Gene Therapy for Hemophilia: Facts and Quandaries in the 21st Century

Gene Therapy for Hemophilia B: Achievements, Open Issues, and Perspectives

Hemophilia B is the first bleeding disorder for which gene therapy clinical programs began. Presently, adenovirus-associated vectors represent the best means to deliver the transgene, and their administration by intravenous route has been used in recent clinical trials. The natural occurring factor IX (FIX) Padua variant, which allows for a 5- to 8-fold higher activity of FIX, while maintaining a normal protein concentration, was subsequently used to enhance the level of transgene expression. All the recent trials using this variant showed good results, and accumulating data suggest that long-term expression durability could be maintained at a significant hemostatic level. However, the risk of loss of transgene expression associated to immune response with liver enzymes elevation remains a concern, especially as to the efficacy and duration of immunosuppressive treatment. Notwithstanding this limitation, the results of clinical trials suggest that gene therapy in hemophilia B has the potential to provide long-term benefits with sustained factor activity levels predicted to last several years in many patients.

The current challenges faced by people with hemophilia B

Hemophilia B (HB) is a rare, hereditary disease caused by a defect in the gene encoding factor IX (FIX) and leads to varying degrees of coagulation deficiency. The prevailing treatment for people with HB (PWHB) is FIX replacement product. The advent of recombinant coagulation products ushered in a new era of safety, efficacy, and improved availability compared with plasma-derived products. For people with severe HB, lifelong prophylaxis with a FIX replacement product is standard of care. Development of extended half-life FIX replacement products has allowed for advancements in the care of these PWHB. Nonetheless, lifelong need for periodic dosing and complex surveillance protocols pose substantive challenges in terms of access, adherence, and healthcare resource utilization. Further, some PWHB on prophylactic regimens continue to experience breakthrough bleeds and joint damage, and subpopulations of PWHB, including women, those with mild-to-moderate HB, and those with inhibitors to FIX, experience additional unique difficulties. This review summarizes the current challenges faced by PWHB, including the unique subpopulations; identifying the need for improved awareness, personalized care strategies, and new therapeutic options for severe HB, which may provide future solutions for some of the remaining unmet needs of PWHB.

Etranacogene dezaparvovec for the treatment of adult patients with severe and moderately severe hemophilia B

INTRODUCTION

Etranacogene dezaparvovec is the first gene therapy approved for treatment of adults with severe and moderately severe hemophilia B.

AREAS COVERED

This review describes the results of the clinical trial program of AMT-060 and etranacogene dezaparvovec, outlining the pharmacokinetic, clinical efficacy and safety data. With the entry of etranacogene dezaparvovec into the market, this review summarizes the treatment landscape in hemophilia B and discusses the current unknowns in the field.

EXPERT OPINION

Gene therapy appears to be a feasible option for adults with severe and moderately severe hemophilia B. Etranacogene dezaparvovec enables most patients to reach stable factor IX (FIX) levels after a single intravenous infusion, eliminating the need for regular prophylaxis; thus, drastically reducing treatment burden and avoiding variable bleeding risk owing to fluctuating FIX activity levels. Efficacy of etranacogene dezaparvovec has been demonstrated even in the presence of preexisting neutralizing antibodies (up to a titer of 1:678), with a relative low risk of transaminitis and its associated potential loss of transgene expression. However, long-term data are required to ascertain the durability of FIX levels achieved and safety. The cost-effectiveness and adoption of innovative payment models for reimbursement are key in choosing gene therapy over existing treatments.

Applications of artificial intelligence in clinical management, research and health administration: imaging perspectives with a focus on hemophilia

INTRODUCTION

Joints of persons with hemophilia are frequently affected by repetitive hemarthrosis. In this paper concepts, perks and quirks of the use of artificial intelligence (AI), machine learning (ML) and deep learning are reviewed within clinical and research contexts of hemophilia and other blood-induced disorders' patient care, targeted to the imaging diagnosis of hemophilic joints, under the perspective of different stakeholders (radiologists, hematologists, nurses, physiotherapists, technologists, researchers, managers and patients/caregivers).

AREAS COVERED

Rubrics that determine the suitability of the utilization of AI in blood-induced disorders' patient care, including diagnosis and follow-up of patients are discussed, focusing on features in which AI can replace or augment the role of radiology in the clinical management and in research of patients. Insights on features in the design and conduct of AI projects in which the human intervention remains critical are provided.

EXPERT OPINION

The author discusses research concepts in radiogenomics, and challenges of the utilization of AI in different healthcare fields such as patient safety, data sharing and privacy regulations, workforce education and future jobs' shortage. Finally, the author proposes alternatives and potential solutions to mitigate challenges in successfully deploying ML algorithms into clinical practice.

