LacZ gene transfer to skeletal muscle using a replication-defective herpes simplex virus type 1 mutant vector

Development of Approaches to Improve the Healing following Muscle Contusion

Muscle injuries are a challenging problem in traumatology, and the most frequent occurrence in sports medicine. Muscle contusions are among the most common muscle injuries. Although this injury is capable of healing, an incomplete functional recovery often occurs, depending on the severity of the blunt trauma. We have developed an animal model of muscle contusion in mice (high energy blunt trauma) and characterized the muscle's ability to heal following this injury using histology and immunohistochemistry to determine the level of muscle regeneration and the development of scar tissue. We have observed a massive muscle regeneration occurring in the first 2 wk postinjury that is subsequently followed by the development of muscle fibrosis. Based on these observations, we propose that the enhancement of muscle growth and regeneration, as well as the prevention of fibrotic development, could be used as approach(es) to improve the healing of muscle injuries. In fact, we have identified three growth factors (bFGF, IGF-1, and NGF) capable of enhancing myoblast proliferation and differentiation in vitro and improving the healing of the injured muscle in vivo. Furthermore, the ability of adenovirus to mediate direct and ex vivo gene transfer of β-galactosidase into the injured site opens possibilities of delivering an efficient and persistent expression of these growth factors in the injured muscle. These studies should help in the development of strategies to promote efficient muscle healing with complete functional recovery following muscle contusion. © 1998 Elsevier Science Inc.

BIOLOGICAL INTERVENTION BASED ON CELL AND GENE THERAPY TO IMPROVE MUSCLE HEALING AFTER LACERATION

Muscle laceration is a challenging problem in traumatology and is common in sports injuries, with functional recovery remaining slow and incomplete. Even though muscles retain their ability to regenerate after injury, muscles' healing process after such injuries has been found to be very slow and often leads to incomplete muscle recovery. Growth factors may have a role in enhancing recovery. Our previous study showed that IGF-1, β-FGF and NGF can improve myoblast proliferation and differentiation in vitro. We then investigated whether the delivery of IGF-1 would improve muscle healing after injuries. We observed that muscle regeneration was enhanced in lacerated muscles treated with IGF-1 protein, which consequently led to an improvement in muscle healing. However, the rapid clearance and short biological half-lives of these proteins may have limited the success of this approach. We then investigated the efficiency of gene therapy based on adenovirus to deliver a stable expression of the growth factor IGF-1. Although a slight improvement in the healing process occurred in the muscle injected with adenovirus (AIGF), the combination of myoblast transplantation and gene therapy with the ex vivo approach further improved the healing process. The injection of normal myoblasts into the injured muscle led to the best improvement of muscle healing at two weeks post-injection. Implantation of normal minced muscle into mdx mice was also capable of improving muscle healing at 2–4 weeks post-implantation. These studies will further our understanding of muscle healing post-injury and help in the development of strategies to promote efficient muscle healing and complete functional recovery after common muscle injuries.

Construction of replication-defective herpes simplex virus vectors

Advances in identification and characterization of gene products responsible for specific diseases of the nervous system have opened opportunities for novel therapies using gene transfer vectors for gene replacement. Herpes simplex virus (HSV)-based vectors are particularly well suited for gene delivery to neurons of the central and peripheral nervous systems. The authors have developed methods to delete HSV-1 IE gene functions and to subsequently introduce foreign genes into the HSV-1 genome using homologous recombination. This unit describes methods for generating cell lines that complement multiple essential gene deletion mutants as well for generating such replication-defective virus recombinants and inserting foreign DNA sequences into replication-defective viral genomes, the last step in preparing a vector. Three support protocols describe methods for preparing virus stocks, titering virus, and preparing viral DNA.

Targeting of lacZ reporter gene expression with radioiodine-labelled phenylethyl-beta- d-thiogalactopyranoside

