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INTRODUCTION Gene therapy has shown promise in clinical trials for patients with haemophilia, but patient preference studies have focused on factor replacement treatments. AIM We conducted a discrete choice experiment (DCE) to investigate the relative importance and differential preferences patients provide for gene therapy attributes. METHODS We surveyed male adults with haemophilia in the United States recruited from patient panels including the National Hemophilia Foundation Community Voices in Research platform using an online survey over 4 months in 2020/21. Participants indicated preferences for gene therapy attributes including dosing frequency/durability, effect on annual bleeding, uncertainty related to side effects, impact on daily activities, impact on mental health, and post-treatment requirements. The relative importance of each attribute was analysed overall and for subgroups based on haemophilia type and severity. RESULTS A total of 183 males with haemophilia A (n = 120) or B (n = 63) were included. Half (47%) had severe haemophilia; most (75%) were White. Overall, participants gave effect on bleeding rate the greatest relative importance (31%), followed by dose frequency/durability (26%), uncertainty regarding safety issues (17%), and impact on daily activities (11%). Dose frequency/durability had the greatest importance for those with haemophilia B (35%). CONCLUSION People with haemophilia prioritised reduced bleeding and treatment burden; the former was more important in haemophilia A and the latter in haemophilia B, followed by safety and impact on daily life in this DCE of gene therapy attributes. These findings and differences can inform clinical and health policy decisions to improve health equity for people with haemophilia.

IntroductionPeople with inherited and long-term conditions such as haemophilia have been shown to adapt to their levels of disability, often reporting better quality of life (QoL) than expected from the general population (the disability paradox).AimTo investigate the disability paradox in people with haemophilia in the United States by examining preference differences in health state valuations versus the general population.MethodsWe conducted a discrete choice experiment including duration to capture valuations of health states based on patient-reported preferences. Participants indicated their preferences for hypothetical health states using the EQ-5D-5L, where each participant completed 15 of the 120 choice tasks. Response inconsistencies were evaluated with dominated and repeated scenarios. Conditional-logit regressions with random sampling of the general population responses were used to match the sample of patients with haemophilia. We compared model estimates and derived preferences associated with EQ-5D-5L health states.ResultsAfter removing respondents with response inconsistencies, 1327/2138 (62%) participants remained (177/283 haemophilia; 1150/1900 general population). Patients with haemophilia indicated higher preference value for 99% of EQ-5D-5L health states compared to the general population (when matched on age and gender). The mean health state valuation difference of 0.17 indicated a meaningful difference compared to a minimal clinically important difference threshold of 0.07. Results were consistent by haemophilia type and severity.ConclusionOur findings indicated the presence of a disability paradox among patients with haemophilia, who reported higher health states than the general population, suggesting the impact of haemophilia may be underestimated if general population value sets are used.

Etranacogene dezaparvovec (AMT-061) is a recombinant AAV5 vector including a gene cassette containing the factor IX (FIX) Padua variant under the control of a liver-specific promoter. A phase 2b study was conducted to confirm that a single dose of 2 × 1013 genome copies per kilogram of etranacogene dezaparvovec will result in FIX activity ≥5% 6 weeks after dosing. Secondary end points included FIX activity at other time points, bleed frequency, FIX replacement, and safety. Etranacogene dezaparvovec was administered as a single IV infusion to 3 adults with severe to moderately severe hemophilia B. Before treatment, participants had low levels of preexisting neutralizing antibodies to AAV5. This article reports a planned 26-week interim assessment. At week 6, mean FIX activity was 31% (23.9%-37.8%), increasing to 47% (33.2%-57.0%) at 26 weeks, with 2 subjects exhibiting sustained activity >40%. Consistent with the FIX activity, etranacogene dezaparvovec was associated with a complete bleed cessation with no need for FIX replacement therapy up to 26 weeks. Etranacogene dezaparvovec was generally well tolerated. No clinically significant elevations in levels of liver enzymes or inflammatory markers were observed, and no use of corticosteroids related to treatment was required. In individuals with severe to moderately severe hemophilia B, etranacogene dezaparvovec resulted in clinically relevant increases in FIX activity, cessation of bleeds, and abrogation of the need for FIX replacement, despite the presence of preexisting anti-AAV5 neutralizing antibodies detected by using a highly sensitive luciferase assay. Consistency of results in the 3 participants supported an expanded evaluation of the safety/efficacy of etranacogene dezaparvovec in the HOPE-B (Health Outcomes With Padua Gene; Evaluation in Hemophilia-B) phase 3 trial. The current trial was registered at www.clinicaltrials.gov as #NCT03489291.

