Multiyear Follow-up of AAV5-hFVIII-SQ Gene Therapy for Hemophilia A

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

Therapy for hemophilia has evolved in the last 40 years from plasma-based concentrates to recombinant proteins and, more recently, to non-factor therapeutics. Along this same timeline, research in adeno-associated viral (AAV) based gene therapy vectors has provided the framework for early phase clinical trials initially for hemophilia B (HB) and now for hemophilia A. Successive lessons learned from early HB trials have paved the way for current advanced phase trials. Nevertheless, questions linger regarding 1) the optimal balance of vector dose to transgene expression, 2) amount and durability of transgene expression required, and 3) long-term safety. Some trials have demonstrated unique findings not seen previously regarding transient elevation of liver enzymes, immunogenicity of the vector capsid, and loss of transgene expression. This review will provide an update on the clinical AAV gene therapy trials in hemophilia and address the questions above. A thoughtful and rationally approached expansion of gene therapy to the clinics would certainly be a welcome addition to the arsenal of options for hemophilia therapy. Further, the global impact of gene therapy could be vastly improved by expanding eligibility to different patient populations and to developing nations. With the advances made to date, it is possible to envision a shift from the early goal of simply increasing life expectancy to a significant improvement in quality of life by reduction in spontaneous bleeding episodes and disease complications.

The Evolution of Gene Therapy in the Treatment of Metabolic Liver Diseases

Monogenic metabolic disorders of hepatic origin number in the hundreds, and for many, liver transplantation remains the only cure. Liver-targeted gene therapy is an attractive treatment modality for many of these conditions, and there have been significant advances at both the preclinical and clinical stages. Viral vectors, including retroviruses, lentiviruses, adenovirus-based vectors, adeno-associated viruses and simian virus 40, have differing safety, efficacy and immunogenic profiles, and several of these have been used in clinical trials with variable success. In this review, we profile viral vectors and non-viral vectors, together with various payloads, including emerging therapies based on RNA, that are entering clinical trials. Genome editing technologies are explored, from earlier to more recent novel approaches that are more efficient, specific and safe in reaching their target sites. The various curative approaches for the multitude of monogenic hepatic metabolic disorders currently at the clinical development stage portend a favorable outlook for this class of genetic disorders.

Gene Therapy for Hemophilia A: Where We Stand

Hemophilia A (HA) is a hereditary hemorrhagic disease caused by a deficiency of coagulation factor VIII (FVIII) in blood plasma. Patients with HA usually suffer from spontaneous and recurrent bleeding in joints and muscles, or even intracerebral hemorrhage, which might lead to disability or death. Although the disease is currently manageable via delivery of plasma-derived or recombinant FVIII, this approach is costly, and neutralizing antibodies may be generated in a large portion of patients, which render the regimens ineffective and inaccessible. Given the monogenic nature of HA and that a slight increase in FVIII can remarkably alleviate the phenotypes, HA has been considered to be a suitable target disease for gene therapy. Consequently, the introduction of a functional F8 gene copy into the appropriate target cells via viral or nonviral delivery vectors, including gene correction through genome editing approaches, could ultimately provide an effective therapeutic method for HA patients. In this review, we discuss the recent progress of gene therapy for HA with viral and nonviral delivery vectors, including piggyBac, lentiviral and adeno-associated viral vectors, as well as new raising issues involving liver toxicity, pre-existing neutralizing antibodies of viral approach, and the selection of the target cell type for nonviral delivery.

