Dose Escalating Study of a Prototype CS6 Subunit Vaccine With a Modified Heat-labile Enterotoxin From Enterotoxigenic Escherichia Coli (ETEC)

This is an open-label clinical trial in which a total of 50 participants will receive three injections of either CssBA alone, dmLT alone or CssBA + dmLT. The vaccine will be administered via IM injection to alternating deltoid regions on days 1, 22, and 43. Each participant will receive the same dose at each vaccination dependent upon group assignment. Group A is considered a pilot group in which all 3 doses will be administered and participants monitored for safety 7 days after the third vaccination, prior to the enrollment of participants in Group B.

• CssBA (Biological), also known as spd_dsc16Bntd14CssBAB7A[His]₆: Recombinant enterotoxigenic Escherichia coli (ETEC) surface antigen 6 containing modified structural subunits A and B
• dmLT (Biological): Escherichia coli double mutant heat-labile toxin with mutations at amino acids 192 and 211

Primary outcomes

• Number of Participants With Solicited Adverse Events [From first vaccination to 28 days after the third vaccination, 71 days.]: Solicited adverse events included vaccine site pain, vaccine site pruritus, vaccine site rash/eruption, vaccine site swelling, vaccine site tenderness, fever, headache, diarrhea, arthralgia, myalgia, malaise, nausea, and vomiting. Adverse events were assessed for severity by the investigator according to the following: Mild (Grade 1): Does not interfere with routine activities, minimal level of discomfort Moderate (Grade 2): Interferes with routine activities, moderate level of discomfort Severe (Grade 3): Unable to perform routine activities, significant level of discomfort Potentially life-threatening (Grade 4): Hospitalization or emergency room (ER) visit for potentially life-threatening event
• Number of Participants With Unsolicited Adverse Events [From first vaccination to 28 days after the third vaccination, 71 days.]: Adverse events were assessed for severity by the investigator according to the following: Mild (Grade 1): Does not interfere with routine activities Minimal level of discomfort Moderate (Grade 2): Interferes with routine activities Moderate level of discomfort Severe (Grade 3): Unable to perform routine activities Significant level of discomfort Potentially life-threatening (Grade 4): Hospitalization or emergency room (ER) visit for potentially life-threatening event

