Concepts and strategies for human gene therapy

Gene therapy and DNA delivery systems

Gene therapy is a promising new technique for treating many serious incurable diseases, such as cancer and genetic disorders. The main problem limiting the application of this strategy in vivo is the difficulty of transporting large, fragile and negatively charged molecules like DNA into the nucleus of the cell without degradation. The key to success of gene therapy is to create safe and efficient gene delivery vehicles. Ideally, the vehicle must be able to remain in the bloodstream for a long time and avoid uptake by the mononuclear phagocyte system, in order to ensure its arrival at the desired targets. Moreover, this carrier must also be able to transport the DNA efficiently into the cell cytoplasm, avoiding lysosomal degradation. Viral vehicles are the most commonly used carriers for delivering DNA and have long been used for their high efficiency. However, these vehicles can trigger dangerous immunological responses. Scientists need to find safer and cheaper alternatives. Consequently, the non-viral carriers are being prepared and developed until techniques for encapsulating DNA can be found. This review highlights gene therapy as a new promising technique used to treat many incurable diseases and the different strategies used to transfer DNA, taking into account that introducing DNA into the cell nucleus without degradation is essential for the success of this therapeutic technique.

Growth of recombinant fibroblasts in alginate microcapsules

To develop a novel strategy of nonautologous somatic gene therapy, we now demonstrate the feasibility of culturing genetically modified fibroblasts within an immunoprotective environment and the optimal conditions required for their continued survival in vitro. When mouse Ltk(-) fibroblasts transfected with the human growth hormone gene were enclosed within permselective microcapsules fabricated from alginate-polylysine-alginate, they continued to secrete human growth hormone at the same rates as the nonencapsulated cells. They also continued to proliferate in vitro for at least 1 month even though their viability gradually declined to about 50%. The viability can be improved by controlling for (a) temperature during encapsulation, (b) duration of treatment with polylysine, (c) duration of liquefying the core alginate with sodium citrate, and (d) cell density at the time of encapsulation. The best conditions leading to improved survival and maximum proliferation of cells within the microcapsules were obtained by encapsulating the cells at 4 to 10 degrees C instead of room temperature, coating the microspheres with polylysine for 6 to 10 min instead of 20 min, liquefying the core alginate by treating with citrate for 20 min instead of 6 to 10 min, and using a concentration of 2 x 10(6) cells/mL of alginate for encapsulation. Under such conditions, normally adherent and genetically engineered mouse fibroblasts survived and proliferated optimally within the microcapsule environment. The encapsulated fibroblasts maintained their level of transgene expression while recombinant gene products such as human growth hormone could diffuse through the microcapsule membrane without impediment. The demonstration that genetically modified fibroblasts can survive and continue to deliver recombinant gene products from within these microcapsules and the optimization for their maximal viability and growth within microcapsules should increase the potential for success in using such microencapsulated recombinant cells for somatic gene therapy. (c) 1994 John Wiley & Sons, Inc.

High Efficiency and Long-Term Foreign Gene Expression in Cultured Liver Sinusoidal Endothelial Cells by Retroviral Transduction

The liver sinusoidal endothelial cells (LSECs) constitute a very specialized endothelium. Due to their multiple functions and privileged location in the liver, these cells constitute an excellent target for gene therapy. In this work, the authors investigate the efficiency of retroviral gene transduction as a method for in vitro gene delivery into murine LSECs. Gene transduction into murine LSECs was performed using the PCMMP-eGFP/pIK-MLVgp retrovirus pseudotyped with the vesicular stomatitis virus G glycoprotein (VSV-g), containing eGFP as a reporter gene. Retroviral transduction resulted in a high efficiency of gene transfer (99%) and stable expression of eGFP in LSECs. The retroviral transduction protocol did not affect the morphology or expression of endothelial cell markers or the biological functions of LSECs. The authors have developed conditions for high-efficiency and stable retroviral gene transduction of LSECs. These results raise the possibility of liver gene therapy using LSECs as vehicle for the delivery of therapeutic proteins by means of retroviral vectors.

Gene therapy and its implications in Periodontics

Gene therapy is a field of Biomedicine. With the advent of gene therapy in dentistry, significant progress has been made in the control of periodontal diseases and reconstruction of dento-alveolar apparatus.Implementation in periodontics include:-As a mode of tissue engineering with three approaches: cell, protein-based and gene delivery approach.-Genetic approach to Biofilm Antibiotic Resistance.Future strategies of gene therapy in preventing periodontal diseases:-Enhances host defense mechanism against infection by transfecting host cells with an antimicrobial peptide protein-encoding gene.-Periodontal vaccination.Gene therapy is one of the recent entrants and its applications in the field of periodontics are reviewed in general here.

Selective tropism of liver stem cells to hepatocellular carcinoma in vivo

AIM: To investigate the selective tropism of liver stem cells to hepatocellular carcinoma (HCC) in an animal model and its feasibility as a vector to deliver therapeutic genes for targeted therapy of HCC.

