Hemophilia gene therapy: ushering in a new treatment paradigm?

Gene therapy as an innovative approach to the treatment of hemophilia B-a review

Hemophilia B is a disease that affects the human coagulation system, causing the absence or deficiency of coagulation factor IX, which may manifest itself in uncontrolled bleeding that is life-threatening to patients. Due to its inheritance, the disease more often affects men, and the severity of symptoms directly correlates with the concentration of the missing factor IX; hence, the aim of therapy is to maintain it at a level that allows for sufficient hemostasis. The basic model of treatment offered to patients is based on primary prevention with coagulation factor IX with a prolonged half-life, which, however, does not solve the numerous problems faced by patients. An innovative proposal that, despite initial concerns, is becoming more and more popular every day is the recently approved genetic therapy in Europe, which uses viral vectors to transfer the correct gene that encodes coagulation factor IX. The introduction of a recombinant gene in place of its defective counterpart seems to be a promising solution and the beginning of a new era in which genetic therapies have a chance to develop their full potential and replace existing therapeutic regimens.

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.

Gene and cell therapy of human genetic diseases: Recent advances and future directions

Disruptions in normal development and the emergence of health conditions often result from the malfunction of vital genes in the human body. Decades of scientific research have focused on techniques to modify or substitute defective genes with healthy alternatives, marking a new era in disease treatment, prevention and cure. Recent strides in science and technology have reshaped our understanding of disorders, medication development and treatment recommendations, with human gene and cell therapy at the forefront of this transformative shift. Its primary objective is the modification of genes or adjustment of cell behaviour for therapeutic purposes. In this review, we focus on the latest advances in gene and cell therapy for treating human genetic diseases, with a particular emphasis on FDA and EMA-approved therapies and the evolving landscape of genome editing. We examine the current state of innovative gene editing technologies, particularly the CRISPR-Cas systems. As we explore the progress, ethical considerations and prospects of these innovations, we gain insight into their potential to revolutionize the treatment of genetic diseases, along with a discussion of the challenges associated with their regulatory pathways. This review traces the origins and evolution of these therapies, from conceptual ideas to practical clinical applications, marking a significant milestone in the field of medical science.

Correlation of antigen expression with epigenetic modifications after rAAV delivery of a human factor IX variant in mice and rhesus macaques

We investigated long-term human coagulation factor IX (huFIX) expression of a novel variant when delivered into mice and rhesus macaques and compared transduction efficiencies using two different adeno-associated virus (AAV) capsids. In hemophilic mice injected with KP1-packaged recombinant AAV (rAAV) expressing the hyperactive FIX variant specific activity plasma levels were 10-fold or 2-fold enhanced when compared with wild-type or Padua huFIX injected mice, respectively. In rhesus macaques AAV-LK03 capsid outperformed AAV-KP1 in terms of antigen expression and liver transduction. Two animals from each group showed sustained low-level huFIX expression at 3 months after administration, while one animal from each group lost huFIX mRNA and protein expression over time, despite comparable vector copies. We investigated whether epigenetic differences in the vector episomes could explain this loss of transcription. Cut&Tag analysis revealed lower levels of activating histone marks in the two animals that lost expression. When comparing rAAV genome associated histone modifications in rhesus macaques with those in mice injected with the same vector, the activating histone marks were starkly decreased in macaque-derived episomes. Differential epigenetic marking of AAV genomes may explain different expression profiles in mice and rhesus macaques, as well as the wide dose response variation observed in primates in both preclinical and human clinical trials.

Consensus-Based Expert Recommendations on the Management of Hemophilia A in the Gulf Region

BACKGROUND

Hemophilia A presents a significant health challenge in the Gulf region, where it has an especially high prevalence. There are several unmet needs associated with the management of hemophilia A in the region. The aim of this manuscript was to contextualize unmet management needs, provide recommendations to optimize care, and specify requirements for the establishment of gene therapy centers in the region.

SUMMARY

An expert panel was assembled comprising ten clinical hematologists from Kuwait, Oman, Saudi Arabia, and the UAE. The Delphi methodology was used to obtain a consensus on statements relating to several aspects of hemophilia A. A consensus was reached for all statements by means of an online, anonymized voting system. The consensus statements pertain to screening and diagnosis, treatment approaches, and requirements for the implementation of gene therapy.

KEY MESSAGES

There are significant challenges that hinder the optimal management of hemophilia A in the Gulf region. The consensus statements presented provide specific recommendations to improve diagnostic and treatment approaches, promote multidisciplinary care, and optimize regional data generation and reporting. These statements also delineate the requirements for the establishment of gene therapy centers for hemophilia A in the region.

