Sustained correction of disease in naive and AAV2-pretreated hemophilia B dogs: AAV2/8-mediated, liver-directed gene therapy

Blood ◽  
2005 ◽  
Vol 105 (8) ◽  
pp. 3079-3086 ◽  
Author(s):  
Lili Wang ◽  
Roberto Calcedo ◽  
Timothy C. Nichols ◽  
Dwight A. Bellinger ◽  
Aaron Dillow ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Nonhuman Primates ◽  
Liver Toxicity ◽  
Factor Ix ◽  
Hemophilia B ◽  
Transduction Efficiency ◽  
Large Animal ◽  
Adeno Associated Virus ◽  
Large Animal Models ◽  
High Level

AbstractAdeno-associated virus 8 (AAV8), a new member of the AAV family isolated from nonhuman primates, is an attractive candidate for hepatic gene transfer applications because of 10- to 100-fold improved transduction efficiency in mouse liver models. Additionally, AAV8 has lesser frequency of pre-existing immunity in humans. These properties could solve some of the problems associated with AAV2 vectors. The benefits of AAV8 demonstrated in mouse models, however, have not been confirmed in larger animals. In this study, we evaluate the efficacy and safety of AAV2/8 vector in both naive and AAV2-pretreated hemophilia B dogs. Two naive hemophilia B dogs that received a single intraportal administration of AAV2/8 vector have achieved sustained expression of 10% and 26% of normal levels of canine factor IX (cFIX) for more than a year. In an AAV2-pretreated hemophilia B dog, cFIX expression increased from less than 1% to 16% of normal levels when treated with an AAV2/8 vector, and a high level of expression has lasted for more than 2 years. No significant liver toxicity or cFIX-specific antibodies have been detected in these animals. Studies here have demonstrated the safety and improved efficacy of AAV2/8 vector in large-animal models for liver-directed gene therapy.

Sustained phenotypic correction of hemophilia B dogs with a factor IX null mutation by liver-directed gene therapy

Blood ◽  
2002 ◽  
Vol 99 (8) ◽  
pp. 2670-2676 ◽  
Author(s):  
Jane D. Mount ◽  
Roland W. Herzog ◽  
D. Michael Tillson ◽  
Susan A. Goodman ◽  
Nancy Robinson ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Coagulation Factor ◽  
Factor Ix ◽  
Hemophilia B ◽  
Large Animal Model ◽  
Null Mutation ◽  
Large Animal ◽  
Adeno Associated Virus ◽  
Increased Risk

Abstract Hemophilia B is an X-linked coagulopathy caused by absence of functional coagulation factor IX (FIX). Using adeno-associated virus (AAV)–mediated, liver-directed gene therapy, we achieved long-term (> 17 months) substantial correction of canine hemophilia B in 3 of 4 animals, including 2 dogs with an FIX null mutation. This was accomplished with a comparatively low dose of 1 × 1012 vector genomes/kg. Canine FIX (cFIX) levels rose to 5% to 12% of normal, high enough to result in nearly complete phenotypic correction of the disease. Activated clotting times and whole blood clotting times were normalized, activated partial thromboplastin times were substantially reduced, and anti-cFIX was not detected. The fourth animal, also a null mutation dog, showed transient expression (4 weeks), but subsequently developed neutralizing anti-cFIX (inhibitor). Previous work in the canine null mutation model has invariably resulted in inhibitor formation following treatment by either gene or protein replacement therapies. This study demonstrates that hepatic AAV gene transfer can result in sustained therapeutic expression in a large animal model characterized by increased risk of a neutralizing anti-FIX response.