Secondary outcomes

• Percentage of Participants With a Serum Immunologic Response to Coli Surface Antigen 6 (CS6) [Baseline (Day 1 predose), Days 22 and 43 predose, and Day 70]: Serum samples were assayed for immunoglobulin G (IgG) and immunoglobulin A (IgA) antibody titers against CS6 using an enzyme-linked Immunosorbent assay (ELISA). Immunologic response was defined as a ≥ 4-fold increase in reciprocal endpoint titer between Baseline and any post-vaccination sample.
• Percentage of Participants With a Serum Immunologic Response to Labile Toxin [Baseline (Day 1 predose), Days 22 and 43 predose, and Day 70]: Serum samples were assayed for immunoglobulin G (IgG) and immunoglobulin A (IgA) antibody titers against labile toxin using an enzyme-linked Immunosorbent assay (ELISA). Immunologic response was defined as a ≥ 4-fold increase in reciprocal endpoint titer between Baseline and any post-vaccination sample.
• Percentage of Participants With a Mucosal Immunologic Response to Coli Surface Antigen 6 (CS6) [Baseline (Day 1 pre-dose), Days 8 and 29 predose, and Day 50]: Peripheral blood mononuclear cells (PBMCs) were collected to determine antibody responses from lymphocyte supernatant against CS6 at Baseline and 7 days after each vaccination. Antibody in lymphocyte supernatant (ALS) is an indirect quantification of antibody secreting cells (ASC) activated in the mucosa that circulate in the peripheral blood about seven days post-mucosal immunization/infection. After incubation, lymphocyte supernatant was assayed for antigen-specific IgG and IgA antibodies using ELISA. A positive ALS response was defined as a four-fold rise in antibody titers between Baseline and any post vaccination sample.
• Percentage of Participants With a Mucosal Immunologic Response to Labile Toxin [Baseline (Day 1 pre-dose), Days 8 and 29 predose, and Day 50]: Peripheral blood mononuclear cells (PBMCs) were collected to determine antibody responses from lymphocyte supernatant against labile toxin at Baseline and 7 days after each vaccination. Antibody in lymphocyte supernatant (ALS) is an indirect quantification of antibody secreting cells (ASC) activated in the mucosa that circulate in the peripheral blood about seven days post-mucosal immunization/infection. After incubation, lymphocyte supernatant was assayed for antigen-specific IgG and IgA antibodies using ELISA. A positive ALS response was defined as a four-fold rise in antibody titers between Baseline and any post vaccination sample.
• Geometric Mean Titer of Serum Anti-CS6 Immunoglobulin G Antibodies [Days 1, 22, and 43 pre-vaccination, and Day 70]: Serum samples were assayed for IgG antibody titers against CS6 using an enzyme-linked Immunosorbent assay (ELISA).
• Geometric Mean Titer of Serum Anti-CS6 Immunoglobulin A Antibodies [Days 1, 22, and 43 pre-vaccination, and Day 70]: Serum samples were assayed for IgA antibody titers against CS6 using an enzyme-linked Immunosorbent assay (ELISA).
• Geometric Mean Titer of Serum Anti-LT Immunoglobulin G Antibodies [Days 1, 22, and 43 pre-vaccination, and Day 70]: Serum samples were assayed for IgG antibody titers against labile toxin using an enzyme-linked Immunosorbent assay (ELISA).
• Geometric Mean Titer of Serum Anti-LT Immunoglobulin A Antibodies [Days 1, 22, and 43 pre-vaccination, and Day 70]: Serum samples were assayed for IgA antibody titers against labile toxin using an enzyme-linked Immunosorbent assay (ELISA).
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-CS6 Immunoglobulin G Antibodies [Days 1, 8, 29 and 50]: Lymphocyte supernatant was assayed for IgG antibody titers against CS6 using ELISA.
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-CS6 Immunoglobulin A Antibodies [Days 1, 8, 29, and 50]: Lymphocyte supernatant was assayed for IgA antibody titers against CS6 using ELISA.
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-LT Immunoglobulin G Antibodies [Days 1, 8, 29, and 50]: Lymphocyte supernatant was assayed for IgG antibody titers against labile toxin using ELISA.
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-LT Immunoglobulin A Antibodies [Days 1, 8, 29, and 50]: Lymphocyte supernatant was assayed for IgA antibody titers against labile toxin using ELISA.

Sex: All, ages: 18 Years to 45 Years, accepts healthy volunteers

Inclusion Criteria:

1. Healthy, adult, male or female, age 18 to 45 years (inclusive) at the time of enrollment.
2. Completion and review of comprehension test (achieved > 70% accuracy).
3. Signed informed consent document.
4. Available for the required follow-up period and scheduled clinic visits.
5. Women: Negative pregnancy test with understanding (through informed consent process) to not become pregnant during the study or within three (3) months following last vaccination.

Exclusion Criteria:

1. Health problems (for example, intercurrent febrile illness, chronic medical conditions such as psychiatric conditions, diabetes mellitus, hypertension or any other condition that might place the subject at increased risk of adverse events) - study clinicians, in consultation with the PI, will use clinical judgment on a case-by-case basis to assess safety risks under this criterion. The PI will consult with the Research Monitor as appropriate.
2. Clinically significant abnormalities on physical examination.
3. Immunosuppressive drugs (use of systemic corticosteroids or chemotherapeutics that may influence antibody development) or illness (including immunoglobulin A \[IgA\] deficiency, defined by serum IgA < 7 mg/dL).
4. Women who are pregnant or planning to become pregnant during the study period plus three (3) months beyond the last received dose and currently nursing women.
5. Participation in research involving another investigational product (defined as receipt of investigational product or exposure to invasive investigational device) 30 days before planned date of first vaccination or anytime through the last study safety visit.
6. Positive blood test for Hepatitis B surface antigen (HBsAg), Hepatitis C virus (HCV), human immunodeficiency virus (HIV)-1/2.
7. Clinically significant abnormalities on basic laboratory screening.
8. Exclusionary skin disease history/findings that would confound assessment or prevent appropriate local monitoring of adverse events (AEs), or possibly increase the risk of a local AE
9. History of chronic skin disease (clinician judgement)
10. Acute skin infection/eruptions on the upper arms including fungal infections, severe acne or active contact dermatitis
11. Allergies that may increase the risk of AEs
12. Regular use (weekly or more often) of antidiarrheal, anti-constipation, or antacid therapy
13. Abnormal stool pattern (fewer than 3 stools per week or more than 3 stools per day) on a regular basis; loose or liquid stools on other than an occasional basis
14. History of microbiologically confirmed ETEC or cholera infection in the last 3 years
15. Travel to countries where ETEC or V. cholerae or other enteric infections are endemic (most of the developing world) within 3 years prior to dosing (clinician judgement)
16. Symptoms consistent with Travelers' Diarrhea or concurrent with travel to countries where ETEC infection is endemic (most of the developing world) within 3 years prior to dosing, OR planned travel to endemic countries during the length of the study
17. Vaccination for or ingestion of ETEC, cholera, or E. coli heat labile toxin within 3 years prior to dosing
18. Occupation involving handling of ETEC or V. cholerae currently, or in the past 3 years

