New methods to titrate EIAV-based lentiviral vectors

Design of a titering assay for lentiviral vectors utilizing direct extraction of DNA from transduced cells in microtiter plates

Using lentiviral vector products in clinical applications requires an accurate method for measuring transduction titer. For vectors lacking a marker gene, quantitative polymerase chain reaction is used to evaluate the number of vector DNA copies in transduced target cells, from which a transduction titer is calculated. Immune Design previously described an integration-deficient lentiviral vector pseudotyped with a modified Sindbis virus envelope for use in cancer immunotherapy (VP02, of the ZVex platform). Standard protocols for titering integration-competent lentiviral vectors employ commercial spin columns to purify vector DNA from transduced cells, but such columns are not optimized for isolation of extrachromosomal (nonintegrated) DNA. Here, we describe a 96-well transduction titer assay in which DNA extraction is performed in situ in the transduction plate, yielding quantitative recovery of extrachromosomal DNA. Vector titers measured by this method were higher than when commercial spin columns were used for DNA isolation. Evaluation of the method’s specificity, linear range, and precision demonstrate that it is suitable for use as a lot release assay to support clinical trials with VP02. Finally, the method is compatible with titering both integrating and nonintegrating lentiviral vectors, suggesting that it may be used to evaluate the transduction titer for any lentiviral vector.

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

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

Development of an equine-tropic replication-competent lentivirus assay for equine infectious anemia virus-based lentiviral vectors

The release of lentiviral vectors for clinical use requires the testing of vector material, production cells, and, if applicable, ex vivo-transduced cells for the presence of replication-competent lentivirus (RCL). Vectors derived from the nonprimate lentivirus equine infectious anemia virus (EIAV) have been directly administered to patients in several clinical trials, with no toxicity observed to date. Because EIAV does not replicate in human cells, and because putative RCLs derived from vector components within human vector production cells would most likely be human cell-tropic, we previously developed an RCL assay using amphotropic murine leukemia virus (MLV) as a surrogate positive control and human cells as RCL amplification/indicator cells. Here we report an additional RCL assay that tests for the presence of theoretical "equine-tropic" RCLs. This approach provides further assurance of safety by detecting putative RCLs with an equine cell-specific tropism that might not be efficiently amplified by the human cell-based RCL assay. We tested the ability of accessory gene-deficient EIAV mutant viruses to replicate in a highly permissive equine cell line to direct our choice of a suitable EIAV-derived positive control. In addition, we report for the first time the mathematical rationale for use of the Poisson distribution to calculate minimal infectious dose of positive control virus and for use in monitoring assay positive/spike control failures in accumulating data sets. No RCLs have been detected in Good Manufacturing Practice (GMP)-compliant RCL assays to date, further demonstrating that RCL formation is highly unlikely in contemporary minimal lentiviral vector systems.

Quantification of HIV-based lentiviral vectors: influence of several cell type parameters on vector infectivity

A human immunodeficiency virus type (HIV-1)-based lentiviral vector pseudotyped with the vesicular stomatitis virus envelope glycoprotein and encoding the GFP reporter gene was used to evaluate different methods of lentiviral vector titration. GFP expression, viral DNA quantification and the efficiency of vector DNA integration were assayed after infection of conventional HIV-1-permissive cell lines and human primary adult fibroblasts with the vector. We found that vector titers based on GFP expression determined by flow cytometry may vary by more than 50-fold depending on the cell type and the promoter-cell combination used. Interestingly, we observed that the viral integration process in primary HDFa cells was significantly more efficient compared to that in SupT1 or 293T cells. We propose that determination of the amount of integrated viral DNA by quantitative PCR be used in combination with the reporter gene expression assay.

Dopamine Gene Therapy for Parkinson’s Disease in a Nonhuman Primate Without Associated Dyskinesia

A gene therapy approach for the treatment of Parkinson’s disease.