There has recently been increasing interest in the development of radioprobes that specifically target proteins transcribed from expression of reporter genes of interest. The purpose of this study was to develop a radioprobe that targets one of the most widely used reporter genes, the bacterial lacZ gene. We synthesised and purified radioiodine-labelled phenylethyl-beta- d-thiogalactopyranoside (PETG), a competitive inhibitor specific against Escherichia coli beta-galactosidase. We showed that [(125)I]iodo-PETG specifically binds to beta-galactosidase as verified by column chromatography and polyacrylamide gel electrophoresis after incubation of radiotracer with the protein. We also showed through enzyme kinetic studies that iodo-PETG retains inhibitory action against beta-galactosidase activity. COS-7 cells infected with a recombinant adenovirus expressing the lacZ gene had viral titre-dependent enhancements in [(125)I]iodo-PETG uptake ( r(2)=0.897; P=0.001), which reached up to 642.5%+/-16.7% of control levels ( P<0.00001). Moreover, the level of uptake was highly correlated to luminescent measurements of beta-galactosidase activity ( r(2)=0.878; P<0.0001). These results confirm that radioiodine-labelled PETG specifically targets beta-galactosidase and that its uptake rates faithfully reflect levels of expression of the lacZ reporter gene. Further investigations were performed in nude mice bearing human neuroblastoma tumours transferred with the lacZ gene. Compared with control tumours, lacZ-expressing tumours were slightly better visualised on [(123)I]iodo-PETG images and had a modest increase in tumour to muscle count ratio (2.6+/-0.2 vs 1.9+/-0.1, P<0.05). The present results provide proof-of-principle for the potential of radiolabelled inhibitors as promising radiotracers to monitor lacZ gene expression levels. Future modifications to improve cell permeability should enhance in vivo contrast levels and may allow the use of radiolabelled beta-galactosidase inhibitors for non-invasive monitoring of lacZ gene expression.

Viral oncoapoptosis of human tumor cells

Many cancer cells refractory to radiation treatment and chemotherapy proliferate because of loss of intrinsic programmed cell death (apoptosis) regulation. Consequently, the resolution of these cancers are many times outside the management capabilities of conventional therapeutics. We now report that replication-defective delta27 herpes simplex virus (rd delta27) triggers apoptosis in three representative transformed human cell lines. Susceptibility to virus-induced cell death is dependent on the abundance and distribution of modified p53 protein in the tumor cells indicating specific targeting of the treatment. Primary human and mouse fibroblast cells that produce modified p53 are resistant to rd delta27 killing but not to apoptosis induced by nonviral environmental factors. These results suggest that induction of apoptosis by nonreplicating virus is a feasible genetic therapy approach for killing human cancer cells. Our findings may have important implications in designing novel virus-based anticancer strategies in appropriate animal model systems.

Gene delivery using herpes simplex virus vectors

Herpes simplex virus (HSV) is a neurotropic DNA virus with many favorable properties as a gene delivery vector. HSV is highly infectious, so HSV vectors are efficient vehicles for the delivery of exogenous genetic material to cells. Viral replication is readily disrupted by null mutations in immediate early genes that in vitro can be complemented in trans, enabling straightforward production of high-titre pure preparations of non-pathogenic vector. The genome is large (152 Kb) and many of the viral genes are dispensable for replication in vitro, allowing their replacement with large or multiple transgenes. Latent infection with wild-type virus results in episomal viral persistence in sensory neuronal nuclei for the duration of the host lifetime. Transduction with replication-defective vectors causes a latent-like infection in both neural and non-neural tissue; the vectors are non-pathogenic, unable to reactivate and persist long-term. The latency active promoter complex can be exploited in vector design to achieve long-term stable transgene expression in the nervous system. HSV vectors transduce a broad range of tissues because of the wide expression pattern of the cellular receptors recognized by the virus. Increasing understanding of the processes involved in cellular entry has allowed preliminary steps to be taken towards targeting the tropism of HSV vectors. Using replication-defective HSV vectors, highly encouraging results have emerged from recent pre-clinical studies on models of neurological disease, including glioma, peripheral neuropathy, chronic pain and neurodegeneration. Consequently, HSV vectors encoding appropriate transgenes to tackle these pathogenic processes are poised to enter clinical trials.

High efficiency transfection of primary skeletal muscle cells with lipid-based reagents

Lipofection is a convenient method for gene transfer into muscle cells but reportedly is inefficient. We tested the efficacy of commercially available lipid-based and polyamine transfection reagents. Primary rat skeletal muscle cell cultures were transfected at three stages of development and assayed after fusion. Efficiency reached 30% during the proliferation stage and up to 23% when most myoblasts had fused into myotubes. Optimization of transfection conditions with three different vectors yielded efficiencies exceeding 50%. Thus, lipid-based transfection into primary skeletal muscle cells can be several times more efficient than previously reported.

Herpes simplex virus type 1/adeno-associated virus rep(+) hybrid amplicon vector improves the stability of transgene expression in human cells by site-specific integration

