Gene Therapy For Hemophilia Research Articles

PBI55 Patient Preferences for GENE Therapy in Hemophilia: Results from the Paving Threshold Technique Survey

The aim of the Patient preferences to Assess Value IN Gene therapies (PAVING) study was to investigate trade-offs that adult Belgian hemophilia A and B patients are willing to make when choosing between prophylactic factor replacement therapy (PFRT) and gene therapy. The threshold technique was used to quantify the minimum acceptable benefit (MAB) of a switch from PFRT to gene therapy for ‘Annual bleeding rate’ (ABR), ‘Chance to stop prophylaxis’ (STOP), and ‘Quality of life’ (QOL). ‘Time that side effects have been studied’ was also included as an attribute. An educational tool provided patients with information on gene therapy. The design was supported by stakeholder (including HTA, payers and patients) involvement. Threshold intervals were analyzed using interval regression models in Stata 16. A total of 117 patients completed the survey. Mean thresholds were identified for all benefits (ABR, STOP and QOL), but substantial preference heterogeneity was observed. Heterogeneity in STOP thresholds was found to be most extreme and the majority of patients could be classified in two opposite groups. Time spent on the educational tool and residence were found to impact MAB thresholds. Most patients (88%) would accept gene therapy if it would result in 0 bleeds per year (vs. 6 for PFRT), 90% chance to stop prophylaxis, had no impact on QOL, and if there was 10 years of follow-up on side effects (vs. 30 for PFRT). Results from this study confirmed the value of educating patients on novel treatments (e.g. through educational tools) prior to measuring their preferences. Moreover, preference heterogeneity for novel treatments can be expected and was confirmed in this study. In making decisions on gene therapy, regulators, HTA and payers should consider preference heterogeneity and the impact of patient education on acceptance.

Reimbursing the value of gene therapy care in an era of uncertainty.

Early-stage gene therapy (GT) clinical trials are demonstrating exciting results for persons with haemophilia (PWH), with the first products possibly licenced over the next few years for haemophilia A and B. These new treatments offer the possibility of a one-off approach to the treatment of haemophilia, with demonstrated increases in factor level expression and substantial reductions in both bleeds and factor utilization. However, clinical trial participants have demonstrated variable expression in factor levels, including decreases, over time, suggesting in some cases the effect may not last. The consequence of this uncertainty has led to challenging discussions on value and reimbursement. In most national healthcare systems, the relatively high cost of paying for GT on a one-off basis may be prohibitive, resulting in a lack of access and less post-marketing data generated, ultimately keeping these performance uncertainties high for payers. Economic models have demonstrated the cost-effectiveness of GT in haemophilia based on current clinical trial inputs, but it is in the certainty of these inputs and concomitant budget impacts where the lack of available data will be a concern for payers. To overcome the 'chicken and egg' discussion in relation to reimbursement and data, GT will necessitate new pricing and reimbursement models that share the risk between the manufacturer and the payer. New models have been described for other conditions. The aim of this paper is to propose illustrative concepts of haemophilia reimbursement models that may be further considered in the assessment of a less predictable therapeutic such as GT.

The role of nursing in gene therapy for haemophilia

The role of nursing in gene therapy for haemophilia

First Data from the Phase 3 HOPE-B Gene Therapy Trial: Efficacy and Safety of Etranacogene Dezaparvovec (AAV5-Padua hFIX variant; AMT-061) in Adults with Severe or Moderate-Severe Hemophilia B Treated Irrespective of Pre-Existing Anti-Capsid Neutralizing Antibodies

First Data from the Phase 3 HOPE-B Gene Therapy Trial: Efficacy and Safety of Etranacogene Dezaparvovec (AAV5-Padua hFIX variant; AMT-061) in Adults with Severe or Moderate-Severe Hemophilia B Treated Irrespective of Pre-Existing Anti-Capsid Neutralizing Antibodies

A long-term study of AAV gene therapy in dogs with hemophilia A identifies clonal expansions of transduced liver cells.

