Two-Year Outcomes of Valoctocogene Roxaparvovec Therapy for Hemophilia A.

BACKGROUND: Valoctocogene roxaparvovec delivers a B-domain-deleted factor VIII coding sequence with an adeno-associated virus vector to prevent bleeding in persons with severe hemophilia A. The findings of a phase 3 study of the efficacy and safety of valoctocogene roxaparvovec therapy evaluated after 52 weeks in men with severe hemophilia A have been published previously. METHODS: We conducted an open-label, single-group, multicenter, phase 3 trial in which 134 men with severe hemophilia A who were receiving factor VIII prophylaxis received a single infusion of 6×1013 vector genomes of valoctocogene roxaparvovec per kilogram of body weight. The primary end point was the change from baseline in the annualized rate of treated bleeding events at week 104 after receipt of the infusion. The pharmacokinetics of valoctocogene roxaparvovec were modeled to estimate the bleeding risk relative to the activity of transgene-derived factor VIII. RESULTS: At week 104, a total of 132 participants, including 112 with data that were prospectively collected at baseline, remained in the study. The mean annualized treated bleeding rate decreased by 84.5% from baseline (P<0.001) among the participants. From week 76 onward, the trajectory of the transgene-derived factor VIII activity showed first-order elimination kinetics; the model-estimated typical half-life of the transgene-derived factor VIII production system was 123 weeks (95% confidence interval, 84 to 232). The risk of joint bleeding was estimated among the trial participants; at a transgene-derived factor VIII level of 5 IU per deciliter measured with chromogenic assay, we expected that participants would have 1.0 episode of joint bleeding per year. At 2 years postinfusion, no new safety signals had emerged and no new serious adverse events related to treatment had occurred. CONCLUSIONS: The study data show the durability of factor VIII activity and bleeding reduction and the safety profile of valoctocogene roxaparvovec at least 2 years after the gene transfer. Models of the risk of joint bleeding suggest that the relationship between transgene-derived factor VIII activity and bleeding episodes is similar to that reported with the use of epidemiologic data for persons with mild-to-moderate hemophilia A. (Funded by BioMarin Pharmaceutical; GENEr8-1 ClinicalTrials.gov number, NCT03370913.).

Valoctocogene Roxaparvovec Gene Therapy for Hemophilia A.

BACKGROUND: Valoctocogene roxaparvovec (AAV5-hFVIII-SQ) is an adeno-associated virus 5 (AAV5)-based gene-therapy vector containing a coagulation factor VIII complementary DNA driven by a liver-selective promoter. The efficacy and safety of the therapy were previously evaluated in men with severe hemophilia A in a phase 1-2 dose-escalation study. METHODS: We conducted an open-label, single-group, multicenter, phase 3 study to evaluate the efficacy and safety of valoctocogene roxaparvovec in men with severe hemophilia A, defined as a factor VIII level of 1 IU per deciliter or lower. Participants who were at least 18 years of age and did not have preexisting anti-AAV5 antibodies or a history of development of factor VIII inhibitors and who had been receiving prophylaxis with factor VIII concentrate received a single infusion of 6×1013 vector genomes of valoctocogene roxaparvovec per kilogram of body weight. The primary end point was the change from baseline in factor VIII activity (measured with a chromogenic substrate assay) during weeks 49 through 52 after infusion. Secondary end points included the change in annualized factor VIII concentrate use and bleeding rates. Safety was assessed as adverse events and laboratory test results. RESULTS: Overall, 134 participants received an infusion and completed more than 51 weeks of follow-up. Among the 132 human immunodeficiency virus-negative participants, the mean factor VIII activity level at weeks 49 through 52 had increased by 41.9 IU per deciliter (95% confidence interval [CI], 34.1 to 49.7; P<0.001; median change, 22.9 IU per deciliter; interquartile range, 10.9 to 61.3). Among the 112 participants enrolled from a prospective noninterventional study, the mean annualized rates of factor VIII concentrate use and treated bleeding after week 4 had decreased after infusion by 98.6% and 83.8%, respectively (P<0.001 for both comparisons). All the participants had at least one adverse event; 22 of 134 (16.4%) reported serious adverse events. Elevations in alanine aminotransferase levels occurred in 115 of 134 participants (85.8%) and were managed with immune suppressants. The other most common adverse events were headache (38.1%), nausea (37.3%), and elevations in aspartate aminotransferase levels (35.1%). No development of factor VIII inhibitors or thrombosis occurred in any of the participants. CONCLUSIONS: In patients with severe hemophilia A, valoctocogene roxaparvovec treatment provided endogenous factor VIII production and significantly reduced bleeding and factor VIII concentrate use relative to factor VIII prophylaxis. (Funded by BioMarin Pharmaceutical; GENEr8-1 ClinicalTrials.gov number, NCT03370913.).

