Viral vectors for gene therapy: the art of turning infectious agents into vehicles of therapeutics

Creation of immune ‘stealth’ genes for gene therapy through fusion with the Gly-Ala repeat of EBNA-1

A major obstacle in gene-therapy protocols is T-cell-mediated destruction of transgene-expressing cells. Therefore new approaches are needed to prevent rapid clearance of transduced cells. We exploited the Gly-Ala repeat (GAr) domain of the Epstein-Barr virus nuclear antigen-1, since the GAr prevents cytotoxic T-lymphocyte-epitope generation. Here we show that three different enzymes (viz. the E. coli LacZ gene encoded beta-galactosidase, firefly luciferase, and HSV1 thymidine kinase) fused with the GAr retained their function. Moreover, linking GAr with beta-galactosidase successfully prevented recognition of GAr-LacZ-expressing cells by beta-galactosidase-specific CTL. Nonetheless, vaccination with a GAr-LacZ adenovirus or with an allogeneic cell line expressing GAr-LacZ resulted in the induction of beta-gal-specific CTL. This demonstrates that the GAr domain does not inhibit cross presentation of antigens, but only affects breakdown of endogenously synthesized proteins. These data demonstrate how the GAr domain can be exploited to create immuno'stealth' genes by hiding transgene products from CTL-mediated immune attack.

Adeno-associated virus mediated gene delivery into coronary microvessels of chronically instrumented dogs

The objective of this study was to assess the potential of adeno-associated virus (AAV)-mediated gene delivery into coronary microvessels in vivo in a large animal. Ten mongrel dogs were chronically instrumented and allowed to recover for 10 days. Dogs were reanesthetized, and the aorta was constricted by a hydraulic occluder, whereby left ventricular (LV) pressure increased by 30% and left circumflex coronary artery blood flow by 50%. Recombinant AAV (serotype 2, CMV enhancer/chicken beta-actin promoter) encoding for green fluorescent protein (GFP) was injected as a bolus into the left atrium during aortic constriction at total titers of 1010 or 1012 infectious units. Dogs were followed for 2 (n = 4)or4wk(n = 6). Hemodynamics or body weight did not change. In LV tissue slices, a fluorescein-labeled antibody to GFP stained endothelial and smooth muscle cells but was absent in myocytes. To quantify transduction, slices were then stained with antibodies against alpha-smooth muscle actin or von Willebrand factor. Approximately 4% of arterioles and 2% of microvessels stained positive for anti-GFP independent from viral titer or duration. By regression analyses, the percent of vessels transfected was proportional to the increase in LV systolic pressure during occlusion. AAV is a potential vector for gene transfer into the coronary microcirculation in large animals, including perhaps humans.

Differential chemokine and chemokine receptor gene induction by ischemia, alloantigen, and gene transfer in cardiac grafts

Transplantation of allogeneic grafts presents several challenges to the innate and adaptive immune systems including chemokine leukocyte recruitment, activation, and effector function. We defined the chemokines and receptors induced by the transplant procedure/ischemia injury, alloantigen and gene transfer vector administration in murine cardiac grafts. E1, E3 deleted AdRSVbetagal was transferred into grafts at the time of transplantation, grafts were harvested after 1-14 days, and a pathway-specific cDNA array was used to evaluate the levels of 67 chemokine and chemokine receptor genes. Transplantation resulted in ischemic injury and induction of a number of similar genes in both the syngeneic and allogeneic grafts, such as CXCL1 and CXCL5, which increased dramatically on day 1 and returned rapidly to baseline in the syngeneic grafts. Alloantigen stimulated the adaptive immune response and induced the presence of more inflammatory genes within the grafts, particularly at later time points. The adenovirus vector induced a broader panel of genes, among them potent inflammatory chemokines CXCL9 and CXCL10, that are induced earlier or more strongly compared with alloantigen stimulation alone. As alloantigen and adenovirus vectors both induce similar sets of genes, targeting these molecules may not only inhibit alloimmunity, but also enhance the utility of the gene transfer vector.

