Efficient gene delivery to the adult and fetal CNS using pseudotyped non-integrating lentiviral vectors

Non-integrating lentiviral vectors show considerable promise for gene therapy applications as they persist as long-term episomes in non-dividing cells and diminish risks of insertional mutagenesis. In this study, non-integrating lentiviral vectors were evaluated for their use in the adult and fetal central nervous system of rodents. Vectors differentially pseudotyped with vesicular stomatitis virus, rabies and baculoviral envelope proteins allowed targeting of varied cell populations. Efficient gene delivery to discrete areas of the brain and spinal cord was observed following stereotactic administration. Furthermore, after direct in utero administration (E14), sustained and strong expression was observed 4 months into adulthood. Quantification of transduction and viral copy number was comparable when using non-integrating lentivirus and conventional integrating vector. These data support the use of non-integrating lentiviral vectors as an effective alternative to their integrating counterparts in gene therapy applications, and highlight their potential for treatment of inherited and acquired neurological disorders.

Persistent episomal transgene expression in liver following delivery of a scaffold/matrix attachment region containing non-viral vector

An ideal gene therapy vector should enable persistent transgene expression without limitations of safety and reproducibility. Here we report the development of a non-viral episomal plasmid DNA (pDNA) vector that appears to fulfil these criteria. This pDNA vector combines a scaffold/matrix attachment region (S/MAR) with a human liver-specific promoter (alpha1-antitrypsin (AAT)) in such a way that long-term expression is enabled in murine liver following hydrodynamic injection. Long-term expression is demonstrated by monitoring the longitudinal luciferase expression profile for up to 6 months by means of in situ bioluminescent imaging. All relevant control pDNA constructs expressing luciferase are unable to sustain significant transgene expression beyond 1 week post-administration. We establish that this shutdown of expression is due to promoter methylation. In contrast, the S/MAR element appears to inhibit methylation of the AAT promoter thereby preventing transgene silencing. Although this vector appears to be maintained as an episome throughout, we have no evidence for its establishment as a replicating entity. We conclude that the combination of a mammalian, tissue-specific promoter with the S/MAR element is sufficient to drive long-term episomal pDNA expression of genes in vivo.

Adenovirus serotype 5 hexon mediates liver gene transfer

Adenoviruses are used extensively as gene transfer agents, both experimentally and clinically. However, targeting of liver cells by adenoviruses compromises their potential efficacy. In cell culture, the adenovirus serotype 5 fiber protein engages the coxsackievirus and adenovirus receptor (CAR) to bind cells. Paradoxically, following intravascular delivery, CAR is not used for liver transduction, implicating alternate pathways. Recently, we demonstrated that coagulation factor (F)X directly binds adenovirus leading to liver infection. Here, we show that FX binds to the Ad5 hexon, not fiber, via an interaction between the FX Gla domain and hypervariable regions of the hexon surface. Binding occurs in multiple human adenovirus serotypes. Liver infection by the FX-Ad5 complex is mediated through a heparin-binding exosite in the FX serine protease domain. This study reveals an unanticipated function for hexon in mediating liver gene transfer in vivo.

Fetal gene transfer

Gene transfer early in development for the treatment of monogenetic and other diseases could overcome major obstacles of intervention in the mature individual. Early gene transfer may prevent the onset of irreversible pathological changes, predispose the individual to immunological tolerance to the introduced protein, take advantage of the high vector to cell ratio, and provide unique access to stem cell/progenitor compartments. The past few years have witnessed the publication of five studies showing long-term correction of monogenetic disorders by fetal gene transfer. Many others have examined the use of new vector systems with therapeutic transgenes, tested their potential for treating diseases in a wide range of organs (including the brain, lung and skin), and examined the hazards of fetal application. This review gives a comprehensive summary of the development of fetal gene transfer over the past few years.

Delivery and long-term expression of a 135 kb LDLR genomic DNA locus in vivo by hydrodynamic tail vein injection

BACKGROUND

The delivery of a complete genomic DNA locus in vivo may prove advantageous for complementation gene therapy, especially when physiological regulation of gene expression is desirable. Hydrodynamic tail vein injection has been shown to be a highly efficient means of non-viral delivery of plasmid DNA to the liver. Here, we apply hydrodynamic tail vein injection to deliver and express large genomic DNA inserts > 100 kb in vivo.

METHODS

Firstly, a size series (12-172 kb) of bacterial artificial chromosome (BAC) plasmids, carrying human genomic DNA inserts, episomal retention elements, and the enhanced green fluorescent protein (EGFP) reporter gene, was delivered to mice by hydrodynamic tail vein injection. Secondly, an episomal BAC vector carrying the whole genomic DNA locus of the human low-density lipoprotein receptor (LDLR) gene, and an expression cassette for the LacZ reporter gene, was delivered by the same method.

RESULTS

We show that the efficiency of delivery is independent of vector size, when an equal number of plasmid molecules are used. We also show, by LacZ reporter gene analysis, that BAC delivery within the liver is widespread. Finally, BAC-end PCR, RT-PCR and immunohistochemistry demonstrate plasmid retention and long-term expression (4 months) of human LDLR in transfected hepatocytes.

