Intraamniotic administration of an adenoviral vector for gene transfer to fetal sheep and mouse tissues

Mechanistic Insights into Factor VIII Immune Tolerance Induction via Prenatal Cell Therapy in Hemophilia A

Purpose of Review

Prenatal stem cell and gene therapy approaches are amongst the few therapies that can promise the birth of a healthy infant with specific known genetic diseases. This review describes fetal immune cell signaling and its potential influence on donor cell engraftment, and summarizes mechanisms of central T cell tolerance to peripherally-acquired antigen in the context of prenatal therapies for Hemophilia A.

Recent Findings

During early gestation, different subsets of antigen presenting cells take up peripherally-acquired, non-inherited antigens and induce the deletion of antigen-reactive T-cell precursors in the thymus, demonstrating the potential for using prenatal cell and gene therapies to induce central tolerance to FVIII in the context of prenatal diagnosis/therapy of Hemophilia A.

Summary

Prenatal cell and gene therapies are promising approaches to treat several genetic disorders including Hemophilia A and B. Understanding the mechanisms of how FVIII-specific tolerance is achieved during ontogeny could help develop novel therapies for HA and better approaches to overcome FVIII inhibitors.

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.

In utero stem cell transplantation and gene therapy: Recent progress and the potential for clinical application

Advances in prenatal diagnosis have led to the prenatal management and treatment of a variety of congenital diseases. Although surgical treatment has been successfully applied to specific anatomic defects that place the fetus at a risk of death or life-long disability, the indications for fetal surgical intervention have remained relatively limited. By contrast, prenatal stem cell and gene therapy await clinical application, but they have tremendous potential to treat a broad range of genetic disorders. If there are biological advantages unique to fetal development that favor fetal stem cell or gene therapy over postnatal treatment, prenatal therapy may become the preferred approach to the treatment of any disease that can be prenatally diagnosed and cured by stem cell or gene therapy. Here, we review the field including recent progress toward clinical application and imminent clinical trials for cellular and gene therapy.

Intra-amniotic rAAV-mediated microdystrophin gene transfer improves canine X-linked muscular dystrophy and may induce immune tolerance

Duchenne muscular dystrophy (DMD) is a severe congenital disease due to mutations in the dystrophin gene. Supplementation of dystrophin using recombinant adenoassociated virus vector has promise as a treatment of DMD, although therapeutic benefit of the truncated dystrophin still remains to be elucidated. Besides, host immune responses against the vector as well as transgene products have been denoted in the clinical gene therapy studies. Here, we transduced dystrophic dogs fetuses to investigate the therapeutic effects of an AAV vector expressing microdystrophin under conditions of immune tolerance. rAAV-CMV-microdystrophin and a rAAV-CAG-luciferase were injected into the amniotic fluid surrounding fetuses. We also reinjected rAAV9-CMV-microdystrophin into the jugular vein of an infant dystrophic dog to induce systemic expression of microdystrophin. Gait and cardiac function significantly improved in the rAAV-microdystrophin-injected dystrophic dog, suggesting that an adequate treatment of rAAV-microdystrophin with immune modulation induces successful long-term transgene expression to analyze improved dystrophic phenotype.

The concept of prenatal gene therapy

This introductory chapter provides a short review of the ideas and practical approaches that have led to the present and perceived future development of prenatal gene therapy. It summarizes the advantages and the potential adverse effects of this novel preventive and therapeutic approach to the management of prenatal diseases. It also provides guidance to the range of conditions to which prenatal gene therapy may be applied and to the technical approaches, vectors, and societal/ethical considerations for this newly emerging field of Fetal Medicine.

Fetal gene therapy: recent advances and current challenges

INTRODUCTION

Fetal gene therapy (FGT) can potentially be applied to perinatally lethal monogenic diseases for rescuing clinically severe phenotypes, increasing the probability of intact neurological and other key functions at birth, or inducing immune tolerance to a transgenic protein to facilitate readministration of the vector/protein postnatally. As the field is still at an experimental stage, there are several important considerations regarding the practicality and the ethics of FGT.

AREAS COVERED

Here, through a review of FGT studies, the authors discuss the role and applications of FGT, the progress made with animal models that simulate human development, possible adverse effects in the recipient fetus and the mother and factors that affect clinical translation.

EXPERT OPINION

Although there are valid safety and ethical concerns, the authors argue that there may soon be enough convincing evidence from non-human primate models to take the next step towards clinical trials in the near future.

Organ targeted prenatal gene therapy--how far are we?

Prenatal gene therapy aims to deliver genes to cells and tissues early in prenatal life, allowing correction of a genetic defect, before long-term tissue damage has occurred. In contrast to postnatal gene therapy, prenatal application can target genes to a large population of dividing stem cells, and the smaller fetal size allows a higher vector-to-target cell ratio to be achieved. Early-gestation delivery may allow the development of immune tolerance to the transgenic protein which would facilitate postnatal repeat vector administration if needed. Targeting particular organs will depend on manipulating the vector to achieve selective tropism and on choosing the most appropriate gestational age and injection method for fetal delivery. Intra-amniotic injection reaches the skin, and other organs that are bathed in the fluid however since gene transfer to the lung and gut is usually poor more direct injection methods will be needed. Delivery to the liver and blood can be achieved by systemic delivery via the umbilical vein or peritoneal cavity. Gene transfer to the central nervous system in the fetus is difficult but newer vectors are available that transduce neuronal tissue even after systemic delivery.