Herpes simplex virus type 1 (HSV-1) amplicon vectors are promising gene delivery tools, but their utility in gene therapy has been impeded to some extent by their inability to achieve stable transgene expression. In this study, we examined the possibility of improving transduction stability in cultured human cells via site-specific genomic integration mediated by adeno-associated virus (AAV) Rep and inverted terminal repeats (ITRs). A rep(-) HSV/AAV hybrid amplicon vector was made by inserting a transgene cassette flanked with AAV ITRs into an HSV-1 amplicon backbone, and a rep(+) HSV/AAV hybrid amplicon was made by inserting rep68/78 outside the rep(-) vector 3' AAV ITR sequence. Both vectors also had a pair of loxP sites flanking the ITRs. The resulting hybrid amplicon vectors were successfully packaged and compared to a standard amplicon vector for stable transduction frequency (STF) in human 293 and Gli36 cell lines and primary myoblasts. The rep(+), but not the rep(-), hybrid vector improved STF in all three types of cells; 84% of Gli36 and 40% of 293 stable clones transduced by the rep(+) hybrid vector integrated the transgene into the AAVS1 site. Due to the difficulty in expanding primary myoblasts, we did not assess site-specific integration in these cells. A strategy to attempt further improvement of STF by "deconcatenating" the hybrid amplicon DNA via Cre-loxP recombination was tested, but it did not increase STF. These data demonstrate that introducing the integrating elements of AAV into HSV-1 amplicon vectors can significantly improve their ability to achieve stable gene transduction by conferring the AAV-like capability of site-specific genomic integration in dividing cells.

Herpes simplex virus type 1 amplicon vector-mediated gene transfer to muscle

Herpes simplex virus type 1 (HSV-1) amplicon vectors were evaluated for feasibility in gene therapy of Duchenne's muscular dystrophy (DMD). An amplicon vector expressing enhanced green fluorescent protein (eGFP) was examined for transduction efficiency and cytotoxicity in cultured muscle cells, and for transduction efficiency, duration of transgene expression, and immunogenicity in tibialis anterior (TA) muscles of neonatal mice. Transduction efficiencies in murine and human myoblasts were 60-90 and 50-60%, respectively, when myoblasts were transduced at multiplicities of infection (MOIs) of 1-5. Similar transduction efficiencies were observed in myotubes of both species. No cytotoxic effects were noticed at an MOI of 10, the highest MOI tested. An amplicon vector, HyMD, containing the full-length mouse dystrophin cDNA and its muscle creatine kinase (MCK) promoter-enhancer, with a total size of 26 kb, was constructed and used to transduce mdx mouse myotubes. The expression of dystrophin in these cells was demonstrated by immunocytochemistry. After injecting 4-6 x 10(5) transduction units (TU) of HSVGN amplicon vectors, 10-50% of myofibers in the injected TA muscles expressed GFP. Although transgene expression was attenuated over time, significant improvement in long-term transgene expression and persistence of vector DNA was achieved, when compared with the first generation of recombinant HSV-1 vectors. Immunohistochemistry showed a modest CD4(+) lymphocyte infiltration in the vicinity of the injection. A gradually developed CD8(+) lymphocyte infiltration was also seen, most likely related to the antigenicity of the transgene product, GFP. We conclude that the HSV-1 amplicon vector is a promising vehicle for gene delivery in DMD. However, new strategies need to be evaluated to increase the stability of transgene expression.

Multiple applications for replication-defective herpes simplex virus vectors

Herpes simplex virus (HSV) is a neurotropic DNA virus. The viral genome is large (152 kb), and many genes are dispensable for viral function, allowing insertion of multiple or large transgene expression cassettes. The virus life cycle includes a latent phase, during which the viral genome remains as a stable episomal element within neuronal nuclei for the lifetime of the host, without disturbing normal function. We have exploited these features of HSV to construct a series of nonpathogenic gene therapy vectors that efficiently deliver therapeutic and experimental transgenes to neural and non-neural tissue. Importantly, transgene expression may be sustained long term; reporter gene expression has been demonstrated for over a year in the nervous system. This article discusses the generation of replication-defective HSV vectors and reviews recent studies investigating their use in several animal models of human disease. We have demonstrated correction or prevention of a number of important neurological phenotypes, including neurodegeneration, chronic pain, peripheral neuropathy, and malignancy. In addition, HSV-mediated transduction of non-neurological tissues allows their use as depot sites for synthesis of circulating and locally acting secreted proteins. New applications for this vector system include the genetic modification of stem cell populations; this may become an important means to direct cellular differentiation or deliver therapeutic genes systemically. Replication-defective HSV vectors are an effective and flexible vehicle for the delivery of transgenes to numerous tissues, with multiple applications.

