Systemic delivery of an adenoviral vector encoding canine factor VIII results in short-term phenotypic correction, inhibitor development, and biphasic liver toxicity in hemophilia A dogs

Gene modification therapies for hereditary diseases in the fetus

Proof-of-principle disease models have demonstrated the feasibility of an intrauterine gene modification therapy (in utero gene therapy (IUGT)) approach to hereditary diseases as diverse as coagulation disorders, haemoglobinopathies, neurogenetic disorders, congenital metabolic, and pulmonary diseases. Gene addition, which requires the delivery of an integrating or episomal transgene to the target cell nucleus to be transcribed, and gene editing, where the mutation is corrected within the gene of origin, have both been used successfully to increase normal protein production in a bid to reverse or arrest pathology in utero. While most experimental models have employed lentiviral, adenoviral, and adeno-associated viral vectors engineered to efficiently enter target cells, newer models have also demonstrated the applicability of non-viral lipid nanoparticles. Amelioration of pathology is dependent primarily on achieving sustained therapeutic transgene expression, silencing of transgene expression, production of neutralising antibodies, the dilutional effect of the recipient's growth on the mass of transduced cells, and the degree of pre-existing cellular damage. Safety assessment of any IUGT strategy will require long-term postnatal surveillance of both the fetal recipient and the maternal bystander for cell and genome toxicity, oncogenic potential, immune-responsiveness, and germline mutation. In this review, we discuss advances in the field and the push toward clinical translation of IUGT.

Transduction Properties of an Adenovirus Vector Containing Sequences Complementary to a Liver-Specific microRNA, miR-122a, in the 3'-Untranslated Region of the E4 Gene in Human Hepatocytes from Chimeric Mice with Humanized Liver

Replication-incompetent adenovirus (Ad) vectors are promising gene delivery vehicles, especially for hepatocytes, due to their superior hepatic tropism; however, in vivo application of an Ad vector often results in hepatotoxicity, mainly due to the leaky expression of Ad genes from the Ad vector genome. In order to reduce the Ad vector-induced hepatotoxicity, we previously developed an Ad vector containing the sequences perfectly complementary to a liver-specific microRNA (miRNA), miR-122a, in the 3'-untranslated region (UTR) of the E4 gene. This improved Ad vector showed a significant reduction in the leaky expression of Ad genes and hepatotoxicity in the mouse liver and primary mouse hepatocytes; however, the safety profiles and transduction properties of this improved Ad vector in human hepatocytes remained to be elucidated. In this study, we examined the transgene expression and safety profiles of Ad vectors with miR-122a-targeted sequences in the 3'-UTR of the E4 gene in human hepatocytes from chimeric mice with humanized liver. The transgene expression levels of Ad vectors with miR-122a-targeted sequences in the 3'-UTR of the E4 gene were significantly higher than those of the conventional Ad vectors. The leaky expression levels of Ad genes of Ad vectors with miR-122a-targeted sequences in the 3'-UTR of the E4 gene in the primary human hepatocytes were largely reduced, compared with the conventional Ad vectors, resulting in an improvement in Ad vector-induced cytotoxicity. These data indicated that this improved Ad vector was a superior gene delivery vehicle without severe cytotoxicity for not only mouse hepatocytes but also human hepatocytes.

High-Capacity Adenoviral Vectors: Expanding the Scope of Gene Therapy

The adaptation of adenoviruses as gene delivery tools has resulted in the development of high-capacity adenoviral vectors (HC-AdVs), also known, helper-dependent or “gutless”. Compared with earlier generations (E1/E3-deleted vectors), HC-AdVs retain relevant features such as genetic stability, remarkable efficacy of in vivo transduction, and production at high titers. More importantly, the lack of viral coding sequences in the genomes of HC-AdVs extends the cloning capacity up to 37 Kb, and allows long-term episomal persistence of transgenes in non-dividing cells. These properties open a wide repertoire of therapeutic opportunities in the fields of gene supplementation and gene correction, which have been explored at the preclinical level over the past two decades. During this time, production methods have been optimized to obtain the yield, purity, and reliability required for clinical implementation. Better understanding of inflammatory responses and the implementation of methods to control them have increased the safety of these vectors. We will review the most significant achievements that are turning an interesting research tool into a sound vector platform, which could contribute to overcome current limitations in the gene therapy field.

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

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

Protein-Engineered Coagulation Factors for Hemophilia Gene Therapy

Hemophilia A (HA) and hemophilia B (HB) are X-linked bleeding disorders due to inheritable deficiencies in either coagulation factor VIII (FVIII) or factor IX (FIX), respectively. Recently, gene therapy clinical trials with adeno-associated virus (AAV) vectors and protein-engineered transgenes, B-domain deleted (BDD) FVIII and FIX-Padua, have reported near-phenotypic cures in subjects with HA and HB, respectively. Here, we review the biology and the clinical development of FVIII-BDD and FIX-Padua as transgenes. We also examine alternative bioengineering strategies for FVIII and FIX, as well as the immunological challenges of these approaches. Other engineered proteins and their potential use in gene therapy for hemophilia with inhibitors are also discussed. Continued advancement of gene therapy for HA and HB using protein-engineered transgenes has the potential to alleviate the substantial medical and psychosocial burdens of the disease.

Platelet Gene Therapy Promotes Targeted Peripheral Tolerance by Clonal Deletion and Induction of Antigen-Specific Regulatory T Cells

Delivery of gene therapy as well as of biologic therapeutics is often hampered by the immune response of the subject receiving the therapy. We have reported that effective gene therapy for hemophilia utilizing platelets as a delivery vehicle engenders profound tolerance to the therapeutic product. In this study, we investigated whether this strategy can be applied to induce immune tolerance to a non-coagulant protein and explored the fundamental mechanism of immune tolerance induced by platelet-targeted gene delivery. We used ovalbumin (OVA) as a surrogate non-coagulant protein and constructed a lentiviral vector in which OVA is driven by the platelet-specific αIIb promoter. Platelet-specific OVA expression was introduced by bone marrow transduction and transplantation. Greater than 95% of OVA was stored in platelet α-granules. Control mice immunized with OVA generated OVA-specific IgG antibodies; however, mice expressing OVA in platelets did not. Furthermore, OVA expression in platelets was sufficient to prevent the rejection of skin grafts from CAG-OVA mice, demonstrating that immune tolerance developed in platelet-specific OVA-transduced recipients. To assess the mechanism(s) involved in this tolerance we used OTII mice that express CD4⁺ effector T cells specific for an OVA-derived peptide. After platelet-specific OVA gene transfer, these mice showed normal thymic maturation of the T cells ruling against central tolerance. In the periphery, tolerance involved elimination of OVA-specific CD4⁺ effector T cells by apoptosis and expansion of an OVA-specific regulatory T cell population. These experiments reveal the existence of natural peripheral tolerance processes to platelet granule contents which can be co-opted to deliver therapeutically important products.

Immune tolerance induced by platelet-targeted factor VIII gene therapy in hemophilia A mice is CD4 T cell mediated

Essentials The immune response is a significant concern in gene therapy. Platelet-targeted gene therapy can restore hemostasis and induce immune tolerance. CD4 T cell compartment is tolerized after platelet gene therapy. Preconditioning regimen affects immune tolerance induction in platelet gene therapy.

