Gene Therapy and Hemophilia: Where Do We Go from Here?

The role of public health in rare diseases: hemophilia as an example

Introduction

The role of public health has evolved from addressing infectious diseases to encompass non-communicable diseases. Individuals with genetic disorders and rare diseases constitute a particularly vulnerable population, requiring tailored public health policies, practical implementation strategies, and a long-term vision to ensure sustainable support. Given the prolonged duration and significant costs often associated with these conditions, comprehensive, patient-centered, and cost-effective approaches are essential to safeguard their physical and mental well-being.

Aims

To summarize definitions and concepts related to health, public health, rare diseases, and to highlight the role of integrating public health interventions into routine care in improving patient outcomes. Hemophilia was selected as an exemplary rare disease due to its significant lifetime treatment costs and the recent approval and pricing of its gene therapy as the world's most expensive drug, highlighting the critical importance of public health policies in ensuring equitable access to care and treatment.

Methods

A narrative literature review was conducted between July 2023 and December 2024, searching PubMed, Google Scholar, and Google for various topics related to rare diseases, public health, and hemophilia.

Results

Public health can play an important role in improving the health outcomes of people with rare diseases by implementing conceptual and applied models to accomplish a set of objectives. Over the past two decades, legislative and regulatory support in high income countries (HICs) has facilitated the development and approval of diagnostics and treatments for several rare diseases leading to important advancements. In contrast, many low- and middle-income countries (LMICs) face obstacles in enacting legislation, developing regulations, and implementing policies to support rare disease diagnosis and treatment. More investment and innovation in drug discovery and market access pathways are still needed in both LMICs and HICs. Ensuring the translation of public health policies into regulatory measures, and in turn implementing, and regularly evaluating these measures to assess their effectiveness is crucial. In the case of hemophilia, public health can play a pivotal role.

Conclusion

Enhancing public health surveillance, policies, and interventions in hemophilia and other rare diseases can bridge data gaps, support access to equitable treatment, promote evidence-based care, and improve outcomes across the socioeconomic spectrum.

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.

Rescue of the endogenous FVIII expression in hemophilia A mice using CRISPR-Cas9 mRNA LNPs

Gene editing provides a promising alternative approach that may achieve long-term FVIII expression for hemophilia A (HemA) treatment. In this study, we investigated in vivo correction of a mutant factor VIII (FVIII) gene in HemA mice. We first developed MC3-based LNPs for efficient mRNA delivery into liver sinusoidal endothelial cells (LSECs), the major site of FVIII biosynthesis. To target a five base pair deletion in FVIII exon 1 in a specific HemA mouse strain, we injected LNPs encapsulating Cas9 mRNA and specifically designed sgRNAs intravenously for in vivo gene editing of the mutant FVIII. Indel variants generated at the mutant site contained mostly a single base-pair deletion, resulting in frameshift correction of FVIII gene. Sustained endogenous FVIII activity up to 6% was achieved over 26 weeks in treated HemA mice. Sequencing data indicated an average gene editing rate of 15.3% in LSECs. Our study suggests that optimized MC3 LNP formulations, combined with CRISPR-Cas9 technology, can effectively correct the mutant FVIII gene in LSECs and restore FVIII activity for therapeutic treatment of HemA.

Recent Advances in Gene Therapy for Hemophilia: Projecting the Perspectives

One of the well-known X-linked genetic disorders is hemophilia, which could be hemophilia A as a result of a mutation in the F8 (factor VIII) gene or hemophilia B as a result of a mutation in the F9 (factor IX) gene, leading to insufficient levels of the proteins essential for blood coagulation cascade. In patients with severe hemophilia, factor VIII or factor IX activities in the blood plasma are considerably low, estimated to be less than 1%. This is responsible for spontaneous or post-traumatic bleeding episodes, or both, leading to disease complications and death. Current treatment of hemophilia relies on the prevention of bleeding, which consists of expensive lifelong replacement infusion therapy of blood plasma clotting factors, their recombinant versions, or therapy with recombinant monoclonal antibodies. Recently emerged gene therapy approaches may be a potential game changer that could reshape the therapeutic outcomes of hemophilia A or B using a one-off vector in vivo delivery and aim to achieve long-term endogenous expression of factor VIII or IX. This review examines both traditional approaches to the treatment of hemophilia and modern methods, primarily focusing on gene therapy, to update knowledge in this area. Recent technological advances and gene therapeutics in the pipeline are critically reviewed and summarized. We consider gene therapy to be the most promising method as it may overcome the problems associated with more traditional treatments, such as the need for constant and expensive infusions and the presence of an immune response to the antibody drugs used to treat hemophilia.

Etranacogene Dezaparvovec: First Approval

Etranacogene dezaparvovec (etranacogene dezaparvovec-drlb; Hemgenix^®) is an adeno-associated virus vector-based gene therapy being developed by uniQure and CSL Behring for the treatment of haemophilia B. In November 2022, etranacogene dezaparvovec was approved in the USA for the treatment of haemophilia B [congenital factor IX (FIX) deficiency] in adults who are currently using FIX prophylaxis therapy, have current or historical life-threatening haemorrhage or have repeated, serious spontaneous bleeding episodes. In December 2022, etranacogene dezaparvovec also received positive opinion in the EU for the treatment of haemophilia B. This article summarizes the milestones in the development of etranacogene dezaparvovec leading to this first approval.

How to translate and implement the current science of gene therapy into haemophilia care?

Gene-based therapy opens an entirely new paradigm in managing people with haemophilia (PWH), offering them the possibility of a functional cure by enabling continuous expression of factor VIII (FVIII) or factor IX (FIX) after transfer of a functional gene designed to replace the PWH's own defective gene. In recent years, significant advances in gene therapy have been made, resulting in clotting factor activity attaining near-normal levels, as reflected by 'zero bleeding rates' in previously severely inflicted patients following a single administration of adeno-associated viral (AAV) vectors. While this new approach represents a major advancement, there are still several issues that must be resolved before applying this technology in clinical practice. First, awareness, communication, and education about the therapeutic potential and modalities of gene therapy must be further strengthened. To this end, objective, unbiased, transparent, and regularly updated information must be shared, in an appropriate way and understandable language with the support of patients' organizations. Second, healthcare providers should adopt a patient-centred approach, as the 'one size fits all' approach is inappropriate when considering gene therapy. Instead, a holistic patient view taking into account their physical and mental dimensions, along with unexpressed expectations and preferences, is mandatory. Third, the consent procedure must be improved, ensuring that patients' interests are maximally protected. Finally, gene therapy is likely to be first delivered in a few centres, with the highest expertise and experience in this domain. Thus, patients should be managed based on a hub-and-spoke model, taking into account that the key to gene therapy's success lies in an optimal communication and collaboration both within and between haemophilia centres sharing their experiences in the frame of international registries. This review describes recent progress and explains outstanding hurdles that must be tackled to ease the implementation of this paradigm-changing new therapy.