Improvement of nonviral gene therapy by Epstein-Barr virus (EBV)-based plasmid vectors

The nonviral gene transfer technologies include naked DNA administration, electrical or particle-mediated transfer of naked DNA, and administration of DNA-synthetic macromolecule complex vectors. Each method has its advantage, such as low immunogenicity, inexpensiveness, ease in handling, etc., but the common disadvantage is that the transfection efficiency has been relatively poor as far as conventional plasmid vectors are involved. To improve the nonviral gene transfer systems, Epstein-Barr virus (EBV)-based plasmid vectors (also referred to EBV-based episomal vectors) have been employed. These vectors contain the EBNA1 gene and oriP element that enable high transfer efficiency, strong transgene expression and long term maintenance of the expression. In the current article, I review recent preclinical gene therapy studies with the EBV plasmid vectors conducted against various diseases. For gene therapy against malignancies, drastic tumor suppression was achieved by gancyclovir administrations following an intratumoral injection with an EBV plasmid vector encoding the HSV1-TK suicide gene. Equiping the plasmid with carcinoembryonic antigen (CEA) promoter sequences enabled targeted killing of CEA-positive tumor cells, which was not accomplished by conventional plasmid vectors without the EBV genetic elements. Transfection with an apoptosis-inducing gene was also effective in inhibiting tumors. Interleukin (IL)-12 and IL-18 gene transfer, either local or systemic, induced therapeutic antitumoral immune responses including augmentation of the cytotoxic T lymphocyte (CTL) and natural killer (NK) activities, while an autologous tumor vaccine engineered to secrete Th1 cytokines via the EBV system also induced growth retardation of tumors. Non-EBV conventional plasmids were much less effective in eliciting these therapeutic outcomes. Intracardiomuscular transfer of the beta-adrenergic receptor gene induced a significant elevation in cardiac output in cardiomyopathic animals, suggesting the usefulness of the EBV system in treating heart failure. The EBV-based nonviral delivery also worked as genetic vaccine that triggered prophylactic cellular and humoral immunity against acute lethal viral infection. All the nonviral delivery vehicles so far tested showed an improved transfection rate when combined with the EBV-plasmids. Collectively, the EBV-based plasmid vectors may greatly contribute to nonviral gene therapy against a variety of disorders, including malignant, congenital, chronic and infectious diseases.     

Nonviral vectors for cancer gene therapy: prospects for integrating vectors and combination therapies

Gene therapy has the potential to improve the clinical outcome of many cancers by transferring therapeutic genes into tumor cells or normal host tissue. Gene transfer into tumor cells or tumor-associated stroma is being employed to induce tumor cell death, stimulate anti-tumor immune response, inhibit angiogenesis, and control tumor cell growth. Viral vectors have been used to achieve this proof of principle in animal models and, in select cases, in human clinical trials. Nevertheless, there has been considerable interest in developing nonviral vectors for cancer gene therapy. Nonviral vectors are simpler, more amenable to large-scale manufacture, and potentially safer for clinical use. Nonviral vectors were once limited by low gene transfer efficiency and transient or steadily declining gene expression. However, recent improvements in plasmid-based vectors and delivery methods are showing promise in circumventing these obstacles. This article reviews the current status of nonviral cancer gene therapy, with an emphasis on combination strategies, long-term gene transfer using transposons and bacteriophage integrases, and future directions.     

Polysaccharide gene transfection agents

Gene delivery is a promising technique that involves in vitro or in vivo introduction of exogenous genes into cells for experimental and therapeutic purposes. Successful gene delivery depends on the development of effective and safe delivery vectors. Two main delivery systems, viral and non-viral gene carriers, are currently deployed for gene therapy. While most current gene therapy clinical trials are based on viral approaches, non-viral gene medicines have also emerged as potentially safe and effective for the treatment of a wide variety of genetic and acquired diseases. Non-viral technologies consist of plasmid-based expression systems containing a gene associated with the synthetic gene delivery vector. Polysaccharides compile a large family of heterogenic sequences of monomers with various applications and several advantages as gene delivery agents. This chapter, compiles the recent progress in polysaccharide based gene delivery, it also provides an overview and recent developments of polysaccharide employed for in vitro and in vivo delivery of therapeutically important nucleotides, e.g. plasmid DNA and small interfering RNA.     