Background: Etranacogene dezaparvovec is an investigational gene therapy for hemophilia B (HB) comprising an adeno-associated virus serotype 5 (AAV5) vector containing a codon-optimized Padua variant human factor IX (FIX) gene with a liver specific promoter. In a Phase 2b study, a single dose of etranacogene dezaparvovec provided mean FIX activity of 41.0% sustained at 1yr post-dose in 3 participants (pts). Although most gene therapy clinical studies exclude pts with pre-existing neutralizing antibodies (NAbs) to the capsid serotype, early clinical studies and nonhuman primate data suggest that generally prevalent titers of anti-AAV5 NAbs may not preclude successful transduction with etranacogene dezaparvovec. Aims: A Phase 3, Health Outcomes with Padua gene; Evaluation in Hemophilia B (HOPE-B; NCT03569891) was established to further assess efficacy and safety of etranacogene dezaparvovec in adults with HB with a wide range of pre-existing NAbs to AAV5. Here we report outcomes at 26 weeks (wks). Methods: HOPE-B is a Phase 3, open-label, single-dose, single-arm, multi-national trial in adult males with severe or moderate-severe HB (FIX≤2%). All pts received routine FIX prophylaxis prior to study. Pts were not excluded based on pre-existing NAbs to AAV5. Pts entered a prospective lead-in period of at least 6 months during which bleeding/factor use was monitored, then received a single intravenous dose of etranacogene dezaparvovec (2x1013 gc/kg). Pts will be followed for 5yrs. Primary endpoints comprised FIX activity (one stage) at 26 and 52wks after dosing and 52wk annualized bleeding rate. For pts with no clean post-treatment FIX samples (≥10d post exogenous FIX), factor activity was imputed as baseline value based on historic disease severity. Secondary endpoints include factor replacement use, adverse events (AEs), and reactive use of corticosteroids. Results: 75 pts were screened, of whom 67 entered lead-in. 54 pts were dosed (44 severe, 10 moderately severe HB) and completed 26wks of follow-up. Mean age (±SD) was 41.5 (15.8) yrs. 38/54 pts (70.4%) had bleeds (n=123) during the lead-in despite prophylaxis, and 23/54 (42.6%) had NAbs to AAV5 at baseline (max titer: 3212.3). Following treatment, FIX activity increased rapidly to a mean (SD; min,max) of 37.2% (±19.6; 1.0, 97.1) at wk26, representing a mean (SD; min,max) change from baseline of 36.0% (±19.7; 0, 96.1 p Conclusions: The first co-primary endpoint of this study was met. This is the first report of a Phase 3 study in HB and the largest gene therapy trial cohort to date. Following a single dose of etranacogene dezaparvovec, FIX activity increased, without the need for prophylactic immunosuppression, into the mild-to-normal range at 26wks in pts with severe/moderately severe HB. Importantly, this included pts with titers of pre-existing anti-AAV5 NAbs. Pts were able to discontinue prophylaxis and bleeding was abolished in the majority. The safety profile was consistent with early phase AAV5 studies and together these data support a favorable safety and efficacy profile for etranacogene dezaparvovec Disclosures Pipe: HEMA Biologics: Consultancy, Other; Catalyst Biosciences: Consultancy; CSL Behring: Consultancy; ApcinteX: Consultancy; Bayer: Consultancy, Other: Contracted Research; BioMarin: Consultancy, Other: Contracted Research; Takeda: Consultancy; uniQure: Consultancy, Other; Siemens: Other; Pfizer: Consultancy; Freeline Therapeutics: Consultancy, Other: Contracted Research; Novo Nordisk: Consultancy, Other: Contracted Research; Roche/Genentech: Consultancy, Other: Contracted Research; Sangamo Therapeutics: Consultancy; Sanofi Genzyme: Consultancy, Other; Spark Therapeutics: Consultancy. Recht:CSL Behring: Consultancy, Other: personal fees; Genentech: Consultancy, Other: personal fees, Research Funding; Pfizer: Consultancy, Other: personal fees, Research Funding; BioMarin: Research Funding; Takeda: Consultancy, Other: personal fees, Research Funding; uniQure: Consultancy, Other: personal fees, Research Funding; Novo Nordisk: Consultancy, Other: personal fees, Research Funding; Spark: Research Funding; Bayer: Research Funding; Grifols: Research Funding; Hema Biologics: Consultancy, Research Funding; LFB: Research Funding; Octapharma: Research Funding; Catalyst Biosciences: Consultancy; Kedrion: Consultancy; Sanofi: Consultancy, Research Funding. Key:Uniqure: Consultancy; Grifols: Research Funding; Takeda: Research Funding; Novo Nordisk: Other: Chair of Grants Committee. Leebeek:Shire/Takeda: Research Funding; uniQure: Consultancy; Shire/Takeda: Consultancy; BioMarin: Consultancy; SOBI: Other: Travel grant; Roche: Other: DSMB member for a study; CSL Behring: Research Funding. Castaman:Bayer, Roche, Sobi, Grifols, Novo Nordick, Werfen, Kedrion: Consultancy, Honoraria, Speakers Bureau; CSL Behring, Pfizer, Sobi: Research Funding; Ablynx, Alexion, Bayer, Takeda, CSL Behring, Novo Nordisk, Pfizer, Roche,Sanofi, SOBI, uniQure: Membership on an entity's Board of Directors or advisory committees. Lattimore:uniQure: Other: Study Steering Committee member. Van Der Valk:Baxalta: Research Funding. Peerlinck:Bayer: Consultancy, Research Funding; CSL Behring: Consultancy, Research