METHODS: WB-F344, a kind of rat liver stem cell, was infected with recombinant virus to establish a cell line with stable, high-level expressing enhanced green fluorescent protein (EGFP). An animal model of HCC in Wistar rats was established by implanting HCC cells (CBRH7919) combined with an immunosuppressive drug. EGFP labeled liver stem cells were injected into caudal veins of the animals and distribution was observed at different time points after injection. SDF-1 and c-kit expression in non-tumor liver and tumor tissue were analysed by immunohistochemistry for the relationshiop between the expression and migration of liver stem cells. Furthermore, hepatic stem cells were injected via the portal vein, hepatic artery, caudal vein, or directly into the pericancerous liver tissue, respectively, and effects on migration, localization, and proliferation of the hepatic stem cells within the tumor tissue were observed and analyzed.

RESULTS: Recombinant adenovirus could deliver the EGFP gene to hepatic stem cells. A new stem cell line, named WB-EGFP, was established that stably expressed EGFP. WB-EGFP cells still showed selective tropism towards HCC and EGFP expression was stable in vivo. According to immunohistochemistry results, SDF-1 may not be related to the mechanisms of tropism of hepatic stem cells. Different application sites affected the distribution of liver stem cells. Injection via the portal vein was superior with regard to selective migration, localization, and proliferation of the hepatic stem cells within the tumor tissue.

CONCLUSION: Liver stem cells have the biological behavior of selective migration to HCC in vivo and they could localize and proliferate within HCC tissue stably expressing the target gene. Liver stem cells are a potential tool for a targeted gene therapy of HCC.

Gene therapy and wound healing

Wound repair involves the sequential interaction of various cell types, extracellular matrix molecules, and soluble mediators. During the past 10 years, much new information on signals controlling wound cell behavior has emerged. This knowledge has led to a number of novel therapeutic strategies. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trails indicates that a crucial aspect of the growth factor wound healing strategy is the effective delivery of these polypeptides to the wound site. A molecular approach in which genetically modified cells synthesize and deliver the desired growth factor in regulated fashion has been used to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. We have summarized the molecular and cellular basis of repair mechanisms and their failure, and we give an overview of techniques and studies applied to gene transfer in tissue repair.

Relationships between the physicochemical properties of an amphiphilic triblock copolymers/DNA complexes and their intramuscular transfection efficiency

Poly(ethyleneoxide)-poly(propyleneoxide)-poly(ethyleneoxide) triblock copolymer (PEO-PPO-PEO) based plasmid delivery systems are increasingly drawing attention in the field of nonviral gene transfer because of their proven in vivo transfection capability. They result from the simple association of DNA molecules with uncharged polymers. We examined the physicochemical properties of PEO-PPO-PEO/DNA mixtures, in which the PEO-PPO-PEO is Lutrol (PEO75-PPO30-PEO75), formulated under various conditions. We found that interactions between PEO-PPO-PEO and DNA are mediated by the central hydrophobic block within the block copolymer. Dynamic light scattering and cryo-electron microscopy showed that the mean diameter of transfecting particles as well as their stability depended on the PEO-PPO-PEO/DNA ratio and on the ionic composition of the formulating medium. The most active formulation promoting a good tissue-distribution and an optimal transfection was characterized by a reduced electrophoretic mobility, a mean hydrodynamic diameter of approximately 250-300 nm and by a conserved B-DNA form as shown by circular dichroism studies. Our study also revealed that the stability of these formulations strongly depended on a concentration balance between the DNA and the PEO-PPO-PEO, over which the DNA conformation was modified, micron-sized particles were generated, and the transgene expression was declined. We showed that the physicochemical properties of PEO-PPO-PEO/DNA formulations directly impact the level of gene expression in transfected muscles.

Gene transfer in tissue repair: status, challenges and future directions

Wound repair involves a complex interaction of various cell types, extracellular matrix molecules and soluble mediators. Details on signals controlling wound cell activities are beginning to emerge. In recent years this knowledge has been applied to a number of therapeutic strategies in soft tissue repair. Key challenges include re-adjusting the adult repair process in order to augment diseased healing processes, and providing the basis for a regenerative rather than a reparative wound environment. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trials indicates that an important aspect of the growth factor wound-healing paradigm is the effective delivery of these polypeptides to the wound site. A molecular genetic approach in which genetically modified cells synthesise and deliver the desired growth factor in a time-regulated manner is a powerful means to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. This article summarises repair mechanisms and their failure, and gives an overview of techniques and studies applied to gene transfer in tissue repair. It also provides perspectives on potential targets for gene transfer technology.

