Gene therapy in the CNS

Adenovirus expressing an NPC1-GFP fusion gene corrects neuronal and nonneuronal defects associated with Niemann pick type C disease

Niemann Pick type C (NPC) disease is an autosomal recessive disorder characterized by abnormal cholesterol metabolism and accumulation in lysosomal and endosomal compartments. Although peripheral organs are affected, the progressive neurodegeneration in the brain is typically most deleterious, leading to dystonia, ataxia, seizures, and premature death. Although the two genes underlying this disorder in humans and mouse models of the disease have been identified (NPC1 in 95% and NPC2/HE1 in 5% of human cases), their cellular roles have not Been fully defined, and there is currently no effective treatment for this disorder. To help address these issues, we constructed a recombinant adenovirus, Ad(NPC1-GFP), which contains a cDNA encoding a mouse NPC1 protein with a green fluorescent protein (GFP) fused to its C-terminus. Fluorescence microscopy and cholesterol trafficking assays demonstrate that the GFP-tagged NPC1 protein is functional and detectable in cells from different species (hamster, mouse, human) and of different types (ovary-derived cells, fibroblasts, astrocytes, neurons from peripheral and central nervous systems) in vitro. Combined with results from time-lapse microscopy and in vivo brain injections, our findings suggest that this adenovirus offers advantages for expressing NPC1 and analyzing its cellular localization, movement, functional properties, and beneficial effects in vitro and in vivo.

Cancer gene therapy

Cancer gene therapy can be defined as transfer of nucleic acids into tumor or normal cells with aim to eradicate or reduce tumor mass by direct killing of cells, immunomodulation or correction of genetic errors, and reversion of malignant status. Initially started with lots of optimism and enthusiasm, cancer gene therapy has shown limited success in treatment of patients. This review highlights current limitations and almost endless possibilities of cancer gene therapy. The major difficulty in advancing gene therapy technology from the bench to the clinical practice is problem with gene delivery vehicles (so called vectors) needed to ferry genetic material into a cell. Despite few reports of therapeutic responses in some patients, there is still no proof of clinical efficacy of most cancer gene therapy approaches, primarily due to very low transduction and expression efficacy in vivo of available vectors. An "ideal" gene therapy vector should be administrated through a noninvasive route and should be targeted not only to primary tumor mass but also to disseminated tumor cells and micrometastases; it should also carry therapeutic gene with tumor-restricted, time-regulated, and sustained expression. Current strategies for combating the cancer with gene therapy can be divided into four basic concepts: (1) replacement of missing tumor suppressor gene and/or blocking of oncogenes or pro-inflammatory genes, (2) suicide gene strategies, (3) induction of immune-mediated destruction, and (4) inhibition of tumor angiogenesis. The advance in the clinical benefit of gene therapy will probably be first achieved with combining it with standard cancer treatment: chemotherapy, radiotherapy, and immunotherapy.

Antiapoptotic effect both in vivo and in vitro of A20 gene when transfected into rat hippocampal neurons

AIM

To evaluate the antiapoptotic effect of the A20 gene in primary hippocampal neurons both in vivo and in vitro.

METHODS

Primary hippocampal neurons in embryonic day 18 (E18) rats were transfected with the A20 gene by using the new Nucleofector electroporation transfection method. We then examined, whether A20-neurons possessed anti-apoptotic abilities after TNF-alpha stimulation in vitro. A20-neurons and pcDNA3-neurons were transplanted into the penumbra of the brains of rats that had been subjected to 90-min of ischemia induced by left middle cerebral artery occlusion (MCAO).

RESULTS

A20-neurons resisted TNF-alpha induced apoptosis in vitro. The apoptosis rate of neurons overexpressing A20 (28.46%+/-3.87%) was lower than that in neurons transfected with pcDNA3 (53.06%+/-5.36%). More A20-neurons survived in the penumbra both 3-d and 7-d after transplantation than did sham pcDNA3 neurons.

CONCLUSION

The novel function of A20 may make it a potential targets for the gene therapy for neurological diseases.

Strategies for replacing lost cochlear hair cells

The auditory sensory epithelium is a mosaic composed of sensory (hair) cells and several types of non-sensory (supporting) cells. All these cells are highly differentiated in their structure and function. Mosaic epithelia (and other complex tissues) are generally formed by differentiation of distinct and specialized cell types from common progenitors. Most types of epithelial tissues maintain a population of undifferentiated (basal) cells which facilitate turnover (renewal) and repair, but this is not the case for the organ of Corti in the cochlea. Therefore, when cochlear hair cells are lost they cannot be replaced. Consequently, sensorineural hearing loss is permanent. In designing therapy for sensorineural deafness, the most important task is to find a way to generate new cochlear hair cells to replace lost cells.

Utilization of an HSV-based amplicon vector encoding the axonal marker hPLAP to follow neurite outgrowth in cultured DRG neurons

Delivery of genes into DRG neurons by viral vectors is a powerful tool for the study of axonal outgrowth. In order to achieve efficient transfer of growth-related genes and simultaneously label neuronal processes, we have utilized the HSV-based amplicon vector system. A bicistronic expression cassette encoding the growth associated protein-43 (GAP-43) and the axonal marker human placental alkaline phosphatase (hPLAP) reporter gene under translation control of an internal ribosomal entry site was cloned into the HGCX amplicon vector. This hPLAP reporter enabled efficient labeling of neurites in both dissociated adult DRG neurons and embryonic DRG explants. Using this reporter, the effect of GAP-43 on neurite outgrowth in transduced DRG neurons could be demonstrated. HSV-based amplicon vectors can contribute to the study of axonal growth and guidance in cultured neurons.

Cell-type-specific gene delivery into neuronal cells in vitro and in vivo

The avian retroviruses reticuloendotheliosis virus strain A (REV-A) and spleen necrosis virus (SNV) are not naturally infectious in human cells. However, REV-A-derived viral vectors efficiently infect human cells when they are pseudotyped with envelope proteins displaying targeting ligands specific for human cell-surface receptors. Here we report that vectors containing the gag region of REV-A and pol of SNV can be pseudotyped with the envelope protein of vesicular stomatitis virus (VSV) and the glycoproteins of different rabies virus (RV) strains. Vectors pseudotyped with the envelope protein of the highly neurotropic RV strain CVS-N2c facilitated cell type-specific gene delivery into mouse and human neurons, but did not infect other human cell types. Moreover, when such vector particles were injected into the brain of newborn mice, only neuronal cells were infected in vivo. Cell-type-specific gene delivery into neurons may present quite specific gene therapy approaches for many degenerative diseases of the brain.

