F8 and hemophilia B: The first gene therapy for hemophilia A (valoctocogene roxaparvovec;Biomarin) has recently been licensed for adults by the European Medicines Agency,87 with the first gene therapy for adults with hemophilia B(etranacogene dezaparvovec; CSL Behring) subsequently approved by the U.S.Food and Drug Administration.88 The impact of tolerance toward the deficient protein (FVIII/FIX) oneligibility for gene therapy remains to be determined.