Electro-Gene-Transfer: A New Approach for Muscle Gene Delivery

Gene transfer into skeletal muscle cells by direct injection of naked plasmid DNA results in sustained gene expression. Intramuscular injection of plasmid DNA might thus be used to correct myopathies, to secrete locally or systematic therapeutic proteins and to elicit an immune response against specific antigens. However, the potential utility of this technique for gene application in humans is limited by the poor transduction efficiency and the low and highly variable level of gene expression. Different methods are thus being developed to increase the efficiency of gene transfer in muscles. It has been recently reported that a dramatic improvement of DNA transfer is achieved by applying an electric field to the muscle fibers subsequent to local DNA injection. Electro-gene-transfer increases gene expression by several orders of magnitude and strongly reduces interindividual variability. Electroinjection of genes encoding for secreted proteins resulted in sustained expression and disease correction in animal models of gene therapy. Moreover, the immunogenicity of DNA vaccines is dramatically increased when antigen-encoding plasmids are delivered by this technique. This technique may thus have broad and important applications in human gene therapy. This review provides a brief overview of the theory of electro-gene-transfer and describes parameters governing its efficiency in muscle. We also summarize the results obtained with electro-gene-transfer in animal models to date and the technical issues that must be solved before its use for human therapy can be considered.     

Transductional targeting with recombinant adenovirus vectors

Replication-deficient adenoviruses are considered as gene delivery vectors for the genetic treatment of a variety of diseases. The ability of such vectors to mediate efficient expression of therapeutic genes in a broad spectrum of dividing and non-dividing cell types constitutes an advantage over alternative gene transfer vectors. However, this broad tissue tropism may also turn disadvantageous when genes encoding potentially harmful proteins (e.g. cytokines, toxic proteins) are expressed in surrounding normal tissues. Therefore, specific restrictions of the viral tropism would represent a significant technological advance towards safer and more efficient gene delivery vectors, in particular for cancer gene therapy applications. In this review, we summarize various strategies used to selectively modify the natural tropism of recombinant adenoviruses. The advantages, limitations and potential impact on gene therapy operations of such modified vectors are discussed.     

Nonviral DNA vectors for immunization and therapy: design and methods for their obtention

The use of plasmid DNA for vaccination and therapy is a relatively novel technology, with advantages and limitations as with other gene transfer techniques. The technology is based on DNA vectors designed for administering genes coding for relevant proteins into a given organism, fulfilling requirements of the regulatory agencies that once properly formulated and delivered the desired vaccine/therapeutic effect can be achieved. Starting from conventional plasmid DNA vectors currently tested in clinical trials, improvement resulted in bacterial element-less vectors, increasing the complexity of the developmental process. The present review focuses on systems described for generating these nonviral DNA vectors for immunization and therapy from bacterial hosts (conventional and conditionally replicating plasmids, nonreplicating minicircles, and linear dumbbell-shaped expression cassettes) in vivo or in vitro. Additionally, nontherapeutic genetic sequences with a negative or positive effect according to the specific application are described, bringing a better comprehension of the technologys state of the art.Abbreviations COR Conditional origin of replication - ISS Immunostimulatory sequences - MIDGE Minimalistic immunogenic defined gene expression - PCR Polymerase chain reaction     

