Induction of immune tolerance with recombinant factor VIII in haemophilia A patients with inhibitors

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Abstract
We report on 11 patients (nine unrelated and a brother pair) with severe haemophilia A and factor VIII (FVIII) inhibitor, in whom immune tolerance (IIT) was induced with recombinant FVIII (r‐FVIII). Their age ranged from 11 months to 47 years. The number of exposure days (ED) at inhibitor detection varied from 11 to 130. Nine of the 11 patients were high responders [>10 Bethesda units (BU)] with peak inhibitor levels ranging from 10 to 566 BU. The other two were low responders with peak levels between 0.7 and 2 BU. Before inhibitor detection, the patients had been receiving products of various purities. The IIT regimens were very heterogeneous, and the treatment schedule varied from a short period with 50 IU kg–1 every 2 days, followed by 100 IU kg–1 every 2 days and then 220 IU kg–1 daily. The outcome was considered successful when the inhibitor level fell to 0.6 BU or lower after IIT treatment. The outcome overall was successful in nine out of 11 patients (81.8%), with the nine successful cases comprising seven of the nine high responders (77.8%) and the two low responders. Definite failure of IIT was observed in one high responder after two different IIT regimens. A second high responder is still on IIT treatment. All patients in whom IIT was successful are currently receiving r‐FVIII on demand or prophylactically at various dosages. Despite the variability of the patient characteristics and the IIT schedules, this study demonstrates that r‐FVIII represents an effective alternative for the eradication of inhibitors through IIT.