SUMMARY

Background Immune responses are a major concern in gene therapy. Our previous studies demonstrated that platelet-targeted factor VIII (FVIII) (2bF8) gene therapy together with in vivo drug selection of transduced cells can rescue the bleeding diathesis and induce immune tolerance in FVIIInull mice. Objective To investigate whether non-selectable 2bF8 lentiviral vector (LV) for the induction of platelet-FVIII expression is sufficient to induce immune tolerance and how immune tolerance is induced after 2bF8LV gene therapy. Methods Platelet-FVIII expression was introduced by 2bF8LV transduction and transplantation. FVIII assays and tail bleeding tests were used to confirm the success of platelet gene therapy. Animals were challenged with rhF8 to explore if immune tolerance was induced after gene therapy. Treg cell analysis, T-cell proliferation assay and memory B-cell-mediated ELISPOT assay were used to investigate the potential mechanisms of immune tolerance. Results We showed that platelet-FVIII expression was sustained and the bleeding diathesis was restored in FVIIInull mice after 2bF8LV gene therapy. None of the transduced recipients developed anti-FVIII inhibitory antibodies in the groups preconditioned with 660 cGy irradiation or busulfan plus ATG treatment even after rhF8 challenge. Treg cells significantly increased in 2bF8LV-transduced recipients and the immune tolerance developed was transferable. CD4+ T cells from treated animals failed to proliferate in response to rhF8 re-stimulation, but memory B cells could differentiate into antibody secreting cells in 2bF8LV-transduced recipients. Conclusion 2bF8LV gene transfer without in vivo selection of manipulated cells can introduce immune tolerance in hemophilia A mice and this immune tolerance is CD4+ T cell mediated.

Gene therapy for immune tolerance induction in hemophilia with inhibitors

The development of inhibitors, i.e. neutralizing alloantibodies against factor (F) VIII or FIX, is the most significant complication of protein replacement therapy for patients with hemophilia, and is associated with both increased mortality and substantial physical, psychosocial and financial morbidity. Current management, including bypassing agents to treat and prevent bleeding, and immune tolerance induction for inhibitor eradication, is suboptimal for many patients. Fortunately, there are several emerging gene therapy approaches aimed at addressing these unmet clinical needs of patients with hemophilia and inhibitors. Herein, we review the mounting evidence from preclinical hemophilia models that the continuous uninterrupted expression of FVIII or FIX delivered as gene therapy can bias the immune system towards tolerance induction, and even promote the eradication of pre-existing inhibitors. We also discuss several gene transfer approaches that directly target immune cells in order to promote immune tolerance. These preclinical findings also shed light on the immunologic mechanisms that underlie tolerance induction.

Canine models of inherited bleeding disorders in the development of coagulation assays, novel protein replacement and gene therapies

Animal models of inherited bleeding disorders are important for understanding disease pathophysiology and are required for preclinical assessment of safety prior to testing of novel therapeutics in human and veterinary medicine. Experiments in these animals represent important translational research aimed at developing safer and better treatments, such as plasma-derived and recombinant protein replacement therapies, gene therapies and immune tolerance protocols for antidrug inhibitory antibodies. Ideally, testing is done in animals with the analogous human disease to provide essential safety information, estimates of the correct starting dose and dose response (pharmacokinetics) and measures of efficacy (pharmacodynamics) that guide the design of human trials. For nearly seven decades, canine models of hemophilia, von Willebrand disease and other inherited bleeding disorders have not only informed our understanding of the natural history and pathophysiology of these disorders but also guided the development of novel therapeutics for use in humans and dogs. This has been especially important for the development of gene therapy, in which unique toxicities such as insertional mutagenesis, germ line gene transfer and viral toxicities must be assessed. There are several issues regarding comparative medicine in these species that have a bearing on these studies, including immune reactions to xenoproteins, varied metabolism or clearance of wild-type and modified proteins, and unique tissue tropism of viral vectors. This review focuses on the results of studies that have been performed in dogs with inherited bleeding disorders that closely mirror the human condition to develop safe and effective protein and gene-based therapies that benefit both species.

In utero stem cell transplantation and gene therapy: rationale, history, and recent advances toward clinical application

Recent advances in high-throughput molecular testing have made it possible to diagnose most genetic disorders relatively early in gestation with minimal risk to the fetus. These advances should soon allow widespread prenatal screening for the majority of human genetic diseases, opening the door to the possibility of treatment/correction prior to birth. In addition to the obvious psychological and financial benefits of curing a disease in utero, and thereby enabling the birth of a healthy infant, there are multiple biological advantages unique to fetal development, which provide compelling rationale for performing potentially curative treatments, such as stem cell transplantation or gene therapy, prior to birth. Herein, we briefly review the fields of in utero transplantation (IUTx) and in utero gene therapy and discuss the biological hurdles that have thus far restricted success of IUTx to patients with immunodeficiencies. We then highlight several recent experimental breakthroughs in immunology, hematopoietic/marrow ontogeny, and in utero cell delivery, which have collectively provided means of overcoming these barriers, thus setting the stage for clinical application of these highly promising therapies in the near future.

Evaluation of transduction properties of an adenovirus vector in neonatal mice

In gene therapy for congenital disorders, treatments during neonate and infant stages are promising. Replication-incompetent adenovirus (Ad) vectors have been used in gene therapy studies of genetic disorders; however, the transduction properties of Ad vectors in neonates and infants have not been fully examined. Accordingly, this study examined the properties of Ad vector-mediated transduction in neonatal mice. A first-generation Ad vector containing a cytomegalovirus (CMV) promoter-driven luciferase expression cassette was administered to neonatal mice on the second day of life via retro-orbital sinus. The highest Ad vector genome copy numbers and transgene expression were found in the neonatal liver. The neonatal heart exhibited the second highest levels of transgene expression among the organs examined. There was an approximately 1500-fold difference in the transgene expression levels between the adult liver and heart, while the neonatal liver exhibited only an approximately 30-fold higher level of transgene expression than the neonatal heart. A liver-specific promoter for firefly luciferase expression conferred a more than 100-fold higher luciferase expression in the liver relative to the other organs. No apparent hepatotoxicity was observed in neonatal mice following Ad vector administration. These findings should provide valuable information for gene therapy using Ad vectors in neonates and infants.

Biological therapies for inherited diseases: social and bioethical considerations. Hemophilia as an example

INTRODUCTION

In hemophilia, advanced therapies are warranted from a conceptual and methodological standpoint. Current advanced therapy strategies are centered on the use of adeno-associated viral vectors, although problems related to immunogenicity and hepatotoxicity still remain.

AREAS COVERED

Future clinical trials will have to scrupulously observe international bioethical standards in terms of patient selection, particularly children. Patient recruitment rates are likely to remain low due to the stringent exclusion criteria usually imposed on the trial population regarding their hepatic and immunological markers and the presence of viral coinfection; and to the existence of an optimal palliative treatment.