Polyion Complex Micelles of pDNA with Acetal-poly(ethylene glycol)-poly(2-(dimethylamino)ethyl methacrylate) Block Copolymer as the Gene Carrier System: Physicochemical Properties of Micelles Relevant to Gene Transfection Efficacy

An acetal-poly(ethylene glycol)-poly(2-(dimethylamino)ethyl methacrylate) (acetal-PEG-PAMA) block copolymer spontaneously associated with plasmid DNA (pDNA) to form water-soluble complexes (polyion complex micelle: PIC micelle) in aqueous solution. Physicochemical characteristics and transfection efficiency of the PIC micelles thus prepared were studied here, focusing on the residual molar mixing ratio (N/P ratio) of AMA units in acetal-PEG-PAMA to the phosphate units in pDNA. With the N/P ratio increasing to unity, acetal-PEG-PAMA cooperatively formed complex micelles with pDNA through electrostatic interaction, allowing pDNA to condense effectively. Dynamic light scattering measurements revealed that the PIC micelle at N/P > or = 3 had a constant size of approximately 90-100 nm. Eventually, acetal-PEG-PAMA/pDNA micelles underwent no precipitation even after long-term storage for more than 1 month at all N/P ratios. The PIC micelles were stable even in the presence of excess polyanions, poly(vinyl sulfate), in contrast to polyplexes based on the PAMA homopolymer, yet this stabilization effect was highly dependent on the N/P ratio to reach a plateau at N/P = 3-4. This character may be attributed to the increased hydrophobicity in the vicinity of the complexed pDNA. Furthermore, the pDNA in the micelle was adequately protected from DNase I attack. The transfection ability of the PIC micelles toward 293 cells was remarkably enhanced with an increasing N/P ratio as high as 25. The zeta-potential of the micelles with a high N/P ratio was an appreciably large positive value, suggesting a noncooperative micelle formation. This deviated micellar composition with an excess cationic nature as well as the presence of free acetal-PEG-PAMA may play a substantial role in the enhanced transfection efficiency of the PIC micelle system in the high N/P ratio (approximately 25) region.

[Experimental pilot study on surface activation of implants with liposomal vectors]

BACKGROUND

Surface coating with mitogenic or morphogenic proteins can improve the healing of bone adjacent to implants and increase the bone-implant interface. Clinical surveys have shown liposome-mediated gene transfer to be a promising and safe new therapeutic method. The aim of our study was to evaluate an experimental model of new approaches for topical treatment of the implant surface and of periimplant defects by using DNA liposomes encoding for BMP-2 (bone morphogenetic protein).

MATERIAL AND METHODS

A total of 27 implants (3.5 x 14 mm) were placed in critically sized defects of the frontal skull bone of adult pigs (n=3). The bottom of the implant was placed in the base of the defect which guaranteed primary stability, whereas the superior part of the implant (10 mm) represented an implant in a defect area. Liposomes containing DNA encoding for BMP-2 and GFP (green fluorescence protein) were used. In a first trial GFP-DNA liposomes on a collagen matrix were directly applied to the periimplant defect. In a second stage, the surface of the implants was encoded with BMP-2 DNA liposomes. Subsequently, these implants were inserted in the manner described. The resulting bone samples were prepared for immunohistochemical staining. Staining for GFP was performed in the area of the defect and for BMP-2 on the bone-implant interface.

RESULTS

Immunohistochemical staining on day 3 postoperatively revealed an increased GFP expression in the periimplant defect. Therefore, the effectiveness of the liposomal vector was verified for the chosen animal model. On the surface of the implants encoded with BMP-2 DNA liposomes an increased BMP-2 expression was found. Thus, the liposomal vector system was validated also for BMP-2 DNA transfer in the chosen animal model. Further, the established system allows a sustainable and delayed release of BMP-2 in the area of the bone-implant interface.

CONCLUSIONS

As a result of the study we were able to collect data concerning the influence of implant surface conditioning on the bone-implant interface and on therapeutically relevant options for the treatment of periimplant defects. These approaches are currently being evaluated in a long-term study.

Prospects for prenatal gene therapy in disorders causing mental retardation

Advances in understanding the genetics and pathogenesis of disease and in prenatal diagnosis have lead to an exploration of ways to intervene earlier and earlier in the disease process. The possibility of prenatal gene therapy for severe genetic and developmental disorders has sparked new research and debate as to its feasibility, reliability, and ethics as a therapeutic option. Recent animal studies have demonstrated the feasibility of introducing a vector into the developing fetus. The optimal timing and best mode of delivery, however, have yet to be defined. Whether or not this research should be pursued also has been the subject of recent bioethical debates. There is additional concern with the possibility of in utero gene transfer inducing mutagenesis and subsequent tumor formation. This review will provide a summary of the current state of knowledge in the field of prenatal gene therapy and possible directions for the future research.

Strategy of liver-directed gene therapy: present status and future prospects

The liver is particularly amenable to gene therapy as it is the site of many metabolic diseases and malignancies. Thus, liver-directed gene therapy is being actively pursued and developed as a method of treatment for various liver diseases. Strategies of liver-directed gene therapy include drug delivery to the liver, compensation of the defective gene(s), anti-tumor activity, anti-viral therapy, and immunomodulation. The strategy chosen for liver-directed gene therapy depends on the genetic basis of the disease. Many aspects are key factors to the success of the chosen strategy: intervention of genes, efficient gene delivery system, stable transgene expression, transgene regulation, target cell transfection, and timing of transgene expression. Several tactics can be used to overcome problems in the above, and these include the use of a gene switch to exogenously regulate transgene expression, targeting at the transcriptional level, circumvention of the immune response (as in the use of adenovirus vector to achieve long-term correction of genetic diseases), and genetically engineered antibodies in gene transfer. At the present rate of research activity and development, gene therapies may soon be more efficient than current standard treatments for some liver diseases.

