Occurrence of inhibitors in previously untreated or minimally treated patients with haemophilia A after exposure to a plasma-derived solvent-detergent factor VIII concentrate

A solvent-detergent virus-inactivated plasma-derived FVIII concentrate (SD-pdFVIII) has been employed for treatment of Italian patients with haemophilia A for 15 years. This product is a nonmonoclonally purified, high purity FVIII concentrate, containing large amounts of von Willebrand factor (VWF). A retrospective survey was carried out in Italy in order to evaluate the immunogenicity of SD-pdFVIII in previously untreated patients (PUPs) or in minimally treated patients (MTPs), i.e. previously exposed for up to 5 days only to other plasmaderived concentrates. The survey included 99 patients with ages ranging from 6 to 64 years (median = 21.3) of whom 31 PUPs and 68 MTPs, the latter with a median of four exposure days (EDs; range 1-5) to other plasma products. Surveyed patients had been exposed to SD-pdFVIII for a median of 83 EDs (range 21-1580). Seven patients (three PUPs and four MTPs), all with severe haemophilia, had developed inhibitors [7.1%, 95%; confidence interval: 3-14%] after a median of 11 EDs (range 4-22). Of them, two were low responders (≤5 BU mL-1) and five high responders. Two low responders and one high responder tolerated inhibitors spontaneously; one high responder underwent immunotolerance treatment with complete, long-standing response. These findings show that SD-pdFVIII is at low risk of inhibitor development in PUPs and MTPs with severe and moderate haemophilia, the risk of inhibitor development being similar to that previously reported for other plasma-derived VWF-containing FVIII products.