Electroporation for Gene Transfer to Skeletal Muscles

Naked plasmid DNA can be used to introduce genetic material into a variety of cell types in vivo. However, such gene transfer and expression is generally very low compared with that achieved with viral vectors and so is unsuitable for clinical therapeutic application in most cases. This difference in efficiency has been substantially reduced by the introduction of in vivo electroporation to enhance plasmid delivery to a wide range of tissues including muscle, skin, liver, lung, artery, kidney, retina, cornea, spinal cord, brain, synovium, and tumors. The precise mechanism of in vivo electroporation is uncertain, but appears to involve both electropore formation and an electrophoretic movement of the plasmid DNA. Skeletal muscle is a favored target tissue for three reasons: there is a pressing need to develop effective therapies for muscular dystrophies; skeletal muscle can act as an effective platform for the long-term secretion of therapeutic proteins for systemic distribution; and introduction of DNA vaccines into skeletal muscle promotes strong humoral and cellular immune responses. All of these applications are significantly improved by the application of in vivo electroporation. Importantly, the increased efficiency of plasmid delivery following electroporation is seen in larger species as well as rodents, in contrast to the decreasing efficiencies with increasing body size for simple intramuscular injection of naked plasmid DNA. As this electroporation-enhanced non-viral gene delivery system works well in larger species and avoids the vector-specific immune responses associated with recombinant viruses, the prospects for clinical application are promising.     

基因治疗的新型载体研究进展

建立和发展一个安全及有效的载体系统对基因治疗是极其重要的。尽管病毒载体已经在临床上用于基因治疗，但其安全性仍然不确切。近年来，许多非病毒性基因载体系统已被广泛开展及应用。本综述将讨论一些新的基因载体系统，特别是本实验室开展研究的载体系统，包括细胞转导肽，电脉冲导入系统，壳聚糖载体等。     

Self-assembled ternary complexes of plasmid DNA, low molecular weight polyethylenimine and targeting peptide for nonviral gene delivery into neurons

Chemical conjugation of targeting ligands to polycation/plasmid DNA complexes has been widely used to improve the transfection efficiency of nonviral gene delivery vectors. However, conjugation reactions may reduce or even inactivate the biological activities of chemically sensitive moieties, such as proteins and peptides. Here we describe a new method for introducing targeting ligands into nonviral vectors, in which ternary complexes are formed via charge interactions among polyethylenimine (PEI) of 600Da, plasmid DNA and targeting peptides with positively charged DNA-binding sequence. Owing to the nerve growth factor (NGF) loop 4 hairpin motif in the targeting peptide, these ternary complexes are capable of mediating gene delivery efficiently and specifically into cells expressing the NGF receptor TrkA. In in vitro experiments, the complexes improved luciferase reporter gene expression by up to 1000-fold while comparing with that produced by complexes with nontargeting control peptide. In an in vivo experiment, the ternary complexes with the targeting peptide was 59-fold more efficient than the control ternary complexes in transfecting dorsal root ganglia (DRG), the peripheral nervous sites with TrkA-expressing neurons. In a cell viability study, the ternary complexes were remarkably different from DNA complexes by PEI of 25 kDa, the gold standard for nonviral gene carriers, displaying no toxicity in tested neuronal cells. Thus, this study demonstrates an alternative method to construct nonviral delivery system for targeted gene transfer into neurons.     

Plasmid DNA-based gene transfer with ultrasound and microbubbles

Gene therapy offers a novel approach for the prevention and treatment of a variety of diseases, but it is not yet a common option in the real world because of various problems. Viral vectors show high efficiency of gene transfer, but they have some problems with toxicity and immunity. On the other hand, plasmid DNA-based gene transfer is very safe, but its efficiency is relatively low. Especially, plasmid DNA gene therapy is used for cardiovascular disease because plasmid DNA transfer is possible for cardiac or skeletal muscle. Clinical angiogenic gene therapy using plasmid DNA gene transfer has been attempted in patients with peripheral artery disease, but a Phase III clinical trial did not show sufficient efficiency. Recently, a Phase III clinical trial of hepatocyte growth factor gene therapy in peripheral artery disease (PAD) showed improvement of ischemic ulcers, but it could not salvage limbs from amputation. In addition, a Phase I/II clinical study of fibroblast growth factor gene therapy in PAD extended amputation-free survival, but it seemed to fail in Phase III. In this situation, we and others have developed plasmid DNA-based gene transfer using ultrasound with microbubbles to enhance its efficiency while maintaining safety. Ultrasound-mediated gene transfer has been reported to augment the gene transfer efficiency and select the target organ using cationic microbubble phospholipids which bind negatively charged DNA. Ultrasound with microbubblesis likely to create new therapeutic options inavariety of diseases.     