Ectopic clotting factor VIII expression and misfolding in hepatocytes as a cause for hepatocellular carcinoma

Hemophilia A gene therapy targets hepatocytes to express B domain deleted (BDD) clotting factor VIII (FVIII) to permit viral encapsidation. Since BDD is prone to misfolding in the endoplasmic reticulum (ER) and ER protein misfolding in hepatocytes followed by high-fat diet (HFD) can cause hepatocellular carcinoma (HCC), we studied how FVIII misfolding impacts HCC development using hepatocyte DNA delivery to express three proteins from the same parental vector: (1) well-folded cytosolic dihydrofolate reductase (DHFR); (2) BDD-FVIII, which is prone to misfolding in the ER; and (3) N6-FVIII, which folds more efficiently than BDD-FVIII. One week after DNA delivery, when FVIII expression was undetectable, mice were fed HFD for 65 weeks. Remarkably, all mice that received BDD-FVIII vector developed liver tumors, whereas only 58% of mice that received N6 and no mice that received DHFR vector developed liver tumors, suggesting that the degree of protein misfolding in the ER increases predisposition to HCC in the context of an HFD and in the absence of viral transduction. Our findings raise concerns of ectopic BDD-FVIII expression in hepatocytes in the clinic, which poses risks independent of viral vector integration. Limited expression per hepatocyte and/or use of proteins that avoid misfolding may enhance safety.

Structural basis of von Willebrand factor multimerization and tubular storage

The von Willebrand factor (VWF) propeptide (domains D1D2) is essential for the assembly of VWF multimers and its tubular storage in Weibel-Palade bodies. However, detailed molecular mechanism underlying this propeptide dependence is unclear. Here, we prepared Weibel-Palade body-like tubules using the N-terminal fragment of VWF and solved the cryo-electron microscopy structures of the tubule at atomic resolution. Detailed structural and biochemical analysis indicate that the propeptide forms a homodimer at acidic pH through the D2:D2 binding interface and then recruits 2 D'D3 domains, forming an intertwined D1D2D'D3 homodimer in essence. Stacking of these homodimers by the intermolecular D1:D2 interfaces brings 2 D3 domains face-to-face and facilitates their disulfide linkages and multimerization of VWF. Sequential stacking of these homodimers leads to a right-hand helical tubule for VWF storage. The clinically identified VWF mutations in the propeptide disrupted different steps of the assembling process, leading to diminished VWF multimers in von Willebrand diseases (VWD). Overall, these results indicate that the propeptide serves as a pH-sensing template for VWF multimerization and tubular storage. This sheds light on delivering normal propeptide as a template to rectify the defects in multimerization of VWD mutants.

Preparing for tomorrow: Defining a future agenda

Gene therapy will be the first long-term therapy with potential to produce a functional cure for haemophilia. As a single dose ('once-and-done') therapy with significant uncertainties regarding impact and duration of factor expression, flexibility and adaptability of (1) value framework, (2) health technology assessment (HTA) methodology, and (3) development of alternative payment models will be needed for adoption of this new technology and to facilitate transparent decision-making to support its implementation. The responsibility for each of these currently lies with distinct entities, underscoring a need for enhanced collaboration between all stakeholders, as expanded engagement by key stakeholders will be critical to optimizing the assessment of value, enabling an optimised approach to HTA, and opening receptivity to new and innovative payment models. This supplement issue describes important considerations for a gene therapy 'toolkit', highlighting key considerations for each of the aforementioned tools, which will be useful for guiding decision-making regarding gene therapy as a novel treatment modality. In this article, we outline how the tools presented in this supplement can be applied as part of a framework to address the requirements of the relevant stakeholders, including payers, manufacturers, treaters, and patients. The paper also provides an illustrative example of how to understand the features of alternative payment models depending on the organization of and payment for healthcare.

A preliminary application of a haemophilia value framework to emerging therapies in haemophilia

INTRODUCTION

Emergence of new therapies are anticipated to improve clinical outcomes and quality of life of persons with haemophilia. Challenges in conducting randomized clinical trials in rare diseases have resulted in a lack of direct head-to-head comparisons to support value-based decision-making between different treatments.

METHODS

We conducted a literature review for new and emerging haemophilia A and B therapies (extended half-life [EHL] replacement factor, non-replacement therapies [NRT], and gene therapies [GT]) to identify differentiating patient-centred outcomes defined previously in a haemophilia value framework. Since the literature included all publication types (e.g., surveys, modelling studies, commentaries/reviews), collected data were assigned level of evidence scores.