Structural characterization of a bat Adeno-associated virus capsid

Adeno-associated viruses (AAVs) are widespread among vertebrates. AAVs isolated from bats display low capsid protein sequence identities (<60%) to AAV2, AAV5, and other primate AAVs. Here we report the first capsid structure of a non-primate AAV which was isolated from bats. The capsid structure of BtAAV-10HB (10HB) was determined by cryo-electron microscopy and three-dimensional image reconstruction to 3.03 Å resolution. Comparison of empty and genome-containing capsids showed that the capsid structures are almost identical except for an ordered nucleotide in a previously described nucleotide-binding pocket, the density in the 5-fold channel, and several amino acids with altered side chain conformations. Compared to other dependoparvoviruses, for example AAV2 and AAV5, 10HB displays unique structural features including insertions and deletions in capsid surface loops. Overall, the 10HB capsid structure superposes with an RMSD of 1.7 Å and 1.8 Å to AAV2 and AAV5, respectively. Currently all approved AAV human gene therapy biologics and vectors in clinical trials are based on primate isolates. However, pre-existing neutralizing antibodies in the human population represents a hurdle to their use. 10HB capsids are capable of packaging AAV2 vector genomes and thus have potential as gene delivery vectors. Significantly, a screen with human sera showed lack of recognition by the 10HB capsid. Thus, the different capsid surface of 10HB vectors likely renders it "invisible" to potential pre-existing neutralizing human anti-AAV antibodies especially because this virus or similar variants do not exist in primate populations.

Failure Mode and Effects Analysis (FMEA) for Immunogenicity of Therapeutic Proteins

Biotherapeutic drugs made by cell-based systems are revolutionizing the practice of medicine. The next generation of biotherapeutics include recombinant proteins, monoclonal antibodies, viral vector expressed proteins, and cell therapies. Immunogenicity associated adverse events is one of the major risks for these biologics. Accurate and precise measurement of the immunogenicity of biologics is a critical component during all phases of drug development. We have utilized the principles of Failure Mode and Effects Analysis (FMEA) in performing assessment of risk of immunogenicity. The multi-dimensional approach involves: i) listing all the potential risks by likelihood of occurrence and severity as part of quality target product profile. ii) ascribing the causes by identifying the risks at each stage of development. iii) predicting the effects. iv) determining the risk mitigation strategy. v) implementing a monitoring process. vi) developing templates for data collection. vii) timely reporting and. viii) life cycle management. FMEA is a continuous process that works throughout the lifecycle of the product or the process and keeps on getting updated with new insights and knowledge.

Advances in gene therapy for hematologic disease and considerations for transfusion medicine

As the list of regulatory agency-approved gene therapies grows, these products are now in the therapeutic spotlight with the potential to cure or dramatically alleviate several benign and malignant hematologic diseases. The mechanisms for gene manipulation are diverse, and include the use of a variety of cell sources and both viral vector- and nuclease-based targeted approaches. Gene editing has also reached the realm of blood component therapy and testing, where cultured products are being developed to improve transfusion support for individuals with rare blood types. In this review, we summarize the milestones in the development of gene therapies for hematologic diseases, mechanisms for gene manipulation, and implications for transfusion medicine and blood centers as these therapies continue to advance and grow.

The evolving landscape of gene therapy for congenital haemophilia: An unprecedented, problematic but promising opportunity for worldwide clinical studies

With liver-directed gene therapy, congenital haemophilia has the potential to progress from an incurable to a phenotypically curable condition. However, the proportion of haemophilia population likely to benefit from gene therapy remains to be established. Achieving a phenotypic curative goal is presently hampered by: 1) availability of effective treatments (e.g. extended half-life products, non-factor therapies) that address major unmet needs in haemophilia; 2) key differences between hope and reality that patients undergoing gene therapy face (e.g. unknown risks and long-term follow-up, durability of the therapeutic effect, possibility of re-administering the vector), 3) lack of expertise of health care professionals (HCP) in managing/monitoring unexpected side effects in patients, and 4) lack of expertise of HCP in advising payers on key issues for cost-effectiveness analyses of gene therapy (e.g., eligibility criteria, predictability of response, unknown risks, long-term complications). There is also uncertainty about the possibility to absorb the cost of the "one-time, one-dose cure" by payers that are used to different payment models. An active partnership between regulators, payers, patients and health care professionals is key to identify patient sub-populations that might benefit the most from gene therapy, and to align the interests of patients (needing effective disease correction and improved quality of life) and pharma companies (reluctant to lose the profitability of lifelong repeated treatments). Educational programs will provide the healthcare chain with information on the strategy that is expected to transform morbidity and mortality patterns and how it should be regarded as part of the future therapeutic options in haemophilia.