A gene-deleted adenoviral vector results in phenotypic correction of canine hemophilia B without liver toxicity or thrombocytopenia

Blood ◽  
2003 ◽  
Vol 102 (7) ◽  
pp. 2403-2411 ◽  
Author(s):  
Anja Ehrhardt ◽  
Hui Xu ◽  
Aaron M. Dillow ◽  
Dwight A. Bellinger ◽  
Timothy C. Nichols ◽  
...  
Keyword(s):  
Gene Transfer ◽  
Adenoviral Vector ◽  
High Efficiency ◽  
Liver Toxicity ◽  
Normal Liver ◽  
Adenoviral Vectors ◽  
Factor Ix ◽  
Hemophilia B ◽  
Large Animal ◽  
Large Animal Models

Abstract Many approaches for treating hemophilia via gene transfer have been attempted in large animal models but all have potential drawbacks. Recombinant adenoviral vectors offer high-efficiency transfer of an episomal vector but have been plagued by the cytotoxicity/immunogenicity of early-generation vectors that contain viral genes. In our current study, we have used a nonintegrating helper-dependent (HD) adenoviral vector for liver-directed gene transfer to achieve hemostatic correction in a dog with hemophilia B. We measured plasma canine factor IX (cFIX) concentrations at a therapeutic range for up to 2.5 months and normalization of the whole blood clotting time (WBCT) for about a month. This was followed by a decrease and stabilized partial correction for 4.5 months. Hepatic gene transfer of a slightly lower dose of the HD vector resulted in WBCTs that were close to normal for 2 weeks, suggesting a dose threshold effect in dogs. In sharp contrast to other studies using first- or second-generation adenoviral vectors, we observed no vector-related elevation of liver enzymes, no fall in platelet counts, and normal liver histology. Taken together, this study demonstrates that injection of an adenoviral HD vector results in complete but transient phenotypic correction of FIX deficiency in canine models with no detectable toxicity. (Blood. 2003;102:2403-2411)

scholarly journals Hemophilia gene therapy comes of age

2017 ◽  
Vol 1 (26) ◽  
pp. 2591-2599 ◽  
Author(s):  
Lindsey A. George
Keyword(s):  
Clinical Trial ◽  
Gene Therapy ◽  
Gene Transfer ◽  
Factor Ix ◽  
Large Animal Model ◽  
Large Animal ◽  
Adeno Associated Virus ◽  
Target Disease ◽  
American Society ◽  
Clinical Trial Results

Abstract Concurrent with the development of recombinant factor replacement products, the characterization of the F9 and F8 genes over 3 decades ago allowed for the development of recombinant factor products and made the hemophilias a target disease for gene transfer. The progress of hemophilia gene therapy has been announced in 3 American Society of Hematology scientific plenary sessions, including the first “cure” in a large animal model of hemophilia B in 1998, first in human sustained vector-derived factor IX activity in 2011, and our clinical trial results reporting sustained vector-derived factor IX activity well into the mild or normal range in 2016. This progression to clinically meaningful success combined with numerous ongoing recombinant adeno-associated virus (rAAV)–mediated hemophilia gene transfer clinical trials suggest that the goal of gene therapy to alter the paradigm of hemophilia care may soon be realized. Although several novel therapeutics have recently emerged for hemophilia, gene therapy is unique in its potential for a one-time disease-altering, or even curative, treatment. This review will focus on the prior progress and current clinical trial investigation of rAAV-mediated gene transfer for hemophilia A and B.

Targeted Modifications in Adeno-Associated Virus Serotype (AAV)- 8 Capsid Improves Its Hepatic Gene Transfer Efficiency in Vivo

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2045-2045
Author(s):  
Dwaipayan Sen ◽  
Nishanth Gabriel ◽  
Sathish Kumar Yesupatham ◽  
Rekha Samuel ◽  
Rupali A Gadkari ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Conflicts Of Interest ◽  
Innate Immune ◽  
Hemophilia B ◽  
Transduction Efficiency ◽  
Egfp Expression ◽  
Adeno Associated Virus ◽  
Virus Serotype ◽  
Antibody Levels