Rapid functional dissection of genetic networks via tissue-specific transduction and RNAi in mouse embryos

Using ultrasound-guided in utero infections of fluorescently traceable lentiviruses carrying RNAi or Cre recombinase into mouse embryos, we have demonstrated noninvasive, highly efficient selective transduction of surface epithelium, in which progenitors stably incorporate and propagate the desired genetic alterations. We achieved epidermal-specific infection using small generic promoters of existing lentiviral short hairpin RNA libraries, thus enabling rapid assessment of gene function as well as complex genetic interactions in skin morphogenesis and disease in vivo. We adapted this technology to devise a new quantitative method for ascertaining whether a gene confers a growth advantage or disadvantage in skin tumorigenesis. Using alpha1-catenin as a model, we uncover new insights into its role as a widely expressed tumor suppressor and reveal physiological interactions between Ctnna1 and the Hras1-Mapk3 and Trp53 gene pathways in regulating skin cell proliferation and apoptosis. Our study illustrates the strategy and its broad applicability for investigations of tissue morphogenesis, lineage specification and cancers.

The developmental stage determines the distribution and duration of gene expression after early intra-amniotic gene transfer using lentiviral vectors

Gene transfer after intra-amniotic injection has, in general, been of low efficiency and limited to epithelial cells in the skin, pulmonary and gastrointestinal system. We have recently shown that early gestational administration results in a more efficient gene transfer to developmentally accessible stem cell populations in the skin and eye. In this study we present a comprehensive analysis of patterns of tissue expression seen after early intra-amniotic gene transfer (IAGT) using lentiviral vectors. To assess the influence of developmental stage on tissue expression, injections were administered from the late head fold/early somite stage (E8) to E18. In early gestation (E8-10), green fluorescent protein (GFP) expression was observed in multiple organs, derived from all three germ layers. Remarkably, GFP expression was observed in tissues derived from mesoderm and neural ectoderm at E8, whereas expression was limited to only epithelial cells of ectoderm- and endoderm-derived organs after E11. The amount and duration of gene expression was much higher after IAGT at early gestational time points. The observed temporal patterns of gene expression correspond to the predicted developmental accessibility of organ-specific cell populations. This model may be useful for the analyses of mechanisms of genetic and/or developmental disease and for the development of prenatal gene therapy for specific disorders.

Prenatal stem cell transplantation and gene therapy

At the present time, the most likely and eminent application of stem cell therapy to the fetus is in utero hematopoietic stem cell transplantation (IUHCT), and this stem cell type will be discussed as a paradigm for all prenatal stem cell therapy. The authors feel that the most likely initial application of IUHCT will use adult HSC derived from bone marrow (BM) or peripheral blood (PB), and will focus this article on this specific approach. The article also reviews the experimental data that support the capacity of IUHCT to induce donor-specific tolerance.

Primary Immunodeficiencies

Primary immunodeficiencies (PIDs), once considered to be very rare, are now increasingly recognized because of growing knowledge in the immunological field and the availability of more sophisticated diagnostic techniques and therapeutic modalities [161]. However in a database of >120,000 inpatients of a general hospital for conditions suggestive of ID 59 patients were tested, and an undiagnosed PID was found in 17 (29%) of the subjects tested [107]. The publication of the first case of agammaglobulinemia by Bruton in 1952 [60] demonstrated that the PID diagnosis is first done in the laboratory. However, PIDs require specialized immunological centers for diagnosis and management [33]. A large body of epidemiological evidence supports the hypothesis of the existence of a close etiopathogenetic relation between PID and atopy [73]. In particular, an elevated frequency of asthma, food allergy (FA), atopic dermatitis and enteric pathologies can be found in various PIDs. In addition we will discuss another subject that is certainly of interest: the pseudo-immunodepressed child with recurrent respiratory infections (RRIs), an event that often requires medical intervention and that very often leads to the suspicion that it involves antibody deficiencies [149].

Efficient in vivo targeting of epidermal stem cells by early gestational intraamniotic injection of lentiviral vector driven by the keratin 5 promoter

At the present time, no efficient in vivo method for gene transfer to skin stem cells exists. In this study, we hypothesized that early in gestation, specific epidermal stem cell populations may be accessible for gene transfer. To test this hypothesis, we injected lentiviral vectors encoding the green fluorescence protein marker gene driven by either the cytomegalovirus promoter or the keratin 5 (K5) promoter into the murine amniotic space at early developmental stages between embryonic days 8 and 12. This resulted in sustained green fluorescent protein (GFP) expression in both basal epidermal stem cells and bulge cells in the hair follicles of the skin. Transduction of stem cell populations was dependent on the developmental stage, and confirmed by the prolonged duration of GFP expression in all skin elements into adulthood. In addition, transduced stem cell populations responded to regenerative signals after wounding and actively participated in wound healing. Finally, we quantified the fraction of epidermal stem cells transduced, and the distribution of transduction related to the promoters utilized, confirming improved efficiency with the K5 promoter. This simple approach has possible biological applications in our study of gene functions in skin, and perhaps future clinical applications for treatment of skin based disorders.

Targeted gene transfer to fetal rat lung interstitium by ultrasound-guided intrapulmonary injection

In utero gene transfer to the developing lung may have clinical or research applications. In this study, we developed a new method for specifically targeting the fetal rat lung with adeno and lentiviral vectors encoding the enhanced green fluorescence protein (EGFP) marker gene at E15.5 using ultrasound biomicroscopy (UBM). Survival rate, morphometric parameters, viral biodistribution, and lung transduction efficiency were analyzed and compared to the intra-amniotic route of administration. Expression of EGFP started as early as 24 and 72 h after the injection of adenoviral and lentiviral vectors, respectively. Both vectors transduced lung parenchyma with gene expression limited to interstitial cells of the injected region, in contrast to intra-amniotic injection, which targeted the pulmonary epithelium. Expression of EGFP was most intense at E18.5 and E21.5 for adenoviral and lentiviral vectors, respectively. In contrast to lentivirus, adenoviral expression significantly declined until final analysis at 1 week of age. This study demonstrates the feasibility of targeting the fetal rat lung interstitium with viral vectors under UBM guidance during the pseudoglandular stage. This model system may facilitate in vivo studies of dynamic lung morphogenesis and could provide insight into the efficacy of prenatal gene transfer strategies for treatment of specific lung disorders.