CONCLUSION

This is the first demonstration of somatic delivery and long-term expression of a genomic DNA transgene > 100 kb in vivo and shows that hydrodynamic tail vein injection can be used to deliver and express large genomic DNA transgenes in the liver.

Stable gene transfer to muscle using non-integrating lentiviral vectors

Human immunodeficiency virus (HIV)-based lentiviral vectors (LVs) hold immense promise for gene delivery applications because of their relatively large packaging capacity and their ability to infect a range of cell types. The genome of HIV non-specifically integrates into the host genome, and this promotes efficient, stable transgene expression in dividing cells. However, integration can also be problematic because of variations in gene expression among cells, possible gene silencing and, most importantly, insertional mutagenesis which can lead to undesirable effects such as malignant transformation. In order to alleviate these problems, we have developed a range of non-integrating LVs (NILVs) by introducing point mutations into the catalytic site, chromosome binding site, and viral DNA binding site of the viral integrase (IN). In addition, we have mutated the IN attachment (att) sites within the HIV long terminal repeats (LTRs). All of the vectors produced show efficient reverse transcription and transgene expression in dividing cells and prolonged expression in non-dividing myotubes. Finally, we show that NILV can be used for achieving highly effective gene transfer and expression in muscle in vivo.

The Influence of Blood on In Vivo Adenovirus Bio-distribution and Transduction

Intravascular delivery of adenovirus (Ad) vectors is being developed for liver-directed gene therapy for targeting disseminated disease in cancer therapeutics and for targeting non-hepatic tissues and organs through vector engineering strategies. The utility of Ad vectors is not limited to serotype 5 (Ad5), and many alternate human serotypes and non-human serotypes of Ad are currently being investigated. Critical to intravascular delivery of Ad is the interaction of the virus with host blood cells and plasma proteins, because immediate contact is observed following injection. Although incompletely understood, recent studies suggest that these interactions are critical in dictating the particle bio-distribution and resulting transduction properties of Ad in vivo. For example, plasma proteins-in particular, vitamin K-dependent coagulation zymogens-are able to directly bind to Ad, and "bridge" the virus to receptors in the liver. Unraveling and characterizing these mechanisms will be of fundamental importance both for understanding basic Ad biology in vivo and for refinement and optimization of Ad vectors for human gene therapy.

Targeting of adenovirus serotype 5 (Ad5) and 5/47 pseudotyped vectors in vivo: fundamental involvement of coagulation factors and redundancy of CAR binding by Ad5

Vitamin K-dependent coagulation factors can promote adenoviral cell transduction in vitro. In vivo, warfarin pretreatment ablates liver targeting of an adenovirus serotype 5 (Ad5) vector deleted of CAR binding capability. Here, we assess in vivo transduction and biodistribution of Ad5 vectors with nonmodified fibers (Ad5) and a serotype 47 fiber-pseudotyped Ad5 (Ad5/47; subgroup D) virus following intravascular injection. Warfarin reduced liver transduction by both viruses. However, no impact on early liver virus accumulation was observed, suggesting no effect on Kupffer cell interactions. Hence, coagulation factors play a pivotal role in selectively mediating liver hepatocyte transduction of Ad5 and Ad5/47 vectors.

Influence of coagulation factor zymogens on the infectivity of adenoviruses pseudotyped with fibers from subgroup D

Recent evidence supports a role for vitamin K-dependent coagulation zymogens in adenovirus serotype 5 (Ad5, subgroup C) infection of hepatocytes. Here, we assessed the effect of virus-zymogen interaction on cellular transduction using a panel of fiber (f)-pseudotyped viruses derived from subgroup D (f47, f33, f24, f45, f17, f30). Each virus directly bound factor X (FX) as determined by surface plasmon resonance, resulting in enhanced cell surface binding. Infection of HepG2 cells was promoted by FX but not by FVII or FIX, while transduction of CHO cells was blocked in heparan sulfate proteoglycan-deficient cells. This suggests a broad role for FX in adenovirus infectivity.

Widespread distribution and muscle differentiation of human fetal mesenchymal stem cells after intrauterine transplantation in dystrophic mdx mouse

Duchenne muscular dystrophy (DMD) is a common X-linked disease resulting from the absence of dystrophin in muscle. Affected boys suffer from incurable progressive muscle weakness, leading to premature death. Stem cell transplantation may be curative, but is hampered by the need for systemic delivery and immune rejection. To address these barriers to stem cell therapy in DMD, we investigated a fetal-to-fetal transplantation strategy. We investigated intramuscular, intravascular, and intraperitoneal delivery of human fetal mesenchymal stem cells (hfMSCs) into embryonic day (E) 14-16 MF1 mice to determine the most appropriate route for systemic delivery. Intramuscular injections resulted in local engraftment, whereas both intraperitoneal and intravascular delivery led to systemic spread. However, intravascular delivery led to unexpected demise of transplanted mice. Transplantation of hfMSCs into E14-16 mdx mice resulted in widespread long-term engraftment (19 weeks) in multiple organs, with a predilection for muscle compared with nonmuscle tissues (0.71% vs. 0.15%, p < .01), and evidence of myogenic differentiation of hfMSCs in skeletal and myocardial muscle. This is the first report of intrauterine transplantation of ontologically relevant hfMSCs into fully immunocompetent dystrophic fetal mice, with systemic spread across endothelial barriers leading to widespread long-term engraftment in multiple organ compartments. Although the low-level of chimerism achieved is not curative for DMD, this approach may be useful in other severe mesenchymal or enzyme deficiency syndromes, where low-level protein expression may ameliorate disease pathology.