Beta-amyloid peptide expression is sufficient for myotube death: implications for human inclusion body myopathy

Inclusion body myositis (sIBM) is the most common disorder of skeletal muscle in aged humans. It shares biochemical features with Alzheimer's disease, including congophilic deposits, which are immunoreactive for beta-amyloid peptide (Abeta) and C'-terminal betaAPP epitopes. However, the etiology of myofiber loss and the role of intracellular Abeta in IBM is unknown. Here we report correlative evidence for apoptotic cell death in myofibers of IBM patients that exhibit pronounced Abeta deposition. HSV-1-mediated gene transfer of Abeta(42) into cultured C2C12 myotubes resulted in a 12.6-fold increase in dUTP-labeled and condensed nuclei over nonexpressing myotubes (P < 0.05). The C'-terminal betaAPP domain C99 also induced myotube apoptosis, but to a significantly lesser extent than Abeta. Apoptosis specific to Abeta-expressing myotubes was also demonstrated through DNA fragmentation, decreased mitochondrial function and the loss of membrane phospholipid polarity. Myotubes laden with Abeta(42), but not other transgene products, developed cytoplasmic inclusions consisting of fibrillar material. Furthermore, injection of normal mouse gastrocnemius muscle with HSV-encoding Abeta cDNA resulted in TUNEL-positive myofibers with pyknotic nuclei. We conclude that Abeta is sufficient to induce apoptosis in myofibers both in vivo and in vitro and suggest it may contribute to myofiber loss and muscle dysfunction in patients with IBM.

The role of receptors in the maturation-dependent adenoviral transduction of myofibers

One of the major hurdles facing the application of adenoviral gene transfer to skeletal muscle is the maturation-dependent transduction of muscle myofibers. It was recently proposed that the viral receptors (Coxsackie and adenovirus receptor (CAR) and the integrins alphavbeta3/beta5) play a major role in the poor adenoviral transduction of mature myofibers. Here we report the findings of morphological studies designed to determine experimentally the role of receptors in the adenoviral transduction of mature myofibers. First, we observed that the expression of both attachment and internalization receptors did not change significantly during muscle development. Second, when an extended tropism adenoviral vector (AdPK) that attaches to heparan sulfate proteoglycan (HSP) is used, a significant reduction of adenoviral transduction still occurs in mature myofibers despite HSP's high expression in mature skeletal muscle fibers. Third, when the adeno-associated virus (AAV) is used, which also utilizes HSP as a viral receptor, muscle fibers at different maturities can be highly transduced. Fourth, the pre-irradiation of the skeletal muscle of newborn mice to inactivate myoblasts dramatically decreased the transduction level of Ad and AdPK, but had no effect on AAV-mediated viral transduction of immature myofibers. These results taken together suggest that the viral receptor(s) is not a major determinant in maturation-dependent adenoviral transduction of myofibers.

The influence of muscle fiber type in myoblast-mediated gene transfer to skeletal muscles

Myoblast transplantation has been hindered by immune rejection problems, as well as the poor survival and spread of transplanted cells. Our recent study has shown that the poor survival of the injected cells can be totally overcome by the use of specific populations of muscle-derived cells. In the present study, we have investigated whether a relationship exists between the fate of transplanted cells and the muscle fiber types. Four kinds of myogenic cells [primary myoblasts at a high purity (PMb), myoblasts isolated from fast single fibers (FMb), mdx (MCL), and MtMd-1 cell lines] were infected with an adenoviral vector carrying a LacZ reporter gene and injected into mdx hindlimb muscle. The LacZ transduced myofibers formed by the fusion of the injected myoblasts at 2-10 days postinjection were colocalized with MyHC stainings. The PMb cells, which expressed both slow and fast MyHCs in vitro, displayed the same phenotypes when injected into the m. soleus and m. gastrocnemius (white) muscles, which contained 70% and 0% of slow myofibers, respectively, and showed a high degree of fusion with host muscle fibers. In contrast, the FMb cells only expressed fast MyHCs in vitro and fused exclusively with each other or with host fast muscle fibers when injected in the m. gastrocnemius. Injected MCL and MtMd-1 fused predominantly with each other and displayed a similar expression of MyHCs to those they expressed in vitro. Just a few host myofibers were found to express the reporter gene product following implantation of both cell lines, indicating that these myogenic cell lines display an intrinsic potential to fuse together rather than with host myofibers. Based on the data, we concluded that 1) the essential key to survival is the ability of the donor cells to fuse with the host myofibers, and 2) the most successful combination is achieved between donor primary muscle cells that express both fast and slow MyHC and a host muscle type that facilitates fusion.

Herpes simplex viral and amplicon vector-mediated gene transfer into glia and neurons in organotypic spinal cord and dorsal root ganglion cultures

The progression of neurodegenerative diseases and secondary consequences of spinal cord injury may be diminished by introducing transgenes to glia, spinal neurons, and/or sensory neurons. Organotypic cultures of spinal cord slices and dorsal root ganglia proved to be an excellent system in which to compare the relative neurotropism of a replication-defective recombinant herpes simplex virus and herpes virus-derived amplicon vectors. Hundreds of beta-galactosidase-expressing cells, transduced by the viral vectors, were observed in spinal cord slices 3 and 8 days postinfection. Immunostaining to identify the infected cell type indicated that oligodendrocytes were permissive for viral vector transduction of beta-galactosidase in the spinal cord slice, whereas neurons were not. Heparan sulfate proteoglycan, the initial receptor for herpes contact with cells, was highly expressed in the white matter of the spinal cord slice, but was negligible in the gray matter. In contrast to the spinal cord, many fewer cells were infected in the dorsal root ganglia (DRG) by these vectors, but a majority of infected cells were identified as sensory neurons. Heparan sulfate proteoglycan expression was abundant in the sensory fibers emanating from the DRG and also surrounded each neuron within the ganglion. Our results demonstrate HSV-induced transgene expression that is amenable to ex vivo assessment of its physiological impact.