Nine hemophilia A dogs were treated with adeno-associated viral (AAV) gene therapy and followed for up to 10 years. Administration of AAV8 or AAV9 vectors expressing canine factor VIII (AAV-cFVIII) corrected the FVIII deficiency to 1.9%−11.3% of normal FVIII levels. In two of nine dogs, FVIII activity increased gradually starting about four years after treatment. None of the dogs showed evidence of tumors or altered liver function. Analysis of integration sites in liver samples from six treated dogs identified 1,741 unique AAV integration events in genomic DNA and expanded cell clones in five dogs, with 44% of these integrations near genes involved in cell growth. All recovered integrated vectors were partially deleted and/or rearranged. Our data suggest that the increase in FVIII protein expression in two dogs may have been due to clonal expansion of cells harboring integrated vectors. These results support the clinical development of liver-directed AAV gene therapy for hemophilia A while emphasizing the importance of long-term monitoring for potential genotoxicity.

Patient perspectives regarding gene therapy in haemophilia: Interviews from the PAVING study.

IntroductionExploring patient perceptions regarding gene therapies may provide insights about their acceptability to patients.ObjectiveTo investigate opinions of people with haemophilia (PWH) regarding gene therapies. Moreover, this study aimed to identify patient‐relevant attributes (treatment features) that influence PWH’s treatment choices.MethodsSemi‐structured individual interviews were conducted with Belgian PWH, types A and B. A predefined interview guide included information sections and open, attribute ranking and case questions. Qualitative data were organized using NVivo 12 and analysed following framework analysis. Sum totals of scores obtained in the ranking exercise were calculated per attribute.ResultsIn total, 20 PWH participated in the interviews. Most participants demonstrated a positive attitude towards gene therapy and were very willing (40%; n = 8) or willing (35%; n = 7) to receive this treatment. The following five attributes were identified as most important to PWH in making their choice: annual bleeding rate, factor level, uncertainty of long‐term risks, impact on daily life, and probability that prophylaxis can be stopped. While participants were concerned about the uncertainty regarding long‐term safety, most participants were less concerned about uncertainty regarding long‐term efficacy.ConclusionsThis qualitative study showed that most PWH have a positive attitude towards gene therapy and that besides efficacy, safety and the related uncertainties, also impact on daily life is important to patients. The identified patient‐relevant attributes may be used by regulators, health technology assessment bodies and payers in their evaluation of gene therapies for haemophilia. Moreover, they may inform clinical trial design, pay‐for‐performance schemes and real‐world evidence studies.

Assessing Patient Experiences with Prophylactic Treatments for Hemophilia a: Concept Elicitation for Gene Therapy

Background: Gene therapy for hemophilia A is designed to be a one-time infusion to deliver functional copies of the defective factor VIII (FVIII) gene, to facilitate the endogenous production of therapeutic FVIII levels. The aim is to achieve long-term protection from bleeds without the burden of regular infusions. Aims: To better understand patients' experiences of living with hemophilia A, the impact of traditional hemophilia A treatments, and patients' perceptions of the potential value of gene therapy versus traditional prophylactic treatments. Methods: Patients were identified from the database of a US rare diseases patient organization, who also recruited and screened patients for the study using materials developed by the outcomes research organization (RTI-HS) and Takeda. Adult males aged ≥18 years with a self-reported diagnosis of moderate or severe hemophilia A, who reported using factor or nonfactor prophylactic treatment and were not currently receiving treatment for inhibitors, were eligible for the study. Eligible patients provided verbal informed consent to participate in a semi-structured, 60-minute telephone interview conducted in English by 2 members of RTI-HS who did not have access to any patient-identifying information at any time during the study. Targeted questions probed perceptions of treatment burden, impact of hemophilia A on daily life, and time spent on treatment. Additionally, questions were posed to assess patients' perceptions of the impact of traditional treatments and the potential benefits they anticipate from gene therapy. Results: Nineteen patients aged 19-55 years with moderate (n = 1) or severe (n = 18) hemophilia A were interviewed. Most (16/19, 89.5%) received prophylactic FVIII therapy, (3/19, 15.8%) were receiving nonfactor prophylactic treatment, of which 1 patient also used FVIII treatment. The aspects of current or past treatments most frequently disliked by patients were lack of efficacy, frequency of infusions, intravenous administration, vein health/scar tissue, and dosing volume. Most patients expressed satisfaction with their current treatment (18/19; 94.7%), though all listed ≥1 negative treatment impact, most frequently related to difficulties with travel (13/19; 68.4%), mood/emotions (12/19; 63.2%), day-to-day activities (10/19; 52.6%), and physical health/activities (7/19; 36.8%), including having to give up or reduce particular activities because of their treatment and needing to be more cautious, especially on nontreatment days. When presented with a hypothetical scenario for gene therapy - a one-time long-acting intravenous infusion to provide a constant level of FVIII that could reduce future bleeds - all patients stated they would choose gene therapy over their current therapy, although several said they would have initial questions regarding safety, efficacy, and duration of protection. Commonly expressed reasons for preferring gene therapy (Figure 1) included fewer infusions and less worry about the need to infuse. All 19 patients said they expected to be highly satisfied with this treatment, largely because of the long-term protection from bleeds, fewer infusions, and less concern about inhibitors. The most commonly anticipated improvements were in mood/emotions (15/19; 78.9%), specifically related to reduced concern about infusions and bleed protection. Other commonly anticipated improvements included gain in time usually spent infusing (13/19; 68.4%), easier travel (12/19; 63.2%), and improved physical health and ability to perform activities (10/19; 52.6%). Conclusions: This study identified specific patient priorities, including treatment convenience, long-lasting bleed protection, frequency of intravenous infusions, and infusion volumes. The results suggest that gene therapy clinical trials should consider evaluating patient concerns in relation to the level of patient confidence in bleed protection. A study limitation is that, at the time of the survey, data on the efficacy and safety of gene therapy were limited. In the future, the study will be expanded to include a larger population of patients with hemophilia. Disclosures Sun: Takeda Pharmaceutical Company Ltd.: Current Employment. Olayinka-Amao:Takeda Pharmaceutical Company Ltd: Other: RTI-HS was contracted by Takeda Pharmaceutical Company Ltd to conduct this work; RTI Health Solutions: Current Employment. DiBenedetti:RTI Health Solutions: Current Employment; Takeda Pharmaceutical Company Ltd: Other: RTI-HS was contracted by Takeda Pharmaceutical Company Ltd to conduct this work.