First study of extended half-life rFVIIIFc in previously untreated patients with hemophilia A: PUPs A-LONG final results.

PUPs A-LONG evaluated the safety and efficacy of recombinant factor VIII Fc fusion protein (rFVIIIFc) in previously untreated patients (PUPs) with hemophilia A. This open-label, phase 3 study enrolled male PUPs (<6 years) with severe hemophilia A to receive rFVIIIFc. The primary endpoint was the occurrence of inhibitor development. Secondary endpoints included annualized bleed rate (ABR). Of 103 subjects receiving ≥1 dose of rFVIIIFc, 80 (78%) were aged <1 year at the study start, 20 (19%) had a family history of inhibitors, and 82 (80%) had high-risk F8 mutations. Twenty subjects began on prophylaxis, while 81 began an on-demand regimen (69 later switched to prophylaxis). Eighty-seven (81%) subjects completed the study. Inhibitor incidence was 31.1% (95% confidence interval [CI], 21.8% to 41.7%) in subjects with ≥10 exposure days (or inhibitor); high-titer inhibitor incidence was 15.6% (95% CI, 8.8% to 24.7%). The median (range) time to high-titer inhibitor development was 9 (4-14) exposure days. Twenty-eight (27%) subjects experienced 32 rFVIIIFc treatment-related adverse events; most were inhibitor development. There was 1 nontreatment-related death due to intracranial hemorrhage (onset before the first rFVIIIFc dose). The overall median (interquartile range [IQR]) ABR was 1.49 (0.00-4.40) for subjects on variable prophylaxis dosing regimens. In this study of rFVIIIFc in pediatric PUPs with severe hemophilia A, overall inhibitor development was within the expected range, although high-titer inhibitor development was on the low end of the range reported in the literature. rFVIIIFc was well-tolerated and effective for prophylaxis and treatment of bleeds. This trial is registered at www.clinicaltrials.gov (NCT02234323).

Current and emerging gene therapies for haemophilia A and B.

INTRODUCTION: After decades of stumbling clinical development, the first gene therapies for haemophilia A and B have been commercialized and have normalized factor (F)VIII and factor (F)IX levels in some individuals in the long term. Several other clinical programs testing adeno-associated viral (AAV) vector gene therapy are at various stages of clinical testing. DISCUSSION: Multiyear follow-up in phase 1/2 and 3 studies showed long-term and sometimes curative but widely variable and unpredictable efficacy. Liver toxicities, mostly low-grade, occur in the 1st year in at least some individuals in all haemophilia A and B trials and are poorly understood. Wide variability and unpredictability of outcome and slow decline of FVIII levels are a major disadvantage because immune responses to AAV vectors preclude repeat dosing, which otherwise could improve suboptimal or restore declining expression, while overexpression may predispose to thrombosis. Long-term safety outcomes will need lifelong monitoring because AAV vectors infused at high doses integrate into chromosomes at rates that raise questions about potential oncogenicity and necessitate vigilance. Alternative gene transfer systems employing gene editing and/or non-viral vectors are under development and promise to overcome some limitations of the current state of the art for both haemophilia A and B. CONCLUSIONS: AAV gene therapies for haemophilia have now become new treatment options but not universal cures. AAV is a powerful but imperfect gene transfer platform. Biobetter FVIII transgenes may help solve some problems plaguing gene therapy for haemophilia A. Addressing variability and unpredictability of efficacy, and delivery of gene therapy to ineligible patient subgroups may require different gene transfer systems, most of which are not ready for clinical translation yet but bring innovations needed to overcome the current limitations of gene therapy.

Promoting pain coping skills in haemophilia: A remote intervention integrating exercise and pain education.

