PB0098 - Long-term persistence of anti-PF4-antibodies following Vaccine-Induced Thrombotic Thrombocytopenia after first ChAdOx1 vaccination.

Sunday, July 10, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Co-Author(s)

Matthias M Engelen, MD

MD, PhD candidate
University Hospitals Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
FM

François Mullier

MPharm, MSc, PhD
Université catholique de Louvain, CHU UCL Namur, NTHC, NARILIS, Hematology Laboratory, Namur, Belgium
Namur, Namur, Belgium
Marc Jacquemin, MD

PhD
Center for Molecular and Vascular Biology, Department of Cardiovascular Sciences, KU Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
MD

Mirjam Debasse

Lab Technician
Department of Vascular Medicine and Hemostasis, University Hospitals Leuven and National Coordinating Hemophilia Center, University Hospitals Leuven, Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
KP

Kathelijne Peerlinck

MD, PhD
University Hospitals Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium
KD

Katrien MJ Devreese, MD, PhD

Head of department
Department of Laboratory Medicine, Department of Diagnostic Sciences, Ghent University Hospital, Ghent University
Ghent, Oost-Vlaanderen, Belgium
CV

Christophe Vandenbriele

MD PhD
Center for Molecular and Vascular Biology, Department of Cardiovascular Sciences, KULeuven, University Hospitals Leuven
Leuven, Vlaams-Brabant, Belgium
PV

Peter Verhamme, MD, PhD

MD, PhD
University Hospitals Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium

Presenting Author(s)

Thomas Vanassche, MD PhD

MD, PhD
University Hospitals Leuven, Belgium
Leuven, Vlaams-Brabant, Belgium

Background: Vaccine-induced Thrombotic Thrombocytopenia (VITT) is a rare but potentially life-threatening complication of the ChAdOx1 COVID-vaccine, which involves binding of IgG antibodies against platelet factor 4 (PF4) to the platelet Fc-gamma receptor. This causes platelet activation with thrombosis and thrombocytopenia. Because of the similarity with heparin-induced thrombocytopenia (HIT), heparin is avoided in the acute treatment of VITT. There is limited information about the long-term persistence of anti-PF4-antibodies and their clinical relevance.

Aims: To describe long-term clinical and serological outcomes after VITT.

Methods: A case series of patients from Leuven University Hospitals with confirmed VITT and at least six months of follow-up. All patients provided informed consent. Anti-PF4 antibodies were measured via chemiluminescence (HemosIL® AcuStar HIT-IgG(PF4-H), Werfen) and enzyme-linked immunosorbent assay (ELISA) with immobilised polyvinylsulfonate/PF4 complexes (PF4-IgG Immucor, GTI Diagnostics); with an optical density (OD) cut-off of 0.4. Aggregation of platelets after exposure to patient plasma with 0, 1 or 200IU/ml of heparin was measured by whole-blood impedance aggregometry (HIMEA) (Roche® multiplate analyser).

Results: Three middle-aged women presented with thrombosis with thrombocytopenia and a positive anti-PF4 ELISA 9 to 16 days after first ChAdOx1 vaccination. Their clinical presentation, lab results and treatment are summarised in Table 1. All patients recovered rapidly after non-heparin anticoagulation with (case 2-3) or without (case 1) intravenous immunoglobulins. All patients received subsequent COVID-vaccination with an mRNA-based vaccine without thrombocytopenia or symptoms. Anti-PF4-antibodies remained elevated in two patients after three months and in one out of three after more than six months, but HIMEA results for all follow-up tests became negative (Figure 1).

Conclusion(s): We report good short- and long-term outcomes of three cases of VITT, including successful subsequent vaccination with an mRNA vaccine. Anti-PF4-antibodies can persist for at least several months. In contrast with the initial presentation, these persistent anti-PF4-antibodies did not trigger platelet activation in our patients.