Adenovirus transduction induces expression of multiple chemokines and chemokine receptors in murine beta cells and pancreatic islets

Adenoviral vectors are highly efficient for transferring genes to islets. However, the inflammatory and immune responses stimulated by adenovirus may be detrimental to islet survival. Given the role of chemokines and their receptors in inflammation, we analyzed their expression in isolated murine islets, in a murine beta cell line and in syngeneic islet grafts after adenovirus transduction (AdRSVLacZ). AdRSVLacZ transduction enhanced and induced the expression of a variety of chemokines. Transduced syngeneic transplanted islets showed significantly enhanced expression of multiple chemokines and receptors, including monocyte chemoattractant protein-1 (MCP-1), CC chemokine receptor 2 (CCR2) and regulated upon activation, normal T cell expressed and secreted (RANTES), compared with untransduced islet grafts. AdRSVLacZ-transduced islet grafts had significant mononuclear infiltrates, and in situ hybridization demonstrated intragraft expression of MCP-1, CCR2 and RANTES. Although adenovirus transduction did not impair in vitro insulin secretion, diabetes was reversed in only one of six recipients of a marginal mass of AdRSVLacZ-transduced islets, compared with six of six control recipients. In conclusion, multiple chemokines and chemokine receptors are expressed by murine islets constitutively and in response to adenovirus transduction. Adenovirus transduction impairs engraftment of marginal mass of transplanted islets. This is not because of direct vector toxicity of islet secretory capacity, but may be related to host innate immunity in response to adenovirus vector.

HIV-2 derived lentiviral vectors: gene transfer in Parkinson's and Fabry disease models in vitro

Lentiviral vectors are prime candidate vectors for gene transfer into dividing and non-dividing cells, including neuronal cells and stem cells. For safety, HIV-2 lentiviral vectors may be better suited for gene transfer in humans than HIV-1 lentiviral vectors. HIV-2 vectors cross-packaged in HIV-1 cores may be even safer. Demonstration of the efficacy of these vectors in disease models will validate their usefulness. Parkinson's disease and Fabry disease provide excellent models for validation. Parkinson's disease is a focal degeneration of dopaminergic neurons in the brain with progressive loss of ability to produce the neurotransmitter dopamine. Current treatment entails administration of increasing doses of L-dopa, with attendant toxicity. We explore here the hypothesis that gene transfer of aromatic acid decarboxylase (AADC), a key enzyme in the pathway, will make neuronal cells more efficiently convert L-dopa into dopamine. Fabry disease on the other hand is a monogenic inherited disease, characterized by alpha-galactosidase A (AGA) deficiency, resulting in glycolipid accumulation in several cell types, including fibroblasts. Animal models for preclinical investigations of both of these diseases are available. We have designed monocistronic HIV-1 and HIV-2 vectors with the AADC transgene and monocistronic and bicistronic HIV-2 vectors with the AGA and puromycin resistance transgenes. They were packaged with either HIV-2 cores or HIV-1 cores (hybrid vectors). Gene transfer of AADC gene in neuronal cells imparted the ability on the transduced cells to efficiently convert L-dopa into dopamine. Similarly, the AGA vectors induced Fabry fibroblasts to produce high levels of AGA enzyme and caused rapid clearance of the glycolipids from the cells. Both monocistronic and bicistronic vectors were effective. Thus, the insertion of a second gene downstream in the bicistronic vector was not deleterious. In addition, both the self-packaged vectors and the cross-packaged hybrid vectors were effective in gene transfer.

Identification of a novel proliferation-inducing determinant using lentiviral expression cloning

One of the major challenges in the post-genome era is the correlation between genes and function or phenotype. We have pioneered a strategy for screening of cDNA libraries, which is based on sequential combination of lentiviral and oncoretroviral expression systems and can be used to identify proliferation-modulating genes. Screening of a lentiviral expression library derived from adult human brain cDNA resulted in cloning of the potent proliferation-inducing determinant termed pi1 (proliferation inducer 1). Transduction experiments using GFP-expressing oncoretroviruses to target proliferation-competent cells suggested that overexpression of pi1 initiates proliferation of human umbilical vein endothelial cells (HUVECs). Growth induction of HUVECs as well as Swiss3T3 fibroblasts was confirmed by Brd-uridine incorporation assays, which correlated increased DNA synthesis with expression of pi1. The identified pi1 cDNA is 297 bp long and encodes a 10 kDa polypeptide. Since deregulation of proliferation control accounts for a number of today's untreatable human diseases such as neurodegenerative disorders and cancer, discovery of novel proliferation-modulating genes is essential for developing new strategies for gene therapy and tissue engineering.