Clinical gene therapy for nonmalignant disease

Gene therapy is envisioned as a potentially definitive treatment for a variety of diseases that have a genetic etiology. We reviewed trials of clinical gene therapy for nonmalignant, single-gene, and multifactorial disorders and infectious diseases, and found limited evidence suggesting that gene therapy may benefit patients who have severe, combined, immunodeficiency disorder; cystic fibrosis; coronary artery disease or peripheral arterial disease; or hemophilia. Effective gene therapy requires the targeted transfer of exogenous genetic material into human cells and the subsequent regulated expression of the corresponding gene product. Because no phase 3 randomized controlled trials have been completed that fulfill these criteria, it is difficult to correlate signs of clinical benefit with the administration of gene therapy in any disease. Additional clinical and basic research is needed to determine the future role of gene therapy.

Calmodulin regulates synaptic plasticity in the anterior cingulate cortex and behavioral responses: a microelectroporation study in adult rodents

We developed a microelectroporation method for the transfer of genes into neurons in the cerebral cortex of adult rodents, both rats and mice. We selectively expressed either green-fluorescent protein (GFP) or a Ca2+-binding deficient calmodulin (CaM) mutant in the anterior cingulate cortex (ACC). In mice that expressed GFP, positive neuronal cell bodies were found specifically at the injection site in the ACC. Mice that expressed CaM12, a mutant CaM with two impaired Ca2+ binding sites in the N-terminal lobe, exhibited significant changes in vocalization, locomotion, and sensory functions. Long-term potentiation and long-term depression, two major forms of central plasticity, were completely abolished by expression of CaM12. Mice that expressed CaM34, a mutant CaM with two impaired Ca2+ binding sites in the C-terminal lobe, did not show any significant behavioral or electrophysiological alterations. These findings provide strong evidence that CaM is critical for bidirectional synaptic plasticity. This new method will be useful for investigating gene function in specific brain regions of freely moving animals. Furthermore, this approach also may facilitate gene therapy in adult human brains.

Nonviral gene delivery to the central nervous system based on a novel integrin-targeting multifunctional protein

Successful introduction of therapeutic genes into the central nervous system (CNS) requires the further development of efficient transfer vehicles that avoid viral vector-dependent adverse reactions while maintaining high transfection efficiency. The multifunctional protein 249AL was recently constructed for in vitro gene delivery. Here, we explore the capability of this vector for in vivo gene delivery to the postnatal rat CNS. Significant transgene expression was observed both in the excitotoxically injured and noninjured brain after intracortical injection of the DNA-contaning-249AL vector. In the injured brain, a widespread expression occurred in the entire lesioned area and retrograde transport of the vector toward distant thalamic nuclei and transgene expression were observed. Neurons, astrocytes, microglia, and endothelial cells expressed the transgene. No recruitment of leukocytes, demyelination, interleukin-1beta expression, or increase in astrocyte/microglial activation was observed at 6 days postinjection. In conclusion, the 249AL vector shows promising properties for gene therapy intervention in the CNS, including the targeting of different cell populations.

Long-term transgene expression can be mediated in the brain by adenoviral vectors when powerful neuron-specific promoters are used

BACKGROUND

Adenoviral (Ad) vectors are one of the most widely used tools for modelling gene therapy strategies. However, they have not been used in long-term models of neurological disease, as the period of time for which they mediate strong transgene expression is limited and/or variable. In this study we investigated the longevity of transgene expression in the brain when the powerful neuron-specific Ad-synapsin (Sy)-EGFP-woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) vector cassette is used at titres that do not elicit an immune response.

METHODS

Adenoviral vectors expressing enhanced green fluorescent protein (EGFP) under the control of either the hCMV, hCMV-WPRE, Sy or Sy-WPRE promoter were constructed. These vectors were injected into the dentate gyrus region of hippocampus and transgene expression and immune cell infiltration assessed by fluorescence microscopy and immunocytochemical techniques, respectively.

RESULTS

The quantitative analysis of EGFP expression showed that there was no significant change in synapsin or synapsin-WPRE driven transcription 9 months after injection when compared with expression levels obtained 3 days after injection. However, when the hCMV promoter or the hCMV-WPRE promoter cassette drove transgene expression, there was a dramatic fall in expression levels and very little expression was seen 9 months post-transfection.

CONCLUSIONS

This study shows that non-integrating vectors can be used to mediate powerful, long-term episomal transgene expression in neurones. This work has important implications for neuronal gene therapy and is of relevance to studies investigating memory, behaviour and neuronal gene function.

Repeated intrathecal administration of plasmid DNA complexed with polyethylene glycol-grafted polyethylenimine led to prolonged transgene expression in the spinal cord

Gene delivery into the spinal cord provides a potential approach to the treatment of spinal cord traumatic injury, amyotrophic lateral sclerosis, and spinal muscular atrophy. These disorders progress over long periods of time, necessitating a stable expression of functional genes at therapeutic levels for months or years. We investigated in this study the feasibility of achieving prolonged transgene expression in the rat spinal cord through repeated intrathecal administration of plasmid DNA complexed with 25 kDa polyethylenimine (PEI) into the lumbar subarachnoid space. With a single injection, DNA/PEI complexes could provide transgene expression in the spinal cord 40-fold higher than naked plasmid DNA. The transgene expression at the initial level persisted for about 5 days, with a low-level expression being detectable for at least 8 weeks. When repeated dosing was tested, a 70% attenuation of gene expression was observed following reinjection at a 2-week interval. This attenuation was associated with apoptotic cell death and detected even using complexes containing a noncoding DNA that did not mediate any gene expression. When each component of the complexes, PEI polymer or naked DNA alone, were tested in the first dosing, no reduction was found. Using polyethylene glycol (PEG)-grafted PEI for DNA complexes, no attenuation of gene expression was detected after repeated intrathecal injections, even in those rats receiving three doses, administered 2 weeks apart. Lumbar puncture is a routine and relatively nontraumatic clinical procedure. Repeated administration of DNA complexed with PEG-grafted PEI through this less invasive route may prolong the time span of transgene expression when needed, providing a viable strategy for the gene therapy of spinal cord disorders.