Abstract Abstract 2045 Recombinant adeno-associated virus vectors based on serotype (AAV)-8 have shown significant promise for liver directed gene therapy of hemophilia B. However, in a recent clinical trial, two patients who received highest dose (2×1012 vg/kg) of the self-complementary (sc)AAV8 vector developed capsid specific T cells that required glucocorticoid therapy to attenuate this response [Nathwani et al, New Eng J Med, 2011]. Thus, the theme of AAV vector dose dependent immunotoxicity seen with AAV2 vectors earlier seem to re-emerge with AAV8 vectors as well. It is therefore important to develop novel AAV8 vectors that provide enhanced gene expression at significantly less vector doses. Since it is known that AAV vectors during intracellular trafficking are targeted for destruction in the cytoplasm by the host-cellular kinase/ubiquitination/proteasomal degradation machinery, we modified specific serine/threonine kinase or ubiquitination targets on AAV8 capsid to improve its transduction efficiency. To test this, point mutations at specific serine (S), threonine (T) or lysine (K) residues were generated on AAV8 capsid. scAAV8-EGFP vectors containing the wild-type (WT) and each one of the 5 S/T/K-mutant capsids were evaluated for their liver transduction efficiency at a dose of 5 × 1010 vgs/ animal in C57BL/6 mice in vivo. Two of the AAV8-S>A mutants (S279A and S501A) and a K137R mutant vector, demonstrated significantly higher EGFP expression (3.6 to 12.5 fold) in the liver compared to animals that received WT-AAV8 vectors alone (Figure 1). The best performing AAV8 mutant (K137R) vector also had significantly reduced ubiquitination of the viral capsid, reduced activation of markers of innate immune response [interleukin (IL)-6, IL-12, tumor necrosis factor α, Kupffer cells (KC) and innate immune responsive toll like receptors (TLR)-9] with a concomitant 2-fold reduction in the levels of neutralizing antibody formation in comparison to WT-AAV8 vectors. Vector bio-distribution studies also revealed that the K137R mutant had a significantly higher and preferential transduction of the liver (22 fold), lungs (9.7 fold) and muscle (8.4 fold) tissue when compared to WT-AAV8 vectors. Further on-going studies with the optimal mutant scAAV8 vector expressing human coagulation factor IX in murine models of hemophilia B, will demonstrate the feasibility of the use of these novel vectors for potential gene therapy of hemophilia B. Figure 1: Efficacy of novel AAV8 S>A and K>R vectors (A) EGFP expression in hepatocytes 4 weeks post administration of AAV8 vectors in C57BL/6 mice, (B) Neutralization antibody levels against AAV8 vectors (C) Ubiquitination levels of K137R-AAV8 compared to the WT-AAV8 vector. Figure 1:. Efficacy of novel AAV8 S>A and K>R vectors (A) EGFP expression in hepatocytes 4 weeks post administration of AAV8 vectors in C57BL/6 mice, (B) Neutralization antibody levels against AAV8 vectors (C) Ubiquitination levels of K137R-AAV8 compared to the WT-AAV8 vector. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Self-complementary adeno-associated virus vectors containing a novel liver-specific human factor IX expression cassette enable highly efficient transduction of murine and nonhuman primate liver

Blood ◽  
2006 ◽  
Vol 107 (7) ◽  
pp. 2653-2661 ◽  
Author(s):  
Amit C. Nathwani ◽  
John T. Gray ◽  
Catherine Y. C. Ng ◽  
Junfang Zhou ◽  
Yunyu Spence ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Human Factor ◽  
Factor Ix ◽  
Expression Cassette ◽  
Hemophilia B ◽  
Adeno Associated Virus ◽  
Knock Out ◽  
Human Factor Ix ◽  
Murine Liver ◽  
Knock Out Mice

AbstractTransduction with recombinant adeno-associated virus (AAV) vectors is limited by the need to convert its single-stranded (ss) genome to transcriptionally active double-stranded (ds) forms. For AAV-mediated hemophilia B (HB) gene therapy, we have overcome this obstacle by constructing a liver-restricted mini–human factor IX (hFIX) expression cassette that can be packaged as complementary dimers within individual AAV particles. Molecular analysis of murine liver transduced with these self-complementary (sc) vectors demonstrated rapid formation of active ds-linear genomes that persisted stably as concatamers or monomeric circles. This unique property resulted in a 20-fold improvement in hFIX expression in mice over comparable ssAAV vectors. Administration of only 1 × 1010 scAAV particles led to expression of hFIX at supraphysiologic levels (8I U/mL) and correction of the bleeding diathesis in FIX knock-out mice. Of importance, therapeutic levels of hFIX (3%-30% of normal) were achieved in nonhuman primates using a significantly lower dose of scAAV than required with ssAAV. Furthermore, AAV5-pseudotyped scAAV vectors mediated successful transduction in macaques with pre-existing immunity to AAV8. Hence, this novel vector represents an important advance for hemophilia B gene therapy.

