In utero cardiac gene transfer via intraplacental delivery of recombinant adenovirus

Intraplacental injection of AAV9-CMV-iCre results in the widespread transduction of multiple organs in double-reporter mouse embryos

Adeno-associated virus serotype 9 (AAV9) has become a popular tool for gene transfer because of its ability to cross the blood-brain barrier and efficiently transduce genetic material into a variety of cell types. The study utilized GRR (Green-to-Red Reporter) mouse embryos, in which the expression of iCre results in the disappearance of Green Fluorescent Protein (GFP) expression and the detection of Discosoma sp. Red Fluorescent Protein (DsRed) expression by intraplacental injection. Our results demonstrate that AAV9-CMV-iCre can transduce multiple organs in embryos at developmental stages E9.5-E11.5, including the liver, heart, brain, thymus, and intestine. These findings suggest that intraplacental injection of AAV9-CMV-iCre is a viable method for the widespread transduction of GRR mouse embryos.

Recent Genome-Editing Approaches toward Post-Implanted Fetuses in Mice

Genome editing, as exemplified by the CRISPR/Cas9 system, has recently been employed to effectively generate genetically modified animals and cells for the purpose of gene function analysis and disease model creation. There are at least four ways to induce genome editing in individuals: the first is to perform genome editing at the early preimplantation stage, such as fertilized eggs (zygotes), for the creation of whole genetically modified animals; the second is at post-implanted stages, as exemplified by the mid-gestational stages (E9 to E15), for targeting specific cell populations through in utero injection of viral vectors carrying genome-editing components or that of nonviral vectors carrying genome-editing components and subsequent in utero electroporation; the third is at the mid-gestational stages, as exemplified by tail-vein injection of genome-editing components into the pregnant females through which the genome-editing components can be transmitted to fetal cells via a placenta-blood barrier; and the last is at the newborn or adult stage, as exemplified by facial or tail-vein injection of genome-editing components. Here, we focus on the second and third approaches and will review the latest techniques for various methods concerning gene editing in developing fetuses.

In vivo genome editing targeted towards the female reproductive system

The discovery of sequence specific nucleases such as ZFNs, TALENs, and CRISPR/Cas9 has revolutionized genome editing. The CRISPR/Cas9 system has particularly emerged as a highly simple and efficient approach towards generating genome-edited animal models of most of the experimental species. The limitation of these novel genome editing tools is that, till date, they depend on traditional pronuclear injection (PI)-based transgenic technologies developed over the last three decades. PI requires expensive micromanipulator systems and the equipment operators must possess a high level of skill. Therefore, since the establishment of PI-based transgenesis, various research groups worldwide have attempted to develop alternative and simple gene delivery methods. However, owing to the failure of chromosomal integration of the transgene, none of these methods gained the level of confidence as that by the PI method in order to be adapted as a routine approach. The recently developed genome editing systems do not require complicated techniques. Therefore, presently, attention is being focused on non-PI-based gene delivery into germ cells for simple and rapid production of genetically engineered animals. For example, a few reports during the previous 1-2 years demonstrated the use of electroporation (EP) in isolated zygotes that helped to overcome the absolute dependency on PI techniques. Recently, another breakthrough technology called genome editing via oviductal nucleic acids delivery (GONAD) that directly delivers nucleic acids into zygotes within the oviducts in situ was developed. This technology completely relieves the bottlenecks of animal transgenesis as it does not require PI and ex vivo handling of embryos. This review discusses in detail the in vivo gene delivery methods targeted towards female reproductive tissues as these methods that have been developed over the past 2-3 decades can now be re-evaluated for their suitability to deliver the CRISPR/Cas9 components to produce transgenic animals. This review also provides an overview of the latest advances in CRISPR-enabled delivery technologies that have caused paradigm shifts in animal transgenesis methodologies.

Placenta-directed gene therapy for fetal growth restriction

Fetal growth restriction (FGR) is a serious pregnancy complication affecting ∼8% of all pregnancies. There is no treatment to increase fetal growth in the uterus. Gene therapy presents a promising treatment strategy for FGR, with the use of adenoviral vectors encoding for proteins such as vascular endothelial growth factor (VEGF) and insulin-like growth factor demonstrating improvements in fetal growth, placental function, and neonatal outcome in preclinical studies. Safety assessments suggest no adverse risk to the mother or fetus for VEGF maternal gene therapy; a clinical trial is in development. This review assesses research into placenta-directed gene therapy for FGR, investigating the use of transgenes and vectors, their route of administration in obstetrics, and the steps that will be needed to take this treatment modality into the clinic.