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.

High resolution ultrasound-guided microinjection for interventional studies of early embryonic and placental development in vivo in mice

Background

In utero microinjection has proven valuable for exploring the developmental consequences of altering gene expression, and for studying cell lineage or migration during the latter half of embryonic mouse development (from embryonic day 9.5 of gestation (E9.5)). In the current study, we use ultrasound guidance to accurately target microinjections in the conceptus at E6.5–E7.5, which is prior to cardiovascular or placental dependence. This method may be useful for determining the developmental effects of targeted genetic or cellular interventions at critical stages of placentation, gastrulation, axis formation, and neural tube closure.

Results

In 40 MHz ultrasound images at E6.5, the ectoplacental cone region and proamniotic cavity could be visualized. The ectoplacental cone region was successfully targeted with 13.8 nL of a fluorescent bead suspension with few or no beads off-target in 51% of concepti microinjected at E6.5 (28/55 injected). Seventy eight percent of the embryos survived 2 to 12 days post injection (93/119), 73% (41/56) survived to term of which 68% (38/56) survived and appeared normal one week after birth. At E7.5, the amniotic and exocoelomic cavities, and ectoplacental cone region were discernable. Our success at targeting with few or no beads off-target was 90% (36/40) for the ectoplacental cone region and 81% (35/43) for the exocoelomic cavity but tended to be less, 68% (34/50), for the smaller amniotic cavity. At E11.5, beads microinjected at E7.5 into the ectoplacental cone region were found in the placental spongiotrophoblast layer, those injected into the exocoelomic cavity were found on the surface or within the placental labyrinth, and those injected into the amniotic cavity were found on the surface or within the embryo. Following microinjection at E7.5, survival one week after birth was 60% (26/43) when the amniotic cavity was the target and 66% (19/29) when the target was the ectoplacental cone region. The survival rate was similar in sham experiments, 54% (33/61), for which procedures were identical but no microinjection was performed, suggesting that surgery and manipulation of the uterus were the main causes of embryonic death.

Conclusion

Ultrasound-guided microinjection into the ectoplacental cone region at E6.5 or E7.5 and the amniotic cavity at E7.5 was achieved with a 7 day postnatal survival of ≥60%. Target accuracy of these sites and of the exocoelomic cavity at E7.5 was ≥51%. We suggest that this approach may be useful for exploring gene function during early placental and embryonic development.

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.

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.

Adenoviral vectors: development and application

One of the prerequisites for the successful application of gene vaccination and therapy is the development of efficient gene delivery vectors. The rate-limiting nature of vectors was clearly manifested during the first wave of gene therapy testing, resulting in the demand for more effective and suitable vector systems. Adenoviral (Ad) vectors have recently played a central role in the development of gene-vector technology due to their practical advantages and potential applications. A large number of preclinical and clinical studies both have generated an overwhelming amount of data and literature on this vector system. It is the intention of this article to provide a systematic and broad spectrum review of this system, outlining the principle, potential, and limitations, and evaluating the rational development of this delivery approach. Recombinant adenoviruses (Ad), helper cell lines, and related technologies have been developed and applied to many indications owing to progress in virological research, molecular and cellular biology, eukaryotic protein expression, recombinant vaccines, and gene therapy. The technical depth this article covers should be useful to both the experienced researcher and to beginners in this field.

Rescue of enzyme deficiency in embryonic diaphragm in a mouse model of metabolic myopathy: Pompe disease

Several human genetic diseases that affect striated muscle have been modeled by creating knockout mouse strains. However, many of these are perinatal lethal mutations that result in death from respiratory distress within hours after birth. As the diaphragm muscle does not contract until birth, the sudden increase in diaphragm activity creates permanent injury to the muscle causing it to fail to meet respiratory demands. Therefore, the impact of these mutations remains hidden throughout embryonic development and early death prevents investigators from performing detailed studies of other striated muscle groups past the neonatal stage. Glycogen storage disease type II (GSDII), caused by a deficiency in acid alpha-glucosidase (GAA), leads to lysosomal accumulation of glycogen in all cell types and abnormal myofibrillogenesis in striated muscle. Contractile function of the diaphragm muscle is severely affected in both infantile-onset and late-onset individuals, with death often resulting from respiratory failure. The knockout mouse model of GSDII survives well into adulthood despite the gradual weakening of all striated muscle groups. Using this model, we investigated the delivery of recombinant adeno-associated virus (rAAV) vectors encoding the human GAA cDNA to the developing embryo. Results indicate specific high-level transduction of diaphragm tissue, leading to activity levels up to 10-fold higher than normal and restoration of normal contractile function. Up to an estimated 50 vector copies per diploid genome were quantified in treated diaphragms. Histological glycogen staining of treated diaphragms revealed prevention of lysosomal glycogen accumulation in almost all fibers when compared with untreated controls. This method could be employed with disease models where specific rescue of the diaphragm would allow for increased survival and thus further investigation into the impact of the gene deletion on other striated muscle groups.

Long-term transgene expression in cardiac and skeletal muscle following fetal administration of adenoviral or adeno-associated viral vectors in mice

BACKGROUND

In utero gene transfer may provide advantages for the correction of congenital genetic disorders. In the present study we compare the ability of adenovirus (AdCMVLacZ), and two serotypes of adeno-associated virus (AAVCMVLacZ serotypes 2 and 2/5), to target cardiac and skeletal muscle after prenatal systemic or intramuscular injection in mice and assess the immune response to the vectors.