Ribozyme-mediated specific gene replacement of the alpha1-antitrypsin gene in human hepatoma cells

BACKGROUND/AIMS

Some of the mutant forms of cellular proteins not only lose their function, but also cause diseases by their toxic effects. One of the challenging tasks in the field of gene therapy will be "gene replacement" accomplished by inhibiting mutant gene expression and providing normal function of the same gene, simultaneously. Although lung involvement in alpha1-antrypsin (alpha1-AT) deficiency is caused by the lack of alpha1-AT function, the liver involvement is due to the accumulation of the mutated alpha1-AT protein. Therefore, one possible approach to prevent and treat the disease manifestations of alpha1-AT deficiency is to inhibit the expression of the mutated gene and replace it with normally functioning alpha1-AT protein in the liver.

METHODS

For the inhibition of alpha1-AT gene expression, panels of alpha1-AT-specific hammerhead ribozymes designed to target different GUC sites in the alpha1-AT mRNA were evaluated in a human hepatoma cell-line, transduced with retroviral vectors which express ribozymes under the control of a human tRNA promoter. A bi-functional vector was also constructed, which contained a functional alpha1-AT ribozyme and was combined with a modified alpha1-AT gene, whose product was engineered to be resistant to the specific alpha1-AT ribozyme. This construct was transduced into target hepatoma cells.

RESULTS

The transduced hepatoma cells showed the effective expression of modified alpha1-AT, under the conditions where the endogenous alpha1-AT gene expression was inhibited.

CONCLUSION

This ribozyme-mediated, specific gene replacement is a first step in the gene therapy of alpha1-AT deficiency.

Amplification of gene expression using both 5'- and 3'-untranslated regions of GLUT1 glucose transporter mRNA

Cis-regulatory elements located at either the 5'- or 3'-untranslated region (UTR) of the GLUT1 glucose transporter mRNA increase the expression of luciferase reporter genes. The aim of the present study was to investigate the possible cooperative effects of 5'- and 3'-UTRs of the GLUT1 mRNA on the expression of a luciferase reporter gene in cultured brain endothelial cells. Luciferase reporter genes containing control elements in nucleotides (nt) 1-171 of GLUT1 5'-UTR, or nt 2100-2300 of GLUT1 3'-UTR produced a 10- and 6-fold increase in the expression of the luciferase reporter gene compared to the control vector containing no GLUT1 regulatory sequences, respectively. The insertion of both GLUT1 mRNA cis-regulatory elements increased 59-fold the activity of luciferase compared to controls. Data presented here demonstrate that cis-regulatory elements located at both the 5'- and 3'-UTR of GLUT1 mRNA increase expression of a reporter gene in an independent manner.

Modulation of growth factor action: implications for the treatment of cardiovascular diseases

Peptide growth factors are involved in fundamental cellular processes relevant for cardiovascular physiology and pathology, namely, atherogenesis and angiogenesis. The modulation of growth factor-related signals represents a novel strategy for the treatment of cardiac and vascular disease. Experimental modulation of growth factor action has already provided a better understanding of cardiovascular biology and pathophysiology. In turn, the development of specific and powerful molecular tools is setting the stage for the exploration of their clinical potentials. Current strategies include the use of recombinant proteins, specific inhibitors of protein-protein interactions, tyrosine kinase inhibitors, the generation and application of dominant-negative molecules, the development of antisense strategies, and a variety of different gene transfer approaches. Parallel avenues of research are heading toward the same goal, the specific suppression of potent pathogenic stimuli that induce and promote atherogenesis or the augmentation of beneficial ones such as induction of therapeutic angiogenesis. The successful application of one of these strategies seems to be in reach and will certainly be a milestone in molecular medicine.

Gene therapy for tissue repair: approaches and prospects

Recent advances in molecular biology have resulted in the development of new technologies for the introduction and expression of genes in human somatic cells. This emerging field, known as gene therapy, is broadly defined as the transfer of genetic material to cells/tissues in order to achieve a therapeutic effect for inherited as well as acquired diseases. We and others are exploring the potential application of this technology to tissue repair. One primary focus has been to transfer genes encoding wound healing growth factors, a broad class of proteins which control local events in tissues such as cell proliferation, cell migration and the formation of extracellular matrix. Using several different strategies for gene transfer, wound healing growth factor genes have been introduced and expressed in cells and tissues in vitro as well as in vivo. Various experimental models of wound healing and tissue repair have been used to evaluate the efficacy of this new and exciting approach to tissue repair.

Stable in vivo gene transduction via a novel adenoviral/retroviral chimeric vector

Gene therapy to correct defective genes requires efficient gene delivery and long-term gene expression. The available vector systems have not allowed the simultaneous achievement of both goals. We have developed a chimeric viral vector system that incorporates favorable aspects of both adenoviral and retroviral vectors. Adenoviral vectors induce target cells to function as transient retroviral producer cells in vivo. The progeny retroviral vector particles are then able to stably transduce neighboring cells. In this system, the nonintegrative adenoviral vector is rendered functionally integrative via the intermediate generation of a retroviral producer cell. The chimeric vectors may allow realization of the requisite goals for specific gene-therapy applications.

