# Functions of human C. difficile-specific memory B cell-derived monoclonal antibodies

> **NIH NIH U19** · UNIVERSITY OF OKLAHOMA HLTH SCIENCES CTR · 2024 · $429,723

## Abstract

PROJECT SUMMARY / ABSTRACT (Project 2)
Clostridioides difficile disease recurrence is a serious problem because severity increases with each round of
infection and converts a regional enteric disease into a systemic fatal disease. We lack a good understanding
of the immune response to infection, which arguably is lacking or mis-directed, as evidenced by recurrent
infection. Serum IgG antibodies (Abs) that neutralize toxin B secreted by C. difficile (TcdB) is the best correlate
of protection. Ideally, infection would stimulate primary toxin-neutralizing Ab responses as well as induce toxin-
specific memory B cells (Bmem) that can respond rapidly to the pathogen and generate new Ab-secreting cells.
However, in mouse models and in analysis of human Bmem, infection results in a response which is dominated
by IgM+ cells, although some IgG+ and IgA+ cells are evident. Isolation and single cell barcoding of human TcdB-
specific Bmem followed by sequencing and repertoire analysis revealed that IgG+ and IgA+ cells had undergone
somatic hypermutation and had breadth of variable gene usage, representing several unique B cell clones.
Production of monoclonal Abs (mAbs) from selected IgG1 gene sequences revealed moderate affinity for TcdB
and poor TcdB neutralization in one in vitro assay. This work has guided us to a hypothesis that TcdB-specific
IgG and IgA encoded by the C. difficile-induced human B cell memory compartment have variable
capacity for toxin-neutralization. In Specific Aim 1 we will measure the impact of TcdB-specific Bmem-derived
mAbs on the mechanisms of host cell intoxication. We will produce mAbs from gene sequences in our database
and recruit new volunteers to expand the number of Bmem-repertoires. We will determine the impact of Bmem-
derived mAbs on the mechanisms controlling host cell intoxication and provide a comprehensive view of the
functions of human Bmem cell-encoded TcdB-specific Abs in individuals following C. difficile infection. In Specific
Aim 2: We will test the ability of Bmem cell-derived mAbs to protect against a live pathogen challenge and
determine mechanism of transport to the gut. We showed that the neonatal Fc receptor (FcRn) was required for
delivery of immunization-induced circulating IgG to the gut and protection against C. difficile, whereas
intraperitoneal delivery to recipient mice bypassed the FcRn requirement . We will deliver intraperitoneal mAb to
B6 mice to determine if human Bmem-derived mAbs are protective in vivo. We will use FcRn-/- mice expressing
the human FcRn and accessory molecule β2 microglobulin (hβ2M) transgenes (hFcRn:hβ2M ) to determine
hFcRn dependence for protection by circulating mAb. Aim 2 will provide critical data on whether Bmem-encoded
mAbs are protective in vivo and determine how they reach the gut. Project 2 has a high degree of relevance to
public health. Our current understanding of the humoral immune response to C. difficile in human subjects lacks
the necessary mechanistic ins...

## Key facts

- **NIH application ID:** 10892828
- **Project number:** 5U19AI174994-02
- **Recipient organization:** UNIVERSITY OF OKLAHOMA HLTH SCIENCES CTR
- **Principal Investigator:** Mark L Lang
- **Activity code:** U19 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $429,723
- **Award type:** 5
- **Project period:** 2023-07-25 → 2028-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10892828

## Citation

> US National Institutes of Health, RePORTER application 10892828, Functions of human C. difficile-specific memory B cell-derived monoclonal antibodies (5U19AI174994-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10892828. Licensed CC0.

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