Analysis of human immunodeficiency virus type 1 vector cis- and trans-acting elements production by means of Semliki Forest virus

Recombinant Semliki Forest virus (SFV) is an attractive viral vector system owing to its ability to allow high efficiency of viral protein expression. To produce recombinant pseudotyped human immunodeficiency virus type 1 (HIV-1) virions, we designed a chimeric SFV/HIV vector system that contains both the HIV-1 cis- and trans-acting elements under the transcriptional control of the SFV replicase and investigated the ability of the hybrid SFV/HIV system to produce lentiviral particles capable of transducing target cells. Co-transfection of target cells with the two helper SFV packaging system RNAs along with each SFV/Gag-Pol, SFV/VSV(G) as well as SFV/HIV-1 vector unit replicon led to the generation of efficient transducing competent recombinant SFV/HIV particles. In contrast, co-transduction of target cells with the SFV/HIV chimeric virions produced recombinant particles with low transducing ability. Our data suggest that both the genomic and the subgenomic RNAs containing the HIV-1 vector unit were negatively selected for incorporation into recombinant particles, despite the fact that the SFV-driven HIV-1 vector replicon was the only one containing a lentiviral packaging sequence. The results of this study provide insights relevant to the design of chimeric lentiviral vectors.

Bone marrow-derived stromal cells home to and remain in the infarcted rat heart but fail to improve function: an in vivo cine-MRI study

Basic and clinical studies have shown that bone marrow cell therapy can improve cardiac function following infarction. In experimental animals, reported stem cell-mediated changes range from no measurable improvement to the complete restoration of function. In the clinic, however, the average improvement in left ventricular ejection fraction is around 2% to 3%. A possible explanation for the discrepancy between basic and clinical results is that few basic studies have used the magnetic resonance (MR) imaging (MRI) methods that were used in clinical trials for measuring cardiac function. Consequently, we employed cine-MR to determine the effect of bone marrow stromal cells (BMSCs) on cardiac function in rats. Cultured rat BMSCs were characterized using flow cytometry and labeled with iron oxide particles and a fluorescent marker to allow in vivo cell tracking and ex vivo cell identification, respectively. Neither label affected in vitro cell proliferation or differentiation. Rat hearts were infarcted, and BMSCs or control media were injected into the infarct periphery (n = 34) or infused systemically (n = 30). MRI was used to measure cardiac morphology and function and to determine cell distribution for 10 wk after infarction and cell therapy. In vivo MRI, histology, and cell reisolation confirmed successful BMSC delivery and retention within the myocardium throughout the experiment. However, no significant improvement in any measure of cardiac function was observed at any time. We conclude that cultured BMSCs are not the optimal cell population to treat the infarcted heart.

Both HIV- and EIAV-based lentiviral vectors mediate gene delivery to pancreatic cancer cells and human pancreatic primary patient xenografts

Few effective treatments for pancreatic cancer exist, especially for patients with advanced disease. Gene therapy alone, or combined with current treatments, offers an alternative approach. Here we examined the potential of primate and nonprimate lentivectors to mediate gene delivery to this cancer type. VSV-G pseudotyped lentivectors based on human immunodeficiency type-1 virus (HIV-1) and equine infectious anemia virus (EIAV), containing the enhanced green fluorescent protein (EGFP) reporter gene were prepared and characterized for titer and RNA content. Vector-mediated gene delivery was examined in five pancreatic cancer cell lines in vitro, and in MiaPaCa-2 cells as well as in five human primary patient biopsies xenografted subcutaneously in nude mice. While individual cell lines showed differential sensitivities to transduction with lentivectors, all cell lines were successfully transduced with both vector types. Similarly, both vectors transduced MiaPaCa-2 and all of the human primary patient xenografts. We observed 6-29% transduction with HIV-based vectors (n=3 xenografts) and 1.8-30% with EIAV-based vectors (n=4 xenografts). Long-term EIAV-mediated gene expression was recorded in cell lines for up to 6 months. We conclude that these vectors have potential as mediators of clinical gene therapy for pancreatic cancer treatment. Moreover, they are useful laboratory research tools for pancreatic cancer research.