BACKGROUND: Chronic joint pain is a significant and widespread symptom in people with haemophilia (PWH). Despite medical advancements, effective pain management remains challenging. AIM: This study presents an innovative approach that integrates remote physical exercises, pain neuroscience education, and coping strategies to address chronic pain in PWH. METHODS: The remote intervention consisted of sixteen 5-min videos encompassing physical exercises for chronic pain management and pain education strategies. These videos formed an 8-week remote intervention program. Clinical and physical assessments were conducted before and after the intervention. RESULTS: A total of thirty-one PWHs, with a median age of 34 years (ranging from 16 to 59 years), completed the remote intervention. The study revealed significant improvements in pain intensity, disability, and physical performance among PWH with chronic pain. Enhanced functional capacity was evident in the Timed Up and Go and Single Leg Stance tests, accompanied by improved scores on the Functional Independence Score in Haemophilia (FISH). Although lacking a control group, our findings are consistent with other successful exercise and pain education programs. CONCLUSIONS: This innovative intervention holds promise for managing chronic pain in PWH, underscoring patient empowerment, education, and collaboration. Notably, our study stands out by uniquely combining pain education and coping strategies, bolstering evidence for effective pain management.

Impaired repair properties of endothelial colony-forming cells in patients with granulomatosis with polyangiitis.

In patients with ANCA-associated vasculitis, interactions between neutrophils and endothelial cells cause endothelial damage and imbalance. Endothelial colony-forming cells (ECFCs) represent a cellular population of the endothelial lineage with proliferative capacity and vasoreparative properties. This study aimed to evaluate the angiogenic capacity of ECFCs of patients with granulomatosis with polyangiitis (GPA). The ECFCs of 13 patients with PR3-positive GPA and 14 healthy controls were isolated and characterized using fluorescence-activated cell sorting, capillary tube formation measurement, scratching assays and migration assays with and without plasma stimulation. Furthermore, three patients with active disease underwent post-treatment recollection of ECFCs for longitudinal evaluation. The ECFCs from the patients and controls showed similar capillary structure formation. However, the ECFCs from the patients with inactive GPA exhibited early losses of angiogenic capacity. Impairments in the migration capacities of the ECFCs were also observed in patients with GPA and controls (12th h, p = 0.05). Incubation of ECFCs from patients with GPA in remission with plasma from healthy controls significantly decreased migration capacity (p = 0.0001). Longitudinal analysis revealed that treatment significantly lowered ECFC migration rates. This study revealed that ECFCs from the patients with PR3-positive GPA in remission demonstrated early losses of tube formation and reduced migration capacity compared to those of the healthy controls, suggesting impairment of endothelial function.

Haemophilia gene therapy-Update on new country initiatives.

INTRODUCTION: Gene therapy is emerging as a potential cure for haemophilia. Gene therapy is a one-time treatment that can elevate factor levels for many years and minimize or eliminate the need for clotting factor concentrate (CFC) replacement therapy. However, there is a paucity of reports on gene therapy efforts in countries outside of North America or Europe, especially in low-and-middle-income countries (LMIC). All indications are that gene therapy will be one of standard care treatments for haemophilia in the future. Still, it may not be accessible to many countries due to various barriers and challenges. At the same time, each country may formulate solutions that may be used globally. AIM: To summarize the approaches taken to establish haemophilia gene therapy in Japan, China, India, South Africa, and Brazil, and to describe the US-initiated multi-LMIC haemophilia gene therapy development program to include Peru, Vietnam, Thailand, Nepal, and Sri Lanka. METHODS: A review of related published information or as accessible by each country's author. RESULTS: Different starting conditions, differing input and level of support from the multitude of stakeholders, and strong leadership have led to various approaches for facilitating research and developing needed infrastructure and regulatory and financing models. Gene therapy programs are at various stages of development and include both adeno-associated viral and lentiviral vectors. CONCLUSION: Global partnerships and collaboration, exchange of knowledge and experience, and alignment of processes across borders will promote further progress towards global access to gene therapy for haemophilia.

Aquatic exercise in patients with haemophilia: Electromyographic and functional results from a prospective cohort study.

INTRODUCTION: Recurrent joint bleeds in haemophilia patients often cause musculoskeletal changes leading to functional capacity impairment. AIM: In this study, we assessed the effects of aquatic activities performed to improve functional capacity in these patients. METHODS: The interventional protocol consisted of 24 hydrotherapy sessions during three months, in comparison with 24 swimming sessions. The pre- and post-intervention assessment consisted of Functional Independence Score, haemophilia joint health score (HJHS), Pediatric Haemophilia Activities List (PedHAL), surface electromyography (SEMG) of thigh muscles to assess muscle electric activity, and load cell on extensor and flexor thigh muscles to evaluate muscular strength. RESULTS: Forty-seven haemophilia patients were enrolled in this study, and 32 (23 severe haemophilia A, one moderate haemophilia A and 8 severe haemophilia B), median age 12y (6 to 40y), concluded the aquatic intervention. We observed a statistically significant increase with substantial improvement in functional capacity in the pre- and post-intervention evaluation of hydrotherapy in comparison with the swimming protocol, with HJHS (p = .006 and p = .001 respectively), PedHAL (Sum score) (p = .022 and p = .001) and score FISH (p = .021). The swimming group revealed significant improvements in muscular strength, in all muscles tested (p = .005 and p = .001). SEMG signal amplitude reached significantly higher levels in all muscles evaluated after both interventions except for the vastus medialis (right) in the hydrotherapy group. CONCLUSION: Our results concluded that both swimming and hydrotherapy were associated with physical improvement in haemophilia patients; however, only hydrotherapy lead to a more significant improvement in functional capacity.

