Induced tolerance in hemophilia patients with antibodies against IX:C.

Two patients with severe hemophilia B complicated with antibodies against factor IX have been treated 13 and 10 times, respectively, with high doses of factor IX concentrate in combination with cyclophosphamide over a period of 10 years. During this treatment a lowering of the anamnestic response was observed over the years. Both patients have now been treated with factor IX and hydrocortisone but no cyclophosphamide in order to find out if real tolerance was induced. One patient received such treatment three times and the other once. Their inhibitor titer following these treatment episodes never exceeded 0.3 U/ml (approximately 0.9 BU/ml) and 0.9 U/ml (approximately 2.7 BU/ml) which is of the same order of magnitude as following the combined treatment (factor IX, hydrocortisone and cyclophosphamide). It is therefore suggested that these patients have been converted from high responders (10-100-fold increase in the inhibitor titer on the original treatment with factor IX and hydrocortisone) into low responders showing a very reasonable inhibitor increase after treatment with factor IX and hydrocortisone but no cyclophosphamide.