METHODS

Day 14 gestation fetal mice underwent direct intraperitoneal or intramuscular injection of AdCMVLacZ, and AAVCMVLacZ serotypes 2 and 2/5 vectors. Tissues were processed for beta-galactosidase expression in frozen or high-resolution thin plastic sections at early and late time points. Neutralizing antibodies to Ad and AAV were analyzed in separate fetal experimental and neonatal or adult control groups after administration and re-administration of the vectors.

RESULTS

A single injection of each vector in utero resulted in sustained expression of beta-galactosidase transgene in skeletal and cardiac muscle. Transgene expression was detected for the length of the study, i.e. 86, 58, and 31 weeks after birth for AdCMVLacZ, and AAVCMVLacZ serotypes 2 and 2/5, respectively. High-level expression in the myocardium was observed independent of the vector or route of administration. Neutralizing antibody responses to AAV and Ad antigens were reduced and long-term expression in muscle was not ablated on postnatal re-administration of vector.

CONCLUSIONS

Sustained, high-level cardiac and skeletal muscle transgene expression can be obtained after prenatal gene transfer with each of these vectors. The potential for immune response to viral antigens is altered, but not entirely ablated after in utero exposure.

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.

The role of fetal breathing motions compared with gasping motions in pulmonary airway uptake of intra-amniotic iron dextran

OBJECTIVE

We hypothesized that normal fetal breathing, not acute asphyxial gasping, results in the movement of iron dextran from the amniotic cavity into the fetal lungs. In addition, the amount of iron dextran moving into the fetal lungs is cumulative with time.

STUDY DESIGN

Twelve pregnant New Zealand White rabbits at 25 days of gestation were sedated and underwent ultrasound-guided injections of iron dextran into the amniotic cavities of the rabbit fetuses in both horns of each pregnant doe. Oxygen saturation was maintained at >90% in the pregnant does. The 12 does were then equally assigned to four groups on the basis of the duration of fetal exposure to the dextran (0, 8, 16, and 24 hours). At the end of each time point, one half of the fetuses received an intracardiac injection of potassium chloride to induce gasping just before necropsy. Gasping was confirmed by ultrasound scanning. At necropsy, the fetal lungs were evaluated grossly and underwent histomorphometry for iron distribution and quantification in the fetal airways.

RESULTS

In the animals that received iron dextran, there was no significant difference in iron accumulation at any time point between those animals that did and did not receive potassium chloride, which suggests that acute gasping does not increase the accumulation of amniotic fluid substances in the lungs. The amount of iron in the fetal airways increased significantly with progressive length of exposure.

CONCLUSION

We conclude that normal fetal breathing, not acute asphyxial gasping, resulted in the movement of intra-amniotic iron dextran into the fetal lungs and that the amount of substances that move into the fetal lungs accumulated with time.

Optimized, highly efficient transfer of foreign genes into newborn mouse hearts in vivo

Expression of foreign genes in vivo is a standard method to disclose functions of specific genes and to alter physiological conditions in distinct cell types and tissues. Virus-mediated gene transfer has proved to be a valuable tool for directed gene expression in vivo complementary to transgenic approaches. However, several problems associated with routes of application, endurance of gene expression, and efficiency of infections still have to be solved. We have optimized a gene transfer protocol into hearts of newborn mice to achieve widespread long-lasting expression using adenoviral vectors. Intrathoracic injection of high-titer adenoviral preparations (10(8)pfu) led to expression of foreign genes in >71+/-8% of all heart cells for >50 days after infection without any morphological signs of cardiac malfunction, inflammation, or immune response. This approach might be adapted to long-term cellular studies in vivo since 5 months after infection up to 20% of all cardiac cells still expressed virally encoded genes. Successful and efficient expression of other gene of interest can be easily controlled by co-injection of low titers of a reporter vector encoding EGFP (10(6)pfu).

Stem cell and genetic therapies for the fetus

In the near future, prenatal therapy may include stem cell-based cellular therapy or gene therapy. There is considerable overlap in the rationale and potential applications for these 2 approaches. The purpose of this manuscript is to consider current progress in both areas relevant to prenatal treatment. Although clinical application is currently limited to a few highly selected disorders that are amenable to cellular therapy, there is reason to believe that a dramatic increase in application will occur in the near future.

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.

Delivery of adeno-associated virus vectors to the fetal retina: impact of viral capsid proteins on retinal neuronal progenitor transduction

The development of fetal ocular gene transfer may be useful as a therapeutic tool for the prevention of retinal genetic disorders with congenital or early clinical manifestations. In this study we explored the neural progenitor transduction patterns of adeno-associated virus (AAV) vectors following delivery to the developing retina. Recombinant vectors with the same genome carrying the enhanced green fluorescent protein (EGFP) transgene packaged in capsids of differing serotypes (serotypes 1, 2, and 5, termed AAV2/1, AAV2/2, and AAV2/5, respectively) were created. Delivery of the AAV vectors during early retinal development resulted in efficient and stable transduction of retinal progenitors. Vector surface proteins and the developmental status of the retina profoundly affected viral tropism and transgene distribution. The procedure is not detrimental to retinal development and function and therefore provides a safe delivery vehicle for potential therapeutic applications and a means of assessing the mechanisms of retina development and disease.