Funding; NovoNordisk: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Roche: Research Funding; Sobi: Consultancy; Takeda: Consultancy, Research Funding. Coppens:Roche: Research Funding; Portola/Alexion: Research Funding; Sanquin Blood Supply: Research Funding; uniQure: Research Funding; NovoNordisk: Consultancy; Pfizer: Consultancy; Sobi: Consultancy; Medcon International: Consultancy; MEDtalks: Consultancy; Bayer: Consultancy, Research Funding; CSL Behring: Consultancy, Research Funding; Daiichi Sankyo: Research Funding. O'Connell:uniQure: Consultancy; F. Hoffmann-La Roche Ltd, Novo Nordisk, SOBI: Speakers Bureau; SOBI: Research Funding. Pasi:Sanofi: Honoraria, Other: Personal fees and nonfinancial support; honoraria as member of scientific advisory boards and symposia, Research Funding; BioMarin: Consultancy, Honoraria, Other: Grants, personal fees, and nonfinancial support; honoraria as member of scientific advisory boards and symposia, Research Funding; uniQure: Other: Grants and nonfinancial support , Research Funding; ApcinteX: Consultancy, Other: Personal fees ; Takeda: Consultancy, Honoraria, Other: Personal fees; honoraria as member of scientific advisory boards and symposia ; Biotest: Consultancy, Honoraria, Other: Personal fees and nonfinancial support; honoraria as member of scientific advisory boards and symposia; Catalyst Biosciences: Consultancy, Other: Personal fees and nonfinancial support; honoraria as member of scientific advisory boards and symposia; Novo Nordisk: Honoraria, Other: Personal fees and nonfinancial support; honoraria as member of scientific advisory boards and symposia ; Octapharma: Honoraria, Other: Personal fees and nonfinancial support; honoraria as member of scientific advisory boards and symposia , Speakers Bureau; Roche: Honoraria, Other; Sobi: Consultancy, Honoraria, Other; Tremeau: Consultancy. Kampmann:Uniqure: Research Funding, Speakers Bureau; Shire Pharmaceuticals: Speakers Bureau. Meijer:Pfizer: Research Funding; Sanquin: Speakers Bureau; Bayer: Speakers Bureau; Sanquin: Research Funding; Bayer: Research Funding; Boehringer Ingelheim: Speakers Bureau; BMS: Speakers Bureau; Aspen: Speakers Bureau; Uniqure: Consultancy. von Drygalski:Biomarin: Consultancy; Bioverativ/Sanofi Genzyme: Consultancy; NovoNordisk: Consultancy; Pfizer: Consultancy; uniQure: Consultancy; Hematherix Inc.: Membership on an entity's Board of Directors or advisory committees. Young:Genentech/Roche, Grifols, and Takeda: Research Funding; BioMarin, Freeline, Genentech/Roche, Grifols, Kedrion, Novo Nordisk, Sanofi Genzyme, Spark, Takeda, and UniQure: Honoraria; Bayer, CSL Behring, Freeline, UniQure: Consultancy. Hermans:WFH: Other; EAHAD: Other; LFB: Consultancy, Speakers Bureau; CSL Behring: Consultancy, Speakers Bureau; CAF-DCF: Consultancy, Speakers Bureau; Biogen: Consultancy, Speakers Bureau; Sobi: Consultancy, Research Funding, Speakers Bureau; Shire, a Takeda company: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Research Funding, Speakers Bureau; Bayer: Consultancy, Research Funding, Speakers Bureau; Novo Nordisk: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; Octapharma: Consultancy, Speakers Bureau; Kedrion: Speakers Bureau. Astermark:Bayer, CSL Behring, Novo Nordisk, Octapharma, Roche, Sobi, Spark, Takeda, uniQure: Consultancy; uniQure: Research Funding. Klamroth:Bayer: Consultancy, Research Funding, Speakers Bureau; Biomarin: Consultancy, Research Funding, Speakers Bureau; CSL Behring: Research Funding, Speakers Bureau; Novo Nordisk: Consultancy, Research Funding, Speakers Bureau; Octapharma: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Research Funding, Speakers Bureau; Roche/Chugai: Consultancy, Speakers Bureau; Takeda/Shire: Consultancy, Research Funding, Speakers Bureau; Sobi: Consultancy, Speakers Bureau; Biotest: Speakers Bureau; LEO: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Lemons:uniQure: Research Funding. Visweshwar:Biogen Idec: Membership on an entity's Board of Directors or advisory committees. Escobar:Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genentech, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; National Hemophilia Foundation: Consultancy, Membership on an entity's Board of Directors or advisory committees; Biomarin, Genetech/Roche, CSL Behring, Kedrion, Magellan Healthcare: Honoraria. Gomez:Global Blood Therapeutics: Speakers Bureau. Kruse-Jarres:CSL Behring, Genentech, Inc., Spark: Research Funding; Biomarin, Chugai Pharmaceutical Co., CSL Behring, CRISPR Therapeutics, Genentech, Inc.: Honoraria; F. Hoffmann-La Roche Ltd: Speakers Bureau; Biomarin, Chugai Pharmaceutical Co., CSL Behring, CRISPR Therapeutics, Genentech, Inc.: Consultancy. Kotowski:uniQure: Research Funding. Quon:Orthopaedic Institute for Children: Current Employment; Bayer: Honoraria; Biomarin: Honoraria, Speakers Bureau; Bioverativ/Sanofi: Honoraria, Speakers Bureau; Genentech, Inc./F. Hoffmann-La Roche Ltd: Honoraria, Speakers Bureau; Novo Nordisk: Honoraria, Speakers Bureau; Octapharma: Honoraria; Shire/Takeda: Speakers Bureau. Wang:Bayer: Honoraria; Takeda: Honoraria; Genentech: Honoraria; Biomarin: Honoraria; CSL Behring: Honoraria; Bioverativ Inc: Honoraria; Catalyst