Immune tolerance induction in patients with hemophilia A.

Replacement therapy with factor VIII (FVIII) concentrates has become the mainstay of treatment for hemophilia, but about 30% of patients with a severe disease develop neutralizing antibodies against FVIII, which can lead to treatment resistance and an increased risk of bleeding. Immune tolerance induction (ITI) overcomes the immune response to FVIII concentrates in the majority of patients. Several factors may influence the efficacy of ITI, including disease-related factors (e.g. peak inhibitor titer and pre-ITI titer), and genetic factors (e.g. type of mutation). Treatment-related factors, such as the type of FVIII concentrate used in ITI will also potentially influence the outcome. Specifically, higher success rates with von Willebrand factor (VWF)-containing factor VIII concentrates than with high-purity FVIII concentrates have been reported, but further studies are needed. Potential mechanisms involved include steric hindrance, inhibition of FVIII degradation, or immunomodulatory effects. However, the exact mechanism by which immune tolerance is induced remains unclear. High-dose FVIII ITI appears to induce immune tolerance more rapidly than low-dose protocols and with a reduced risk of bleeding episodes. The addition of immunosuppressive therapy, such as rituximab, to ITI may improve outcomes, although the optimal approach to combined ITI/immunosuppression has not been established. Ongoing studies are likely to provide further insight into the role of genetic features and the type of FVIII concentrate on the success rate of ITI.