EXPERT OPINION

Accordingly, the results obtained are likely to be of low statistical significance, which could hinder their application to clinical practice. Another important issue is the degree to which society embraces these new emerging therapies. The unfamiliarity of society with these new methods, together with the many unresolved questions about them that remain, may threaten their acceptance not only by society at large but also by health-care professionals, which would limit their translational application to clinical practice.

Hemophilia A: an ideal disease to correct in utero

Hemophilia A (HA) is the most frequent inheritable defect of the coagulation proteins. The current standard of care for patients with HA is prophylactic factor infusion, which is comprised of regular (2-3 times per week) intravenous infusions of recombinant or plasma-derived FVIII to maintain hemostasis. While this treatment has greatly increased the quality of life and lengthened the life expectancy for many HA patients, its high cost, the need for lifelong infusions, and the fact that it is unavailable to roughly 75% of the world's HA patients make this type of treatment far from ideal. In addition, this lifesaving therapy suffers from a high risk of treatment failure due to immune response to the infused FVIII. There is thus a need for novel treatments, such as those using stem cells and/or gene therapy, which have the potential to mediate long-term correction or permanent cure following a single intervention. In the present review, we discuss the clinical feasibility and unique advantages that an in utero approach to treating HA could offer, placing special emphasis on a new sheep model of HA we have developed and on the use of mesenchymal stromal cells (MSC) as cellular vehicles for delivering the FVIII gene.

Suppression of leaky expression of adenovirus genes by insertion of microRNA-targeted sequences in the replication-incompetent adenovirus vector genome

Leaky expression of adenovirus (Ad) genes occurs following transduction with a conventional replication-incompetent Ad vector, leading to an induction of cellular immunity against Ad proteins and Ad protein-induced toxicity, especially in the late phase following administration. To suppress the leaky expression of Ad genes, we developed novel Ad vectors by incorporating four tandem copies of sequences with perfect complementarity to miR-122a or miR-142-3p into the 3′-untranslated region (UTR) of the E2A, E4, or pIX gene, which were mainly expressed from the Ad vector genome after transduction. These Ad vectors easily grew to high titers comparable to those of a conventional Ad vector in conventional 293 cells. The leaky expression of these Ad genes in mouse organs was significantly suppressed by 2- to 100-fold, compared with a conventional Ad vector, by insertion of the miRNA-targeted sequences. Notably, the Ad vector carrying the miR-122a–targeted sequences into the 3′-UTR of the E4 gene expressed higher and longer-term transgene expression and more than 20-fold lower levels of all the Ad early and late genes examined in the liver than a conventional Ad vector. miR-122a–mediated suppression of the E4 gene expression in the liver significantly reduced the hepatotoxicity which an Ad vector causes via both adaptive and non-adaptive immune responses.

Advancements in gene transfer-based therapy for hemophilia A

Gene therapy has promised clinical benefit to those suffering with hemophilia A, but this benefit has not yet been realized. However, during the past two decades, basic and applied gene therapy research has progressed and the goal of gene therapy for hemophilia A is once again in our sights. The hemophilia A patient population suffers from a disease that requires invasive, lifelong management, is exorbitantly expensive to treat, has geographically limited treatment access and can become untreatable due to immune reactions to the treatment product. Subsequent to the cloning of the factor VIII gene and cDNA in the early 1980s, academic and commercial research laboratories began to pursue gene transfer-based therapies to supplement or supplant the available protein replacement therapy. However, to date, clinical trials for gene therapy of hemophilia A have been unsuccessful. Three trials have been conducted with each having tested a different gene-transfer strategy and each demonstrating that there is a considerable barrier to achieving sustained expression of therapeutic amounts of factor VIII. Recent progress has been made in gene-transfer technology and, relevant to hemophilia A, towards increasing the biosynthetic efficiency of factor VIII. These advances are now being combined to develop novel strategies to treat and possibly cure hemophilia A.

Treatment of Hemophilia A in Utero and Postnatally using Sheep as a Model for Cell and Gene Delivery

Hemophilia A represents the most common inheritable deficiency of the coagulation proteins. Current state-of- the-art treatment consists of frequent prophylactic infusions of plasma-derived or recombinant FVIII protein to maintain hemostasis, and has greatly increased life expectancy and quality of life for many hemophilia A patients. This treatment approach is, however, far from ideal, due to the need for lifelong intravenous infusions, the high treatment cost, and the fact that it is unavailable to a large percentage of the world's hemophiliacs. There is thus a need for novel treatments that can promise long-term or permanent correction. In contrast to existing protein based therapeutics, gene therapy offers to provide a permanent cure following few, or even a single, treatment. In the present paper, we review ongoing work towards this end, focusing on studies we have performed in a large animal model. Some of the key topics covered in this review include the unique opportunities sheep offer as a model system, the re-establishment and clinical and molecular characterization of a line of sheep with severe hemophilia A, the advantages and feasibility of treating a disease like hemophilia A in utero, and the use of Mesenchymal Stem Cells (MSC) as cellular delivery vehicles for the FVIII gene. The review finishes with a brief discussion of our recent success correcting ovine hemophilia A with a postnatal transplant with gene-modified MSC, and the limitations of this approach that remain to be overcome.

Animal models of hemophilia

The X-linked bleeding disorder hemophilia is caused by mutations in coagulation factor VIII (hemophilia A) or factor IX (hemophilia B). Unless prophylactic treatment is provided, patients with severe disease (less than 1% clotting activity) typically experience frequent spontaneous bleeds. Current treatment is largely based on intravenous infusion of recombinant or plasma-derived coagulation factor concentrate. More effective factor products are being developed. Moreover, gene therapies for sustained correction of hemophilia are showing much promise in preclinical studies and in clinical trials. These advances in molecular medicine heavily depend on availability of well-characterized small and large animal models of hemophilia, primarily hemophilia mice and dogs. Experiments in these animals represent important early and intermediate steps of translational research aimed at development of better and safer treatments for hemophilia, such a protein and gene therapies or immune tolerance protocols. While murine models are excellent for studies of large groups of animals using genetically defined strains, canine models are important for testing scale-up and for long-term follow-up as well as for studies that require larger blood volumes.

In vitro transdifferentiation of HepG2 cells to pancreatic-like cells by CCl₄, D-galactosamine, and ZnCl₂

OBJECTIVE

The objective of the study was to induce transdifferentiation of human hepatoma HepG2 cells into pancreatic-like cells without direct genetic intervention.

METHODS

HepG2 cells were transfected with plasmids for the hepatocyte marker protein green fluorescent protein (albumin-GFP) and the pancreatic cell marker Discosoma spp red fluorescent protein (elastase-DsRed) to create FAE-HepG2 cells. Fluorescent marker expression was used to monitor in vitro transdifferentiation stimulated 100 mM CCl₄, 2 mM D-galactosamine, or 200 μM ZnCl₂. Concentrations were selected for optimal cell survival rate. Transdifferentiation was also characterized by immunohistochemical detection of amylase, glucagon, and insulin and by polymerase change reaction analysis of amylase and insulin mRNA production.

RESULTS

Control cells expressed albumin-GFP but no elastase-DsRed. By 30 days of culture, all 3 agents induced expression of pancreatic-like cell marker elastase-DsRed. ZnCl₂ was the most effective as most cells expressed elastase-DsRed in the absence of simultaneous expression of albumin-GFP. For CCl₄ and D-galactosamine, elastase-DsRed was expressed in the same cells as albumin-GFP. Cells treated by each agent also expressed amylase, insulin, and glucagon proteins and mRNAs.

