Hemophilia gene therapy: first, do no harm.

The introduction of adeno-associated virus-mediated, liver-directed gene therapy into the hemophilia treatment landscape brings not only great promise but also considerable uncertainty to a community that has a history punctuated by the devastating effects of HIV and hepatitis C virus. These infections were introduced into people with hemophilia through the innovation of factor concentrates in the 1970s and 1980s. Concentrates, heralded as a major advance in treatment at the time, brought devastation and death to the community already challenged by the complications of bleeding into joints, vital organs, and the brain. Over the past 5 decades, considerable advances in hemophilia treatment have improved the survival, quality of life, and participation of people with hemophilia, although challenges remain and health equity with their unaffected peers has not yet been achieved. The decision to take a gene therapy product is one in which an informed, holistic, and shared decision-making approach must be employed. Bias on the part of health care professionals and people with hemophilia must be addressed and minimized. Here, we review data leading to the regulatory authorization of valoctocogene roxaparvovec, an adeno-associated virus 5 gene therapy, in Europe to treat hemophilia A and etranacogene dezaparvovec-drlb in the United States and Europe to treat hemophilia B. We also provide an overview of the decision-making process and recommend steps that should be taken by the hemophilia community to ensure the safety of and optimal outcomes for people with hemophilia who choose to receive a gene therapy product.

Valoctocogene Roxaparvovec Gene Therapy for Hemophilia A.

BACKGROUND: Valoctocogene roxaparvovec (AAV5-hFVIII-SQ) is an adeno-associated virus 5 (AAV5)-based gene-therapy vector containing a coagulation factor VIII complementary DNA driven by a liver-selective promoter. The efficacy and safety of the therapy were previously evaluated in men with severe hemophilia A in a phase 1-2 dose-escalation study. METHODS: We conducted an open-label, single-group, multicenter, phase 3 study to evaluate the efficacy and safety of valoctocogene roxaparvovec in men with severe hemophilia A, defined as a factor VIII level of 1 IU per deciliter or lower. Participants who were at least 18 years of age and did not have preexisting anti-AAV5 antibodies or a history of development of factor VIII inhibitors and who had been receiving prophylaxis with factor VIII concentrate received a single infusion of 6×1013 vector genomes of valoctocogene roxaparvovec per kilogram of body weight. The primary end point was the change from baseline in factor VIII activity (measured with a chromogenic substrate assay) during weeks 49 through 52 after infusion. Secondary end points included the change in annualized factor VIII concentrate use and bleeding rates. Safety was assessed as adverse events and laboratory test results. RESULTS: Overall, 134 participants received an infusion and completed more than 51 weeks of follow-up. Among the 132 human immunodeficiency virus-negative participants, the mean factor VIII activity level at weeks 49 through 52 had increased by 41.9 IU per deciliter (95% confidence interval [CI], 34.1 to 49.7; P<0.001; median change, 22.9 IU per deciliter; interquartile range, 10.9 to 61.3). Among the 112 participants enrolled from a prospective noninterventional study, the mean annualized rates of factor VIII concentrate use and treated bleeding after week 4 had decreased after infusion by 98.6% and 83.8%, respectively (P<0.001 for both comparisons). All the participants had at least one adverse event; 22 of 134 (16.4%) reported serious adverse events. Elevations in alanine aminotransferase levels occurred in 115 of 134 participants (85.8%) and were managed with immune suppressants. The other most common adverse events were headache (38.1%), nausea (37.3%), and elevations in aspartate aminotransferase levels (35.1%). No development of factor VIII inhibitors or thrombosis occurred in any of the participants. CONCLUSIONS: In patients with severe hemophilia A, valoctocogene roxaparvovec treatment provided endogenous factor VIII production and significantly reduced bleeding and factor VIII concentrate use relative to factor VIII prophylaxis. (Funded by BioMarin Pharmaceutical; GENEr8-1 ClinicalTrials.gov number, NCT03370913.).

Achieving the unimaginable: Health equity in haemophilia.

Historically, treatment based on the availability of clotting factor replacement has resulted in an arcane guideline for the correction of factor deficiencies in people with haemophilia (PwH). While all other disease entities seek to restore function to a normal level, PwH are restricted to factor nadirs still equivalent to mild or moderate disease, resulting in continued risk of bleeding. A new treatment paradigm is needed based on the defined needs of PwH. A treatment model was developed by a panel of haemophilia providers, patient advocates and health economists to establish specific treatment milestones and targeted outcomes. The panel defined a series of treatment milestones to characterize the activity and outcomes linked to level of factor deficiency correction. All agreed that the ultimate goal should be 'functional cure' and 'health equity'. Seven levels to achieving a functional cure were identified, (a) Sustain life; (b) Minimal joint impairment; (c) Freedom from any spontaneous bleeds; (d) Attainment of 'normal' mobility; (e) Able to sustain minor trauma without additional intervention; (f) Ability to sustain major surgery or trauma; and (g) Normal haemostasis. A parallel set of patient-reported outcomes to achieve health equity was identified. These guidelines are now comparable with other disorders where the goal is to replace missing proteins to attain normal activity levels. As we are no longer limited by plasma supply due to the manufacture of recombinant factors, mimetics, and the early success of gene therapy, health equity is now achievable.

How to discuss gene therapy for haemophilia? A patient and physician perspective.

Gene therapy has the potential to revolutionise treatment for patients with haemophilia and is close to entering clinical practice. While factor concentrates have improved outcomes, individuals still face a lifetime of injections, pain, progressive joint damage, the potential for inhibitor development and impaired quality of life. Recently published studies in adeno-associated viral (AAV) vector-mediated gene therapy have demonstrated improvement in endogenous factor levels over sustained periods, significant reduction in annualised bleed rates, lower exogenous factor usage and thus far a positive safety profile. In making the shared decision to proceed with gene therapy for haemophilia, physicians should make it clear that research is ongoing and that there are remaining evidence gaps, such as long-term safety profiles and duration of treatment effect. The eligibility criteria for gene therapy trials mean that key patient groups may be excluded, eg children/adolescents, those with liver or kidney dysfunction and those with a prior history of factor inhibitors or pre-existing neutralising AAV antibodies. Gene therapy offers a life-changing opportunity for patients to reduce their bleeding risk while also reducing or abrogating the need for exogenous factor administration. Given the expanding evidence base, both physicians and patients will need sources of clear and reliable information to be able to discuss and judge the risks and benefits of treatment.