Participant flow

Outcome results

• Number of Participants With Solicited Adverse Events (Primary), Count of participants, Participants: Group A1: CssBA 5 µg 2; Group A2: DmLT 100 ng 5; Group B: CssBA 5 µg + DmLT 100 ng 9; Group C: CssBA 5 µg + DmLT 500 ng 9; Group D: CssBA 15 µg + DmLT 500 ng 10; Group E: CssBA 45 µg + DmLT 500 ng 10
• Percentage of Participants With a Serum Immunologic Response to Coli Surface Antigen 6 (CS6) (Secondary), Number, percentage of participants: Group A1: CssBA 5 µg 0.0; Group A2: DmLT 100 ng 0.0; Group B: CssBA 5 µg + DmLT 100 ng 0.0; Group C: CssBA 5 µg + DmLT 500 ng 44.4; Group D: CssBA 15 µg + DmLT 500 ng 30.0; Group E: CssBA 45 µg + DmLT 500 ng 50.0
• Percentage of Participants With a Serum Immunologic Response to Labile Toxin (Secondary), Number, percentage of participants: Group A1: CssBA 5 µg 0.0; Group A2: DmLT 100 ng 50.0; Group B: CssBA 5 µg + DmLT 100 ng 22.2; Group C: CssBA 5 µg + DmLT 500 ng 77.8; Group D: CssBA 15 µg + DmLT 500 ng 50.0; Group E: CssBA 45 µg + DmLT 500 ng 70.0
• Percentage of Participants With a Mucosal Immunologic Response to Coli Surface Antigen 6 (CS6) (Secondary), Number, percentage of participants: Group A1: CssBA 5 µg 0.0; Group A2: DmLT 100 ng 0.0; Group B: CssBA 5 µg + DmLT 100 ng 33.3; Group C: CssBA 5 µg + DmLT 500 ng 88.9; Group D: CssBA 15 µg + DmLT 500 ng 80.0; Group E: CssBA 45 µg + DmLT 500 ng 100.0
• Percentage of Participants With a Mucosal Immunologic Response to Labile Toxin (Secondary), Number, percentage of participants: Group A1: CssBA 5 µg 0.0; Group A2: DmLT 100 ng 100.0; Group B: CssBA 5 µg + DmLT 100 ng 22.2; Group C: CssBA 5 µg + DmLT 500 ng 77.8; Group D: CssBA 15 µg + DmLT 500 ng 90.0; Group E: CssBA 45 µg + DmLT 500 ng 100.0
• Geometric Mean Titer of Serum Anti-CS6 Immunoglobulin G Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 39.0 (18.2 to 83.6); Group A2: DmLT 100 ng 29.6 (17.5 to 50.1); Group B: CssBA 5 µg + DmLT 100 ng 39.1 (22.2 to 69.1); Group C: CssBA 5 µg + DmLT 500 ng 36.9 (20.5 to 66.6); Group D: CssBA 15 µg + DmLT 500 ng 40.5 (24.6 to 66.7); Group E: CssBA 45 µg + DmLT 500 ng 51.5 (26.1 to 101.4)
• Geometric Mean Titer of Serum Anti-CS6 Immunoglobulin A Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 269.9 (133.6 to 545.1); Group A2: DmLT 100 ng 213.4 (73.0 to 623.6); Group B: CssBA 5 µg + DmLT 100 ng 308.5 (181.4 to 524.4); Group C: CssBA 5 µg + DmLT 500 ng 330.0 (176.1 to 618.6); Group D: CssBA 15 µg + DmLT 500 ng 368.2 (192.3 to 705.0); Group E: CssBA 45 µg + DmLT 500 ng 370.8 (180.9 to 760.0)
• Number of Participants With Unsolicited Adverse Events (Primary), Count of participants, Participants: Group A1: CssBA 5 µg 4; Group A2: DmLT 100 ng 3; Group B: CssBA 5 µg + DmLT 100 ng 5; Group C: CssBA 5 µg + DmLT 500 ng 6; Group D: CssBA 15 µg + DmLT 500 ng 10; Group E: CssBA 45 µg + DmLT 500 ng 9