BACKGROUND

Hemophilia A presents a significant health challenge in the Gulf region, where it has an especially high prevalence. There are several unmet needs associated with the management of hemophilia A in the region. The aim of this manuscript was to contextualize unmet management needs, provide recommendations to optimize care, and specify requirements for the establishment of gene therapy centers in the region.

SUMMARY

An expert panel was assembled comprising ten clinical hematologists from Kuwait, Oman, Saudi Arabia, and the UAE. The Delphi methodology was used to obtain a consensus on statements relating to several aspects of hemophilia A. A consensus was reached for all statements by means of an online, anonymized voting system. The consensus statements pertain to screening and diagnosis, treatment approaches, and requirements for the implementation of gene therapy.

KEY MESSAGES

There are significant challenges that hinder the optimal management of hemophilia A in the Gulf region. The consensus statements presented provide specific recommendations to improve diagnostic and treatment approaches, promote multidisciplinary care, and optimize regional data generation and reporting. These statements also delineate the requirements for the establishment of gene therapy centers for hemophilia A in the region.

Gene therapy for hemophilia, a clinical viewpoint

Gene therapy for hemophilia has been investigated for decades but no breakthroughs were made until Nathwani et al. achieved a significant and sustainable factor IX increase in hemophilia B patients in 2011. About eleven years later, in August 2022, the first hemophilia A gene therapy product was approved by the European Commission and hemophilia treatment entered a new era. This review does not focus on the newest advances but rather the practical aspects of gene therapy aiming to provide an overview for physicians who treat hemophiliacs who did not participate in the clinical trials. The current status of gene therapy, focusing particularly on products likely to be clinically available soon, are reviewed and summarized. Currently, possible limitations of gene therapy are pre-existing neutralizing antibodies toward the vector, liver health, age, and inhibitor status. Possible safety concerns include infusion reactions, liver damage, and adverse effects from immune suppressants or steroids. In summary, generally speaking, gene therapy is effective, at least for several years, but the exact effect may be unpredictable and intensive monitoring for several months is needed. It can also be considered safe with careful practice on selected patients. In its current form, gene therapy will not replace all hemophilia treatments. Advances in non-factor therapy will also improve hemophilia care greatly in the future. We envisage that gene therapy may be included in multiple novel therapies for hemophilia and benefit some hemophilia patients while novel non-factor therapies may benefit others, together fulfilling the unmet needs of all hemophilia patients.

Efficient gene transduction in pigs and macaques with the engineered AAV vector AAV.GT5 for hemophilia B gene therapy

Gene therapy using adeno-associated virus (AAV)-based vectors has become a realistic therapeutic option for hemophilia. We examined the potential of a novel engineered liver-tropic AAV3B-based vector, AAV.GT5, for hemophilia B gene therapy. In vitro transduction with AAV.GT5 in human hepatocytes was more than 100 times higher than with AAV-Spark100, another bioengineered vector used in a clinical trial. However, liver transduction following intravenous injection of these vectors was similar in mice with a humanized liver and in macaques. This discrepancy was due to the low recovery and short half-life of AAV.GT5 in blood, depending on the positive charge of the heparin-binding site in the capsid. Bypassing systemic clearance with the intra-hepatic vascular administration of AAV.GT5, but not AAV-Spark100, enhanced liver transduction in pigs and macaques. AAV.GT5 did not develop neutralizing antibodies (NAbs) in two of four animals, while AAV-Spark100 induced serotype-specific NAbs in all macaques tested (4 of 4). The NAbs produced after AAV-Spark100 administration were relatively serotype specific, and challenge with AAV.GT5 through the hepatic artery successfully boosted liver transduction in one animal previously administered AAV-Spark100. In summary, AAV.GT5 showed different vector kinetics and NAb induction compared with AAV-Spark100, and intra-hepatic vascular administration may minimize the vector dose required and vector dissemination.

Gene Therapy in Hemophilia: A Transformational Patient Experience

Hemophilia is a bleeding disorder caused by a single absent/defective gene and characterized by a lack of functional clotting factors. People with hemophilia may experience joint damage, pain, and psychological impairments, all of which could contribute to reduced health-related quality of life (HRQoL). The current standard of care is clotting factor replacement, which is associated with regular infusions; therefore, alternative treatments such as gene therapy (GT) are in development. GT involves the delivery of a functional copy of the clotting factor 8/9 gene by a single infusion into the patient's cells, enabling them to produce their own clotting factor VIII/IX. The impact of treatment on patients' HRQoL can be assessed using hemophilia-specific patient-reported outcome (PRO) measures. Since these measures were designed before the advent of GT, there is a need for updated individualized PRO measures. Patient groups and regulatory authorities emphasize the need for increased patient engagement when considering clinical trial design. Here, we provide patients' perspective on undergoing GT and discuss how to capture the patient voice when measuring the therapy's transformative impact.