Long-term safety and sustained efficacy for up to 5 years of treatment with recombinant factor IX Fc fusion protein in subjects with haemophilia B: Results from the B-YOND extension study.

INTRODUCTION: Recombinant factor IX Fc fusion protein (rFIXFc) has demonstrated efficacy for treatment of haemophilia B in the Phase 3 B-LONG and Kids B-LONG studies. However, long-term rFIXFc safety and efficacy data have not yet been reported. AIM: To report long-term rFIXFc safety and efficacy in subjects with haemophilia B. METHODS: B-YOND (NCT01425723) was an open-label extension for eligibl previously treated subjects who completed B-LONG or Kids B-LONG. Subjects received ≥1 treatment regimen: weekly prophylaxis (WP), individualized interval prophylaxis (IP), modified prophylaxis or episodic treatment. Subjects could switch regimens at any time. The primary endpoint was inhibitor development. RESULTS: Ninety-three subjects from B-LONG and 27 from Kids B-LONG (aged 3-63 years) were enrolled. Most subjects received WP (B-LONG: n = 51; Kids B-LONG: n = 23). For subjects from B-LONG, median (range) treatment duration was 4.0 (0.3-5.4) years and median (range) number of exposure days (EDs) was 146 (8-462) EDs. Corresponding values for paediatric subjects were 2.6 (0.2-3.9) years and 132 (50-256) EDs. No inhibitors were observed (0 per 1000 subject-years; 95% confidence interval, 0-8.9) and the overall rFIXFc safety profile was consistent with prior studies. Annualized bleed rates remained low and extended-dosing intervals were maintained for most subjects. Median dosing interval for the IP group was approximately 14 days for adults and adolescents (n = 31) and 10 days for paediatric subjects (n = 5). CONCLUSIONS: B-YOND results confirm the long-term (up to 5 years, with cumulative duration up to 6.5 years) well-characterized safety and efficacy of rFIXFc treatment for haemophilia B.

Longitudinal sequencing of RUNX1 familial platelet disorder: new insights into genetic mechanisms of transformation to myeloid malignancies.

The mechanisms by which patients with RUNX1 familial platelet disorder with propensity to myeloid malignancies (FPDMM) develop myeloid malignancies (MM) are not fully understood. We report the results of targeted next-generation sequencing on three patients with RUNX1 FPDMM who developed acute myeloid leukaemia or myelodysplastic syndromes (AML/MDS). DNA samples were collected from bone marrow, peripheral blood and buccal swabs at different time points. One patient had clonal haematopoiesis, represented by an SRSF2 p.P95R variant, prior to his AML diagnosis, when he developed an additional NRAS p.G12D variant. His sister presented to us with MDS, with a TET2 p.S471fs and identical NRAS p.G12D variant. The third patient, from another family, had an additional RUNX1 p.R204X and an NFE2 p.Q139fs variant at AML diagnosis. This constitutes the first report of NFE2 variants in AML without extramedullary disease and NRAS variants in AML/MDS in the setting of FPDMM. A systematic review of the literature including our findings distinguishes two genetic landscapes at AML transformation from FPDMM characterized by either the presence or absence of somatic abnormalities in RUNX1 with or without variants in genes usually associated with MM. Whether clonal haematopoiesis precedes transformation only in patients without somatic abnormalities in RUNX1 needs further confirmation.

Gene Therapy: Paving New Roads in the Treatment of Hemophilia.

Hemophilia is a monogenic disease with robust clinicolaboratory correlations of severity. These attributes coupled with the availability of experimental animal models have made it an attractive model for gene therapy. The road from animal models to human clinical studies has heralded significant successes, but major issues concerning a previous immunity against adeno-associated virus and transgene optimization remain to be fully resolved. Despite significant advances in gene therapy application, many questions remain pertaining to its use in specific populations such as those with factor inhibitors, those with underlying liver disease, and pediatric patients. Here, the authors provide an update on viral vector and transgene improvements, review the results of recently published gene therapy clinical trials for hemophilia, and discuss the main challenges facing investigators in the field.