scholarly journals 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

Blood ◽  
2020 ◽  
Vol 136 (Supplement 1) ◽  
pp. 13-13
Author(s):  
Annette von Drygalski ◽  
Adam Giermasz ◽  
Giancarlo Castaman ◽  
Nigel S. Key ◽  
Susan U. Lattimore ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Board Of Directors ◽  
Research Funding ◽  
Factor Ix ◽  
Hemophilia B ◽  
Advisory Committees ◽  
Adeno Associated Virus ◽  
Human Factor Ix ◽  
Virus Serotype ◽  
Serotype 5

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.

Six-Year Follow-Up of Inhibitor Prone Hemophilia B Dogs Treated with Muscle and Liver-Directed AAV2 Mediated Factor IX Gene Therapy.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 3282-3282
Author(s):  
Glenn P. Niemeyer ◽  
Roland W. Herzog ◽  
Jane D. Mount ◽  
Valder Arruda ◽  
Michael Tillson ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Tumor Formation ◽  
Factor Ix ◽  
Hemophilia B ◽  
Clotting Time ◽  
Adeno Associated Virus ◽  
Normal Ranges ◽  
Sperm Dna ◽  
One Year

Abstract Hemophilia B, caused by factor IX (FIX) deficiency, is intensively studied as a model for gene therapy. Preclinical studies in mice, dogs and initial clinical trials have documented the feasibility of adeno-associated virus (AAV) mediated gene therapy for hemophilia B. The purpose of this study is to report 6 year follow-up of inhibitor prone hemophilia B dogs treated with muscle or liver directed AAV2 FIX gene therapy. Short term, one year follow-up of these dogs (n=6) has been previously reported. The dogs treated with liver directed AAV2 FIX have not had a single bleed requiring FIX replacement in the 6 years since vector administration. The dogs undergoing muscle directed gene therapy have continued to have a bleed frequency similar to untreated FIX deficient dogs. The whole blood clotting time (WBCT), activated clotting time (ACT), and activated partial thromboplastin time (APTT) have remained at the upper limits of the normal ranges for the six year follow-up in the two liver treated dogs. The FIX activity has remained stable between 4–10% in both liver treated dogs but undetectable in the dogs undergoing muscle directed therapy. The vector/FIX sequences have persisted in liver biopsies but were undetectable in WBC and sperm DNA. Administration of purified canine FIX protein resulted in an immune response to FIX in the muscle treated dogs but not the dogs treated with liver directed gene therapy, suggesting FIX tolerance had been established in the hemophilia B dogs with liver directed gene therapy. A complete clinical evaluation of the dogs undergoing liver directed gene therapy including CBC, serum chemistries, bile acid profile, hepatic MRI and CT scans and liver biopsy was normal with no evidence for tumor formation. These results demonstrate that AAV mediated liver directed gene therapy completely corrects the hemophilia phenotype without toxicity or inhibitor development in the inhibitor prone null mutation dogs for more than six years.

scholarly journals Targeting ON-bipolar cells by AAV gene therapy stably reverses LRIT3-congenital stationary night blindness

2021 ◽  
Author(s):  
Keiko Miyadera ◽  
Evelyn Santana ◽  
Karolina Roszak ◽  
Sommer Iffrig ◽  
Meike Visel ◽  
...  
Keyword(s):  
Gene Therapy ◽  
Night Blindness ◽  
Canine Model ◽  
Bipolar Cells ◽  
Large Animal Model ◽  
Transduction Efficiency ◽  
Large Animal ◽  
Congenital Stationary Night Blindness ◽  
Scotopic Vision ◽  
Large Animal Models

