Evaluating Gene Therapy as a Potential Paradigm Shift in Treating Severe Hemophilia

Economic Burden of Haemophilia from a Societal Perspective: A Scoping Review

INTRODUCTION

Haemophilia is a rare genetic bleeding disorder that leads to musculoskeletal complications. The high cost of haemophilia treatment necessitates a thorough evaluation of its economic burden. However, due to the difficulty of estimating direct non-medical, indirect, and intangible costs, studies often underestimate the actual economic burden of haemophilia. This scoping review aims to summarise economic studies in haemophilia conducted from a societal perspective.

METHODS

A systematic search across eight scholarly databases, grey literature, and reference lists until the 5th of July 2023 was conducted to identify relevant studies. The inclusion criteria encompassed full-text, English-language publications of economic analyses in congenital haemophilia from a societal perspective. Model-based studies and those adopting a payer perspective were excluded. Costs were adjusted to international dollars (I$) and US dollars (US$) in 2022 for comparability.

RESULTS

Out of 2993 potential sources identified, 25 studies met the inclusion criteria, covering 7226 persons with haemophilia across 22 countries. All studies reported direct medical costs, with four excluding the cost of haemostatic therapy. Fifteen studies reported direct formal non-medical costs, while eight reported direct informal non-medical costs. All but one study reported the indirect costs. The average annual costs of haemophilia varied widely based on treatment modality, disease severity, geographical location, and included cost categories. When including the cost of clotting factor replacement therapy (CFRT), the total cost for severe haemophilia without inhibitors ranged from 1566 I$ to 700,070 I$ per person per year (lowest value reported in India and highest in the United States). CFRT represented up to 99.9% of the total cost for those receiving prophylaxis and up to 95.1% for episodic treatment. Haemostatic therapies accounted for 82% of the total cost in patients with inhibitors.

CONCLUSION

There is a significant heterogeneity in defining cost categories required for a comprehensive economic analysis from a societal perspective. While haemostatic therapies constitute a substantial portion of the overall cost, direct non-medical and indirect costs are crucial as they are often paid out-of-pocket and may impede access to treatment. It is essential for haematologists and economists to establish a standardised costing framework for future studies, particularly in the era of novel therapies.

Gene Therapy in Hemophilia A: Achievements, Challenges, and Perspectives

Strides in advancements of care of persons with hemophilia include development of long-acting factor replacement therapies, novel substitution and hemostatic rebalancing agents, and most recently approved gene therapy. Several decades of preclinical and clinical trials have led to development of adeno-associated viral (AAV) vector-mediated gene transfer for endogenous production of factor VIII (FVIII) in hemophilia A (HA). Only one gene therapy product for HA (valoctocogene roxaparvovec) has been approved by regulatory authorities. Results of valoctocogene roxaparvovec trial show significant improvement in bleeding rates and use of factor replacement therapy; however, sustainability and duration of response show variability with overall decline in FVIII expression over time. Further challenges include untoward adverse effects involving liver toxicity requiring immunosuppression and development of neutralizing antibodies to AAV vector rendering future doses ineffective. Real-life applicability of gene therapy for HA will require appropriate patient screening, infrastructure setup, long-term monitoring including data collection of patient-reported outcomes and innovative payment schemes. This review article highlights the success and development of HA gene therapy trials, challenges including adverse outcomes and variability of response, and perspectives on approach to gene therapy including shared decision-making and need for future strategies to overcome the several unmet needs.

Gene therapy in hemophilia: the dawn of a new era

Hemophilia A and B are hereditary bleeding disorders associated with the X chromosome, stemming from genetic defects in the coding of coagulation factor (F)VIII or FIX protein, leading to partial or complete deficiency. In the absence of effective prophylaxis, these deficiencies can result in irreversible joint damage, known as hemophilic arthropathy, and subsequent disability. Despite advancements in hemophilia treatment, individuals with severe forms of the disease continue to face a high risk of bleeding, particularly in instances of trauma or major surgical procedures. In such scenarios, it remains imperative to administer replacement or bypassing drugs, especially when inhibitors are present. Within this context, gene therapy emerges as a compelling alternative, ensuring sustained expression of the deficient factor at levels often surpassing current recommendations. Some studies report an effect lasting up to 8 years, contributing significantly to clinical improvement and enhancing the quality of life for patients. However, a comprehensive evaluation of this innovative therapy is essential, encompassing both its benefits and potential risks. It is crucial to undertake a multidisciplinary assessment, engage in thoughtful discussions with the patient, and closely monitor the therapy's effects and any eventual side effects of therapy. This approach aims to facilitate an informed and collaborative decision-making process, ultimately maximizing the benefits for each individual patient.