Single HSV-amplicon vector mediates drug-induced gene expression via dimerizer system

A variety of viral vectors have been used to deliver genes into various tissues. Most have typically relied on either viral or cell-specific mammalian promoters to express transgenes. More recently, regulated promoter systems have been developed to fine-tune gene expression. Due to limited transgene capacity in most viral vectors, regulatory elements are typically subcloned into two separate vectors, which must be delivered simultaneously to a target cell. Here, we have cloned all the components of the rapamycin-based "dimerizer" system into the pantropic HSV-amplicon vector and used it to deliver and regulate red fluorescent protein (RFP) expression in cultured cells in a drug-dose-dependent manner. 293T/17 cells infected at an m.o.i. of 1 transducing unit/cell and induced with 20 nM rapamycin resulted in a 25-fold increase in RFP mRNA levels after 24 h as assessed by quantitative RT-PCR. However, due to a reduced ability to detect RFP optically, only a 5-fold induction in the number of RFP-expressing cells was noted by FACS analysis 48 h after infection. Further, there was at least 100-fold variation in the levels of RFP in individual, infected cells in the induced state. Gene induction in several neuronal models, including primary cell culture and organotypic cultures, as well as in rodent brain, was observed.

Regulated transgene delivery by ganciclovir in the brain without physiological alterations by a live attenuated herpes simplex virus vector

The distribution of a live attenuated herpes simplex virus (betaH1)-mediated gene delivery into the central nervous system (CNS) was regulated by growth inhibition with ganciclovir (GCV) and the effect of this transgene expression system on the physiologic response was characterized by the acoustic startle response and its prepulse inhibition. We inoculated betaH1 expressing beta-galactosidase (beta-gal) driven by the latency associated transcripts promoter into the right caudate putamen of rats. Histochemical analysis demonstrated that the inoculation of betaH1 in the right caudate putamen resulted in a high level of beta-gal expression in the neurons of the area projecting to the inoculation site. On 14 days after inoculation without GCV-treatment, beta-gal activity localized in the anterior olfactory nucleus, frontal, insular, orbital, parietal, perirhinal, piriform cortices and the temporal region including the amygdala. In contrast, the distribution of beta-gal activity was regulated by the interval between virus inoculation and GCV-treatment and maintained after its cessation without significant alteration. The whole process of transgene expression did not influence the emotional behavior, indicating that this vector system is a suitable model for analyzing the transgene function or applying the gene therapy for the CNS diseases.

Endovascular restorative neurosurgery: a novel concept for molecular and cellular therapy of the nervous system

The amalgam of molecular biology and neurosurgery offers immense promise for neurorestoration and the management of neurodegenerative deficiencies, developmental disorders, neoplasms, stroke, and trauma. This article summarizes present strategies for and impediments to gene therapy and stem cell therapy of the central nervous system and advances the concept of a potential new approach, namely endovascular restorative neurosurgery. The objectives of gene transfer to the central nervous system are efficient transfection of host cells, selective sustained expression of the transgene, and lack of toxicity or immune excitation. The requisite elements of this process are the identification of candidate diseases, the construction of vehicles for gene transfer, regulated expression, and physical delivery. In the selection of target disorders, the underlying genetic events to be overcome, as well as their spatial and temporal distributions, must be considered. These factors determine the requirements for the physical dispersal of the transgene, the duration of transgene expression, and the quantity of transgene product needed to abrogate the disease phenotype. Vehicles for conveying the transgene to the central nervous system include viral vectors (retroviruses, lentiviruses, adenoviruses, adeno-associated viruses, and herpes simplex virus), liposomes, and genetically engineered cells, including neural stem cells. Delivery of the transgene into the brain presents several challenges, including limited and potentially risky access through the cranium, sensitivity to volumetric changes, restricted diffusion, and the blood-brain barrier. Genetic or cellular therapeutic agents may be injected directly into the brain parenchyma (via stereotaxy or craniotomy), into the cerebrospinal fluid (in the ventricles or cisterns), or into the bloodstream (intravenously or intra-arterially). The advantages of the endovascular route include the potential for widespread distribution, the ability to deliver large volumes, limited perturbation of neural tissue, and the feasibility of repeated administration.

Tetracycline-regulated gene expression in replication-incompetent herpes simplex virus vectors

Although herpes simplex virus (HSV) vectors appear to have great potential as gene delivery vectors both in vitro and in vivo, the expression of foreign genes in such vectors cannot be easily regulated. Of the known eukaryotic regulatory systems, the tetracycline-inducible gene expression system is perhaps the most widely used because of its induction characteristics and because of the well-known pharmacological properties of tetracycline (Tet) and analogs such as doxycycline. Here, we describe the adaptation of the Tet-inducible system for use in replication-incompetent HSV vectors. HSV vectors were constructed that contained several types of Tet-inducible promoters for foreign gene expression. These promoters contained a tetracycline response element (TRE) linked to either a minimal cytomegalovirus (CMV) immediate-early promoter, a minimal HSV ICP0 promoter, or a truncated HSV ICP0 promoter containing one copy of the HSV TAATGARAT cis-acting immediate-early regulatory element (where R represents a prime base). All three promoter constructs were regulated appropriately by doxycycline, as shown by the expression of the marker gene lacZ in cell lines engineered to express Tet transactivators. The ICP0 promoter constructs expressed the highest and most sustained levels of lacZ, but the CMV promoter construct had the highest relative level of induction, suggesting their use in different applications. To extend the utility of Tet-regulated HSV vectors, vectors were constructed that coexpressed an inducible Tet transactivator in addition to the inducible lacZ marker gene. This modification resulted in tetracycline-inducible gene expression that was not restricted to specific cell lines, and this vector was capable of inducible expression in irreversibly differentiated NT2 cells (NT-neurons) for several days. Finally, HSV vectors were constructed that expressed modified Tet transactivators, resulting in improved induction properties and indicating the flexibility of the Tet-regulated system for regulation of foreign gene expression in HSV vector-infected cells.

