Characterization of Long-Term Survival of Syngeneic Hepatocytes in Rat Peritoneum

Hepatocyte transplantation is a potential therapy for both acute and chronic hepatic insufficiency and also for treatment of inborn errors of metabolism affecting the liver. The peritoneum is one site for implantation and has several advantages: cells implanted there can be easily identified and observed, and it has a relatively large capacity. Long-term survival using “pure” hepatocytes in the peritoneum have been disappointing. We hypothesized that cotransplantation of hepatocytes with nonparenchymal cells would help maintain differentiated hepatocyte function. Rat liver cells transplanted intraperitoneally into August rats were sacrificed at 7 days, 1, 3, 6, 9, and 12 months and analyzed for presence, basal proliferation, and functionality of hepatocytes. To demonstrate that ectopic hepatocytes remained susceptible to exogenous growth factors affecting cell proliferation, rats 9 and 12 months after transplantation were stimulated with tri-iodothyronine and KGF. Hepatocytes were identified 7 days to >12 months, by H&E and immunohistochemically, as ectopic islands in the omental fat. Functionality was confirmed by glycogen deposition. Basal proliferation in 7-day rats was 28.0 ± 10/1000 hepatocytes in ectopic islands (cf. 5.70 ± 2.7/1000 in recipient liver). Proliferation in ectopic islands was greater than host liver. Growth factor-stimulated proliferation in ectopic islands induced a 70-fold increase in DNA synthesis. In conclusion, hepatocytes transplanted with nonparenchymal cells survive, proliferate, and function in the peritoneum of normal rats, and respond to exogenous growth stimuli. Their survival and proliferation in the presence of a normal functioning liver has implications for the potential use of the peritoneal site clinically for supplementation of liver function in metabolic disorders.

Lentivirus-meditated frataxin gene delivery reverses genome instability in Friedreich ataxia patient and mouse model fibroblasts

Friedreich ataxia (FRDA) is a progressive neurodegenerative disease caused by deficiency of frataxin protein, with the primary sites of pathology being the large sensory neurons of the dorsal root ganglia and the cerebellum. FRDA is also often accompanied by severe cardiomyopathy and diabetes mellitus. Frataxin is important in mitochondrial iron-sulfur cluster (ISC) biogenesis and low-frataxin expression is due to a GAA repeat expansion in intron 1 of the FXN gene. FRDA cells are genomically unstable, with increased levels of reactive oxygen species and sensitivity to oxidative stress. Here we report the identification of elevated levels of DNA double strand breaks (DSBs) in FRDA patient and YG8sR FRDA mouse model fibroblasts compared to normal fibroblasts. Using lentivirus FXN gene delivery to FRDA patient and YG8sR cells, we obtained long-term overexpression of FXN mRNA and frataxin protein levels with reduced DSB levels towards normal. Furthermore, γ-irradiation of FRDA patient and YG8sR cells revealed impaired DSB repair that was recovered on FXN gene transfer. This suggests that frataxin may be involved in DSB repair, either directly by an unknown mechanism, or indirectly via ISC biogenesis for DNA repair enzymes, which may be essential for the prevention of neurodegeneration.

Transduction of fetal mice with a feline lentiviral vector induces liver tumors which exhibit an E2F activation signature

Lentiviral vectors are widely used in basic research and clinical applications for gene transfer and long-term expression; however, safety issues have not yet been completely resolved. In this study, we characterized hepatocarcinomas that developed in mice 1 year after in utero administration of a feline-derived lentiviral vector. Mapped viral integration sites differed among tumors and did not coincide with the regions of chromosomal aberrations. Furthermore, gene expression profiling revealed that no known cancer-associated genes were deregulated in the vicinity of viral integrations. Nevertheless, five of the six tumors exhibited highly significant upregulation of E2F target genes, of which a majority are associated with oncogenesis, DNA damage response, and chromosomal instability. We further show in vivo and in vitro that E2F activation occurs early on following transduction of both fetal mice and cultured human hepatocytes. On the basis of the similarities in E2F target gene expression patterns among tumors and the lack of evidence implicating insertional mutagenesis, we propose that transduction of fetal mice with a feline lentiviral vector induces E2F-mediated major cellular processes that drive hepatocytes toward uncontrolled proliferation culminating in tumorigenesis.

