Live Attenuated ETEC Vaccine ACE527 With and Without dmLT Adjuvant in Adults

Study Overview
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Brief Summary
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This is a research study about an experimental (investigational) oral ETEC vaccine (ACE527). ACE527 is a live attenuated vaccine that is being made to prevent disease from enterotoxigenic Escherichia coli (ETEC), which causes watery diarrhea, largely in children living in developing countries and in travelers to those countries. This research study is also testing an investigational adjuvant called dmLT. An adjuvant is something that is added to a vaccine to make it work better. The purpose of this study is two-fold. First, Part A aims to find out if the vaccine by itself or the vaccine combined with the adjuvant is safe, tolerable, and initiates an immune response. Second, Part B aims to find out if the vaccine by itself or the vaccine combined with the adjuvant prevents diarrheal disease when challenged with ETEC H10407. About 60 healthy adults, ages 18-50, will participate in Part A, and they will be required to stay in the research facility for several nights for the first dose, but will not be required to stay overnight for the second and third doses. Participants will be assigned to receive either the vaccine alone, the vaccine with adjuvant, or placebo by mouth. Study procedures include: stool samples, blood samples, and documentation of side effects. Participants will be involved in study related procedures for about 8 months. Interested volunteers from Part A will along with volunteers who were never vaccinated in Part A will return to participate in Part B. These volunteers will be required to stay overnight in the research facility for several nights after challenge, after which they will be treated with antibiotics and sent home. Study procedures include stool samples, blood samples, and documentation of infection with ETEC H10407. If the vaccine with/without adjuvant is effective, the volunteers should not development diarrhea, but if the vaccine with/without adjuvant is not effective, the volunteers will have diarrhea for a few days.

Detailed Description
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This study is a clinical trial in healthy adult volunteers to evaluate the safety, immunogenicity and efficacy of a live attenuated ETEC vaccine, ACE527, with and without a mucosal adjuvant, dmLT. This study was designed initially as a single site, Phase 1, double-blind, randomized, placebo-controlled, clinical trial in healthy adult volunteers to evaluate the safety and immunogenicity of a live attenuated ETEC vaccine, ACE527, with and without a mucosal adjuvant, dmLT (Part A). The addition of a challenge step provides a unique opportunity to evaluate the efficacy of the new lyophilized formulation of ACE527 vaccine, given in a two or three dose regimen, with and without dmLT, against wild type ETEC strain H10407 challenge (designated as Part B: Phase 2b Open Label Challenge Study). In addition, challenging the volunteers may allow for the identification of immune correlates of protection, taking advantage of newly available technologies (immune proteomics, transcriptomics, etc.) ACE527 comprises three genetically attenuated and engineered strains of E. coli, with antigen profiles covering a wide range of ETEC surface colonization factor antigens (CFA/I, CFA/II [CS1, CS2, CS3] and CFA/IV [CS5, CS6]) and also expressing LT-B, the inactive subunit of LT (ETEC heat labile toxin). LT(R192G/L211A), or dmLT, is a derivative of wild-type enterotoxigenic Escherichia coli heat-labile enterotoxin that has been genetically modified by replacing the arginine at amino acid position 192 with glycine and the leucine at amino acid position 211 with alanine. Volunteers were enrolled in Part A into each of two separate Cohorts. Cohort 1 and 2 volunteers received 10^10 colony-forming units (cfu) total dose of ACE527, 10^10 cfu total dose of ACE527 with 25 µg dmLT, or placebo at 0, 1, and 2 months. Enrollment and dosing of Cohort 2 was dependent on an acceptable safety profile of the first dose of Cohort 1, based on evaluation of data up until Day 3 by the Safety Review Committee (SRC). The first immunization of each Cohort was administered in the Center for Immunization Research (CIR) Inpatient Unit, followed by 72 hours of direct post-immunization observation. The SRC met after the first dose of cohort to determine continuation of volunteer dosing on an outpatient basis, and enrollment of Cohort 2. The SRC met again after the first dose of Cohort 2 after concluding that the first dose appeared safe and well tolerated, subsequent doses would be administered on an outpatient basis. Safety was assessed by solicited symptoms/subject memory aid and laboratory evaluations. Adverse events (AE)s were graded according to standardized criteria. The immunogenicity outcome measures of interest include serum immunoglobulin G (IgG) and immunoglobulin A (IgA) antibodies by enzyme-linked immunosorbent assay (ELISA) against all vaccine antigens, cytokine assays, B and T cell memory responses, shedding profile of ACE527, and vaccine specific mucosal IgA responses. Part B challenge cohorts were recruited among those participating in Part A; plus additional unvaccinated control volunteers sufficient to enroll up to a total of 60 recruited, as needed. Volunteers in the Phase 2b study were enrolled and challenged in 2-4 cohorts due to the CIR Inpatient Unit capacity of 30 beds. A minimum of 8-10 controls were challenged with each cohort of vaccinees to ensure comparability of attack rates across challenge cohorts. Volunteers were admitted as inpatients and challenged, with approximately 2 x 10^7 cfu of the fully virulent ETEC strain, H10407, followed by 5 days of direct observation. A Data Review Committee (DRC) will be convened to review the clinical data for all challenged volunteers and verify all outcomes per protocol definitions before any vaccine efficacy assessments were made.

