A study published this month in Haemophilia focuses on the use of a recombinant factor VIII product in immune tolerance induction (ITI) to eliminate inhibitors in hemophilia A patients.
Researchers led by Leonard Valentino, MD, Rush Hemophilia and Thrombophilia Center, Rush University Medical Center, Chicago, IL, studied 12 children with severe hemophilia A who underwent ITI with the rFVIII product Advate® (manufactured by Baxter Healthcare) for more than 30 months. The time of inhibitor detection varied for each child, with one receiving a diagnosis as early as seven months and one as late as six years (the average was 19.8 months). Of the children, 10 were “high titer” patients, a classification representing a potent inhibitor that is not easily treated or eliminated.
Inhibitors result when the body’s immune system identifies infused factor VIII as a foreign substance and releases antibodies to attack it, thereby “inhibiting” the protein’s ability to form a blood clot. ITI is the optimal treatment for an inhibitor because if successful, it can essentially eliminate the undesired immune response. ITI involves regular (once daily or several times per week), high doses of factor product to train the immune system to accept the therapy by ceasing to produce antibodies—desensitizing the immune system, a process similar to allergy therapy. However, this can take weeks or years. Once the immune system is “tolerized,” the inhibitor is eradicated. ITI, though time-consuming and costly, is effective in approximately 70%-85% of FVIII inhibitor cases. Success is defined by an absence of antibodies, which translates into a negative Bethesda titer and a return of normal factor function inside the body.
Tolerance was reached in 9 of 12 patients (75%) at a median of four months. The success rate in the high-titer patients was 70%. Of the remaining three patients, two were still undergoing ITI with tolerance yet to be achieved and one patient experienced failure of the therapy.
The study, “Experience with a third generation recombinant factor VIII concentrate (Advate®) for immune tolerance induction in patients with haemophilia A,” was published in the March 2009 issue of Haemophilia.