Hemophilia gene therapy comes of age

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.

Emerging drugs for hemophilia A: insights into phase II and III clinical trials

INTRODUCTION

Hemophilia is a lifelong, genetic-bleeding disorder, which inadequately treated results in permanent joint damage. It is characterized by spontaneous and trauma-related bleeding episodes. In the last 50 years, treatment has seen dramatic improvements which have improved the quality of life of persons with hemophilia.

AREAS COVERED

This review will provide a summary of current pharmacological approaches for hemophilia A as well as discuss novel agents which are either approved recently or in phase II-III clinical trials, plasma-derived and recombinant factor VIII (FVIII) products, extended half-life FVIII products, bypassing agents and non-replacement therapies.

EXPERT OPINION

Novel therapies are already changing the way that hemophilia A is managed, and as more new therapies get approved, there will be a revolution in the management of this serious condition. Clinicians will have both the opportunities as well as the challenges of incorporating such new technologies into clinical practice.

High-throughput 5' UTR engineering for enhanced protein production in non-viral gene therapies

Despite significant clinical progress in cell and gene therapies, maximizing protein expression in order to enhance potency remains a major technical challenge. Here, we develop a high-throughput strategy to design, screen, and optimize 5' UTRs that enhance protein expression from a strong human cytomegalovirus (CMV) promoter. We first identify naturally occurring 5' UTRs with high translation efficiencies and use this information with in silico genetic algorithms to generate synthetic 5' UTRs. A total of ~12,000 5' UTRs are then screened using a recombinase-mediated integration strategy that greatly enhances the sensitivity of high-throughput screens by eliminating copy number and position effects that limit lentiviral approaches. Using this approach, we identify three synthetic 5' UTRs that outperform commonly used non-viral gene therapy plasmids in expressing protein payloads. In summary, we demonstrate that high-throughput screening of 5' UTR libraries with recombinase-mediated integration can identify genetic elements that enhance protein expression, which should have numerous applications for engineered cell and gene therapies.

Activated protein C has a regulatory role in factor VIII function

Mechanisms thought to regulate activated factor VIII (FVIIIa) cofactor function include A2-domain dissociation and activated protein C (APC) cleavage. Unlike A2-domain dissociation, there is no known phenotype associated with altered APC cleavage of FVIII, and biochemical studies have suggested APC plays a marginal role in FVIIIa regulation. However, the in vivo contribution of FVIIIa inactivation by APC is unexplored. Here we compared wild-type B-domainless FVIII (FVIII-WT) recombinant protein with an APC-resistant FVIII variant (FVIII-R336Q/R562Q; FVIII-QQ). FVIII-QQ demonstrated expected APC resistance without other changes in procoagulant function or A2-domain dissociation. In plasma-based studies, FVIII-WT/FVIIIa-WT demonstrated dose-dependent sensitivity to APC with or without protein S, whereas FVIII-QQ/FVIIIa-QQ did not. Importantly, FVIII-QQ demonstrated approximately fivefold increased procoagulant function relative to FVIII-WT in the tail clip and ferric chloride injury models in hemophilia A (HA) mice. To minimize the contribution of FV inactivation by APC in vivo, a tail clip assay was performed in homozygous HA/FV Leiden (FVL) mice infused with FVIII-QQ or FVIII-WT in the presence or absence of monoclonal antibody 1609, an antibody that blocks murine PC/APC hemostatic function. FVIII-QQ again demonstrated enhanced hemostatic function in HA/FVL mice; however, FVIII-QQ and FVIII-WT performed analogously in the presence of the PC/APC inhibitory antibody, indicating the increased hemostatic effect of FVIII-QQ was APC specific. Our data demonstrate APC contributes to the in vivo regulation of FVIIIa, which has the potential to be exploited to develop novel HA therapeutics.