Hemophilia gene therapy-New country initiatives

Gene therapy is an opportunity for haemophilia patients to receive a one-time treatment and have lasting factor levels for years or decades instead of dependence on repeated administration within short intervals and on sustained supply of drug. Great strides have been made in the development of gene therapy for haemophilia in the last decade. Adeno-associated virus (AAV) vector-mediated gene transfer in haemophilia A and B has entered the phase III trial stage. Gene transfer by lentiviral vector or gene editing technologies using factor VIII (FVIII) or IX (FIX) genes are now entering clinical evaluation. It is expected that the first FVIII and FIX gene therapy products will soon be approved and distributed in major markets. Global access to gene therapy is a critical goal. This review presents new and ongoing efforts towards this goal in countries other than North America and Europe. In Japan, researchers, regulators and funders have established a promising gene therapy development platform for multiple diseases including haemophilia. Decades of scientific and clinical research in haemophilia gene therapy in China have led to a recently registered clinical trial of AAV-mediated gene therapy for haemophilia B. Other countries are in earlier phases of building gene therapy programmes or participate in international trials. A phase 2 feasibility trial of AAV-mediated FIX gene therapy in low- and middle-income countries aims to demonstrate that gene therapy could become available in resource-constrained socio-economic settings. The different strategies for establishing gene therapy provide opportunities for closing the global gap in haemophilia care.

Prophylaxis for hemophilia A without inhibitors: treatment options and considerations

INTRODUCTION

Hemophilia A is a bleeding disorder traditionally managed with standard half-life (SHL) factor (F) VIII concentrates. Extended half-life (EHL) FVIII products and emicizumab-kywh, a nonfactor therapy, are newer treatment options. Additional nonfactor agents and gene therapy are expected to reach the market in the near future.

AREAS COVERED

A PubMed (MEDLINE) search from 1962 to April 2020 related to hemophilia A, its management, and the products currently available for prophylaxis was performed to comprehensively review these topics and analyze the benefits and drawbacks of each therapeutic.

EXPERT OPINION

Prophylaxis with SHL FVIII concentrates remains the standard of care for patients with severe hemophilia A and may also be considered for selected individuals with moderate disease. Several years of real-world experience with EHL FVIII, emicizumab-kywh, and other agents in development will be necessary to determine their ultimate roles in the prevention of bleeding and its complications. Gene therapy may not provide a permanent cure for hemophilia A.

WFH State-of-the-art paper 2020: In vivo lentiviral vector gene therapy for haemophilia

Over the last decade, the development of new treatments for haemophilia has progressed at a very rapid pace. Despite all the promising advances in protein products, the prospect offered by gene therapy of a single potentially lifelong treatment remains attractive for people with haemophilia. Transfer to the liver of coagulation factor VIII (FVIII) or factor IX (FIX) transgenes has indeed the potential to stably restore the dysfunctional coagulation process. Recombinant adeno‐associated virus (AAV)‐derived vectors are widely employed for liver‐directed gene therapy, given their very good efficacy and safety profile, shown in several preclinical and clinical studies. However, there are some limitations associated with AAV vectors, such as their predominantly episomal nature in the nucleus of target cells and the widespread pre‐existing immunity against the parental virus in humans. By contrast, HIV‐derived lentiviral vectors (LV) integrate into the target cell chromatin and are maintained as the cells duplicate their genome, a potential advantage for establishing long‐term expression especially in paediatric patients, in which the liver undergoes substantial growth. Systemic administration of LV allowed stable multi‐year transgene expression in the liver of mice and dogs. More recently, improved phagocytosis‐shielded LV were generated, which, following intravenous administration to non‐human primates, showed selective targeting of liver and spleen and enhanced hepatocyte gene transfer, achieving up to supra‐normal activity of both human FVIII and FIX transgenes. These studies support further preclinical assessment and clinical evaluation of in vivo liver‐directed LV gene therapy for haemophilia.

An overview of development in gene therapeutics in China

After setbacks related to serious adverse events 20 years ago, gene therapy is now coming back to the central stage worldwide. In the past few years, gene therapy has shown astonishing efficacy against genetic diseases and cancers. In history, China carried out the world's second gene therapy clinical trial in 1991 for hemophilia B and approved the world's first gene therapy product-Gendicine-in 2003. In recent years, numerous efforts have been made on gene editing. Here, we reviewed the past of gene therapy in China and highlighted recent advances. We also discussed the regulations and future perspectives of gene therapy in China.

