Self-inactivating lentiviral vectors with enhanced transgene expression as potential gene transfer system in Parkinson's disease

Functional reinnervation from remaining DA terminals induced by GDNF lentivirus in a rat model of early Parkinson's disease

Glial cell-line derived neurotrophic factor (GDNF) is a good candidate agent for restoring functional reinnervation and/or neuroprotection of dopamine (DA) nigrostriatal system and thus for the treatment of Parkinson's disease (PD). Viral delivery is currently the most likely in vivo strategy for delivery of the therapeutic protein into the brain for treatment of neurological diseases. However, one of the important unresolved issues for this strategy is the threshold number of DA nigral neurons and/or of striatal DA terminals necessary for optimal benefit from GDNF therapy. In this study, we examined the intrastriatal neurotrophic effects of long-term GDNF delivery using a lentiviral vector in a new rat model of early PD. Lenti-GDNF was injected into the striatum 4 weeks after partial substantia nigra pars compacta 6-hydroxydopamine-induced lesion. Striatal denervation was evaluated by assessing tyrosine hydroxylase-positive DA fiber density and corroborated by testing motor deficit by means of a staircase test. GDNF treatment restored complete striatal DA innervation in the previously denervated area and this was associated with significant behavioral improvements.

Lentivirus-mediated expression of glutathione peroxidase: neuroprotection in murine models of Parkinson's disease

Reactive oxygen species are considered to contribute to the pathogenesis of Parkinson's disease (PD). In order to study viral vector-mediated overexpression of the antioxidant enzyme glutathione peroxidase (GPX) as a potential neuroprotective approach in both an in vitro and in vivo model of PD, we have developed a lentiviral vector carrying the human GPX1 gene. Neuroblastoma cells infected with this vector showed a 2-fold increase in GPX activity compared to cells infected with a control vector. In addition, overexpression of GPX protected 83.0 +/- 14.2% of these cells against 6-hydroxydopamine (6-OHDA)-induced toxicity, while only 22.9 +/- 4.6% of the cells infected with a control vector survived. Furthermore, lentivirus-mediated expression of GPX1 in nigral dopaminergic neurons in vivo prior to intrastriatal injection of 6-OHDA led to a small, but significant protection of these cells against drug-induced toxicity. These results indicate that antioxidative gene therapy strategies may be relevant for PD.

Progressive and selective striatal degeneration in primary neuronal cultures using lentiviral vector coding for a mutant huntingtin fragment

A lentiviral vector expressing a mutant huntingtin protein (htt171-82Q) was used to generate a chronic model of Huntington's disease (HD) in rat primary striatal cultures. In this model, the majority of neurons expressed the transgene so that Western blot analysis and flow cytometry measurement could complement immunohistological evaluation. Mutant huntingtin produced a slowly progressing pathology characterized after 1 month by the appearance of neuritic aggregates followed by intranuclear inclusions, morphological anomalies of neurites, loss of neurofilament 160, increased expression in stress response protein Hsp70, and later loss of neuronal markers such as NeuN and MAP-2. At 2 months post-infection, a significant increase in TUNEL-positive cells confirmed actual striatal cell loss. Interestingly, cortical cultures infected with the same vector showed no sign of neuronal dysfunction despite accumulation of numerous inclusions. We finally examined whether the trophic factors CNTF and BDNF that were found neuroprotective in acute HD models could prevent striatal degeneration in a chronic model. Results demonstrated that both agents were neuroprotective without modifying inclusion formation. The present study demonstrates that viral vectors coding for mutant htt provides an advantageous system for histological and biochemical analysis of HD pathogenesis in primary striatal cultures.

Overexpression of glial cell line-derived neurotrophic factor using a lentiviral vector induces time- and dose-dependent downregulation of tyrosine hydroxylase in the intact nigrostriatal dopamine system

The effects of continuous glial cell line-derived neurotrophic factor (GDNF) overexpression in the intact nigrostriatal dopamine (DA) system was studied using recombinant lentiviral (rLV) vector delivery of GDNF to the striatum or substantia nigra (SN) in the rat. Intrastriatal delivery of rLV-GDNF resulted in significant overexpression of GDNF in the striatum (2-4 ng/mg tissue) and anterograde transport of GDNF protein to the SN. Striatal rLV-GDNF delivery initially induced an increase in DA turnover (1-6 weeks), accompanied by significant contralateral turning in response to amphetamine, suggesting an enhancement of the DA system on the injected side. Starting 6 weeks after continuous GDNF delivery, we observed a selective downregulation of tyrosine hydroxylase (TH) protein (approximately 70%) that was maintained until the end of the experiment (24 weeks). A similar effect was observed when rLV-GDNF was injected into the SN. The magnitude of TH downregulation was related to the level of GDNF expression and was most pronounced in animals in which the striatal GDNF level exceeded 0.7 ng/mg tissue. The decreased TH protein levels were associated with similar reductions in the in vitro TH enzyme activity (approximately 70%); however, in vivo L-3,4-dihydroxyphenylalanine production rate and DA tissue levels were maintained at normal levels. The results indicate that downregulation of TH protein reflects a compensatory effect in response to continuous GDNF stimulation of the DA neurons mediated by a combination of overactivity at the DA synapse and a direct GDNF-induced action on TH gene expression. This compensatory mechanism is proposed to maintain long-term DA neuron function within the normal range.

Lentiviral-mediated silencing of SOD1 through RNA interference retards disease onset and progression in a mouse model of ALS

Mutations in Cu/Zn superoxide dismutase (encoded by SOD1), one of the causes of familial amyotrophic lateral sclerosis (ALS), lead to progressive death of motoneurons through a gain-of-function mechanism. RNA interference (RNAi) mediated by viral vectors allows for long-term reduction in gene expression and represents an attractive therapeutic approach for genetic diseases characterized by acquired toxic properties. We report that in SOD1(G93A) transgenic mice, a model for familial ALS, intraspinal injection of a lentiviral vector that produces RNAi-mediated silencing of SOD1 substantially retards both the onset and the progression rate of the disease.