Enhanced in vivo gene transfer into the placenta using RGD fiber-mutant adenovirus vector

Among viral vectors, the fiber-mutant adenovirus vector carrying the Arg-Gly-Asp (RGD) peptide sequence (Ad-RGD) seems to have potential for both clinical gene therapy and basic research. As a part of a thorough evaluation of Ad-RGD in preclinical studies, we designed an experiment to investigate in detail the distribution of Ad-RGD compared with conventional adenovirus vector (WT-Ad) in pregnant mice. Surprisingly, Ad-RGD had substantial placental tropism, at 10-100 times that of WT-Ad. Transgene expression was sustained for at least 7 days, and Ad-RGD expressing firefly luciferase or red fluorescent protein has so far caused no placental dysfunction leading to fetal death. Ad-RGD showed high levels of transduction efficiency in in vitro-differentiated trophoblast stem cells, in which higher expression of αvβ3 integrin than in undifferentiated cells was observed. Our results suggest that the use of Ad-RGD or another RGD-mediated targeting strategy holds promise for drug delivery to the placenta.

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.

Fetal gene therapy: opportunities and risks

Advances in human prenatal medicine and molecular genetics have allowed the diagnosis of many genetic diseases early in gestation. In-utero transplantation of allogeneic hematopoietic stem cells (HSC) has been successfully used as a therapy in different animal models and recently also in human fetuses. Unfortunately, clinical success of this novel treatment is limited by the lack of donor cell engraftment in non-immunocompromised hosts and is thus restricted to diseases where the fetus is affected by severe immunodeficiency. Gene therapy using genetically modified autologous HSC circumvents allogeneic HLA barriers and constitutes one of the most promising new approaches to correct genetic deficits in the fetus. Recent developments of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells include the use of new vector constructs and transduction protocols. These improvements open new perspectives for gene therapy in general and for prenatal gene transfer in particular. The fetus may be especially susceptible for successful gene therapy due to the immunologic naiveté of the immature hematopoietic system during gestation, precluding an immune reaction towards the transgene. Ethical issues, in particular those regarding treatment safety, must be taken into account before clinical trials with fetal gene therapy in human pregnancies can be initiated.

Perinatal stem-cell and gene therapy for hemoglobinopathies

Most genetic diseases of the lymphohematopoietic system, including hemoglobinopathies, can now be diagnosed early in gestation. However, as yet, prenatal treatment is not available. Postnatal therapy by hematopoietic stem cell (HSC) transplantation from bone marrow, mobilized peripheral blood, or umbilical cord blood is possible for several of these diseases, in particular for the hemoglobinopathies, but is often limited by a lack of histocompatible donors, severe treatment-associated morbidity, and preexisting organ damage that developed before birth. In-utero transplantation of allogeneic HSC has been performed successfully in various animal models and recently in humans. However, the clinical success of this novel treatment is limited to diseases in which the fetus is affected by severe immunodeficiency. The lack of donor cell engraftment in nonimmunocompromised hosts is thought to be due to immunologic barriers, as well as to competitive fetal marrow population by host HSCs. Among the possible strategies to circumvent allogeneic HLA barriers, the use of gene therapy by genetically corrected autologous HSCs in the fetus is one of the most promising approaches. The recent development of strategies to overcome failure of efficient transduction of quiescent hematopoietic cells using new vector constructs and transduction protocols opens new perspectives for gene therapy in general, as well as for prenatal gene transfer in particular. The fetus might be especially susceptible for successful gene therapy approaches because of the developing, expanding hematopoietic system during gestation and the immunologic naiveté early in gestation, precluding immune reaction towards the transgene by inducing tolerance. Ethical issues, in particular regarding treatment safety, must be addressed more closely before clinical trials with fetal gene therapy in human pregnancies can be initiated.