CONCLUSIONS

Without direct genetic intervention, select low small molecules can induce in vitro transformation of hepatoma cells into pancreatic-like cells.

Implications of the innate immune response to adenovirus and adenoviral vectors

Adenovirus (AdV) is a common cause of respiratory illness in both children and adults. Respiratory symptoms can range from those of the common cold to severe pneumonia. Infection can also cause significant disease in the immunocompromised and among immunocompetent subjects in close quarters. Fortunately, infection with AdV in the normal host is generally mild. This is one reason why its initial use as a gene-therapy vector appeared to be so promising. Unfortunately, both innate and adaptive responses to the virus have limited the development of AdV vectors as a tool of gene therapy by increasing toxicity and limiting duration of transgene expression. This article will focus on the innate immune response to infection with wild-type AdV and exposure to AdV gene-therapy vectors. As much of the known information relates to the pulmonary inflammatory response, this organ system will be emphasized. This article will also discuss how that understanding has led to the creation of new vectors for use in gene therapy.

Analysis of in vitro transfection by sonoporation using cationic and neutral microbubbles

The objective of the study was to examine the role of acoustic power intensity and microbubble and plasmid concentrations on transfection efficiency in HEK-293 cells using a sonoporator with a 1-MHz transducer. A green fluorescent protein (GFP) reporter plasmid was delivered in as much as 80% of treated cells, and expression of the GFP protein was observed in as much as 75% of cells, using a power intensity of 2 W/cm(2) with a 25% duty cycle. In addition, the relative transfection abilities of a lipid noncationic and cationic microbubble platform were investigated. As a positive control, cells were transfected using Lipofectamine reagent. Cell survival and transfection efficiency were inversely proportional to acoustic power and microbubble concentration. Our results further demonstrated that high-efficiency transfection could be achieved, but at the expense of cell loss. Moreover, direct conjugation of plasmid to the microbubble did not appear to significantly enhance transfection efficiency under the examined conditions, although this strategy may be important for targeted transfection in vivo.

Low-dose simultaneous delivery of adenovirus encoding hepatocyte growth factor and vascular endothelial growth factor in dogs enhances liver proliferation without systemic growth factor elevation

BACKGROUND

Hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF) gene transfer proved to enhance liver regeneration. However, elevation of their plasma levels may induce potentially serious distant effects such as tumorigenesis or proliferative retinopathy.

AIMS

This study was performed to examine whether simultaneous administration of low-dose adenovirus encoding HGF and VEGF genes in dogs will stimulate liver proliferation but without inducing liver toxicity or systemic elevation of HGF and VEGF levels.

METHODS

Adult dogs received an intravenous injection of low-dose adenoviral vectors encoding human HGF and VEGF (HGF/VEGF), beta-galactosidase (lacZ) or phosphate-buffered saline (PBS). Liver proliferation was measured using the proliferating cell nuclear antigen (PCNA) immunostaining labelling index. HGF and VEGF plasma concentrations and transaminases were repeatedly measured. Transgene expression was evaluated using reverse-transcription polymerase chain reaction.

RESULTS

Human HGF and VEGF expressions were detected only in the liver of HGF/VEGF dogs at day 2 after injection but declined at sacrifice (day 7). No expression was detected in the liver of the lacZ or PBS groups. Plasma levels of HGF and VEGF were not statistically different from those in the lacZ group (P=0.81, P=0.22 respectively). The PCNA labelling index was five-fold higher in the HGF/VEGF group compared with the lacZ group (P<0.01). No immunostaining was detected in the PBS group. Transaminases were only elevated (P<0.01) in the lacZ group compared with the other groups.

CONCLUSIONS

We showed that simultaneous administration of low-dose adenoviral vectors encoding human HGF and VEGF genes can induce transgene expression and liver proliferation without liver toxicity or systemic growth factor elevation.

In vitro reprogramming of adult hepatocytes into insulin-producing cells without viral vectors

The pancreas and the liver share the same endodermal origin. We have been studying whether mature hepatocytes can be induced to differentiate into pancreatic beta-cells by in vitro delivery of transcriptional factors using a non-viral approach. Here we showed that nucleofection allowed suitable transfection of primary hepatocytes employing various non-viral methods. We introduced either pancreatic and duodenal homeobox 1 (Pdx1) or neurogenin 3 (Ngn3), or both, into the mature cells using nucleofection. Co-expression of pdx1 and ngn3 using a bicistronic vector activated the transcription of various islet-related genes, and the transfected hepatocytes acquired the ability to synthesize and secrete insulin. Our results suggest that simultaneous expression of Pdx1 and Ngn3 is an excellent inducer of liver-to-pancreas reprogramming, and that reprogramming will occur even in mature somatic cells without the need for viral vectors. These findings are of considerable significance for further therapeutic development for various intractable diseases including diabetes.

Indoleamine 2,3-dioxygenase attenuates inhibitor development in gene-therapy-treated hemophilia A mice

A serious impediment to gene and protein replacement therapy in hemophilia A is the development of inhibitors. Mechanisms responsible for inhibitor development include T-cell-dependent adaptive immune responses and the CD28-B7 signaling pathway that eventually leads to the formation of antibodies directed against factor VIII (FVIII). Indoleamine 2,3-dioxygenase (IDO) is a potent immunosuppressive enzyme that can inhibit T-cell responses and induce T-cell apoptosis by regulation of tryptophan metabolism. Kynurenine, one of the metabolites of tryptophan, has been implicated as an immune modulator. Here we hypothesize that co-delivery of the genes for FVIII and IDO can attenuate inhibitor formation. Using transposon-based gene delivery, we observed long-term therapeutic FVIII expression and significantly reduced inhibitor titers when the genes were co-delivered. Co-expression of FVIII and IDO in the liver was associated with increased plasma kynurenine levels, an inhibition of T-cell infiltration and increased apoptosis of T cells within the liver. These experiments suggest that modulation of tryptophan catabolism through IDO expression provides a novel strategy to reduce inhibitor development in hemophilia gene/protein therapy.

Transient blockade of the inducible costimulator pathway generates long-term tolerance to factor VIII after nonviral gene transfer into hemophilia A mice

Formation of inhibitory antibodies is a common problem encountered in clinical treatment for hemophilia. Human factor VIII (hFVIII) plasmid gene therapy in hemophilia A mice also leads to strong humoral responses. We demonstrate that short-term therapy with an anti-ICOS monoclonal antibody to transiently block the inducible costimulator/inducible costimulator ligand (ICOS/ICOSL) signaling pathway led to sustained tolerance to hFVIII in hFVIII plasmid-treated hemophilia A mice and allowed persistent, high-level FVIII functional activity (100%-300% of normal). Anti-ICOS treatment resulted in depletion of ICOS(+)CD4(+) T cells and activation of CD25(+)Foxp3(+) Tregs in the peripheral blood, spleen, and lymph nodes. CD4(+) T cells from anti-ICOS-treated mice did not proliferate in response to hFVIII stimulation and produced high levels of regulatory cytokines, including interleukin-10 and transforming growth factor-beta. Moreover, CD4(+)CD25(+) Tregs from tolerized mice adoptively transferred dominant tolerance in syngeneic hFVIII plasmid-treated hemophilia A mice and reduced the production of antibodies against FVIII. Anti-ICOS-treated mice tolerized to hFVIII generated normal primary and secondary antibody responses after immunization with the T-dependent antigen, bacteriophage Phix 174, indicating maintenance of immune competency. Our data indicate that transient anti-ICOS monoclonal antibody treatment represents a novel single-agent immunomodulatory strategy to overcome the immune responses against transgene product after gene therapy.