Viral based gene therapy for prostate cancer

In the last few years, significant advances in gene therapy have been made as a result of advances in many areas of molecular and cell biology, including the improvement of both viral and nonviral gene delivery systems, discovery of new therapeutic genes, better understanding of mechanism of disease progression, exploration of tissue specific promoter, receptor- and antibody-mediated targeting delivery, and development of better prodrug enzyme/prodrug systems. In this article, viral based gene therapy for prostate cancer will be reviewed and discussed. The areas of emphasis in this review are: choice of viral vectors, comparison of delivery routes, development of prostate-targeted viruses, choice of therapeutic genes and strategies including corrective gene therapy (tumor suppressor gene and anti-oncogene gene approaches), suicide gene therapy, programmed cell death therapy, immunomodulation therapy, and conditional oncolytic virus approach. Among them, several examples will be discussed in detail for the scientific basis and therapeutic applications. In addition, prostate cancer gene therapy clinical trials, unresolved problems and future directions in this field will also be described.     

Viral vectors in cancer immunotherapy: which vector for which strategy?

Gene therapy involves the transfer of genetic information to a target cell to facilitate the production of therapeutic proteins and is now a realistic prospect as a cancer treatment. Gene transfer may be achieved through the use of both viral and non-viral delivery methods and the role of this method in the gene therapy of cancer has been demonstrated. Viruses represent an attractive vehicle for cancer gene therapy due to their high efficiency of gene delivery. Many viruses can mediate long term gene expression, while some are also capable of infecting both dividing and non-dividing cells. Given the broadly differing capabilities of various viral vectors, it is imperative that the functionality of the virus meets the requirements of the specific treatment. A number of immunogene therapy strategies have been undertaken, utilising a range of viral vectors, and studies carried out in animal models and patients have demonstrated the therapeutic potential of viral vectors to carry genes to cancer cells and induce anti-tumour immune responses. This review critically discusses the advances in the viral vector mediated delivery of immunostimulatory molecules directly to tumour cells, the use of viral vectors to modify tumour cells, the creation of whole cell vaccines and the direct delivery of tumour antigens in animal models and clinical trials, specifically in the context of the suitability of vector types for specific strategies.     

A calcium phosphate-based gene delivery system

Although nonviral vectors have lower transfection efficiency than viral vectors, the excellent safety profile of nonviral vectors is appealing for gene therapy. An efficient, simple nonviral vector gene delivery system has been designed that includes plasmid DNA-calcium phosphate precipitates (pDNA-CaP) and porous collagen spheres (Cultispherestrade mark). The hypothesis for this study was the pDNA-CaP would achieve efficient plasmid DNA transfection and the porous collagen spheres would provide a suitable delivery carrier system for three-dimensional (3D) administration. To test the hypothesis, plasmid DNA including the LacZ reporter gene encoding beta-galactosidase was precipitated with CaP to form particles of compacted LacZ-CaP and delivered directly or by Cultispherestrade mark to cells in vitro. The transfection efficiency was determined by beta-galactosidase gene expression. Results indicated that pLacZ-CaP promoted 25-84% of transfection efficiency in a broad cell line spectrum and in flexible experimental conditions. Maximum transfection efficiency was achieved by having mostly nano-sized partles (50-200 nm in diameter) of pDNA-CaP precipitates. Seeding density of 0.7-4 x 10(4) cells/cm2 provided sufficient transfection efficiency, and storage of pDNA-CaP at 4 degrees C was most efficient to preserve transfection efficacy for up to 3 days. The pDNA-CaP worked well in the presence of serum and serum-free conditions and was less cytotoxic than the liposomes. Cultispherestrade mark carrying plasmid LacZ-CaP was an effective 3D system for gene delivery. The technique described here is a simple and safe procedure to deliver genes, and may have application to regenerate bone and other tissues.     