Regulated delivery of glial cell line-derived neurotrophic factor into rat striatum, using a tetracycline-dependent lentiviral vector

In this study, a tetracycline-regulated lentiviral vector system, based on the tetracycline-dependent transactivator rtTA2(S)-M2, was developed for controlled expression of glial cell line-derived neurotrophic factor (GDNF) in the rat brain. Expression of the marker gene green fluorescent protein (GFP) and GDNF was tightly regulated in a dose-dependent manner in neural cell lines in vitro. Injection of high-titer lentiviral vectors into the rat striatum resulted in a 7-fold induction of GDNF tissue levels (1060 pg/mg tissue), when doxycycline (a tetracycline analog) was added to the drinking water. However, low levels of GDNF (150 pg/mg tissue) were also detected in animals that did not receive doxycycline, indicating a significant background leakage from the vector system in vivo. The level of basal expression was markedly reduced when a 10-fold lower dose of the tetracycline-regulated GDNF vector was injected into the striatum (3-11 pg/mg tissue), and doxycycline-induced GDNF tissue levels obtained in these animals were about 190 pg/mg tissue. Doxycycline-induced expression of GDNF resulted in a significant downregulation of the tyrosine hydroxylase (TH) protein in the intact striatum. Removal of doxycycline from the drinking water rapidly (within 3 days) turned off transgenic GDNF mRNA expression and GDNF protein levels in the tissue were completely reduced by 2 weeks, demonstrating the dynamics of the system in vivo. Accordingly, TH protein expression returned to normal by 2-8 weeks after removal of doxycycline, indicating that GDNF-induced downregulation of TH is a reversible event.

Lentiviral nigral delivery of GDNF does not prevent neurodegeneration in a genetic rat model of Parkinson's disease

Viral delivery of glial cell line-derived neurotrophic factor (GDNF) currently represents one of the most promising neuroprotective strategies for Parkinson's Disease (PD). However, the effect of this neurotrophic factor has never been tested in the newly available genetic models of PD based on the viral expression of mutated alpha-synuclein. In this study, we evaluated the ability of lentiviral vectors coding for GDNF (lenti-GDNF) to prevent nigral dopaminergic degeneration associated with the lentiviral mediated expression of the A30P mutant human alpha-synuclein (lenti-A30P). This virally based rat model develops a progressive and selective loss of dopamine neurons associated with the appearance of alpha-synuclein containing inclusions, thus recapitulating the major hallmarks of PD. Lenti-GDNF was injected in the substantia nigra 2 weeks before nigral administration of lenti-A30P. Although a robust expression of GDNF was observed in the whole nigrostriatal pathway due to retrograde and/or anterograde transport, lenti-GDNF did not prevent the alpha-synuclein-induced dopaminergic neurodegeneration in the lentiviral-based genetic rat model of PD. These results suggest that sustained GDNF treatment cannot modulate the cellular toxicity related to abnormal folded protein accumulation as mutated human alpha-synuclein.

Lentiviral vector delivery of parkin prevents dopaminergic degeneration in an alpha-synuclein rat model of Parkinson's disease

Parkinson's disease (PD) is characterized by a progressive loss of midbrain dopamine neurons and the presence of cytoplasmic inclusions called Lewy bodies. Mutations in several genes including alpha-synuclein and parkin have been linked to familial PD. The loss of parkin's E3-ligase activity leads to dopaminergic neuronal degeneration in early-onset autosomal recessive juvenile parkinsonism, suggesting a key role of parkin for dopamine neuron survival. To evaluate the potential neuroprotective role of parkin in the pathogenesis of PD, we tested whether overexpression of wild-type rat parkin could protect against the toxicity of mutated human A30P alpha-synuclein in a rat lentiviral model of PD. Animals overexpressing parkin showed significant reductions in alpha-synuclein-induced neuropathology, including preservation of tyrosine hydroxylase-positive cell bodies in the substantia nigra and sparing of tyrosine hydroxylase-positive nerve terminals in the striatum. The parkin-mediated neuroprotection was associated with an increase in hyperphosphorylated alpha-synuclein inclusions, suggesting a key role for parkin in the genesis of Lewy bodies. These results indicate that parkin gene therapy may represent a promising candidate treatment for PD.

Dissociation between short-term increased graft survival and long-term functional improvements in Parkinsonian rats overexpressing glial cell line-derived neurotrophic factor

The present study was designed to analyse whether continuous overexpression of glial cell line-derived neurotrophic factor (GDNF) in the striatum by a recombinant lentiviral vector can provide improved cell survival and additional long-term functional benefits after transplantation of fetal ventral mesencephalic cells in Parkinsonian rats. A four-site intrastriatal 6-hydroxydopamine lesion resulted in an 80-90% depletion of nigral dopamine cells and striatal fiber innervation, leading to stable motor impairments. Histological analysis performed at 4 weeks after grafting into the GDNF-overexpressing striatum revealed a twofold increase in the number of surviving tyrosine hydroxylase (TH)-positive cells, as compared with grafts placed in control (green fluorescent protein-overexpressing) animals. However, in animals that were allowed to survive for 6 months, the numbers of surviving TH-positive cells in the grafts were equal in both groups, suggesting that the cells initially protected at 4 weeks failed to survive despite the continued presence of GDNF. Although cell survival was similar in both grafted groups, the TH-positive fiber innervation density was lower in the GDNF-treated grafted animals (30% of normal) compared with animals with control grafts (55% of normal). The vesicular monoamine transporter-2-positive fiber density in the striatum, by contrast, was equal in both groups, suggesting that long-term GDNF overexpression induced a selective down-regulation of TH in the grafted dopamine neurons. Behavioral analysis in the long-term grafted animals showed that the control grafted animals improved their performance in spontaneous motor behaviors to approximately 50% of normal, whereas the GDNF treatment did not provide any additional recovery.

A synthetic Rev-independent bovine immunodeficiency virus-based packaging construct

Replication competent lentivirus (RCL) has been the major safety concern associated with applications of lentivirus-based gene transfer systems for human gene therapy. Minimization and elimination of overlaps between the packaging and the transfer vector constructs are expected to reduce the potential to generate RCL. We previously developed second- and third-generation bovine immunodeficiency virus (BIV)-based gene transfer systems. However, some sequence homologies between the vector and gag/pol packaging constructs remained. In order to minimize the sequence homologies, we recoded gag/pol with codon usage optimized for expression in human cells in this report. Expression of the recoded gag/pol was Rev/RRE independent. Thus, RRE was eliminated from the packaging construct, thereby removing a 312 bp block of homology. In addition, recoding gag/pol minimized overall homologies between the packaging and transfer vector constructs. Vectors generated by the recoded packaging construct with a four plasmid system had titers greater than 1 x 10(6) transducing units per milliliter, equivalent to those of the earlier generation systems. The vectors were functional in vitro and efficiently transduced rat pigment epithelial cells in vivo. Generation of the synthetic packaging construct provides further advances to the safety of lentiviral vectors for clinical applications.

Gene therapy in Parkinson?s disease

Gene therapy in Parkinson's disease appears to be at the brink of the clinical study phase. Future gene therapy protocols will be based on a substantial amount of preclinical data regarding the use of ex vivo and in vivo genetic modifications with the help of viral or non-viral vectors. To date, the supplementation of neurotrophic factors and substitution for the dopaminergic deficit have formed the focus of trials to achieve relief in animal models of Parkinson's disease. Newer approaches include attempts to influence detrimental cell signalling pathways and to inhibit overactive basal ganglia structures. Nevertheless, current models of Parkinson's disease do not mirror all aspects of the human disease, and important issues with respect to long-term protein expression, choice of target structures and transgenes and safety remain to be solved. Here, we thoroughly review available animal data of gene transfer in models of Parkinson's disease.

