Desensitization and immune tolerance induction in children with severe factor IX deficiency; inhibitors and adverse reactions to replacement therapy: a case-report and literature review

Hemophilia B is a rare X-linked recessive disorder with plasma factor IX (FIX) deficiency. 1-3% of patients treated with exogenous FIX-containing products develop inhibitors (i.e. polyclonal high affinity immunoglobulins) that neutralize the procoagulant activity of a specific coagulation factor. Although the incidence of inhibitors in hemophilia B patients is low, most are "high titer" and frequently associated with the development of severe allergic or anaphylactic reactions. Immune tolerance induction as a strategy for inhibitor eradication was first described in 1984. Unfortunately, the overall reported success of immune tolerance induction in FIX deficiency with inhibitors is approximately 25-40%.We report the case of a 2-year-old boy with hemophilia B severe FIX deficiency (<1%), inhibitor antibodies to FIX development, and a history of adverse reactions to FIX infusions, who underwent a successful desensitization and immune tolerance induction with a daily FIX infusion. With this regimen the inhibitor titer decreased with effective bleeding prevention.