Matching host muscle and donor myoblasts for myosin heavy chain improves myoblast transfer therapy

Intensive efforts have been made to develop an effective therapy for Duchenne muscular dystrophy (DMD). Although myoblast transplantation has been found capable of transiently delivering dystrophin and improving the strength of the injected dystrophic muscle, this approach has been hindered by the immune rejection problems as well as the poor survival and limited spread of the injected cells. In the present study, we have investigated whether the careful selection of donor myoblasts and host muscle for the myosin heavy chain expression (MyHCs) plays a role in the success of myoblast transfer. Highly purified normal myoblasts derived from the m. soleus and m. gastrocnemius white of normal mice were transplanted into the m. soleus (containing 70% of type I fibers) and gastrocnemius white (100% of type II fibers) of dystrophin deficient mdx mice. At several time-points after injection (10, 20 and 30 days), the number of dystrophin-positive fibers was monitored and compared among the different groups. A significantly higher number and better persistence of dystrophin-positive myofibers were observed when the injected muscle and donor myoblasts expressed a similar MyHC in comparison with myoblast transfer between host muscle and donor myoblasts that were not matched for MyHC. These results suggest that careful matching between the injected myoblasts and injected muscle for the MyHC expression can improve the efficiency of myoblast-mediated gene transfer to skeletal muscle. Gene Therapy (2000) 7, 428-437.

The use of adeno-associated virus to circumvent the maturation-dependent viral transduction of muscle fibers

Muscle-based gene therapy using adenovirus, retrovirus, and herpes simplex virus has been hindered by viral cytotoxicity, host immune response, and the maturation-dependent viral transduction of muscle fibers. The development of new mutant vectors has greatly reduced the toxicity and the immune rejection problems, but the inability of viral vectors to penetrate and transduce mature myofibers remains an important issue. Research has been focused on the characterization of barriers to viral transduction in mature myofibers to develop strategies to circumvent the maturation-dependent viral transduction of myofibers. Here, we report that adeno-associated virus (AAV) can be used to overcome the maturation-dependent viral transduction of myofibers. We have investigated by which mechanism AAV can penetrate and efficiently transduce mature muscle fibers, and have shown that this viral vector is not blocked by the basal lamina and that AAV transduction of myofibers is independent of myoblast mediation. Although AAV can efficiently transduce mature myofibers, a differential transduction is still observed among the different types of myofibers that correlates with the expression of the heparan sulfate proteoglycan receptors, the muscle maturity, the number of viral particles used, and the time postinjection. The identification of the mechanisms by which AAV transduces mature myofibers will help in the development of strategies to achieve an efficient muscle-based gene therapy for inherited and acquired diseases.

Use of growth factors to improve muscle healing after strain injury

Muscle injuries represent a large number of professional and recreational sports injuries. Muscle strains habitually occur after an eccentric contraction, which often leads to an injury located in the myotendinous junction. Treatment varies widely, depending on the severity of the trauma, but has remained limited mostly to rest, ice, compression, elevation, antiinflammatory drugs, and mobilization. The authors' research group aims to develop new biologic approaches to improve muscle healing after injuries, including muscle strains. To achieve this goal, the authors investigated several parameters that will lead to the development of new strategies to enhance muscle healing. The authors first evaluated natural muscle healing after strain injuries and showed that muscle regeneration occurs in the early phase of healing but becomes impaired with time by the development of tissue fibrosis. Several growth factors capable of improving muscle regeneration were investigated; basic fibroblast growth factor, insulin-like growth factor, and nerve growth factors were identified as substances capable of enhancing muscle regeneration and improving muscle force in the strained injured muscle. The current study should aid in the development of strategies to promote efficient muscle healing and complete recovery after strain injury.

Vectors for gene therapy of cardiovascular disease

Several phase I/II clinical trials are currently ongoing in gene therapy of cardiovascular disease. Whereas the indications vary, including peripheral artery disease, ischemic heart disease, post-angioplasty restenosis, and vein graft failure, these trials are mostly based on the use of adenoviral vectors and nonviral vectors. Novel vectors aimed at improving the efficacy and safety of gene delivery in target organs, such as heart, skeletal muscle, vasculature, and liver, have been recently generated. Some of them have already been successfully validated in preclinical models of cardiovascular disease. This review focuses on the most recent advances in vector development that could substantially increase the spectrum of cardiovascular pathologies amenable to gene transfer-based treatments.

