A new human challenge model for testing heat-stable toxin-based vaccine candidates for enterotoxigenic Escherichia coli diarrhea - dose optimization, clinical outcomes, and CD4+ T cell responses

Abstract

ClinicalTrials.gov ClinicalTrials.gov, Project ID: NCT02870751.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1. Flow diagram.

CONSORT flow diagram as applies for human challenge studies. In total 22 adult volunteers were assessed for eligibility, and 1 volunteer did not meet the inclusion criteria, resulting in a total of 21 volunteers allocated to experimental infection with different doses of ETEC: 1×106 (n = 3), 1×107 (n = 3), 1×108 (n = 3), 1×109 (n = 3) and 1×1010 (n = 9) CFU. Clinical data were analyzed for all volunteers, as well as the immunological data on day 10 and day 28 after experimental infection. There were none lost to follow-up, however, immunological data from 6 months, 1 year and 2 years after experimental infection were obtained from subgroups of the study population due to limited availability of personnel to perform the analyses.

Fig 2. Antigen-specific CD4+ T cell responses after infection with STh-only ETEC strain TW10722.

The graph displays the mean percentage of CD4+ T cells that co-express CS25 and CD134 for each sampling timepoint and virulence factor after incubating whole blood with ETEC proteins CS6A, CS5 and YghJ. Grey circles represent volunteers in the 1×106 to 1×109 CFU dose groups, red circles represent volunteers in the 1×1010 CFU dose group. Error bars represent the 95% confidence intervals. Due to limited availibility of purified CS6 antigen in the initial parts of the study, CS6-specific CD4+ T cell responses were only measured for a subgroup of the volunteers (n = 12). Also, due to the stepwise inclusion of volunteers to the study, the long-term follow-up timepoints of each volunteer varied according to time of enrollment, with the first subgroup of volunteers (n = 9) having their follow-up at 2 years, while the last subgroup of volunteers (n = 12) had their follow-up at 6 months and 1 year after experimental infection. Abbreviations: d0: day 0, d10: day 10, d28: day 28, m6: 6 months, y1: 1 year, y2: 2 years, N: Number of volunteers, Stim: Antigen used for stimulation. a Antigen preparation differed from other timepoints.

Fig 3. Antigen-specific serum IgG and IgA responses after infection with STh-only ETEC strain TW10722.

The graphs display the median fluorescence intensity (MFI) value of CS5-, CS6AB-, and YghJ-specific IgG and IgA at each sampling time point for each volunteer. Grey circles represent volunteers in the 1×106 to 1×109 CFU dose groups, red circles represent volunteers in the 1×1010 CFU dose group. Error bars represent the 95% confidence intervals. Number of volunteers indicated in parentheses. Abbreviations: d0: day 0, d10: day 10, d28: day 28, m6: 6 months, y2: 2 years.