Gene therapy for murine mucopolysaccharidosis type VII

Mucopolysaccharidosis type VII (MPS VII) is caused by a deficiency in the lysosomal enzyme beta-glucuronidase resulting in the accumulation of undegraded glycosaminoglycans in many tissues. A murine model of MPS VII shares many of the clinical, biochemical and histopathological features of human MPS VII and has provided an opportunity to study novel therapeutic approaches in a system with a uniform genetic background. Retroviral mediated gene therapy directed to the hematopoietic system or to artificial neo-organs resulted in low levels of enzyme in several tissues and reduced lysosomal storage in the liver and spleen. Partial correction of the disease in the eye was observed following an intravitreal injection of recombinant adenovirus. Neither retroviral nor adenoviral mediated gene transfer techniques resulted in a systemic reduction of lysosomal storage. Here we discuss several novel gene transfer approaches designed to increase the systemic levels of beta-glucuronidase in the MPS VII mouse.

Transfection with aFGF cDNA improves wound healing

Somatic gene therapy is a potentially useful strategy for the delivery of growth factors or cytokines to enhance wound healing. Experimental excisional and incisional wounds in impaired-healing diabetic mice (db/db) were treated with aFGF and with a plasmid coding for aFGF. A eukaryotic expression plasmid composed of the Hst signal peptide sequence in-frame with the human aFGF sequence was used. Transfection of tissues was accomplished either by direct plasmid uptake or by uptake facilitated with cationic liposomes. The results show that the closure of excisional wounds was significantly accelerated (p < 0.05) by topical application of human recombinant aFGF or by transfection with the aFGF plasmid but not by vehicle or control plasmid not containing the aFGF sequence. In incisional wounds, aFGF or transfection with the plasmid significantly increased the wound-breaking strength compared to their corresponding controls (p < 0.05). Quantitative histology of the plasmid-treated incisional wound sections revealed improved wound quality. The transcription of mRNA from human aFGF cDNA in the incisional wound tissue extracts was confirmed by RT-PCR, and the expressed aFGF was detected by immune dot blot and immunohistochemistry assays. The transfection was a transient process with a peak at 9 d in db/+ (littermates of the diabetic mice) incisional wounds, at 36 d in db/db incisional wounds, and at 27 d in db/db excisional wounds. Cells transfected with human aFGF occupied up to 6.4% of the transectional area in the wound sites. Thus, aFGF gene delivery resulted in both gene expression and a functional improvement in healing.

New cationic lipid formulations for gene transfer

PURPOSE

To develop appropriate dosage forms of DNA for gene delivery.

METHODS

3 beta [N-(N', N' dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) was mixed either with Tween 80 alone, or with additional lipid components including castor oil and phosphatidylcholine (PC) or dioleoylphosphatidylethanolamine (DOPE) to make different lipid formulations. The particle size and the physical stability of the formulations upon mixing with plasmid DNA containing the luciferase cDNA were examined using laser light scattering measurement. The transfection activity of the DNA/lipid complexes was tested in presence or absence of serum using a cell culture system.

RESULTS

We demonstrated that many favorable properties as a gene carrier could be achieved by formulating DNA into new dosage forms using Tween 80 as the major emulsifier. Compared to the cationic liposomes, these new formulations transfected different cell lines with an equivalent or higher efficiency. Not only are they resistant to serum, but also form stable DNA complexes which could be stored for longer periods of time without losing transfection activity.

CONCLUSIONS

Cationic lipids formulated into different lipid formulations using Tween 80 as a surfactant appeared to have more favorable physical and biological activities than traditional cationic liposomes as a carrier for gene delivery.

Gene therapy for PNET

A new era has been reached in cancer therapeutics in which the techniques of molecular biology can be applied to human brain tumors. Ongoing studies are determining the best vector system with which to deliver genes to cells. Choices include the retroviral, adenoviral, and Herpes simplex virus vector systems. The optimum mode of delivering the vector specifically to the tumor is being explored through intravenous, intraarterial, and direct intra-tumoral injections. Finally, efforts to achieve adequate vector expression throughout an entire tumor are being realized with our greater understanding of vector design and gene expression. The PNET may be amenable in the future to gene therapy strategies because of its rapid proliferative potential, its tendency to spread within the CSF pathways, and its high recurrence rate. In this regard, a number of novel strategies for treating PNET are described herein.

Progress in human gene therapy

There have been major advances in our understanding of the molecular biology and pathophysiology of human disease over the past decade. This expanding knowledge of the basic mechanisms of human disease coupled with the development of efficient methods of transferring genes to mammalian cells has stimulated considerable interest in treating diseases with gene therapy. Clinical trials have demonstrated that human gene transfer is possible, that several strategies exist for successfully introducing exogenous genes to human cells, that a variety of transgenes can evoke biologic responses important to human diseases, and that gene transfer can provide valuable insights into the pathophysiology of human disorders. Initial clinical trials have yielded encouraging results and adverse reactions have been uncommon. Despite the advances in human gene transfer, significant obstacles need to be overcome before it becomes a firmly established therapeutic option for human illness. The potential benefits of utilizing human gene therapy in the treatment of hereditary and acquired disease have generated interest in further advancing this remarkable technology.