Relative proximity of chromosome territories influences chromosome exchange partners in radiation-induced chromosome rearrangements in primary human bronchial epithelial cells

It is well established that chromosomes exist in discrete territories (CTs) in interphase and are positioned in a cell-type specific probabilistic manner. The relative localisation of individual CTs within cell nuclei remains poorly understood, yet many cancers are associated with specific chromosome rearrangements and there is good evidence that relative territorial position influences their frequency of exchange. To examine this further, we characterised the complexity of radiation-induced chromosome exchanges in normal human bronchial epithelial (NHBE) cells by M-FISH analysis of PCC spreads and correlated the exchanges induced with their preferred interphase position, as determined by 1/2-colour 2D-FISH analysis, at the time of irradiation. We found that the frequency and complexity of aberrations induced were reduced in ellipsoid NHBE cells in comparison to previous observations in spherical cells, consistent with aberration complexity being dependent upon the number and proximity of damaged CTs, i.e. lesion proximity. To ask if particular chromosome neighbourhoods could be identified we analysed all radiation-induced pair-wise exchanges using SCHIP (statistics for chromosome interphase positioning) and found that exchanges between chromosomes (1;13), (9;17), (9;18), (12;18) and (16;21) all occurred more often than expected assuming randomness. All of these pairs were also found to be either sharing similar preferred positions in interphase and/or sharing neighbouring territory boundaries. We also analysed a human small cell lung cancer cell line, DMS53, by M-FISH observing the genome to be highly rearranged, yet possessing rearrangements also involving chromosomes (1;13) and (9;17). Our findings show evidence for the occurrence of non-random exchanges that may reflect the territorial organisation of chromosomes in interphase at time of damage and highlight the importance of cellular geometry for the induction of aberrations of varying complexity after exposure to both low and high-LET radiation.

Reduced chromosome aberration complexity in normal human bronchial epithelial cells exposed to low-LET γ-rays and high-LET α-particles

Purpose:

Cells of the lung are at risk from exposure to low and moderate doses of ionizing radiation from a range of environmental and medical sources. To help assess human health risks from such exposures, a better understanding of the frequency and types of chromosome aberration initially-induced in human lung cell types is required to link initial DNA damage and rearrangements with transmission potential and, to assess how this varies with radiation quality.

Materials and methods:

We exposed normal human bronchial lung epithelial (NHBE) cells in vitro to 0.5 and 1 Gy low-linear energy transfer (LET) γ-rays and a low fluence of high-LET α-particles and assayed for chromosome aberrations in premature chromosome condensation (PCC) spreads by 24-color multiplex-fluorescence in situ hybridization (M-FISH).

Results:

Both simple and complex aberrations were induced in a LET and dose-dependent manner; however, the frequency and complexity observed were reduced in comparison to that previously reported in spherical cell types after exposure to comparable doses or fluence of radiation. Approximately 1–2% of all exposed cells were categorized as being capable of transmitting radiation-induced chromosomal damage to future NHBE cell generations, irrespective of dose.

Conclusion:

One possible mechanistic explanation for this reduced complexity is the differing geometric organization of chromosome territories within ellipsoid nuclei compared to spherical nuclei. This study highlights the need to better understand the role of nuclear organization in the formation of exchange aberrations and, the influence three-dimensional (3D) tissue architecture may have on this in vivo.

The fetal mouse is a sensitive genotoxicity model that exposes lentiviral-associated mutagenesis resulting in liver oncogenesis

Genotoxicity models are extremely important to assess retroviral vector biosafety before gene therapy. We have developed an in utero model that demonstrates that hepatocellular carcinoma (HCC) development is restricted to mice receiving nonprimate (np) lentiviral vectors (LV) and does not occur when a primate (p) LV is used regardless of woodchuck post-translation regulatory element (WPRE) mutations to prevent truncated X gene expression. Analysis of 839 npLV and 244 pLV integrations in the liver genomes of vector-treated mice revealed clear differences between vector insertions in gene dense regions and highly expressed genes, suggestive of vector preference for insertion or clonal outgrowth. In npLV-associated clonal tumors, 56% of insertions occurred in oncogenes or genes associated with oncogenesis or tumor suppression and surprisingly, most genes examined (11/12) had reduced expression as compared with control livers and tumors. Two examples of vector-inserted genes were the Park 7 oncogene and Uvrag tumor suppressor gene. Both these genes and their known interactive partners had differential expression profiles. Interactive partners were assigned to networks specific to liver disease and HCC via ingenuity pathway analysis. The fetal mouse model not only exposes the genotoxic potential of vectors intended for gene therapy but can also reveal genes associated with liver oncogenesis.

