae, Giardia lamblia or Entamoeba histolytica)supports that the isolated DS26-1
strain was pathogenic in this individual. Each clinical isolate was used to generate a cGMP
master cell bank and procedures were established to create a fresh inoculum to administer
orally in a sodium bicarbonate solution for challenge. Refer to Section 8 for full details
on the isolation and preparation of these strains.

Inclusion Criteria:

1. Male or female between 18 and 45 years of age, inclusive.

2. General good health, without significant medical illness, abnormal physical
examination findings or clinical laboratory abnormalities as determined by principal
investigator (PI) or PI in consultation with the medical monitor and Sponsor.

3. Demonstrate comprehension of the protocol procedures and knowledge of ETEC illness by
passing a written examination (pass grade ≥ 70%)

4. Willing to participate after informed consent obtained.

5. Available for entire inpatient portion of study and all outpatient study visits.

6. Negative serum pregnancy test at screening (initial visit and day -7 to - 3) and a
negative urine pregnancy test on the day of admission to the inpatient phase for
female subjects of childbearing potential. Females of childbearing potential must
agree to use an efficacious hormonal or barrier method of birth control during the
study. Alternatively, abstinence alone is acceptable. Female subjects who are unable
to bear children must provide supporting documentation (e.g., prior tubal ligation or
hysterectomy).

Exclusion Criteria:

1. Presence of a significant medical condition, (e.g., psychiatric conditions or
gastrointestinal disease, such as peptic ulcer, symptoms or evidence of active
gastritis or gastroesophageal reflux disease, inflammatory bowel disease, alcohol or
illicit drug abuse/dependency), or other laboratory abnormalities which in the
opinion of the investigator precludes participation in the study.

2. Immunosuppressive illness or IgA deficiency (below the normal limits)

3. Positive serology results for HIV, HBsAg, or HCV antibodies.

4. Significant abnormalities in screening laboratory hematology, serum chemistry,
urinalysis, as determined by PI or PI in consultation with the medical monitor and
Sponsor.

5. Allergy to fluoroquinolones, cotrimoxazole, or ampicillin/penicillin (excluded if
allergic to two of three).

6. Fewer than 3 stools per week or more than 3 stools per day as the usual frequency;
loose or liquid stools other than on an occasional basis.

7. History of diarrhea in the 2 weeks prior to planned inpatient phase.

8. Regular use of laxatives or any agent that increases gastric pH (regular defined as
at least weekly).

9. Use of antibiotics during the 7 days before bacterial dosing or proton pump
inhibitors, H2 blockers, or antacids within 48 hours of dosing.

10. Travel to countries where ETEC or cholera infection is endemic (most of the
developing world) within two years prior to dosing.

11. History of vaccination for or ingestion of ETEC, cholera, or LT toxin.

12. Stool culture (collected no more than 1 week prior to admission) positive for ETEC or
other bacterial enteric pathogens (Salmonella, Shigella and Campylobacter).

13. Use of any investigational product within 30 days preceding the receipt of the
challenge inoculum, or planned use during the active study period.

14. Use of any medication known to affect the immune function (e.g., corticosteroids)
within 30 days preceding receipt of the challenge inoculum or planned use during the
active study period. (Topical and intra-articular steroids will not exclude
subjects). MANAGEMENT