Evaluation of prenatal intra-amniotic LAMB3 gene delivery in a mouse model of Herlitz disease

Prenatal gene therapy has been considered for Herlitz junctional epidermolysis bullosa (H-JEB), a lethal genodermatosis caused by the absence of any of the three subunits of laminin-5, resulting from birth in widespread blistering and erosions of skin and mucosae. To investigate this strategy in an animal model, adenovirus type 5- and adeno-associated virus (AAV) type 2-derived vectors carrying a beta-galactosidase reporter gene or LAMB3 cDNA encoding the beta3 chain of laminin-5 were generated, tested for stability in amniotic fluid and evaluated in vitro on murine H-JEB keratinocytes, and in vivo by prenatal injection into the amniotic cavities of laminin-5 beta3-deficient mice. The different vectors were administered individually or combined at maximum doses on day 14 post coitum. Adenoviral vectors infected preferentially the foetal epidermis, whereas AAV delivered the transgene mainly to mucous membranes of the airways and the upper digestive tract. The LAMB3 transgene was expressed in target epithelia of newborn laminin-5 beta3-deficient mice, and the transgenic beta3 chain was shown to assemble with its endogenous partner chains, resulting in detectable amounts of laminin-5 in the basement membranes of skin and mucosae and in a lower extent of tissue separation in the skin. However, only combined delivery of the two vector types led to a minor increase of the life span of H-JEB mice. Failure to rescue diseased animals was, at least in part, due to abandonment of any conspicuous pup by the heterozygous mother. This is the first study of a prenatal gene therapy approach to a heritable blistering disorder. Although our findings indicate that prenatal combined administration of adenoviral and adeno-associated LAMB3 vectors provides therapeutic benefit to H-JEB mice, this animal model appears unsuitable for long-term investigations of the therapeutic concept.

Clinically applicable procedure for gene delivery to fetal gut by ultrasound-guided gastric injection: toward prenatal prevention of early-onset intestinal diseases

Targeting gene therapy vectors to the fetal intestinal tract could provide a novel means toward prevention of the early postnatal intestinal pathology of cystic fibrosis and other conditions, such as congenital enteropathy, that cause intestinal failure. Among these conditions, cystic fibrosis is by far the most common lethal genetic disease. It is caused by a functional absence or deficiency of the cystic fibrosis transmembrane conductance regulator and manifests in the gut as meconium ileus. Prenatal treatment of genetic disease may avoid early-onset tissue damage and immune sensitization, and may target cells that are less accessible in the adult. We investigated gene transfer to the fetal gut, using a minimally invasive injection technique. First-generation replication-deficient adenoviral vectors encoding the beta-galactosidase gene and transduction-enhancing agents were injected into the stomach of early-gestation fetal sheep (n = 8, 60 days of gestation; term, 145 days) under ultrasound guidance. Reporter gene expression was observed 2 days after injection in the villi of the gastrointestinal epithelia after 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside staining and beta-galactosidase immunohistochemistry of fetal tissues. Expression of beta-galactosidase, as measured by enzyme-linked immunosorbent assay, was enhanced after pretreatment of the fetal gut with sodium caprate, which opens tight junctions, and after adenovirus complexation with DEAE-dextran, which confers a positive charge to the virus. Instillation of the fluorocarbon perflubron after virus delivery resulted in tissue transduction from the fetal stomach to the colon. Using a clinically relevant technique, we have demonstrated widespread gene transfer to the fetal gastrointestinal epithelia.

Multiple vitamin K-dependent coagulation zymogens promote adenovirus-mediated gene delivery to hepatocytes

Upon local delivery, adenovirus (Ad) serotype 5 viruses use the coxsackie and Ad receptor (CAR) for cell binding and alpha(v) integrins for internalization. When administered systemically, however, their role in liver tropism is limited because CAR-permissive and mutated viruses show similar biodistribution, a finding recently attributed to blood coagulation factor (F) IX or complement protein C4BP binding to the adenovirus fiber and "bridging" to either low-density lipoprotein receptor-related protein or heparan sulfate proteoglycans. Here, we show that hepatocyte transduction in vitro can be enhanced by the vitamin K-dependent factors FX, protein C, and FVII in addition to FIX but not by prothrombin (FII), FXI, and FXII. This phenomenon was not dependent on proteolytic activation or cell signaling activity and for FX was mediated by direct virus-factor binding. Human FX substantially enhanced hepatocyte transduction by CAR-permissive and mutated viruses in an ex vivo liver perfusion model. In vivo, global down-regulation of vitamin K-dependent zymogens by warfarin significantly diminished liver uptake of CAR-deleted Ads; however, this phenomenon was fully rescued by acute infusion of human FX. Our results indicate a common and pivotal role for distinct vitamin K-dependent coagulation factors in mediating hepatocyte transduction by adenoviruses in vitro and in vivo.

