Abstract Number: OC 14.3
Meeting: ISTH 2021 Congress
Background: Developing neutralizing antibodies against replacement clotting factors remains a major complication of hemophilia therapy. Rebalancing approaches, which target anticoagulant pathways, are an attractive alternative to FIX or FVIII replacement. Monoclonal antibodies (mAbs) that target activated protein C (APC) show promise in hemophilic plasma and animal models. However, they can disrupt important anti-inflammatory roles, and developing alternative approaches to restoring hemostasis is warranted.
Aims: Develop novel mAbs that bind to and protect FV/FVa from APC-mediated inactivation and restore hemostasis in the context of hemophilia.
Methods: A panel of hybridoma clones secreting mAbs against FV were screened in a thrombin generation assay (TGA) using normal human plasma (NHP) in the presence and absence of an APC system. Lead candidate mAbs that restored thrombin generation were purified and characterized for binding to FV using biolayer interferometry (BLI). mAbs that bound tightly to FV and restored thrombin generation in initial screens were subsequently assessed in TGAs with hemophilic plasma.
Results: By stimulating the endogenous APC system using soluble thrombomodulin (sTM) or exogenously adding APC, we monitored the effects of the mAbs on the anticoagulant system. 20 nM sTM or 2 nM APC reduced the thrombin generation potential to similar baseline levels in NHP. Several mAbs restored thrombin generation in NHP in the presence of our APC system. mAb GB5, our lead candidate, restored thrombin generation to levels ~12-fold higher than without mAb. Moreover, GB5 bound tightly to FV, FVa, and FV-short with a Kd between 1-3 nM. In hemophilic plasma with APC, GB5 (20 nM) produced a 10-fold increase in thrombin generation compared to the controls. At equivalent concentrations using nonimmune IgG, thrombin generation was not restored.
Conclusions: mAbs that bind tightly to FV/FVa can protect it from APC-mediated inactivation and may prove efficacious in vivo at restoring hemostasis in the context of hemophilia.
To cite this abstract in AMA style:Quinn S, Ayombil F, Camire RM. Development of Monoclonal Antibodies that Protect FV/FVa from APC-mediated Inactivation for the Treatment of Bleeding [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 1). https://abstracts.isth.org/abstract/development-of-monoclonal-antibodies-that-protect-fv-fva-from-apc-mediated-inactivation-for-the-treatment-of-bleeding/. Accessed September 24, 2021.
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