Current Clinical Applications of In Vivo Gene Therapy with AAVs

Hereditary diseases are caused by mutations in genes, and more than 7,000 rare diseases affect over 30 million Americans. For more than 30 years, hundreds of researchers have maintained that genetic modifications would provide effective treatments for many inherited human diseases, offering durable and possibly curative clinical benefit with a single treatment. This review is limited to gene therapy using adeno-associated virus (AAV) because the gene delivered by this vector does not integrate into the patient genome and has a low immunogenicity. There are now five treatments approved for commercialization and currently available, i.e., Luxturna, Zolgensma, the two chimeric antigen receptor T cell (CAR-T) therapies (Yescarta and Kymriah), and Strimvelis (the gammaretrovirus approved for adenosine deaminase-severe combined immunodeficiency [ADA-SCID] in Europe). Dozens of other treatments are under clinical trials. The review article presents a broad overview of the field of therapy by in vivo gene transfer. We review gene therapy for neuromuscular disorders (spinal muscular atrophy [SMA]; Duchenne muscular dystrophy [DMD]; X-linked myotubular myopathy [XLMTM]; and diseases of the central nervous system, including Alzheimer’s disease, Parkinson’s disease, Canavan disease, aromatic l-amino acid decarboxylase [AADC] deficiency, and giant axonal neuropathy), ocular disorders (Leber congenital amaurosis, age-related macular degeneration [AMD], choroideremia, achromatopsia, retinitis pigmentosa, and X-linked retinoschisis), the bleeding disorder hemophilia, and lysosomal storage disorders.

Origins, Development, Current Challenges and Future Directions with Activated Prothrombin Complex Concentrate for the Treatment of Patients with Congenital Haemophilia with Inhibitors

Congenital haemophilia A (HA) is caused by deficiency of coagulation factor VIII (FVIII) activity, leading to spontaneous or traumatic bleeding events. While FVIII replacement therapy can treat and prevent bleeds, approximately 30% of patients with severe HA develop inhibitor antibodies that render FVIII replacement therapy ineffective. The bypassing agents (BPAs), activated prothrombin complex concentrate (aPCC) and recombinant activated FVII, first approved in 1977 and 1996, respectively, act to generate thrombin independent of pathways that involve factors IX and VIII. Both may be used in patients with congenital haemophilia and inhibitors (PwHIs) for the treatment and prevention of acute bleeds and quickly became standard of care. However, individual patients respond differently to different agents. While both agents are approved for on-demand treatment and perioperative management for patients with congenital haemophilia with inhibitors, aPCC is currently the only BPA approved worldwide for prophylaxis in PwHI. Non-factor therapies (NFTs) have a mechanism of action distinct from BPAs and have reported higher efficacy rates as prophylactic regimens. Nonetheless, treatment challenges remain with NFTs, particularly regarding the potential for synergistic action on thrombin generation with concomitant use of other haemostatic agents, such as BPAs, for the treatment of breakthrough bleeds and in perioperative management. Concomitant use of NFTs with other haemostatic agents could increase the risk of adverse events such as thromboembolic events or thrombotic microangiopathy. This review focuses on the origins, development and on-going role of aPCC in the evolving treatment landscape in the management of PwHI.

Core data set on safety, efficacy, and durability of hemophilia gene therapy for a global registry: Communication from the SSC of the ISTH

BACKGROUND

Gene therapy for people with hemophilia (PWH) will soon become available outside current clinical trials. The World Federation of Hemophilia (WFH), in collaboration with International Society of Thrombosis and Hemostasis Scientific and Standardization Committee (ISTH SSC), the European Haemophilia Consortium (EHC), the US National Hemophilia Foundation (NHF), the American Thrombosis and Hemostasis Network (ATHN), industry gene therapy development partners and Regulatory liaisons have developed the Gene Therapy Registry (GTR), designed to collect long-term data on all PWH who receive hemophilia gene therapy.

OBJECTIVE

The objectives of the GTR are to record the long-term safety and efficacy data post gene therapy infusion and to assess the changes in quality of life and burden of disease post-gene-therapy infusion.

METHODS

The GTR is a prospective, observational, and longitudinal registry developed under the guidance of a multi-stakeholder GTR Steering Committee (GTR SC), composed of health care professionals, patient advocates, industry representatives, and regulatory agency liaisons. All PWH who receive gene therapy by clinical trial or commercial product will be invited to enrol in the registry through their hemophilia treatment centers (HTCs). The registry aims to recruit 100% of eligible post gene therapy PWH globally. Through an iterative process, and following the guidance of the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA), the GTR SC has developed a core set of data to be collected on all patients post gene therapy.

RESULTS

The core data set includes demographic information, vector infusion details, safety, efficacy, quality of life and burden of disease.

CONCLUSIONS

The GTR is a global effort to ensure that long term safety and efficacy outcomes are recorded and analysed and rare adverse events, in a small patient population, are identified. Many unknowns on the long-term safety and efficacy of gene therapy for hemophilia may also be addressed.