Phospholipids-based microbubbles sonoporation pore size and reseal of cell membrane cultured in vitro

OBJECTIVE

To investigate phospholipids-based microbubbles induced sonoporation and cell membrane reseal in vitro under various conditions.

METHODS

A breast cancer cell line SK-BR-3 was used to investigate ultrasonic sonoporation under various conditions. Atomic force microscopy (AFM) scanning techniques were employed to observe the change of membrane pores.

RESULTS

Normal SK-BR-3 cells membrane pores were evenly distributed and less than 1 microm. After ultrasound exposure, membrane pores were enlarged at different degree depending on ultrasound exposure durations, filling gas species and microbubble suspension concentration. With microbubble suspension concentration being increased to 5% or ultrasound exposure reached 30 s, membrane pores in fluorocarbon (C(3)F(8) or SF(6))-filled microbubble groups exceeded 1 microm, which were significantly larger than that of air-filled microbubble group. Membrane pores were about 2-3 microm under ultrasound 60 s with 5% fluorocarbon-filled microbubble suspension. After 24 h of incubation, most of the enlarged membrane pores could reseal to normal size, which corresponded to cell viability.

CONCLUSIONS

Membrane pores can be obviously enlarged by ultrasonic sonoporation of fluorocarbon-filled microbubbles, whose reseal time depended on ultrasound exposure duration and microbubble suspension concentration.

Blood-derived smooth muscle cells as a target for gene delivery

OBJECTIVE

To examine the feasibility of using blood-derived smooth muscle cells (BD-SMCs) as a target for to deliver therapeutic proteins.

MATERIALS AND METHODS

Mononuclear cells (MNC) were isolated from peripheral blood. The outgrowth colonies from MNC culture were differentiated into BD-SMCs in media containing platelet-derived growth factor BB. Phenotypic characterization of BD-SMCs was assessed by immunocytochemistry. Cell proliferation, gene transfer efficiency with a retroviral vector, apoptosis, and the biological activity of the transduced gene product from the BD-SMCs were evaluated in vitro and in vivo in comparison with vascular derived SMC (VSMCs).

RESULTS

BD-SMCs stained positive for SMC markers. No significant difference was observed between BD-SMCs and VSMCs in cell proliferation, migration, adhesiveness, and gene transfer efficiency. After BD-SMCs were transduced with a retroviral vector carrying the secreted alkaline phosphatase gene (SEAP), 174 +/- 50 mug biologically active SEAP was produced per 10(6) cells over 24 hours. After injecting 5 x 10(6) cells expressing SEAP intravenously into rabbits, SEAP concentration increased significantly in the circulation from 0.14 +/- 0.04 mug/ml to 2.34 +/- 0.16 mug/ml 3 days after cell injection (P < .01, n = 3). Circulating levels of SEAP decreased to 1.76 mug /ml 1 week later and remained at this level up to 8 weeks, then declined to pre-cell injection level at 12 weeks. VSMC in vivo gene expression data were equivalent.

CONCLUSION

BD-SMCs have similar characteristics to mature VSMCs and can be used as a novel target for gene transfer to deliver a therapeutic protein.

Staunch protections: the ethics of haemophilia gene transfer research

Haemophilia has long been considered an ideal system for validating human gene transfer (GT). However, haemophilia GT trials present a particular ethical challenge because they involve subjects whose medical condition is stabilized by standard therapies. Below, I review the ethics and risks of haemophilia GT clinical research. I propose several conditions and practices that strengthen the ethical basis for such trials. These include consultation with haemophilia advocacy organizations as trials are designed and executed, high standards of supporting evidence before trials are initiated, pretrial publication of this evidence, and the offer of indemnification for participants. I further argue against the conduct of paediatric haemophilia GT studies at this time, and raise questions about the fairness of recruiting economically disadvantaged subjects into studies that are primarily directed towards the health needs of persons in the developed world.

Gene therapy for treatment of inherited haematological disorders

Gene therapy, a molecular medicine based on vector-mediated transfer of therapeutic genes, holds promise for a cure of monogenetic inherited diseases. In recent years, tremendous progress has been reported in the treatment of haematological disorders: clinical trials in severe combined immune deficiencies have been successful by using retroviral vectors to express target genes in haematopoietic stem cells, which after transplantation efficiently reconstituted the immune system concomitant with substantial improvement in the clinical status of patients. Conversely, unexpected adverse events were also encountered. In other work, progress towards clinical studies on ex vivo gene transfer for Fanconi anaemia and haemoglobinopathies has been made. Each approach features a unique treatment strategy and also faces various impediments to success. In the case of the X-linked bleeding disorder haemophilia, several Phase I/II clinical trials were conducted, including in vivo administration of viral vectors to skeletal muscle and liver. Adeno-associated viral gene transfer of coagulation Factor IX has been documented in human subjects, reaching therapeutic levels after infusion into a hepatic blood vessel. However, sustained expression of therapeutic levels (as shown in large animal models of haemophilia) has not yet been achieved in humans. In general, long-term follow-up will be important for assessment of the safety of all existing gene therapy strategies.

Adenovirus-platelet interaction in blood causes virus sequestration to the reticuloendothelial system of the liver

Intravenous (i.v.) delivery of recombinant adenovirus serotype 5 (Ad5) vectors for gene therapy is hindered by safety and efficacy problems. We have discovered a new pathway involved in unspecific Ad5 sequestration and degradation. After i.v. administration, Ad5 rapidly binds to circulating platelets, which causes their activation/aggregation and subsequent entrapment in liver sinusoids. Virus-platelet aggregates are taken up by Kupffer cells and degraded. Ad sequestration in organs can be reduced by platelet depletion prior to vector injection. Identification of this new sequestration mechanism and construction of vectors that avoid it could improve levels of target cell transduction at lower vector doses.

Sleeping beauty transposon-mediated nonviral gene therapy

Safe and effective delivery of genetic material to mammalian tissues would significantly expand the therapeutic possibilities for a large number of medical conditions. Unfortunately, the promise of gene therapy has been hampered by technical challenges, the induction of immune responses, and inadequate expression over time. Despite these setbacks, progress continues to be made and the anticipated benefits may come to fruition for certain disorders. In terms of delivery, nonviral vector systems are particularly attractive as they are simple to produce, can be stored for long periods of time, and induce no specific immune responses. A significant drawback to nonviral systems has been the lack of persistent expression, as plasmids are lost or degraded when delivered to living tissues. The recent application of integrating transposons to nonviral gene delivery has significantly helped to overcome this obstacle, because it allows for genomic integration and long-term expression. Recent advances in transposon-based vector systems hold promise as new technologies that may unlock the potential of gene therapy; however, technical and safety issues still need refinement.