A novel splice variant of the DNA-PKcs gene is associated with clinical and cellular radiosensitivity in a patient with xeroderma pigmentosum

BACKGROUND

Radiotherapy-induced DNA double-strand breaks (DSBs) are critical cytotoxic lesions. Inherited defects in DNA DSB repair pathways lead to hypersensitivity to ionising radiation, immunodeficiency and increased cancer incidence. A patient with xeroderma pigmentosum complementation group C, with a scalp angiosarcoma, exhibited dramatic clinical radiosensitivity following radiotherapy, resulting in death. A fibroblast cell line from non-affected skin (XP14BRneo17) was hypersensitive to ionising radiation and defective in DNA DSB repair.

AIM

To determine the genetic defect causing cellular radiation hypersensitivity in XP14BRneo17 cells.

METHODS

Functional genetic complementation whereby copies of human chromosomes containing genes involved in DNA DSB repair (chromosomes 2, 5, 8 10, 13 and 22) were individually transferred to XP14BRneo17 cells in an attempt to correct the radiation hypersensitivity. Clonogenic survival assays and gamma-H2AX immunofluorescence were conducted to measure radiation sensitivity and repair of DNA DSBs. DNA sequencing of defective DNA repair genes was performed.

RESULTS

Transfer of chromosome 8 (location of DNA-PKcs gene) and transfection of a mammalian expression construct containing the DNA-PKcs cDNA restored normal ionising radiation sensitivity and repair of DNA DSBs in XP14BRneo17 cells. DNA sequencing of the DNA-PKcs coding region revealed a 249-bp deletion (between base pairs 3656 and 3904) encompassing exon 31 of the gene.

CONCLUSION

We provide evidence of a novel splice variant of the DNA-PKcs gene associated with radiosensitivity in a patient with xeroderma pigmentosum and report the first double mutant in distinct DNA repair pathways being consistent with viability.

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.

Ultrasound-guided injection and occlusion of the trachea in fetal sheep

OBJECTIVES

To access the fetal sheep trachea by ultrasound-guided transthoracic injection in order to deliver gene therapy vectors or occlude the trachea with a detachable balloon.

METHODS

Fetal sheep were operated on at a mean gestational age of 102 (range, 81-116) days (term = 145 days). Under ultrasound guidance, either a 20-G spinal (for vector delivery) or a 16-G Kellett (for placement of an occlusive balloon) needle was inserted via the fetal thorax into the fetal trachea.

RESULTS

Using the 20-G spinal needle the trachea was accessed successfully in 33/36 fetuses, with 97% survival. Failure to inject was related to fetal position and gestational age. Blood vessel damage causing significant morbidity occurred in two fetuses (6%). Tracheal occlusion was achieved by puncturing the trachea with the 16-G needle and advancing an endoluminal balloon in three out of five attempts in a mean time of 17 (range, 16-19) min, with 100% survival. In one case, the balloon became sited within the accessory lobe bronchus and was not inflated. At postmortem examination 21 days later, all balloons remained inflated and occluded the trachea, and the lung-to-body weight ratio and airways morphometric indices were consistent with relative pulmonary hyperplasia in the obstructed lungs.

CONCLUSIONS

Ultrasound-guided transthoracic tracheal puncture is a reliable technique in fetal sheep, with low morbidity and mortality. Using this technique, a detachable endotracheal balloon can be placed to provoke pulmonary growth. Advances in needle design and balloon size may improve the success rate.

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

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

Factors influencing adenovirus-mediated airway transduction in fetal mice

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

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

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

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

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

Fetal and neonatal gene therapy: benefits and pitfalls

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

Characteristics of murine histidinaemia and its potential for genetic manipulation

BACKGROUND

Histidinaemia is an autosomal recessive disorder affecting the hepatic enzyme histidine ammonia lyase (histidase) resulting in elevated plasma and urinary histidine and is prototypic of a series of hepatic cytosolic enzyme defects.

AIMS

To characterise the physiology of murine histidinaemia with respect to histidine excretion and catabolism, and explore the potential for manipulating cellular and whole body histidase metabolism by gene transfer.

MATERIALS AND METHODS

We studied his/his mice which have a G to A substitution in the gene encoding histidase, using both in vitro transduction of isolated hepatocytes by lipofection with wild-type histidase cDNA, and in vivo transduction of whole liver using a retroviral construct.

RESULTS AND CONCLUSION

Histidase cDNA expression restored histidase activity in vivo and in vitro towards normal levels, demonstrated both at the cellular level and by whole body metabolic studies, establishing the potential of this model for the development of new gene therapeutic approaches.

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

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

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

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

Hepatic stem cells: from inside and outside the liver?

