- Participants with acquired hemophilia with autoimmune inhibitory antibodies to human factor VIII with a clinical diagnosis established by the following criteria: a) Prolonged activated partial thromboplastin time (aPTT), b) Prothrombin time (PT) ≤ upper limit of normal (ULN) + 2 seconds and platelet count within normal range, c) Abnormal aPTT mixing study (patient-normal control 1:1) consistent with a factor VIII inhibitors reduced factor VIII activity level (below 10%)