Evaluation of Tet-on system to avoid transgene down-regulation in ex vivo gene transfer to the CNS

Ex vivo gene transfer to the CNS has so far been hampered by instability of transgene expression. To avoid the phenomenon of transgene down-regulation, we have employed strong, constitutive promoters and compared this expression system with the inducible Tet expression system incorporated in a single plasmid vector or in lentiviral vectors. Plasmid-based transgene expression directed by the constitutive, human ubiquitin promoter, UbC, was stable in transfected HiB5 cells in vitro and comparable in strength to the CMV promoter. However, after transplantation of UbC and CMV HiB5 clones to the rat striatum, silencing of the transgene occurred in most cells soon after implantation of transfected cells. The Tet-on elements were incorporated in a single plasmid vector and inducible HiB5 clones were generated. Inducible clones displayed varying basal expression activity, which could not be ascribed to an effect of cis-elements in the vector, but rather was due, at least in part, to intrinsic activity of the minimal promoter. Basal expression activity could be blocked in a majority of cells by stable expressing the transrepressor tTS. Fully induced expression levels were comparable to CMV and UbC promoters. Similar to the constitutive promoters transgene expression was down-regulated soon after grafting of inducible HiB5 clones to the rat striatum. Lentiviral vectors can direct long-term stable in vivo transgene expression. To take advantage of this quality of the lentiviral vector, the Tet-on elements were incorporated in two lentiviral transfer vectors followed by transduction of Hib5 cells. Interestingly, all HiB5 clones established by lentiviral transduction showed very similar expression patterns and tight regulatability that apparently was independent of transgene copy number and integration site. Nevertheless, transgene expression in all lentiviral HiB5 clones was down-regulated shortly after transplantation to the rat striatum. These results confirm the general phenomenon of transgene down-regulation. Moreover, the results suggest that the considerable advantages offered by lentiviral vectors for direct gene delivery cannot necessarily be transferred directly to ex vivo gene delivery. This emphasizes the need for alternative vector strategies for ex vivo gene transfer.

Adenovirus infection induces microglial activation: involvement of mitogen-activated protein kinase pathways

Non-replicating adenovirus vectors (AdV) represent effective tools for long-term gene expression in the central nervous system (CNS), but they also elicit inflammation. The cellular and molecular mechanisms of such a response are not understood. In the present study, we show that infection with AdV causes activation of microglial cells, the key cells involved in inflammatory and immune-regulatory functions in the brain. Exposure of cultured rat brain microglia to AdV resulted in an induced production of nitric oxide (NO) and the expression of inducible nitric oxide synthase (iNOS) and the pro-inflammatory cytokine, TNFalpha. The roles of signal transduction pathways believed to be involved in microglial activation in particular, mitogen-activated protein kinases (MAPKs) and nuclear factor kappaB (NFkappaB) were explored by determining their activation in response to AdV infection and by testing the effects of specific pharmacological inhibitors. It was found that AdV strongly activates extracellular signal-regulated kinase (ERK) and to a lesser extent, p38 MAPK but not NFkappaB. Addition of the kinase inhibitor, i.e. PD98059 (specific for the ERK pathway), inhibits and, in combination with the p38 MAPK inhibitor, SB203580, drastically suppresses AdV-induced expression of iNOS and TNFalpha. The results suggest that AdV uses cellular signal transduction machinery, in particular the MAPK pathways, to elicit microglial activation and that increased production by these cells of inflammatory mediators may primarily contribute to CNS inflammatory responses commonly seen in models of gene therapy using AdV vectors.

Diffusion and convection in collagen gels: implications for transport in the tumor interstitium

Diffusion coefficients of tracer molecules in collagen type I gels prepared from 0-4.5% w/v solutions were measured by fluorescence recovery after photobleaching. When adjusted to account for in vivo tortuosity, diffusion coefficients in gels matched previous measurements in four human tumor xenografts with equivalent collagen concentrations. In contrast, hyaluronan solutions hindered diffusion to a lesser extent when prepared at concentrations equivalent to those reported in these tumors. Collagen permeability, determined from flow through gels under hydrostatic pressure, was compared with predictions obtained from application of the Brinkman effective medium model to diffusion data. Permeability predictions matched experimental results at low concentrations, but underestimated measured values at high concentrations. Permeability measurements in gels did not match previous measurements in tumors. Visualization of gels by transmission electron microscopy and light microscopy revealed networks of long collagen fibers at lower concentrations along with shorter fibers at high concentrations. Negligible assembly was detected in collagen solutions pregelation. However, diffusion was similarly hindered in pre and postgelation samples. Comparison of diffusion and convection data in these gels and tumors suggests that collagen may obstruct diffusion more than convection in tumors. These findings have significant implications for drug delivery in tumors and for tissue engineering applications.

Evaluation and optimization of DNA delivery into gliosarcoma 9L cells by a cholesterol-based cationic liposome

This paper reports results concerning the transfection of gliosarcoma cells 9L using an original cholesterol-based cationic liposome as carrier. This cationic liposome was prepared from triethyl aminopropane carbamoyl cholesterol (TEAPC-Chol) and a helper lipid, dioleoyl phosphatidyl ethanolamine (DOPE). The used concentration of liposome was not cytotoxic as revealed by the MTT test. TEAPC-Chol/DOPE liposomes allowed the plasmids encoding reporter genes to enter the nucleus as observed both by electron microscopy and functionality tests using fluorescence detection of green fluorescent protein (GFP) and luminometric measurements of luciferase activity. By changing the cationic lipid/DNA molar charge ratio, optimal conditions were determined. Further, improvement of the transfection level has been obtained by either precondensing plasmid DNA with poly-L-lysine or by adding polyethylene glycol (PEG) in the transfection medium. The optimal conditions determined are different depending on whether the transfection is made with cells in culture or with tumors induced by subcutaneous (s.c.) injection of cells in Nude mice. For in vivo assays, a simple method to overcome the interference of haemoglobin with the chemiluminescence intensity of luciferase has been used. These results would be useful for gaining knowledge about the potential for the cationic liposome TEAPC-Chol/DOPE to transfect brain tumors efficiently.