Human and Animal Viruses

This chapter provides an overview of the human and animal viruses. Viruses held to a low number of passages in animals or cell cultures represent a viral population that is similar to that found in nature, and freezing these pools guards against genetic mutations that occur during subsequent passage. Aliquots of viral stocks frozen at a designated passage level can then be used for multiple and repeatable experiments with the same viral population. Furthermore, it is important that consistency should be maintained during the production of viral vaccines; new lots of final product are prepared with frozen viral seed stocks that consistently reproduce the desired immunogenic and attenuation characteristics. To better appreciate the requirements for freezing and freeze drying of human and animal viruses, some consideration is given to understanding the structural and functional organization of this diverse group of microorganisms. The classification of viruses is based on morphological and physiochemical properties. Thus, viruses are divided into those with DNA or RNA genomes and subdivided into families based on size and structural properties. Several methods for preservation of viruses are included in the chapter.

Overexpression of genes in health and sickness. A bird's eye view

Many human disorders are associated with gene alterations, such as translocations, deletions, insertions, inversions, rearrangements and point mutations. However, an overexpression of certain normal genes could also contribute to the pathology of neurological disorders, retinal degeneration, diabetes, fibrosis of lung, cardiac and skin, programmed cell death and cancer. This implies that the regulated expression of normal genes is an important factor in determining human health. An understanding of the mechanisms involved in the control of expression of normal genes may provide a greater or more refined success in correcting, delaying or possibly preventing the disorders by a gene therapeutic approach.

Adenovirus vectors for cytokine gene expression

Recombinant Adenovirus type 5 constructs containing IL-6 cDNA can be used to infect cells in vitro and obtain a high level of IL-6 expression and secretion into culture media. Furthermore, Ad5-IL-6 viruses can also be used to infect Balb/c mice or Sprague-Dawley rats and obtain a high level of IL-6 expression that is sustained over a period of 3-5 days. Intratracheal infection was accompanied by dramatic increases in virus-encoded IL-6 mRNA levels in rat lung tissue, raised levels of IL-6 detected in bronchoalveolar lavage fluids and in serum, and IL-6-dependent sequelae such as liver acute phase responses. This occurs in a tissue-specific manner, depending on routes of infection by the virus. Rat lungs showed a prominent expansion (10 fold in numbers) of all classes of lymphocytes, including B cells, T helper cells (CD4+) and CTL (CD8+) at day 7 after infection which resolved significantly by day 12. Thus the associated biological effects of viral vector mediated IL-6 over-expression was also transient in nature. Other tissues can be infected with Ad5 and thus can also be induced to express selected genes in a transient fashion. We are currently examining the potential for Ad recombinant cytokine vectors in therapy for cancer and for bone marrow reconstitution after transplantation. Thus the use of recombinant Ad5 vectors may have a broad application in the study of cytokine function and possibly in future therapy as a transient gene transfer approach.

Gene therapy in surgical oncology

BACKGROUND

Surgery remains the only potentially curative treatment modality for the majority of patients with solid tumors. Conventional chemotherapy and radiotherapy only have roles as adjuvant or palliative therapies for most common cancers. Two decades of research have led to the first attempts at producing and introducing clinically useful genetically modified cells into humans.

METHODS

Modern molecular methods have been developed that allow the stable transfer of foreign DNA sequences into human and other mammalian somatic cells. At the present time, gene therapy predominantly involves gene insertion either directly into a target cell in situ or into an appropriate cell in vitro that is then introduced to a physiologically relevant site. We present an overview of the potential applications of molecular biology for practicing surgeons, particularly in the field of surgical oncology, to show how genes are harnessed and inserted into target somatic cells.

CONCLUSIONS

Although significant clinical therapies have and will continue to emerge from these initial experiments, only the future will provide evidence of whether the present technical skills are sufficient to have an impact on the long-term benefits for patients with cancer and genetic defects.

Amplified and tissue-directed expression of retroviral vectors using ping-pong techniques

Ping-pong amplification is an efficient process by which helper-free retrovirions replicate in cocultures of cell lines that package retroviruses into distinct host-range envelopes [11]. Transfection of a retroviral vector DNA into these cocultures results in massive virus production, with potentially endless cross-infection between different types of packaging cells. Because the helper-free virus spreads efficiently throughout the coculture, it is unnecessary to use dominant selectable marker genes, and the retroviral vectors can be simplified and optimized for expressing a single gene of interest. The most efficient ping-pong vector, pSFF, derived from the Friend erythroleukemia virus, has been used for high-level expression of several genes that could not be expressed with commonly employed two-gene retroviral vectors. Contrary to previous claims, problems of vector recombination are not inherent to ping-pong methods. Indeed, the pSFF vector has not formed replication-competent recombinants as shown by stringent assays. Here we review these methods, characterize the ping-pong process using the human erythropoietin gene as a model, and describe a new vector (pSFY) designed for enhanced expression in T lymphocytes. Factors that limit tissue-specific expression are reviewed.