Etranacogene Dezaparvovec (AAV5-Padua hFIX variant), an Enhanced Vector for Gene Transfer in Adults with Severe or Moderate-Severe Hemophilia B: Two Year Data from a Phase 2b Trial

Background: Gene therapy for hemophilia offers the possibility to ameliorate disease severity to a mild or functionally curative state through a single administration. Etranacogene dezaparvovec (AMT-061) is an investigational gene therapy for hemophilia B comprising an adeno associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) gene with liver specific promoter. Aims: We have previously shown a single dose of etranacogene dezaparvovec to provide sustained FIX activity into the mild-to normal range for up to 52 weeks post-dose in participants with severe or moderate-severe hemophilia B. This time, 2 years of follow-up data will be presented for the first time. Methods: A Phase 2b, open-label, single-dose, single-arm, multi-center trial (NCT03489291) in adult hemophilia B subjects. Interestingly, participants were not excluded based on neutralizing antibodies to AAV5. All subjects received a single intravenous dose of etranacogene dezaparvovec (2x1013 gc/kg) and will be followed for 5-years. The primary endpoint was FIX activity at Week 6. Secondary endpoints include e-diary recordings of bleeds and FIX concentrate use, laboratory parameters, joint health, patient reported outcomes, and adverse events (AEs). Results: All participants had FIX ≤1% (severe or moderately-severe FIX deficiency), required routine FIX prophylaxis, and had neutralizing activity to AAV5 at baseline. Following AMT-061 treatment, FIX activity increased rapidly to a mean of 31% at Week 6. At Week 52, mean FIX activity increased further to 41% with FIX activity levels of 50%, 31% and 41% in participants 1-3 respectively. There was no relationship between the presence of anti-AAV5 NAbs and response to etranacogene dezaparvovec. As of 52 weeks, there were no bleeds post-treatment and no requirement for FIX replacement aside from protocol-specified use for perioperative management in participant 3. There were no clinically significant elevations in liver enzymes and no participants required steroids related to the treatment. One participant experienced 2 mild AEs possibly related to treatment shortly after dosing (self-limiting headache and slightly elevated CRP). One patient had hip surgery due to worsening of pre-existing avascular necrosis deemed unrelated by investigator to etranacogene dezaparvovec and received FIX per protocol according to standard clinical practice. No participant developed inhibitors to FIX. Updated results to 2 years of follow-up will be presented with the main focus on FIX activity, FIX replacement therapy use and reported bleeds. Conclusions: Patients with AAV5 NAbs were included in the Phase 2b etranacogene dezaparvovec trial and have shown sustained FIX activity into the mild-to normal range. All participants were able to discontinue routine prophylaxis, and there have been no bleeds post-treatment with etranacogene dezaparvovec. Disclosures Giermasz: BioMarin: Consultancy, Research Funding, Speakers Bureau; Genentech/Roche: Consultancy, Research Funding, Speakers Bureau; uniQure: Consultancy, Research Funding; Sangamo Therapeutics: Research Funding; Bioverativ/Sanofi: Consultancy, Research Funding, Speakers Bureau. Castaman:Alexion: Honoraria; Roche: Consultancy, Honoraria, Speakers Bureau; CSL Behring: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Ablynx: Honoraria; Baxalta/Shire: Honoraria; Bayer: Honoraria; Uniqure: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kedrion: Speakers Bureau; Werfen: Speakers Bureau; Sobi: Honoraria, Research Funding, Speakers Bureau; Novo Nordisk: Honoraria, Speakers Bureau. Key:Novo Nordisk: Other: Chair of Grants Committee; Takeda: Research Funding; Grifols: Research Funding; Uniqure: Consultancy. Miesbach:Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; BioMarin Pharmaceutical Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; UniQure: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Recht:Spark: Research Funding; Novo Nordisk: Consultancy, Other: personal fees, Research Funding; uniQure: Consultancy, Other: personal fees, Research Funding; Takeda: Consultancy, Other: personal fees, Research Funding; BioMarin: Research Funding; Pfizer: Consultancy, Other: personal fees; Genentech: Consultancy, Other: personal fees, Research