AAV gene therapies aimed at curing inherited retinal diseases to date have typically focused on photoreceptors and retinal pigmented epithelia within the relatively accessible outer retina. However, therapeutic targeting in diseases such as congenital stationary night blindness (CSNB) that involve defects in ON-bipolar cells (ON-BCs) within the mid-retina has been challenged by the relative inaccessibility of the target cell in intact retinas, the limited transduction efficiency of these cells by existing AAV serotypes, poor availability of established ON-BC-specific promoters, and absence of appropriate patient-relevant large animal models. Here, we demonstrate safe and effective ON-BC targeting by AAV gene therapy in a recently characterized naturally-occurring canine model of CSNB, LRIT3-CSNB. To effectively target ON-BCs, new AAV capsid variants with ON-BC tropism and ON-BC specific modified GRM6 promoters were adopted to ensure cell-specific transgene expression. Notably, subretinal injection of one vector, AAVK9#4-shGRM6-cLRIT3-WPRE, significantly recovered rod-derived b-wave in all treated eyes (6/6) of adult dogs injected at 1-3 years of age. The robust therapeutic effect was evident 7 weeks post-injection and was sustained for at least 1 year in all treated eyes. Scotopic vision was significantly improved in treated eyes based on visually-guided obstacle course navigation. Restoration of LRIT3 signals was confirmed by immunohistochemistry. Thus, we report on the first ON-BC functional rescue in a large animal model using a novel AAV capsid variant and modified promoter construct optimized for ON-BC specificity, thereby establishing both proof-of-concept and a novel translational platform for treatment of CSNB in patients with defects in photoreceptor-to-bipolar signaling.

Congenital Hemorrhagic Disorders: New Insights into the Pathophysiology and Treatment of Hemophilia

Hematology ◽  
2000 ◽  
Vol 2000 (1) ◽  
pp. 241-265 ◽  
Author(s):  
Ulla Hedner ◽  
David Ginsburg ◽  
Jeanne M. Lusher ◽  
Katherine A. High
Keyword(s):  
Gene Therapy ◽  
Factor Viii ◽  
Factor Viia ◽  
Factor Ix ◽  
Therapeutic Window ◽  
Large Animal ◽  
Target Tissue ◽  
Dna Diagnosis ◽  
Regulatory Review ◽  
Large Animal Models

Abstract The diagnostic and treatment strategies related to hemophilia are rapidly evolving. This article focuses on some of the issues of importance. Diagnostic advances in molecular genetics are reviewed by Dr. Ginsburg in Section I, including the current state of knowledge regarding the mutations responsible for hemophilia, with reference to the potential clinical applications of DNA diagnosis and prenatal testing. Within the area of new therapeutic approaches in hemophilia, recombinant factor VIII and factor IX concentrates, their use and availability are addressed by Dr. Lusher in Section II as well as the use of so-called “primary prophylaxis” with the aim of decreasing long-term hemophilia athropathy. The use of radionuclide synovectomy as replacement for more invasive methods is also reviewed. Various approaches to the ongoing challenge of the management of hemophilia patients with inhibitors against factor VIII and factor IX are reviewed by Dr. Hedner in Section III, including the principles for immune tolerance induction and the use of recombinant factor VIIa to induce hemostasis in bleeding patients with inhibitors. In Section IV, gene therapy in hemophilia is reviewed by Dr. High, who focuses on recent developments in the rapidly moving field of gene therapy for hemophilia. Three phase I trials of gene therapy for hemophilia were initiated in 1999, and additional proposed trials are currently in the regulatory review process. Certain aspects of the pathophysiology of hemophilia make it an attractive model for a gene-based approach to treatment. These include latitude in choice of target tissue, a wide therapeutic window, the availability of small and large animal models of the disease, and the ease of determining therapeutic efficacy. Since there is very little published information regarding the ongoing trials, this section reviews the approaches being used, the published pre-clinical data, and considerations affecting clinical trial design in hemophilia gene therapy.

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