The impact of gene therapy on dentistry

To the casual observer, gene therapy--an emerging science--appears likely to have little impact on dentistry. However, even in these early research stages, it is clear that gene therapy will have a broad effect on dentistry. This article is designed to provide the practitioner with a general understanding of gene therapy, as well as several examples of how it is being used today in efforts to manage dental and oral problems better.

AAV as a viral vector for human gene therapy. Generation of recombinant virus

Investigation of the adeno-associated virus (AAV) life cycle has enabled the establishment of methodology and identification of critical cis-acting sequences required for recombinant AAV production. Vectors derived from the defective human parvovirus (AAV) have been used for successful gene transfer and expression in many diverse mammalian cell types, such as erythroid, airway epithelium, and neuronal cells. One of the crucial steps in the continued case of AAV as a vector is the development of packaging systems that will allow efficient encapsidation of foreign genes into AAV virions. For this reason, the focus of this article will be generation of recombinant AAV vectors.

Further studies on targeted DNA transfer to cells using a highly efficient delivery system of biotinylated transferrin and biotinylated polylysine complexed to streptavidin

Conjugates consisting of biotinylated transferrin and biotinylated poly-L-lysine attached to streptavidin have been prepared and found to transfer luciferase plasmid DNA very efficiently to HeLa cells in the presence of chloroquine. Transfection was dependent on (i) use of biotinylated short chain polylysine containing 70 lysine residues, (ii) biotinylated transferrin containing 1-2 biotin moieties, (iii) reaction of biotinylated transferrin with streptavidin followed by isolation of the resulting conjugate on Sephadex G-200 and (iv) interaction of streptavidin-biotinylated transferrin with biotinylated polylysine giving a complex suitable for DNA transfection. It was found that if the above sequence of steps resulting in the formation of streptavidin-biotinylated transferrin/biotinylated polylysine was followed without isolation of intermediate conjugates by Sephadex G-200 chromatography, pRSVL DNA transfer was still very efficient. Transfer of luciferase DNA by the streptavidin conjugates and subsequent expression of luciferase activity was almost completely inhibited by excess free transferrin, showing that gene transfer was through the transferrin receptor pathway via receptor-mediated endocytosis. The streptavidin (bio2-transferrin) bio10-pLys70 conjugate used in the present experiments was approximately one hundred times more efficient in pRSVL DNA transfection with the HeLa cells than the previously described avidin-pLys460 (bio-transferrin) complex.

Receptor mediated glycotargeting

Glycotargeting relies on carrier molecules possessing carbohydrates that are recognized and internalized by cell surface mammalian lectins. Numerous types of glycotargeting vehicles have been designed based on the covalent attachment of saccharides to proteins, polymers and other aglycones. These carriers have found their major applications in antiviral therapy, immunoactivation, enzyme replacement therapy and gene therapy. This review compared different types of glycotargeting agents and the lectins which have been successfully targeted to treat both model and human diseases. It may be concluded that the discovery of new mammalian lectins which endocytose their ligands will lead to the rapid development of new glycotargeting agents founded on the principles of carbohydrate-protein interactions.

Germ-line therapy to cure mitochondrial disease: protocol and ethics of in vitro ovum nuclear transplantation

The combination of genuine ethical concerns and fear of learning to use germ-line therapy for human disease must now be confronted. Until now, no established techniques were available to perform this treatment on a human. Through an integration of several fields of science and medicine, we have developed a nine step protocol at the germ-line level for the curative treatment of a genetic disease. Our purpose in this paper is to provide the first method to apply germ-line therapy to treat those not yet born, who are destined to have a life threatening, or a severely debilitating genetic disease. We hope this proposal will initiate the process of a thorough analysis from both the scientific and ethical communities. As such, this proposal can be useful for official groups studying the advantages and disadvantages of germ-line therapy.

An evaluation of receptor-mediated gene transfer using synthetic DNA-ligand complexes

Receptor-mediated gene transfer is an attractive method for therapeutically correcting human genetic diseases since it permits the targeting of DNA to cellular receptors in specific tissues of adult animals. Genes introduced by this technique have been shown to be expressed in the target tissue for varying periods. However, to be useful for gene therapy, it is critical that both the chemical properties and physical interactions of the reagents involved in the design of the DNA delivery vehicle be rigorously characterized. In this review, we discuss the critical steps in the preparation of the DNA-ligand complex and the factors involved in the delivery and regulated expression of a transgene in animal tissues. The feasibility of using this technique for the therapeutic delivery of genes to mammalian tissues will also be evaluated.