Lentiviral vectors

Vectors based on lentiviruses have reached a state of development such that clinical studies using these agents as gene delivery vehicles have now begun. They have particular advantages for certain in vitro and in vivo applications especially the unique capability of integrating genetic material into the genome of non-dividing cells. Their rapid progress into clinical use reflects in part the huge body of knowledge which has accumulated about HIV in the last 20 years. Despite this, many aspects of viral assembly on which the success of these vectors depends are rather poorly understood. Sufficient is known however to be able to produce a safe and reproducible high titre vector preparation for effective transduction of growth-arrested tissues such as neural tissue, muscle and liver.

Local GDNF expression mediated by lentiviral vector protects facial nerve motoneurons but not spinal motoneurons in SOD1G93A transgenic mice

Approximately 2% of amyotrophic lateral sclerosis (ALS) cases are associated with mutations in the cytosolic Cu/Zn superoxide dismutase 1 (SOD1) gene. Transgenic SOD1 mice constitute useful models of ALS to screen therapeutical approaches. Glial cell line-derived neurotrophic factor (GDNF) holds promises for the treatment of motoneuron disease. In the present study, GDNF expression in motoneurons of SOD1(G93A) transgenic mice was assessed by facial nucleus or intraspinal injection of lentiviral vectors (LV) encoding GDNF. We show that lentiviral vectors allow the expression for at least 12 weeks of GDNF that was clearly detected in motoneurons. This robust intraspinal expression did, however, not prevent the loss of motoneurons and muscle denervation of transgenic mice. In contrast, LV-GDNF induced a significant rescue of motoneurons in the facial nucleus and prevented motoneuron atrophy. The differential effect of GDNF on facial nucleus versus spinal motoneurons suggests different vulnerability of motoneurons in ALS.

Neuroprotection in a rat Parkinson model by GDNF gene therapy using EIAV vector

Vectors based on lentiviruses are opening up new approaches for the treatment of neurodegenerative diseases. Currently, the equine infectious anaemia virus (EIAV) vector is one of the most attractive gene delivery systems with respect to neuronal tropism. The aim was to validate EIAV-lentiviral vectors as a gene delivery system for neurotrophic factor genes in an animal model of Parkinson's disease. EIAV carrying the glial cell line-derived neurotrophic factor (GDNF) gene was unilaterally injected into rat striatum and above the substantia nigra (SN). One week later, the rats received a 6-OHDA lesion into the ipsilateral striatum. GDNF delivery led to extensive expression of GDNF protein within the striatum. In addition, near complete protection against dopaminergic cell death was observed in the GDNF-treated group.

Protective effects of intracerebral adenoviral-mediated GDNF gene transfer in a rat model of Parkinson's disease

This study focuses on the potential protective effects of intracerebral adeno-viral mediated glial cell line derived neurotrophic factor (GDNF) gene transfer in a rat model of Parkinson's disease (PD). Thirty-five SD rats were divided into three groups to receive perinigral injections of recombinant adenovirus encoding GDNF (Ad-GDNF), LacZ (Ad-LacZ) or PBS, respectively. One week later, an intrastriatal injection of 6-hydroxydopamine (6-OHDA) was administered to induce the progressive degeneration of dopaminergic neurons. Immunohistochemistry showed that GDNF treatment prior to neuronal damage could promote survival and morphological recovery of tyrosine hydroxylase (TH)-positive neurons in the midbrain. Approximately 70% of nigral TH-positive cells survived in the Ad-GDNF group, compared to approximately 30% for the Ad-LacZ or PBS control group. Histochemical analysis of monoamine levels in the striatum demonstrated that the dopamine content was higher for the Ad-GDNF group than the control groups. Similarly, Ad-GDNF treated animals showed improved apomorphine-induced rotational behavior. The exogenous GDNF gene was efficiently expressed in the brain as detected by ELISA. This work demonstrates that intracerebral adeno-viral mediated GDNF gene transfer can protect dopaminergic neurons in vivo from 6-OHDA-induced injuries. The approach used in this study could potentially be used therapeutically in patients with PD and further work is required to explore this idea in depth.

Long-term lentiviral-mediated expression of ciliary neurotrophic factor in the striatum of Huntington's disease transgenic mice

Ciliary neurotrophic factor (CNTF) has been shown to prevent behavioral deficits and striatal degeneration in neurotoxic models of Huntington's disease (HD), but its effect in a genetic model has not been evaluated. Lentiviral vectors expressing the human CNTF or LacZ reporter gene were therefore injected in the striatum of wild-type (WT) and transgenic mice expressing full-length huntingtin with 72 CAG repeats (YAC72). Behavioral analysis showed increased locomotor activity in 5- to 6-month-old YAC72-LacZ mice compared to WT-LacZ animals. Interestingly, CNTF expression reduced the activity levels of YAC72 mice compared to control animals. In both WT and YAC72 mice, CNTF expression was demonstrated in striatal punches, up to a year after lentiviral injection. Stereological analysis revealed that the number of LacZ and DARPP-32-positive neurons were decreased in YAC72-LacZ mice compared to WT-LacZ animals. Assessment of the benefit of CNTF expression in the YAC72 mice was, however, complicated by a down-regulation of DARPP-32 and to a lesser extent of NeuN in all mice treated with CNTF. The expression of the neuronal marker NADPH-d was unaffected by CNTF, but expression of the astrocytic marker glial fibrillary acidic protein (GFAP) was increased. Finally, a reduction of the number of striatal dark cells was observed in YAC mice treated with CNTF compared to LacZ. These data indicate that sustained striatal expression of CNTF can be achieved with lentiviruses. Further studies are, however, needed to investigate the intracellular signaling pathways mediating the long-term effects of CNTF expression on dopamine signaling, glial cell activation and how these changes may affect HD pathology.

Lentiviral Vector: A Useful Tool for Transduction of Human Liver Endothelial Cells

Endothelial cells play multiple roles in pathophysiologic processes and are increasingly being recognized as target cells of gene therapy. Lentiviral vectors derived from human immunodeficiency virus type 1 have an ability to infect both dividing and nondividing cells and currently receive a great deal of attention as an innovative tool for transduction of target cells. The purpose of the present work was to evaluate the efficacy of a lentiviral vector for transducing human liver endothelial cells (HLECs) in vitro. For the present study, a pseudotyped lentiviral vector encoding a green fluorescent protein (GFP) gene, LtV-GFP, was generated by means of FuGENE 6 method and allowed to infect HLECs. Approximately 95% of HLECs were positive for GFP expression after LtV-GFP infection at a multiplicity of infection of 10. Notably, LtV-GFP transduced HLECs had stable and long term GFP expression, showed gene expression of endothelial markers including CD 34, factor VIII, flt-1, KDR/flk-1 and HGF, and maintained in vitro angiogenic potential in a Matrigel assay to the same extent as primarily cultured HLECs. These findings provide evidence that lentivirus based gene delivery is an efficient tool for transduction of endothelial cells that could be considered for cell and gene therapies and hybrid artificial organs.