Foamy virus vectors

Gene therapy is a promising novel treatment for a variety of human diseases. Successful application of gene therapy requires the availability of vehicles with the ability to efficiently deliver and express genes. Viral vectors are efficient means of transferring a gene of interest into target cells. Current available vehicles for gene transfer are either inefficient or potentially unsafe for human gene therapy applications. Foamy viruses offer a fresh alternative vector system for gene transfer with the potential to overcome the concerns of the current vectors. Foamy viruses are nonpathogenic and have a broad host range with the ability to infect various types of cells from different species. Foamy virus replication is distinct and may provide an edge for foamy virus vector usage over other retroviral vectors. These features offer the foamy vectors unique opportunities to deliver several genes into a number of different cell types in vivo safely and efficiently. The principal problems for the design of foamy virus vectors have been solved, and several foamy virus vectors that efficiently transduce a variety of cell types are available. This chapter reviews specific features of foamy virus vector systems and recent advances in the development and use of these vectors.

In vivo targeting of tumor endothelial cells by systemic delivery of lentiviral vectors

Tumor angiogenesis is a rate-limiting factor for tumor growth, and the endothelial cells of tumor vessels display specific features that can be exploited for the selective delivery of cancer therapeutics. To specifically target exogenous genes to angiogenic tumor vessels, we generated a panel of vesicular stomatitis virus-pseudotyped lentiviral vectors (LVs) engineered for endothelial cell (EC)-specific expression. We cloned a wide repertoire of transcription regulatory sequences from genes preferentially expressed in ECs (Tie1, Tie2, Flk-1, VE-Cad, and ICAM-2) into self-inactivating LVs to drive expression of the marker gene encoding green fluorescent protein (GFP) or of the conditionally toxic gene encoding nitroreductase, and compared them with the ubiquitously expressing phosphoglycerate kinase (PGK) and cytomegalovirus (CMV) promoters. We evaluated the efficiency and specificity of vector expression in vitro in a panel of human primary cultures, including ECs, fibroblasts, neurons, lymphocytes, and hematopoietic progenitors, and in tumor cell lines. We found that vectors containing promoter and enhancer sequences from the Tie2 gene achieved remarkable specificity of expression in ECs in vitro and in vivo. On intravenous delivery into tumor-bearing mice, the Tie2 vector targeted expression to the ECs of tumor vessels. In contrast, LVs carrying the PGK or CMV promoter gave widespread GFP marking in ECs and non-ECs of tumors and other organs. The previously reported upregulation of the Tie2 gene in ECs activated for angiogenesis may explain the remarkable selectivity of expression of the Tie2 vector in ECs of tumor vessels. The new vector provides the means for selective delivery of gene therapy to tumor sites in vivo.

Invasive drug delivery

The central nervous system is a very attractive target for new therapeutic strategies since many genes involved in neurological diseases are known and often only local low level gene expression is required. However, as the blood brain barrier on one hand prevents some therapeutic agents given systematically from exerting their activity in the CNS, it also provides an immune privileged environment. Neurosurgical technology meanwhile allows the access of nearly every single centre of the CNS and provides the surgical tool for direct gene delivery via minimal invasive surgical approaches to the brain. Successful therapy of the central nervous system requires new tools for delivery of therapeutics in vitro and in vivo (Fig. 1). The application of therapeutic proteins via pumps into the CSF was shown to be only of limited value since the protein mostly is not sufficiently transported within the tissue and the half life of proteins limits the therapeutic success. Direct gene delivery into the host cell has been a main strategy for years, and in the beginning the direct DNA delivery or encapsulation in liposomes or other artificial encapsulation have been applied with different success. For several years the most promising tools have been vectors based on viruses. Viruses are able to use the host cell machinery for protein synthesis, and some of them are able to stably insert into the host cell genome and provide long term transgene expression as long as the cell is alive. The increasing knowledge of viruses and their live cycle promoted the development of viral vectors that function like a shuttle to the cell, with a single round of infection either integrating or transiently expressing the transgene. Viral vectors have proven to be one of the most efficient and stable transgene shuttle into the cell and have gained increasing importance. The limitations of some viral vectors like the adenoviral vector and adeno-associated viral vector have been improved by new constructs like HIV-1 based lentiviral vectors. The immune response caused by expression of viral proteins, or the inability of some viral vectors like the retroviral vector to infect only dividing cells have been overcome by these new constructs. Lentiviral vectors allow an efficient and stable transgene expression over years in vivo without effecting transgene expression or immune response. In this Chapter we will describe synthetic vectors, give an overview of the most common viral vectors and focus our attention on lentiviral vectors, since we consider them to be the most efficient tool for gene delivery in the CNS.