Efficient infection of mature skeletal muscle with herpes simplex virus vectors by using dextran sulfate as a co-receptor

The use of herpes simplex virus (HSV) vectors for gene delivery to skeletal muscle is hampered by a maturation-dependent loss of muscle fiber infectivity. Previous studies of HSV type 1 (HSV-1) infection in the rodent show that the loss of infectivity may be due, at least in part, to the development of the basal lamina throughout the course of maturation, which may block the initial events in HSV infection. To initiate infection, HSV normally attaches to cell surface heparan sulfate, which stabilizes the virus such that it can interact with secondary protein receptors required for entry into host cells. In this study, we demonstrate that heparan sulfate biosynthesis is downregulated during skeletal muscle maturation. When myofibers were treated with a variety of enzymes, including collagenase type IV or chondroitin ABC lyase, HSV infection was restored, which suggests that virus secondary receptors were present but not readily accessible to the virus in the intact myofiber. Surprisingly, we also found that HSV-1 infectivity could be restored in vitro and in vivo by exposing myofibers to low concentrations of the glycosaminoglycan analog dextran sulfate, which appears to act as a surrogate receptor to stabilize the virus at the myofiber surface such that HSV can engage additional receptors. This demonstration that the basal lamina is not an absolute block to HSV-1 infection is remarkable because it allows for the nondestructive targeting of HSV-1 to mature myofibers and greatly expands the usefulness of HSV as a gene therapy vector for the treatment of inherited and acquired diseases.

Herpes simplex virus vector-mediated dystrophin gene transfer and expression in MDX mouse skeletal muscle

BACKGROUND

Duchenne muscular dystrophy (DMD) results from mutations that prevent the expression of functional dystrophin in muscle fibers. Herpes simplex virus type-1 (HSV-1) represents a potentially useful vector for treatment of DMD because it has the capacity to accommodate the 14-kb full-length dystrophin cDNA and can efficiently transduce muscle cells. We have tested the ability of first- and second-generation replication-defective HSV vectors to deliver full-length dystrophin to dystrophin-deficient mdx muscle cells in vitro and in vivo.

METHODS

First-generation replication-defective HSV vectors harboring full-length or truncated (Becker) dystrophin expression cassettes and lacking a single viral immediate-early (IE) gene were constructed and tested by immunofluorescence and immunoblotting for their ability to direct dystrophin expression in infected mdx cells in culture. To reduce vector cytotoxicity and safety concerns, a second-generation dystrophin vector missing additional IE genes was constructed and tested in vitro and in vivo.

RESULTS

Dystrophin expression was observed in infected mdx myotubes in vitro in all cases. Confocal microscopy showed exclusive localization of full-length dystrophin to the cell membrane whereas the Becker variant was also found abundantly throughout the cytoplasm. Dystrophin expression in mdx mice was restored in muscle cells near the site of vector injection.

CONCLUSION

Highly defective HSV-1 vectors which lack the ability to spread systemically and are greatly reduced in toxicity for infected cells, thus removing an impediment to prolonged transgene expression, can direct the delivery and proper expression of full-length dystrophin whose considerable size is compatible with few other modes of delivery. These vectors may offer a legitimate opportunity toward the development of effective gene therapy treatments for DMD.

Safe and effective regulation of hematocrit by gene gun administration of an erythropoietin-encoding DNA plasmid

This work examines the effect of delivering a DNA plasmid encoding murine erythropoietin (pVRmEpo) to BALB/c mice by gene gun. Whereas intramuscular injection elicits a rise in hematocrit persisting >8 months, intradermal delivery triggers the dose-dependent secretion of biologically active erythropoietin (Epo) for approximately 1 month. Repeated administration of pVRmEpo by gene gun elicits a stable increase in hematocrit. The source of the Epo produced following gene gun delivery was analyzed by periodically grafting the site of injection onto naive recipients. Results indicate that both stationary cells (presumably keratinocytes) and migratory (presumably dendritic) cells were transfected and secreted biologically active Epo in vivo. Gene gun administration of plasmid DNA appears to be safe, and provides an additional strategy for achieving the regulated secretion of an exogenous gene product.

Gene therapy for cerebrovascular disease

OBJECTIVE

To review the principles of and the experimental and clinical results of gene therapy for cerebrovascular disease.

METHODS

Literature review.