Progress, and prospects in the therapeutic armamentarium of persons with congenital hemophilia. Defining the place for liver-directed gene therapy

In persons with congenital severe hemophilia A (HA) living in high-income countries, twice weekly intravenous infusions of extended half-life (EHL) factor VIII (FVIII) products, or weekly/biweekly/monthly subcutaneous injections of emicizumab are the gold standard home treatments to grant days without hurdles and limitations. Once weekly/twice monthly infusions of EHL Factor IX (FIX) products achieve the same target in severe hemophilia B (HB). Gene therapy, which is likely to be licensed for clinical use within 1-2 years, embodies a shift beyond these standards. At an individual patient level, a single functional gene transfer leads to a > 10-yr almost full correction of the hemostatic defect in HB and to a sustained (3-6-yrs) expression of FVIII sufficient to discontinue exogenous clotting factor administrations. At the doses employed, the limited liver toxicity of systemically infused recombinant adeno-associated virus (rAAV) vectors is documented by long-term (12-15 yrs) follow-ups, and pre-existing high-titer neutralizing antibodies to the AAV5 vector are no longer an exclusion criterion for effective transgene expression with this vector. A safe durable treatment that converts a challenging illness to a phenotypically curable disease, allows persons to feel virtually free from the fears and the obligations of hemophilia for years/decades. Along with patient organizations and health care professionals, communicating to government authorities and reimbursement agencies the liberating potential of this substantial innovation, and disseminating across the Centers updated information on benefits and risks of this strategy, will align expectations of different stakeholders and establish the notion of a potentially lifelong cure of hemophilia.

Adeno-Associated Virus Gene Therapy for Hemophilia

In vivo gene therapy is rapidly emerging as a new therapeutic paradigm for monogenic disorders. For almost three decades, hemophilia A (HA) and hemophilia B (HB) have served as model disorders for the development of gene therapy. This effort is soon to bear fruit with completed pivotal adeno-associated viral (AAV) vector gene addition trials reporting encouraging results and regulatory approval widely anticipated in the near future for the current generation of HA and HB AAV vectors. Here we review the clinical development of AAV gene therapy for HA and HB and examine outstanding questions that have recently emerged from AAV clinical trials for hemophilia and other monogenic disorders.

Adeno-associated virus-mediated expression of activated factor V (FVa) for hemophilia phenotypic correction

Adeno-associated virus (AAV) gene therapy has been successfully applied in hemophilia patients excluding patients with inhibitors. During the coagulation pathway, activated factor V (FVa) functions downstream as a cofactor of activated factor X (FXa) to amplify thrombin generation. We hypothesize that the expression of FVa via gene therapy can improve hemostasis of both factor IX and FVIII deficiencies, regardless of clotting factor inhibitor. A human FVa (hFVa) expression cassette was constructed, and AAV8 vectors encoding hFVa (AAV8/TTR-hFVa) were intravenously administrated into mice with hemophilia A and B with or without FVIII inhibitors. Hemostasis, including hFVa level, activated partial thromboplastin time (aPTT), tail clip, and the saphenous vein bleeding assay (SVBA), was evaluated. In hemophilia B mice, a dose of 4 × 1013 vg/kg AAV8/TTR-hFVa vectors achieved a complete phenotypic correction over 28 weeks. In hemophilia A mice, hemostasis improvement was also achieved, regardless of FVIII inhibitor development. In vivo hemostasis efficacy was confirmed by tail clip and SVBA. Interestingly, while minimal shortening of aPTT was observed at a lower dose of AAV8 vectors, hemostasis improvement was still achieved via in vivo bleeding assays. Collectively, FVa-based AAV gene therapy shows promise for hemostasis correction in hemophilia, regardless of inhibitor development and no potential risk for thrombosis.

Comprehensive approach to hemophilia

Hemophilia A, B are X-linked recessive bleeding disorder that typically results from a deficiency of clotting factor VIII (FVIII) and factor IX (FIX). The severity of the disease is determined according to the FVIII and FIX levels. Hemophilia A and B have similar symptoms and are both characterized by bleeding, particularly in large joints such as ankles, knees, elbows. Recurrent bleeding in joints eventually causes progressive hemophilic arthropathy. Life-threatening hemorrhages may occur rarely. Treatment of hemophilia has improved significantly in recent years with clotting factor concentrates. The average life expectancy was