Epitope location on tissue factor determines the anticoagulant potency of monoclonal anti-tissue factor antibodies

Citation
D. Kirchhofer et al., Epitope location on tissue factor determines the anticoagulant potency of monoclonal anti-tissue factor antibodies, THROMB HAEM, 84(6), 2000, pp. 1072-1081
Citations number
60
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Cardiovascular & Hematology Research
Journal title
THROMBOSIS AND HAEMOSTASIS
ISSN journal
0340-6245 → ACNP
Volume
84
Issue
6
Year of publication
2000
Pages
1072 - 1081
Database
ISI
SICI code
0340-6245(200012)84:6<1072:ELOTFD>2.0.ZU;2-X
Abstract
Tissue factor (TF), the cellular cofactor for the serine protease factor VI Ia (F.VIIa), triggers blood coagulation and is involved in the pathogenesis of various thrombosis-related disorders. Therefore, agents which specifica lly target tissue factor, such as monoclonal antibodies, may provide promis ing new antithrombotic therapy. We mapped the epitopes of several anti-TF a ntibodies using a panel of soluble TF mutants. They bound to three distinct TF regions. The epitope of the 7G11 antibody included Phe50 and overlapped with a TF-F.VIIa light chain contact area. The common epitope of the antib odies 6B4 and HTF1 included residues Tyr94 and Phe76 both of which make cri tical contacts to the catalytic domain of F.VIIa. The antibodies D3 and 5G6 had a common epitope outside the TF-F.VIIa contact region. It included res idues Lys165, Lys166, Asn199, Arg200 and Lys201 and thus overlapped with th e substrate interaction region of tissue factor. The anti bodies 5G6 and D3 were potent anticoagulants when infused to flowing human blood in an ex-vi vo thrombosis model. Plasma fibrinopeptide A levels and fibrin deposition w ere completely inhibited. In contrast, 6B4 was a weak inhibitor in this ex- vivo thrombosis model, and HTF1 displayed no inhibition at all. These dispa rate activities were also reflected in TF-dependent F.X activation assays p erformed with human plasma. The potency differences could neither be explai ned by the determined binding affinities nor by the on-rates of antibodies. Therefore, the results suggest that antibody binding epitope and hence the particular mechanism of inhibition, is the main determinative factor of an ticoagulant potency of anti-TF antibodies.