# Examining Immune Circuits Responsible for Anamnestic RBC Alloimmunization

> **NIH NIH R01** · BRIGHAM AND WOMEN'S HOSPITAL · 2022 · $652,511

## Abstract

Summary: Prior alloimmunization places patients at risk for anamnestic alloantibody formation following
alloantigen re-exposure that can result in accelerated RBC clearance and lead to a potentially fatal delayed
hemolytic transfusion reaction (DHTR). The inability to prevent DHTRs largely stems from a fundamental lack
of understanding regarding key immune pathways that govern anamnestic RBC alloantibody responses capable
of driving DHTRs. Our long-term goal is to identify and then target critical pathways that regulate the development
of anamnestic alloantibody formation. Our central hypothesis is that anamnestic RBC alloantibody formation
occurs through a distinct toll-like receptor (TLR), bridging channel dendritic cell (DC) and follicular (FO) B cell-
dependent pathway that fundamentally differs from primary RBC alloimmunization. Our hypothesis is formulated
on the basis of our discovery that unlike initial RBC alloimmunization, which requires marginal zone (MZ) B cells,
MZ B cells are not required for anamnestic alloantibody formation, but are required for early priming events that
occur following initial RBC alloantigen exposure. In addition to differences in MZ B cell requirements, while initial
alloantibody formation is CD4 T cell independent (TI), increased alloantibody levels observed following RBC re-
exposure is entirely CD4 T cell dependent (TD). Furthermore, while T follicular helper cell (TFH) and follicular
(FO) B cells are not required for initial alloantibody formation, initial RBC transfusion does increase TFH and FO
B cell numbers. Re-transfusion also increases 33D1+ DC activation and chemokine receptor expression. These
results suggest that initial RBC transfusion primes recipients by generating distinct alloantigen-specific TFH and
FO B cell populations that can, in turn, be activated by 33D1+ DCs following RBC alloantigen re-exposure
independent of MZ B cells. In addition, while type I interferons (IFNab) are required for primary alloantibody
formation, TLR signaling is dispensable for initial alloantibody development, yet is required for anamnestic
alloantibody formation. Given the ability of MZ B cells to directly activate CD4 T cells and traffic antigen to the
B cell follicle, our data suggest that initial priming events require MZ B cell-mediated CD4 T cell and FO B cell
development through an IFNab-dependent process. However, as anamnestic alloantibody formation occurs
through a MZ B cell-independent pathway and DCs can also traffic antigen to B cells and directly activate CD4
T cells, DCs likely orchestrate anamnestic alloantibody formation through a TLR-dependent pathway. To test
this hypothesis, we will pursue the following specific aims: Specific Aim 1: Define the role of MZ B cells and
IFNab in the development of CD4 T cells and FO B cells required for a subsequent anamnestic
alloantibody response. Specific Aim 2: Define the role of TLRs and DCs in the development of an
anamnestic alloantibody response following R...

## Key facts

- **NIH application ID:** 10535284
- **Project number:** 1R01HL165975-01
- **Recipient organization:** BRIGHAM AND WOMEN'S HOSPITAL
- **Principal Investigator:** Sean R Stowell
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $652,511
- **Award type:** 1
- **Project period:** 2022-07-01 → 2026-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10535284

## Citation

> US National Institutes of Health, RePORTER application 10535284, Examining Immune Circuits Responsible for Anamnestic RBC Alloimmunization (1R01HL165975-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10535284. Licensed CC0.

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