Official Title
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Safety, Reactogenicity, Tolerability, Immunogenicity and Efficacy of Live Attenuated ETEC ACE527 Vaccine Administered Alone or With a Double Mutant E. Coli Heat Labile Toxin (dmLT) in Healthy Adult Volunteers

Conditions
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Diarrhea

Intervention / Treatment
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* Biological: ACE527
* Biological: dmLT
* Biological: CeraVacx placebo
* Biological: H10407 challenge strain


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Male and female healthy adults between 18 and 50 years of age at the time of enrollment. General good health, without clinically significant medical history, physical examination findings or clinical laboratory abnormalities per clinical judgment of PI. Negative pregnancy test at screening and before the first (V0), second (V28), and third vaccinations (V56) for female volunteers of childbearing potential. Females of childbearing potential must agree to use an efficacious hormonal or barrier method of birth control during the study. Abstinence is acceptable. Female volunteers unable to bear children must have this documented (e.g. tubal ligation or hysterectomy) or must have negative pregnancy tests. Willingness to participate in the study after all aspects of the protocol have been explained and written informed consent obtained. Completion of a training session and demonstrated comprehension of the protocol procedures and knowledge of ETEC associated illness by passing a written examination (70% pass score). Availability for the study duration, including all planned follow-up visits. Received at least 2 doses of ACE527 vaccine alone or in combination with 25 ug dmLT 4-6 months prior to challenge (Part B only) Exclusion Criteria: Presence of a significant medical or psychiatric condition which in the opinion of the investigator precludes participation in the study. Some medical conditions which are adequately treated and stable would not preclude entry into the study. These conditions might include stable asthma controlled with inhalers or mild hypertension stably controlled with a single agent. Significant abnormalities in screening hematology, or serum chemistry as determined by PI or PI in consultation with the Medical Officer and sponsor. Presence in the serum of HIV antibody, HBsAg, or HCV antibody. Evidence of IgA deficiency (serum IgA < 7 mg/dl or limit of detection of assay). Evidence of current excessive alcohol consumption or drug dependence. Volunteers whose Body Mass Index (BMI) is less than 19.0 or greater than 34.0 (kg/m2) Recent vaccination or receipt of an investigational product (within 30 days before vaccination). Intention to donate blood or blood products within one month following the completion of study participation (note: The Red Cross will not allow blood donations for 1 year following participation in an investigational research study). Any other criteria which, in the investigator's opinion, would compromise the ability of the volunteer to participate in the study, the safety of the study, or the results of the study Working as a food handler, in child-care or as a healthcare worker with direct patient contact. Have household contacts who are <2 years old or >80 years old or infirm or immunocompromised (for reasons including corticosteroid therapy, HIV infection, cancer chemotherapy, or other chronic debilitating disease). Abnormal stool pattern (fewer than 3 per week or more than 3 per day). Regular (≥ weekly) use of laxatives, antacids, or other agents to lower stomach acidity. Use of any medication known to affect the immune function (e.g., corticosteroids and others) within 30 days preceding the first vaccination or planned use during the active study period. Symptoms consistent with Traveler's Diarrhea concurrent with travel to countries where ETEC infection is endemic (most of the developing world) within two years prior to dosing, OR planned travel to endemic countries during the length of the study. Vaccination for or ingestion of ETEC, cholera, or LT toxin within 3 years prior to dosing. Use of antibiotics during the 7 days before dosing or proton pump inhibitors, H2 blockers or antacids within 48hours prior to dosing. History of diarrhea in the 7 days prior to vaccination (outpatient diarrhea is defined as ≥ 3 unformed (grade 3 or greater) loose stools in 24 hours). Known allergy to two of the three following antibiotics: Ciprofloxacin, amoxicillin, and/or trimethoprim/sulfamethoxazole