Gabor Than Award Lecture 2006: pre-eclampsia and villous trophoblast turnover: perspectives and possibilities

Placental apoptosis is exaggerated in pre-eclampsia and cytotrophoblast proliferation is enhanced. This imbalance may be a primary pathogenic event, whereby excessive syncytiotrophoblast apoptosis counters cytotrophoblast fusion, promoting the liberation of syncytial material which perturbs the maternal vascular endothelium. We have previously shown that primary trophoblasts and explant cultured villous fragments from pre-eclamptic pregnancies elicit greater levels of terminal differentiation and apoptosis. This review considers current opinions in trophoblast cell turnover in normal pregnancy and pre-eclampsia. In the context of other findings, this review highlights: (i) the disparity in expression of pro-apoptotic transcription factor p53 in the syncytiotrophoblast in pre-eclampsia, (ii) the importance of reactive oxygen species and hypoxia in initiating villous trophoblast apoptosis and (iii) the concept that aberrant intervillous haemodynamics, as opposed to oxygen per se, initiates excessive syncytiotrophoblast shedding. Finally, therapeutic ways of restoring the syncytiotrophoblast in pre-eclampsia and preventing excessive placental apoptosis are considered, including a role for mitotic manipulators and growth factor replacement strategies.

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.

No evidence for germ-line transmission following prenatal and early postnatal AAV-mediated gene delivery

BACKGROUND

Recombinant adeno-associated viruses have been used successfully in a number of pre-clinical and clinical gene therapy studies. Since there is a broad consensus that gene therapy must not lead to germ-line transmission, the potential of such vectors for inadvertent gene transfer into germ cells deserves special attention. This applies in particular to pre- or perinatal vector application which has been considered for diseases presenting with morbidity already at birth.

METHODS

AAV serotype 2 derived vectors carrying a beta-galactosidase reporter gene or human clotting factor IX cDNA were injected intraperitoneally or via a yolk sac vein into mouse fetuses or administered intravascularly to newborn mice. Tissue samples of the treated animals including the gonads as well as sperm DNA, obtained by differential lysis of one testis of each male animal, and the offspring of all treated mice were investigated for the presence of vector DNA by nested PCR. In positive samples, the copy number of the vector was determined by quantitative real-time PCR.

RESULTS

AAV vectors administered intraperitoneally or intravascularly to fetal or newborn mice reached the gonads of these animals and persisted there for time periods greater than one year. Intravascular injection of the vector resulted more frequently in gene transfer to the gonads than intraperitoneal injection. Vector copy numbers in the gonads ranged from 0.3 to 74 per 10(4) cell equivalents. However, neither in isolated sperm DNA from the treated animals nor in their offspring were vector sequences detectable.

CONCLUSIONS

These data suggest the risk of inadvertent germ-line transmission following prenatal or early postnatal AAV type 2 mediated gene delivery to be very low.

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.

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).

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.

Possible mechanism of gene transfer into early to mid-gestational mouse fetuses by tail vein injection

Our aim is to develop a simple gene transfer method into egg cylinder and mid-gestational murine embryos. We examined whether plasmid/lipid complexes injected into the tail veins of pregnant transgenic mice can be transferred to fetuses at E 4.5-13.5. When pregnant CETZ-17 mice carrying a transgene consisting of a ubiquitous promoter, floxed EGFP/CAT and the LacZ gene, were injected with a Cre expression vector DNA/lipid complex, Cre-mediated excision of the transgenes, as evaluated by X-gal staining, occurred in 10-50% of fetuses treated at E 11.5-13.5. Although younger embryos remained unstained, PCR analysis revealed low levels of the Cre vector DNA and recombined transgene. To examine the fate of a solution given intravenously, we injected trypan blue or fluorescence-labeled plasmid DNA/lipid complexes into females at E 5.5-11.5 and E 6.5, respectively. Both collected in the visceral endoderm (VE) lineage, but were undetectable in the embryo proper. These findings suggest that substances in maternal blood are delivered to post-implantation embryos via cells of the VE lineage and placenta, but that most are trapped in the VE. If significantly improved, gene transfer to fetuses by injection into the maternal circulation may become a promising tool in fetal gene therapy and embryological studies.

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.

