Deconstructing gene therapy in hemophilia for the clinician

After decades of research, gene therapy for hemophilia is now commercially available for both hemophilia A and B. Currently, two products, valoctocogene roxaparvovec (for hemophilia A) and etranacogene dezaparvovec (for hemophilia B), have been licensed following approval in the United States and several other countries. Therefore, clinicians must familiarize themselves with these novel treatment options just as they do with other newly available products in order to provide their patients the opportunity to consider which treatment may suit them best. Undoubtedly, gene therapy is a novel platform for treating human disease, and unlike other hemophilia treatments, its biology, mechanisms, and administration logistics are quite complex. Furthermore, additional products using different approaches have entered clinical trials, with more in the preclinical stages of development. This review's aims are (1) to deconstruct gene therapy in hemophilia and provide a basic framework for understanding its components and processes, including the transgene, the vector, and the delivery systems, in order to help clinicians present gene therapy as a treatment option in a shared decision-making model, better understand the clinical data, and explain gene therapy to their patients; (2) to gain knowledge of the currently approved gene therapies for hemophilia A and B, including their eligibility and exclusion criteria and the range of expected outcomes; and (3) to comprehend the shared decision-making process for these therapies and their implementation in clinical practice. In addition, a brief review of the currently approved products and those in clinical trials is presented, followed by a discussion of practical considerations for implementing gene therapy in practice.