Genetic engineering for haemophilia A

At first sight, haemophilia A would appear to be an ideal candidate for treatment by gene therapy. There is a single gene defect; cells in different parts of the body, but especially the liver, produce Factor VIII, and only 5% of normal levels of Factor VIII are necessary to prevent the serious symptoms of bleeding. This review attempts to outline the status of gene therapy at present and efforts that have been made to overcome the difficulties and remaining problems that require solving. Undoubtedly, success will be achieved, but it is likely that considerably more work will be necessary before experimental models can be introduced into the clinic with any likelihood of success. The most successful results in animals that may have clinical application were from introducing the Factor VIII gene to newborn animals before antibodies are produced, presumably inducing a state of tolerance.

Helper-dependent adenoviral gene therapy mediates long-term correction of the clotting defect in the canine hemophilia A model

BACKGROUND

Adenoviral vector-mediated gene therapy might have potential for long-term correction of the monogenic disease hemophilia A.

OBJECTIVE

In this study, we tested the efficacy of administering a helper-dependent adenoviral vector (HDV) designed for maximal liver-restricted canine factor VIII (cFVIII) expression on three out-bred hemophilia A dogs.

METHODS

Three FVIII-deficient animals from the University of North Carolina colony were injected with 1 x 10(12) (Dog A), and 3 x 10(12) (Dog B and C) vp kg(-1) helper-dependent adenoviral vector, and we performed systematic analysis of toxicity, persistence of therapeutic gene expression, and molecular analysis of gene transfer.

RESULTS

We observed acute dose-dependent elevation in liver enzymes and thrombocytopenia after injection, although both were transient and resolved within 2 weeks. The whole blood clotting time (WBCT), plasma FVIII concentration, FVIII activity, and activated partial thromboplastin time in all animals improved significantly after treatment, and two animals receiving a higher dose reached near normal WBCT with low-level FVIII activity until terminal sacrifice at 3 months, and 2 years. Importantly, the treated dogs suffered no bleeding events after injection. Moreover, we observed persistent vector-specific DNA and RNA in liver tissue collected from one high-dose animal at days 18 and 79, and could not detect the formation of inhibitory antibodies.

CONCLUSION

Although vector-associated toxicity remains an obstacle, a single injection of HDV led to long-term transgene expression and vector persistence in two FVIII-deficient animals with conversion of their severe phenotype to a moderate one.

Advances in gene therapy using factor VIIa in hemophilia

The development of recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) has provided an effective, alternative treatment strategy for hemophilia patients with inhibitors. However, its short half-life necessitates frequent infusions and results in high treatment costs. One potential solution to this problem may lie in the use of FVIIa gene transfer, which would achieve long-lasting therapeutic levels of expression from a single injection. Studies in animal models have shown that a recombinant adeno-associated viral vector can be used to insert both murine and human FVIIa into murine liver. Following FVIIa gene transfer, mice with hemophilia B demonstrated a long-term, dose-dependent increase in circulating levels of FVIIa, reduced prothrombin time, and correction of activated partial thromboplastin time into the normal range. In addition, blood loss following a modified tail-clip assay was significantly reduced. Ongoing studies in mice engineered to express a wide range of FVIIa levels aim to analyze organ histology and evaluate long-term survival, reproductive fitness, and real-time in vivo clot formation in the microvasculature. These studies are expanding our knowledge of the effects of continuously expressed rFVIIa, and it is hoped that they may eventually provide a new avenue for treatment of hemophilia.

Gene therapy and uterine leiomyoma: a review

Leiomyomas (fibroids) are common estrogen-dependent uterine tumours that cause significant morbidity for women and a substantial economic impact on health delivery systems. Currently, there is no effective medical treatment option for this condition-hysterectomy is the mainstay of management. This is not an attractive choice for many women, especially patients desiring to preserve their fertility potential. Gene therapy is becoming a clinical reality, with more than 600 clinical trials worldwide. Researchers have recently attempted to develop a gene-therapy-based approach for the ablation of uterine fibroids. The localized nature of this condition and its accessibility using different imaging or endoscopic techniques make it an attractive target for direct delivery of gene-based vectors. Recent work from our laboratory suggests the potential use of a dominant-negative form of estrogen receptor (ER) to inactivate estrogen signalling in leiomyoma cells and induce apoptosis. Our in vivo data in a mouse model demonstrate the ability of an adenovirus-expressing dominant-negative ER to arrest leiomyoma growth. We and others also have described the utility of the herpes simplex virus-thymidine kinase (HSV-TK) plus ganciclovir (GCV) suicide gene-therapy system to effectively eradicate leiomyoma cells by utilizing the bystandard effect phenomena and the high expression of gap-junction protein in these tumours. Further work on rat models will pave the way for future leiomyoma gene-therapy clinical trials and allow the realization of gene therapy as a viable non-surgical option for this common problem in women's health.

Multiyear therapeutic benefit of AAV serotypes 2, 6, and 8 delivering factor VIII to hemophilia A mice and dogs

Hemophilia A, a deficiency of functional coagulation factor VIII (FVIII), is treated via protein replacement therapy. Restoring 1% to 5% of normal blood FVIII activity prevents spontaneous bleeding, making the disease an attractive gene therapy target. Previously, we have demonstrated short-term activity of a liver-specific AAV2 vector expressing canine B-domain-deleted FVIII (cFVIII) in a hemophilia canine model. Here, we report the long-term efficacy and safety of AAV-cFVIII vectors of serotypes 2, 5, 6, and 8 in both hemophilia A mice and dogs. AAV6-cFVIII and AAV8-cFVIII restored physiologic levels of plasma FVIII activity in hemophilia A mice. The improved efficacy is attributed to more efficient gene transfer in liver compared with AAV2 and AAV5. However, supraphysiologic cFVIII levels correlated with the formation of cFVIII-neutralizing antibodies in these mice. Of importance, hemophilia A dogs that received AAV2-cFVIII, AAV6-cFVIII, and AAV8-cFVIII have persistently expressed therapeutic levels of FVIII, without antibody formation or other toxicities, for more than 3 years. However, liver transduction efficiencies are similar between AAV2, AAV6, and AAV8 serotypes in hemophilia A dogs, in contrast to mice. In summary, this is the first report demonstrating multiyear therapeutic efficacy and safety of multiple AAV-cFVIII vectors in hemophilia A dogs and provides the basis for human clinical studies.

Sustained FVIII expression and phenotypic correction of hemophilia A in neonatal mice using an endothelial-targeted sleeping beauty transposon

Hemophilia A, deficiency of coagulation factor VIII (FVIII), is an attractive candidate for gene therapy as expression of modest amounts of FVIII can provide therapeutic benefit. Most gene transfer approaches for hemophilia have focused on the liver, as this is the major source of endogenous FVIII; however, increasing evidence suggests that endothelial cells are capable of synthesis and release of FVIII. Here the Sleeping Beauty (SB) transposon is employed to target long-term expression of the human B-domain-depleted FVIII gene (approved gene symbol F8) within lung endothelia of hemophilic mice. As the formation of inhibitory antibodies to FVIII has been a significant impediment toward achieving therapeutic plasma levels after gene or protein therapy, we chose to perform gene transfer in neonatal mice, which are more likely to be immune tolerant. Using this approach, low therapeutic levels of FVIII ( approximately 10%), as well as phenotypic correction of the bleeding disorder, were achieved in all animals that received the FVIII transposon and functional transposase throughout the duration of the study (24 weeks). Rechallenge of these animals with additional gene transfer did not result in significant increases in FVIII levels, due mainly to increases in inhibitory antibodies. These studies demonstrate the feasibility of using endothelial-targeted SB transposons for the treatment of hemophilia A.

