Low-dose immune tolerance induction for paediatric haemophilia patients with factor VIII inhibitors

The development of an inhibitor against factor VIII (FVIII) is a serious complication in children with haemophilia A. Immune tolerance induction (ITI) therapy is generally considered to be the best approach to eradicate the inhibitor. In this paper, the low-dose (<= 50 IU kg(-1) twice or three times weekly with plasma-derived factor concentrates) ITI regimen used in Turkey is discussed. This regimen was given to 21 haemophilia A patients with high titer inhibitors. The median age at the beginning of ITI was 9 years and exposure days were 25. The median pre-ITI historical peak inhibitor titer, and inhibitor titer when ITI started were 80 BU (range 6.0-517), 19.2 BU (range 3.6-515), respectively. Complete immune tolerance was defined as the time at which at least two negative inhibitor assays was obtained with no anamnestic response. Our two cases were not reached in follow-up period. Immune tolerance could be achieved in 5 of 19 (26.3%) patients within a median time of 6 months. Partial tolerance was obtained in 7 patients while treatment failed in spite of significant decreased inhibitor levels in the other patients. A relapse developed in one immune-tolerized patient, one year later. The level of inhibitor titer at the beginning of ITI (<= 10 BU), the pre-ITI historical peak inhibitor titer (< 50 BU), and the time between the first diagnosis inhibitor to starting ITI (< 12 months) were main factors in the success (complete or partial tolerance) of ITI. In conclusion, the outcome of low-dose ITI protocol was not satisfactory in this retrospective study.