Phase 1 meCS6 + LT(R192G) Vaccine Study

The study will enroll approximately 60 volunteers. The vaccine is given as a drink in flavored soda water. Volunteers will either receive a 3-dose vaccination with doses spaced two weeks apart or a 4-dose vaccination with doses spaced 2 days apart depending upon their availability for follow-up. Once assigned to a vaccination schedule, volunteers will be randomly assigned to receive the meCS6 vaccine with or without the mLT adjuvant for all vaccine doses. Neither the study investigators nor the volunteers will know which group they are assigned. Volunteers will be asked to be available for clinic visits and telephone follow-ups during the study period and provide blood and stool specimens for testing.

The Phase 1 section of this study is a randomized double blind trial in which a total of 60 subjects (minimum of 52 allowable) will receive on of two oral vaccine doses according to the following chart: Group Subset N CS6(Encapsulated) LT(R192G) I A 15 0.95mg 2 micrograms II B 15 0.95mg -- III A 15 0.95mg 2 micrograms IV B 15 0.95mg -- *minimum of 13 volunteers/group Volunteers in Group I will receive three immunizations (study days 0, 14, and 28) during the vaccine series. Volunteers in Group II will receive four immunizations (study days 0, 2, 4, and 6) during the vaccine series. The two groups will be vaccinated separately for logistical purposes. Blood and stool specimens will be collected at intervals to examine systemic and mucosal vaccine antigen-specific immune responses. Vaccine safety will be actively evaluated during vaccination and for 4 weeks following the final vaccine dose.

Inclusion Criteria: Available for required follow-up period Women must have a negative pregnancy test Women must not to try to become pregnant while on study and for 2 months after study is completed Exclusion Criteria: History of travellers' diarrhea Occupation that involves handling of E. coli or cholera bacteria, or E. coli vaccine Regular use of anti-diarrheal, anti-constipation, or antacid therapy Abnormal bowel habits Pregnant or nursing women History of chronic gastrointestinal illness or major gastrointestinal surgery Allergies to vaccines Positive HIV, Hepatitis B or Hepatitis C tests Regular use of oral steroid medication Clinically significant abnormalities on physical examination