Double genetic modification of adenovirus fiber with RGD polylysine motifs significantly enhances gene transfer to isolated human pancreatic islets

BACKGROUND

New strategies for improving durable functional islet mass will be instrumental in facilitating islet transplantation as a cure for type 1 diabetes mellitus. The ability to transfer immunoregulatory or cytoprotective genes into pancreatic islets may enhance survival. Adenoviral vectors (Ad5) have been used widely to deliver therapeutic genes to different tissues. Limitations associated with the use of Ad5 for gene therapy are related to the reliance of the virus on the presence of its primary receptor, the transient nature of the transgene expression, and the immediate inflammatory and immune response elicited by the infection. Because the arginine-glycine-aspartame (RGD) and polylysine (pK7) motifs have been shown to enhance Ad5 infection through an Ad5 receptor-independent pathway, we hypothesized that they could act additively to improve infectivity and reduce toxicity to isolated human pancreatic islets (IHPI).

METHODS

Hand-picked IHPI were infected with nonmodified Ad5, single-modified Ad5 with RGD (Ad5RGD) or pK7 (ad5pK7), and Ad5RGDpK7. Transfection efficiency was evaluated by green fluorescent protein and luciferase expression. Apoptosis was assessed using a quantitative assay, activation of caspase 3 by a colorimetric assay, nuclear factor (NF)-kappaB nuclear translocation using a promoter-luciferase NF-kappaB responsive construct, regulated on activation normal T-cell expressed and secreted (RANTES) by enzyme-linked immunosorbent assay. In vivo functionality was evaluated after transplantation into diabetic nonobese diabetic severe combined immunodeficiency mice.

RESULTS

Compared with unmodified and singly-modified Ad5 vectors, Ad5RGDpK7 demonstrated the highest infectivity. After the infection of IHPI with adenoviral vectors using the minimal dose required to infect greater than 80% of the islet cells (Ad5, 500 viral particles [VP]/cell; Ad5RGD and Ad5pK7, 10 VP/cell; Ad5RGDpK7, 0.1 VP/cell), islets infected with Ad5RGDpK7 presented a significant reduction in apoptosis, NF-kappaB nuclear translocation, RANTES expression, and higher glucose disposal rate; reduced Ad5-driven specific Th1 and antibody response were also observed.

CONCLUSIONS

Ad5RGDpK7 exhibited higher transfection efficiency, allowing a significant reduction in the viral dose required to infect greater than 80% of the islet cells. The reduction in the viral dose was associated with reduced toxicity, inflammation, and immune responses related to Ad5 infection. This strategy may thus be used to successfully modify isolated pancreatic islets.