Adenoviral-mediated, high-level, cell-specific transgene expression: a SYN1-WPRE cassette mediates increased transgene expression with no loss of neuron specificity

Viral vectors are excellent tools for studying gene function in the brain, although a limitation has been the ability to effectively target transgene expression to specific neuronal populations. This generally cannot be overcome by the use of neuron-specific promoters, as most are too large to be used with current viral vectors and expression from these promoters is often relatively weak. We therefore developed a composite expression cassette, comprising 495 bp of the weak human SYN1 (synapsin-1) promoter and 800 bp of the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE). Studies in hippocampal cultures, organotypic cultures, and in vivo showed that the 3' addition of the WPRE to the SYN1 element greatly increased enhanced green fluorescent protein expression levels with no loss of neuronal specificity. In vivo studies also showed that transgene expression was enhanced with no loss of neuronal specificity in dentate-gyrus neurons for at least 6 weeks following transfection. Therefore, unlike most powerful promoter systems, which mediate expression in neurons and glia, this SYN1-WPRE cassette can target powerful long-term transgene expression to central nervous system neurons when delivered at relatively low titers of adenovirus. Its use should therefore facilitate both gene therapy studies and investigations of neuronal gene function.

Syngeneic central nervous system transplantation of genetically transduced mature, adult astrocytes

Advances in the development of highly infectious, replication-deficient recombinant retroviruses provide an efficient means of stable transfer of gene expression. Coupled with ex vivo transduction, surrogate cell populations can be readily implanted into the brain, thus serving as vehicles for delivering selected gene products into the central nervous system (CNS). Here we report that rat astrocytes can be routinely and safely isolated from brain tissue of a living donor by use of short-term gelatin sponge implants. The mature, nontransformed astrocytes were easily expanded, maintained in long-term tissue cultures and were efficiently transduced with an amphotropic retrovirus harboring a heterologous, fused transgene. In vitro retroviral infection rendered the nontransformed cells essentially 100% viable after exposure. The level of efficiency of infection (30-50% effective genome integration of provirus and expression of transgene in target cell populations) and minimal cell toxicity obviated the need to harvest large numbers of target cells. Cultured transduced astrocytes were resilient and exhibited select peptide expression for up to 1 year. Subsequently, transduced astrocytes were used in a series of experiments in which cells were transplanted intracerebrally in syngeneic animals. Post-implantation, astrocytes seeded locally and either insinuated into the surrounding parenchyma in situ or exhibited a variable degree of migration, depending on the anatomic source of astrocytes and the targeted brain implantation site. Transduced astrocytes remained viable in excess of 8 months post-transplantation and exhibited sustained transgenic peptide expression of green fluorescent protein/neomycin phosphotransferase in vivo. The sequential isolation and culture of nontransformed, mature, adult astrocytes and recombinant retrovirus-mediated transduction in vitro followed by brain reimplantation represents a safe and effective means for transferring genetic expression to the CNS. This study lays the foundation for exploring the utility of using a human autologous transplantation system as a potential gene delivery approach to treat neurological disorders. Prepared and utilized in this manner, autologous astrocytes may serve as a vehicle to deliver gene therapy to the CNS.

Critical issues in gene therapy for neurologic disease

Gene therapy for the nervous system is a newly emerging field with special issues related to modes of delivery, potential toxicity, and realistic expectations for treatment of this vital and highly complex tissue. This review focuses on the potential for gene delivery to the brain, as well as possible risks and benefits of these procedures. This includes discussion of appropriate vectors, such as adeno-associated virus, lentivirus, gutless adenovirus, and herpes simplex virus hybrid amplicons, and cell vehicles, such as neuroprogenitor cells. Routes of delivery for focal and global diseases are enumerated, including use of migratory cells, facilitation of vascular delivery across the blood-brain barrier, cerebrospinal fluid delivery, and convection injection. Attention is given to examples of diseases falling into different etiologic types: metabolic deficiency states, including Canavan disease and lysosomal storage disorders; and degenerative conditions, including Parkinson's disease and other neurodegenerative conditions.

Potential of bovine herpesvirus 4 as a gene delivery vector

A cloning system was developed for construction of BHV-4 recombinants and recombinant virus BHV-4EGFPDeltaTK containing an enhanced green fluorescent protein (EGFP) gene was constructed. The host range of BHV-4EGFPDeltaTK was characterized in vitro. When cell lines from various species and tissues were infected, most of the non-bovine cell lines exhibited neither cytopathic effect (CPE) nor supported viral replication, but EGFP expression was clearly observed. Next, embryonic stem cells were infected and induced to either non-specific or neural differentiation to determine whether they could survive and differentiate after BHV-4EGFPDeltaTK infection. Embryonic stem cells were infected successfully, as indicated by EGFP expression prior to differentiation, and EGFP expression could be detected in many differentiated cells. No CPE was noted. Therefore, BHV-4EGFPDeltaTK infection caused neither cell death nor interfered with non-specific or neural differentiation of embryonic stem cells. Finally, to assess the capability of BHV-4EGFPDeltaTK to infect post-mitotic neurons, cultures from brains of 2-weeks old mice were infected. No death of neuronal cells due to infection was observed and EGFP expression persisted for at least 15 days. Several biological characteristics of BHV-4 demonstrated previously make it a good candidate for a gene delivery vector. These include: little or no pathogenicity, unlikely oncogenicity, ability to establish persistent infection, and capability of herpesviruses to accommodate large amounts of foreign genetic material. These findings add the ability to infect several cell types coming from different animal species, usually without CPE, lack of interference with differentiation, and ability to maintain transgene expression in both undifferentiated and differentiated cells.

Targeted gene repair and its application to neurodegenerative disorders

Synthetic DNA oligonucleotides can direct the exchange of single nucleotides within coding regions of mammalian genes by hybridizing to their complementary sequence in the chromosome and creating a recombination joint structure with a single mismatched base pair. Inherent DNA repair processes recognize the mismatch and resolve it using the DNA sequence of the oligonucleotide vector as the template. This gene surgery approach can be used to repair mutations or to disrupt tri-nucleotide repeats in dysfunctional genes responsible for neurological disorders.

Brain engraftment of autologous macrophages transduced with a lentiviral flap vector: an approach to complement brain dysfunctions

Transplantation of ex vivo gene-corrected autologous cells represents an attractive therapeutic approach for brain diseases. Among the cells of the central nervous system, brain macrophages are promising candidates due to their role in tissue homeostasis and their implication in several neurological diseases. Up to now, gene transfer into macrophages has proven difficult by most currently available gene delivery methods. We describe herein, an efficient transduction of rat bone marrow-derived and brain macrophages with an HIV-1-derived vector containing a central DNA flap and encoding the GFP reporter gene (TRIP-DeltaU3-GFP). In primary cultures of macrophages our results show that more than 90% of the cells were transduced by the TRIP vector and that GFP expression remained stable for 1 month without cytopathic effect. In vivo, transplants of transduced macrophages into the striatum of adult rats exhibited long-term expression of GFP up to 3 months. Transduced macrophages were observed around the brain injection site and exhibited the brain macrophage/microglia phenotype. There was no significant sign of astrogliosis around the graft. These results confirm the potential of lentiviral vectors for efficient and stable ex vivo transduction of macrophages. Moreover, transduced autologous macrophages appear as a valuable vehicle for long-term and localized gene expression into the brain.

