Distinct Localization of Coagulation Factor VIII, Von Willebrand Factor and Factor VIIIa-Mimetic Bispecific Antibody Contributing to Thrombus Formation Under Whole Blood Flow Conditions

• Published in: Blood 2014-12, Vol.124 (21), p.1483-1483
• Main Authors: Shida, Yasuaki, Nogami, Keiji, Minami, Hiroaki, Yaoi, Hiroaki, Matsumoto, Tomoko, Kitazawa, Takehisa, Hattori, Kunihiro, Shima, Midori
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V124.21.1483.1483

Background Factor VIII (FVIII) is an essential factor for coagulation system in the intrinsic pathway. Due to the short survival of FVIII in the plasma circulation, it requires von Willebrand factor (VWF) as a carrier protein to maintain the optimal level for hemostasis. VWF also plays an important role in primary hemostasis by bridging platelets to exposed subendothelial collagens, especially under high shear flow environment. Since VWF carries FVIII, it is conceivable that VWF takes FVIII to the sites of vascular injury. However, the role of FVIII at the local sites under flow conditions is not fully understood despite of the fact that increased level of FVIII is associated with the risk of venous thrombosis and the deficiency of FVIII is the pathology of the bleeding disorder, hemophilia A. The treatment of hemophilia A largely depends on the infusion of FVIII concentrates, which is often complicated by the development of the inhibitor. Recently, bispecific antibody（ACE910）that mimics the role of FVIIIa by recognizing FIXa and FX has been developed and is currently under clinical trial. This antibody theoretically works regardless of the presence of devastating inhibitors against FVIII. Furthermore, it could also improve the clinical outcome of the other bleeding disorders, such as von Willebrand disease (VWD). Aim To analyze the role of FVIII and VWF, and impact of ACE910 at the sites of vascular injury under various shear conditions, we have developed the flow-mediated thrombosis model using flow chamber system. Method Whole blood obtained from healthy donors, hemophilia A and VWD patients were perfused into the collagen coated flow chamber under high (2,500s-1) or low shear (50s-1) flow conditions with/without FVIII concentrate, FVIII/VWF concentrate and ACE910. Formed thrombus was fixed and immunostaining was performed with phalloidin (Platelet), anti-FVIII antibody (FVIII) and anti-thrombin antibody (Thrombin). For the detection of ACE910, anti-human IgG or anti-ACE antibody (rAQ8 or rAJ540) were used. Size of thrombi and distribution of platelet, FVIII, thrombin and ACE910 were analyzed. Result 1) Under high shear flow, thrombus formation of VWD blood was significantly impaired while blood from Hemophilia A demonstrated nearly normal thrombus formation. Addition of FVIII/VWF but not FVIII concentrate to the blood of these patients rescued the impaired thrombus formation. ACE910 enhanced the thrombus formation of blood from both VWD and hemophilia