Effect of adeno-associated virus-specific immunoglobulin G in human amniotic fluid on gene transfer

Intra-amniotic administration of adeno-associated virus (AAV) vector may be an effective way to deliver gene therapy for treatment of congenital pulmonary and intestinal disorders. In an effort to understand potential barriers to intra-amniotic gene therapy better, we determined whether human amniotic fluid (AF) could act as an inhibitor of AAV2-mediated gene transfer. AF samples were obtained from 21 different human pregnancies during routine amniocentesis at 16-20 weeks of gestation. An immortalized fetal human tracheal epithelial cell line (FHTE) was infected with AAV2 containing a luciferase reporter gene driven by the SV40 promoter in the presence and absence of each AF sample. Inhibition of transgene expression was observed in 8 (38%) of the AF samples (inhibitory AF) and resulted in luciferase levels of only 1.4% +/- 0.6% of those obtained with infection in normal media. Infections in 13 samples (62%) resulted in transgene expression comparable or in excess of infection in media alone (noninhibitory AF). Removal of immunoglobulin G (IgG) from inhibitory AF samples with Protein A returned luciferase expression to control levels (119% +/- 37% of control), suggesting the possible presence of inhibiting antibody. Eleven of the AF samples were evaluated by enzyme-linked immunosorbent assay (ELISA) for specific anti-AAV antibodies. All noninhibitory AF samples were negative (titers of < 1:20; n = 3), and 6 of the 8 inhibitory samples contained specific anti-AAV antibodies at titers ranging from 1:40 to 1:160. These studies demonstrate that AF from some individuals contains AAV-specific IgG that can inhibit gene transfer.

A preliminary evaluation of recombinant adeno-associated virus biodistribution in rhesus monkeys after intrahepatic inoculation in utero

The ability to deliver genes to fetuses in utero may prove crucial for those genetic diseases that are associated with severe fetal morbidity and for which there is no effective postnatal therapy. In utero therapy may be especially useful in diseases that affect the central nervous system because the immature blood-brain barrier may facilitate gene delivery to neural target cells. We investigated whether in utero inoculation of recombinant adeno-associated virus (rAAV) into rhesus monkey fetuses would be a useful method of gene delivery, especially to the central nervous system. When the monkeys were sacrificed after birth, we found vector genomes distributed in many tissues, including the brain and peripheral blood. Pericapillary astrocytes expressing transgene products were detected by immunohistochemistry. In addition, we occasionally found vector genomes in the maternal blood. No adverse clinical or pathologic effects were observed in the inoculated monkeys. We concluded that (1) in utero intrahepatic inoculation of rAAV is a potentially safe and useful method of delivering genes to many fetal tissues; (2) astrocytes may be the cell type most easily targeted in the central nervous system (CNS) after systemic administration; and (3) the potential of inadvertent gene transfer to the mother must be considered.

Adenovirus-mediated prenatal gene transfer to murine central nervous system

In some lysosomal storage disorders pathological alterations in the central nervous system (CNS) occur as early as the prenatal period and the neuropathology progresses rapidly soon after birth. In these diseases, postnatal therapies alone are often insufficient. Therefore prenatal gene therapy to the CNS may be necessary. In order to investigate the feasibility of gene transfer to the CNS prenatally, we administered recombinant adenovirus carrying LacZ gene to rat embryos from embryonic day 9 to 12 (E9-E12). Results showed that efficient transduction of the reporter gene to the CNS was achieved when adenoviruses were injected at E12. The regions where the reporter gene was transduced mainly localized at the telencephalon and hypophysis of the embryo, and the gene expression persisted at least 1 week after birth. In addition, when adenoviruses were injected at E9, E10 and E11, no transgene expression was detected in the CNS, but was mainly observed in the liver, the heart and the skin, respectively.

Fetal gene transfer by intrauterine injection with microbubble-enhanced ultrasound

Intrauterine injection of naked DNA expressing luciferase, green fluorescent protein (GFP), or beta-galactosidase (beta-gal) and fluorescein isothiocyanate-labeled oligodeoxynucleotide (FITC-ODN), in combination with microbubble-enhanced ultrasound (US), referred to as the "shotgun method" (SGM), produced high-level protein expression in fetal mice. With the SGM, luciferase expression increased approximately 10(3)-fold in comparison with expression after injection of naked DNA alone. Electron microscopic analysis demonstrated transient formation of pores on the skin surface after intraamniotic (i.a.) injection with the SGM. Widespread expression of GFP and beta-gal and delivery of FITC-ODN were observed in multiple fetal tissues adjacent to the injection points. PCR analysis indicated that germline transfection was only transient following intraperitoneal (i.p) injection, and there was no evidence of transfer of the reporter gene to the offspring. Thus, SGM might provide a useful means to clarify the molecular mechanisms of genetic diseases in utero, as well as a tool to develop gene therapies in utero.

Gene therapy and reproductive medicine

OBJECTIVE

To review the literature on the principles of gene therapy and its potential application in reproductive medicine.

DESIGN

Literature review.

SETTING

Gene therapy involves transfer of genetic material to target cells using a delivery system, or vector. Attention has primarily focused on viral vectors. Significant problems remain to be overcome including low efficacy of gene transfer, the transient expression of some vectors, safety issues with modified adenoviruses and retroviruses, and ethical concerns. If these issues can be resolved, gene therapy will be applicable to an increasing spectrum of single and multiple gene disorders, as the Human Genome Project data are analyzed, and the genetic component of human disease becomes better understood. Gynecologic gene therapy has advanced to human clinical trials for ovarian carcinoma, and shows potential for the treatment of uterine leiomyomata. Obstetric applications of gene therapy, including fetal gene therapy, remain more distant goals.

CONCLUSION(S)

Concerns about the safety of human gene therapy research are being actively addressed, and remarkable progress in improving DNA transfer has been made. The first treatment success for a genetic disease (severe combined immunodeficiency disease) has been achieved, and ongoing research efforts will eventually yield clinical applications in many spheres of reproductive medicine.