Gene Delivery Approaches for Mesenchymal Stem Cell Therapy: Strategies to Increase Efficiency and Specificity

A significant number of clinical trials have been undertaken to explore the use of mesenchymal stem cells (MSCs) for the treatment of several diseases such as Crohn’s disease, diabetes, bone defects, myocardial infarction, stroke etc., Due to their efficiency in homing to the tissue injury sites, their differentiation potential, the capability to secrete a large amount of trophic factors and their immunomodulatory effects, MSCs are becoming increasingly popular and expected to be one of the promising therapeutic approaches. However, challenges associated with the isolation of pure MSC populations, their culture and expansion, specific phenotypic characterization, multi-potential differentiation and challenges of efficient transplantation limit their usage. The current strategies of cell-based therapies emphasize introducing beneficial genes, which will improve the therapeutic ability of MSCs and have better homing efficiency. The continuous improvement in gene transfer technologies has broad implications in stem cell biology. Although viral vectors are efficient vehicles for gene delivery, construction of viral vectors with desired genes, their safety and immunogenicity limit their use in clinical applications. We review current gene delivery approaches, including viral and plasmid vectors, for transfecting MSC with beneficial genes. The review also discusses the use of a few emerging technologies that could be used to improve the transfer/induction of desirable genes for cell therapy.     

Nonviral gene therapy

The last 10 years have seen substantial progress in the development and application of nonviral vectors in gene therapy. Several novel nonviral methods have been developed that approach viruses with respect to transfection efficiency. A variety of nonviral delivery systems that can be used for gene therapy in different clinical settings are also available. In this review article, we will detail all of the major nonviral vectors that are currently used in gene therapy while highlighting some recent developments, particularly the progress towards the understanding of the cellular and in vivo barriers in gene transfer. Recent advancement in achieving sustained and regulated gene expression will also be addressed. Finally, this review will briefly cover targeted gene repair using nonviral delivery systems. Their impact in gene therapy will also be discussed.     

Intracellular barriers to non-viral gene transfer

Non-viral vector mediated gene transfer, compared to viral vector mediated one, is a promising tool for the safe delivery of therapeutic DNA in genetic and acquired human diseases. Although the lack of specific immune response favor the clinical application of non-viral vectors, comprising of an expression cassette complexed to cationic liposome or cationic polymer, the limited efficacy and short duration of transgene expression impose major hurdles in the widespread application of non-viral gene therapy. The trafficking of transgene, complexed with chemical vectors, has been the subject of intensive investigations to improve our understanding of cellular and extracellular barriers impeding gene delivery. Here, we review those physical and metabolic impediments that account, at least in part, for the inefficient translocation of transgene into the nucleus of target cells. Following the internalization of the DNA-polycation complex by endocytosis, a large fraction is targeted to the lysosomal compartment by default. Since the cytosolic release of heterelogous DNA is a prerequisite for nuclear translocation, entrapment and degradation of plasmid DNA in endo-lysosomes constitute a major impediment to efficient gene transfer. Only a small fraction of internalized plasmid DNA penetrates the cytoplasm. Plasmid DNA encounters the diffusional and metabolic barriers of the cytoplasm, further decreasing the number of intact plasmid molecules reaching the nuclear pore complex (NPC), the gateway of nucleosol. Nuclear translocation of DNA requires either the disassembly of the nuclear envelope or active nuclear transport via the NPC. Comparison of viral and plasmid DNA cellular trafficking should reveal strategies that viruses have developed to overcome those cellular barriers that impede non-viral DNA delivery in gene therapy attempts.     