Funding; CSL Behring: Consultancy, Other: personal fees. Gomez:Global Blood Therapeutics: Speakers Bureau. Gut:uniQure: Current Employment. Pipe:Siemens: Research Funding; Medical and Scientific Advisory Council to the National Hemophilia Foundation; Medical Advisory Board to World Federation of Hemophilia: Membership on an entity's Board of Directors or advisory committees; Apcintex, Bayer, BioMarin, Catalyst Biosciences, CSL Behring, HEMA Biologics, Freeline, Novo Nordisk, Pfizer, F. Hoffmann-La Roche Ltd/Genentech, Inc., Sangamo Therapeutics, Sanofi, Takeda, Spark Therapeutics, uniQure: Consultancy. OffLabel Disclosure: Etranacogene dezaparvovec (AMT-061) is an investigational gene therapy for hemophilia B comprising an adeno associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) gene with liver specific promoter.

Evaluation of Maternal Safety Following Prenatal Cell and Gene Therapy for Hemophilia a in a Large Animal Model Demonstrates Absence of Maternal Exposure to the Cells or Gene Products Infused into the Fetus

Prenatal transplantation (PNT) using stem/progenitor cells has been performed in more than 50 patients using an ultrasound-guided approach, proving that this procedure poses minimal risk to both the fetus and the mother. Since 75% of hemophilia A (HA) patients have a family history of HA, and prenatal diagnosis is available to pregnant HA carriers in most western countries, PNT constitutes a clinically viable approach to treat these patients. In addition, the type of mutation and family history can predict the severity of the disease and the patient's likelihood of developing FVIII inhibitors, thus allowing intervention in those who could most benefit from this approach. Nevertheless, maternal safety is a critical consideration for PNT, particularly with respect to possible exposure to the cells or gene products produced by the cells infused into the fetus. We have previously demonstrated that transplanting sheep fetuses (n=23) with human placental cells (PLC) transduced with a lentiviral vector encoding a bioengineered fVIII transgene (mcoET3), at a dose of 107-108 cells/kg, increased plasma fVIII activity levels for at least 3 years after transplant. Therefore, here we studied ewes (n=4) during pregnancy and those who had given birth (n=6) to lambs treated in utero. The latter were assessed longitudinally over a course of 5 months, ranging from 18 to 32 months after delivery of a PNT recipient. First, we investigated whether any of the ewes, during pregnancy or at any point thereafter,developed an immune response to the transplanted product, PLC-mcoET3. Peripheral blood mononuclear cells (PBMC) harvested from the different ewes readily proliferated in response to human PBMC and upon PHA stimulation, but PLC-mcoET3 and non-transduced PLCs did not elicit an immune response from PBMC from any of the ewes, demonstrating that PNT did not immunize the ewe to the transplanted cells. We also used an mcoET3-specific ELISA to investigate whether the ewes developed antibodies to the mcoET3 protein. At no time point were ewes ever found to harbor anti-mcoET3 IgGs in their plasma. To determine whether mcoET3-specific T effector cells developed in the ewes, we performed ELISpot assays using PBMC collected during pregnancy and at various time points thereafter, and no mcoET3-specific Th1 or Th2 cells were detected in these ewes. To assess the potential circulation and/or engraftment of PLC-mcoET3 in the ewes during pregnancy or at any time after delivery, maternal PBMC collected during pregnancy, and maternal-side placental tissue and umbilical cord tissue (UBC) collected at birth were analyzed using RT-qPCR (detection limit <0.01%) with primers specific for human FVIII (produced constitutively by the PLC) and mcoET3. Maternal PBMC, UBC, and placental tissue were all devoid of PLC-mcoET3, as evidenced by the complete absence of mcoET3 and human FVIII mRNA. Histopathologic analysis of the placental tissue demonstrated no abnormalities or ectopic tissue formation. Overall, these studies suggest that the administration of PLC-mcoET3 to the fetus during gestation does not result in detectable maternal exposure to the cells or gene products, attesting to the safety of this approach. Disclosures Doering: Kilpatrick, Townsend & Stockton: Consultancy; Expression Therapeutics, LLC: Current equity holder in private company, Patents & Royalties, Research Funding.

