Immune tolerance to Factor VIII: the international registry data.

Abstract

Among the problems related to the treatment of classic hemophilia, the presence of inhibitors (alloantibodies) to foreign Factor VIII (F.VIII) is one of the most serious. These antibodies may arise at any age, but the cumulative risk of developing an inhibitor one year after the first treatment with a factor concentrate is between 22% and 25%. 1,2The presence of such antibodies can render any further administration of F.VIII ineffective. On the basis of the speed and degree of immune response to F.VIII, patients have been divided into high- and low-responders.3This is an arbitrary classification, but it is related to important treatment characteristics. Low responders, that is patients whose maximum inhibitor titer is <10 Bethesda Units (B.U.), can be treated with F.VIII, albeit at higher doses; however, high-responders can seldom be treated with F.VIII and comprise the so-called “refractory hemophiliacs.”