Gene therapy progress and prospects: fetal gene therapy--first proofs of concept--some adverse effects

Somatic gene delivery in utero is a novel approach to gene therapy for genetic disease based on the hypothesis that prenatal intervention may avoid the development of severe manifestations of early-onset disease, allow targeting of otherwise inaccessible tissues including expanding stem cell populations, induce tolerance against the therapeutic transgenic protein and thereby provide permanent somatic gene correction. This approach is particularly relevant in relation to prenatal screening programmes for severe genetic diseases as it could offer prevention as a third option to families faced with the prenatal diagnosis of a genetically affected child. Most investigations towards in utero gene therapy have been performed on mice and sheep fetuses as model animals for human disease and for the application of clinically relevant intervention techniques such as vector delivery by minimally invasive ultrasound guidance. Other animals such as dogs may serve as particular disease models and primates have to be considered in immediate preparation for clinical trials. Proof of principle for the hypothesis of fetal gene therapy has been provided during the last 2 years in mouse models for Crigler Najjar Disease, Leber's congenital amaurosis, Pompe's disease and haemophilia B showing long-term postnatal therapeutic effects and tolerance of the transgenic protein after in utero gene delivery. However, recently we have also observed a high incidence of liver tumours after in utero application of an early form of third-generation equine infectious anaemia virus vectors with SIN configuration. These findings highlight the need for more investigations into the safety and the ethical aspects of in utero gene therapy as well as for science-based public information on risks and benefits of this preventive gene therapy approach before application in humans can be contemplated.

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

Transduction 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 x 10(10) 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.

Factors influencing adenovirus-mediated airway transduction in fetal mice

Intra-amniotic injection of adenovirus allows transduction of the fetal airways following natural fetal breathing movements. This administration method is promising for use in gene therapy for cystic fibrosis and other diseases for which the main target for exogenous gene expression is the lung. Here we have investigated factors that may affect the efficacy of gene transfer to the murine fetal lung. We examined marker compound distribution and transgene expression (from a first-generation adenoviral vector) at different stages of development. This demonstrated that fetal breathing movements at 15-16 days of gestation are of sufficient intensity to carry marker/vector into the fetal lungs. These movements can be significantly stimulated by the combination of intra-amniotic theophylline administration and postoperative exposure of the dam to elevated CO(2) levels. However, the most important factor for efficient and consistent pulmonary transgene delivery is the dose of adenoviral vector used, as both the degree of transduction and the percentage of lungs transduced increases with escalating viral dose.

Oncogenesis Following Delivery of a Nonprimate Lentiviral Gene Therapy Vector to Fetal and Neonatal Mice

Gene therapy by use of integrating vectors carrying therapeutic transgene sequences offers the potential for a permanent cure of genetic diseases by stable vector insertion into the patients' chromosomes. However, three cases of T cell lymphoproliferative disease have been identified almost 3 years after retrovirus gene therapy for X-linked severe combined immune deficiency. In two of these cases vector insertion into the LMO2 locus was implicated in leukemogenesis, demonstrating that a more profound understanding is required of the genetic and molecular effects imposed on the host by vector integration or transgene expression. In vivo models to test for retro- and lentiviral vector safety prior to clinical application are therefore needed. Here we present a high incidence of lentiviral vector-associated tumorigenesis following in utero and neonatal gene transfer in mice. This system may provide a highly sensitive model to investigate integrating vector safety prior to clinical application.

Permanent partial phenotypic correction and tolerance in a mouse model of hemophilia B by stem cell gene delivery of human factor IX

Immune responses against an introduced transgenic protein are a potential risk in many gene replacement strategies to treat genetic disease. We have developed a gene delivery approach for hemophilia B based on lentiviral expression of human factor IX in purified hematopoietic stem cells. In both normal C57Bl/6J and hemophilic 129/Sv recipient mice, we observed the production of therapeutic levels of human factor IX, persisting for at least a year with tolerance to human factor IX antigen. Secondary and tertiary recipients also demonstrate long-term production of therapeutic levels of human factor IX and tolerance, even at very low levels of donor chimerism. Furthermore, in hemophilic mice, partial functional correction of treated mice and phenotypic rescue is achieved. These data show the potential of a stem cell approach to gene delivery to tolerize recipients to a secreted foreign transgenic protein and, with appropriate modification, may be of use in developing treatments for other genetic disorders.