Long-Term Follow-Up of the First in Human Intravascular Delivery of AAV for Gene Transfer: AAV2-hFIX16 for Severe Hemophilia B

Adeno-associated virus (AAV) vectors are a leading platform for gene-based therapies for both monogenic and complex acquired disorders. The success of AAV gene transfer highlights the need to answer outstanding clinical questions of safety, durability, and the nature of the human immune response to AAV vectors. Here, we present longitudinal follow-up data of subjects who participated in the first trial of a systemically delivered AAV vector. Adult males (n = 7) with severe hemophilia B received an AAV2 vector at doses ranging from 8 × 10¹⁰ to 2 × 10¹² vg/kg to target hepatocyte-specific expression of coagulation factor IX; a subset (n = 4) was followed for 12-15 years post-vector administration. No major safety concerns were observed. There was no evidence of sustained hepatic toxicity or development of hepatocellular carcinoma as assessed by liver transaminase values, serum α-fetoprotein, and liver ultrasound. Subjects demonstrated persistent, increased AAV neutralizing antibodies (NAbs) to the infused AAV serotype 2 (AAV2) as well as all other AAV serotypes tested (AAV5 and AAV8) for the duration of follow-up. These data represent the longest available longitudinal follow-up data of subjects who received intravascular AAV and support the preliminary safety of intravascular AAV administration at the doses tested in adults. Data demonstrate, for the first time, the persistence of high-titer, multi-serotype cross-reactive AAV NAbs for up to 15 years post- AAV vector administration. Our observations are broadly applicable to the development of AAV-mediated gene therapy.

Delivering on the promise of gene therapy for haemophilia

The promise of gene therapy is a single treatment ('one and done') that leads to steady-state expression of endogenous factor VIII or factor IX sufficient to achieve a functional cure (free of recurrent haemophilic bleeding) if not normalized haemostasis. The elimination of the need for continued prophylaxis, or factor replacement following trauma or prior to surgery would lead to annual cost savings. Such optimized health and well-being would be reaching a level of health equity that was unimaginable several decades ago. 'Before anything else, preparation is the key to success'-Alexander Graham Bell. This quote from the famous inventor, scientist and engineer highlights that, although we currently stand on the threshold of this achievement, delivering on this promise will require broad-based multistakeholder preparation (scientists, manufacturers, federal regulators, health technology assessors, persons with haemophilia, national advocacy groups and multidisciplinary healthcare teams) with a focused emphasis on education, approval of safe and effective therapies, removal of barriers to access and excellence in clinical delivery.

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.

Uncertainty in an era of transformative therapy for haemophilia: Addressing the unknowns

Haemophilia is at the dawn of a new era in therapeutic management, one that can generate greater protection from bleeding and a functional cure in some individuals. Prior advances in protein engineering and monoclonal antibody technology have facilitated therapeutic options to maintain decreased risk of bleeding and less burdensome treatment. The use of gene transfer, first proposed in 1971 for monogenic diseases, is emerging as an effective long-term treatment for a variety of diseases. Transfer of functional factor VIII (FVIII) and factor IX (FIX) genes has witnessed a series of advances and setbacks since the first non-clinical experiments in animals were initiated nearly 30 years ago. More recently, multiyear therapeutic levels of FVIII and FIX activity have been achieved in human clinical trials, translated into meaningful clinical benefit and a functional cure. While clinical progress has been definitive, many questions remain unanswered as prelicensure phase 3 clinical trials are underway. These unanswered questions translate into a state of uncertainty about the known unknowns and unknown unknowns intrinsic to any new therapeutic platform. Accepting this modality as a means to functionally cure haemophilia also means accepting the uncertainty regarding the biology of viral vector-mediated gene transfer, which remains inadequately understood. Gene therapy is a far more complex biological 'drug' than small molecule and protein drugs, where manufacturing processes and the drugs themselves are now well characterized. Extent of community acceptance of uncertainty and acknowledgement of the need for an uncompromising drive for answers to the unknowns will characterize the introduction of this first generation of gene therapy for haemophilia to the wider patient population in both resource-rich and resource-poor countries.