The critical need for postmarketing surveillance in gene therapy for haemophilia

INTRODUCTION

The goal of gene therapy for haemophilia is to alter the clinical phenotype to a milder form or even cure, by increasing endogenous coagulation factor levels through transfer of a functional gene encoding the respective deficient coagulation factor and subsequent transgene expression. Over the past decade, there has been tremendous progress in gene therapy, particularly in use of liver-directed adeno-associated viral vectors, such that several programmes for both haemophilia A and B are in phase 3 trials. With regulatory approval of the first gene therapy product expected as early as mid-2020, there is an urgent need for a mechanism to collect long-term data on safety and variability and durability of efficacy. There will be elements required by regulators for postmarketing surveillance and additional data needed to enhance our understanding of gene therapy outcomes and their impact on the lives of people with haemophilia.

AIM

The aim of this manuscript was to describe efforts underway by the American Thrombosis and Hemostasis Network and the World Federation of Hemophilia to collect long-term harmonized data and considerations of the European and US regulatory agencies, which will inform ongoing data collection.

METHODS

The status of data collection around gene therapy in haemophilia and important outcome measures were obtained by literature review. Each author described elements relevant to the activities of their organization.

CONCLUSION

Support of all stakeholders in gene therapy, providers, patients, industry and regulators, augers successful capture of uniform long-term safety and efficacy data to ensure optimal treatment of people with haemophilia.

Liver Expression of a MiniATP7B Gene Results in Long-Term Restoration of Copper Homeostasis in a Wilson Disease Model in Mice

Gene therapy with an adeno-associated vector (AAV) serotype 8 encoding the human ATPase copper-transporting beta polypeptide (ATP7B) complementary DNA (cDNA; AAV8-ATP7B) is able to provide long-term copper metabolism correction in 6-week-old male Wilson disease (WD) mice. However, the size of the genome (5.2 kilobases [kb]) surpasses the optimal packaging capacity of the vector, which resulted in low-yield production; in addition, further analyses in WD female mice and in animals with a more advanced disease revealed reduced therapeutic efficacy, as compared to younger males. To improve efficacy of the treatment, an optimized shorter AAV vector was generated, in which four out of six metal-binding domains (MBDs) were deleted from the ATP7B coding sequence, giving rise to the miniATP7B protein (Δ57-486-ATP7B). In contrast to AAV8-ATP7B, AAV8-miniATP7B could be produced at high titers and was able to restore copper homeostasis in 6- and 12-week-old male and female WD mice. In addition, a recently developed synthetic AAV vector, AAVAnc80, carrying the miniATP7B gene was similarly effective at preventing liver damage, restoring copper homeostasis, and improving survival 1 year after treatment. Transduction of approximately 20% of hepatocytes was sufficient to normalize copper homeostasis, suggesting that corrected hepatocytes are acting as a sink to eliminate excess of copper. Importantly, administration of AAVAnc80-miniATP7B was safe in healthy mice and did not result in copper deficiency. Conclusion: In summary, gene therapy using an optimized therapeutic cassette in different AAV systems provides long-term correction of copper metabolism regardless of sex or stage of disease in a clinically relevant WD mouse model. These results pave the way for the implementation of gene therapy in WD patients.

Hemophilia trials in the twenty-first century: Defining patient important outcomes

Treatment for hemophilia has advanced dramatically over the past 5 decades. Success of prophylactic therapy in preventing bleeding and decreasing associated complications has established a new standard of care. However, with the advent of gene therapy and treatments that effectively mimic sustained coagulation factor replacement, outcome measures that worked well for assessing factor replacement therapies in past clinical trials need to be reassessed. In addition, while therapies have advanced, so has the science of outcome assessment, including recognition of the importance of patient important and patient reported outcomes. This manuscript reviews strengths and limitations of outcome measures used in hemophilia from both a provider and patient perspective.

Hemophilia in a Changing Treatment Landscape

The mainstay of hemophilia management has been the regular, prophylactic infusion of missing coagulation factors VIII/IX. This approach is limited by the need for frequent intravenous infusions, high cost, limited availability, and the development of inhibitory antibodies to factors VIII/IX. Numerous recent breakthroughs are addressing many of these limitations. These include the development of extended half-life factors that require less frequent infusions and the development of various novel agents that can be given subcutaneously and infrequently, including FVIII-mimetic antibody and downregulators of natural anticoagulants. Finally, gene therapy is set to offer patients a possibility for a cure.