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. 2023 Nov 2;11(11):2689.
doi: 10.3390/microorganisms11112689.

A First in Human Clinical Trial Assessing the Safety and Immunogenicity of Two Intradermally Delivered Enterotoxigenic Escherichia coli CFA/I Fimbrial Tip Adhesin Antigens with and without Heat-Labile Enterotoxin with Mutation LT(R192G)

Ramiro L Gutiérrez  1 , Mark S Riddle  1 , Chad K Porter  1   2 , Milton Maciel Jr  1   2   3 , Steven T Poole  1   3 , Renee M Laird  1   3 , Michelle Lane  1 , George W Turiansky  2 , Abel Jarell  4 , Stephen J Savarino  1   2
Affiliations

A First in Human Clinical Trial Assessing the Safety and Immunogenicity of Two Intradermally Delivered Enterotoxigenic Escherichia coli CFA/I Fimbrial Tip Adhesin Antigens with and without Heat-Labile Enterotoxin with Mutation LT(R192G)

Ramiro L Gutiérrez et al. Microorganisms. .

Abstract

Introduction: Enterotoxigenic E. coli (ETEC) is a leading cause of diarrhea in travelers as well as for children living in low- to middle-income countries. ETEC adhere to intestinal epithelium via colonization factors (CFs). CFA/I, a common CF, is composed of a polymeric stalk and a tip-localized minor adhesive subunit, CfaE. Vaccine delivery by the transcutaneous immunization of dscCfaE was safe but was poorly immunogenic in a phase 1 trial when administered to volunteers with LTR(192G) and mLT. To potentially enhance the immunogenicity of CfaE while still delivering via a cutaneous route, we evaluated the safety and immunogenicity of two CfaE constructs administered intradermally (ID) with or without mLT.

Methods: CfaE was evaluated as a donor strand-complemented construct (dscCfaE) and as a chimeric construct (Chimera) in which dscCfaE replaces the A1 domain of the cholera toxin A subunit and assembles non-covalently with the pentamer of heat-labile toxin B (LTB). Subjects received three ID vaccinations three weeks apart with either dscCfaE (1, 5, and 25 µg) or Chimera (2.6 and 12.9 µg) with and without 0.1 µg of mLT. Subjects were monitored for local and systemic adverse events. Immunogenicity was evaluated by serum and antibody-secreting cell (ASC) responses.

Results: The vaccine was well-tolerated with predominantly mild and moderate local vaccine site reactions characterized by erythema, induration and post-inflammatory hyperpigmentation. High rates of serologic and ASC responses were seen across study groups with the most robust responses observed in subjects receiving 25 µg of dscCfaE with 0.1 mcg of LT(R192G).

Conclusion: Both ETEC adhesin vaccine prototypes were safe and immunogenic when co-administered with mLT by the ID route. The observed immune responses induced with the high dose of dscCfaE and mLT warrant further assessment in a controlled human infection model.

Keywords: enterotoxigenic E. coli; immunogenicity; intradermal; vaccine.

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Conflict of interest statement

The views expressed in this article reflect the results of research conducted by the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. nor the U.S. Government. There are no restrictions on its use. This article was prepared while M. Maciel, Jr. and S. T. Poole were employed at the Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. for the U.S. Military ETEC Vaccine Research Program. The opinions expressed in this article are the authors’ own and do not reflect the view of the National Institutes of Health, the Department of Health and Human Services, or the United States government. There were no financial conflict of interest among any of the authors. Authors are military service members (or employees of the U.S. Government). This work was prepared as part of official duties. Title 17 U.S.C. §105 provides that ‘Copyright protection under this title is not available for any work of the United States Government.’ Title 17 U.S.C. §101 defines a U.S. Government work as a work prepared by a military service member or employee of the U.S. Government as part of that person’s official duties.

Figures

Figure 1
Figure 1
Study subject enrollment flow diagram. Footnote: Reasons for exclusion: chronic medical condition and/or abnormalities on physical exam (n = 6); participation in another study (n = 1); travel to ETEC endemic area (n = 9); clinically significant lab abnormalities (n = 15); multiple exclusion criteria (n = 6); eligible but did not participate (n = 12).
Figure 2
Figure 2
Serologic responses to CfaE (2A: IgG; 2B: IgA) and LT (2C: IgG; 2D: IgA) by study group throughout the vaccination and follow-up period. Serum IgG responses to CfaE (A); serum IgG responses to LT (B); serum IgA responses to CfaE (C); serum IgA responses to LT (D). Footnote: Endpoint titers are presented on a log scale as the mean with standard error. Subjects were vaccinated on study days 0, 21 and 42 and only those subjects receiving at least two vaccine doses are included.
Figure 3
Figure 3
Maximum number of post-vaccination antibody-secreting cells (ASCs) to CfaE (3A: IgG; 3B: IgA) and LT (3C: IgG; 3D: IgA) per 106 peripheral blood mononuclear cells (PBMCs). IgG ASC responses to CfaE (A); IgG ASC responses to LT (B); IgA ASC responses to CfaE (C); IgA ASC responses to LT (D). Footnote: The maximum number of antibody-secreting cells (ASCs) post-vaccination is reported with accompanying box and whisker plots where the mid-line in the box represents the median, the top and bottom of the box represent the 1st and 3rd quartiles, respectively, and the whiskers extend to 1.5xIQR (interquartile range). Subjects were vaccinated on study days 0, 21 and 42, and only those subjects receiving at least two vaccine doses are included. ASC samples were collected at baseline and seven days after each vaccination.
Figure 4
Figure 4
Hemagglutination inhibition (HAI) from serum samples by study group throughout the vaccination and follow-up period. Footnote: Each sample was tested in duplicate, and the HAI titer was expressed as the average of the reciprocal of the highest serum dilution that completely inhibited MRHA. Data are presented on a log scale as the mean with standard error. Subjects were vaccinated on study days 0, 21 and 42 and only those subjects receiving at least two vaccine doses are included.
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