Factors that influence VSV-G pseudotyping and transduction efficiency of lentiviral vectors—in vitro andin vivo implications

Pseudotyping viral vectors with vesicular stomatitis virus glycoprotein (VSV-G) enables the transduction of an extensive range of cell types from different species. We have discovered two important parameters of the VSV-G-pseudotyping phenomenon that relate directly to the transduction potential of lentiviral vectors: (1) the glycosylation status of VSV-G, and (2) the quantity of glycoprotein associated with virions. We measured production-cell and virion-associated quantities of two isoform variants of VSV-G, which differ in their glycosylation status, VSV-G1 and VSV-G2, and assessed the impact of this difference on the efficiency of mammalian cell transduction by lentiviral vectors. The glycosylation of VSV-G at N336 allowed greater maximal expression of VSV-G in HEK293T cells, thus facilitating vector pseudotyping. The transduction of primate cell lines was substantially affected (up to 50-fold) by the degree of VSV-G1 or VSV-G2 incorporation, whereas other cell lines, such as D17 (canine), were less sensitive to virion-associated VSV-G1/2 quantities. These data indicate that the minimum required concentration of virion-associated VSV-G differs substantially between cell species/types. The implications of these data with regard to VSV-G-pseudotyped vector production, titration, and use in host-cell restriction studies, are discussed.

Comparison of lentiviral vector titration methods

Background

Lentiviral vectors are efficient vehicles for stable gene transfer in dividing and non-dividing cells. Several improvements in vector design to increase biosafety and transgene expression, have led to the approval of these vectors for use in clinical studies. Methods are required to analyze the quality of lentiviral vector production, the efficiency of gene transfer and the extent of therapeutic gene expression.

Results

We compared lentiviral vector titration methods that measure pg p24/ml, RNA equivalents/ml, transducing units (TU/ml) or mRNA equivalents. The amount of genomic RNA in vector particles proves to be reliable to assess the production quality of vectors encoding non-fluorescent proteins. However, the RNA and p24 titers of concentrated vectors are rather poor in predicting transduction efficiency, due to the high variability of vector production based on transient transfection. Moreover, we demonstrate that transgenic mRNA levels correlate well with TU and can be used for functional titration of non-fluorescent transgenes.

Conclusion

The different titration methods have specific advantages and disadvantages. Depending on the experimental set-up one titration method should be preferred over the others.

Lentiviral Vectors Mediate Efficient and Stable Gene Transfer in Adult Neural Stem CellsIn Vivo

Modulation of adult neurogenesis may offer new therapeutic strategies for various brain disorders. In the adult mammalian brain the subventricular zone (SVZ) of the lateral ventricle is a region of continuous neurogenesis. Lentiviral vectors stably integrate into dividing and nondividing cells, in contrast to retroviral vectors, which integrate only into dividing cells. We compared their potential for gene transfer into both quiescent and slowly dividing stem cells as well as into more rapidly dividing progenitor cells. In contrast to retroviral vectors, stereotactic injection of lentiviral vectors into the SVZ of adult mice resulted in efficient and long-term marker gene expression in cells with characteristics of both immature type B cells and migrating precursor cells. After migration along the rostral migratory stream and differentiation, the number of enhanced green fluorescent protein (eGFP)-expressing granular and periglomerular interneurons increased over time in the ipsilateral olfactory bulb. Moreover, the number of eGFP-labeled neuronal progenitor cells in the SVZ increased over time. By intraventricular injection of lentiviral vectors we could restrict gene transfer to ependymal cells and type B astroglial-like stem cells. In conclusion, lentiviral vectors surpass retroviral vectors in efficient long-term in vivo marking of subventricular zone stem cells for basic research and therapeutic applications.

