# Developing broad-spectrum therapeutics against C. difficile toxins

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA-IRVINE · 2022 · $779,693

## Abstract

Project Summary
Clostridioides difficile (C. difficile) is a major opportunistic pathogen that colonizes the colon when normal gut
microbiota is disrupted. The large protein toxin TcdB is a major virulence factor responsible for diseases
associated with C. difficile infection (CDI). However, prior efforts to develop neutralizing monoclonal antibodies
and vaccines against TcdB have yielded unexpectedly low efficacy or even failure. We believe that a key
weakness of these previous studies might be the complexity of toxin variations seen clinically. While a single
toxin sequence from a reference strain has been widely used in all previous therapeutic development,
sequencing TcdB in clinical isolates in recent years has revealed a growing number of C. difficile strains as well
as variations in toxin sequences. This may account for the reduced neutralization efficacy of the only FDA-
approved monoclonal antibody, bezlotoxumab, against some TcdB variants such as the one produced by a
hypervirulent strain (ribotype 027). The sequence variation and the toxin’s large size (~270 kDa) also pose
daunting challenges to develop effective vaccines using the traditional toxoid approach. Building on our recent
progress in identification of toxin receptors and understanding the structure and function of TcdB, here we
propose to develop receptor-decoy-based therapeutic proteins as broad-spectrum antitoxins and a new
generation of epitope-focused fragment-based vaccines, which could provide effective protection against most
of the known TcdB variants. Frizzled proteins (FZDs) and CSPG4 are two major host receptors for TcdB, and
we previously have revealed the mechanism by which TcdB recognizes FZDs. The first aim in this project is to
establish a structural understanding of TcdB binding to CSPG4. Our second aim will focus on design and
characterization of a family of bi-specific receptor-decoy proteins, which are composed of the optimized TcdB-
binding fragments of CSPG4 and FZDs. In the third aim, we will take advantage of our knowledge of the
structures of TcdB holotoxin, TcdB–antibody complexes, and TcdB–receptor complexes to design candidate
vaccines based on the selected highly conserved and functionally critical TcdB fragments. This project is built
on long-standing productive collaborations between the Jin lab and the Dong lab, combining their highly
complementary expertise in structural biology and protein engineering (Jin lab) and TcdB receptors/CDI
pathogenesis/animal models (Dong lab). Successful completion of this project will provide prototypes of
antitoxins for immunoprophylactic therapy and broad-spectrum candidate vaccines that offer prophylactic and
long-lasting protection.

## Key facts

- **NIH application ID:** 10348784
- **Project number:** 5R01AI158503-02
- **Recipient organization:** UNIVERSITY OF CALIFORNIA-IRVINE
- **Principal Investigator:** Rongsheng Jin
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $779,693
- **Award type:** 5
- **Project period:** 2021-02-11 → 2026-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10348784

## Citation

> US National Institutes of Health, RePORTER application 10348784, Developing broad-spectrum therapeutics against C. difficile toxins (5R01AI158503-02). Retrieved via AI Analytics 2026-05-21 from https://api.ai-analytics.org/grant/nih/10348784. Licensed CC0.

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