4D-QSAR analysis of a set of ecdysteroids and a comparison to CoMFA modeling

The ecdysteroid-responsive Drosophila melanogaster B(II) cell line is a prototypical homologous inducible gene expression system. A training set of 71 ecdysteroids, for which the -log(EC(50)) potencies in the ecdysteroid-responsive B(II) cell line were measured, was used to construct 4D-QSAR models. Four nearly equivalent optimum 4D-QSAR models, for two modestly different alignments, were identified (Q(2) = 0.76-0.80). These four models, together with two CoMFA models, were used in consensus modeling to arrive at a three-dimensional pharmacophore. The C-2 and C-22 hydroxyls are identified as hydrogen-bond acceptor sites which enhance activity. A hydrophobic site near C-12 is consistent with increasing activity. The side-chain substituents at C-17 are predicted to adopt semiextended "active" conformations which could fit into a cylinder-shaped binding pocket lined largely with nonpolar residues for enhanced activity. A test set of 20 ecdysteroids was used to evaluate the QSAR models. Two 4D-QSAR models for one alignment were identified to be superior to the others based on having the smallest average residuals of prediction for the prediction set (0.69 and 1.13 -log[EC(50)] units). The correlation coefficients of the optimum 4D-QSAR models (R(2) = 0.87 and 0.88) are nearly the same as those of the best CoMFA model (R(2) = 0.92) determined for the same training set. However, the cross-validation correlation coefficient of the CoMFA model is less significant (Q(2) = 0.59) than those of the 4D-QSAR models (Q(2) = 0.80 and 0.80).

Insulators coupled to a minimal bidirectional tet cassette for tight regulation of rAAV-mediated gene transfer in the mammalian brain

Recombinant AAV is increasingly becoming the vector of choice for many gene therapy applications in the CNS, due to its lack of toxicity and high level of sustained expression. With recent improvements in the generation of pure, high titer vector stocks, the regulation of gene expression is now a key issue for successful translation of gene therapy-based treatments to the clinic. The level of the transgene protein may need to be maintained within a narrow therapeutic window for the successful treatment of human disease. The doxycycline responsive system directs a dose-responsive, tightly regulated level of gene expression and has been used successfully in transgenic mouse models. Here, we have optimized an autoregulatory, bidirectional doxycyline responsive cassette specifically for use in rAAV. We minimized the size of the cassette and decreased the basal leakiness of the system, leading to tight regulation in the rat

Sustained delivery of GDNF: towards a treatment for Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the progressive loss of nigral dopaminergic neurons. Although symptomatic therapies to substitute for the missing neurotransmitter dopamine are efficient at the early stages of the disease, the goal is to find alternative therapies which could protect dopaminergic neurons from the degenerative process. We have used two distinct gene therapy approaches to deliver the neuroprotective molecule glial cell line-derived neurotrophic factor (GDNF) in animal models of the disease: (i) an encapsulated genetically engineered cell line releasing GDNF (ex vivo gene therapy); and (ii) a lentiviral vector encoding the GDNF gene (in vivo gene therapy). Both approaches allowed protection of nigral dopaminergic neurons against lesion-induced cell death in rodent as well as monkey models of PD. Behavioral symptoms were also ameliorated in these animals. In addition, co-transplantation of embryonic dopaminergic neuronal grafts and a GDNF-releasing capsule allowed improvement of graft survival and differentiation, thereby accelerating behavioral recovery. These results should lead to clinical application in the near future.

A high-efficiency synthetic promoter that drives transgene expression selectively in noradrenergic neurons

Gene promoter systems that drive high-level, long-term, and cell-specific transgene expression are of great interest because of their potential utility for gene therapy. To generate an efficient promoter system specific for noradrenergic (NA) neurons, we multimerized an NA-specific cis-regulatory element (PRS2) identified in the human dopamine beta-hydroxylase (hDBH) promoter, and combined it with a minimal promoter (containing a TATA box and transcription start site). Forms of this synthetic promoter that contain 8 or more copies of PRS2 were >50 times more effective than the 1.15-kb hDBH promoter at driving reporter gene expression in cell lines originated from NA neurons. Neither the synthetic promoter nor the 1.15-kb hDBH promoter drove reporter gene expression in nonneuronal cells. Microinjections of an adenoviral vector containing the synthetic promoter directly into rat brain caused more strict NA-specific reporter gene expression than that caused by a vector containing the 1.15-kb hDBH promoter when the targeted region contained large numbers of NA neurons (locus coeruleus). Furthermore, the vector containing the synthetic promoter caused less nonspecific ("leaky") reporter gene expression than that caused by the vector containing the 1.15-kb hDBH promoter when the targeted region was devoid of NA neurons (cerebellum, dentate gyrus). Together, these studies provide in vitro and in vivo evidence that this novel synthetic promoter can target transgene expression to NA neurons even more efficiently and selectively than the naturally occurring, 1.15-kb hDBH promoter.

Transplants of cells genetically modified to express neurotrophin-3 rescue axotomized Clarke's nucleus neurons after spinal cord hemisection in adult rats

To test the idea that genetically engineered cells can rescue axotomized neurons, we transplanted fibroblasts and immortalized neural stem cells (NSCs) modified to express neurotrophic factors into the injured spinal cord. The neurotrophin-3 (NT-3) or nerve growth factor (NGF) transgene was introduced into these cells using recombinant retroviral vectors containing an internal ribosome entry site (IRES) sequence and the beta-galactosidase or alkaline phosphatase reporter gene. Bioassay confirmed biological activity of the secreted neurotrophic factors. Clarke's nucleus (CN) axons, which project to the rostral spinal cord and cerebellum, were cut unilaterally in adult rats by T8 hemisection. Rats received transplants of fibroblasts or NSCs genetically modified to express NT-3 or NGF and a reporter gene, only a reporter gene, or no transplant. Two months postoperatively, grafted cells survived at the hemisection site. Grafted fibroblasts and NSCs expressed a reporter gene and immunoreactivity for the NGF or NT-3 transgene. Rats receiving no transplant or a transplant expressing only a reporter gene showed a 30% loss of CN neurons in the L1 segment on the lesioned side. NGF-expressing transplants produced partial rescue compared with hemisection alone. There was no significant neuron loss in rats receiving grafts of either fibroblasts or NSCs engineered to express NT-3. We postulate that NT-3 mediates survival of CN neurons through interaction with trkC receptors, which are expressed on CN neurons. These results support the idea that NT-3 contributes to long-term survival of axotomized CN neurons and show that genetically modified cells rescue axotomized neurons as efficiently as fetal CNS transplants.

