Continuous infusion of factor IX concentrate to induce immune tolerance in two patients with haemophilia B

Two patients with haemophilia B and high-responding inhibitor to factor IX were subjected to immune tolerance induction according to the Malmo protocol, including high dosage of factor IX, cyclophosphamide and intravenous gammaglobulin. In one of the patients the treatment was preceded by extracorporeal protein A adsorption. Both patients had previously been subjected to immune tolerance induction without success and as an attempt to improve the tolerance induction regimen and lower cost, factor IX was given as continuous infusion, with a dose of around 300 units per kg body weight daily for 3 weeks. The inhibitor level declined in one of the patients but tolerance was not achieved. In the second patient the inhibitor level remained high. Despite the failure of the treatment in these two cases, we propose that the constant antigen load provided by the continuous infusion of modern, safe, purified factor IX concentrate may theoretically be of greater benefit in immune tolerance induction than the varying load resulting from intermittent infusions. Larger study materials are needed to show if this is so.