Targeting the respiratory muscles of fetal sheep for prenatal gene therapy for Duchenne muscular dystrophy

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a lethal degenerative muscular disease. Fetal gene therapy may correct the primary genetic defect. Our aim was to achieve expression of a reporter gene in the respiratory muscles of early gestation fetal sheep.

STUDY DESIGN

An adenovirus vector containing the beta-galactosidase reporter gene (AdRSVbetagal) was injected into the thoracic musculature (n = 3) and pleural cavity (n = 6) of fetal sheep (61-67 days' gestation) under ultrasound guidance. Tissues were harvested after 48 hours and site and intensity of beta-galactosidase expression were assessed.

RESULTS

Limited transgene expression observed after a single injection was improved by multiple injections, but remained localized. Ultrasound-guided creation of a hydrothorax led to an increase in the intensity of beta-galactosidase expression (ELISA). X-gal staining and immunohistochemistry showed that vector spread was confined to the innermost intercostal musculature.

CONCLUSION

Ultrasound-guided injection can deliver gene therapy vectors to the fetal pleural cavity and achieve transduction of the respiratory muscles.

In utero gene therapy: current challenges and perspectives

Over the past few years, considerable progress in prenatal diagnosis and surgery combined with improvements in vector design vindicate a reappraisal of the feasibility of in utero gene therapy for serious monogenetic diseases. As adult gene therapy gathers pace, several apparent obstacles to its application as a treatment may be overcome by pre- or early postnatal treatment. This review will examine the concepts and practice of prenatal vector administration. We aim to highlight the advantages of early therapeutic intervention focusing on diseases that could benefit greatly from a prenatal gene therapy approach. We will pay special attention to the strategies and vectors that are most likely to be used for this application and will speculate on their expected developments for the near future.

Fetal and neonatal gene therapy: benefits and pitfalls

The current approaches to gene therapy of monogenetic diseases into mature organisms are confronted with several problems including the following: (1) the underlying genetic defect may have already caused irreversible pathological changes; (2) the level of sufficient protein expression to ameliorate or prevent the disease requires prohibitively large amounts of gene delivery vector; (3) adult tissues may be poorly infected by conventional vector systems dependent upon cellular proliferation for optimal infection, for example, oncoretrovirus vectors; (4) immune responses, either pre-existing or developing following vector delivery, may rapidly eliminate transgenic protein expression and prevent future effective intervention. Early gene transfer, in the neonatal or even fetal period, may overcome some or all of these obstacles. The mammalian fetus enjoys a uniquely protected environment in the womb, bathed in a biochemically and physically supportive fluid devoid of myriad extra-uterine pathogens. Strong physical and chemical barriers to infection might, perhaps, impede the frenetic cell division. The physical support and the biochemical support provided by the fetal-maternal placental interface may, therefore, minimize the onset of genetic diseases manifest early in life. The fetal organism must prepare itself for birth, but lacking a mature adaptive immune system may depend upon more primordial immune defences. It is the nature of these defences, and the vulnerabilities they protect, that are poorly understood in the context of gene therapy and might provide useful information for approaches to gene therapy in the young, as well as perhaps the mature organism.

Permanent phenotypic correction of hemophilia B in immunocompetent mice by prenatal gene therapy

Hemophilia B, also known as Christmas disease, arises from mutations in the factor IX (F9) gene. Its treatment in humans, by recombinant protein substitution, is expensive, thus limiting its application to intermittent treatment in bleeding episodes and prophylaxis during surgery; development of inhibitory antibodies is an associated hazard. This study demonstrates permanent therapeutic correction of his disease without development of immune reactions by introduction of an HIV-based lentiviral vector encoding the human factor IX protein into the fetal circulation of immunocompetent hemophiliac and normal outbred mice. Plasma factor IX antigen remained at around 9%, 13%, and 16% of normal in the 3 hemophilia B mice, respectively, until the last measurement at 14 months. Substantial improvement in blood coagulability as measured by coagulation assay was seen in all 3 mice and they rapidly stopped bleeding after venipuncture. No humoral or cellular immunity against the protein, elevation of serum liver enzymes, or vector spread to the germline or maternal circulation were detected.

Highly efficient EIAV-mediated in utero gene transfer and expression in the major muscle groups affected by Duchenne muscular dystrophy

Gene therapy for Duchenne muscular dystrophy has so far not been successful because of the difficulty in achieving efficient and permanent gene transfer to the large number of affected muscles and the development of immune reactions against vector and transgenic protein. In addition, the prenatal onset of disease complicates postnatal gene therapy. We have therefore proposed a fetal approach to overcome these barriers. We have applied beta-galactosidase expressing equine infectious anaemia virus (EIAV) lentiviruses pseudotyped with VSV-G by single or combined injection via different routes to the MF1 mouse fetus on day 15 of gestation and describe substantial gene delivery to the musculature. Highly efficient gene transfer to skeletal muscles, including the diaphragm and intercostal muscles, as well as to cardiac myocytes was observed and gene expression persisted for at least 15 months after administration of this integrating vector. These findings support the concept of in utero gene delivery for therapeutic and long-term prevention/correction of muscular dystrophies and pave the way for a future application in the clinic.