• Geometric Mean Titer of Serum Anti-LT Immunoglobulin G Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 46.1 (16.4 to 129.7); Group A2: DmLT 100 ng 25.1 (NA to NA); Group B: CssBA 5 µg + DmLT 100 ng 84.5 (31.8 to 224.0); Group C: CssBA 5 µg + DmLT 500 ng 88.9 (54.0 to 146.5); Group D: CssBA 15 µg + DmLT 500 ng 75.0 (37.4 to 150.4); Group E: CssBA 45 µg + DmLT 500 ng 48.8 (25.0 to 95.2)
• Geometric Mean Titer of Serum Anti-LT Immunoglobulin A Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 25.1 (NA to NA); Group A2: DmLT 100 ng 25.1 (NA to NA); Group B: CssBA 5 µg + DmLT 100 ng 28.4 (21.4 to 37.7); Group C: CssBA 5 µg + DmLT 500 ng 25.8 (24.2 to 27.6); Group D: CssBA 15 µg + DmLT 500 ng 28.6 (21.3 to 38.5); Group E: CssBA 45 µg + DmLT 500 ng 25.1 (NA to NA)
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-CS6 Immunoglobulin G Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 4.0 (NA to NA); Group A2: DmLT 100 ng 4.0 (NA to NA); Group B: CssBA 5 µg + DmLT 100 ng 4.0 (NA to NA); Group C: CssBA 5 µg + DmLT 500 ng 5.7 (2.5 to 12.8); Group D: CssBA 15 µg + DmLT 500 ng 4. (NA to NA); Group E: CssBA 45 µg + DmLT 500 ng 4.0 (NA to NA)
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-CS6 Immunoglobulin A Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 2.5 (NA to NA); Group A2: DmLT 100 ng 2.5 (NA to NA); Group B: CssBA 5 µg + DmLT 100 ng 2.5 (NA to NA); Group C: CssBA 5 µg + DmLT 500 ng 2.5 (NA to NA); Group D: CssBA 15 µg + DmLT 500 ng 2.5 (NA to NA); Group E: CssBA 45 µg + DmLT 500 ng 2.5 (2.5 to 2.5)
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-LT Immunoglobulin G Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 2.5 (NA to NA); Group A2: DmLT 100 ng 2.5 (NA to NA); Group B: CssBA 5 µg + DmLT 100 ng 3.5 (1.6 to 7.8); Group C: CssBA 5 µg + DmLT 500 ng 2.5 (NA to NA); Group D: CssBA 15 µg + DmLT 500 ng 3.1 (2.0 to 4.8); Group E: CssBA 45 µg + DmLT 500 ng 2.5 (NA to NA)
• Geometric Mean Titer of Antibody Lymphocyte Supernatant Anti-LT Immunoglobulin A Antibodies (Secondary), Geometric mean, titer: Group A1: CssBA 5 µg 2.0 (NA to NA); Group A2: DmLT 100 ng 2.0 (NA to NA); Group B: CssBA 5 µg + DmLT 100 ng 2.0 (NA to NA); Group C: CssBA 5 µg + DmLT 500 ng 2.8 (1.3 to 5.9); Group D: CssBA 15 µg + DmLT 500 ng 2.0 (NA to NA); Group E: CssBA 45 µg + DmLT 500 ng 2.0 (NA to NA)

Adverse events

Time frame: From the day of the first vaccination up to 28 days after the third vaccination, 71 days.

Other adverse events by term

• Study Protocol (PDF, 2018-08-31)
• Statistical Analysis Plan (PDF, 2019-02-25)

• Tida K Lee, MD, PhD, Principal investigator, Naval Medical Research Center