The liver is normally proliferatively quiescent, but hepatocyte loss through partial hepatectomy, uncomplicated by virus infection or inflammation, invokes a rapid regenerative response from all cell types in the liver to perfectly restore liver mass. Moreover, hepatocyte transplants in animals have shown that a certain proportion of hepatocytes in foetal and adult liver can clonally expand, suggesting that hepatoblasts/hepatocytes are themselves the functional stem cells of the liver. More severe liver injury can activate a potential stem cell compartment located within the intrahepatic biliary tree, giving rise to cords of bipotential transit amplifying cells (oval cells), that can ultimately differentiate into hepatocytes and biliary epithelial cells. A third population of stem cells with hepatic potential resides in the bone marrow; these haematopoietic stem cells may contribute to the albeit low renewal rate of hepatocytes, but can make a more significant contribution to regeneration under a very strong positive selection pressure. In such instances, cell fusion rather than transdifferentiation appears to be the underlying mechanism by which the haematopoietic genome becomes reprogrammed.

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

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

The Hopes and Fears of In Utero Gene Therapy for Genetic Disease—A Review

Somatic gene delivery in utero is a novel approach to gene therapy for genetic disease. It is based on the concept that application of gene therapy vectors to the fetus in utero may prevent the development of early disease related tissue damage, may allow targeting of otherwise inaccessible organs, tissues and still expanding stem cell populations and may also provide postnatal tolerance against the therapeutic transgenic protein. This review outlines the hypothesis and scientific background of in utero gene therapy and addresses some of the frequently expressed concerns raised by this still experimental, potentially preventive gene therapy approach. We describe and discuss the choice of vectors, of animal models and routes of administration to the fetus. We address potential risk factors of prenatal gene therapy such as vector toxicity, inadvertent germ line modification, developmental aberration and oncogenesis as well as specific risks of this procedure for the fetus and mother and discuss their ethical implications.

Mutational effects of retrovirus insertion on the genome of V79 cells by an attenuated retrovirus vector: implications for gene therapy

Attenuated retroviruses are currently the most widely used vectors in clinical gene therapy because of their potential to effect stable and permanent gene transfer. Since gene delivery is accompanied by random insertion of foreign genetic material into the recipient chromosomal DNA, the potential for insertional mutagenesis exists. In this study, we used a defective retrovirus vector containing a selectable marker, the hygromycin phosphotransferase gene, to investigate the mutagenic effects of vector integration on the mammalian genome. V79 Chinese hamster cells were infected with virus supernatants or by coculture with virus producer cells, and provirus insertion events occurred at low and high frequencies, respectively. The frequency of hprt mutagenesis was increased by a factor of 2.3 over the spontaneous hprt mutation frequency only following multiple provirus insertions/cell genome. Multiple provirus insertions (>3/genome) resulted in instability at the hprt locus in 63% of the virally induced hprt mutants, as indicated by rearrangements at the molecular level, whereas no rearrangements were found when the provirus copy number was 1-2/genome. To demonstrate direct proviral involvement in mutagenesis, the defective MLV vector was retrieved along with flanking genomic hprt sequences from one mutant, and localized within intron 5 of the hprt gene. These data suggest that provirus copy number is a key factor when considering the potential hazards of using retrovirus vectors for gene therapy.

Percutaneous ultrasound-guided injection of the trachea in fetal sheep: a novel technique to target the fetal airways

OBJECTIVE

To access the fetal airways percutaneously using ultrasound-guided injection of the fetal trachea in sheep.

METHODS

Adenoviral gene therapy vectors and transduction-enhancing agents were delivered to the trachea via a needle inserted through the thorax or the neck of late-gestation (0.9 term, n = 3) or mid-gestation (0.5-0.8 term, n = 18) fetal sheep using ultrasound guidance.

RESULTS

Injection of the trachea in the fetal thorax was successful in 16 out of 18 fetuses and achieved at the first attempt in 9 fetuses within 12 min [mean 7 min and 31 s +/- (SD) 3 min and 4 s]. Survival was 100%. Injecting the trachea in the neck was less successful.

CONCLUSIONS

The fetal trachea of the sheep can be safely accessed by percutaneous ultrasound-guided injection to deliver vectors directly to the fetal airways for gene therapy. It may also enable tracheal occlusion for the antenatal treatment of congenital diaphragmatic hernia without the need for endoscopy or open surgery.

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.