Targeted transgene expression in rat brain using lentiviral vectors

Direct gene transfer to the adult brain is dependent on vectors that transduce non-dividing cells, such as lentiviral vectors. Another aspect of the development of gene therapy to the brain is the need for cell-specific transgene expression. Expression from vesicular stomatitis virus G-protein (VSV-G) pseudotyped lentiviral vectors has been reported to be mainly neuron specific in the brain. We constructed cell-specific lentiviral vectors using the neuron-specific enolase (rNSE) or the glial fibrillary acidic protein (hGFAP) promoters and compared them to the ubiquitous human cytomegalovirus promoter (hCMV), a hybrid CMV/beta-actin promoter (CAG) and the promoter for human elongation factor 1 alpha (EF1 alpha). Our results showed that the hGFAP promoter was expressed only in glial cells, whereas rNSE was purely neuron specific, showing that VSV-G is pantropic in the rat striatum. We conclude that the VSV-G allows transduction of both glial and neuronal cells and the promoter dictates in what cell type the transgene will be expressed. The expression of transgenes exclusively in astrocytes would allow for local delivery of secreted transgene products, such as glial cell line-derived neurotrophic factor (GDNF), circumventing the anterograde transport that may induce unwanted side effects.

Activity analysis of housekeeping promoters using self-inactivating lentiviral vector delivery into the mouse retina

For most retinal degeneration disorders, no efficient treatment exists to preserve photoreceptors (PRs) and, consequently, to maintain vision. Gene transfer appears to be a promising approach to prevent PR loss. In order to design adequate vectors to target specific retinal cell types, we have analyzed the expression pattern of three different promoters (mouse phosphoglycerate kinase 1 (PGK), elongation factor-1 (EFS), rhodopsin (Rho)) in newborn and adult DBA/2 mice retinas using self-inactivating lentiviral vectors. At 7 days after intraocular injection and in optimal conditions, cell transduction was observed up to 1.5 mm from the injection site. PGK promoter expression was predominant in the retinal pigment epithelium (RPE), especially in adult mice, whereas the EFS promoter allowed a broad expression in the retina. Finally, as expected, the Rho promoter was specifically expressed in PRs. Differences in the cell types transduced and in transduction efficiency were observed between newborn and adult injected eyes emphasizing the importance of such basic studies for further gene therapy approaches as well as for understanding the transcriptional changes during retinal maturation. Thus, for future attempts to slow or rescue retinal degeneration by lentiviral delivery, PGK and EFS are more suitable to control the expression of a supporting secreted factor, PGK being mainly expressed in RPE and EFS in different cell types throughout the entire retina, whereas Rho should allow to specifically deliver the therapeutic gene to PRs.

Long-term replacement of a mutated nonfunctional CNS gene: reversal of hypothalamic diabetes insipidus using an EIAV-based lentiviral vector expressing arginine vasopressin

Due to the complexity of brain function and the difficulty in monitoring alterations in neuronal gene expression, the potential of lentiviral gene therapy vectors to treat disorders of the CNS has been difficult to fully assess. In this study, we have assessed the utility of a third-generation equine infectious anemia virus (EIAV) in the Brattleboro rat model of diabetes insipidus, in which a mutation in the arginine vasopressin (AVP) gene results in the production of nonfunctional mutant AVP precursor protein. Importantly, by using this model it is possible to monitor the success of the gene therapy treatment by noninvasive assays. Injection of an EIAV-CMV-AVP vector into the supraoptic nuclei of the hypothalamus resulted in expression of functional AVP peptide in magnocellular neurons. This was accompanied by a 100% recovery in water homeostasis as assessed by daily water intake, urine production, and urine osmolality lasting for a 1-year measurement period. These data show that a single gene defect leading to a neurological disorder can be corrected with a lentiviral-based strategy. This study highlights the potential of using viral gene therapy for the long-term treatment of disorders of the CNS.

Specific transgene expression in human and mouse CD4+ cells using lentiviral vectors with regulatory sequences from the CD4 gene

Achieving cell-specific expression of a therapeutic transgene by gene transfer vectors represents a major goal for gene therapy. To achieve specific expression of a transgene in CD4(+) cells, we have generated lentiviral vectors expressing the enhanced green fluorescent protein (eGFP) reporter gene under the control of regulatory sequences derived from the CD4 gene--a minimal promoter and the proximal enhancer, with or without the silencer. Both lentiviral vectors could be produced at high titers (more than 10(7) infectious particles per milliliter) and were used to transduce healthy murine hematopoietic stem cells (HSCs). On reconstitution of RAG-2-deficient mice with transduced HSCs, the specific vectors were efficiently expressed in T cells, minimally expressed in B cells, and not expressed in immature cells of the bone marrow. Addition of the CD4 gene-silencing element in the vector regulatory sequences led to further restriction of eGFP expression into CD4(+) T cells in reconstituted mice and in ex vivo-transduced human T cells. Non-T CD4(+) dendritic and macrophage cells derived from human CD34(+) cells in vitro expressed the transgene of the specific vectors, albeit at lower levels than CD4(+) T cells. Altogether, we have generated lentiviral vectors that allow specific targeting of transgene expression to CD4(+) cells after differentiation of transduced mice HSCs and human mature T cells. Ultimately, these vectors may prove useful for in situ injections for in vivo gene therapy of HIV infection or genetic immunodeficiencies.

In vivo gene delivery of glial cell line--derived neurotrophic factor for Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects approximately 1,000,000 Americans. The cause of the disease remains unknown. The histopathological hallmarks of the disease are dopaminergic striatal insufficiency secondary to a loss of dopaminergic neurons in the substantia nigra pars compacta and intracellular inclusion called Lewy bodies. Currently, only symptomatic treatment for PD is available. Although some treatments are efficacious for many years, all have significant limitations and new therapeutic approaches are needed. Gene therapy is ideal for delivering therapeutic molecules to site-specific regions of the central nervous system. Via gene therapy, a piece or pieces of DNA placed into a carrying vector encoding for a substance of interest can be introduced into specific cells. Although there are several ways that gene therapy can be applied for PD, this review focuses on in vivo gene delivery of glial cell line-derived neurotrophic factor (GDNF) as a neuroprotective strategy for PD.