Widespread and efficient marker gene expression in the airway epithelia of fetal sheep after minimally invasive tracheal application of recombinant adenovirus in utero

Cystic fibrosis is a common lethal genetic disease caused by functional absence of the cystic fibrosis transmembrane conductance regulator (CFTR). Although a candidate disease for in utero gene therapy, demonstration of potentially therapeutic levels of transgene expression in the fetal airways after minimally invasive gene delivery is a mandatory prerequisite before application of this approach in humans can be considered. We report here on the delivery of a beta-galactosidase expressing adenovirus directly to the airways of fetal sheep in utero using ultrasound-guided percutaneous injection of the trachea in the fetal chest. Injection of adenoviral particles to the fetal airways was not associated with mortality and resulted in low-level expression in the peripheral airways. However, complexation of the virus with DEAE dextran, which confers a positive charge to the virus, and pretreatment of the airways with Na-caprate, which opens tight junctions, increased transgene expression, and a combination of these two enhancers resulted in widespread and efficient gene transfer of the fetal trachea and bronchial tree. Using a percutaneous ultrasound-guided injection technique, we have clearly demonstrated proof of principle for substantial transgene delivery to the fetal airways providing levels of gene expression that could be relevant for a therapeutic application of CFTR expressing vectors.

Reduced toxicity of F-deficient Sendai virus vector in the mouse fetus

Current concerns over insertional mutagenesis by retroviral vectors mitigate investigations into alternative, potentially persistent gene therapy vector systems not dependent on genomic integration, such as Sendai virus vectors (SeVV). Prenatal gene therapy requires efficient gene delivery to several tissues, which may not be achievable by somatic gene transfer to the adult. Initially, to test the potential and tropism of the SeVV for gene delivery to fetal tissues, first-generation (replication- and propagation-competent) recombinant SeVV, expressing beta-galactosidase was introduced into late gestation immunocompetent mice via the amniotic and peritoneal cavities and the yolk sac vessels. At 2 days, this resulted in very high levels of expression particularly in the airway epithelium, mesothelium and vascular endothelium, respectively. However, as expected, substantial vector toxicity was observed. The efficiency of gene transfer and the level of gene expression were then examined using a second-generation SeVV. The second generation was developed to be still capable of cytoplasmic RNA replication and therefore high-level gene expression, but incapable of vector spread due to lack of the gene for viral F-protein. Vector was introduced into the fetal amniotic and peritoneal cavities, intravascularly, intramuscularly and intraspinally; at 2 days, expression was observed in the airway epithelia, peritoneal mesothelia, unidentified cells in the gut wall, locally at the site of muscle injection and in the dorsal root ganglia, respectively. Mortality was dramatically diminished compared with the first-generation vector.

Long-term transgene expression by administration of a lentivirus-based vector to the fetal circulation of immuno-competent mice

Inefficient gene transfer, inaccessibility of stem cell compartments, transient gene expression, and adverse immune and inflammatory reactions to vector and transgenic protein are major barriers to successful in vivo application of gene therapy for most genetic diseases. Prenatal gene therapy with integrating vectors may overcome these problems and prevent early irreparable organ damage. To this end, high-dose attenuated VSV-G pseudotyped equine infectious anaemia virus (EIAV) encoding beta-galactosidase under the CMV promoter was injected into the fetal circulation of immuno-competent MF1 mice. We saw prolonged, extensive gene expression in the liver, heart, brain and muscle, and to a lesser extent in the kidney and lung of postnatal mice. Progressive clustered hepatocyte staining suggests clonal expansion of cells stably transduced. We thus provide proof of principle for efficient gene delivery and persistent transgene expression after prenatal application of the EIAV vector and its potential for permanent correction of genetic diseases.

In utero gene transfer of human factor IX to fetal mice can induce postnatal tolerance of the exogenous clotting factor

The fundamental hypotheses behind fetal gene therapy are that it may be possible (1) to achieve immune tolerance of transgene product and, perhaps, vector; (2) to target cells and tissues that are inaccessible in adult life; (3) to transduce a high percentage of rapidly proliferating cells, and in particular stem cells, with relatively low absolute virus doses leading to clonal transgene amplification by integrating vectors; and (4) to prevent early disease manifestation of genetic diseases. This study provides evidence vindicating the first hypothesis; namely, that intravascular prenatal administration of an adenoviral vector carrying the human factor IX (hFIX) transgene can induce immune tolerance of the transgenic protein. Following repeated hFIX protein injection into adult mice, after prenatal vector injection, we found persistence of blood hFIX and absence of hFIX antibodies in 5 of 9 mice. Furthermore, there was substantial hFIX expression after each of 2 reinjections of vector without detection of hFIX antibodies. In contrast, all adult mice that had not been treated prenatally showed a rapid loss of the injected hFIX and the development of high hFIX antibody levels, both clear manifestations of a strong immune reaction.