RESULTS

Vectors for gene transfer into the brain or into the cerebral vasculature include naked plasmid deoxyribonucleic acid, cationic liposomes, and viruses such as adenovirus, retrovirus, adeno-associated virus, and herpes simplex virus. Experiments using these vectors showed that intra- or perivascular application to systemic arteries can lead to transfection and expression of a foreign transgene in the adventitia and the endothelium. Intrathecal administration can lead to transfection and foreign transgene expression in leptomeningeal cells as well as in fibroblasts of blood vessel adventitia. Biological effects demonstrated thus far include increased nitric oxide production by transfection of cerebral arterial adventitia with adenovirus expressing nitric oxide synthase. Adenoviruses carrying foreign genes have been used to decrease neuronal damage in cerebral ischemia and to decrease blood pressure in spontaneously hypertensive rats. Vectors and therapeutic applications for gene therapy are evolving rapidly.

CONCLUSION

Gene therapy for cerebrovascular disease is likely to have clinical application in the near future and will have a major impact on neurosurgery. Neurosurgeons will need to be aware of the literature in this area.

Efficient gene delivery into epstein-barr virus (EBV)-transformed human B cells mediated by replication-defective herpes simplex virus-1 (HSV-1): A gene therapy model for EBV-related B cell malignancy

Subgroups of the B cell malignancies are known to be associated with Epstein-Barr virus (EBV) infection, especially in immunocompromised patients. These are fatal and refractory to conventional antineoplastic therapy. B cells are usually post-mitotic cells and even mitogen activated or transformed B cells have shown relative resistance against viral mediated gene transfer. To address this issue, we employed a replication-defective herpes simplex virus-1 (HSV-1) to mediate gene transfer into EBV-transformed B cells. The virus expresses the herpes simplex virus thymidine kinase (HSV-TK) and the E. coli lacZ reporter genes and is designated T0Z.1. We used the lymphoblastoid cell line SWEIG as a model for human EBV-related B cell malignancy. This cell line was established by in vitro EBV infection of primary human peripheral blood mononuclear cells. When SWEIG cells were infected with T0Z.1, X-gal staining revealed lacZ expression in more than 20% cells even at multiplicity of infection (MOI) as low as 1 and the expression persisted for at least one week. Ganciclovir (GCV) administration after T0Z.1 infection effectively decreased the number of the infected tumor cells in a dose-responsive manner. Viral toxicity was analyzed by cell proliferation assay (MTS assay) and found to be little even at 10 MOI infection. Three MOI of the virus yielded maximum antineoplastic effect and more than 50% tumor cells were killed by HSV-TK/GCV. These results suggest the potential utility of replication-defective HSV-1 for the treatment of EBV-related B cell malignancies.

Development of approaches to improve cell survival in myoblast transfer therapy

Myoblast transplantation has been extensively studied as a gene complementation approach for genetic diseases such as Duchenne Muscular Dystrophy. This approach has been found capable of delivering dystrophin, the product missing in Duchenne Muscular Dystrophy muscle, and leading to an increase of strength in the dystrophic muscle. This approach, however, has been hindered by numerous limitations, including immunological problems, and low spread and poor survival of the injected myoblasts. We have investigated whether antiinflammatory treatment and use of different populations of skeletal muscle-derived cells may circumvent the poor survival of the injected myoblasts after implantation. We have observed that different populations of muscle-derived cells can be isolated from skeletal muscle based on their desmin immunoreactivity and differentiation capacity. Moreover, these cells acted differently when injected into muscle: 95% of the injected cells in some populations died within 48 h, while others richer in desmin-positive cells survived entirely. Since pure myoblasts obtained from isolated myofibers and myoblast cell lines also displayed a poor survival rate of the injected cells, we have concluded that the differential survival of the populations of muscle-derived cells is not only attributable to their content in desmin-positive cells. We have observed that the origin of the myogenic cells may influence their survival in the injected muscle. Finally, we have observed that myoblasts genetically engineered to express an inhibitor of the inflammatory cytokine, IL-1, can improve the survival rate of the injected myoblasts. Our results suggest that selection of specific muscle-derived cell populations or the control of inflammation can be used as an approach to improve cell survival after both myoblast transplantation and the myoblast-mediated ex vivo gene transfer approach.

Muscle maturation: implications for gene therapy

Skeletal muscle is a promising target tissue for gene therapy, for both muscle and non-muscle disorders. A variety of methods have been studied to transfer genes into skeletal muscle, including retroviral, adenoviral and herpes simplex viral vectors. However, various factors impede muscle-based viral gene therapy. Here, we discuss why some viral vectors cannot efficiently transduce mature muscle fibers, and describe some new approaches to overcome this barrier.