Lentiviral vectors for gene delivery to normal and demyelinated white matter

Lentiviral vectors are increasingly used for gene delivery to neurons and in experimental models of neurodegeneration. Their use in gene delivery to white matter and their potential value in preventing or repairing CNS demyelination has received less attention. Here we show using a VSV-G-pseudotyped HIV-derived vector expressing the marker gene LacZ that lentiviral vectors transduce the major macroglial cell types present in normal white matter (astrocytes, oligodendrocytes, and oligodendrocyte progenitors). Injection of lentiviral vectors causes an inflammatory response at the injection site characterized by OX42(+) and ED1(+) macrophages, but only a few CD8(+) and no CD4(+) lymphocytes, and mild demyelination. Injection of lentiviral vectors into areas of toxin-induced demyelination resulted in significant numbers of cells expressing the marker gene and was a more effective means of gene delivery than was a LacZ-expressing murine retroviral vector.

Recent advances in stem cell neurobiology

1. Neural stem cells can be cultured from the CNS of different mammalian species at many stages of development. They have an extensive capacity for self-renewal and will proliferate ex vivo in response to mitogenic growth factors or following genetic modification with immortalising oncogenes. Neural stem cells are multipotent since their differentiating progeny will give rise to the principal cellular phenotypes comprising the mature CNS: neurons, astrocytes and oligodendrocytes. 2. Neural stem cells can also be derived from more primitive embryonic stem (ES) cells cultured from the blastocyst. ES cells are considered to be pluripotent since they can give rise to the full cellular spectrum and will, therefore, contribute to all three of the embryonic germ layers: endoderm, mesoderm and ectoderm. However, pluripotent cells have also been derived from germ cells and teratocarcinomas (embryonal carcinomas) and their progeny may also give rise to the multiple cellular phenotypes contributing to the CNS. In a recent development, ES cells have also been isolated and grown from human blastocysts, thus raising the possibility of growing autologous stem cells when combined with nuclear transfer technology. 3. There is now an emerging recognition that the adult mammalian brain, including that of primates and humans, harbours stem cell populations suggesting the existence of a previously unrecognised neural plasticity to the mature CNS, and thereby raising the possibility of promoting endogenous neural reconstruction. 4. Such reports have fuelled expectations for the clinical exploitation of neural stem cells in cell replacement or recruitment strategies for the treatment of a variety of human neurological conditions including Parkinson's disease (PD), Huntington's disease, multiple sclerosis and ischaemic brain injury. Owing to their migratory capacity within the CNS, neural stem cells may also find potential clinical application as cellular vectors for widespread gene delivery and the expression of therapeutic proteins. In this regard, they may be eminently suitable for the correction of genetically-determined CNS disorders and in the management of certain tumors responsive to cytokines. Since large numbers of stem cells can be generated efficiently in culture, they may obviate some of the technical and ethical limitations associated with the use of fresh (primary) embryonic neural tissue in current transplantation strategies. 5. While considerable recent progress has been made in terms of developing new techniques allowing for the long-term culture of human stem cells, the successful clinical application of these cells is presently limited by our understanding of both (i) the intrinsic and extrinsic regulators of stem cell proliferation and (ii) those factors controlling cell lineage determination and differentiation. Although such cells may also provide accessible model systems for studying neural development, progress in the field has been further limited by the lack of suitable markers needed for the identification and selection of cells within proliferating heterogeneous populations of precursor cells. There is a further need to distinguish between the committed fate (defined during normal development) and the potential specification (implying flexibility of fate through manipulation of its environment) of stem cells undergoing differentiation. 6. With these challenges lying ahead, it is the opinion of the authors that stem-cell therapy is likely to remain within the experimental arena for the foreseeable future. In this regard, few (if any) of the in vivo studies employing neural stem cell grafts have shown convincingly that behavioural recovery can be achieved in the various model paradigms. Moreover, issues relating to the quality control of cultured cells and their safety following transplantation have only begun to be addressed. 7. While on the one hand cell biotechnologists have been quick to realise the potential commercial value, human stem cell research and its clinical applications has been the subject of intense ethical and legislative considerations. The present chapter aims to review some recent aspects of stem cell research applicable to developmental neurobiology and the potential applications in clinical neuroscience.

Doxycycline-regulated lentiviral vector system with a novel reverse transactivator rtTA2S-M2 shows a tight control of gene expression in vitro and in vivo

Regulated expression of therapeutic genes is required for long-term gene therapy applications for many disorders. Here we describe a doxycycline (dox)-regulated lentiviral vector system consisting of two HIV-1-based self-inactivating viruses. One of the vectors is constitutively expressing a novel improved version of the tetracycline reverse transactivator rtTA2(S)-M2 and the other has a rtTA responsive promoter driving the expression of beta-galactosidase gene (lacZ). The rtTA2(S)-M2 has highly improved properties with respect to specificity, stability and inducibility. Functionality of the system by dox was confirmed after in vitro cotransduction of Chinese hamster ovary and human endothelial hybridoma (EAhy926) cells. Regulation of the system showed tight control of the gene expression. Dose dependence for dox was seen with concentrations that can be obtained in vivo with doses normally used in clinical practice. LacZ expression could be switched on/off during long-term (3 months) culturing of cotransduced cells. The system was next tested in vivo after cotransduction into rat brain and studying expression of the lacZ gene in dox-treated and control rats. Nested RT-PCR confirmed that the tight control of the gene expression was achieved in vivo. Also, X-gal staining showed positive cells in the dox-treated rats, but not in the controls 10 days after cotransduction with 4 days preceding treatment with dox. It is concluded that our doxycycline-regulated vector system shows significant potential for long-term gene therapy treatments.

Optimization of human erythropoietin secretion from MLV-infected human primary fibroblasts used for encapsulated cell therapy

BACKGROUND

The transplantation of encapsulated cells genetically engineered to secrete human erythropoietin (hEpo) represents an alternative to repeated injections of the recombinant hormone for the treatment of Epo-responsive anemia. In the present study, the ability of primary human foreskin fibroblasts to secrete high levels of hEpo and the importance of cis-acting elements and infection conditions on transgene expression level were assessed.

METHODS

The transduction efficiency was first evaluated with beta-galactosidase (LacZ)-encoding retroviral vectors derived from the murine leukemia retrovirus (MLV) pseudotyped either with an amphotropic envelope or with the G glycoprotein of vesicular stomatitis virus (VSV-G). Human fibroblasts were then infected with an amphotropic hEpo-expressing retroviral vector, which was modified by insertion of a post-transcriptional regulatory element from the woodchuck hepatitis virus (WPRE) and a Kozak consensus sequence (KZ). Human Epo production was further optimized by increasing the multiplicity of infection and by selecting high producer cells. The survival and the transgene expression of these fibroblasts were finally evaluated in vivo. The cells were encapsulated into microporous hollow fibers and subcutaneously implanted in nude mice.