Sustained delivery of therapeutic concentrations of human clotting factor IX--a comparison of adenoviral and AAV vectors administered in utero

BACKGROUND

Prenatal somatic gene therapy has been considered for genetic disorders presenting with morbidity at birth. Haemophilia is associated with an increased risk of catastrophic perinatal bleeding complications such as intracranial haemorrhage, which could be prevented by gene transfer in utero. Prenatal gene therapy may be more promising than postnatal treatment, as the fetus may be more amenable to uptake and integration of therapeutic DNA and the immaturity of its immune system may permit life-long immune tolerance of the transgenic protein, thus avoiding the dominant problem in haemophilia treatment, the formation of inhibitory antibodies.

METHODS

Adenovirus serotype 5-derived or AAV serotype 2-derived vectors carrying human clotting factor IX (hfIX) cDNA or a reporter gene were administered intramuscularly, intraperitoneally or intravascularly to late-gestation mouse fetuses. Both vector types were evaluated with respect to the kinetics of hfIX delivery to the systemic circulation and possible immune responses against the vector or the transgene product.

RESULTS

Mice treated in utero by intramuscular injection of an adenoviral vector carrying hfIX cDNA exhibited high-level gene expression at birth and therapeutic--albeit continuously decreasing--plasma concentrations of hfIX over the entire 6 months of the study. Adenoviral vector spread to multiple organs was detected by polymerase chain reaction (PCR). Intramuscular, intraperitoneal or intravascular application of AAV vectors carrying hfIX cDNA led to much lower plasma concentrations of hfIX shortly after birth, which appeared to decline during the first month of life but stabilized in some of the mice at detectable levels. No signs of immune responses were found, either against the different viral vectors or against hfIX.

CONCLUSION

This study demonstrates for the first time that sustained systemic delivery of a therapeutic protein can be achieved by prenatal gene transfer. It thus shows the feasibility of gene therapy in utero and provides a basis for considering this concept as a preventive therapeutic strategy for haemophilia and perhaps also for other plasma protein deficiencies.

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.

Angiographically guided utero-placental gene transfer in rabbits with adenoviruses, plasmid/liposomes and plasmid/polyethyleneimine complexes

We examined the feasibility of gene transfer to rabbit placenta using adenoviruses, plasmid/liposomes and plasmid/polyethyleneimine (PEI) complexes. Pregnant New Zealand White rabbits (n = 17) were anesthetized and local gene transfer was done via a catheter inserted in uterine arteries under direct angiographic control. Either nuclear targeted LacZ adenoviruses (1.0 x 10(10) p.f.u.), nuclear targeted LacZ plasmid (500 microg)/liposome (DOTMA:DOPE 1:1) complexes or nuclear targeted LacZ plasmid (250 microg)/PEI (25 kDa) complexes (charge ratio +/-4) were used. Animals were killed 3 days later and detection of the transgene expression was done by X-gal staining and RT-PCR. Adenovirus-mediated gene transfer resulted in a high transfection efficiency (34 +/- 10%) in placental trophoplastic cells. Very little, if any, transfection was seen in fetal membranes. Plasmid/liposomes and plasmid/PEI complexes led to a very low (<0.01%) transfection efficiency in trophoblastic cells, but some transfection was seen in fetal membranes. A total of 25 fetuses were analyzed for the presence of transgene at the time of death. In most fetuses expression of the LacZ gene was below the sensitivity of the X-gal staining, but expression was detected by PCR in 50%, 50% and 42% of the analyzed fetuses after adenoviral, plasmid/PEI and plasmid/liposome gene transfer, respectively. No major inflammatory changes were present in the transfected placentas as analyzed by general histology and macrophage- and T cell-specific immunostainings. We conclude that catheter-mediated intravascular gene transfer with adenoviruses can be used for the transfection of placental trophoplastic cells, but plasmid complexes are inefficient for this purpose. However, selective angiographically guided gene transfer also led to leakage of the vector to fetuses. Therefore, if gene therapy is developed for the treatment of placental disorders, the gene-vector combination should not be harmful to the fetus and the expression of the transgene should only occur in placenta.

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.

