PB0684 - A murine model of vaccine-induced immune thrombotic thrombocytopenia (VITT) leads to anti-NAP2 and anti-PF4 antibodies and may involve TLR9 activation

Monday, June 24, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

LR

Lubica Rauova

Associate Professor
Children's Hospital of Philadelphia
Philadelphia, Pennsylvania, United States

Co-Author(s)

JO

Jenna Oberg

Research Technician
The Children's Hospital of Philadelphia
Philadelphia, Pennsylvania, United States
JR

Jérôme Rollin

Researcher
Inserm UMR1327, University of Tours
Tours, Pays de la Loire, France
YG

Yves Gruel

Professor
Regional University Hospital Centre Tours, Department of Hemostasis, Tours, France; University of Tours, EA4245, T2i, Tours, France.
Tours, Pays de la Loire, France
SG

Sarah Gilbert

Saïd Professor of Vaccinology
Pandemic Sciences Institute, Nuffield Department of Medicine, University of Oxford
Oxford, England, United Kingdom
DC

Douglas B. Cines

Professor of Medicine
University of Pennsylvania, Perelman School of Medicine, Philadelphia, PA
Philadelphia, Pennsylvania, United States
Mortimer Poncz, MD

Professor of Pediatrics
Children's Hospital of Philadelphia
Philadelphia, Pennsylvania, United States

Background: VITT is a rare complication of adenoviral-based vaccination for COVID-19. Its pathogenesis is unclear, but clinically results in antibodies directed against the platelet chemokine, platelet factor 4 (PF4). We have proposed that VITT antibodies can also recognize the related platelet chemokine, neutrophil activating peptide 2 (NAP2), and that induction of VITT may be directed at NAP2 or against PF4.

Aims: To develop a murine model of post-adenoviral VITT that recreates the observed thrombocytopenia and thrombosis and antibody development to understand VITT’s pathogenesis.

Methods: Mice expressing human (h) PF4 and hFc𝝲RIIA were injected IM with 5x10^9 viral particles/mouse of ChAdOx1-nCoV-19 (“nCoV-19”), expressing the spike receptor, or control ChAdOx-GFP (“GFP”), expressing green fluorescent protein, ± an oligodeoxynucleotide adjuvant (ODN-CpG) that activates TLR9 or ODN-Ctl that does not. ODN-CpG and vehicle served as controls (Table 1). Clinical course, blood counts and ELISA for Abs to spike protein, hPF4 and mNAP2 were followed. Terminally, organs were harvested for histology.

Results: Mice injected with nCoV-19 developed spike receptor antibodies. Of the nCoV-19 or GFP without ODN or with ODN Ctl (n=37) mice, 4 developed thrombocytopenia and died, 3 with anti-mNAP2 and 1 with anti-hPF4 antibodies. Three of the 15 mice injected with ChAdOx1 with ODN-CpG, a TLR9-stimulating ODN adjuvant, died with thrombocytopenia and developed anti-hPF4 antibodies that were directed to the VITT antigenic site and activated platelets. No control mice developed thrombocytopenia or antibodies (Table 1).

Conclusion(s): We have developed a murine model that simulates the salient features VITT. The immunothrombotic disorder did not require spike-receptor expression. These mice developed antibodies mostly to mNAP2. If concurrently treated with a TLR9-stimulating ODN adjuvant, the mice developed hPF4-targeting antibodies. These anti-hPF4 antibodies were platelet-activating and directed against the VITT antigenic target on hPF4. This model may be useful in understanding adenoviral-induced immunothrombotic disorders and in designing safer adenoviral vaccines.