Characterization of long-term survival of syngeneic hepatocytes in rat peritoneum

Hepatocyte transplantation is a potential therapy for both acute and chronic hepatic insufficiency and also for treatment of inborn errors of metabolism affecting the liver. The peritoneum is one site for implantation and has several advantages: cells implanted there can be easily identified and observed, and it has a relatively large capacity. Long-term survival using "pure" hepatocytes in the peritoneum have been disappointing. We hypothesized that cotransplantation of hepatocytes with nonparenchymal cells would help maintain differentiated hepatocyte function. Rat liver cells transplanted intraperitoneally into August rats were sacrificed at 7 days, 1, 3, 6, 9, and 12 months and analyzed for presence, basal proliferation, and functionality of hepatocytes. To demonstrate that ectopic hepatocytes remained susceptible to exogenous growth factors affecting cell proliferation, rats 9 and 12 months after transplantation were stimulated with tri-iodothyronine and KGF. Hepatocytes were identified 7 days to >12 months, by H&E and immunohistochemically, as ectopic islands in the omental fat. Functionality was confirmed by glycogen deposition. Basal proliferation in 7-day rats was 28.0 +/- 10/1000 hepatocytes in ectopic islands (cf. 5.70 +/- 2.7/1000 in recipient liver). Proliferation in ectopic islands was greater than host liver. Growth factor-stimulated proliferation in ectopic islands induced a 70-fold increase in DNA synthesis. In conclusion, hepatocytes transplanted with nonparenchymal cells survive, proliferate, and function in the peritoneum of normal rats, and respond to exogenous growth stimuli. Their survival and proliferation in the presence of a normal functioning liver has implications for the potential use of the peritoneal site clinically for supplementation of liver function in metabolic disorders.

A novel human suspension culture packaging cell line for production of high-titre retroviral vectors

Retroviruses are currently the most widely used vectors in clinical trials for gene therapy. These vectors are, however, limited by low titres partly due to the restrictive nature of monolayer cell culture. We have developed a stable suspension producer cell line derived from human lymphoblastoid cells (WIL-2) by electroporating these cells with the necessary trans components required for production of defective retrovirus particles which encode a nuclear localising beta-galactosidase gene. We show that this anchorage-independent cell line generates viruses at a titre of 7 x 10(5) iu/ml on NIH3T3 indicator cells which remains constant after at least 2 months in culture. The producer cells can be cultured at a density of 6 x 10(6) cells/ml with consistent virus titre production. WIL-2 can also be grown as single cells by rotation culture while maintaining virus production. By treating the cells with the transcriptional activator sodium butyrate titres above 1 x 10(6) i.u./ml are achieved. Concentrating viral supernatants by ultrafiltration can further increase virus titre to 5 x 10(8) i.u./ml. Even at these high titres no replication-competent virus was detected. Virus titre fell only slightly when cells were placed in serum-free media before harvest. The generation of this novel cell line provides proof-of-principle that large-scale production of retroviral vectors in serum-free growth conditions can be safely generated for use in gene therapy.

Retargeting of adenoviral vectors to neurons using the Hc fragment of tetanus toxin

The Hc fragment of tetanus toxin (Hc) retains the specific nerve cell binding and transport properties of the holotoxin, but lacks any toxicity. We are investigating the potential for utilising its neurotropism for targeted gene delivery to the central nervous system. Previously we reported the use of Hc-polylysine conjugates for selective gene transfer into neuronal cells in vitro. However, as attempts to apply these constructs in vivo were not successful, we have extended these studies to modification of the tropism of adenoviral vectors. Either Hc-polylysine conjugates or the Fab fragment of a neutralising anti-knob antibody covalently bound to Hc were attached to the virus. Infection of neuronal and non-neuronal cell lines with retargeted virus showed highly increased neuronal cell selectivity, but no significant enhancement of gene delivery into these cells. High concentrations of free Hc blocked the infectivity of the retargeted vector efficiently. Intramuscular injection of retargeted virus into mouse tongues resulted in selective gene transfer to the neurons of the hypoglossal nucleus, where no pathological changes were observed. As differentiated neurons do not undergo cell division, appropriate vectors carrying a thymidine kinase gene, which allows selective elimination of dividing cells, may be exploitable for the treatment of tumours of the central nervous system. The demonstrated suitability of the Hc fragment of tetanus toxin as targeting moiety for viral vectors also indicates a potential for gene therapy of inherited neurodegenerative diseases such as spinal muscular atrophy.