Prospects for gene therapy for inherited cardiomyopathies

Over the last few years the genes responsible for a number of genetic diseases of the cardiovascular system have been identified. These have included X-linked and autosomal dominant dilated cardiomyopathy, and hypertrophic cardiomyopathy. Genetic heterogeneity has been described in both of these diseases but a commonality of function has been apparent: defects in cytoskeletal proteins cause dilated cardiomyopathy and mutations in sarcomeric proteins cause hypertrophic cardiomyopathy. This led us to develop a 'final common pathway' hypothesis as a framework for selecting candidate genes for mutation screening in families with these diseases. The characterization of gene mutations has led to the development of therapies specifically targeting the defective protein or the pathway in which it is involved. These have included the use of pharmaceutical agents to replace or to antagonize the mutated protein, and replacement of the defective gene with a functional one (gene therapy). While early studies using gene therapy vectors were promising, translating studies in animals to viable therapeutic options for humans has remained problematic. There have been many publications describing the use of vectors to transduce target cells for the correction of gene defects, including recombinant retroviruses, adenoviruses, and adeno-associated viruses, as well as non-viral vectors. In this review we will discuss the identification of gene defects associated with cardiomyopathies, and the potential of gene therapy for the treatment of these diseases, as well as addressing some concerns related to the use of adenovirus-based vectors, a virus known to be an etiologic agent of acquired dilated cardiomyopathy.

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.

Detection of microorganisms in the tracheal aspirates of preterm infants by polymerase chain reaction: association of adenovirus infection with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is recognized as an important cause of morbidity and mortality in preterm infants. Because the role of congenital infections in BPD has been debated, the purpose of this study was to test the hypothesis that detection of infectious agents in tracheal aspirate samples was associated with the development of BPD. Tracheal aspirate samples were obtained within the 1st week of life and screened by polymerase chain reaction for adenovirus, cytomegalovirus, parvovirus, enteroviruses, Ureaplasma urealyticum, Mycoplasma hominis, Mycoplasma pneumoniae, and Chlamydia species. BPD was defined as persistent oxygen dependence at 28 d of age and 36 wk postconceptional age (PCA). Infants that expired before these time points were excluded from statistical analysis. Out of 89 infants studied, at 28 d of life, 13 had expired, 45 had BPD, and 31 had no BPD (controls). At 36 wk PCA, 15 infants expired, 39 still had BPD, and 35 did not. A significant increase in the frequency of adenovirus genome was identified in BPD patients compared with controls, both at 28 d of life (12/45 = 27% versus 1/31 = 3%: p< or =0.01) and at 36 wk PCA (10/39 = 29% versus 2/35 = 6%: p = 0.01). Other microorganisms were rarely detected and not associated with the development of BPD. This is the first study reporting the frequency of detection of adenovirus DNA in tracheal aspirate samples obtained during the 1st week of life from infants with BPD and suggests that prenatal acquisition may be important in the development of BPD.

Comparative in vivo approaches for selective adenovirus-mediated gene delivery to the placenta

Gene delivery to the placenta is one potential way of specifically modifying placental biological processes and fetal development. The aim of this study was to determine the most efficient and least invasive route of placental adenovirus delivery. The feasibility of adenovirus-mediated gene transfer to the rat placenta was addressed by maternal intravenous or direct intraplacental injection of adenoviral vectors expressing the glucose transporter GLUT3, a noncirculating integral membrane protein. Both routes led to transgene expression in the placenta. However, direct intraplacental delivery on day 14 of gestation yielded a higher transduction efficiency than maternal intravenous administration, and markedly reduced transgene expression in maternal liver. Most importantly, the amount of the GLUT3 transgene and the adenovirus itself in fetal tissues was only 1 to 3% of that found in the placenta. These results indicate that the nature of the transgene and the route of adenovirus administration are key parameters in selective placental somatic gene transfer. This novel strategy may prove useful for modifying a placental function without altering the fetal genome.

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.

Disruption of Trkb-mediated signaling induces disassembly of postsynaptic receptor clusters at neuromuscular junctions

Neurotrophins and tyrosine receptor kinase (Trk) receptors are expressed in skeletal muscle, but it is unclear what functional role Trk-mediated signaling plays during postnatal life. Full-length TrkB (trkB.FL) as well as truncated TrkB (trkB.t1) were found to be localized primarily to the postsynaptic acetylcholine receptor- (AChR-) rich membrane at neuromuscular junctions. In vivo, dominant-negative manipulation of TrkB signaling using adenovirus to overexpress trkB.t1 in mouse sternomastoid muscle fibers resulted in the disassembly of postsynaptic AChR clusters at neuromuscular junctions, similar to that observed in mutant trkB+/- mice. When TrkB-mediated signaling was disrupted in cultured myotubes in the absence of motor nerve terminals and Schwann cells, agrin-induced AChR clusters were also disassembled. These results demonstrate a novel role for neurotrophin signaling through TrkB receptors on muscle fibers in the ongoing maintenance of postsynaptic AChR regions.

