# Project 1: Mucosal toxin subunit immunization as a strategy for C. difficile vaccine development

> **NIH NIH U19** · VANDERBILT UNIVERSITY MEDICAL CENTER · 2024 · $255,771

## Abstract

PROJECT 1 SUMMARY
Clostridioides difficile is a spore-forming anaerobic bacterium that is the leading cause of
hospital-acquired gastrointestinal infection in the United States.
Elderly people who have been
treated with broad spectrum antibiotics are at greatest risk for infection, although reports of
community-acquired infections in young adults are increasing. Clinically, C. difficile infection (CDI)
presents as mild to severe diarrhea and can often recur with worsening outcomes. The symptoms
result from the activity of one or more of the large toxins secreted by C. difficile: TcdA, TcdB, and
CDT (binary toxin). High serum levels of antibodies against TcdA have been linked to
asymptomatic carriage of the organism, and an acquired TcdA or TcdB immune response reduces
the risk of recurrence. These data provide the rationale for developing a toxin-based C. difficile
vaccine. While a recently completed clinical trial from Pfizer using a TcdA/TcdB toxoid did not
meet its primary endpoint, there were promising secondary indicators that suggest opportunities
for improvement in the next iteration. Project 1 will define toxin antigens that elicit robust mucosal
immune responses in humans and in mice. Our first objective will be to define the epitopes of
TcdA, TcdB, and CDT that provide effective and broadly neutralizing IgA, secreted IgA (sIgA),
and IgG responses in humans (Aim 1),
incorporating current information on TcdB sequence
diversity across C. difficile strains.
Purified monoclonal antibodies will be produced based on high-
throughput sequence analysis of toxin-specific B cell receptors from human clinical samples. The
antibodies will be evaluated for toxin binding and neutralization, and the epitopes associated with
broad, potent neutralization will be defined using cryo-electron microscopy (cryo-EM). This aim
will culminate in the creation of toxin subunits that will be evaluated for sIgA responses in patient
saliva samples. The second aim will evaluate variants of TcdA, TcdB, and CDT as immunogens
and the impact of specific toxin domains in generating protective immunity. The experimental
workflow involves a systematic approach to evaluating the potential benefits of a rectal
immunization method in the generation of robust mucosal immunity against the toxins. It will
establish an immunization regimen that can be used to evaluate defined toxin subunits and the
novel non-toxin antigens that emerge from Project 2. Finally, immunization strategies that promote
durable protection will be used to study the correlates of protection, specifically, the mucosal T
cell populations that promote robust and durable immunological memory.

## Key facts

- **NIH application ID:** 10800733
- **Project number:** 5U19AI174999-02
- **Recipient organization:** VANDERBILT UNIVERSITY MEDICAL CENTER
- **Principal Investigator:** Dana Borden Lacy
- **Activity code:** U19 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $255,771
- **Award type:** 5
- **Project period:** 2023-03-03 → 2028-02-29

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10800733

## Citation

> US National Institutes of Health, RePORTER application 10800733, Project 1: Mucosal toxin subunit immunization as a strategy for C. difficile vaccine development (5U19AI174999-02). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10800733. Licensed CC0.

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