Haemophilia, the journey in search of a cure. 1960-2020.

The single most important step on the path to our modern understanding of blood coagulation and haemophilia in the 20th century was taken by British pathologist Robert Gwyn Macfarlane with his 1964 publication 'An enzyme cascade in the blood clotting mechanism, and its function as a biochemical amplifier'. In the same year, Ratnoff and Davie in the USA reached the same conclusion. Macfarlane and Rosemary Biggs had previously, in 1952, discovered factor IX as the factor deficient in haemophilia B. In 1973, Arthur Bloom defined the distinct role of Factor VIII and von Willebrand factor in haemophilia A and von Willebrand's disease respectively. This inspired the efforts of Tuddenham and his group towards the purification of Factor VIII which reached homogeneity in 1982, leading to the cloning of the Factor VIII gene in 1984 in collaboration with US scientists at Genentech, which in turn enabled development of safe recombinant factor concentrates for patients with haemophilia. Brownlee cloned the factor IX gene in 1982 at the Sir William Dunn Institute of Pathology in Oxford. This led eventually to the first successful trial of gene therapy for haemophilia B in 2011 by the Nathwani group at UCL, which built on pioneering work of US groups and was partnered with St Jude in Memphis where Nathwani started the project. This trial has fuelled the current quest for a functional cure of haemophilia A and B. The UK has, therefore, made a rich contribution to advances in haemostasis over the last 60years, often in partnership with other groups across the world.

Advances in gene therapy for β-thalassemia and hemophilia based on the CRISPR/Cas9 technology

Thalassemia and hemophilia are common inherited blood disorders caused by genetic abnormalities. These diseases are difficult to cure and can be inherited to the next generation, causing severe family and social burden. The emergence of gene therapy provides a new treatment for genetic diseases. However, since its first clinical trial in 1990, the development of gene therapy has not been as optimistic in the past three decades as one could hope. The development of gene-editing technology, particularly the third generation gene-editing technology CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9), has given hope in such therapeutic approach for having advantages in high editing efficiency, simple operation, and low cost. Gene editing-mediated gene therapy has thus received increasing attention from the biomedical community. It has shown promises for the treatment of inherited blood disorders, such as thalassemia and hemophilia. This paper reviews the fundamental research progress of gene therapy for β-thalassemia and hemophilia based on CRISPR/Cas9 technology in the past six years. It also summarizes the CRISPR/Cas9-based clinical trials of gene therapy. The problems and possible solutions to this technology for gene therapy are also discussed, thereby providing a reference for the research on gene therapy of inherited blood disorders based on CRISPR/Cas9 technology.

State of the art on clinical trials of gene therapy in haemophilia

State of the art on clinical trials of gene therapy in haemophilia

Development of a Clinical Candidate AAV3 Vector for Gene Therapy of Hemophilia B.