Arginase in glomerulonephritis

l-Arginine is converted to nitric oxide and citrulline by the enzyme nitric oxide synthase (NOS). Its in vivo inhibition has led to the revelation of a multitude of diverse, often conflicting functions in the inflammatory melee. l-Arginine is also converted to ornithine and urea by the enzyme arginase as a part of the hepatic urea cycle. However, a more holistic interpretation of the two pathways and the associated metabolism (summarized in Fig. 1) has led to its reassessment as a pathologically significant enzyme. This is reflected by the continued increase over the past five years of the number of publications discussing both nitric oxide and arginase. The strong association between inflammation and high arginase and NOS activity is epitomized by immune complex-induced glomerulonephritis and other glomerulonephritides. Arginase is encoded by two recently discovered genes (Arginase I and Arginase II). There is now substantial evidence for an interaction between both arginase isoforms and all three NOS isoforms in pathological situations. This review considers the relationship between Arginases I and II and the inflammation-associated isoform of NOS called NOS II. In particular, it consolidates the current understanding of arginase and associated metabolic pathways, and highlights some of the issues that are often overlooked in such studies.

Arginase in glomerulonephritis

Arginase metabolizes L-arginine to L-ornithine and urea. Two arginase isoforms, AI (liver arginase) and AII (ubiquitously expressed, functions unknown), have been identified. It is clear that arginases potentially have important roles in addition to urea generation for high concentrations are present at inflammatory sites. Regulation occurs through cytokines, substrate competition and products of nitric oxide (NO) metabolism. The functions of arginases at inflammatory sites are unknown, but may include regulation of apoptosis and NO production and generation of structural and cellular protein precursors. In glomerulonephritis there is increased arginase activity in nephritic glomeruli following a pattern similar to that in wound healing. The level can be further increased by NO inhibition suggesting substrate competition. The potential sources in the inflamed glomerulus include infiltrating leucocytes and mesangial cells, and the predominant isoform expressed is AI (AII predominates under physiological conditions). The recent identification of different isoforms of arginase has been an important step towards understanding the significance of arginase activity in glomerulonephritis.

Induced nitric oxide (NO) synthesis in heterologous nephrotoxic nephritis; effects of selective inhibition in neutrophil-dependent glomerulonephritis

Increased NO synthesis, due to inducible NO synthase (iNOS) activity, is found in macrophage-associated glomerulonephritis. Little is known about NO in neutrophil-dependent immune complex inflammation, and its role remains controversial. We therefore studied early phase heterologous nephrotoxic nephritis (HNTN) induced in rats by nephrotoxic globulin and the effects of selective iNOS inhibition of this model. At 2 h of the model iNOS mRNA was induced and nitrite (NO-2) was generated in glomeruli incubated ex vivo (5.2 +/- 1.0 nmol/2000 glomeruli per 24 h). There were 14.7 +/- 2.2 polymorphonuclear neutrophils (PMN)/glomerulus (normal controls 0.1 +/- 0.1). At 8 h urinary protein was 69 +/- 15.3 (normal controls 0. 6 +/- 0.2 mg/24 h). Peritoneal PMN expressed iNOS and produced significant NO-2 (basal 11.2 +/- 0.3 nmol/106 cells per 24 h). Selective iNOS inhibition with L-N6-(1-iminoethyl)-lysine (L-NIL) in vitro inhibited nephritic glomerular and PMN NO-2 synthesis. In HNTN L-NIL in vivo significantly suppressed elevated plasma NO-2/NO-3 levels (representative experiment: 17 +/- 2 microM, untreated 40 +/- 4 microM, P = < 0.01, normal control 18 +/- 2 microM). This inhibition did not affect leucocyte infiltration into glomeruli or induce thrombosis. There was no consistent effect on proteinuria. This is the first demonstration of glomerular iNOS induction and high output NO production in the acute phase of PMN-dependent acute immune complex glomerulonephritis. Selective iNOS inhibition does not affect the primary mechanism of injury (leucocyte infiltration) in this model.

Inducible nitric oxide synthase induction in Thy 1 glomerulonephritis is complement and reactive oxygen species dependent