Reversal of neurochemical changes and pain-related behavior in a model of neuropathic pain using modified lentiviral vectors expressing GDNF

In this study, we evaluated the possible use of lentiviral vectors in the treatment of neuropathic pain. We chose to administer GDNF-expressing vectors because of the known beneficial effect of this trophic factor in alleviation of neuropathic pain in adult rodents. Lentiviral vectors expressing either GDNF or control, green fluorescent protein or beta-galactosidase, were injected unilaterally into the spinal dorsal horn 5 weeks before a spinal nerve ligation was induced (or sham surgery for the controls). We observed that intraspinally administered lentiviral vectors resulted in a large and sustained expression of transgenes in both neurons and glial cells. Injection of GDNF-expressing viral vectors induced a significant reduction of ATF-3 up-regulation and IB4 down-regulation in damaged DRG neurons. In addition, it produced a partial but significant reversal of thermal and mechanical hyperalgesia observed following the spinal nerve ligation. In conclusion, our study suggests that lentiviral vectors are efficient tools to induce a marked and sustained expression of trophic factors in specific areas of the CNS and can, even if with some limitations, be efficient in the treatment of neuropathic pain.

Iron particles for noninvasive monitoring of bone marrow stromal cell engraftment into, and isolation of viable engrafted donor cells from, the heart

Stem cells offer a promising approach to the treatment of myocardial infarction and prevention of heart failure. We have used iron labeling of bone marrow stromal cells (BMSCs) to noninvasively track cell location in the infarcted rat heart over 16 weeks using cine-magnetic resonance imaging (cine-MRI) and to isolate the BMSCs from the grafted hearts using the magnetic properties of the donor cells. BMSCs were isolated from rat bone marrow, characterized by flow cytometry, transduced with lentiviral vectors expressing green fluorescent protein (GFP), and labeled with iron particles. BMSCs were injected into the infarct periphery immediately following coronary artery ligation, and rat hearts were imaged at 1, 4, 10, and 16 weeks postinfarction. Signal voids caused by the iron particles in the BMSCs were detected in all rats at all time points. In mildly infarcted hearts, the volume of the signal void decreased over the 16 weeks, whereas the signal void volume did not decrease significantly in severely infarcted hearts. High-resolution three-dimensional magnetic resonance (MR) microscopy identified hypointense regions at the same position as in vivo. Donor cells containing iron particles and expressing GFP were identified in MR-targeted heart sections after magnetic cell separation from digested hearts. In conclusion, MRI can be used to track cells labeled with iron particles in damaged tissue for at least 16 weeks after injection and to guide tissue sectioning by accurately identifying regions of cell engraftment. The magnetic properties of the iron-labeled donor cells can be used for their isolation from host tissue to enable further characterization.

Real-time quantitative PCR for the design of lentiviral vector analytical assays

From the recent and emerging concerns for approving lentiviral vector-mediated gene transfer in human clinical applications, several analytical methods have been applied in preclinical models to address the lentiviral vector load in batches, cells or tissues. This review points out the oldest generation methods (blots, RT activity, standard PCR) as well as a full description of the newest real-time quantitative PCR (qPCR) applications. Combinations of primer and probe sequences, which have worked in the lentiviral amplification context, have been included in the effort to dress an exhaustive list. Also, great variations have been observed from interlaboratory results, we have tempted to compare between them the different analytical methods that have been used to consider (i) the titration of lentiviral vector batches, (ii) the absence of the susceptible emerging replicative lentiviruses or (iii) the lentiviral vector biodistribution in the organism.

Retinoic acid receptor β2 promotes functional regeneration of sensory axons in the spinal cord

The embryonic CNS readily undergoes regeneration, unlike the adult CNS, which has limited axonal repair after injury. Here we tested the hypothesis that retinoic acid receptor beta2 (RARbeta2), critical in development for neuronal growth, may enable adult neurons to grow in an inhibitory environment. Overexpression of RARbeta2 in adult rat dorsal root ganglion cultures increased intracellular levels of cyclic AMP and stimulated neurite outgrowth. Stable RARbeta2 expression in DRG neurons in vitro and in vivo enabled their axons to regenerate across the inhibitory dorsal root entry zone and project into the gray matter of the spinal cord. The regenerated neurons enhanced second-order neuronal activity in the spinal cord, and RARbeta2-treated rats showed highly significant improvement in sensorimotor tasks. These findings show that RARbeta2 induces axonal regeneration programs within injured neurons and may thus offer new therapeutic opportunities for CNS regeneration.