RESULTS

A secretion level of approximately 5 IU hEpo/10(6) cells/day was obtained with the basal vector. A 7.5-fold increase in transgene expression was observed with the insertion of WPRE and KZ elements. Finally, according to the optimization of infection conditions, we obtained a 40-fold increase in hEpo secretion, reaching approximately 200 IU hEpo/10(6) cells/day. The in vivo experiments showed an increase in the hematocrit during the first 2 weeks and elevated levels exceeding 60% were maintained over a 6-week period.

CONCLUSIONS

These results indicate that primary human fibroblasts represent a promising source for encapsulated cell therapy.

Comparative study of GDNF delivery systems for the CNS: polymer rods, encapsulated cells, and lentiviral vectors

Glial cell line-derived neurotrophic factor (GDNF) holds great promise for the treatment of Parkinson's disease. In humans, its intracerebroventricular administration leads to limiting side effects. Direct parenchymal delivery using mechanical means, or cell and gene therapy represent potential alternatives. In the present study, a representative of each of these three approaches, i.e. polymer rods, genetically modified encapsulated cells and lentiviral vectors was analyzed for its ability to release GDNF in the striatum of rats. One week post-surgery, GDNF was detected over a distance of 4 mm with all three methods. At 4 weeks GDNF staining diminished with rods and to a lesser extent with encapsulated cells, whereas it increased with lentiviral vectors. Nanogram range of GDNF was measured with all methods at 1 week. At 4 weeks, GDNF levels decreased significantly with rods, whereas they remained stable with encapsulated cells and lentiviral vectors. We conclude that all three methods investigated allow striatal delivery of GDNF, but the time during which it needs to be released will determine the approach chosen for clinical application.

Delivery of ciliary neurotrophic factor via lentiviral-mediated transfer protects axotomized retinal ganglion cells for an extended period of time

Ciliary neurotrophic factor (CNTF) has recently been demonstrated to be one of the most promising neurotrophic factors to improve both the survival and regeneration of injured retinal ganglion cells (RGCs). In the present study, we used optic nerve transection as an in vivo model to evaluate the effectiveness of a self-inactivating, replication-deficient lentiviral-mediated transfer of human ciliary neurotrophic factor (SIN-PGK-CNTF) on the survival of axotomized adult rat RGCs. Counts of dextran-fluorescein isothiocyanate conjugated (D-FITC)-retrogradely labeled RGCs revealed that the percentage of RGCs was drastically reduced (<90% cell death) 21 days after optic nerve transection. Retinal sections stained with X-gal revealed that intravitreal injection of the control LacZ-expressing lentiviral vector (LV-LacZ) resulted in the transduction of RGCs and retinal pigment epithelium (RPE) cells. A single intravitreal injection of LV-CNTF at the time of axotomy significantly enhanced RGC survival at 14 and 21 days postaxotomy compared to controls. These results demonstrate for the first time that rapid and prolonged delivery of CNTF using lentiviral-mediated gene transfer to the retina is an effective treatment for rescuing axotomized RGCs for an extended period of time. These results suggest that early and continuous administration of CNTF could serve as a potential treatment for retinal disorders involving optic neuropathy and RGC injury such as in glaucoma.

Gene therapy for Parkinson's disease: current status and future potential

Parkinson's disease appears to be a good candidate for gene therapy. The primary biochemical defect associated with the disease has been clearly determined as an absence of dopamine in the caudate-putamen, and the anatomical region where the neuropathologic hallmark of the disease, death of the nigral dopamine-producing neurons, occurs, remains circumscribed. Based on the biochemical and anatomical information gathered on Parkinson's disease, different gene therapy strategies have been devised to treat it. The first, and most explored strategy so far, consists in engineering cells to produce levodopa or dopamine so they will replace dopaminergic neurotransmission. Several types of cells have been employed in these experiments, and behavioral recovery has been reported in animal models of the disease. However, this approach cannot prevent neuronal death, nor reconstruct brain circuits. Another strategy is to protect cells by transferring genes that encode neurotrophic factors. Effort is now being concentrated into this research area, and promising results have recently been reported. Finally, an additional strategy aims at generating cells with a dopaminergic phenotype so they will be capable of replacing the missing dopaminergic neurons in biochemical, anatomical and functional terms. This has the potential to become an important constituent for an effective cure. Gene therapy holds significant promise for the treatment of neurodegenerative disorders, and Parkinson's disease treatment will benefit greatly from the knowledge and information arising from gene therapy research.

Multicistronic lentiviral vector-mediated striatal gene transfer of aromatic L-amino acid decarboxylase, tyrosine hydroxylase, and GTP cyclohydrolase I induces sustained transgene expression, dopamine production, and functional improvement in a rat model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the selective loss of dopaminergic neurons in the substantia nigra. This loss leads to complete dopamine depletion in the striatum and severe motor impairment. It has been demonstrated previously that a lentiviral vector system based on equine infectious anemia virus (EIAV) gives rise to highly efficient and sustained transduction of neurons in the rat brain. Therefore, a dopamine replacement strategy using EIAV has been investigated as a treatment in the 6-hydroxydopamine (6-OHDA) animal model of PD. A self-inactivating EIAV minimal lentiviral vector that expresses tyrosine hydroxylase (TH), aromatic amino acid dopa decarboxylase (AADC), and GTP cyclohydrolase 1 (CH1) in a single transcription unit has been generated. In cultured striatal neurons transduced with this vector, TH, AADC, and CH1 proteins can all be detected. After stereotactic delivery into the dopamine-denervated striatum of the 6-OHDA-lesioned rat, sustained expression of each enzyme and effective production of catecholamines were detected, resulting in significant reduction of apomorphine-induced motor asymmetry compared with control animals (p < 0.003). Expression of each enzyme in the striatum was observed for up to 5 months after injection. These data indicate that the delivery of three catecholaminergic synthetic enzymes by a single lentiviral vector can achieve functional improvement and thus open the potential for the use of this vector for gene therapy of late-stage PD patients.

Lentiviral-mediated RNA interference

RNA interference (RNAi) is a form of posttranscriptional gene silencing mediated by short double-stranded RNA, known as small interfering RNA (siRNA). These siRNAs are capable of binding to a specific mRNA sequence and causing its degradation. The recent demonstration of a plasmid vector that directs siRNA synthesis in mammalian cells prompted us to examine the ability of lentiviral vectors to encode siRNA as a means of providing long-term gene silencing in mammalian cells. The RNA-polymerase III dependent promoter (H1-RNA promoter) was inserted in the lentiviral genome to drive the expression of a small hairpin RNA (shRNA) against enhanced green fluorescent protein (EGFP). This construct successfully silenced EGFP expression in two stable cell lines expressing this protein, as analyzed by fluorescence microscopy, flow cytometry, and Western blotting. The silencing, which is dose dependent, occurs as early as 72 hr postinfection and persists for at least 25 days postinfection. The ability of lentiviruses encoding siRNA to silence genes specifically makes it possible to take full advantage of the possibilities offered by the lentiviral vector and provides a powerful tool for gene therapy and gene function studies.