Use of genetically engineered mice in drug discovery and development: wielding Occam's razor to prune the product portfolio

Genetically engineered mice (GEMs) that either overexpress (transgenic) or lack (gene-targeted, or "knock-out") genes are used increasingly in industry to investigate molecular mechanisms of disease, to evaluate innovative therapeutic targets, and to screen agents for efficacy and/or toxicity. High throughput GEM construction in drug discovery and development (DDD) serves two main purposes: to test whether a given gene participates in a disease condition, or to determine the function(s) of a protein that is encoded by an expressed sequence tag (EST, an mRNA fragment for a previously uncharacterized protein). In some instances, phenotypes induced by such novel GEMs also may yield clues regarding potential target organs and toxic effects of potential therapeutic molecules. The battery of tests used in phenotypic analysis of GEMs varies between companies, but the goal is to define one or more easily measured endpoints that can be used to monitor the disease course--especially during in vivo treatment with novel drug candidates. In many DDD projects, overt phenotypes are subtle or absent even in GEMs in which high-level expression or total ablation of an engineered gene can be confirmed. This outcome presents a major quandary for biotechnology and pharmaceutical firms: given the significant expense and labor required to generate GEMs, what should be done with "negative" constructs? The 14th century philosophical principle known as Occam's razor-that the simplest explanation for a phenomenon is likely the truth-provides a reasonable basis for pruning potential therapeutic molecules and targets. In the context of DDD, Occam's razor may be construed to mean that correctly engineered GEMs lacking obvious functional or structural phenotypes have none because the affected gene is not uniquely essential to normal homeostasis or disease progression. Thus, a "negative" GEM construct suggests that the gene under investigation encodes a ligand or target molecule without significant therapeutic potential. This interpretation indicates that, at least in a market-driven industrial setting, such "negative" projects should be pruned aggressively so that resources may be redirected to more promising DDD ventures.

Lentiviral vector gene transfer into fetal rhesus monkeys (Macaca mulatta): lung-targeting approaches

We previously reported the efficiency of gene transfer in fetal monkeys using retroviral vectors and an intraperitoneal (IP) approach. Here, we explored intrapulmonary administration to determine whether gene transfer can be limited to the developing lung. The HIV-1-derived lentiviral vector (VSV-G pseudotyped; 1 x 10(7) infectious particles/fetus), using the enhanced green fluorescent protein (EGFP) as a reporter, was directly injected into fetal lung with ultrasound guidance (n=4; 55 or 70 days gestation; term 165+/-10 days). Fetuses were monitored sonographically, fetal/maternal blood samples collected during gestation, and four of four healthy newborns were delivered at term. All lung lobes were positive for the transgene (< or = 1%) when assessed by PCR, and transgene expression was observed by direct fluorescence microscopy and flow cytometry. The results of this study show the following: (1) successful gene transfer in fetal monkeys using an intrapulmonary approach; (2) less transduction of non-pulmonary tissues with gene transfer at 70 days gestation compared with 55 days gestation or use of an IP approach; (3) that the pulmonary epithelium was EGFP-positive by immunohistochemistry; and (4) no evidence of transplacental transport of vector sequences or antibody responses in the dams. The results of these investigations indicate the efficiency of fetal gene transfer by intrapulmonary delivery, and emphasize the importance of the fetal monkey as a preclinical model system for exploring in utero genetic treatment strategies for pulmonary disorders.

In utero AAV-mediated gene transfer to rabbit pulmonary epithelium

In utero intra-amniotic administration of adeno-associated virus (AAV) for treatment of cystic fibrosis (CF) has the potential to be an efficient way to target the rapidly dividing undifferentiated cells of the fetal pulmonary epithelium, while simultaneously treating other tissues involved in CF (such as the intestines), but has never before been studied. Intra-amniotic administration of 1x10(12) particles of AAV-luciferase vector to 110 fetal rabbits at 24-25 days gestation resulted in transgene expression in amniotic membranes, trachea, and pulmonary epithelium. The highest level of transgene expression was found in amniotic membranes. Transgene expression peaked in the lungs 10 days after vector delivery, decreased at day 17, and was no longer detectable after 24 days. The number of pulmonary cells transduced was approximately 1 in 500 and immunohistochemical analysis showed expression in varying cell types, including alveolar cells. Transgene expression was not detected in fetal rabbit intestines, skin or liver, nor in maternal ovaries or liver. Intra-amniotic administration of AAV does not result in the tissue inflammation and fetal loss previously documented with in utero adenoviral administration, and results in high levels of transgene expression in amniotic membranes with lower levels in fetal pulmonary epithelium.

Prospects for prenatal gene therapy in disorders causing mental retardation

Advances in understanding the genetics and pathogenesis of disease and in prenatal diagnosis have lead to an exploration of ways to intervene earlier and earlier in the disease process. The possibility of prenatal gene therapy for severe genetic and developmental disorders has sparked new research and debate as to its feasibility, reliability, and ethics as a therapeutic option. Recent animal studies have demonstrated the feasibility of introducing a vector into the developing fetus. The optimal timing and best mode of delivery, however, have yet to be defined. Whether or not this research should be pursued also has been the subject of recent bioethical debates. There is additional concern with the possibility of in utero gene transfer inducing mutagenesis and subsequent tumor formation. This review will provide a summary of the current state of knowledge in the field of prenatal gene therapy and possible directions for the future research.

In utero delivery of adeno-associated viral vectors: intraperitoneal gene transfer produces long-term expression

Recombinant adeno-associated viruses (rAAV) are promising gene transfer vectors that produce long-term expression without toxicity. To investigate future approaches for in utero gene delivery, the efficacy and safety of prenatal administration of rAAV were determined. Using luciferase as a reporter, expression was assessed by whole-body imaging and by analysis of luciferase activity in tissue extracts, at the time of birth and monthly thereafter. Transgene expression was detected in all injected animals. Highest levels of luciferase activity were detected at birth in the peritoneum and liver, while the heart, brain, and lung demonstrated low-level expression. In vivo luciferase imaging revealed persistent peritoneal expression for 18 months after in utero injection and provided a sensitive whole-body assay, useful in identifying tissues for subsequent analyses. There was no detectable hepatocellular injury. Antibodies that reacted with either luciferase or rAAV were not found. AAV sequences were not detected in germ-line tissues of injected animals or in tissues of their progeny. In utero AAV-mediated gene transfer in this animal model demonstrates that novel therapeutic vectors and strategies can be rapidly tested in vivo and that rAAV may be developed to ameliorate genetic diseases with perinatal morbidity and mortality.