Tri-iodothyronine and a deleted form of hepatocyte growth factor act synergistically to enhance liver proliferation and enable in vivo retroviral gene transfer via the peripheral venous system

Retroviral vectors integrate into the target cell genome in a stable manner and therefore offer the potential for permanent correction of the genetic diseases that affect the liver. These vectors, however, usually require cell division to occur in order to allow provirus entry into the nucleus. We have explored clinically acceptable methods to improve the efficiency of retroviral gene transfer to the liver, which avoid the need for liver damage. Tri-iodothyronine (T3) and recombinant hepatocyte growth factor have previously been used to induce hepatocyte proliferation in rat livers and allow in vivo retroviral gene transfer. We investigated the combined effects of these growth factors, with their differing mechanisms of action, on hepatocyte proliferation in vivo and assessed their effectiveness in priming cells for retroviral gene transfer. During the phase of hepatocyte proliferation retrovirus was administered via either the portal or tail vein. Acting synergistically, T3 and a truncated form of recombinant hepatocyte growth factor (dHGF) induced 30% of hepatocytes in normal rat liver to enter DNA synthesis at 24 h. This increased proliferation enabled the liver to be transduced in vivo by retroviral vectors via either the portal or peripheral venous system, achieving transduction efficiencies of 6.9 +/- 1.6% and 4.3 +/- 0.4% respectively. Thus, the liver can be simply and conveniently transduced in vivo with integrating vectors, introduced via the peripheral venous system during a wave of growth factor-induced proliferation, pointing the way to clinically applicable gene transfer techniques.

Selective in vivo transfection of murine biliary epithelia using polycation-enhanced adenovirus

We have investigated the use of polycations to increase adenovirus-mediated expression of transgenic protein to the biliary epithelia with a view to gene therapy for hepatobiliary disease in CF. We have shown that adenovirus carrying the beta-galactosidase transgene transfect both human and mouse biliary epithelia in primary culture and that in both instances adenovirus transfection can be significantly increased by co-complexing with polycation. In vivo administration of 1 x 109 p.f.u. adenovirus co-complexed with the polyamine polyethyenimine (PEI) into the mouse biliary duct leads to >80% positively stained biliary epithelia while adenovirus alone at the same titre infected <5% biliary epithelia. We suggest that the use of low titre polycation enhanced adenoviral delivery to the biliary tree of CF patients could be of therapeutic significance. As a prelude to an extensive in vivo functional investigation in CF null mice we have shown that Ad5/polycation complexes deliver functional CFTR to non-CFTR expressing cells in vitro more efficiently than Ad5 alone.

Synergistic growth factors enhance rat liver proliferation and enable retroviral gene transfer via a peripheral vein

BACKGROUND & AIMS

Genetic diseases reflecting abnormal hepatocyte function are potentially curable through gene therapy. Retroviral vectors offer the potential for permanent correction of such conditions. These vectors generally require cell division to occur to allow provirus entry into the nucleus, initiated in many experimental protocols by partial hepatectomy. We have explored methods to improve the efficiency of retroviral gene transfer that avoid the need for liver damage.

METHODS

Triiodothyronine (T3) and keratinocyte growth factor (KGF) were used to induce hepatic proliferation in rats. The effects of intraportal and peripheral administration of a modified retrovirus that encoded the Lac Z gene during growth factor-induced liver hyperplasia were analyzed.

RESULTS

T3 initiated hepatocyte proliferation midzonally; after KGF, proliferation was more diffuse. Optimal concentrations of T3 and KGF acted synergistically to induce proliferation in 61% of hepatocytes in the intact liver. This enabled in vivo hepatocyte transduction, leading to gene expression by up to 7.3% of hepatocytes after intraportal retroviral vector administration and 7. 1% after peripheral venous administration.

CONCLUSIONS

T3 and KGF act synergistically to induce hepatocyte proliferation in undamaged liver. The liver can be simply transduced with integrating vectors via the peripheral venous system during a wave of growth factor-induced proliferation.

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.

Successful expression of beta-galactosidase and factor IX transgenes in fetal and neonatal sheep after ultrasound-guided percutaneous adenovirus vector administration into the umbilical vein

In utero somatic gene therapy in the later stages of pregnancy may allow targeting of organ systems which are difficult to reach later in life and to prevent the development of tissue damage otherwise caused by the early onset of inherited diseases. We report here on the percutaneous delivery of two adenoviral vectors, containing the beta-galactosidase reporter gene and the human Factor IX gene respectively, to the fetal liver and circulation by ultrasound-guided umbilical vein puncture similar to procedures used in human pregnancy. Vector spread, as detected by PCR analysis for the beta-galactosidase encoding vector, was found in almost all fetal and neonatal organs and in the maternal liver. Expression of the beta-galactosidase transgene was detected in many fetal tissues by RT-PCR. High beta-galactosidase production was shown by immuno-histochemistry predominantly in the liver, where about 30percent of the hepatocytes stained positive, and in the adrenal cortex. Production of factor IX was determined by ELISA in the plasma of treated fetuses and newborn lambs and reached at birth up to 80percent of the normal human plasma concentration. This demonstrates a very hopeful proof of principle for the development of prenatal treatment of many genetic diseases but also requires more detailed investigations with respect to the observed systemic spread of the vector.