Haemophilia Experiences, Results and Opportunities (HERO study) in Brazil: Assessment of the psychosocial effects of haemophilia in patients and caregivers.

INTRODUCTION: The international Haemophilia Experiences, Results and Opportunities (HERO) study assessed the psychosocial aspects of life for people with haemophilia (PWH) and their caregivers in several countries. Brazil was not included in this initiative. AIM AND METHODS: An observational, multicentre, cross-sectional study was performed involving PWH (moderate-to-severe haemophilia) and their caregivers, from November 2014 to July 2015. The primary objective was to quantify the extent of the primary psychosocial factors affecting PWH in their everyday life. Descriptive statistics and comparisons between Brazilian and global respondents are presented. RESULTS: A total of 100 adult male PWH and 100 caregivers (responding on behalf of their oldest affected child aged <18 years) completed the survey. Sixty-eight per cent of the PWH had haemophilia A without inhibitors. Chronic pain and hepatitis C were the most common conditions related to haemophilia. On the EQ-5D assessment, 64% of PWH reported extreme/moderate pain. Treatment for depression or anxiety was reported by 18% of PWH and by 29% of caregivers. There was a lower employment rate for PWH in Brazil, compared to the countries included in the original HERO survey (51% vs 60%); 71% of PWH stated that haemophilia has a negative impact on their work. Over the previous 5 years, 58% of PWH and 68% of caregivers did not have difficulties in obtaining the concentrated factor for treatment. CONCLUSIONS: Our study presents an overview of the psychosocial aspects of life with haemophilia in Brazil, providing a basis for health policy decisions and may further improve comprehensive care for PWH.

Correction to: Routine clinical care data for population pharmacokinetic modeling: the case for Fanhdi/Alphanate in hemophilia A patients.

The article Routine clinical care data for population pharmacokinetic modeling: the case for Fanhdi/Alphanate in hemophilia A patients, written by Pierre Chelle, Cindy H. T. Yeung, Santiago Bonanad, Juan Cristóbal Morales Muñoz, Margareth C. Ozelo, Juan Eduardo Megías Vericat, Alfonso Iorio, Jeffrey Spears, Roser Mir, Andrea Edginton, was originally published electronically on the publisher's internet portal (currently SpringerLink) on 21 May 2019 without open access.

Routine clinical care data for population pharmacokinetic modeling: the case for Fanhdi/Alphanate in hemophilia A patients.

Fanhdi/Alphanate is a plasma derived factor VIII concentrate used for treating hemophilia A, for which there has not been any dedicated model describing its pharmacokinetics (PK). A population PK model was developed using data extracted from the Web-Accessible Population Pharmacokinetic Service-Hemophilia (WAPPS-Hemo) project. WAPPS-Hemo provided individual PK profiles for hemophilia patients using sparse observations as provided in routine clinical care by hemophilia centers. Plasma factor activity measurements and covariate data from hemophilia A patients on Fanhdi/Alphanate were extracted from the WAPPS-Hemo database. A population PK model was developed using NONMEM and evaluated for suitability for Bayesian forecasting using prediction-corrected visual predictive check (pcVPC), cross validation, limited sampling analysis and external evaluation against a population PK model developed on rich sampling data. Plasma factor activity measurements from 92 patients from 12 centers were used to derive the model. The PK was best described by a 2-compartment model including between subject variability on clearance and central volume, fat free mass as a covariate on clearance, central and peripheral volumes, and age as covariate on clearance. Evaluations showed that the developed population PK model could predict the PK parameters of new individuals based on limited sampling analysis and cross and external evaluations with acceptable precision and bias. This study shows the feasibility of using real-world data for the development of a population PK model. Evaluation and comparison of the model for Bayesian forecasting resulted in similar results as a model developed using rich sampling data.

Haemophilia care in Latin America: Assessment and perspectives.