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

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

In vivo evaluation of an EIAV vector for the systemic genetic delivery of therapeutic antibodies

Lentiviral-based vectors hold great promise as gene delivery vehicles for the treatment of a wide variety of diseases. We have previously reported the development of a nonprimate lentiviral vector system based on the equine infectious anaemia virus (EIAV), which is able to efficiently transduce dividing and nondividing cells both in vitro and in vivo. Here, we report on the application of EIAV vectors for the systemic delivery of an antibody fusion protein designed for the treatment of cancer. The therapeutic potential of a single chain antibody against the tumour-associated antigen, 5T4, fused to immune enhancer moieties has been demonstrated in vitro and here we evaluate the genetic delivery of a 5T4 scFv fused to B7.1 (scFvB7) using an EIAV vector. The kinetics and concentration of protein produced following both intravenous (i.v.) and intramuscular (i.m.) administration was determined in immune competent adult mice. In addition, the immune response to the EIAV vector and the transgene were determined. Here, we show that a single injection of EIAV expressing scFv-B7 can give rise to concentrations of protein in the range of 1-5 microg/ml that persist in the sera for more than 50 days. After a second injection, concentrations of scFv-B7.1 rose as high as 20 microg/ml and levels greater than 2 microg/ml were present in the sera of all mice injected i.v. after 210 days despite the detection of antibodies against both the transgene and viral envelope for the duration of this study. These results demonstrate the potential of EIAV as a gene therapy vector for long-term production of therapeutic recombinant proteins.

Silencing mutant SOD1 using RNAi protects against neurodegeneration and extends survival in an ALS model

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease resulting in the selective death of motor neurons in the brain and spinal cord. Some familial cases of ALS are caused by dominant mutations in the gene encoding superoxide dismutase (SOD1). The emergence of interfering RNA (RNAi) for specific gene silencing could be therapeutically beneficial for the treatment of such dominantly inherited diseases. We generated a lentiviral vector to mediate expression of RNAi molecules specifically targeting the human SOD1 gene (SOD1). Injection of this vector into various muscle groups of mice engineered to overexpress a mutated form of human SOD1 (SOD1(G93A)) resulted in an efficient and specific reduction of SOD1 expression and improved survival of vulnerable motor neurons in the brainstem and spinal cord. Furthermore, SOD1 silencing mediated an improved motor performance in these animals, resulting in a considerable delay in the onset of ALS symptoms by more than 100% and an extension in survival by nearly 80% of their normal life span. These data are the first to show a substantial extension of survival in an animal model of a fatal, dominantly inherited neurodegenerative condition using RNAi and provide the highest therapeutic efficacy observed in this field to date.

Lentiviral-Mediated Delivery of Bcl-2 or GDNF Protects against Excitotoxicity in the Rat Hippocampus

Nutrient deprivation during ischemia leads to severe insult to neurons causing widespread excitotoxic damage in specific brain regions such as the hippocampus. One possible strategy for preventing neurodegeneration is to express therapeutic proteins in the brain to protect against excitotoxicity. We investigated the utility of equine infectious anemia virus (EIAV)-based vectors as genetic tools for delivery of therapeutic proteins in an in vivo excitotoxicity model. The efficacy of these vectors at preventing cellular loss in target brain areas following excitotoxic insult was also assessed. EIAV vectors generated to overexpress the human antiapoptotic Bcl-2 or growth factor glial-derived neurotrophic factor (GDNF) genes protected against glutamate-induced toxicity in cultured hippocampal neurons. In an in vivo excitotoxicity model, adult Wistar rats received a unilateral dose of the glutamate receptor agonist N-methyl-D-aspartate to the hippocampus that induced a large lesion in the CA1 region. Neuronal loss could not be protected by prior transduction of a control vector expressing beta-galactosidase. In contrast, EIAV-mediated expression of Bcl-2 and GDNF significantly reduced lesion size thus protecting the hippocampus from excitotoxic damage. These results demonstrate that EIAV vectors can be effectively used to deliver putative neuroprotective genes to target brain areas and prevent cellular loss in the event of a neurological insult. Therefore these lentiviral vectors provide potential therapeutic tools for use in cases of acute neurotrauma such as cerebral ischemia.