Adeno-associated virus therapies: Pioneering solutions for human genetic diseases

Adeno-associated virus (AAV) has emerged as a fundamental component in the gene therapy landscape, widely acknowledged for its effectiveness in therapeutic gene delivery. The success of AAV-based therapies, such as Luxturna and Zolgensma, underscores their potential as a leading vector in gene therapy. This article provides an in-depth review of the development and mechanisms of AAV vector-based therapies, offering a comprehensive analysis of the latest clinical trial outcomes in central nervous system (CNS) diseases, ocular conditions, and hemophilia, where AAV therapies have shown promising results. Additionally, we discusse the selection of administration methods and serotypes tailored to specific diseases. Our objective is to showcase the innovative applications and future potential of AAV-based gene therapy, laying the groundwork for continued clinical advancements.

Liver-related aspects of valoctocogene roxaparvovec gene therapy for hemophilia A: expert guidance for clinical practice

Adeno-associated virus-based gene therapy (valoctocogene roxaparvovec) is an attractive treatment for hemophilia A. Careful clinical management is required to minimize the risk of hepatotoxicity, including assessment of baseline liver condition to determine treatment eligibility and monitoring liver function after gene therapy. This article describes recommendations (developed by a group of hemophilia experts) on hepatic function monitoring before and after gene therapy. To prevent harmful liver-related effects, gene therapy is contraindicated in patients with uncontrolled liver infections, autoimmune hepatitis, liver stiffness ≥8 kPa, or cirrhosis. Before using gene therapy in patients with liver steatosis or other liver disorders, the risk of liver damage should be considered using a highly individualized approach. Treatment is not recommended in patients with abnormal liver enzymes, including alanine aminotransferase (ALT) at any level above the upper limit of normal (ULN). Therefore, pretreatment assessment of liver health should include laboratory tests, abdominal ultrasound, and liver stiffness measurements by transient elastography (TE). In the first year after therapy, ALT levels should be monitored 1 to 2 times per week to detect elevations ≥1.5× ULN, which may require immunosuppressant therapy. Patients with ALT elevation should receive prednisone 60 mg/d for 2 weeks, followed by stepwise tapering when ALT returns to baseline. ALT monitoring should continue long term (every 3-6 months), along with abdominal ultrasound (every 6 months) and TE (yearly) evaluations. When patients with good liver health are selected for treatment and closely monitored thereafter, ALT elevations can be promptly treated and are expected to resolve without long-term hepatic sequelae.

Liver health in hemophilia in the era of gene therapy

Gene therapy for hemophilia is a groundbreaking treatment approach with promising results and potential to reduce the burden of the disease. However, uncertainties remain, particularly regarding the liver side effects of AAV gene therapy, which are more common in hemophilia A. Unlike some other diseases, such as spinal muscular atrophy, where the target cell for gene therapy is different from the one affected by side effects, hemophilia gene therapy operates within the same cellular domain-the hepatocyte. This overlap is challenging and requires a targeted strategy to mitigate the risks associated with liver injury, which often requires temporary immunosuppressive therapy. A comprehensive approach is essential to increase the efficacy of gene therapy and reduce the likelihood of hepatocyte damage. Key components of this strategy include a thorough pre-gene therapy assessment of liver health, careful post-gene therapy liver monitoring, and prompt therapeutic intervention for loss of transgene expression and liver injury. Collaboration between hematologists and hepatologists is essential to ensure a well-coordinated management plan for patients undergoing hemophilia gene therapy. This review addresses the critical aspect of hepatic comorbidities in patients with hemophilia, emphasizing the need to identify and address these issues prior to initiating gene therapy. It examines the known mechanisms of liver damage and emphasizes the importance of liver monitoring after gene therapy. In addition, the review draws insights from experiences with other AAV-based gene therapies, providing valuable lessons that can guide hemophilia centers in effectively managing liver damage associated with hemophilia gene therapy.