Effect of immunity on gene delivery into anterior horn motor neurons by live attenuated herpes simplex virus vector

Efficient and prolonged foreign gene expression has been demonstrated in the bilateral anterior horn motor neurons of the spinal cord by intramuscular inoculation with attenuated herpes simplex virus (HSV) expressing latency associated transcript promoter-driven beta-galactosidase (betaH1). To examine the effect of immunity on the gene delivery, betaH1 was applied in rats immunized subcutaneously or intramuscularly with the parent HF strain. Rats were immunized subcutaneously with HF strain and 28 days later when the high antibody titer was maintained, betaH1 was inoculated into the right gastrocnemius muscle. Second, 35 days after inoculation with HF strain into the right gastrocnemius muscle, betaH1 was inoculated at the same site. In both ways of immunization, immunity did not abolish or prevent the transgene expression in the anterior horn motor neurons, but attenuated the range and the number of the beta-galactosidase-positive neurons from about 85% to 50-65% on 28 days after inoculation with betaH1. However, beta-galactosidase activity was observed in a wide range of the bilateral anterior horn motor neurons without significant pathological changes. These findings support the feasibility of the attenuated HSV vector in gene delivery into the central nervous system, even in the presence of immunity.

Bcl-2 expression by retrograde transport of adenoviral vectors with Cre-loxP recombination system in motor neurons of mutant SOD1 transgenic mice

We investigated genes expression by retrograde axonal transport of replication-defective adenoviruses carrying genes for LacZ (AdLacZ) and Bcl-2 in motor neurons of transgenic mice expressing mutant human Cu/Zn superoxide dismutase (SOD1) gene containing a substitution of alanine for glycine at position 93. We found that intramuscular injection of AdLacZ into the tongue of mutant SOD1 transgenic mice and their wild-type littermates at various ages results in high expression of the transgene and similar time course of expression in hypoglossal cranial nerve nuclei, suggesting no difference in the behavior of the transgene expression between the two groups. Subsequently, we employed a molecular switching cassette for Bcl-2 designed to express Bcl-2 by Cre-loxP recombination using adenoviral vectors, and examined the COS7 and primary neuronal cells with the mutant SOD1 gene. The overexpression of Bcl-2 in both cells and the neuronal protection against staurosporine-induced apoptosis were observed, after dual infection of adenoviral vectors with cassette for Bcl-2 (AxCALNLBcl-2) and Cre recombinase (AxCANCre). After inoculation of AxCALNLBcl-2 followed by AxCANCre into the tongue of both mutant SOD1 transgenic mice and wild-type littermates, Bcl-2 was detected in both the injection site and the hypoglossal nuclei of brainstems, suggesting that this was the result of retrograde transport of AxCALNLBcl-2 and AxCANCre and expression of Bcl-2 by Cre recombinase in the hypoglossal nuclei. This strategy for delivery of exogenous genes such as Bcl-2 will be useful for studying neuronal death/survival and introducing foreign genes into postmitotic motor neurons, and in gene therapy for motor neuron diseases such as ALS.

Transgene Expression in the Brain Stem Effected by Intramuscular Injection of Polyethylenimine/DNA Complexes

Gene delivery into the CNS without tissue destruction is challenging. As neurons are capable of taking up exogenous particulates from the muscles that they innervate, we investigated the feasibility of achieving gene transfer in CNS neurons by peripheral intramuscular injection of plasmid DNA complexed with the cationic polymer polyethylenimine (PEI) in the rat hypoglossal system. Using the luciferase reporter gene driven by a Rous sarcoma virus promoter, transgene expression of up to 4 x 10(6) RLU per brain stem at 20 microg of plasmid DNA was achieved after tongue injection. Using lacZ as a reporter gene, transgene expression in the brain stem was detected in hypoglossal motor neurons, a group of neurons that innervate tongue muscles. The plasmid DNA was detected by PCR analysis in the brain-stem samples, demonstrating that the PEI/DNA complexes had migrated by retrograde axonal transport to neuronal cell bodies in the brain stem after being internalized by nerve terminals in the tongue muscle. Using a therapeutic bcl-2 gene driven by a cytomegalovirus promoter and Western blotting, transgene expression was detectable in the brain stem as early as 18 h after tongue injection and lasted for at least 2 weeks. Two lipid transfection agents, GenePORTER and TransFast, mediated a weak gene expression in the hypoglossal system, but not two polymers, poly-l-lysine and chitosan. The nonviral neuronal gene delivery method established in this study bypasses the blood-brain barrier and suggests a possible therapeutic strategy for noninvasive CNS gene transfer.

Nonviral gene delivery to the lateral ventricles in rat brain: initial evidence for widespread distribution and expression in the central nervous system

The use of DNA for nonviral gene expression depends on several factors. These include (i) delivery and accessibility to the targeted tissue, (ii) protection from extracellular degradation, (iii) sufficient uptake by cells of interest, and (iv) protection from intracellular degradation to allow translation of adequate levels of intracellular or secreted proteins. As an initial step in demonstrating the feasibility of nonviral, cationic lipid-mediated gene therapy, we present evidence for the successful delivery and expression of heat shock protein Hsp70 and reporter gene enzymes in the central nervous system (CNS) of the rat after injection into the lateral ventricle. Gene delivery is accomplished using optimized formulations of plasmid DNA, which have been complexed with the cationic lipid MLRI. Results from DNA vectors encoding for green fluorescent protein (GFP), luciferase, and Hsp70 are reported. Standard immunofluorescent methods were used to demonstrate widespread expression of the reporter proteins and of Hsp70. Stereology analysis has been completed on three coronal sections, which illustrates the distribution of expression along the longitudinal axis. These initial findings support the further development of nonviral, lipid-mediated gene delivery technology for transient expression of protective, intracellular proteins and represent an important step leading to in vivo studies to identify potential clinical benefits.