Musculo-skeletal problems of the hand in haemophilia

Musculo-skeletal complications of the hand in the haemophilia patient are rare, and they include synovitis, arthropathy, pseudotumours, carpal tunnel syndrome and vascular aneurysms and pseudoaneurysms.

The best way to prevent the aforementioned musculo-skeletal complications is early continuous haematological primary prophylaxis (intravenous infusion of the deficient coagulation factor, ideally from cradle to death).

There is a wide range of procedures that a hand surgeon treating these patients should be able to manage, including synovectomy, prosthetic replacement of small joints, removal or curettage of pseudotumours, release of carpal tunnel and, occasionally, vascular reconstruction of aneurysms.

The treatment of these patients should be made at an institution with close collaboration between haematologists and hand surgeons (all surgical procedures must always be performed under cover of the deficient coagulation factor).

Cite this article: EFORT Open Rev 2020;5:328-333. DOI: 10.1302/2058-5241.5.190078

Gene doping and genomic science in sports: where are we?

The misuse of sport-related gene transfer methods in elite athletes is a real and growing concern. The success of gene therapy in the treatment of hereditary diseases has been most evident since targets in gene therapy products can be used in healthy individuals to improve sports performance. Performing these practices threatens the sporting character of competitions and may pose potential health hazards. Since the World Anti-Doping Agency pronouncement on the prohibition of such practices in 2003, several researchers have been trying to address the challenge of developing an effective method for the detection of genetic doping. This review presents an overview of the published methods developed for this purpose, the advantages and limitations of technologies and the putative target genes. At last, we present the perspective related to the application of the detection methods in the doping control field.

Assessing the potential cost-effectiveness of a gene therapy for the treatment of hemophilia A

Aim: Hemophilia A is a genetic, chronic disorder classified by deficient or defective coagulation factor VIII (FVIII) that puts those affected at risk for spontaneous bleeding episodes, which lead to joint damage and chronic pain over time. Currently, most severe hemophilia A patients are treated with prophylactic FVIII, which requires costly and frequent infusions and life-long adherence to medication. A gene therapy (valoctocogene roxaparvovec) is currently in development for the treatment of severe hemophilia A. This model assessed the potential cost-effectiveness of treating patients with valoctocogene roxaparvovec rather than prophylactic therapy.Materials and methods: We developed an individual-based, state-transition microsimulation model for assessing the likely cost-effectiveness of valoctocogene roxaparvovec compared to prophylactic FVIII. Men aged 30 with severe hemophilia A were modeled over a lifetime horizon, and costs were reported from the perspective of the United States health care system. Through microsimulation, patient-level heterogeneity was captured in starting weight, starting Pettersson score (PS), durability of valoctocogene roxaparvovec, and annual bleed rate (ABR).Results: The model projects that treatment with single-administration valoctocogene roxaparvovec would be cost-saving to people with hemophilia A at a price point comparable to other currently available gene therapy products due to its potential to reduce FVIII utilization, direct medical costs, lifetime bleeds, and accumulated joint damage.Limitations: The model relies upon evidence-based assumptions for clinical inputs due to limited data availability. Such uncertainty was mitigated by modeling heterogeneity across the population, specifically with regards to long-term gene therapy durability, lifetime bleed rates, and joint damage progression.Conclusion: Valoctocogene roxaparvovec was found to be cost-saving-on average by about $6.8 million per patient-and more effective than prophylactic therapy for treatment of hemophilia A. The comparative benefit of gene therapy was observed across a broad range of simulated patients that were representative of the real-world severe hemophilia A population.