Mapping of the bovine immunodeficiency virus packaging signal and RRE and incorporation into a minimal gene transfer vector

Gene transfer systems based on lentiviruses have emerged as promising gene delivery vehicles for human gene therapy due to their ability to efficiently transduce nondividing target cells. Both primate and nonprimate lentiviruses have been used for construction of lentiviral vectors. An early generation of gene transfer system based on bovine immunodeficiency virus (BIV) has been developed (R. D. Berkowitz, H. Ilves, W. Y. Lin, K. Eckert, A. Coward, S. Tamaki, G. Veres, and I. Plavec, 2001, J. Virol. 75, 3371-3382). In this study, we mapped the BIV Rev response element (RRE) to 312 bp of the Env coding region. Furthermore, we compared transduction efficiencies of vectors containing different portions of the BIV Gag coding region and found that the first 104 bp of gag contains a functional part of the BIV packaging signal. These findings enabled the generation of a minimal BIV-based lentiviral vector. The minimal transfer vector construct consists of a self-inactivating long terminal repeats (LTR), minimal packaging sequence, putative central polypurine tract, minimal RRE, an internal promoter driving the gene of interest, and a woodchuck hepatitis posttranscriptional regulatory element. In addition, we constructed a BIV packaging construct containing gag/pol, minimal Rev/RRE, and the accessory gene vpy. The regulatory gene tat and the accessory genes vif and vpw have been inactivated or truncated. The current system has significantly reduced regions of homologies between the transfer vector and the packaging constructs. The vectors generated from this system achieved a titer of greater than 1 x 10(6) transducing units per milliliter and are fully functional as indicated by their ability to efficiently transduce both dividing and nondividing cells. These modifications should provide improved safety features for the BIV-based gene transfer system.

Dose-dependent neuroprotective effect of ciliary neurotrophic factor delivered via tetracycline-regulated lentiviral vectors in the quinolinic acid rat model of Huntington's disease

The ability to regulate gene expression constitutes a prerequisite for the development of gene therapy strategies aimed at the treatment of neurologic disorders. In the present work, we used tetracycline (Tet)-regulated lentiviral vectors to investigate the dose-dependent neuroprotective effect of human ciliary neurotrophic factor (CNTF) in the quinolinic acid (QA) model of Huntington's disease (HD). The Tet system was split in two lentiviruses, the first one containing the CNTF or green fluorescent protein (GFP) cDNAs under the control of the Tet-response element (TRE) and a second vector encoding the transactivator (tTA). Preliminary coinfection study demonstrated that 63.8% +/- 2.0% of infected cells contain at least two viral copies. Adult rats were then injected with CNTF- and GFP-expressing viral vectors followed 3 weeks later by an intrastriatal administration of QA. A significant reduction of apomorphine-induced rotations was observed in the CNTF-on group. In contrast, GFP-treated animals or CNTF-off rats displayed an ipsilateral turning behavior in response to apomorphine. A selective sparing of DARPP-32-, choline acetyltransferase (ChAT)-, and NADPH-d-positive neurons was observed in the striatum of CNTF-on rats compared to GFP animals and CNTF-off group. Enzyme-linked immunosorbent assay (ELISA) performed on striatal samples of rats sacrificed at the same time point indicated that this neuroprotective effect was associated with the production of 15.5 +/- 4.7 ng CNTF per milligram of protein whereas the residual CNTF expression in the off state (0.54 +/- 0.02 ng/mg of protein) was not sufficient to protect against QA toxicity. These results establish the proof of principle of neurotrophic factor dosing for neurodegenerative diseases and demonstrate the feasibility of lentiviral-mediated tetracycline-regulated gene transfer in the brain.

Alphaviral gene transfer in neurobiology

Semliki Forest virus (SFV), Sindbis virus (SIN), and Venezuelan equine encephalitis virus are simple, enveloped plus-strand RNA viruses belonging to the Alphavirus genus of the Togaviridae family. They have been developed into expression vectors that infect a wide host cell range and cause rapid and high-level transgene expression. Their easy and fast generation, classification into biosafety levels 1 and 2, and preferential transduction of neurons in cell and tissue cultures makes them an increasingly used gene transfer system. This review summarizes the alphaviral replication and expression, the replicon system, and its application in neurobiology. Alphaviral vectors can introduce multiple transgenes into host cells, and mutants with low or absent cytotoxicity and increased or decreased transgene expression levels are available. Temperature-dependent mutants permit to control the host cell specificity as well as the on- and offset of gene expression. These features, together with the transduction characteristics revealed in a direct comparison of alphaviral and other viral vectors in hippocampal slice cultures, make SFV and SIN vectors a powerful tool for neurobiological studies.

Neurospheres modified to produce glial cell line-derived neurotrophic factor increase the survival of transplanted dopamine neurons

Glial cell line-derived neurotrophic factor (GDNF) has been shown to increase the survival of dopamine neurons in a variety of in vitro and in vivo model systems. Therefore, it constitutes an important therapeutic protein with the potential to ameliorate dopamine neuronal degeneration in Parkinson's disease or to support dopamine neuronal replacement strategies. However, biophysical and practical considerations present obstacles for the direct delivery of the GDNF protein to CNS neurons. Here we show that rodent neural precursor cells isolated and expanded in culture as neurospheres (NS) can be genetically modified to express green fluorescent protein (GFP) or to release GDNF using lentiviral constructs. GDNF-NS increased the fibre outgrowth of primary embryonic dopamine neurons in cocultures, showing that the protein was released in biologically significant quantities. Furthermore, after transplantation into the 6-hydroxydopamine-lesioned rat striatum, GDNF-NS significantly increased the survival of cografted primary dopamine neurons. However, this was not reflected in behavioural recovery in these animals. We found that, by 6 weeks, few cells expressed GDNF or GFP, suggesting either that transgene expression was down-regulated over time or that the cells died. This may explain the initial effects on dopamine neuronal survival within the graft but the lack of long-term effect on subsequent fibre outgrowth and behaviour. Providing sustained levels of neural precursor-mediated transgene expression can be achieved following transplantation in the future; this approach may prove beneficial as an alternative therapeutic strategy in the cell-based management of Parkinson's disease.