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 50 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: ACE527 alone<br>In Part A of the study, subjects were split into two cohorts whereby enrollment of the second cohort depended on the safety profile of the first cohort. In Part A, subjects received three oral doses of ACE527 at 0, 1, and 2 months. For Part B of the study, eligible subjects who expressed interest of the study were administered H10407 challenge strain 5-7 months after the three-dose vaccination series. | Biological: ACE527<br>* 3x10^9 cfu ACE527 vaccine strain. Comprised of three genetically attenuated and engineered strains of E. coli, with antigen profiles covering a wide range of ETEC surface colonization factor antigens (CFA/I, CFA/II [CS1, CS2, CS3] and CFA/IV [CS5, CS6]) and also expressing LTB, the inactive subunit of LT (ETEC heat labile toxin). The constituent strains of ACE527 were: ACAM2025: a live, attenuated, CFA/I, LTB positive strain ACAM2022: a live, attenuated, CS5, CS6, LTB positive strain, and ACAM2027: a live, attenuated, CS1, CS2, CS3, LTB positive strain.<br>Biological: H10407 challenge strain<br>* Approximately 2 x 10^7 cfu of the fully virulent ETEC strain. Previously administered to 91 volunteers at this challenge dose by the CIR clinical team over the previous 4 years in conjunction with other Phase 1/2b trials.<br>* Other names: ST+, LT+, CFA/I toxin;|
| Experimental: ACE527 plus dmLT<br>In Part A of the study, subjects were split into two cohorts whereby enrollment of the second cohort depended on the safety profile of the first cohort. In Part A, subjects received three oral doses of ACE527 with mucosal adjuvant (dmLT) at 0, 1, and 2 months. For Part B of the study, eligible subjects who expressed interest of the study were administered H10407 challenge strain 5-7 months after the three-dose vaccination series. | Biological: ACE527<br>* 3x10^9 cfu ACE527 vaccine strain. Comprised of three genetically attenuated and engineered strains of E. coli, with antigen profiles covering a wide range of ETEC surface colonization factor antigens (CFA/I, CFA/II [CS1, CS2, CS3] and CFA/IV [CS5, CS6]) and also expressing LTB, the inactive subunit of LT (ETEC heat labile toxin). The constituent strains of ACE527 were: ACAM2025: a live, attenuated, CFA/I, LTB positive strain ACAM2022: a live, attenuated, CS5, CS6, LTB positive strain, and ACAM2027: a live, attenuated, CS1, CS2, CS3, LTB positive strain.<br>Biological: dmLT<br>* A derivative of wild-type enterotoxigenic Escherichia coli heat-labile enterotoxin that has been genetically modified by replacing the arginine at amino acid position 192 with glycine and the leucine at amino acid position 211 with alanine (13). These two amino acid substitutions take place in proteolytic cleavage sites which are critical for activation of the secreted toxin molecules.<br>* Other names: LT(R192G/L211A);Biological: H10407 challenge strain<br>* Approximately 2 x 10^7 cfu of the fully virulent ETEC strain. Previously administered to 91 volunteers at this challenge dose by the CIR clinical team over the previous 4 years in conjunction with other Phase 1/2b trials.<br>* Other names: ST+, LT+, CFA/I toxin;|
| Active Comparator: Control: Part A and B<br>In Part A of the study, subjects were split into two cohorts whereby enrollment of the second cohort depended on the safety profile of the first cohort. In Part A, subjects received three oral doses of CeraVacx placebo at 0, 1, and 2 months. For Part B of the study, eligible subjects who expressed interest of the study were administered H10407 challenge strain 5-7 months after the three-dose vaccination series. | Biological: CeraVacx placebo<br>* CeraVacx® is used to neutralize gastric acidity upon ingestion of vaccine. It was also used as the placebo in this study. CeraVacx® was prepared from the commercial product (Cera Products, Inc.); 9.5 grams were added to sterile water for each dose and mixed. Each dose contained 7 grams of rice syrup, 2 grams of sodium bicarbonate, and 0.5 grams of trisodium citrate.<br>Biological: H10407 challenge strain<br>* Approximately 2 x 10^7 cfu of the fully virulent ETEC strain. Previously administered to 91 volunteers at this challenge dose by the CIR clinical team over the previous 4 years in conjunction with other Phase 1/2b trials.<br>* Other names: ST+, LT+, CFA/I toxin;|
| Active Comparator: Control: Part B only<br>Eligible participants were screened and administered H10407 challenge strain concurrently with other arms in Part B of the study. Their results for Part B are combined with that of the Control Arm in Part A, which received three oral doses of CeraVacx placebo. | Biological: H10407 challenge strain<br>* Approximately 2 x 10^7 cfu of the fully virulent ETEC strain. Previously administered to 91 volunteers at this challenge dose by the CIR clinical team over the previous 4 years in conjunction with other Phase 1/2b trials.<br>* Other names: ST+, LT+, CFA/I toxin;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Part A: Number of Serious Adverse Events and Adverse Events Leading to Withdrawal | Unsolicited adverse events were collected throughout Part A of the study, were graded for severity, and assessed for relationship to vaccine. Withdrawal from the study due to adverse event was determined at the discretion of the study staff. | up to 1 month after last vaccination (3 months) | 