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.

Intrauterine gene transfer: gestational stage-specific gene delivery in mice

Intrauterine gene transfer in mice by intraplacental microinjection of recombinant adenoviral or retroviral vectors carrying beta-galactosidase (beta-gal) reporter gene was analyzed in relation to gestational stage, viral titer and promoters. After injections of viral vectors on days 9.5, 11.5 or 14.5 post coitum (p.c.), embryos, fetuses and adult animals were analyzed for beta-gal expression on days 13.5 p.c., 18.5 p.c. and at 2 months of age, respectively. Injection of adenoviral vectors on day 9.5 or day 11.5 p.c. resulted in high beta-gal expression in the heart or liver, respectively. Injection on either day also gave expression in other tissues including vasculature and hindbrain. This temporal pattern of adenoviral transduction correlated with the expression level of integrin beta3 subunit, which is known to be a component involved in adenoviral transduction. Adenovirus-mediated intrauterine gene transfer resulted in persistent beta-gal expression in multiple cell foci in the liver and hearts of 2-month-old adult animals treated in utero, indicating stable integration of the transgene into the host cell genome at a low frequency. Although at low efficiency, injection of retroviral vector on day 9.5 and 11.5 p.c. resulted in beta-gal expression in embryonic liver, while day 9.5 p.c. injection resulted in persistent beta-gal expression in 2-month-old adult heart. This is the first study to show gestational stage-specific gene transfer via intraplacental microinjection of adenoviral vectors.

Prospects for in utero human gene therapy

Gene therapy for the treatment of disease in children and adults is being actively pursued at many medical centers. However, a number of genetic disorders result in irreversible damage to the fetus before birth. In these cases, as well as for those with genetic diseases who may benefit from therapy before symptoms are manifested, in utero gene therapy (IUGT) could be beneficial. Although some successes with in utero gene transfer have been reported in animals, significant questions remain to be answered before IUGT clinical trials would be acceptable. This review analyzes the state of the art and delineates the studies that still need to be performed before it would be appropriate to consider human IUGT.

Temporally regulated expression patterns following in utero adenovirus-mediated gene transfer

Developmental patterns of gene expression were determined following intravascular administration of adenovirus in utero, during sequential stages of murine development. Replication-deficient adenovirus (AdCMV.LacZ) was injected into yolk sac vessels of mouse embryos 12, 13, 15 and 18 days post-conception (d.p.c.). beta-Galactosidase (beta-gal) expression was evaluated 24-48 h after injection, at birth, and 5 weeks following normal delivery. Gene expression was detected in myocardial cells, endothelial cells of heart, lung, kidney, adrenal, gut, and in hepatocytes. The patterns of expression were distinct for each stage of virus administration and time-point of analysis. Intensity of individual organ expression varied with injection time-point, with the largest number of organs express- ing the transgene when embryos were injected at 15 d.p.c. beta-Gal activity was detected in only a subset of cells expressing the murine coxsackievirus and adenovirus receptor (CAR), indicating factors other than receptor distribution were responsible for the pattern of transgene expression observed. These studies begin to define critical parameters affecting intravascular gene delivery in utero and indicate that intrinsic developmental regulatory mechanisms may control exogenous gene expression. Intravenous administration of adenovirus provides a unique approach for in utero gene transduction and will be a useful adjunct in evaluating genes which have early lethal mutations.

Prenatal gene therapy: can the technical hurdles be overcome?

Fifty years ago, a medical breakthrough in the prenatal diagnosis of genetic disorders was made with the introduction of amniocentesis. Until recently, there was little hope that diseases diagnosed in utero could be treated before birth. Today, prenatal gene therapy is emerging as a new concept for treating pre- and postnatal manifestations of genetic diseases and developmental disorders. Research studies have generated a degree of optimism by demonstrating the feasibility of fetal gene transfer. Nevertheless, enthusiasm is tempered by the considerable technical and ethical issues raised by such studies. Undoubtedly, the future of prenatal gene transfer as a therapeutic approach for birth defects mostly depends on addressing and overcoming these concerns.