Sustained phenotypic correction of canine hemophilia B after systemic administration of helper-dependent adenoviral vector

We have evaluated the potential of liver-directed, helper-dependent adenoviral (HDAd) vector-mediated gene therapy in the hemophilia B dog. Two dogs were injected intravenously with HDAd (3 x 10(12) VP/kg) bearing a liver-restricted canine coagulation factor IX (FIX) expression cassette. After injection, the whole blood clotting time for both dogs declined from >60 min to </=20 min for at least 604 and 446 days, respectively. Peak FIX activities of 34.1 and 129.2% were detected at 12x14 days and then slowly declined to 2 to 5% by 120 days and stabilized at these therapeutic levels for at least 418 and 257 days. For one dog, a peak FIX level of 500 ng/ml was achieved and stabilized at >170 ng/ml for at least 256 days. For the other dog, a peak FIX level of 1258 ng/ml was achieved and stabilized at >400 ng/ml for at least 213 days. Inhibitor formation was not evident in either animal. Importantly, whereas untreated hemophilia B dogs suffer five or six spontaneous bleeds per year, the treated dogs suffered no such bleeds postinjection. Significantly, this study is the first to demonstrate long-term phenotypic correction of a genetic disorder in a large animal with HDAd. Although no evidence of chronic toxicity was observed in either animal, systemic vector administration at 3 x 10(12) VP/kg was accompanied by acute, albeit transient and variable laboratory abnormalities (alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, creatine phosphokinase, and platelet counts). The results of this study highlight both the potential benefit and the risk associated with systemic intravascular delivery of high-dose HDAd for liver-directed gene therapy.

Large animal models and gene therapy

Over the last two decades, gene transfer experiments for the treatment of inherited or acquired diseases have mainly been performed in mice. While mice provide proof of principle and allow testing of a variety of therapeutic modalities, mouse models have some limitations, as only short-term experiments can be performed, their homogenous genetic background is unlike humans, and the knockout models do not always faithfully represent the human disease. Naturally occurring large animal models of human genetic diseases have become increasingly important despite the costs and the extensive clinical attention they require because of their similarities to human patients. Large animals are reasonably outbred, long lived allowing for longitudinal studies, are more similar in size to a neonate or small child providing an opportunity to address issues related to scaling up therapy, and many physiological parameters including the immune system are more similar to those in humans versus those in mice.

Gene transfer for hemophilia: can therapeutic efficacy in large animals be safely translated to patients?

Gene transfer is a novel area of therapeutics in which the active agent is a nucleic acid rather than a protein or small molecule. As early as 1997, investigators reported long-term expression of therapeutic levels of factor IX using gene transfer techniques in hemophilia B mice, and similar data were thereafter reported in mice with hemophilia A. Efforts to translate these results to hemophilic dog models at first yielded only marginally therapeutic levels (1%-2% normal circulating levels), but within the past few years have achieved levels in the range of 10%-20% through multiple different gene transfer strategies. Early phase clinical testing has revealed that many aspects of gene transfer in humans were accurately predicted by studies in hemophilic dogs, but that other aspects were not, and were only appreciated as a result of clinical testing. Studies in the next few years will determine whether the problems identified in preclinical and early phase clinical testing can be solved to develop a therapeutic gene transfer approach to hemophilia.

Persistent expression of factor VIII in vivo following nonprimate lentiviral gene transfer

Hemophilia A is a clinically important coagulation disorder caused by the lack or abnormality of plasma coagulation factor VIII (FVIII). Gene transfer of the FVIII cDNA to hepatocytes using lentiviral vectors is a potential therapeutic approach. We investigated the efficacy of feline immunodeficiency virus (FIV)-based vectors in targeting hepatocytes and correcting FVIII deficiency in a hemophilia A mouse model. Several viral envelope glycoproteins were screened for efficient FIV vector pseudotyping and hepatocyte transduction. The GP64 glycoprotein from baculovirus Autographa californica multinuclear polyhedrosis virus pseudo-typed FIV efficiently and showed excellent hepatocyte tropism. The GP64-pseudotyped vector was stable in the presence of human or mouse complement. Inclusion of a hybrid liver-specific promoter (murine albumin enhancer/human alpha1-antitrypsin promoter) further enhanced transgene expression in hepatocytes. We generated a GP64-pseudotyped FIV vector encoding the B domain-deleted human FVIII coding region driven by the liver-specific promoter, with 2 beneficial point mutations in the A1 domain. Intravenous vector administration conferred sustained FVIII expression in hemophilia A mice for several months without the generation of anti-human FVIII antibodies and resulted in partial phenotypic correction. These findings demonstrate the utility of GP64-pseudotyped FIV lentiviral vectors for targeting hepatocytes to correct disorders associated with deficiencies of secreted proteins.

Heterogeneity of the immune response to adenovirus-mediated factor VIII gene therapy in different inbred hemophilic mouse strains

BACKGROUND

The development of anti-factor VIII (FVIII) antibodies (inhibitors) is a critical concern when considering gene therapy as a potential treatment modality for hemophilia A. We used a hemophilia A mouse model bred on different genetic backgrounds to explore genetically controlled differences in the immune response to FVIII gene therapy.

METHODS

C57BL/6 FVIII knockout (C57-FVIIIKO) mice were bred with normal BALB/c (BAL) mice, to generate a recombinant congenic BAL-FVIIIKO model of hemophilia A. Early generation adenoviral (Ad) vectors containing the canine FVIII B-domain-deleted transgene under the control of either the CMV promoter or a tissue-restricted (TR) promoter were administered to C57-FVIIIKO, C57xBAL(F1)-FVIIIKO crosses, and BAL-FVIIIKO mice. FVIII expression, inhibitor development, inflammation, and vector-mediated toxicity were assessed.

RESULTS

In response to administration of Ad-CMV-cFVIII, C57-FVIIIKO mice attain 3-fold higher levels of FVIII expression than BAL-FVIIIKO. All strains injected with Ad-CMV-FVIII displayed FVIII expression lasting only 2 weeks, with associated inhibitor development. C57-FVIII-KO mice that received Ad-TR-FVIII expressed FVIII for 12 months post-injection, whereas FVIII expression was limited to 1 week in C57xBAL(F1)-FVIIIKO and BAL-FVIIIKO mice. This loss of expression was associated with anti-FVIII inhibitor development. BAL-FVIIIKO mice showed increased hepatotoxicity with alanine aminotransferase levels reaching 4-fold higher levels than C57-FVIIIKO mice. However, C57-FVIIIKO mice initiate a more rapid and effective cell-mediated clearance of virally transduced cells than BAL-FVIIIKO, as evidenced by real-time PCR analysis of transduced tissues. Overall, strain-dependent differences in the immune response to FVIII gene delivery were only noted in the adaptive response, and not in the innate response.