Design and in vivo characterization of self-inactivating human and non-human lentiviral expression vectors engineered for streptogramin-adjustable transgene expression

Adjustable transgene expression is considered key for next-generation molecular interventions in gene therapy scenarios, therapeutic reprogramming of clinical cell phenotypes for tissue engineering and sophisticated gene-function analyses in the post-genomic era. We have designed a portfolio of latest generation self-inactivating human (HIV-derived) and non-human (EIAV-based) lentiviral expression vectors engineered for streptogramin-adjustable expression of reporter (AmyS(DeltaS), EYFP, SAMY, SEAP), differentiation-modulating (human C/EBP-alpha) and therapeutic (human VEGF) transgenes in a variety of rodent (CHO-K1, C2C12) and human cell lines (HT-1080, K-562), human and mouse primary cells (NHDF, PBMC, CD4+) as well as chicken embryos. Lentiviral design concepts include (i) binary systems harboring constitutive streptogramin-dependent transactivator (PIT) and PIT-responsive transgene expression units on separate lentivectors; (ii) streptogramin-responsive promoters (P(PIR8)) placed 5' of desired transgenes; (iii) within modified enhancer-free 3'-long terminal repeats; and (iv) bidirectional autoregulated configurations providing streptogramin-responsive transgene expression in a lentiviral one-vector format. Rigorous quantitative analysis revealed HIV-based direct P(PIR)-transgene configurations to provide optimal regulation performance for (i) adjustable expression of intracellular and secreted product proteins, (ii) regulated differential differentiation of muscle precursor cell lines into adipocytes or osteoblasts and (iii) conditional vascularization fine-tuning in chicken embryos. Similar performance could be achieved by engineering streptogramin-responsive transgene expression into an autoregulated one-vector format. Powerful transduction systems equipped with adjustable transcription modulation options are expected to greatly advance sophisticated molecular interventions in clinically and/or biotechnologically relevant primary cells and cell lines.

VEGF delivery with retrogradely transported lentivector prolongs survival in a mouse ALS model

Amyotrophic lateral sclerosis (ALS) causes adult-onset, progressive motor neuron degeneration in the brain and spinal cord, resulting in paralysis and death three to five years after onset in most patients. ALS is still incurable, in part because its complex aetiology remains insufficiently understood. Recent reports have indicated that reduced levels of vascular endothelial growth factor (VEGF), which is essential in angiogenesis and has also been implicated in neuroprotection, predispose mice and humans to ALS. However, the therapeutic potential of VEGF for the treatment of ALS has not previously been assessed. Here we report that a single injection of a VEGF-expressing lentiviral vector into various muscles delayed onset and slowed progression of ALS in mice engineered to overexpress the gene coding for the mutated G93A form of the superoxide dismutase-1 (SOD1(G93A)) (refs 7-10), even when treatment was only initiated at the onset of paralysis. VEGF treatment increased the life expectancy of ALS mice by 30 per cent without causing toxic side effects, thereby achieving one of the most effective therapies reported in the field so far.

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

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

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.

Identification of potential stroke targets by lentiviral vector mediated overexpression of HIF-1 alpha and HIF-2 alpha in a primary neuronal model of hypoxia

The identification of genes differentially regulated by ischemia will lead to an improved understanding of cell death pathways such as those involved in the neuronal loss observed following a stroke. Furthermore, the characterization of such pathways could facilitate the identification of novel targets for stroke therapy. We have used a novel approach to amplify differential gene expression patterns in a primary neuronal model of stroke by employing a lentiviral vector system to specifically bias the transcriptional activation of hypoxically regulated genes. Overexpression of the hypoxia-induced transcription factor subunits HIF-1 alpha and HIF-2 alpha elevated hypoxia-mediated transcription of many known HIF-regulated genes well above control levels. Furthermore, many potentially novel HIF-regulated genes were discovered that were not previously identified as hypoxically regulated. Most of the novel genes identified were activated by a combination of HIF-2 alpha overexpression and hypoxic insult. These included several genes with particular importance in cell survival pathways and of potential therapeutic value. Hypoxic induction of HIF-2 alpha may therefore be a critical factor in mediating protective responses against ischemic injury. Further investigation of the genes identified in this study may provide increased understanding of the neuronal response to hypoxia and may uncover novel therapeutic targets for the treatment of cerebral ischemia.

