# The Immunobiology of Vaccine-induced Immune Thrombotic Thrombocytopenia

> **NIH NIH P01** · VERSITI BLOOD HEALTH, INC. · 2024 · $650,240

## Abstract

ABSTRACT
 Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a complication of adenoviral (AdV)-based
COVID-19 vaccination. Antibodies (Abs) against the 70-aa chemokine, platelet (Plt) factor 4 (PF4), have been
noted in both VITT and in the related immune, prothrombotic disorder, heparin-induced thrombocytopenia (HIT),
but target different sites on the human (h) PF4 tetramer. The site on hPF4 targeted in VITT is conserved in the
related chemokine, 94-aa -granule, Plt-basic protein (PBP) and its N-terminal-truncated isoforms (PBPi),
including 70-aa neutrophil-activating peptide 2 (NAP2) that uniquely activates neutrophils (PMNs) via CXCR2.
We hypothesize that PF4 and/or PBP can initiate VITT and contribute to its prothrombotic state. We show that
VITT Abs bind hPBPi and activate Plts. Mice injected with VITT plasma develop a prothrombotic state even in
the absence of PF4, and unlike in murine HIT, PMNs become incorporated into arterial as well as venular
thrombi. We also show by dynamic light scattering (DLS) that both chemokines bind directly to AdVs. In a murine
VITT model, Abs develop to either PF4 or PBPi. We will pursue our observation and test the above hypothesis
as follows: Aim 1: Characterize the range of antigenic targets of VITT Abs. We will confirm that VITT Abs,
VITT monoclonal (mo) Abs, and murine Abs generated in Aim 3 bind to hPBPi. We will also determine where
VITT Abs bind on hPBPi using select amino acid substitutions of hPBP. Aim 2: Examine the importance of
hPF4 and hPBPi in VITT in vitro and in vivo. We will test the relative contribution of hPF4 vs. hPBPi to
thrombus formation in vitro using an injured-endothelium microfluidic model. Transgenic FcRIIA+ mice that
express either no PF4 or PBP, or have the murine or human versions, will be injected with VITT Abs to recreate
the prothrombotic state to validate the importance of PF4 vs. PBP in the development of thrombi in vivo. Aim 3:
Examine the mechanistic basis for the onset of VITT in a murine model. We have developed a novel murine
VITT model that suggests that the prothrombotic state occurs after AdV vaccination independent of expressing
the COVID-19 spike protein. Both anti-PF4 and anti-PBPi Abs were noted. These studies were supported by
DLS studies which showed that both chemokines complex with AdV, but that some AdV bind better to hPF4 and
others to hPBPi. The mechanistic basis of VITT will be further pursued, including defining the site(s) by which
these chemokines interact with AdV, and the characterization of the formed Abs. Taken together, Project 3
should provide important, novel conceptual insights into VITT. A number of new VITT-like pro-thrombotic
disorders are being recognized, and our studies should also be applicable to these disorders. Finally, AdV-based
vaccines have been developed for other disorders, and our models in Aim 3 may guide AdV modifications to
enhance vaccine safety. These advances will greatly benefit from synergy between Dr. Ponc...

## Key facts

- **NIH application ID:** 10934145
- **Project number:** 1P01HL167668-01A1
- **Recipient organization:** VERSITI BLOOD HEALTH, INC.
- **Principal Investigator:** Mortimer Poncz
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $650,240
- **Award type:** 1
- **Project period:** 2024-08-01 → 2029-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10934145

## Citation

> US National Institutes of Health, RePORTER application 10934145, The Immunobiology of Vaccine-induced Immune Thrombotic Thrombocytopenia (1P01HL167668-01A1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10934145. Licensed CC0.

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