Genetic therapy for pain management

Two approaches to genetic therapy for the management of chronic pain have recently been investigated in animal models of pain. First, transgene-mediated delivery of antinociceptive molecules to the cerebrospinal fluid has been performed with engineered cell lines transplanted to the subarachnoid space and with recombinant adenoviruses that transduce pia mater cells. Second, the phenotype of nociceptive neurons has been altered by recombinant herpes viruses overexpressing antinociceptive peptides or reducing expression of endogenous nociceptive molecules. Both approaches attenuate or reverse persistent nociceptive states, suggesting use in the development of genetic therapy for pain management in humans.

Dopamine increases glial cell line-derived neurotrophic factor in human fetal astrocytes

The use of fetal astrocytes for gene delivery into brains with neurodegenerative diseases has been suggested. Therefore, the effects of neurotransmitters in the brain on such cells are of interest. The presence of D1(D1A) receptors and the effect of dopamine on a fetal human astrocyte cell line (SVG cells) in vitro were examined. SVG cells expressed D1(D(1A)), but not D5(D1B) receptors, as shown by RT-PCR. Exposure to dopamine, apomorphine, and the specific D1 agonist, SKF-38393, increased glial-derived neurotrophic factor production of SVG cells, as well as intracellular free calcium. Exposure to the specific D1 antagonist, SCH 23390, blocked these effects. Thus, if implanted into a brain region rich in dopamine, or if transfected with the tyrosine hydroxylase gene, fetal astrocytes may serve as paracrine/autocrine cells capable of supplying critical growth factors to diseased brain tissue.

From gene transfer to gene therapy in lysosomal storage diseases affecting the central nervous system

Gene transfer into the central nervous system (CNS) is one of the foremost scientific challenges today. To give a brief survey of possible approaches to gene therapy in diseases affecting the CNS, we have selected the lysosomal storage diseases (LDS), which are an excellent model of both early-onset infantile neurological forms and late-onset adult psychiatric forms. Lysosomal storage diseases represent a group of about 50 monogenic metabolic disorders resulting from a deficiency in intralysosomal enzymes involved in macromolecule catabolism. The clinical severity, including neuropsychiatric symptoms, and the absence of an efficient therapy for the majority of these disorders prompted the various trials of gene therapy now in progress. Most of the genes encoding the normal lysosomal enzymes have been cloned, and the size of the corresponding cDNAs is generally compatible with their transfer by recombinant vectors. New vectors with improved immunogenicity, transduction efficacy, insert capacity, and specificity of targeting are under development. Here we discuss several gene therapy strategies for the correction of LSD-induced anomalies in the CNS. Interesting results have been obtained by animal model brain, which raises hopes that large-scale clinical trials may soon be started.

Combined injection of rAAV with mannitol enhances gene expression in the rat brain

Recombinant adeno-associated viruses (rAAV) are highly efficient vectors for gene transfer into the central nervous system (CNS). However, a major hurdle for gene delivery to the mammalian brain is to achieve high-level transduction in target cells beyond the immediate injection site. Therefore, in addition to improvements in expression cassettes and viral titers, optimal injection parameters need to be defined. Here, we show that previous studies of somatic cell gene transfer to the mammalian brain have used suboptimal injection parameters, with even the lowest reported perfusion rates still excessively fast. Moreover, we evaluated the effect of local administration of mannitol to further enhance transgene expression and vector spread. Ultraslow microperfusion of rAAV, i.e., <33 nl/min, resulted in significantly higher gene expression and less injury of surrounding tissue than the previously reported rates of 100 nl/min or faster. Co-infusion of mannitol facilitated gene transfer to neurons, increasing both the total number and the distribution of transduced cells by 200-300%. Gene transfer studies in the CNS using rAAV should use very slow infusion rates and combined injection with mannitol to maximize transduction efficiency and spread.

Helper-dependent adenoviral vector-mediated gene transfer in aged rat brain

Transfer of the neurotrophin gene into brain can attenuate age-related deficits such as neuronal atrophy and memory loss, but a suitable vector for this procedure has been lacking. The toxicity and immunogenicity of first-generation adenoviral vectors with E1 deletion (fgAdv) prohibit the application of gene transfer in the majority of central nervous system disorders. Here, we report less toxic and persistent gene expression mediated by helper-dependent adenovirus (hdAdv) in aged rat brain. After intrahippocampal or intraventricular inoculation of the vector, transgene expression was monitored by X-Gal staining and compared with fgAdv-mediated expression. Host inflammatory and immune responses against these vectors were evaluated by immunohistochemical detection of microglia, astrocytes, and infiltrating macrophages, as well as by enzyme-linked immunosorbent assay of cytokines TNF-alpha and IL-1beta. Transgene expression mediated by hdAdv persisted for more than 183 days regardless of inoculation site, as compared with 33 and 66 days for fgAdv-mediated expression after intraventricular and intrahippocampal inoculation, respectively. Inoculation with hdAdv was also associated with reduced numbers of activated microglial cells, astrocytes, and infiltrating macrophages in brain tissue. Secretion of the proinflammatory cytokines TNF-alpha and IL-1beta was minimal after hdAdv but not after fgAdv inoculation. These findings indicate that hdAdv would provide a safe and effective means to transfer therapeutic genes into aged brain.

Gene therapy in wound repair and regeneration

The potential use of gene therapy to treat human disease increases with the development of various physical, chemical, and biological methods to deliver genes to mammalian cells, and with our rapidly expanding knowledge of the human genome. One area of therapeutic interest for gene therapy is the treatment of wound healing disorders. Most recently, recombinant human growth factor therapy has been examined as a means to treat problem wounds. However, this approach suffers from the difficulty in providing an accurate dose of growth factor and the expense of the recombinant proteins. Delivery of a gene that could be expressed within the wound is an attractive alternative to application of the protein. This review discusses several methods that have been used to deliver genes encoding growth factor proteins into wounds and the advantages/disadvantages of each approach. Novel methods to regulate the expression of the transgene are also presented, highlighting the ability of these unique vector systems to adjust gene dose as the wound heals. We expect that gene therapy will become a significant treatment modality for those wound healing pathologies refractory to other wound management approaches in the years ahead.