Transduction Patterns of Pseudotyped Lentiviral Vectors in the Nervous System

We have developed a non-primate-based lentiviral vector based on the equine infectious anemia virus (EIAV) for efficient gene transfer to the central and peripheral nervous systems. Previously we have demonstrated that pseudotyping lentiviral vectors with the rabies virus glycoprotein confers retrograde axonal transport to these vectors. In the present study we have successfully produced high-titer EIAV vectors pseudotyped with envelope glycoproteins from Rhabdovirus vesicular stomatitis virus (VSV) serotypes (Indiana and Chandipura strains); rabies virus [various Evelyn-Rokitnicki-Abelseth ERA strains and challenge virus standard (CVS)]; Lyssavirus Mokola virus, a rabies-related virus; and Arenavirus lymphocytic choriomeningitis virus (LCMV). These vectors were delivered to the striatum or spinal cord of adult rats or muscle of neonatal mice by direct injection. We report that the lentiviral vectors pseudotyped with envelopes from the VSV Indiana strain, wild-type ERA, and CVS strains resulted in strong transduction in the striatum, while Mokola- and LCMV-pseudotyped vectors exhibited moderate and weak transduction, respectively. Furthermore ERA- and CVS-pseudotyped lentiviral vectors demonstrated retrograde transport and expression in distal neurons after injection in brain, spinal cord, and muscle. The differences in transduction efficiencies and retrograde transport conferred by these envelope glycoproteins present novel opportunities in designing therapeutic strategies for different neurological diseases.

Long-term transgene expression by administration of a lentivirus-based vector to the fetal circulation of immuno-competent mice

Inefficient gene transfer, inaccessibility of stem cell compartments, transient gene expression, and adverse immune and inflammatory reactions to vector and transgenic protein are major barriers to successful in vivo application of gene therapy for most genetic diseases. Prenatal gene therapy with integrating vectors may overcome these problems and prevent early irreparable organ damage. To this end, high-dose attenuated VSV-G pseudotyped equine infectious anaemia virus (EIAV) encoding beta-galactosidase under the CMV promoter was injected into the fetal circulation of immuno-competent MF1 mice. We saw prolonged, extensive gene expression in the liver, heart, brain and muscle, and to a lesser extent in the kidney and lung of postnatal mice. Progressive clustered hepatocyte staining suggests clonal expansion of cells stably transduced. We thus provide proof of principle for efficient gene delivery and persistent transgene expression after prenatal application of the EIAV vector and its potential for permanent correction of genetic diseases.

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.

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.

Lentiviruses in gene therapy clinical research

Gene therapy vectors derived from lentiviruses offer many potentially unique advantages over more conventional retroviral gene delivery systems. Principal amongst these is their ability to provide long-term and stable gene expression and to infect non-dividing cells, such as neurons. However, the use of lentiviral-based vectors in the clinic also raises specific safety and ethical issues. Concerns include the possible generation of replication competent lentiviruses during vector production, mobilisation of the vector by endogenous retroviruses in the genomes of patients, insertional mutagenesis leading to cancer, germline alteration resulting in trans-generational effects and dissemination of new viruses from gene therapy patients. Investigators proposing to conduct this type of research should take due account of the potential risks for interaction of lentiviral gene therapy vectors with other retroviral elements in human subjects, such as Human Immunodeficiency Virus. In addition, strict quality control for replication competent lentiviruses and suitable measurements of lentiviral infectious particle number will be required before these types of viral vector can proceed to the clinic.