Variants of recombinant factor VIIa with increased intrinsic activity

Following vascular damage, blood clotting is triggered when factor VIIa (FVIIa) forms a complex with tissue factor (TF). In hemophilia A and B, the propagation phase of blood coagulation is disrupted due to the lack of factors VIII (FVIII) and IX (FIX), leading to excessive bleeding. However, high doses of recombinant FVIIa (rFVIIa) can bypass the FVIII/FIX deficiency and ameliorate bleeding problems. Although the precise mechanism of action of rFVIIa at pharmacological doses remains a matter of debate, rFVIIa-catalyzed (TF-independent) activation of factor X (FX) on the surface of the activated platelet appears to be important. Variants of rFVIIa with increased intrinsic (TF-independent) activity have been developed, which may offer improved treatment of bleeding episodes, for example, in hemophiliacs with inhibitory antibodies to FVIII; they can also help us to understand how FVIIa works at the molecular level. This article reviews the properties of these molecules.