alpha -Synucleinopathy and selective dopaminergic neuron loss in a rat lentiviral-based model of Parkinson's disease

Parkinson's disease (PD) is characterized by the progressive loss of substantia nigra dopaminergic neurons and the presence of cytoplasmic inclusions named Lewy bodies. Two missense mutations of the alpha-synuclein (alpha-syn; A30P and A53T) have been described in several families with an autosomal dominant form of PD. alpha-Syn also constitutes one of the main components of Lewy bodies in sporadic cases of PD. To develop an animal model of PD, lentiviral vectors expressing different human or rat forms of alpha-syn were injected into the substantia nigra of rats. In contrast to transgenic mice models, a selective loss of nigral dopaminergic neurons associated with a dopaminergic denervation of the striatum was observed in animals expressing either wild-type or mutant forms of human alpha-syn. This neuronal degeneration correlates with the appearance of abundant alpha-syn-positive inclusions and extensive neuritic pathology detected with both alpha-syn and silver staining. Lentiviral-mediated expression of wild-type or mutated forms of human alpha-syn recapitulates the essential neuropathological features of PD. Rat alpha-syn similarly leads to protein aggregation but without cell loss, suggesting that inclusions are not the primary cause of cell degeneration in PD. Viral-mediated genetic models may contribute to elucidate the mechanism of alpha-syn-induced cell death and allow the screening of candidate therapeutic molecules.

Development of second- and third-generation bovine immunodeficiency virus-based gene transfer systems

Lentivirus-based gene transfer systems have demonstrated their utility in mediating gene transfer to dividing and nondividing cells both in vitro and in vivo. An early-generation gene transfer system developed from bovine immunodeficiency virus (BIV) has been described (Berkowitz et al., J. Virol. 2001;75:3371-3382). In this paper, we describe the development of second-generation (three-plasmid) and third-generation (four-plasmid) BIV-based systems. All accessory genes (vif, vpw, vpy, and tmx) and the regulatory gene tat were deleted or largely truncated from the packaging construct. Furthermore, we split the packaging function into two constructs by expressing Rev in a separate plasmid. Together with our minimal BIV transfer vector construct and a vesicular stomatitis virus G glycoprotein-expressing plasmid, the BIV vectors were generated. The vectors produced by the three- and four-plasmid systems had titers greater than 1 x 10(6) transducing units per milliliter and were fully functional as indicated by their ability to efficiently transduce both dividing and nondividing cells. These results suggest that the accessory genes vif, vpw, vpy, and tmx are dispensable for functional BIV vector development. The modifications made to the packaging constructs improve the safety profile of the vector system. Finally, BIV vectors provide an alternative to human immunodeficiency virus-based gene transfer systems.

Lentivirally delivered glial cell line-derived neurotrophic factor increases the number of striatal dopaminergic neurons in primate models of nigrostriatal degeneration

The primate striatum contains tyrosine hydroxylase (TH)-immunoreactive (ir) neurons, the numbers of which are augmented after dopamine depletion. Glial cell line-derived neurotrophic factor (GDNF) strongly modulates the viability and phenotypic expression of dopamine ventral mesencephalic neurons. The effect of GDNF on TH-ir neurons intrinsic to the striatum has yet to be investigated. In the present study, stereological counts of TH-ir striatal neurons in aged and parkinsonian nonhuman primates revealed that GDNF delivered via a lentiviral vector (lenti-) further increased the number of these cells. Aged monkeys treated with lenti-GDNF displayed an eightfold increase in TH-ir neurons relative to lenti-beta-galactosidase-treated monkeys. Unilateral 1-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine treatment alone in young monkeys resulted in a bilateral eightfold increase in TH-ir striatal cells. This effect was further magnified sevenfold on the side of lenti-GDNF treatment. These cells colocalized with the neuronal marker neuronal-specific nuclear protein. Some of these cells colocalized with GDNF-ir, indicating that an alteration in phenotype may occur by the direct actions of this trophic factor. Thus, GDNF may mediate plasticity in the dopamine-depleted primate brain, which may serve to compensate for cell loss by converting striatal neurons to a dopaminergic phenotype.

Lentiviral-mediated delivery of mutant huntingtin in the striatum of rats induces a selective neuropathology modulated by polyglutamine repeat size, huntingtin expression levels, and protein length

A new strategy based on lentiviral-mediated delivery of mutant huntingtin (htt) was used to create a genetic model of Huntington's disease (HD) in rats and to assess the relative contribution of polyglutamine (CAG) repeat size, htt expression levels, and protein length on the onset and specificity of the pathology. Lentiviral vectors coding for the first 171, 853, and 1520 amino acids of wild-type (19 CAG) or mutant htt (44, 66, and 82 CAG) driven by either the phosphoglycerate kinase 1 (PGK) or the cytomegalovirus (CMV) promoters were injected in rat striatum. A progressive pathology characterized by sequential appearance of ubiquitinated htt aggregates, loss of dopamine- and cAMP-regulated phosphoprotein of 32 kDa staining, and cell death was observed over 6 months with mutant htt. Earlier onset and more severe pathology occurred with shorter fragments, longer CAG repeats, and higher expression levels. Interestingly, the aggregates were predominantly located in the nucleus of PGK-htt171-injected rats, whereas they were present in both the nucleus and processes of CMV-htt171-injected animals expressing lower transgene levels. Finally, a selective sparing of interneurons was observed in animals injected with vectors expressing mutant htt. These data demonstrate that lentiviral-mediated expression of mutant htt provides a robust in vivo genetic model for selective neural degeneration that will facilitate future studies on the pathogenesis of cell death and experimental therapeutics for HD.

Characterization of lentiviral vector-mediated gene transfer in adult mouse brain

Lentiviral vectors are promising tools for gene transfer into the central nervous system. We have characterized in detail transduction with human immunodeficiency virus type 1 (HIV-1)-derived vectors encoding enhanced green fluorescent protein (eGFP) in the adult mouse brain. Different brain regions such as the striatum, hippocampus, and the lateral ventricle were targeted. The eGFP protein was transported anterogradely in the nigrostriatal pathway, but we have found no evidence of transport of the lentiviral vector particle. The performance levels of the different generations of packaging and transfer plasmid were compared. Omission of the accessory genes from the packaging plasmid resulted in a modest decrease in transgene expression. Inclusion of the woodchuck hepatitis posttranscriptional regulatory element, on the one hand, and the central polypurine tract and termination sequences, on the other hand, in the transfer vector each resulted in a 4- to 5-fold increase in transgene expression levels. Combination of both elements enhanced expression levels more than the sum of the individual components, suggesting a synergistic effect. In the serum of mice injected with lentiviral vectors a humoral response to vector proteins was detected, but this did not compromise transgene expression. Immune response to the transgene was found only in a minority of the animals.