Thy 1 glomerulonephritis (GN) is a rat model of complement-dependent immune mesangial injury with induced glomerular nitric oxide (NO) synthesis. To examine mechanisms of inducible nitric oxide synthase (iNOS) induction, we studied the effects of treatment with the antioxidant N-acetyl-cysteine (NAC) and soluble complement receptor 1 (sCR1). Thy 1 GN was induced by intravenous anti-Thy 1 antibody. Glomeruli were isolated and kidney tissue taken from 30 min to 24 h after induction. Nitrite (NO-2) synthesis, luminol chemiluminescence for reactive oxygen species (ROS), and iNOS and cytokine mRNA were assayed in isolated glomeruli. Mesangial injury (mesangiolysis) and leucocyte infiltration were quantitated on tissue sections. NAC (i.p. 1,000 mg/kg, 1 h prior to anti-Thy 1) reduced glomerular NO-2 synthesis (3.5 +/- 0.66 vs. untreated 8.2 +/- 1.1, p = 0.02), and iNOS mRNA expression, and abolished enhanced chemiluminescence. In vitro incubation of nephritic glomeruli with 20 mM NAC also suppressed nitrite production (4.7 +/- 0.8 vs. untreated 12.2 +/- 0. 7 nmol NO-2/2,000 glomeruli/48 h, p = 0.003), and chemiluminescence. In NAC-treated animals, neutrophil infiltration (0.5 +/- 0 vs. untreated 9.6 +/- 1.6 glomerulus, p = 0.0005), and macrophage infiltration (1.7 +/- 0.4 vs. untreated 12.0 +/- 0.1, p = 0.006) were abolished, and mesangiolysis was significantly reduced (45.9 +/- 1.3 vs. untreated 34.4 +/- 2.1 cells/glomerulus, p = 0.009). NAC did not inhibit anti-Thy 1 antibody deposition. C1q was unaffected, but C3 was reduced. sCR1 treatment prevented iNOS mRNA induction, the enhanced chemiluminescence, and the neutrophil infiltration at 1 h. IL-1beta and TNFalpha mRNAs were not affected by either NAC or sCR1. These results show that NAC inhibits iNOS induction and NO synthesis in this model, and suppresses ROS synthesis and injury. They suggest that complement-dependent ROS generation is the critical initiating event that follows fixation of anti-Thy 1 antibody.

Arginase AI is upregulated in acute immune complex-induced inflammation

Previous studies have shown high arginase activity at inflammatory sites. Arginase converts L-arginine to L-ornithine, sharing a common substrate with nitric oxide synthase. It exists as two isoforms, AI and AII. While the function of liver arginase (AI) in ureagenesis has been defined, the role and isoform of arginase in cells without a complete urea cycle are unknown. We therefore determined arginase isoform mRNA expression in glomerular acute immune complex inflammation, and its cultured constituent cells. AI was induced in nephritic glomeruli, and in mesangial cells stimulated with IL-4 and cAMP, and was present in elicited neutrophils and macrophages. AII was constitutively expressed. Our data strongly suggest that AI, thought to be restricted to the liver, accounts for high arginase activity at inflammatory sites where it may limit high output nitric oxide production and generate polyamines and proline essential for cell proliferation and matrix production. This identification of AI in inflamed tissue is an important step for understanding the consequences of increased arginase activity.

Anti-GBM glomerulonephritis in mice lacking nitric oxide synthase type 2

Nitric oxide is synthesized in experimental immune complex glomerulonephritis due to local induction of type 2 nitric oxide synthase (NOS2). To determine the role of NOS2, the course of accelerated anti-glomerular basement membrane glomerulonephritis (anti-GBM) was examined in mice homozygous for disruption of the NOS2 gene compared with heterozygous littermates. Disease in the wild type strain (129Sv) was characterized by heavy albuminuria, glomerular neutrophil and macrophage infiltration and glomerular thrombosis. NOS2, interleukin 1B (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) mRNA were induced by 24 hours. The NOS2-deficient mutant mice and the heterozygous mice displayed early (24 hr) and full autologous phase (day 6) injury indistinguishable from the wild-type mice. The equivalent degree of albuminuria and glomerular inflammation indicates that NOS2 does not play an essential role in this form of glomerulonephritis in the mouse.

Arginase activity is modulated by IL-4 and HOArg in nephritic glomeruli and mesangial cells

Arginase shares a common substrate, L-arginine, with nitric oxide synthase (NOS). Both enzymes are active at inflammatory sites. To understand regulation of arginase and its relationship to nitric oxide (NO) production, we studied effects of NG-hydroxy-L-arginine (HOArg) and interleukin-4 (IL-4) on urea and NO2- synthesis by glomeruli during rat immune glomerulonephritis and compared these with macrophages and glomerular mesangial cells (MC). In nephritic glomeruli, elicited macrophages, and MC stimulated with IL-1 and adenosine 3',5'-cyclic monophosphate agonists, increased arginase and induced NOS activity was found. Urea production was inhibited by HOArg and increased by IL-4. NO inhibition [NG-monomethyl-L-arginine (L-NMMA)] increased arginase activity in nephritic glomeruli and macrophages but not MC. NO2- synthesis was inhibited by L-NMMA and IL-4. It was increased with HOArg under conditions of NO inhibition. In contrast, in normal glomeruli and basal MC, where there was no induced NO synthesis, IL-4 had no effect on arginase activity, whereas HOArg consistently reduced it in glomeruli only. Type II arginase (Arg II) mRNA was detected in normal glomeruli; nephritic glomeruli expressed both Arg I and Arg II mRNAs. This is the first demonstration of arginase modulation in glomeruli and MC and of the expression of arginase isoforms in glomeruli. The differential responses to two endogenous compounds generated by inflammation suggest this may be part of coordinated regulation of arginase and inducible NOS in immune injury, whereby arginase is inhibited during high-output NO production and stimulated with NO suppression. This, together with control of arginase and NOS isoforms, may be important in controlling the balance of inflammatory and repair mechanisms.