von Willebrand factor in factor VIII concentrates protects against neutralization by factor VIII antibodies of haemophilia A patients

We investigated the neutralization activity of factor VIII (FVIII) antibodies of 12 haemophilia A patients, acquired during treatment with plasma‐derived FVIII concentrates. All plasma samples, drawn in a clinically stable situation before any immunotolerance treatment, contained anti‐A2 domain and anti‐light‐chain FVIII antibodies. In nine patients’ plasmas, containing relatively high amounts of FVIII light‐chain antibodies (53–96%), a higher neutralization activity was found against recombinant FVIII concentrate (Recombinate) than against plasma‐derived von Willebrand factor (vWF)‐containing concentrate (Haemoctin SDH). No difference in neutralization of the two concentrates was found in two patients’ plasmas with almost equal content of FVIII light‐ and heavy‐chain antibodies, or one plasma with predominantly heavy‐chain antibodies. These results suggest that haemophilia A patients with relatively high amounts of FVIII light‐chain antibodies in plasma might benefit by infusion of FVIII concentrates containing vWF because vWF appears to have some protective effect on FVIII. This hypothesis should be tested by a clinical study.