Human Challenge Model With ST-only Enterotoxigenic Escherichia Coli

Inclusion Criteria:

• Provide written informed consent before initiation of any study procedures.

• Healthy as judged by the Principal Investigator (PI) and determined by medicalhistory, physical examination, and medication history.

• Within 15 days of vaccination, have normal screening laboratories for white bloodcells (WBC), hemoglobin (Hgb), platelets, absolute neutrophil count (ANC), sodium,potassium, chloride, bicarbonate, blood urea nitrogen (BUN), creatinine, alanineaminotransferase (ALT), C-reactive protein (CRP).

• Demonstrate comprehension of the protocol procedures and knowledge of study by passinga written examination (passing grade is at least 80 percent).

• Capable of understanding, consenting and complying with the entire study protocol.

• Female subjects must be of non-childbearing potential, (as defined as surgicallysterile or postmenopausal for more than 1 year), or if of childbearing potential mustbe practicing abstinence or using an effective licensed method of birth control (e.g.,history of hysterectomy or tubal ligation; use hormonal or barrier birth control suchas implants, injectables, combined oral contraceptives, some intrauterine devices (IUDs), cervical sponges, diaphragms, condoms with spermicidal agents, or must have avasectomized partner) within 2 months of infection and must agree to continue suchprecautions during the study and for 30 days after the Day 56 study visit. Malesubjects must agree not to father a child for 90 days after the Day 28 study visit. Awoman is eligible if she is monogamous with a vasectomized male.

• Agrees not to participate in another clinical trial during the study period.

Exclusion Criteria:

• Women who are pregnant or lactating or have a positive serum pregnancy test atscreening or positive urine pregnancy test upon admission to inpatient facility.

• Abnormal Vital signs, defined as:

• Hypertension (systolic blood pressure >140 mm Hg or diastolic blood pressure >90mm Hg) at rest on 2 separate days; or (heart rate <55 at rest on 2 separate days)

• Respiratory rate >17

• Temperature >/= 38.0 C (100.4 F) or symptoms of an acute self-limited illnesssuch as an upper respiratory infection or gastroenteritis within 7 days ofinoculum.

• Active positive Hepatitis B, C, and Human Immunodeficiency Virus (HIV) serologies.

• History of antimicrobial treatment in the 2 weeks before bacterial inoculum

• Received previous experimental E. coli, LT, or cholera vaccines or live E. coli orVibrio cholerae challenges; or previous infection with cholera or diarrheagenic E.coli.

• Abnormal bowel habits as defined by fewer than 3 stools per week or more than 2 stoolsper day in the past 6 months.

• History of chronic gastrointestinal illness, including severe dyspepsia (mild ormoderate heartburn or epigastric pain occurring no more than 3 times per week ispermitted), lactose intolerance, or other significant gastrointestinal tract disease.

• Regular use (weekly or more often) of laxatives, anti-diarrheal, anti-constipation, orantacid therapy.

• History of major gastrointestinal surgery, excluding uncomplicated appendectomy orcholecystectomy.

• Long-term use of oral steroids, parenteral steroids, or high-dose inhaled steroids (>800 mcg/day of beclomethasone dipropionate or equivalent) within the preceding 6months (Nasal and topical steroids are allowed).

• Have a diagnosis of schizophrenia or other major psychiatric diagnosis.

• Receiving the following psychiatric drugs: aripiprazole, clozapine, ziprasidone,haloperidol, molindone, loxapine, thioridazine, molindone, thiothixene, pimozide,fluphenazine, risperidone, mesoridazine, quetiapine, trifluoperazine, chlorprothixene,chlorpromazine, perphenazine, trifluopromazine, olanzapine, carbamazepine, divalproexsodium, lithium carbonate or lithium citrate

• History of receiving immunoglobulin or other blood product within the 3 months beforeenrollment in this study.

• Traveled to Enterotoxigenic Escherichia coli (ETEC) endemic areas within the past 2years, ever having used Cholera/ETEC vaccine (Dukoral) or having been raised in acholera or ETEC endemic area.

• Received any licensed vaccine within 2 weeks (for inactivated vaccines) or 4 weeks (for live vaccines) before enrollment in this study.

• An acute or chronic medical condition that, in the opinion of the investigator, wouldrender ETEC infection unsafe or would interfere with the evaluation of responses. Thisincludes, but is not limited to: known or suspected immunodeficiency, known chronicliver disease, significant renal disease, unstable or progressive neurologicaldisorders, history of diabetes, cancer (other than a healed skin lesion), heartdisease (in the hospital for a heart attack, history of irregular heart beat orfainting caused by an irregular heart beat), unconsciousness (other than a singlebrief "concussion"), seizures (other than with fever when subject was a child <5 yearsold), asthma requiring treatment with inhaler or medication in the prior 2 years,autoimmune disease or eating disorder, and transplant recipients.

• Received an experimental agent (vaccine, drug, biologic, device, blood product ormedication) within 1 month before enrollment in this study or expects to receive anexperimental agent during the study.

• History of alcohol or drug abuse in the last 5 years.

• Planned to travel abroad in the time between vaccination and 30 days following theETEC inoculum dose.

• Any condition that would, in the opinion of the Site Investigator, place the subjectat an unacceptable risk of injury or render the subject unable to meet therequirements of the protocol.

• Use of prescription and over-the-counter (OTC) medications that contain acetaminophen,aspirin, ibuprofen, and other nonsteroidal anti-inflammatory drugs within 48 hoursprior to receiving the investigational product.

• Use of prescription acid suppression medication or OTC antacids within 72 hours ofinvestigational product administration.

• Subjects with autoimmune disorders, chronic inflammatory disorders or neurologicaldisorders with a potential autoimmune correlation.