Outcome measures in hemophilia: current and future perspectives

INTRODUCTION

Hemophilia can detrimentally affect patients' quality of life and likelihood of survival. In the evolving landscape of therapies, the therapeutic gain of each treatment must be understood to accurately position it in the therapeutic armamentarium. Accordingly, appropriate outcomes must be measured with appropriate tools.

AREAS COVERED

Our narrative review (PubMed search for 'hemophilia AND outcome' until June 2023), provides a compendium of outcome measures used in hemophilia clinical research. To define each outcome measure's relative value and applicability, several characteristics are critically discussed.

EXPERT OPINION

Bleeding assessment, first annual/annualized bleeding rate, remains central in evaluating the efficacy and safety of hemophilia treatments. As modern therapies improve clinical outcomes toward zero bleeding events, this endpoint may become less sensitive to detect differences between therapeutic approaches. Technological advancements necessitate the adaptation of outcome measures to address infrequent bleeding events, age-related comorbidities, and laboratory parameters with limited comparability after different treatments. Considerable effort has been dedicated to the development of tools that comprehensively assess coagulation, such as thrombin generation assays. Patient-reported outcome measures are gaining importance although limited by their subjectivity. A definitive set of research outcome measures remains elusive. Outcomes may need to be tailored to different therapeutic interventions.

Minimum factor VIII levels to prevent joint bleeding in mild hemophilia A

The severity of the bleeding phenotype in patients with hemophilia A (HA) broadly correlates with the degree of coagulation factor VIII (FVIII) deficiency in plasma. However, the FVIII level necessary to achieve the goal of zero joint bleeds remains unclear. This study aimed to identify the minimum FVIII level necessary to prevent joint bleeds in patients with HA. In this retrospective study, patients with congenital mild HA treated on demand, aged ≥16 years, with no history of FVIII inhibitors, followed at the Angelo Bianchi Bonomi Hemophilia and Thrombosis Center in Milan, were enrolled. We investigated 270 male patients with a median age of 45 years (16-88) and median lifelong FVIII of 21 IU/dL. One hundred patients (37%) had a lifelong history of at least 1 joint bleed. The mean annualized joint bleeding rate (AJBR) and spontaneous AJBR were 0.016 (standard deviation [SD], 0.032) and 0.001 (SD, 0.010), respectively. After adjusting for age, for each IU/dL increase in FVIII, there was a 6% reduction in AJBR and an 11% reduction in spontaneous AJBR. The minimum FVIII levels needed to prevent lifelong any joint bleeds and spontaneous joint bleeds resulted to be 19.2 IU/dL and 17.7 IU/dL, respectively. In this large cohort of persons with mild HA, we identified the minimum FVIII levels needed to prevent total and spontaneous joint bleeds (19.2 IU/dL and 17.7 IU/dL, respectively). These findings could suggest important implications for the accurate design of prophylactic therapies for persons with moderate and severe HA, including gene therapy.

Etranacogene dezaparvovec-drlb gene therapy for patients with hemophilia B (congenital factor IX deficiency)

INTRODUCTION

Congenital hemophilia B (HB) is an X-linked bleeding disorder resulting in Factor IX (FIX) deficiency and bleeding of variable severity. There is no cure for HB. Typical management consists of prophylactic intravenous (IV) recombinant or plasma-derived FIX infusions. Etranacogene dezaparvovec-drlb (Hemgenix, AMT-061) is an adeno-associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant of the human F9 gene with a liver-specific promoter. Etranacogene dezaparvovec-drlb received FDA approval on 22 November 2022 for the treatment of HB in adult patients who use FIX prophylaxis therapy, have current or historical life-threatening hemorrhage, or have experienced repeated, serious spontaneous bleeding episodes.

AREAS COVERED

This drug profile discusses the safety and efficacy of etranacogene dezaparvovec-drlb in patients with HB.

EXPERT OPINION

Etranacogene dezaparvovec-drlb therapy results in stable and sustained expression of near-normal to normal FIX levels in patients with HB regardless of neutralizing antibodies to AAV5 up to a titer of 678. Its use has led to significant reduction in bleeding and FIX prophylaxis. Etranacogene dezaparvovec-drlb was well tolerated; however, 17% of patients required corticosteroid therapy for alanine aminotransferase (ALT) elevation. Etranacogene dezaparvovec-drlb therapy marks the beginning of an exciting era in HB treatment and opens questions regarding treatment longevity and long-term safety.