| Part A: Number of Participants Experiencing Unsolicited Adverse Events, by Severity and Relationship to Vaccination | Unsolicited adverse events were collected throughout Part A of the study, were graded for severity, and assessed for relationship to vaccine. Generally, mild severity is discomfort with no disruption of normal daily activities and relieved with or without symptomatic treatment; moderate severity is discomfort sufficient to reduce or affect normal daily activity somewhat and only partially relieved with symptomatic treatment; and severe is discomfort sufficient to reduce or affect normal daily activity considerably; prevents regular activities, and not relieved with symptomatic treatment. Additional description of severity for diarrhea, body temperature, and vomiting is described in the protocol. | up to 1 month after last vaccination (3 months) | 
| Part A: Number of Solicited Reactions | Solicited reactions were collected 1 week after each vaccination. | up to 1 week after each vaccination (at 0, 1, and 2 months) | 
| Part A: Number and Percentage of Subjects With Positive Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Heat Labile Toxin B Subunit (LTB) | Defined as a four-fold rise or greater in geometric mean titer. | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Fold Change in Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Heat Labile Toxin B Subunit (LTB) |  | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Titer of Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Heat Labile Toxin B Subunit (LTB) |  | Pre and day 7 post all vaccinations; day 3 post-vaccination 1 and 2; week 4 post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) | Defined as a four-fold rise or greater in geometric mean titer. | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Fold Change in Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) |  | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Titer of Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) |  | Pre and day 7 post all vaccinations; day 3 post-vaccination 1 and 2; week 4 post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 3 (CS3) | Defined as a four-fold rise or greater in geometric mean titer. | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Fold Change in Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 3 (CS3) |  | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Titer of Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 3 (CS3) |  | Pre all vaccinations; day 3 post-vaccination 1 and 2; day 7 post all vaccinations; 4 weeks post-vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 6 (CS6) | Defined as a four-fold rise or greater in geometric mean titer. | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Fold Change in Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 6 (CS6) |  | Vaccination 1 Day 3 and 7; Vaccination 2 pre-vaccination, Day 3, and Day 7; Vaccination 3 pre-vaccination, Day 7, and Week 4 | 
| Part A: Geometric Mean Titer of Antibody in Lymphocyte Supernatant (ALS) Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 6 (CS6) |  | Pre and day 7 post all vaccinations; day 3 post-vaccination 1 and 2; week 4 post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Heat Labile Toxin B Subunit (LTB) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Antibody in Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Heat Labile Toxin B Subunit (LTB) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Antibody in Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Heat Labile Toxin B Subunit (LTB) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin A (IgA) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Serum ELISA Immunoglobulin A (IgA) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Serum ELISA Immunoglobulin A (IgA) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 3 (CS3) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 3 (CS3) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 3 (CS3) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 6 (CS6) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Antibody in Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 6 (CS6) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Serum ELISA Immunoglobulin A (IgA) Response to E. Coli Surface Antigen 6 (CS6) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Heat Labile Toxin B Subunit (LTB) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Antibody in Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Heat Labile Toxin B Subunit (LTB) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Antibody in Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Heat Labile Toxin B Subunit (LTB) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin G (IgG) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Serum ELISA Immunoglobulin G (IgG) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Serum ELISA Immunoglobulin G (IgG) Response to Enterotoxigenic Escherichia Coli (ETEC) Colonization Factor 1 (CFA/I) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Surface Antigen 3 (CS3) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Surface Antigen 3 (CS3) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Surface Antigen 3 (CS3) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part A: Number and Percentage of Subjects With Positive Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Surface Antigen 6 (CS6) | Defined as a 2.5-fold rise or greater in geometric mean titer. | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Fold Change in Antibody in Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Surface Antigen 6 (CS6) |  | Day 7 post-all vaccinations; pre-vaccination 2 and 3; week 4 post-vaccination 3 | 
| Part A: Geometric Mean Titer of Serum ELISA Immunoglobulin G (IgG) Response to E. Coli Surface Antigen 6 (CS6) |  | Pre and day 7 post all vaccinations; and 4 weeks post vaccination 3 | 
| Part B: Number and Percentage of Subjects Experiencing Severe Diarrhea Following H10407 Challenge Strain | Severe diarrhea was defined as >800 grams of grade 3-5 stools passed over the 120-hour observation period. For episodes starting at or before 120 hours post-challenge, volunteers were followed to resolution and the total stool output weight was considered in determining whether a specific volunteer met the primary definition of severe diarrhea. The end of a diarrheal episode occurred when a volunteer did not pass any grade 3-5 stool in a 24-hour period. Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Part A: Number of Participants Shedding E. Coli on Qualification Plate |  | Pre- and day 7 post-all vaccinations; and Day 3 post-vaccinations 1 and 2; and 4 weeks post vaccination 3 | 
| Part A: Number of Participants With Positive Shedding Results for ACE527 |  | Pre- and day 7 post-all vaccinations; and Day 3 post-vaccinations 1 and 2; and 4 weeks post vaccination 3 | 
| Number of Participants Shedding Vaccine Strains Included in ACE527 |  | 3 days after the first and second vaccinations | 
| Part B: Number and Percentage of Subjects Experiencing Diarrhea of Any Severity | Defined as mild, moderate, or severe diarrhea, specifically: Mild diarrhea: 2 or 3grade 3-5 stools totaling 200 g - 400 g, or 1 grade 3-5 stool of >300 g Moderate diarrhea: 4-5 grade 3-5 stools totaling >200 g or 401 - 800g Severe diarrhea: > 800g grade 3-5 stool(s) Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 
| Part B: Mean Total Weight of Grade 3-5 Stools Passed Per Volunteer | Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 
| Part B: Median Total Weight of Grade 3-5 Stools Passed Per Volunteer | Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 
| Part B: Mean Number of Grade 3-5 Stools Passed Per Volunteer | Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 
| Part B: Median Number of Grade 3-5 Stools Passed Per Volunteer | Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 
| Part B: Number of Subjects Experiencing Solicited Reactions Graded as Moderate or Severe | Solicited reactions were generally graded as mild if there was discomfort, but no disruption of normal daily activities; moderate if if discomfort was sufficient to affect normal daily activity and partially relieved with symptomatic treatment; severe if discomfort was sufficient to affect normal daily activity considerably, prevent regular activity, and not relieved with symptomatic treatment. | 1 week | 
| Part B: Number and Percentage of Subjects Who Would Have Reduced Daily Activity | When asking about adverse events, subjects were asked whether their illness resulting from ETEC would have reduced their daily activity because of their illness if they had been vacationing or traveling on business. | 5 days | 
| Part B: Mean Time to Onset of Diarrhea Among Subjects Who Had Diarrhea | Defined as mild, moderate, or severe diarrhea, specifically: Mild diarrhea: 2 or 3grade 3-5 stools totaling 200 g - 400 g, or 1 grade 3-5 stool of >300 g Moderate diarrhea: 4-5 grade 3-5 stools totaling >200 g or 401 - 800g Severe diarrhea: > 800g grade 3-5 stool(s) Grades were defined as follows: Grade 1: firm, formed (normal) Grade 2: soft, formed (normal) Grade 3: viscous opaque liquid or semi-liquid which assumes the shape of the container Grade 4: watery, non-viscous, opaque liquid which assumes the shape of the container Grade 5: clear or translucent, watery or mucoid liquid which assumes the shape of the container | 5 days | 
| Part B: Quantity of H10407 Per Gram of Stool on Day 2 Post-challenge |  | 2 days after vaccination | 
| Part B: Number of Subjects Requiring Early Antibiotic Treatment and Intravenous (IV) Fluids |  | 5 days |