Cerebrovascular diseases in hemophiliacs: A real, but underestimated risk

Immune tolerance against infused FVIII in hemophilia A is mediated by PD-L1+ Tregs

A major complication of hemophilia A therapy is the development of alloantibodies (inhibitors) that neutralize intravenously administered coagulation factor VIII (FVIII). Immune tolerance induction therapy (ITI) by repetitive FVIII injection can eradicate inhibitors, and thereby reduce morbidity and treatment costs. However, ITI success is difficult to predict and the underlying immunological mechanisms are unknown. Here, we demonstrated that immune tolerance against FVIII under nonhemophilic conditions was maintained by programmed death (PD) ligand 1-expressing (PD-L1-expressing) regulatory T cells (Tregs) that ligated PD-1 on FVIII-specific B cells, causing them to undergo apoptosis. FVIII-deficient mice injected with FVIII lacked such Tregs and developed inhibitors. Using an ITI mouse model, we found that repetitive FVIII injection induced FVIII-specific PD-L1+ Tregs and reengaged removal of inhibitor-forming B cells. We also demonstrated the existence of FVIII-specific Tregs in humans and showed that such Tregs upregulated PD-L1 in patients with hemophilia after successful ITI. Simultaneously, FVIII-specific B cells upregulated PD-1 and became killable by Tregs. In summary, we showed that PD-1-mediated B cell tolerance against FVIII operated in healthy individuals and in patients with hemophilia A without inhibitors, and that ITI reengaged this mechanism. These findings may impact monitoring of ITI success and treatment of patients with hemophilia A.

Combined use of antifibrinolytics and activated prothrombin complex concentrate (aPCC) is not related to thromboembolic events in patients with acquired haemophilia A: data from FAIR Registry

Antifibrinolytics combined with aPCC are not routinely administered to patients with acquired hemophilia A due to increased thrombotic risk. This association normalizes clot stability, and improves the efficacy of therapy, but can increase the risk of severe side effects. Due to these premises it has always raised doubts and perplexities in the clinics. We now report the data of the "FEIBA® on acquired haemophilia A Italian Registry (FAIR Registry)", a retrospective-prospective study that included 56 patients. This is the first study that assessed the clinical response of the combination of aPCC and antifibrinolytic agents in patients with acquired haemophilia A. A total of 101 acute bleeds were treated with aPCC. Antifibrinolytic agents were used in the treatment of 39.6% of total bleeds, based on both, a clinical assessment and an evaluation of bleeding. Twenty-five of the 30 patients (57.1%) treated with antifibrinolytic drugs showed serious co-morbidity. Among them, 40% presented severe cardiovascular diseases. All bleeds treated with combined therapy had a shorter duration of treatment (mean reduction 16.3%). All the treated patients presented a good tolerability and no arterial or venous thromboembolic events were reported. In our retrospective registry the combination of antifibrinolytics and aPCC appears safe and effective in the treatment of patients with AHA, especially in the case of severe and life-threatening bleeding, but this hypothesis needs to be confirmed in adequate, larger clinical trials.