Biologics: Consultancy; NovoNordisk: Consultancy; Hema biologics / LFB: Consultancy. Wheeler:Takeda: Membership on an entity's Board of Directors or advisory committees; uniQure: Membership on an entity's Board of Directors or advisory committees; Biomarin: Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees. Sawyer:uniQure: Current Employment, Current equity holder in publicly-traded company. Verweij:uniQure: Current Employment. Colletta:uniQure: Current Employment. Bajma:uniQure: Current Employment. Gut:uniQure: Current Employment. Miesbach:Bayer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Biomarin: Consultancy, Membership on an entity's Board of Directors or advisory committees; Freeline: Consultancy, Membership on an entity's Board of Directors or advisory committees; LFB: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Octapharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novo Nordisk: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy; Sanofi: Consultancy, Membership on an entity's Board of Directors or advisory committees; uniQure: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Biotest: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding. OffLabel Disclosure: Etranacogene dezaparvovec is an investigational gene therapy

Background: Gene therapy aims to provide long-term therapeutic benefit from a single administration. AMT-060 is an adeno-associated virus serotype 5 (AAV5) vector with a codon-optimized wildtype human factor IX (FIX) gene and liver-specific promoter. AMT-060 is being evaluated in an ongoing study of 10 participants with severe/moderate-severe hemophilia B (Phase 1/2 study, NCT02396342) over 5 years. Aim: To describe efficacy and safety outcomes from an analysis at up to 5-years post-AMT-060. Methods: Adult males with FIX activity ≤2% and a severe bleeding phenotype received a single intravenous infusion of AMT-060 (5x1012 gc/kg, Cohort 1, n=5) or (2×1013 gc/kg, Cohort 2, n=5). Assessments included FIX activity, FIX replacement use, annualized bleeding rate (ABR), treatment-related adverse events (TRAE), immunological and inflammatory biomarkers up to 5 years (Cohort 1) and 4.5 years (Cohort 2). Results: As of November 2019, for Cohort 1 the mean FIX activity (at 4.0 years) was 5.1% as compared to 4.4% in the first year, 6.8% in the second year, 7.3% in the third year and 7.0% in the fourth year. Mean FIX activity for Cohort 2 was 7.5% as compared to 7.1% in the first year, 8.4% in the second year 7.9% in the third year, and 7.4% in the fourth year. Eight of 9 participants using prophylaxis at baseline were able to discontinue use. During the last 12, and 6 months of observation respectively, the mean annualized bleed rate (ABR) was 3.3. for Cohort 1 and 0.0 for Cohort 2. These represent, respectively, a reduction in mean ABR to the year prior to treatment of 77% and 100% for Cohort 1 and Cohort 2. During this same period the consumption of FIX replacement therapy declined 90% and 100% relative to pre-treatment, respectively for Cohort 1 and Cohort 2. No participants developed FIX inhibitors or signs of sustained AAV5 capsid-specific T-cell activation. As previously reported, TRAE were mainly reported in the first 3.5 months after treatment, including three participants who experienced transient mild elevations in alanine aminotransferase. One additional TRAE (joint swelling post-exercise) was observed during the last 12 months of observation post-treatment. Updated data, up to 5-years of observation, will be presented for the first time. Conclusions: Long-term stable endogenous FIX activity and reductions in ABR and FIX replacement use were sustained over multiple years following a single treatment with AMT-060. There were no additional safety concerns with longer term follow-up. This data supports the ongoing Phase 3 study of the enhanced construct etranacogene dezaparvovec (AMT-061), which encodes the highly active Padua FIX variant. Disclosures Meijer: Bayer: Research Funding; Sanquin: Research Funding; Pfizer: Research Funding; Bayer: Speakers Bureau; Sanquin: Speakers Bureau; Boehringer Ingelheim: Speakers Bureau; BMS: Speakers Bureau; Aspen: Speakers Bureau; Uniqure: Consultancy. Kampmann:Uniqure: Speakers Bureau; Shire Pharmaceuticals: Speakers Bureau. Klamroth:CSL Behring: Research Funding, Speakers Bureau; Novo Nordisk: Consultancy, Research Funding, Speakers Bureau; Octapharma: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Research Funding, Speakers Bureau; Roche: Consultancy, Speakers Bureau; Takeda/Shire: Consultancy, Research Funding, Speakers Bureau; Sobi: Consultancy, Speakers Bureau; Biotest: Speakers Bureau; Grifols: Speakers Bureau; Biomarin: Consultancy, Research Funding, Speakers Bureau; Bayer: Consultancy, Research Funding, Speakers Bureau. Castaman:Novo Nordisk: Honoraria, Speakers Bureau; Roche: Consultancy, Honoraria, Speakers Bureau; Pfizer: Honoraria, Research Funding; Ablynx: Honoraria; Alexion: Honoraria; Bayer: Honoraria; CSL Behring: Honoraria, Research Funding; Kedrion: Speakers Bureau; Sobi: Honoraria, Research Funding, Speakers Bureau; Uniqure: Honoraria, Membership on an entity's Board of Directors or advisory committees; Werfen: Speakers Bureau; Baxalta/Shire: Honoraria. Bönig:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Genzyme: Consultancy, Membership on an entity's Board of Directors or advisory committees; Healthineers: Current equity holder in publicly-traded company; Sandor-Hexal: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Polyphor: Research Funding; Miltenyi: Honoraria, Research Funding; Erydel: Research Funding; Chugai: Honoraria, Research Funding; Bayer: Research Funding; Terumo BCT: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kiadis: Honoraria; Uniqure: Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Stage: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Fresenius: Honoraria; medac: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Sawyer:uniQure: Current Employment. Miesbach:UniQure: 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; BioMarin Pharmaceutical Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. OffLabel Disclosure: AMT-060 = AAV5 vector gene therapy in subjects with moderate to severe hemophilia B

Introduction The treatment paradigm for people with severe hemophilia B in the US typically involves prophylaxis with factor IX (FIX) replacement therapy, the primary aim of which is to provide sufficient FIX levels to reduce the frequency of bleeding events. The clinical benefits of FIX prophylaxis are well understood, however the cost of FIX products as well as costs associated with healthcare resource utilization present a significant burden to the healthcare system. Substantive costs may also accrue in patients who continue to bleed while on prophylaxis, due to the impact on both short and long-term joint-related outcomes. In the absence of existing data in the US, the 'Cost of Hemophilia Across the USA: a Socioeconomic Survey' (CHESS US) study was conducted to establish a population-based estimate of the real-world US healthcare system burden associated with severe hemophilia. Using data drawn from the CHESS US study, this analysis examines the real-world healthcare system costs and clinical outcomes of people with severe hemophilia B on FIX prophylaxis. Methods CHESS US, a retrospective, cross-sectional dataset of adults with severe hemophilia in the USA, gathered information on patient cost via a patient record form. Data on the following parameters are included in this analysis: FIX consumption, annualized bleeding rate (ABR), the presence of one or more chronically damaged joints ("problem joint"), as well as costs associated with annual (prophylactic) factor consumption and hospitalizations (i.e., number of admissions, number of day cases, total inpatient days, and total intensive care unit [ICU] days). All variables report retrospective data of the 12 months prior to enrolment in the study. Results are presented as mean (± standard deviation) or N (%). Results In total, 132 of 576 patients profiled in the CHESS US study had severe hemophilia B. Among them, 77 patients were on FIX prophylaxis, of whom 44 patients reported FIX dosing regimen and were included in the current analyses. Among them, 20 patients were treated with conventional FIX and 24 patients with extended half-life (EHL) FIX products. The cohort has a mean age of 27.64 (± 11.05) and mean weight (kg) of 75.71 (± 13.41). In the last 12 months, the mean number of international units (IU) prescribed for FIX prophylaxis across the full cohort was 257,216 IU (± 213,591), with an associated annual cost of $610,966 (± $495,869). Among patients treated with conventional FIX, mean prescribed FIX was 287,141 IU (± 264,906) at an annual cost of $397,491 (± $359,788), while patients treated with EHL FIX reported a mean prescribed FIX of 232,278 IU (± 160,914) at an annual cost of $788,861 (± $529,258). The cohort reported a mean ABR of 1.73 (± 1.39); 8 (18%) were reported to have a target joint meeting the International Society on Thrombosis and Haemostasis (ISTH) definition; and 11% were reported to have had at least one chronically damaged joint (i.e., problem joint). Healthcare resource utilization associated with bleed events were reported as follows: hospital admissions days [0.18 (± 0.62)]; inpatient days [0.34 (± 1.22)]; and ICU days [0.23 (± 0.86)]. The direct medical cost to the healthcare system was $2,885 (± $7,857; excluding FIX cost) and $614,886 (± $498,839; including FIX cost). Discussion Data from the CHESS US study showed substantial costs and resource utilization among patients with severe hemophilia B receiving FIX prophylaxis, of which the cost of FIX replacement therapy constituted most of the total cost to healthcare system. Although the ABR observed in the analysis population was low, bleed-related hospitalizations comprised a significant non-drug cost to the healthcare system. A proportion of patients also still experienced joint arthropathy. Such substantial clinical and economic burden highlights that unmet needs remain in patients with severe hemophilia B on FIX prophylaxis in the US. Disclosures Noone: HCD Economics: Employment. Pedra:HCD Economics: Employment. Asghar:HCD Economics: Employment. O'Hara:HCD Economics: Employment, Equity Ownership. Sawyer:uniQure Inc.: Employment. Li:uniQure Inc.: Employment.

