Anti-VWF single-domain antibody.

Von Willebrand Factor (VWF) is a multimeric adhesive plasma glycoprotein that is important in the maintenance of hemostasis. It promotes adhesion of platelets to the sites of vessel injury by forming a bridge between subendothelial collagen and the platelet GPIb-IX-V receptor complex. VWF also acts as a chaperone for coagulation factor VIII, by delivering it to the site of injury, stabilizing its heterodimeric structure and protecting it from premature clearance from plasma. Defects in VWF cause von Willebrand disease (VWD), a common inherited bleeding disorder characterized by excessive mucocutaneous bleeding. Type I VWD is the most common form and is characterized by a partial quantitative deficiency of a structurally and functionally normal VWF; type II VWD is caused by a qualitative deficiency and functional abnormalities of VWF; type III VWD is the most severe form and is associated with a total or near-total absence of VWF in plasma and cells, which also causes the profound deficiency of coagulation factor VIII in plasma.