Inhibition of factor VIII with a partially inhibitory human recombinant monoclonal antibody prevents thrombotic events in a transgenic model of type II HBS antithrombin deficiency in mice

Abstract

Summary. Venous thromboembolic disease is a major cause of morbidity and mortality, necessitating antithrombotic therapy. A human monoclonal anti-factor (F)VIII antibody, LCL-mAb-LE2E9, produced by a lymphoblastoid cell line derived from a hemophilia A patient with inhibitor to wild-type but not mutant self FVIII, was previously reported to achieve ef®cient inhibition of thrombosis in an experimental vena cava thrombosis model in mice. Here, the antithrombotic ef®cacy of a recombinant DNAderived version of this anti-FVIII antibody (rec-mAb-LE2E9) was tested in mice which carry a type II heparin binding site antithrombin de®ciency mutation and display spontaneous chronic thrombosis in several sites including the penile vein of sexually active males. The recombinant anti-FVIII antibody (100 mg, repeated after 3 days) prevented thrombotic priapism in all treated males, whereas all control animals treated with saline (group of four animals) developed priapism within 6 days after mating (P < 0.05 for treated vs. saline). The rec-mAb-LE2E9 and the original LCL-mAb-LE2E9 were equally effective (®ve and seven males/group, respectively). These results con®rm that FVIII inhibition represents a potent antithrombotic strategy, and show that both LCL-mAb-LE2E9 and rec-mAb-LE2E9 ef®-ciently prevent thrombosis in a physiological model representative of thrombosis in patients with a severe prothrombotic risk.

Variable region heavy chain glycosylation determines the anticoagulant activity of a factor VIII antibody

“…Two animals in the control group died before the end of the observation period but none in the group treated with Mab-LE2E9Q. Similar results were obtained when animals were treated with Mab-LE2E9, which inhibits 90% FVIII activity [20].…”

“…Tail clipping experiment in mice treated with one or the other antibody demonstrated that in vivo they both only partially inhibit FVIII activity [20].…”

“…On the basis of that concept, we have tested the human monoclonal antibody Mab-LE2E9Q, which inhibits 40% FVIII activity, for its ability to prevent thrombosis in mice with a strong prothombotic phenotype resulting from a type II deficiency mutation in the heparin binding site of antithrombin (AT m/m mice) [20]. The assay evaluated the prevention of thrombosis-related priapism in sexually active AT m/m males.…”

Antidote strategies to reverse anticoagulation with TB‐402, a long‐acting partial inhibitor of factor VIII

“…The mutation removed a glycosylation site in the variable region of the heavy chain. Whereas mAb-LE2E9 inhibits FVIII activity (FVIII:C) by approximately 80-90%, TB-402 inhibits FVIII:C by approximately 30-40% in vitro [2,3]. An anticoagulant that exerts stable partial inhibition of the target coagulation factor may thus avoid excessive anticoagulation and allow substantial hemostasis to be retained, with the aim of avoiding excess bleeding risks.…”

Inhibitory antibodies against factor VIII C1 domain

“…4 One anti-C1 antibody that blocks von Willebrand factor (VWF) binding prolongs plasma circulation to the same extent as VWF, confirming the relationship of the C1 domain to the clearance pathway and indicating the potential of antibodies to prolong circulation of fVIII. 5 Most inhibitory antibodies only partially block fVIII activity. A paradox of hemophilia A patient care is that the degree to which inhibitory antibodies inhibit fVIII activity in standard assays has poor predictive value for the risk of bleeding.…”