Background: The aim of gene therapy is to provide long-term therapeutic effect from a single administration, yet information on response durability is currently limited. AMT-060 is an adeno-associated virus serotype 5 (AAV5) vector with a codon-optimized wildtype human factor IX (FIX) gene and liver-specific promoter. AMT-060 is being analyzed in an ongoing study of 10 participants with severe/moderate-severe hemophilia B (Phase 1/2 study, NCT02396342). Aim: To describe efficacy and safety outcomes from a planned interim analysis at up to 4-years post-AMT-060. Methods: Adult males with FIX activity ≤2% and a severe bleeding phenotype received a single intravenous infusion of AMT-060 (5x1012gc/kg, Cohort 1, n=5) or (2×1013 gc/kg, Cohort 2, n=5). Assessments included FIX activity, FIX replacement use, annualized bleeding rate (ABR), treatment-related adverse events (TRAE), immunological and inflammatory biomarkers up to 4 years (Cohort 1) and 3.5 years (Cohort 2). Results: As of 8 May 2019, for Cohort 1 the mean yearly FIX activity (annualized to 4 years) was 6.0 as compared to 4.4% in the first year, 6.8% in the second year and 7.3% in the third year. Mean yearly FIX activity for Cohort 2 at 3 years was 7.9% as compared to 7.1% in the first year and 8.4% in the second year. Factor IX activity for each patient over the length of follow up is shown in Figure 1. Eight of 9 participants using prophylaxis at baseline were able to discontinue use. During the last 12 months of observation, the mean annualized bleed rate (ABR) was 1.7 for Cohort 1 and 0.7 for Cohort 2. Respectively, these represent a reduction in mean ABR to the year prior to treatment of 88% and 83%. During this same period the consumption of FIX replacement therapy declined 93% and 96% relative to pre-treatment respectively for Cohort 1 and Cohort 2. No participants developed FIX inhibitors or signs of sustained AAV5 capsid-specific T-cell activation. TRAE were mainly reported in the first 3.5-months after treatment, including three participants who experienced transient mild elevations in alanine aminotransferase as previously described. One new TRAE (joint swelling post-exercise) was observed during the last 12 months of observation post-treatment. Updated data, up to 4-years of observation, will be presented for the first time. Conclusions: Long-term stable endogenous FIX activity and reductions in ABR and FIX replacement use were observed following a single treatment with AMT-060. There were no additional safety concerns with longer term follow-up. These findings support the ongoing Phase III study of the enhanced construct, AMT-061, which encodes the highly active Padua FIX variant. Figure 1 Disclosures Miesbach: Bayer, BioMarin, CSL Behring, Chugai, Freeline, Novo Nordisk, Octapharma, Pfizer, Roche, Takeda/Shire, UniQure: Consultancy; Bayer, Novo Nordisk, Octapharma, Pfizer, Takeda/Shire: Research Funding; Bayer, Chugai, Novo Nordisk, Octapharma, Pfizer, Takeda/Shire, UniQure: Speakers Bureau. Meijer:Pfizer, Sanquin, Uniqure: Research Funding; Uniqure, BMS, Aspen, Boehringer Ingelheim, Sanquin, Bayer: Consultancy, Honoraria; Sanquin: Research Funding; Bayer: Research Funding. Coppens:Pfizer: Honoraria; Portola Pharmaceuticals, Inc: Honoraria; Daiichi Sankyo: Honoraria, Research Funding; Uniqure: Research Funding; Boehringer Ingelheim: Research Funding; Sanquin Blood Supply: Research Funding; Bayer: Honoraria, Research Funding; CSL Behring: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria. Kampmann:Uniqure BV: Research Funding. Klamroth:Bayer, Biomarin, CSL Behring, Novo Nordisk, Octapharma, Pfizer, Roche, SOBI, Takeda: Consultancy; Bayer, Novo Nordisk, SOBI: Research Funding. Schutgens:Baxalta Shire, Novo Nordisk, Bayer, CSL Behring, Pfizer, UniQure BV: Research Funding. Castaman:Bayer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Sobi: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; CSL Behring: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda (SHIRE): Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Kedrion: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Werfen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Research Funding; Uniqure: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sanofi: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Seifried:Medac: Other: BSD owns IP and is contract manufacturer; Uniqure BV: Research Funding. Schwaeble:Uniqure BV: Research Funding. Bönig:Celgene, Novartis, Sandoz Hexal: Consultancy; Kiadis Pharma: Other: Contract manufacturing of ATIR101; Sandoz Hexal, Uniqure: Research Funding; Miletenyi: Speakers Bureau. Sawyer:Uniqure BV: Employment. Leebeek:CSL Behring: Research Funding; UniQure: Consultancy; Shire/Takeda: Research Funding; Novo Nordisk: Consultancy; Sobi: Other: Travel grant; Shire/Takeda: Consultancy.

