SummaryAntibodies (Ab) that inhibit factor VIII (fVIII) may develop in patients with hemophilia A and rarely in individuals without congenital fVIII deficiency (acquired hemophilia). Synthesis of fVIII inhibitors requires CD4+ T cells. We investigated the proliferative response of blood CD4+ cells from 11 patients with congenital or acquired hemophilia and 12 healthy subjects, to recombinant human fVIII, and to pools of overlapping synthetic peptides spanning the sequences of individual fVIII domains. All patients had CD4+ cells that responded to fVIII. The intensity of the responses fluctuated over time: several patients had brief periods when they did not respond to fVIII. All healthy subjects had transient CD4+ responses to fVIII, that were significantly lower than those of hemophilia patients. Also, healthy subjects responded to fVIII less frequently and for shorter periods than hemophilia patients. All patients and healthy subjects recognized several fVIII domains: the A3 domain was recognized most strongly and frequently. The transient sensitization of CD4+ cells to fVIII in healthy subjects suggests that inadequate tolerization of CD4+ cells to fVIII, due to lack of endogenous fVIII, is an important factor in the development of clinically significant anti-fVIII antibodies in hemophilia A.

Despite being associated with a significant incidence of infection, we believe the benefits of IVADs for children with hemophilia and their families outweigh the risks. Possible explanations for the observed infection rates are discussed.

Iliopsoas haemorrhage in patients with bleeding disorders is a potentially life-threatening condition, with significantly associated morbidity. Despite its clinical importance, little has been published on the frequency, complications or outcomes of this entity since the advent of modern therapies for haemophilia. In a retrospective review of 297 patients with bleeding disorders followed at our centre, we identified 46 episodes of iliopsoas haemorrhage in 31 patients. Patients presented primarily with thigh, hip and/or groin pain, and frequently had flexion hip contracture, femoral nerve paresthesia, and >2 g dL(-1) haemoglobin drop. The duration of symptoms prior to seeking medical attention was 3.8 +/- 4 days. Nineteen of 155 patients (12.3%) with haemophilia A had 28 episodes of iliopsoas bleed; 52.6% of these patients had severe haemophilia. Of these 19 patients with haemophilia A who had iliopsoas haemorrhage, seven (36.8%) had an inhibitor to factor VIII (FVIII), and accounted for one-half of the bleeding episodes. Nine of 66 patients (13.6%) with haemophilia B had 15 episodes of iliopsoas haemorrhage; 22.2% of these patients had severe haemophilia, including one patient with an inhibitor to FIX who had two iliopsoas bleeds. The mean duration of therapy was 18.7 +/- 11.9 days, and the duration of hospitalization was 12.3 +/- 9.1 days. The length of hospital stay was significantly longer in patients with inhibitors, when compared with patients without inhibitors (19.1 +/- 5.8 days vs. 7.6 +/- 7.8 days; P<0.0001) with higher factor consumption, although the total duration of therapy was not significantly different. Patients with inhibitors were over-represented in the cohort of haemophiliacs with iliopsoas bleed. Patients with inhibitors who had iliopsoas bleeds remained hospitalized longer, although the duration of therapy was the same as patients with no inhibitors. There was a low frequency of recurrent bleed (2.8%).