Expression of dystrophin driven by the 1.35-kb MCK promoter ameliorates muscular dystrophy in fast, but not in slow muscles of transgenic mdx mice

Successful gene therapy of Duchenne muscular dystrophy may require the lifelong expression of a therapeutic gene in all affected muscles. The most promising gene delivery vehicles, viral vectors, suffer from several limitations, including immunogenicity, loss of therapeutic gene expression, and a limited packaging capacity. Therefore, various efforts were previously undertaken to use small therapeutic genes and to place them under the control of a strong and muscle-specific promoter. Here we report the effects of a minidystrophin (6.3 kb) under the control of a short muscle-specific promoter (MCK 1.35 kb) over most of the lifetime (4-20 months) of a transgenic mouse model. Dystrophin expression remained stable and muscle-specific at all ages. The dystrophic phenotype was greatly ameliorated and, most importantly, muscle function in limb muscles was significantly improved not only in young adult but also in aged mice compared to nontransgenic littermates. Dystrophin expression was strong in fast-twitch skeletal muscles such as tibialis anterior and extensor digitorum longus, but weak or absent in heart, diaphragm, and slow-twitch muscles. Additionally, expression was strong in glycolytic but weak in oxidative fibers of fast-twitch muscles. This study may have important implications for the design of future gene therapy trials for muscular dystrophy.

Applications of gene therapy to kidney disease

PURPOSE OF REVIEW

This review summarizes recent applications of somatic cell gene therapy to the treatment of monogenetic renal diseases, renal cell carcinoma, and for the induction of tolerance in solid organ transplantation. In addition, several new gene therapy techniques will be discussed including gene and messenger RNA repair strategies, as well as methods designed to modify the expression of normal genes that may have application in the treatment of multigenetic disorders.

RECENT FINDINGS

Animal studies have demonstrated prolonged graft survival after the successful induction of tolerance to alloantigens via hematopoietic molecular chimerism. Ongoing clinical trials for renal cell carcinoma are encouraging, in that IL-2 gene therapy using non-viral vector systems can reduce the tumor burden. However, limited progress has been made towards applying gene therapy for the most common genetic disorders of the kidney, autosomal dominant polycystic kidney disease and Alport syndrome. Basic research on novel gene repair and expression modulation techniques provide additional gene therapy options for the treatment of viral infections such as HIV-1 and monogenetic disorders.

SUMMARY

Gene therapy holds enormous potential for the treatment of genetic and acquired diseases. Current pre-clinical studies and clinical trials provide encouraging results that gene therapy can become a useful treatment option. However, before gene therapy has widespread application, technical progress must be made in all aspects of treatment design, including optimizing vector and delivery systems and the ability to modify long-term cell populations such as stem cells.

Effect of an adenoviral vector that expresses the canine p53 gene on cell growth of canine osteosarcoma and mammary adenocarcinoma cell lines

OBJECTIVE

To generate an adenoviral vector that expressed the canine p53 gene and investigate its growth-inhibiting effect on canine osteosarcoma and mammary adenocarcinoma cell lines.

SAMPLE POPULATION

2 canine osteosarcoma cell lines (HOS, OOS) and 3 canine mammary adenocarcinoma cell lines (CHMp, CIPm, and CNMm).

PROCEDURE

An adenoviral vector that expressed the canine p53 gene (AxCA-cp53) was generated. p53 gene expression was examined by use of reverse transcription (RT)-polymerase chain reaction (PCR) assay and immunohistochemistry. Susceptibility of cell lines to the adenoviral vector was determined by infection with an adenoviral vector that expresses beta-galactosidase (AxCA-LacZ) and 3-indolyl-beta-D-galactopyranoside staining. Growth inhibitory effects were examined by monitoring the numbers of cells after infection with mock (PBS) solution, AxCA-LacZ, or AxCA-cp53. The DNA contents per cell were measured by flow cytometry analysis. Apoptotic DNA fragmentation was detected by use of a terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay.

RESULTS

AxCA-cp53-derived p53 gene mRNA and P53 protein were detected by RT-PCR analysis and immunohistochemistry, respectively. Multiplicity of infection at which 50% of cells had positive 3-indolyl-beta-D-galactopyranoside staining results ranged from 10 to 50. AxCA-cp53 induced growth inhibition in a dose-dependent manner. Arrest of the G1-phase population and apoptotic DNA fragmentation were observed in cells infected with AxCA-cp53.

CONCLUSIONS AND CLINICAL RELEVANCE

AxCA-cp53 inhibits cell growth via induction of cell cycle arrest and apoptosis in canine osteosarcoma and mammary adenocarcinoma cell lines that lack a functional p53 gene. AxCA-cp53 may be useful to target the p53 gene in the treatment of dogs with tumors.