Electroporation-enhanced nonviral gene transfer for the prevention or treatment of immunological, endocrine and neoplastic diseases

Nonviral gene transfer is markedly enhanced by the application of in vivo electroporation (also denoted electro-gene transfer or electrokinetic enhancement). This approach is safe and can be used to deliver nucleic acid fragments, oligonucleotides, siRNA, and plasmids to a wide variety of tissues, such as skeletal muscle, skin and liver. In this review, we address the principles of electroporation and demonstrate its effectiveness in disease models. Electroporation has been shown to be equally applicable to small and large animals (rodents, dogs, pigs, other farm animals and primates), and this addresses one of the major problems in gene therapy, that of scalability to humans. Gene transfer can be optimized and tissue injury minimized by the selection of appropriate electrical parameters. We and others have applied this approach in preclinical autoimmune and/or inflammatory diseases to deliver either cytokines, anti-inflammatory agents or immunoregulatory molecules. Electroporation is also effective for the intratumoral delivery of therapeutic vectors. It strongly boost DNA vaccination against infectious agents (e.g., hepatitis B virus, human immunodeficiency virus-1) or tumor antigens (e.g., HER-2/neu, carcinoembryonic antigen). In addition, we found that electroporation-enhanced DNA vaccination against islet-cell antigens ameliorated autoimmune diabetes. One of the most likely future applications, however, may be in intramuscular gene transfer for systemic delivery of either endocrine hormones (e.g., growth hormone releasing hormone and leptin), hematopoietic factors (e.g., erythropoietin, GM-CSF), antibodies, enzymes, or numerous other protein drugs. In vivo electroporation has been performed in humans, and it seems likely it could be applied clinically for nonviral gene therapy.     

Gene therapy in soft tissue reconstruction

Gene therapy is defined as the introduction of a therapeutic gene into a cell, whose expression can lead to a cure of a disease or offer a transient advantage for tissue growth and regeneration. The delivery of genes can be undertaken for a number of purposes, usually it is attempted to enhance or add a function to a cell or a tissue or to delete or reduce another function. In this brief overview we describe various vehicles and techniques that have been developed to deliver therapeutic genes into cells, such as viral vectors and physical/chemical gene delivery methods including naked DNA and particle-mediated gene transfer, the microseeding technique and the application of lipids. Furthermore we review the potential utility of gene therapy from the perspective of a reconstructive surgeon. Several tissues will be discussed, particularly muscle, tendon, nerve, bone, skin and wounds.     

Applications of muscle electroporation gene therapy

Muscle is a convenient and accessible site for non-viral gene delivery, which can manufacture gene products and provide a long-duration of gene expression. The level of gene expression after administration of naked DNA plasmid or polymer-formulated DNA plasmid containing a reporter gene to muscle via syringe injection, however, is very low. As a result, no significant therapeutic effect can be detected after saline- or polymer-mediated gene delivery into muscle. In 1998, investigators published a striking new approach--electrotransfection--for intramuscular gene delivery (now commonly referred to as electroporation or electroinjection). Electroporation of a non-viral gene into the muscles of small animals has increased the level of gene expression by as much as two orders of magnitude, which is comparable to levels achieved with adenoviral gene delivery. Three years later, intramuscular electroporation gene delivery technology has blossomed. Treatments for different diseases using this approach in animal models have been reported. In this review, I discuss the applications of intramuscular electroporation gene therapy to treat malignancies, renal disease, and anemia, and to prevent drug toxicity to sensory nerves.     

Application of in vivo electroporation to cancer gene therapy

Much intensive research has gone into the development of safe and efficient methods for the delivery of therapeutic genes. In vivo electroporation is a non-viral delivery protocol in which plasmid DNA solutions are injected into targeted tissues, followed by electric pulses (typically 100 V, 50 ms). In general, in vivo electroporation enhances gene expression in targeted tissues by 2-3 orders of magnitude, as compared to the injection of plasmid DNA solutions without electric pulses, and the tissue damage appears to be minimal. Among the other advantages of this technique are that it can safely be administered repeatedly, and it is simpler and more economical to use than viral vectors, especially in clinical cases. Using this approach, highly efficient gene transfer has already been achieved in muscle and liver as well as in tumors. In fact, gene therapies for cancer utilizing in vivo electroporation have been proved effective in a number of experimental murine tumor models. The therapeutic genes delivered in those cases were diverse including, for example, cytokine genes (IL-12) and cytotoxic genes (TRAIL), making possible a wide range of therapeutic strategies. Moreover, systemic antitumor effects were also observed, suggesting that this approach may be effective for the treatment of metastatic as well as primary tumors.