RESULTS

Across different classes of therapies, bleeding was determined as the most frequently reported differentiating outcome, with EHL, NRT, and GT each demonstrating an advantage over comparator replacement therapies. EHL therapies for haemophilia A and B and NRT for haemophilia A showed good representation across Tier 1 outcomes (health status achieved/retained), while more publications were identified with Tier 2 (process of recovery) outcomes for NRT than EHL or GT. In Tier 3 (sustainability of health), frequency of breakthrough bleeds represented a differentiating outcome for EHL (both haemophilia A and B), NRT (haemophilia A only), and GT (haemophilia B only), whereas sustained good health was differentiating for most comparisons.

CONCLUSIONS

We demonstrate the utility of the haemophilia value framework as a common core outcome set for effectively comparing therapies. Application of this framework will serve as a useful decision-making tool for patients, clinicians, and within health technology assessments.

KEY POINTS OF CONSIDERATION

With the emergence of high-cost, paradigm changing treatments across multiple areas of medicine, we, the haemophilia community, need to be equipped to meet the growing demands for more rigorous evidence-based value assessments using the tools expected by assessors. The traditional access toolbox needs to evolve to meet the paradigm shift in treatment options. Value can no longer be defined by annualized bleed rates alone. To realize the full impact of new therapies, we need to utilize tools, such as a value framework, to organize evidence, identify data gaps, and assess patient-defined, meaningful outcomes across a multi-faceted dimension. The haemophilia value framework is an effective tool for organizing the available evidence and identifying gaps in the evidence. This can be used for assessing the value of emerging therapies in haemophilia utilizing data generated through randomized clinical trials and real world evidence generation. This is a call for incorporating the Value Framework into official submissions to authorities, as it captures a broader range of outcomes, including patient meaningful outcomes, in ways that better assess the potential benefits of new therapies.

AAV-mediated gene therapy for galactosialidosis: A long-term safety and efficacy study

AAV-mediated gene therapy holds promise for the treatment of lysosomal storage diseases (LSDs), some of which are already in clinical trials. Yet, ultra-rare subtypes of LSDs, such as some glycoproteinoses, have lagged. Here, we report on a long-term safety and efficacy preclinical study conducted in the murine model of galactosialidosis, a glycoproteinosis caused by a deficiency of protective protein/cathepsin A (PPCA). One-month-old Ctsa -/- mice were injected intravenously with a high dose of a self-complementary AAV2/8 vector expressing human CTSA in the liver. Treated mice, examined up to 12 months post injection, appeared grossly indistinguishable from their wild-type littermates. Sustained expression of scAAV2/8-CTSA in the liver resulted in the release of the therapeutic precursor protein in circulation and its widespread uptake by cells in visceral organs and the brain. Increased cathepsin A activity resolved lysosomal vacuolation throughout the affected organs and sialyl-oligosacchariduria. No signs of hyperplasia or inflammation were detected in the liver up to a year of age. Clinical chemistry panels, blood cell counts, and T cell immune responses were normal in all treated animals. These results warrant a close consideration of this gene therapy approach for the treatment of galactosialidosis, an orphan disease with no cure in sight.

Seven-year follow-up of durability and safety of AAV CNS gene therapy for a lysosomal storage disorder in a large animal

Delivery of adeno-associated viral vectors (AAVs) to cerebrospinal fluid (CSF) has emerged as a promising approach to achieve widespread transduction of the central nervous system (CNS) and peripheral nervous system (PNS), with direct applicability to the treatment of a wide range of neurological diseases, particularly lysosomal storage diseases. Although studies in small animal models have provided proof of concept and experiments in large animals demonstrated feasibility in bigger brains, there is not much information on long-term safety or durability of the effect. Here, we report a 7-year study in healthy beagle dogs after intra-CSF delivery of a single, clinically relevant dose (2 × 10¹³ vg/dog) of AAV9 vectors carrying the canine sulfamidase, the enzyme deficient in mucopolysaccharidosis type IIIA. Periodic monitoring of CSF and blood, clinical and neurological evaluations, and magnetic resonance and ultrasound imaging of target organs demonstrated no toxicity related to treatment. AAV9-mediated gene transfer resulted in detection of sulfamidase activity in CSF throughout the study. Analysis at tissue level showed widespread sulfamidase expression and activity in the absence of histological findings in any region of encephalon, spinal cord, or dorsal root ganglia. Altogether, these results provide proof of durability of expression and long-term safety for intra-CSF delivery of AAV-based gene transfer vectors encoding therapeutic proteins to the CNS.