In vitro selection of viral vectors with modified tropism: the adeno-associated virus display

Improving the efficiency and specificity of gene vectors is critical for the success of gene therapy. In an effort to generate viral mutants with controlled tropism we produced a library of adeno-associated virus (AAV) clones with randomly modified capsids and used it for the selection of receptor-targeting mutants. After several rounds of selection on different cell lines that were resistant to infection by wild-type (wt) AAV, infectious mutants were harvested at high titers. These mutants transduced target cells with an up to 100-fold increased efficiency, in a receptor-specific manner and without interacting with the primary receptor for wt AAV. The results demonstrate for the first time that a combinatorial approach based on a eukaryotic virus library allows one to generate efficient, receptor-specific targeting vectors with desired tropism.

Modeling CNS neurodegeneration by overexpression of disease-causing proteins using viral vectors

Defective handling of proteins is a central feature of major neurodegenerative diseases. The discovery that neuronal dysfunction or degeneration can be caused by mutations in single cellular proteins has given new opportunities to model the underlying disease processes by genetic modification of cells in vitro or by generation of transgenic animals carrying the disease-causing gene. Recent developments in recombinant viral-vector technology have opened up an interesting alternative possibility, based on direct gene transfer to selected subregions or subsets of neurons in the brain. Using the highly efficient adeno-associated virus or lentivirus vectors, recent reports have shown that overexpression of mutated human huntingtin or alpha-synuclein in neurons in the striatum or substantia nigra induces progressive neuropathology and neurodegeneration, similar to that seen in Huntington's and Parkinson's diseases. Targeted overexpression of disease-causing genes by recombinant viral vectors provides a new and highly flexible approach for in vivo modeling of neurodegenerative diseases, not only in mice and rats but also in primates.

Molecular basis of the inflammatory response to adenovirus vectors

Adenovirus vectors are extensively studied in experimental and clinical models as agents for gene therapy. Recent generations of helper-dependent adenovirus vectors have the majority of viral genes removed and result in vectors with a large carrying capacity, reduced host adaptive immune responses and improved gene transfer efficiency. Adenovirus vectors, however, activate innate immune responses shortly after administration in vivo. Unlike the adaptive response, the innate response to adenovirus vectors is transcription independent and is caused by the viral particle or capsid. This response results in inflammation of transduced tissues and substantial loss of vector genomes in the first 24 h. The adenovirus capsid activates a number of signaling pathways following cell entry including p38 mitogen-activated protein kinase and extracellular signal-regulated kinase (ERK) that ultimately lead to expression of proinflammatory genes. Various cytokines, chemokines and leukocyte adhesion molecules are induced by the adenovirus particle in a wide range of cell types providing a molecular basis for the inflammatory properties of these vectors. An understanding of the innate response to adenovirus vectors is essential to overcome the last remaining hurdle to improve the safety and effectiveness of these agents.

Immunity to adenovirus and adeno-associated viral vectors: implications for gene therapy

Viral vectors have provided effective methods for in vivo gene delivery for therapeutic purposes. The ability of viruses to infect a wide variety of cell types in vivo has been exploited for several applications, such as liver, lung, muscle, brain, eye and many others. Immune responses directed towards the viral capsids and the transgene products have severely affected the ability of these vectors to induce long-term gene expression. This paper reviews the influence of viral vectors on antigen-presenting cells (APC), which are central to the induction of innate as well as adaptive immune responses. In this respect, we have focused on adenovirus and adeno-associated viruses because of the polar responses these vector systems induce in vivo. While adenovirus vector can induce significant inflammatory responses, adeno-associated viral vectors are characterized by their inability to consistantly induce immune responses to the transgene product. Understanding the mechanism of infection, transduction and activation of APC by viral vectors will provide strategies to develop safe vectors and prevent immune responses in gene therapies.

In situ transduction of target cells on solid surfaces by immobilized viral vectors

BACKGROUND

For both in vitro and in vivo gene transfer applications, recombinant viral vectors have almost always been used free in solution. Some site-specificity of the delivery of viral vectors can be achieved by applying a solution containing viral particles specifically to the site of interest. However, such site-specificity is seriously limited since viral vectors can diffuse freely in solution after application.

