OC 42.4 - Usefulness of 1E12, a monoclonal anti-Platelet Factor 4 antibody to improve diagnosis of vaccine-induced immune thrombotic thrombocytopenia

Monday, June 26, 2023

15:30 – 15:45 ET

Room: 710A

Session Available As: On-Demand

Presenting Author(s)

Jérôme Rollin, PhD

University of Tours
Tours, Centre, France

Co-Author(s)

CV

Caroline Vayne

Academic researcher
Regional University Hospital Centre Tours
Tours, Centre, France
RC

Rumi Clare

Research Associate
Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada
Hamilton, Ontario, Canada
MA

Merveille Atsouawe

Technical person
EA 4245, T2i
Tours, Centre, France
CC

Charlotte Cordonnier

Professor
Univ. Lille, Inserm, CHU Lille, U1172
Lille, Nord-Pas-de-Calais, France
SL

Sandrine Lemoine

Physician
Université d’Angers, Nantes Université, CHU Angers, Inserm, CNRS, CRCI2NA
Angers, Pays de la Loire, France
AG

Alban Godon

Physician
Université d’Angers, Nantes Université, CHU Angers, Inserm, CNRS, CRCI2NA
Angers, Pays de la Loire, France
Sophie Susen, MD, PhD (she/her/hers)

MD, PhD
Univ. Lille, Inserm, CHU Lille, Institut Pasteur de Lille, U1011- EGID, F-59000 Lille, France
Lille, Nord-Pas-de-Calais, France
Ishac Nazy, PhD

Associate Professor
Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada,
Hamilton, Ontario, Canada
YG

Yves Gruel

Professor
EA 4205, University of Tours, Tours, France
Tours, Centre, France
Claire Pouplard (she/her/hers)

Professor
University Hospital of Tours
Tours, Centre, France

Background: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare complication of adenovirus-based SARS-COV-2 vaccines due to anti-PF4 antibodies, which strongly activate platelets. In some patients receiving heparin to distinguish VITT from heparin-induced thrombocytopenia (HIT) can be challenging.

Aims: We evaluated whether a competitive enzyme immunoassay (EIA) using monoclonal antibodies mimicking human VITT and HIT anti-PF4 antibodies may facilitate VITT diagnosis.

Methods: The ability of Fab’2 fragments of 1E12, 1C12 and 2E1, three chimeric monoclonal anti-PF4 antibodies, to inhibit the binding of human VITT or HIT antibodies to modified PF4 was evaluated using an EIA. Alanine scanning mutagenesis was performed on PF4 to define amino acids (AA) involved in the interactions between these three monoclonals and human patient antibodies with PF4.

Results: A strong inhibition of VITT IgG binding to PF4 was measured with 1E12 Fab’2 (median of inhibition: 93%, n=8), whereas it had no effect on the binding of HIT antibodies (median of inhibition: 6%, n=8). In contrast, the Fab’2 of 1C12 and 2E1 similarly inhibited the binding of VITT (median of inhibition: 74 and 76%, respectively) and HIT antibodies (median of inhibition: 68 and 53%, respectively) to PF4. 1E12 Fab’2 was therefore tested in competitive EIA with 19 additional VITT plasma samples, and we confirmed it strongly inhibited IgG binding to PF4, except for one patient, who had actually developed HIT according to his clinical history. Finally, epitope mapping showed that 1E12 interacts with 5 AA on PF4, of which 4 are also required in the binding of human VITT antibodies, whereas none are involved for HIT antibody binding. This result probably explains the selective inhibitory effect of 1E12 on VITT antibody binding to PF4.

Conclusion(s): A competition EIA with 1E12 Fab’2 can distinguish VITT from HIT antibodies in specific patients when both diagnoses are possible.

Learning Objectives:

upon completion, participants will be able to describe the VITT syndrome
upon completion, participants will be able to define the similarities and differences between VITT and HIT antibodies
upon completion, participants will be able to differentiate VITT and HIT antibodies