Novel vectors and approaches for gene therapy in liver diseases

Gene therapy is becoming an increasingly valuable tool to treat many genetic diseases with no or limited treatment options. This is the case for hundreds of monogenic metabolic disorders of hepatic origin, for which liver transplantation remains the only cure. Furthermore, the liver contains 10-15% of the body's total blood volume, making it ideal for use as a factory to secrete proteins into the circulation. In recent decades, an expanding toolbox has become available for liver-directed gene delivery. Although viral vectors have long been the preferred approach to target hepatocytes, an increasing number of non-viral vectors are emerging as highly efficient vehicles for the delivery of genetic material. Herein, we review advances in gene delivery vectors targeting the liver and more specifically hepatocytes, covering strategies based on gene addition and gene editing, as well as the exciting results obtained with the use of RNA as a therapeutic molecule. Moreover, we will briefly summarise some of the limitations of current liver-directed gene therapy approaches and potential ways of overcoming them.

Hematological manifestations and complications of Gaucher disease

Introduction: Gaucher disease (GD), although pan-ethnic and rare (common in Ashkenazi Jews), is of great importance to hematologists both for diagnosis and management. The need for increased awareness of GD is that delayed diagnosis may lead to preventable irreversible complications (mainly skeletal) or unnecessary invasive procedures (e.g. bone marrow biopsy), and the birth of another affected sibling due to lack of genetic consulting.Areas covered: The review outlines the common hematological manifestations of GD, including splenomegaly, thrombocytopenia, and anemia. Other hematological manifestations such as coagulation abnormalities, platelet dysfunction, gammopathy, and other hematological malignancies associated with GD are also discussed. Current and future treatment modalities are delineated, including enzyme replacement and substrate reduction therapy, pharmacological chaperon, and gene therapy. A literature search was conducted to identify original research articles relevant to hematology manifestations and GD published before November 2020.Expert opinion: Patients with GD should be ideally followed and treated in a center of excellence where the GD expert benefits from experienced consultants in relevant disciplines. Due to the availability of several very expensive treatment options, it is important to have an unbiased expert who can select the most suitable management for the individual patients (including withholding prescription in asymptomatic patients).

Haemophilia, state of the art and new therapeutic opportunities, a regulatory perspective

Haemophilia A and B are rare bleeding disorders. Over the past decades, they have been transformed from debilitating diseases to manageable conditions in the Western world. However, optimizing haemophilia care remains challenging in developing countries. Several challenges and unmet needs remain in the treatment of the haemophilia limiting the QoL of patients. These challenges are now being addressed by extended half‐life recombinant factors, rebalancing and substitution therapies. Gene therapy and genome editing show promise for a definite clinical cure. Here, we provide an overview of new therapeutic opportunities for haemophilia and their advances and limitations from a regulatory perspective. The database on human medicines from the European Medicines Agency (EMA) was used and data from rare disease (orphan) designations and EPARs were retrieved for the analysis. Clinical trial databases were used to query all active studies on haemophilia. Gene therapy medicinal products based on AAV and lentiviral vectors are in development and clinical trials have reported substantial success in ameliorating bleeding tendency in haemophilia patients. The prospect of gene editing for correction of the underlying mutation is on the horizon and has considerable potential. With regard to the benefit of the gene therapy medicinal products, more long‐term efficacy and safety data are awaited. We are entering an era of innovation and abundance in treatment options for those affected by bleeding disorders, but issues remain about the affordability and accessibility to patients.

Patient Preferences to Assess Value IN Gene Therapies: Protocol Development for the PAVING Study in Hemophilia

Introduction: Gene therapies are innovative therapies that are increasingly being developed. However, health technology assessment (HTA) and payer decision making on these therapies is impeded by uncertainties, especially regarding long-term outcomes. Through measuring patient preferences regarding gene therapies, the importance of unique elements that go beyond health gain can be quantified and inform value assessments. We designed a study, namely the Patient preferences to Assess Value IN Gene therapies (PAVING) study, that can inform HTA and payers by investigating trade-offs that adult Belgian hemophilia A and B patients are willing to make when asked to choose between a standard of care and gene therapy.

Methods and Analysis: An eight-step approach was taken to establish the protocol for this study: (1) stated preference method selection, (2) initial attributes identification, (3) stakeholder (HTA and payer) needs identification, (4) patient relevant attributes and information needs identification, (5) level identification and choice task construction, (6) educational tool design, (7) survey integration, and (8) piloting and pretesting. In the end, a threshold technique survey was designed using the attributes “Annual bleeding rate,” “Chance to stop prophylaxis,” “Time that side effects have been studied,” and “Quality of Life.”

Ethics and Dissemination: The Medical Ethics Committee of UZ KU Leuven/Research approved the study. Results from the study will be presented to stakeholders and patients at conferences and in peer-reviewed journals. We hope that results from the PAVING study can inform decision makers on the acceptability of uncertainties and the value of gene therapies to patients.