Introduction Hemophilia is an inherited disorder that causes a deficiency of a blood clotting factor resulting in a lifelong bleeding diathesis. People with hemophilia (PWH) may experience significant morbidity including potentially life-threatening hemorrhages and accumulation of joint damage and require burdensome and costly chronic treatment with factor replacement therapies. Gene therapies aimed at providing endogenous production of the missing clotting factor have the potential to yield significant health benefits for PWH. Economic evaluation is an important component for the commissioning and funding of new treatments like gene therapies. In economic evaluation, quality-of-life (QoL) is measured using health state utility valuations (HSUV). However, people with inherited and long-term health conditions may adapt to their given health state and adjust their expectations, therefore biasing the estimates of QoL/HSUV (i.e., disease state adaptation (DSA) or "disability paradox"; Albrecht and Devlieger, 1999). Here, we describe the first stages of research to evaluate DSA experienced by PWH. Methods To facilitate the selection of research methodology, a systematic litearure review (SLR) was performed to examine existing studies on QoL/HSUVs for PWH. A SLR was conducted to identify full-text studies by searching electronic databases (e.g. MEDLINE, Web of Science, Cochrane Library). Studies were included in the review using predefined inclusion/exclusion criteria for population, study type, language (English). Additionally, a manual search (last three years) for conferences abstracts was performed to capture the most up-to-date research. Findings from the SLR informed the conceptualisation of a study framework. The proposed research approach was then discussed with an expert panel consisting of clinicians, patient advocacy representatives, and Health Technology Assessment (HTA) specialists. Results The SLR identified 32 studies reporting HSUVs in hemophilia. The studies identified applied a mix of direct and indirect HSUV elicitation techniques. Two studies applied direct time trade-off methodology and the remaining 30 studies adopted indirect valuation methodologies. Utility values were found to vary by disease severity, musculoskeletal damage, bleed frequency, inhibitors, hemophilia subtype, treatment regimen, and adherence. Interestingly, HSUVs derived from valuations from the general public were found to be valued lower than those derived from PWH for the same health states. For example, in Carlsson et al. (2017), general public participants consistently rated significantly lower HSUVs for hemophilia disease states compared to PWH (range: 0.54-0.60 vs. 0.67-0.73), suggesting DSA might exist for PWH. Based on SLR findings, an expert panel discussed the feasibility and acceptability of an approach for conducting a preference elicitation study to directly evaluate DSA in PWH. Preference elicitation is an established research framework that is widely used in health economics. A comparative preference elicitation study was proposed to describe and quantify DSA by comparing responses from PWH, caregivers of PWH, and the general public. Conclusion Based on the SLR and expert panel inputs from clinicians, patients and HTA experts, an agreement was achieved about the research methodology for a new study directly assessing DSA experienced by PWH. Experts agreed that a comparative preference elicitation approach among PWH, caregivers of PWH, and the general public was fit-for-purpose for this research. The impact of DSA on QoL/HSUV should be characterized within economic evaluations of novel treatments with transformative impact on patients' lives, such as gene therapies. Disclosures Martin: HCD Economics: Employment. Mulhern:HCD Economics: Consultancy. Shaikh:HCD Economics: Employment. Asghar:HCD Economics: Employment. O'Hara:HCD Economics: Employment, Equity Ownership. Pedra:HCD Economics: Employment. Sawyer:uniQure Inc.: Employment. Li:uniQure Inc.: Employment.

Introduction Current adeno-associated viral (AAV) vector-based gene therapy strategies for hemophilia rely on systemic administration of the vector. Durable expression of the transgene over the span of years has been reported from several trials, yet information on the clearance of vector material from bodily fluids is still limited and monitoring of "shedding" is required during trials despite lack of evidence of environmental or transmission risk. Here, we examined the magnitude and duration of the presence of vector DNA in participants from a Phase I/II study of an AAV5-hFIX wildtype construct (AMT-060; NCT02396342) and from a Phase IIb study utilizing the enhanced version, AAV5-hFIX Padua (AMT-061; NCT03489291). Methods Adult male participants with severe or moderately severe hemophilia B received a single intravenous infusion of either AMT-060 at 5x1012 genome copies(gc)/kg (low dose) or 2×1013 gc/kg (high dose), or AMT-061 at 2x1013gc/kg in one of two ongoing trials. Assessments in both trials included efficacy and safety outcomes as well as vector shedding in whole blood and semen. Vector shedding was also measured in nasal secretions, feces, urine, and saliva in participants receiving AMT-060. Vector shedding was analyzed using a validated quantitative real time polymerase chain reaction (qPCR) based assay measuring presence of vector DNA in the bodily fluids. Vector clearance was reached when vector DNA was either zero or below the limit of detection (LOD) for three consecutive measurements. The range in time to the first and the third consecutive negative measurement for each dose group are provided. Results Treatment with AMT-060 resulted in sustained improvement in FIX activity for up to 3.5 years [Mean FIX activity was 5.1% (low dose group at 3.5 years) and 7.5% (high dose group at 3 years)] and treatment with AMT-061 resulted in mean FIX activity of 45% over 36 weeks. AMT-060 and AMT-061 reduced the mean number of annualized bleeds by between 82% and 100% respectively. AMT-060 reduced the requirement for exogenous FIX administration by 86% and was abrogated with AMT-061. Both AAV5-hFIX and AAV5-hFIX Padua were safe and well tolerated and no unexpected TRAEs have been observed with longer-term follow up. Table 1 describes the time in weeks to the first and last of three consecutive measures of vector DNA of either zero or Conclusions Post-AMT-060 treatment, vector DNA was undetectable in all participants in the high dose group by 10 months and considered cleared by 16 months in all bodily fluids except blood. AMT-060 was cleared from the blood in 100% of participants in the low dose group at 3 years and 80% of participants in the high dose group by 2.5 years. As expected, AMT-061 vector DNA was detectable at 36 weeks in blood and in the semen of 1 of 3 participants, although clearance had not yet been established in the remaining participants. The presence of vector DNA in bodily fluids assessed was not associated with any adverse safety or efficacy findings. Disclosures Sawyer: Uniqure BV: Employment. Gielen:uniQure Biopharma: Employment. Twisk:uniQure Biopharma: Employment. Long:Uniqure BV: Employment. Gut:Uniqure BV: Employment.