Translational Potential of Immune Tolerance Induction by AAV Liver-Directed Factor VIII Gene Therapy for Hemophilia A

Hemophilia A (HA) is an X-linked bleeding disorder due to deficiencies in coagulation factor VIII (FVIII). The major complication of current protein-based therapies is the development of neutralizing anti-FVIII antibodies, termed inhibitors, that block the hemostatic effect of therapeutic FVIII. Inhibitors develop in about 20-30% of people with severe HA, but the risk is dependent on the interaction between environmental and genetic factors, including the underlying F8 gene mutation. Recently, multiple clinical trials evaluating adeno-associated viral (AAV) vector liver-directed gene therapy for HA have reported promising results of therapeutically relevant to curative FVIII levels. The inclusion criteria for most trials prevented enrollment of subjects with a history of inhibitors. However, preclinical data from small and large animal models of HA with inhibitors suggests that liver-directed gene therapy can in fact eradicate pre-existing anti-FVIII antibodies, induce immune tolerance, and provide long-term therapeutic FVIII expression to prevent bleeding. Herein, we review the accumulating evidence that continuous uninterrupted expression of FVIII and other transgenes after liver-directed AAV gene therapy can bias the immune system toward immune tolerance induction, discuss the current understanding of the immunological mechanisms of this process, and outline questions that will need to be addressed to translate this strategy to clinical trials.

Adeno-Associated Virus D-Sequence-Mediated Suppression of Expression of a Human Major Histocompatibility Class II Gene: Implications in the Development of Adeno-Associated Virus Vectors for Modulating Humoral Immune Response

A 20-nt long sequence, termed the D-sequence, in the adeno-associated virus (AAV) inverted terminal repeat was observed to share a partial sequence homology with the X-box in the regulatory region of the human leukocyte antigen DRA (HLA-DRA) promoter of the human major histocompatibility complex class II (MHC-II) genes. The D-sequence was also shown to specifically interact with the regulatory factor binding to the X-box (RFX), binding of which to the X-box is a critical step in the MHC-II gene expression, suggesting that D-sequence might compete for RFX transcription factor binding, thereby suppressing expression from the MHC-II promoter. In DNA-mediated transfection experiments, using a reporter gene under the control of the HLA-DRA promoter, D-sequence oligonucleotides were found to inhibit expression of the reporter gene expression in HeLa and 293 cells by ∼93% and 96%, respectively. No inhibition was observed when nonspecific synthetic oligonucleotides were used. D-sequence oligonucleotides had no effect on expression from the cytomegalovirus immediate-early gene promoter. Interferon-γ-mediated activation of MHC-II gene expression was also inhibited by D-sequence oligonucleotides as well as after infection with either the wild-type AAV or transduction with recombinant AAV vectors. These studies suggest that the D-sequence-mediated downregulation of the MHC-II gene expression may be exploited toward the development of novel AAV vectors capable of dampening the host humoral response, which has important implication in the optimal use of these vectors in human gene therapy.

Human Immune Responses to Adeno-Associated Virus (AAV) Vectors

Recombinant adeno-associated virus (rAAV) vectors are one of the most promising in vivo gene delivery tools. Several features make rAAV vectors an ideal platform for gene transfer. However, the high homology with the parental wild-type virus, which often infects humans, poses limitations in terms of immune responses associated with this vector platform. Both humoral and cell-mediated immunity to wild-type AAV have been documented in healthy donors, and, at least in the case of anti-AAV antibodies, have been shown to have a potentially high impact on the outcome of gene transfer. While several factors can contribute to the overall immunogenicity of rAAV vectors, vector design and the total vector dose appear to be responsible of immune-mediated toxicities. While preclinical models have been less than ideal in predicting the outcome of gene transfer in humans, the current preclinical body of evidence clearly demonstrates that rAAV vectors can trigger both innate and adaptive immune responses. Data gathered from clinical trials offers key learnings on the immunogenicity of AAV vectors, highlighting challenges as well as the potential strategies that could help unlock the full therapeutic potential of in vivo gene transfer.

The Unusual Properties of the AAV Inverted Terminal Repeat

Although the sequence of the AAV inverted terminal repeat has been known for 40 years, there are still unanswered questions about functions attributable to the terminal 125 nucleotides.