Enhanced in vitro and in vivo gene delivery using cationic agent complexed retrovirus vectors

Retroviruses are, at present, the most efficient integrative vectors available for gene delivery. However, these viruses are still limited by relatively low titres. Although several protocols exist to improve virus titre most of them are time-consuming and unable to provide sufficient virus for in vivo applications. Virus titre can be enhanced by polybrene and other cationic agents. By investigating a broad range of cationic agents for their ability to enhance virus infectivity we found that both ecotropic and amphotropic retrovirus infection could be increased. In particular, the lipopolyamine dioctadecylamidoglycylspermine (DOGS) gave up to one order of magnitude enhancement above polybrene-mediated infection without cytotoxicity. To increase virus infectivity further we combined the enhancing effect of DOGS on virus infectivity with concentration of virus particles by ultrafiltration to reach titres of 1 x 10(9) IU/ml. The in vivo transduction of regenerating rat liver, by an amphotropic retrovirus was increased approximately five-fold by the addition of DOGS compared with virus alone. There was no animal toxicity observed following the administration of DOGS. The improved transduction efficiency seen both in vitro and in vivo following the co-administration of DOGS/virus complexes may be useful for future gene therapy applications.

Retroviral gene transfer to the liver in vivo during tri-iodothyronine induced hyperplasia

The liver is an important target organ for gene therapy but its mitotic quiescence makes it resistant to integrative gene transfer. Retrovirus-based vectors integrate into liver cells in vivo but require the liver to be primed before transduction; experimentally a 70% hepatectomy is commonly used to stimulate regeneration, rendering the liver susceptible to transduction during the resulting wave of cell proliferation. Our aim was to develop a clinically acceptable method of inducing hepatocyte replication before in vivo retroviral gene transfer which is both simple and effective. We have used the physiological hormone tri-iodothyronine (T3) to stimulate hepatocyte replication. A single dose of T3 (400 micrograms/100 g bw) was given subcutaneously to euthyroid rats. This produced a labelling index of 31.7% in the hepatocyte population without histological or biochemical evidence of preceding liver damage. Following T3 administration the rat livers were transfected in vivo with an amphotropic retrovirus, TELCeB/AF-7 which encodes the beta-galactosidase reporter gene together with a nuclear localisation signal. Transgene expression was noted only within the liver where 1.3% of hepatocytes expressed the beta-galactosidase enzyme. This compared to 5.2% of hepatocytes transduced following a 70% hepatectomy, and 0.02% in animals receiving neither T3 nor partial hepatic resection before transduction. T3 administration is a simple way to prime the liver before in vivo retroviral vector-based gene transfer.

Foetal gene delivery in mice by intra-amniotic administration of retroviral producer cells and adenovirus

With the aim of developing foetal gene therapy for cystic fibrosis, we have investigated the possibility of gene targeting to the mouse foetus with two different viral vector systems and at different times of gestation. We report here that recombinant retrovirus producing cells administered into the intra-amniotic cavity of mid- to late-gestation mouse MF1 foetuses survive in the amniotic fluid and are able to engraft to a certain extent in foetal tissues. By production of infectious virus they mediate transduction and beta-galactosidase transgene expression in neighbouring foetal tissues 24 to 72 h following injection. Retrovirus producer cells could, therefore, become a means to overcome the limitations of low retroviral titre, for in vivo foetal gene transfer. To investigate the developmental stage at which transduction of the airways and enteral systems can be obtained we also administered a highly infective first generation adenoviral vector (AdRSV beta gal) into the amniotic cavity of foetal mice between 13 to 16 days post coitus, beta-galactosidase activity was detected between 24 to 120 h after injection. The highest levels of transgene expression were generally observed between 48 to 72 h following injection of the adenoviral vector. We demonstrate that infection of the pulmonary airways is dependent on the developmental stage of the foetus and can be achieved on the 15th day of gestation.

Effect of amniotic fluid on cationic lipid mediated transfection and retroviral infection