Introduction: AMT-060 consists of an adeno-associated virus serotype 5 (AAV5) vector containing a codon-optimized wildtype human factor IX (FIX) gene under control of a liver-specific promoter. We have previously reported on the safety and efficacy of AMT-060 gene therapy at 2 dose levels in adults with moderate-severe or severe hemophilia B with up to 1-year follow-up. Here we present longer-term follow-up data on reductions in annualized bleed rates and FIX consumption up to 2.5 years post-treatment. Methods: Multi-national, open-label, dose-escalating study in participants (pts) with FIX activity ≤2 % of normal, and a severe bleeding phenotype (NCT02396342). Pts received either 5x1012 gc/kg (Cohort 1, n=5) or 2×1013 gc/kg (Cohort 2, n=5) of AMT-060 iv. Duration of follow-up was 2.5 and 2 years in Cohort 1 and Cohort 2, respectively. Efficacy assessments include FIX activity (measured ≥10 days after use of exogenous FIX), reduction of FIX use, and annualized total bleeding rates. Bleeds were counted for each individual patient starting after discontinuation of prophylaxis post-AMT-060. For Cohort 1, exogenous FIX use and bleeds for "year 3" are presented as a calculated annualized mean using data captured between 2 and 2.5 years. Safety assessments include treatment-related adverse events, immunological and inflammatory biomarkers. Results: Nine pts with severe (FIX 5% in Cohort 1, a single bleed was reported in year 2 and no bleeds were reported to data cut-off in year 3. For the two patients with FIX activity Conclusions: Stable endogenous FIX concentrations >4% have now been observed out to 2.5 years post-treatment with AMT-060. In addition, we have observed continued reductions in annualized bleeds to near zero with the higher dose of AMT-060, and a 78-93% reduction in exogenous FIX use. The lack of additional safety concerns or treatment-related adverse events over the longer study period, including no recurring changes in ALT, support the continued development and transition of AMT-060 to AMT-061, which will use the same AAV5 vector to deliver the 2×1013 gc/kg dose with the enhanced Padua transgene, which is anticipated to increase FIX activity 6-8 fold. Disclosures Leebeek: CSL Behring: Research Funding; Uniqure: Research Funding; Baxalta/Shire: Research Funding. Meijer:BMS: Honoraria; Aspen: Honoraria; Boehringer Ingelheim: Honoraria; Pfizer: Research Funding; Sanquin: Honoraria, Research Funding; Bayer: Honoraria, Other: Travel support, Research Funding; UniQure: Research Funding. Coppens:Bayer: Honoraria, Other: Non-financial support, Research Funding; CSL Behring: Honoraria, Other: non-financial support, Research Funding; Uniqure BV: Research Funding. Kampmann:Uniqure BV: Research Funding. Klamroth:Baxalta (Shire), Bayer, CSL Behring, Novo Nordisk, Octapharma, Pfizer, Shire, and SOBI: Consultancy; Baxalta (Shire), Bayer, CSL Behring, Novo Nordisk, Octapharma, Pfizer, Shire, and SOBI: Research Funding. Schutgens:Baxalta/Shire: Research Funding; Novo Nordisk: Research Funding; Bayer: Research Funding; CSL Behring: Research Funding; Pfizer: Research Funding; Uniqure BV: Research Funding. Seifried:Medac: Other: BSD owns IP and is contract manufacturer; Uniqure BV: Research Funding. Schwaeble:UniQure BV: Research Funding. Bonig:Kiadis Pharma: Consultancy. Sawyer:Uniqure BV: Employment. Miesbach:Bayer, Shire, Biotest, pfizer, Octapharma, LFB, CSL Behring, SOBI, Biogen, BPL: Consultancy; UniQure BV: Research Funding; Novo Nordisk: Consultancy, Research Funding.