Long-term gene transfer to mouse fetuses with recombinant adenovirus and adeno-associated virus (AAV) vectors

We have developed a micro-injection technique to deliver recombinant adenovirus and AAV to mouse fetuses at day 15 after conception. Several routes of delivery, including injections to the amniotic fluid, the front limb, the placenta, the liver, and the retro-orbital venus plexus, were tested using an E1-deleted recombinant adenovirus (Ad.CBlacZ) or a recombinant adeno-associated virus (AAV.CMVlacZ) carrying a beta-galactosidase (lacZ) gene. Injection of Ad.CBlacZ into the amniotic cavity led to transgene expression in the skin and in the digestive tract of the fetuses. Injection of Ad.CBlacZ in the front limb resulted in LacZ expression in all major muscle groups around the injection site and at low levels in the liver. The other three routes of delivery, ie intra-placental, intra-hepatic and retro-orbital injections of Ad.CBlacZ, all led to lacZ expression predominantly in the liver. Further studies revealed a maximal tolerant dose (defined as the highest viral dose with < or =20% mortality in the injected fetuses) of 1 x 10(9) particles per fetus for intra- hepatic injections, 3 x 10(9) particles per fetus for intra-placental injection, 1 x 1010 particles per fetus for retro-orbital and intra-amniotic injections, and 2 x 10(10) particle per fetus for intra-muscular injection. The adenovirus-mediated lacZ expression in liver and muscle persisted for at least 6 weeks. Intra-muscular injection of AAV.CMVlacZ also resulted in lacZ expression in the muscle up to 3 months after birth with no indication of cellular immune response at the injection site. Taken together, our results demonstrated that prolonged transgene expression can be achieved by in utero gene transfer using either adenoviral or AAV vectors. The distribution of virus-mediated gene transfer appeared to determined mostly by the route of viral administration.

Reexpression following readministration of an adenoviral vector in adult mice after initial in utero adenoviral administration

Adenovirus-mediated gene delivery is limited by the induction of immune responses that produce toxicity and prevent reexpression. To determine whether adenoviral delivery in the preimmune fetus would produce tolerance, we assessed luciferase (luc) expression following sequential pre- and postnatal adenoviral-mediated gene delivery. Day 15 fetuses were injected intrahepatically with 1 x 10(7) pfu of an adenoviral-luc vector (Ad-luc). Following in utero injection, hepatic luc expression persisted 1 month postnatally. No humoral response to adenovirus or luc was detected. Adult mice, previously injected in utero, were reinjected intravenously with 5 x 10(8) pfu of Ad-luc at 3 months of age and again at 6 months with either 5 x 10(8) pfu of Ad-luc or cationic liposome-DNA complexes (CLDC). Following the first postnatal injection, animals injected in utero had levels of luc comparable to those of age-matched naive controls. However, both control and experimental animals subsequently developed antibodies to adenovirus and luc. No further expression was achieved with a second postnatal injection of Ad-luc or with delivery of CLDC-luc. These studies demonstrate that the delivery of adenoviral vectors in utero at E15 does not elicit an immune response. However, delivery of recombinant adenovirus postnatally results in brisk and limiting immune responses regardless of the in utero exposure.

Adenovirus-mediated in utero gene transfer in mice and guinea pigs: tissue distribution of recombinant adenovirus determined by quantitative TaqMan-polymerase chain reaction assay

Fetal somatic cell gene therapy could become an attractive solution for some congenital genetic diseases or the disorders which manifest themselves during the fetal period. We performed adenovirus-mediated gene transfer to mice and guinea pig fetuses in utero and evaluated the efficiency of gene transfer by histochemical analysis and a quantitative TaqMan-polymerase chain reaction (TaqMan-PCR) assay. We first injected a replication-deficient recombinant adenovirus containing the Escherichia coli LacZ gene driven by a CAG promoter (AxCALacZ) into pregnant mice through the amniotic space, placenta, or intraperitoneal space of the fetus. Histochemical analysis showed limited transgene expression in fetal tissues. We then administered AxCALacZ to guinea pig fetuses in the late stage of pregnancy through the umbilical vein. The highest beta-galactosidase expression was observed in liver followed by moderate expression in heart, spleen, and adrenal gland. The transgene expression was also present in kidney, intestine, and placenta to a lesser degree. No positively stained cells were observed in lung, muscle, or pancreas except in the vascular endothelium of these organs. Quantitative measurement of recombinant adenoviral DNA by the TaqMan-PCR assay showed that the vast majority of the injected viruses was present in liver. The current study indicated that adenovirus-mediated gene transfer into guinea pig fetus through the umbilical vein is feasible and results in efficient transgene expression in fetal tissues. The experimental procedures using pregnant guinea pigs might serve as a good experimental model for in utero gene transfer. Since our TaqMan-PCR assay detects the LacZ gene, one of the most widely used reporter genes, it may be generally applicable to adenovirus quantification in various gene transfer experiments.

High-efficiency, long-term cardiac expression of foreign genes in living mouse embryos and neonates

BACKGROUND

The development of improved strategies for efficient and reproducible in vivo gene transfer into the murine heart will ultimately allow the intersection of somatic and germline gene transfer strategies to study complex features of cardiac biology and diseases.