CONCLUSIONS

Our results indicate that the genetic background of the murine model of hemophilia A influences FVIII expression levels, the development of anti-FVIII inhibitors, clearance of transduced cells, and the severity of vector-mediated hepatotoxicity.

Absence of a desmopressin response after therapeutic expression of factor VIII in hemophilia A dogs with liver-directed neonatal gene therapy

Hemophilia A (HA) is a bleeding disorder caused by factor VIII (FVIII) deficiency. FVIII replacement therapy can reduce bleeding but is expensive, inconvenient, and complicated by development of antibodies that inhibit FVIII activity in 30% of patients. Neonatal hepatic gene therapy could result in continuous secretion of FVIII into blood and might reduce immunological responses. Newborn HA mice and dogs that were injected i.v. with a retroviral vector (RV) expressing canine B domain-deleted FVIII (cFVIII) achieved plasma cFVIII activity that was 139 +/- 22% and 116 +/- 5% of values found in normal dogs, respectively, which was stable for 1.5 yr. Coagulation tests were normalized, no bleeding had occurred, and no inhibitors were detected. This is a demonstration of long-term fully therapeutic gene therapy for HA in a large animal model. Desmopressin (DDAVP; 1-deamino-[d-Arg(8)]vasopressin) is a drug that increases FVIII activity by inducing release of FVIII complexed with von Willebrand factor from endothelial cells. It has been unclear, however, if the FVIII is synthesized by endothelial cells or is taken up from blood. Because the plasma cFVIII in these RV-treated dogs derives primarily from transduced hepatocytes, they provided a unique opportunity to study the biology of the DDAVP response. Here we show that DDAVP did not increase plasma cFVIII levels in the RV-treated dogs, although von Willebrand factor was increased appropriately. This result suggests that the increase in FVIII in normal dogs after DDAVP is due to release of FVIII synthesized by endothelial cells.

Nonviral gene transfer to surface skin of mid-gestational murine embryos by intraamniotic injection and subsequent electroporation

The surface epithelium of mid-gestational murine embryos is thought to be an attractive target for gene therapy in vivo, due to its visibility and accessibility from the external surface of the maternal uterus. Almost all studies of in utero gene transfer have adopted viral vectors for infection of fetal epithelium, and depended on intraamniotic introduction and simple incubation of vectors, leading to only infection of the surface layer (periderm) of fetal skin. Here we report a simple and convenient method of gene transfer of plasmid DNA into the deeper portion of surface skin of murine mid-gestational fetus. One to two microlitres of a solution containing a lacZ expression plasmid (0.5-1 microg) and trypan blue (0.05%) were placed onto the surface of a fetus (E 14.5) near the eye by a micropipette attached to a mouthpiece. This fetus was immediately electroporated by placing it between tweezer-type electrodes attached to a square-pulse generator. At 1 and 4 days after gene transfer, fetuses were subjected to histochemical staining for lacZ activity in the presence of X-Gal, a substrate for lacZ. Focal reactions were observed in the skin epidermal layers including periderm and basal layer 1 day after DNA introduction. However, lacZ-positive cells were limited to a skin surface layer, the stratum corneum, in the samples obtained 4 days after gene transfer. Similar observation was also made in the transgenic fetuses (carrying a lacZ gene placed immediately downstream of the loxP-flanked sequence) injected with Cre expression vector. These findings suggest rapid movement of fetal epidermal cells toward the surface during late developmental stages. This local gene transfer approach appears to be effective as a method for skin-targeted gene transfer, enabling study of the role of genes of interest and tracing of cell lineage during fetal skin development.

Ultrasound-mediated gene delivery: kinetics of plasmid internalization and gene expression

Sonoporation is an approach that can be used to transfer DNA or drugs into cells. However, very little is known about the mechanism of ultrasound-mediated membrane permeabilization. In this investigation, DNA transport post-sonoporation and the subsequent plasmid internalization and protein expression kinetics have been studied. Using a plasmid encoding for the green fluorescent protein (GFP), labelled or not with an intercalating agent (YOYO-1), it was found that, as compared to lipofection that requires endocytosis, sonoporation allowed a rapid and direct transfer of naked DNA into the cell cytoplasm probably via ultrasound-induced pores in the membrane. The kinetics of protein expression were significantly faster for sonoporation than for lipofection, the mechanism of which requires endocytosis. However, unprotected DNA in the cytoplasm could be degraded by resident cytosolic DNases, thereby decreasing ultrasound-mediated gene delivery efficiency.

Naked DNA transfer of Factor VIII induced transgene-specific, species-independent immune response in hemophilia A mice

The development of antibodies to a previously unexpressed protein product may limit the success of human gene therapy approaches. We inserted B-domain-deleted factor VIII (FVIII) cDNA of human, canine, or murine origin into the multiple cloning site of a liver-specific vector, pBS-HCRHPI-A, to yield plasmids pBS-HCRHPI-FVIIIA, pBS-HCRHPI-cFVIIIA, and pBS-HCRHPI-mFVIIIA, respectively. Fifty micrograms of each plasmid in 2 ml of solution was rapidly injected into the tail vein of three groups of hemophilia A mice. Factor VIII levels ranging from 3 to 12 IU/ml were obtained from all three groups (normal is 1 IU/ml in human plasma) 3 days after treatment. These initial very high levels of functional human, canine, or murine factor VIII, however, fell gradually to undetectable levels within 2-3 weeks, and their disappearance correlated with the generation of high-titer, inhibitory anti-FVIII antibodies. Notably, this immune response occurred independent of the species of origin of the exogenous factor VIII. Antibody titers to factor VIII were detected beginning at 2 weeks, reached a plateau and remained at high levels for over 6 months. The majority of anti-hFVIII IgG was IgG1 isotype specific, suggesting a humoral response mediated by Th2-induced signals. Consistent with this idea, in a separate group of mice treated with pBS-HCRHPI-FVIIIA, transient immunosuppression by cyclophosphamide significantly delayed (5/6) or abolished (1/6) inhibitory antibody formation against the transgene.

Regional intravascular delivery of AAV-2-F.IX to skeletal muscle achieves long-term correction of hemophilia B in a large animal model

In earlier work, we showed that adeno-associated virus-mediated delivery of a Factor IX gene to skeletal muscle by direct intramuscular injection resulted in therapeutic levels of circulating Factor IX in mice. However, achievement of target doses in humans proved impractical because of the large number of injections required. We used a novel intravascular delivery technique to achieve successful transduction of extensive areas of skeletal muscle in a large animal with hemophilia. We provide here the first report of long-term (> 3 years, with observation ongoing), robust Factor IX expression (circulating levels of 4%-14%) by muscle-directed gene transfer in a large animal, resulting in essentially complete correction of the bleeding disorder in hemophilic dogs. The results of this translational study establish an experimental basis for clinical studies of this delivery method in humans with hemophilia B. These findings also have immediate relevance for gene transfer in patients with muscular dystrophy.