Implications of maturation for viral gene delivery to skeletal muscle

Different viral vectors have been analyzed as gene delivery vehicles to skeletal muscle for potentially therapeutic purposes. In this review, we evaluate the application of retroviral, adenoviral, and herpes simplex viral vectors to deliver genes to skeletal muscle and focus on the dramatic loss of viral transduction detected throughout muscle maturation. Recent results suggested that there are several factors involved in the reduced viral transducibility of mature skeletal muscle: muscle cells become post-mitotic in an early stage, the extracellular matrix develops into a physical barrier, and a loss of myoblast mediation occurs since myoblasts progressively become quiescent. Approaches to improve viral gene delivery to mature skeletal muscle may include the use of particular enzymes to increase the permeability of the extracellular matrix, the pre-treatment of the muscle with a myonecrotic agent to induce myoblast mediation, or the application of the myoblast-mediated ex vivo gene transfer.

Efficient and stable adeno-associated virus-mediated transduction in the skeletal muscle of adult immunocompetent mice

Recombinant adeno-associated virus (rAAV) vectors were evaluated for gene transfer into the skeletal muscle of adult immunocompetent mice. A study using a vector encoding nuclear localized beta-galactosidase (rAAV-nls-lacZ) examined: (i) the efficiency and duration of transgene expression; (ii) the status of the AAV genome in the transduced fibers; and (iii) the possibility of improving gene transfer by inducing muscle regeneration. In the absence of regeneration, the injection of 1.7 x 10(7) particles in the quadriceps resulted in gene transfer to 10-70% of myofibers. Histological analysis indicated that the vector was able to reach myofiber nuclei distant from the injection point. Cellular infiltrates were absent at early time points but became conspicuous in the vicinity of some positive fibers at 4-8 weeks and subsided by 26 weeks. Southern analysis indicated that one to three copies of the vector genome were present per cell genome equivalent. They were associated with high-molecular-weight DNA in the form of tandem oligomers or interlocked circles. Gene transfer was not facilitated in the regenerating muscle. Rather, an early inflammatory response resulted in the elimination of most positive fibers after 8 weeks. The presence of regenerated fibers with beta-galactosidase-positive nuclei suggested that myoblasts had been transduced and were able to fuse to form new fibers. Gene transfer in the absence of immune reactions against the transgene product was studied by injecting mice with a rAAV carrying the murine erythropoietin (mEpo) cDNA. Dose-dependent elevation in the hematocrit was measured for over 200 days and corresponded to 5- to 20-fold increases in plasma Epo levels. We conclude that AAV vectors efficiently and stably transduce post-mitotic muscle fibers and myoblasts in vivo.

Myoblast-mediated gene transfer to the joint

Several genetic and acquired pathologic conditions of the musculoskeletal system, such as arthritis and damage to ligament, cartilage, and meniscus, may be amenable to gene therapy. Even though ex vivo gene transfer with synovial cells has been shown to deliver genes encoding for anti-arthritic proteins into the rabbit knee joint, its success has been limited by a transient transgene expression. In this study, data were investigated regarding the use of muscle cells as an alternative gene-delivery vehicle to the joint in newborn rabbit and adult severe combined immunodeficiency mice. We demonstrated that myoblasts were transduced more efficiently than synovial cells with use of the same adenoviral preparation in vitro. After intra-articular injection, the engineered muscle cells adhered to several structures in the joint, including the ligament, capsule, and synovium. In addition, myoblasts fused to form many post-mitotic myotubes and myofibers at different locations of the joint of the newborn rabbit 5 days after the injection. In the knee of the adult mouse, myoblasts fused and expressed the reporter gene for at least 35 days after the injection. The presence of post-mitotic myofibers in the knee joint raises the possibility of long-term expression of the secreted protein. Currently, numerous tissues in the joint (ligament, meniscus, and cartilage) have poor intrinsic healing capacity and frequently need surgical corrections. A stable gene-delivery vehicle to the joint producing proteins that ameliorate these different musculoskeletal conditions may change the clinical implications of these pathologies.

Progress in development of herpes simplex virus gene vectors for treatment of rheumatoid arthritis

Arthritis is presently incurable and poorly treatable, but there are good grounds for expecting gene therapy to improve matters considerably. Although local ex vivo delivery of anti-arthritic genes to the synovial lining of joints has shown considerable promise, intraarticular gene delivery may be desirable. Herpes simplex virus (HSV) may be a viable vector for in vivo transfer of anti-arthritic genes to joints. HSV has the advantages of high infectivity, large carrying capacity and high titer. The large packaging capacity would permit the inclusion of multiple anti-arthritic genes and necessary regulatory elements. Recombinant vectors produced by this laboratory infect synovial cells efficiently, permitting prolonged expression of transgenes in vitro and in vivo without evidence of cytotoxicity. Further improvements to this vector system include taking advantage of an endogenous HSV 'stealthing' gene, ICP47, which interferes with formation of antigen-class I complexes. Inclusion of inducible promoters to appropriately regulate expression of anti-arthritic genes should further improve this system.