# Project 1 - Examining the impact of microbial dynamics on B cells responsible for anti-blood group antibody formation

> **NIH NIH P01** · BRIGHAM AND WOMEN'S HOSPITAL · 2024 · $432,332

## Abstract

SUMMARY: Despite being the first human polymorphisms described, ABO(H) blood group antigens and
corresponding anti-ABO(H) antibodies continue to be the most common immunological barrier to transfusion and
transplantation. Remarkably, however, the factors responsible for generating anti-ABO(H) antibodies capable of
causing a hemolytic transfusion reaction (HTR) remain relatively unknown. Our long-term goal is to identify the
key factors responsible for the development of anti-ABO(H) antibodies. Our central hypothesis is that a distinct
developmental window exists in which host innate-like B1 B cells are uniquely sensitive to stimulation by ABO
blood group decorated microbes (BG+ microbes) and that continual exposure to BG+ microbes is required for
sustained anti-blood group antibody production. As ABO(H) blood group antigens (hereafter referred to as BG)
are carbohydrate structures that, as polymorphisms, are largely confined to humans, preclinical models capable
of defining factors that influence anti-BG antibody formation have not been available. To address this, we
generated a novel preclinical model by genetic removal of the enzyme required for murine blood group B-like
antigen (murine B or Bm) synthesis, to generate blood group O-like (murine O or Om) mice. Om mice
spontaneously develop varying levels of anti-Bm antibodies, where antibodies levels correlate with their ability to
induce hemolytic transfusion reactions (HTRs). Anti-Bm antibodies eluted from Bm RBCs recognize distinct
microbiota and isolation of anti-Bm antibody reactive microbiota identified a strain of Klebsiella pneumoniae that
specifically expresses the Bm antigen, suggesting a microbial influence on anti-Bm antibody formation. Consistent
with this, exposure of Om recipients with undetectable anti-Bm antibodies to Bm+ K. pneumoniae induced anti-Bm
antibodies that can cause HTRs. However, robust anti-Bm antibody formation only occurred following Bm+ K.
pneumoniae exposure within the first month of life, while sustained anti-Bm antibody formation required continual
microbial colonization. These results suggest that distinct B1 B cell populations, which are uniquely sensitive to
early developmental cues, may be responsible for anti-Bm antibody formation. Consistent with this, Bm+ K.
pneumoniae exposure increased Bm specific B1 B cells, a B cell population that undergoes unique developmental
programs early in life. The possible role of B1 B cells is not unique to this model, as ABO(H) specific B1 B cells
were likewise detected in human subjects. These results suggest that early exposure to distinct BG+ microbes
drives proliferation of antigen specific B1 B cells, which then requires ongoing microbial input later in life to
sustain antibody production. To test this, we will weld clinical correlative data with our preclinical model through
the following specific aims. Aim 1. Define the role of early BG+ microbe exposure in the development of
anti-BG antibodies. Aim 2. Define the r...

## Key facts

- **NIH application ID:** 10782165
- **Project number:** 1P01HL171803-01
- **Recipient organization:** BRIGHAM AND WOMEN'S HOSPITAL
- **Principal Investigator:** Sean R Stowell
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $432,332
- **Award type:** 1
- **Project period:** 2024-08-01 → 2029-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10782165

## Citation

> US National Institutes of Health, RePORTER application 10782165, Project 1 - Examining the impact of microbial dynamics on B cells responsible for anti-blood group antibody formation (1P01HL171803-01). Retrieved via AI Analytics 2026-06-12 from https://api.ai-analytics.org/grant/nih/10782165. Licensed CC0.

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