METHODS AND RESULTS

For embryonic gene transfer, an adenovirus vector expressing beta-galactosidase was injected in utero into the ventricular cavity of living embryos via microsurgical approaches. The injected embryos were developed to term, and efficient expression of the transgene was detected in all cell types in the heart. For postnatal cardiac gene transfer, adenovirus was injected into the cardiac ventricle of neonatal mice, resulting in efficient expression of the transgene in the outer layer of the myocardium as well as cardiomyocytes in the middle and inner layers of the cardiac wall. Mice examined after 3 weeks displayed a pattern of expression that completely mimicked the pattern seen after 3 days, and gene expression was also found after 6 months. The infected myocytes can be identified by coinfection of an adenovirus expressing green fluorescent protein without affecting their normal physiological function.

CONCLUSIONS

We have developed a new strategy to achieve efficient and long-term foreign gene expression in both embryonic and postnatal mouse myocardium via direct intracardiac injection of recombinant adenovirus. The strategy should allow the functional assessment of the expression of dominantly acting exogenous genes, overexpression of wild-type genes, and Cre recombinase-mediated gene ablations at the single-cell level in the context of the intact adult mouse myocardium.

Prospects for fetal gene therapy

Advances in prenatal diagnosis and gene transfer technology have allowed consideration of prenatal gene therapy. A compelling argument can be made for this strategy in treating genetic diseases that are fatal in the prenatal or perinatal period. In other diseases, the fetal environment may offer unique biological advantages that favor a prenatal gene therapy strategy over treatment after birth. Although issues of safety and efficacy must be resolved before clinical application, the development of fetal gene therapy may become a new molecular therapeutic arm in the field of prenatal intervention.

Short-term correction of factor VIII deficiency in a murine model of hemophilia A after delivery of adenovirus murine factor VIII in utero

Development of in utero gene transfer approaches may provide therapies for genetic disorders with perinatal morbidity. In hemophilia A, prenatal and postnatal bleeding may be catastrophic, and modest increments in factor VIII (FVIII) activity are therapeutic. We performed transuterine i.p. gene transfer at day 15 of gestation in a murine model of hemophilia A. Normal, carrier (X(H)X), and FVIII-deficient (X(H)Y and X(H)X(H)) fetuses injected with adenoviral vectors carrying luciferase or beta-galactosidase reporter genes showed high-level gene expression with 91% fetal survival. The live-born rates of normal and FVIII-deficient animals injected in utero with adenovirus murine FVIII (3.3 x 10(5) plaque-forming units) was 87%. FVIII activity in plasma was 50.7 +/- 10.5% of normal levels at day 2 of life, 7.2 +/- 2.2% by day 15 of life, and no longer detectable at day 21 of life in hemophilic animals. Injection of higher doses of murine FVIII adenovirus at embryonic day 15 produced supranormal levels of FVIII activity in the neonatal period. PCR analysis identified viral genomes primarily in the liver, intestine, and spleen, although adenoviral DNA was detected in distal tissues when higher doses of adenovirus were administered. These studies show that transuterine i.p. injection of adenoviral vectors produces therapeutic levels of circulating FVIII throughout the neonatal period. The future development of efficient and persisting vectors that produce long-term gene expression may allow for in utero correction of genetic diseases originating in the fetal liver, hematopoietic stem cells, as well as other tissues.

Therapeutic plasma concentrations of human factor IX in mice after gene delivery into the amniotic cavity: a model for the prenatal treatment of haemophilia B

BACKGROUND

Several groups including our own have reported gene delivery to fetal organs by vector administration into the amniotic cavity. Based on these studies we hypothesised that the large surface of the fetal skin may be exploitable for high level production of systemically required gene products to be released into the fetal circulation.

METHODS

We administered E1/E3-deleted adenoviral vectors carrying a bacterial beta-galactosidase gene or the human coagulation factor IX gene into the amniotic cavities of mid- to late-gestation mouse fetuses. The concentrations of human factor IX in the plasma of fetal or new-born mice were determined by ELISA. Reverse transcription PCR was used to identify sites of transgene expression.

RESULTS

Application of 5 x 10(8) infectious units of the factor IX gene vector in utero resulted in plasma concentrations of human factor IX of up to 1.2 microg/ml without significant decrease in fetal survival. Transgenic protein was found to be produced in the fetal skin, mucosae and amniotic membranes and was shown to be present for several days after birth of healthy pups.

CONCLUSION

As ultrasound-guided amniocentesis in humans is a well-established diagnostic procedure, delivery of the factor IX gene into the amniotic cavity appears to be a safe route for prenatal treatment of haemophilia B and may prevent haemorrhagic complications such as intracranial bleeding during delivery. Our study allowed for the first time a quantification of the expression of a potentially therapeutic transgene in rodents after prenatal gene delivery. It thus provides a model for the prenatal treatment of haemophilia B, but may also serve as a pathfinder to gene therapy of inheritable skin disorders such as epidermolysis bullosa.

Ultrasonographically guided direct gene transfer in utero: successful induction of beta-galactosidase in a rabbit model

OBJECTIVE

We sought to determine whether the transfer of enzyme-encoding genes in utero can be detected after birth.

STUDY DESIGN

An adenoviral vector carrying the gene for beta-galactosidase was injected under ultrasonographic guidance into the livers of 4 rabbit fetuses per litter (3 litters total) at 27 days' gestation. On delivery of the pups 2 to 3 days later, the livers were analyzed for beta-galactosidase activity by using 5-bromo-4-chloro-3-indolyl-beta-D -galactopyranoside (X-gal) staining. Polymerase chain reaction was also performed on liver extracts as an additional independent measure of successful vector delivery.

RESULTS

Successful targeting of the livers of fetal rabbits was demonstrated by beta-galactosidase activity in the nuclei of liver serosal cells, parenchymal hepatocytes, or columnar cells of the gallbladder in 7 (58%) of 12 injected pups and by polymerase chain reaction in liver extracts from 10 (83%) of 12 injected pups.

CONCLUSIONS

These results suggest that vectors that carry genes for specific enzymes can be delivered to fetal organs in utero and that expression of the enzyme can be detected after delivery.