Improved cell survival by the reduction of immediate-early gene expression in replication-defective mutants of herpes simplex virus type 1 but not by mutation of the virion host shutoff function

Derivatives of herpes simplex virus type 1 (HSV-1) have elicited considerable interest as gene transfer vectors because of their ability to infect a wide range of cell types efficiently, including fully differentiated neurons. However, it has been found that infection of many types of cell with vectors derived from replication-defective mutants of HSV-1 is associated with cytopathic effects (CPE). We have previously shown that viral gene expression played an important role in the induction of CPE caused by an HSV-1 mutant deleted for the essential immediate-early gene 3 (IE 3) (P.A. Johnson, A. Miyanohara, F. Levine, T. Cahill, and T. Friedmann, J. Virol. 66:2952-2965, 1992). We have investigated which viral genes might be responsible for CPE by comparing the ability of each of the individual genes expressed by an IE 3 deletion mutant during a nonproductive infection to inhibit biochemical transformation after cotransfection of BHK or CV-1 cells with a selectable marker gene. Transfection of IE genes 1,2, and 4 individually all caused a marked inhibition of colony formation, while transfection of IE 5 and the large subunit of ribonucleotide reductase had little effect. These results suggested that it would be necessary to mutate or reduce the expression of nearly all HSV-1 IE genes to reduce virus-induced CPE. Therefore, we have used VP16 mutants, which are unable to transinduce IE gene expression (C. I. Ace, T. A. McKee, J. M. Ryan, J. M. Cameron, and C. M. Preston, J. Virol. 63:2260-2269, 1989), to derive two replication-defective strains: 14H delta 3, which is deleted for both copies of IE 3, and in 1850 delta 42, which has a deletion in the essential early gene UL42. The IE 3-VP16 double mutant, 14H delta 3, is significantly less toxic than a single IE 3 deletion mutant over a range of multiplicities of infection, as measured in a cell-killing assay, and has an enhanced ability to persist in infected cells in a biologically retrievable form. In contrast, the UL42-VP16 double mutant, in 1850 delta 42, showed reduced toxicity only at low multiplicities of infection. To test the role of the virion host shutoff function as an additional candidate to influence virus-induced CPE, we have introduced a large insertion mutation into the virion host shutoff gene of an IE 3 deletion mutant and the double mutant 14H delta 3.(ABSTRACT TRUNCATED AT 400 WORDS)

Gene therapy: applications to the treatment of gastrointestinal and liver diseases

There has been much progress in our understanding of molecular mechanisms in the pathogenesis of inherited metabolic disorders. In addition, powerful new molecular techniques have made possible phenotypic alterations by delivery of foreign genes to target cells. As a result, concepts and methods that would have been considered purely science fiction 10 years ago can now be found in human clinical trials engaged in the treatment of these disorders. In this review, we have attempted to provide an introduction and survey of the topic of gene therapy, with specific examples of laboratory and clinical achievements to date, and highlights on potentials for applications in digestive diseases.

Identification of genetic defect of an epilepsy: strategies for therapeutic advances

Advances in molecular genetics and molecular biology are transforming the biology of human disease. Cures for diseases previously refractory to all treatments have become the reality for some disorders and the legitimate promise for others. In the case of the epilepsies, identification of mutant genes underlying familial epilepsies may lead to a new pharmacology, through the development of in vitro expression systems permitting rapid search for novel drugs, creation of highly specific animal models based on expression of the precise mutation, and correction of disease phenotype by introducing novel and highly specific genetic information into the person with epilepsy.

The new frontier: gene and oligonucleotide therapy

Gene and oligonucleotide therapy are emerging as clinically viable therapeutic regimens for genetic, neoplastic, and infectious diseases. Approaches include insertion of human genes in viral vectors including recombinant retrovirus, adenovirus, adeno-associated virus, and herpes simplex virus-1, or recombinant bacterial plasmids. Viral vectors transfect cells directly; plasmid DNA is delivered with the help of cationic liposomes (lipofection), polylysine conjugates, gramicidin S, artificial viral envelopes or other such intracellular carriers. Major areas of interest include replacement of the cystic fibrosis transmembrane regulator gene and the alpha 1-antitrypsin gene; arrest of human immunodeficiency virus infection; and reversal of tumorigenicity and cancer immunization, among others. Oligonucleotide therapy is principally focusing on the same areas, although the approach is to halt DNA transcription or messenger RNA translation with code-blocking triple-helix-forming or "antisense" oligomers. Contributions from the pharmaceutical sciences are expected in pharmaceutical chemistry, drug delivery systems design, analytical chemistry, and biopharmaceutics.

Delivery of recombinant gene products with microencapsulated cells in vivo

If established cultured cell lines genetically modified to secrete desired gene products could be implanted in different allogeneic recipients without immune rejection, novel gene products would be delivered more cost effectively. We tested this strategy by encapsulating mouse Ltk- cells transfected with the human growth hormone (hGH) gene in immunoprotective perm-selective alginate microcapsules. Allogeneic mice implanted with these microcapsules demonstrated hGH in their circulation (0.1-1.5 ng/ml serum) within the first 2 weeks. Control mice implanted with only the transfected cells without microcapsules did not demonstrate significant levels of circulating hGH. By about 3 weeks, antibodies against hGH developed in the microcapsule-implanted mice. The immune response was detected only against the hGH and no other secretory products from the transfected cells. The antibody titer continued to escalate for more than three months, thus demonstrating indirectly the continued delivery of the growth hormone. The persistent expression of the transgene and survival of the transfected cells were verified when the microcapsules were retrieved periodically to demonstrate that the encapsulated cells remained viable, proliferative, and productive of hGH even by 78-111 days. In conclusion, delivering gene products with genetically modified allogeneic cells in vivo has been shown feasible for prolonged periods. This technology should have potential applications in somatic gene therapy and in treatment of other somatic diseases.