In preparation for foetal gene therapy by intra-amniotic gene application, we have investigated the effect of amniotic fluid on several gene transfer systems. In vitro lipofection of embryonically derived 3T3 cells by several of the tested cationic lipids decreases in the presence of human amniotic fluid, while two formulations, Lipid 67 and Tfx-50, remain highly active. As some body fluids are known to inactivate most retroviral vectors, we investigated the influence of amniotic fluid on the efficiency of infection of 3T3 cells by murine leukaemia virus (MoMLV)-based vectors, including amphotropic and ecotropic retrovirus, and a vesicular stomatitis virus G (VSV-G) glycoprotein pseudotyped retroviral vector. All showed a decrease of infectivity from 21 to 56% in the presence of amniotic fluid. The ecotropic retrovirus is the most infectious under normal conditions as well as in amniotic fluid. Our results suggest that intra-amniotic injection may allow efficient gene transfer using either amniotic fluid-resistant cationic lipids or ecotropic retroviral vectors in a murine in vivo model for foetal gene therapy. The VSV-G-pseudotyped vector, although displaying a decrease of infectivity, remains of great interest for gene delivery, because of its broad host range and because of the high virus titers achievable. Finally, a baculovirus-based vector shows no decrease of its infectivity and does not seem to be affected by amniotic fluid but has only low infectivity on the tested foetal fibroblast cell line.

Fetal somatic gene therapy

Fetal somatic gene therapy is emerging as a new experimental approach, in particular to prevent irreversible perinatal disease manifestation for many inherited conditions. Early therapeutic gene application may also allow targeting of still expanding stem cell populations of organ or cell systems inaccessible later in life and help to avoid immune sensitization against the therapeutic vector system or transgene protein product. The progress in development of ultrasound scanning and embryofetoscopy over the last decade has made minimally invasive administration of therapeutic gene transfer vectors to the fetus in utero possible in principle. We review here the different considerations in choosing candidate diseases, the possible routes of administration and times in fetal development for application of a therapeutic gene and discuss the benefits and problems of present vector systems in this context. Given the many unknown aspects of fetal gene transfer, it is essential to extensively investigate this new approach to gene therapy in animal models for specific diseases, to improve on the technology of delivery and to assess efficacy of expression as well as the possible side effects before application to humans can be considered.

Novel use of a selectable fusion gene as an "in-out" marker for studying genetic loss in mammalian cells

Recent demonstrations of loss of heterozygosity in a wide variety of human cancers suggest that large multilocus genetic deletions (presumably including tumor suppressor genes) constitute a major class of genetic alteration in human carcinogenesis. Here we show that a bifunctional fusion gene (Hytk), suitable for both positive and negative selection, is an effective marker for studying genetic loss in mammalian cells with minimal interference from point-mutational changes. Studies with a transgenic V79 cell line in which a single functional copy of Hytk was stably inserted into the genome in a retroviral vector showed that loss of the marker (and presumably flanking cellular genetic material) could be induced efficiently by ionizing radiation (gamma-rays and fast neutrons) but only weakly by the powerful point-mutagen benzo[a]pyrene diol epoxide. In a first application of the system, we provide evidence that radiation-induced loss can occur through an indirect mechanism after a high-frequency event. Collectively, our results suggest that the Hytk marker should be a valuable tool for studying genome position effects on the tolerance of genetic loss in cultured human cells that represent different stages in clonal evolution and tumor progression.

Construction and characterization of a highly stable human: rodent monochromosomal hybrid panel for genetic complementation and genome mapping studies

Human:rodent somatic cell hybrids carrying a single, intact, selectable human chromosome are valuable both for functional somatic cell genetic analysis and genome mapping procedures. Here, we describe the construction and detailed molecular cytogenetic characterization of a panel of 23 stable hybrids, representing all 22 human autosomes plus the X-chromosome. Individual normal human chromosomes have been tagged with a selectable fusion gene (Hytk) introduced into the chromosome in a small (4.2 kbp) retroviral vector. Use of the Hytk marker permits both positive and negative ("in-out") selection to be applied to the human chromosome in any mammalian cell background. The panel includes 18 new hybrids isolated by direct microcell transfer from normal human diploid fibroblasts into mouse A9 cells.

Cell immortalization as a key, rate-limiting event in malignant transformation: approaches toward a molecular genetic analysis

Recent advances using somatic cell genetic approaches have provided a convincing body of evidence that the senescence of mammalian cells in culture is controlled by a small group of genes, one or more of which are functionally deleted in the process of immortalization. Microcell-mediated mono-chromosomal transfer methods should permit precise mapping of these genes to specific chromosomal regions. Cloning of senescence genes, using either conventional 'positional cloning' techniques or retroviral insertion mutagenesis, is now a realistic possibility. The leap in our understanding of the molecular genetic events driving the alternative cellular states of limited proliferative capacity and immortality, which such advances should precipitate, will finally permit the question of the role of cell immortalization in cancer to be addressed, and may open the door to the design of new modes of cancer therapy. In addition, the precise mechanism underlying the wide difference in transformability between human and rodent cells, which should also emerge from these investigations, is likely to make a significant contribution towards resolving the key issue of the relevance of rodent tumour induction assays in assessing the potential carcinogenicity of environmental chemicals.