Although recombinant adeno-associated virus serotype 8 (AAV8) and serotype 5 (AAV5) vectors have shown efficacy in Phase 1 clinical trials for gene therapy of hemophilia B, it has become increasingly clear that these serotypes are not optimal for transducing primary human hepatocytes. We have previously reported that among the 10 most commonly used AAV serotypes, AAV serotype 3 (AAV3) vectors are the most efficient in transducing primary human hepatocytes in vitro as well as in "humanized" mice in vivo, and suggested that AAV3 vectors expressing human coagulation factor IX (hFIX) may be a more efficient alternative for clinical gene therapy of hemophilia B. In the present study, we extended these findings to develop an AAV3 vector incorporating a compact yet powerful liver-directed promoter as well as optimized hFIX cDNA sequence inserted between two AAV3 inverted terminal repeats. When packaged into an AAV3 capsid, this vector yields therapeutic levels of hFIX in hemophilia B and in "humanized" mice in vivo. Together, these studies have resulted in an AAV3 vector predicted to achieve clinical efficacy at reduced vector doses, without the need for immune-suppression, for clinical gene therapy of hemophilia B.

Gene therapy for hemophilia: anticipating the unexpected

Gene therapy for hemophilia: anticipating the unexpected

Utilizing Platelets as a Targeted for Gene Therapy of Hemophilia a and Hemophilia B

Utilizing Platelets as a Targeted for Gene Therapy of Hemophilia a and Hemophilia B

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.

Advances in gene therapy for hemophilia

Hemophilia is a hereditary disorder that can be life-threatening in individuals who have severe spontaneous bleeding resulting from minor trauma or surgery. Although replacement therapy of the missing exogenous factor has improved patients' quality of life, it has not been possible to establish a long-term treatment. Due to the severity of the disease and the need for repetitive doses throughout the patient's life, replacement therapy has become a high-cost treatment option; therefore, the development of self-sustainable long-term therapies is critical. Hemophilia is a good candidate for gene therapy because it is a monogenic disease that can be counteracted by expression of the missing factor. In this article, we review some of the most relevant advances in gene therapy for this illness.

B Cell Depletion Eliminates FVIII Memory B Cells and Enhances AAV8-coF8 Immune Tolerance Induction When Combined With Rapamycin.

Hemophilia A is an inherited coagulation disorder resulting in the loss of functional clotting factor VIII (FVIII). Presently, the most effective treatment is prophylactic protein replacement therapy. However, this requires frequent life-long intravenous infusions of plasma derived or recombinant clotting factors and is not a cure. A major complication is the development of inhibitory antibodies that nullify the replacement factor. Immune tolerance induction (ITI) therapy to reverse inhibitors can last from months to years, requires daily or every other day infusions of supraphysiological levels of FVIII and is effective in only up to 70% of hemophilia A patients. Preclinical and recent clinical studies have shown that gene replacement therapy with AAV vectors can effectively cure hemophilia A patients. However, it is unclear how hemophilia patients with high risk inhibitor F8 mutations or with established inhibitors will respond to gene therapy, as these patients have been excluded from ongoing clinical trials. AAV8-coF8 gene transfer in naïve BALB/c-F8e16−/Y mice (BALB/c-HA) results in anti-FVIII IgG1 inhibitors following gene transfer, which can be prevented by transient immune modulation with anti-mCD20 (18B12) and oral rapamycin. We investigated if we could improve ITI in inhibitor positive mice by combining anti-mCD20 and rapamycin with AAV8-coF8 gene therapy. Our hypothesis was that continuous expression of FVIII protein from gene transfer compared to transient FVIII from weekly protein therapy, would enhance regulatory T cell induction and promote deletion of FVIII reactive B cells, following reconstitution. Mice that received anti-CD20 had a sharp decline in inhibitors, which corresponded to FVIII memory B (Bmem) cell deletion. Importantly, only mice receiving both anti-mCD20 and rapamycin failed to increase inhibitors following rechallenge with intravenous FVIII protein therapy. Our data show that B and T cell immune modulation complements AAV8-coF8 gene therapy in naïve and inhibitor positive hemophilia A mice and suggest that such protocols should be considered for AAV gene therapy in high risk or inhibitor positive hemophilia patients.

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.

The critical need for postmarketing surveillance in gene therapy for haemophilia.

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. 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. 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. 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.