Escape or Fight: Inhibitors in Hemophilia A

Replacement therapy with coagulation factor VIII (FVIII) represents the current clinical treatment for patients affected by hemophilia A (HA). This treatment while effective is, however, hampered by the formation of antibodies which inhibit the activity of infused FVIII in up to 30% of treated patients. Immune tolerance induction (ITI) protocols, which envisage frequent infusions of high doses of FVIII to confront this side effect, dramatically increase the already high costs associated to a patient's therapy and are not always effective in all treated patients. Therefore, there are clear unmet needs that must be addressed in order to improve the outcome of these treatments for HA patients. Taking advantage of preclinical mouse models of hemophilia, several strategies have been proposed in recent years to prevent inhibitor formation and eradicate the pre-existing immunity to FVIII inhibitor positive patients. Herein, we will review some of the most promising strategies developed to avoid and eradicate inhibitors, including the use of immunomodulatory drugs or molecules, oral or transplacental delivery as well as cell and gene therapy approaches. The goal is to improve and potentiate the current ITI protocols and eventually make them obsolete.

Towards a global multidisciplinary consensus framework on haemophilia gene therapy: Report of the 2nd World Federation of Haemophilia Gene Therapy Round Table

INTRODUCTION

With approval of gene therapy for haemophilia likely in the near future, policy frameworks are needed to guide the path forward for this disruptive and novel therapeutic advance.

AIM

The WFH has initiated a series of multi-stakeholder Gene Therapy Round Tables (GTRT) to better understand where guidance is needed and develop initial consensus statements to inform policy.

METHODS

The first day of the 2nd GTRT was devoted to didactic presentations on models of access to gene therapy, payment and health technology assessment considerations, regulatory issues and the generation of evidence on safety and durable efficacy of gene therapy products. On the second day, participants were tasked with developing and voting on consensus statements that reflected the information presented and multi-stakeholder views expressed during discussions in the 1st and 2nd WFH GTRTs. The statements covered global access to gene therapy for all people with haemophilia (PWH), collection of long-term safety and efficacy data, ensuring gene therapy is available for all subgroups of PWH including those who have been largely excluded from clinical trials and characterizing acceptable and ideal factor expression levels for gene therapy products.

RESULTS

The first 3 statements achieved consensus (at least 80% agreement) by this group of experts. The statement on identifying an ideal and an acceptable factor level expression elicited a lively discussion but failed to achieve consensus by this group.

CONCLUSIONS

This issue of ideal and acceptable factor level expression and other unresolved issues will be brought to the 3rd WFH GTRT in 2020.

Practical aspects of inner ear gene delivery for research and clinical applications

The application of gene therapy is widely expanding in research and continuously improving in preparation for clinical applications. The inner ear is an attractive target for gene therapy for treating environmental and genetic diseases in both the auditory and vestibular systems. With the lack of spontaneous cochlear hair cell replacement, hair cell regeneration in adult mammals is among the most important goals of gene therapy. In addition, correcting gene defects can open up a new era for treating inner ear diseases. The relative isolation and small size of the inner ear dictate local administration routes and carefully calculated small volumes of reagents. In the current review, we will cover effective timing, injection routes and types of vectors for successful gene delivery to specific target cells within the inner ear. Differences between research purposes and clinical applications are also discussed.

Hemophilia therapy: the future has begun

The success story of hemophilia care first began in the 1970s, when the availability of plasma-derived concentrates of coagulation factor VIII (FVIII) and factor IX (FIX) provided efficacious treatment of bleeding in patients with hemophilia A and B. This positive scenario was consolidated in terms of greater safety and availability in the 1990s, when the first recombinant coagulation factors were produced. This meant that, instead of only treating episodic bleeding events, prophylaxis regimens could be implemented as a preventive measure. Following the demonstration of its superiority in the frame of two randomized clinical trials, prophylaxis became evidence-based standard of care. In high-income countries, these achievements have led to a patients’ life expectancy being extended to close to that of the general male population. Alongside this, the last decade has witnessed further spectacular therapeutic progress, such as the availability of coagulation factors with a longer plasma half-life that allow for wider intervals between treatment. Moreover, new therapeutic products based on new mechanisms other than the replacement of the deficient factor, have become available (emicizumab) or are at an advanced stage of development. This review celebrates the success story of hemophilia care, while also discussing current limitations, issues and as yet unmet needs. The prospects of cure by means of gene therapy are also outlined.