Targeting of a Conserved Epitope in Mouse and Human GPVI Differently Affects Receptor Function and in vivo Depletion

S. Navarro^1,2, H. Brown^1,2, M. Kuijpers³, J. Heemskerk³, D. Stegner¹, B. Nieswandt^1,2

¹Institute of Experimental Biomedicine I, University Hospital Würzburg, Würzburg, Germany, ²Rudolf Virchow Center, University of Würzburg, Würzburg, Germany, ³Cardiovascular Research Institute Maastricht (CARIM), Department of Biochemistry, Maastricht, the Netherlands

Abstract Number: PB1733

Meeting: ISTH 2020 Congress

Theme: Platelets and Megakaryocytes » Platelet Receptors

Background: Platelet glycoprotein (GP) VI is the major platelet collagen receptor and a promising antithrombotic target since its functional inhibition protects from arterial thrombosis without affecting haemostasis. This was first demonstrated in mice using the monoclonal antibody JAQ1, which completely blocks the collagen/CRP binding site on mouse GPVI. Injection of JAQ1-IgG induces transient thrombocytopenia and depletion of GPVI from platelets, whereas its F(ab´) fragment only blocks GPVI without affecting platelet count or GPVI expression in vivo. A possible in vivo downregulation of human GPVI (hGPVI) by antibodies has not been studied systematically.

Aims: To test the effects of JAQ1 on human GPVI function in vitro and the targeted downregulation of the receptor in newly generated hGPVI-knockin (hGPVI^KI) mice in vivo.

Methods: We used flow cytometry, aggregometry, spreading assays and ex vivo flow adhesion studies to characterize the effect of JAQ1 on human platelets and hGPVI^KI mouse platelets. The effects of JAQ1 treatment on hGPVI expression in vivo was analyzed in hGPVI^KI mice.

Results: Flow cytometry revealed binding of JAQ1 to human GPVI, but not other species, including rat, hamster, rabbit, swine, cat, dog, horse, and cow. In human or hGPVI^KI mouse platelets, JAQ1 binding did not cause detectable activation unless cross-linked, comparable to the effect on wild-type platelets. Remarkably, in contrast to mouse GPVI, JAQ1 did not inhibit CRP or collagen binding of human GPVI. In vivo, JAQ1-treatment induced complete depletion of mGPVI in wild-type mice, but only partially downregulated the receptor in hGPVI^KI mice, which was in both groups accompanied by a comparable transient thrombocytopenia.

Conclusions: The binding site of JAQ1 on GPVI is conserved between mouse and human, but differs in its functional significance. In vivo targeting of this site with JAQ1 IgG results in different immunodepletion efficacies, indicating that epitope-specific effects could be involved in this process.

To cite this abstract in AMA style:

Navarro S, Brown H, Kuijpers M, Heemskerk J, Stegner D, Nieswandt B. Targeting of a Conserved Epitope in Mouse and Human GPVI Differently Affects Receptor Function and in vivo Depletion [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/targeting-of-a-conserved-epitope-in-mouse-and-human-gpvi-differently-affects-receptor-function-and-in-vivo-depletion/. Accessed October 1, 2023.

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