INTRODUCTION: The study is the first application of the Principles of Haemophilia Care for Europe (PHCE) in other regions of the world, specifically in Latin America. OBJECTIVE: To identify strengths in the care of haemophilia, and the aspects that should be improved. METHODS: The information was obtained through a questionnaire designed according to the PHCE and answered by specialists in mid-2016. The countries included were as follows: Argentina, Brazil, Chile, Colombia, Costa Rica, El Salvador, Mexico, Panama, Dominican Republic and Venezuela. RESULTS: In most countries, there is a central organization for haemophilia care supported by local groups. The existence of a national registry of people with haemophilia (PWH) was verified in eight countries. Centres of integrated care are located in large cities. In the majority of countries, there was no evidence of the participation of multiple actors in the decision-making. The supply of factor concentrates presents constraints, although it is reported as adequate in half of the countries. In most countries, home treatment is available under special conditions. In most countries, there are restrictions on the use of prophylaxis. The coordination of specialized and emergency services depends on each centre. Unrestricted treatment of inhibitors is performed in most countries. In all countries, there are human resources training programmes; however, clinical and health services researches are not widely developed. CONCLUSION: The study identifies the initial situation of principles of care, as well as the alternatives that must be implemented to achieve improvements in the quality of life of PWH in the region.

Phase 3 study of recombinant factor IX Fc fusion protein in hemophilia B.

BACKGROUND: Prophylactic factor replacement in patients with hemophilia B improves outcomes but requires frequent injections. A recombinant factor IX Fc fusion protein (rFIXFc) with a prolonged half-life was developed to reduce the frequency of injections required. METHODS: We conducted a phase 3, nonrandomized, open-label study of the safety, efficacy, and pharmacokinetics of rFIXFc for prophylaxis, treatment of bleeding, and perioperative hemostasis in 123 previously treated male patients. All participants were 12 years of age or older and had severe hemophilia B (endogenous factor IX level of ≤2 IU per deciliter, or ≤2% of normal levels). The study included four treatment groups: group 1 received weekly dose-adjusted prophylaxis (50 IU of rFIXFc per kilogram of body weight to start), group 2 received interval-adjusted prophylaxis (100 IU per kilogram every 10 days to start), group 3 received treatment as needed for bleeding episodes (20 to 100 IU per kilogram), and group 4 received treatment in the perioperative period. A subgroup of group 1 underwent comparative sequential pharmacokinetic assessments of recombinant factor IX and rFIXFc. The primary efficacy end point was the annualized bleeding rate, and safety end points included the development of inhibitors and adverse events. RESULTS: As compared with recombinant factor IX, rFIXFc exhibited a prolonged terminal half-life (82.1 hours) (P<0.001). The median annualized bleeding rates in groups 1, 2, and 3 were 3.0, 1.4, and 17.7, respectively. In group 2, 53.8% of participants had dosing intervals of 14 days or more during the last 3 months of the study. In groups 1, 2 and 3, 90.4% of bleeding episodes resolved after one injection. Hemostasis was rated as excellent or good during all major surgeries. No inhibitors were detected in any participants receiving rFIXFc; in groups 1, 2, and 3, 73.9% of participants had at least one adverse event, and serious adverse events occurred in 10.9% of participants. These events were mostly consistent with those expected in the general population of patients with hemophilia. CONCLUSIONS: Prophylactic rFIXFc, administered every 1 to 2 weeks, resulted in low annualized bleeding rates in patients with hemophilia B. (Funded by Biogen Idec; ClinicalTrials.gov number, NCT01027364.).

Omental implantation of BOECs in hemophilia dogs results in circulating FVIII antigen and a complex immune response.

Ex vivo gene therapy strategies avoid systemic delivery of viruses thereby mitigating the risk of vector-associated immunogenicity. Previously, we delivered autologous factor VIII (FVIII)-expressing blood outgrowth endothelial cells (BOECs) to hemophilia A mice and showed that these cells remained sequestered within the implanted matrix and provided therapeutic levels of FVIII. Prior to translating this strategy into the canine (c) model of hemophilia A, we increased cFVIII transgene expression by at least 100-fold with the use of the elongation factor 1 alpha (EF1α) promoter and a strong endothelial enhancer element. BOECs isolated from hemophilia A dogs transduced with this lentiviral vector express levels of cFVIII ranging between 1.0 and 1.5 U/mL per 10(6) cells over 24 hours. Autologous BOECs have been implanted into the omentum of 2 normal and 3 hemophilia A dogs. These implanted cells formed new vessels in the omentum. All 3 hemophilia A dogs treated with FVIII-expressing autologous BOECs developed anti-FVIII immunoglobulin G2 antibodies, but in only 2 of the dogs were these antibodies inhibitory. FVIII antigen levels >40% in the absence of FVIII coagulant function were detected in the circulation for up to a year after a single gene therapy treatment, indicating prolonged cellular viability and synthesis of FVIII.