In vivo bypass of hemophilia A coagulation defect by Factor XIIa implant

Hemophilia A and B coagulation defects, which are caused by deficiencies of Factor VIII and Factor IX, respectively, can be bypassed by administration of recombinant Factor VIIa. However, the short half-life of recombinant Fa ctor VIIa in vivo negates its routine clinical use. We report here an in vi vo method for the continuous generation of Factor VIIa. The method depends on the implantation of a porous chamber that contains Factor Xa or XIIa, an d continuously generates Factor VIIa bypass activity from the subject's own Factor VII, which enters the chamber by diffusion. Once inside, the Factor VII is cleaved to Factor VIIa by the immobilized Factor Xa or XIIa. The ne wly created Factor VIIa diffuses out of the chamber and back into the circu lation, where it can bypass the deficient Factors VIII or IX, and enable co agulation to occur. In vitro, this method generates sufficient Factor VIIa to substantially correct Factor VIII-deficient plasma when assessed by the classical aPTT coagulation assay. In vivo, a Factor XIIa peritoneal implant generates bypass activity for up to one month when tested in rhesus monkey s. Implantation of such a chamber in a patient with hemophilia A or B could eventually provide a Viable alternative to replacement therapies using exo genous coagulation factors.