RESULTS

We have developed a novel strategy for in situ transduction of target cells on solid surfaces by viral vectors. In this strategy, adenoviral vectors are attached stably to solid surfaces by using the extremely tight interaction between (strept)avidin and biotin, while maintaining the infectivity of the viral vectors. Target cells are cultured directly on such virus-coated solid surfaces, resulting in the transduction of the cells, in situ, on the solid surface. When compared using an equal number of viral particles present in each well (either immobilized or free), the efficiencies of such in situ transduction on solid surfaces were equivalent to those seen with the adenoviral vectors used free in solution. Since viral particles can be attached at desired locations on solid surfaces in any sizes, shapes, and patterns, the ultimate spatial arrangements of transduced cells on solid surfaces can be predetermined at the time of the preparation of the virus-coated solid surfaces.

CONCLUSIONS

We have devised a method of immobilizing adenoviral vectors, tightly and stably, on solid surfaces, while maintaining their ability to infect cells. Such immobilized viral vectors can infect target cells, in situ, on solid surfaces. This strategy should be very useful for the development of a variety of both in vitro and in vivo applications, including the creation of cell-based expression arrays for proteomics and drug discovery and highly site-specific delivery of transgenes for gene therapy and tissue engineering.

Gene therapy for cerebral vascular disease: update 2003

Gene therapy is a promising strategy for cerebrovascular diseases. Several genes that encode vasoactive products have been transferred via cerebrospinal fluid for the prevention of vasospasm after subarachnoid hemorrhage. Transfer of neuroprotective genes, including targeting of proinflammatory mediators, is a current strategy of gene therapy for ischemic stroke. Stimulation of growth of collateral vessels, stabilization of atherosclerotic plaques, inhibition of thrombosis, and prevention of restenosis are important objectives of gene therapy for coronary and limb arteries, but application of these approaches to carotid and intracranial arteries has received little attention. Several fundamental advances, including development of safer vectors, are needed before gene therapy achieves an important role in the treatment of cerebrovascular disease and stroke.

HSV-1 VP22 augments adenoviral gene transfer to CNS neurons in the retina and striatum in vivo

One of the obstacles to efficient vector-mediated gene transfer to the CNS is limited transduction of target neurons. The VP22 tegument protein of HSV-1 can cross biological membranes and translocate the VP22 protein from primarily transfected cells to many surrounding cells in vitro. Here, we employed an adenoviral vector coding for a VP22-GFP fusion protein driven by a CMV promoter to test its capability of transducing CNS neurons in vivo. Intraocular administration of Ad.VP22-GFP in the rat doubled both the retinal area containing transduced, GFP-expressing cells and the absolute number of GFP-expressing retinal neurons compared to Ad.GFP transduction. Following injection of Ad.VP22-GFP into the mouse brain, the transduced striatal area was increased by a factor of 7 compared to intracerebral injection of Ad.GFP. In both retina and striatum, GFP-expressing cells were identified as mainly neurons. Thus, VP22 greatly augments adenovirus-mediated transgene delivery to CNS neuronsin vivo, making VP22 a promising tool for enhancing the efficacy of adenoviral gene transfer of protective factors to the CNS.

Repopulation of rat liver by fetal hepatoblasts and adult hepatocytes transduced ex vivo with lentiviral vectors

Recent studies have shown that nondividing primary cells, such as hepatocytes, can be efficiently transduced in vitro by human immunodeficiency virus-based lentivirus vectors. Other studies have reported that, under certain conditions, the liver can be repopulated with transplanted hepatocytes. In the present study, we combined these procedures to develop a model system for ex vivo gene therapy by repopulating rat livers with hepatocytes and hepatoblasts transduced with a lentivirus vector expressing a reporter gene, green fluorescent protein (GFP). Long-term GFP expression in vivo (up to 4 months) was achieved when the transgene was driven by the liver-specific albumin enhancer/promoter but was silenced when the cytomegalovirus (CMV) enhancer/promoter was used. Transplanted cells were massively amplified ( approximately 10 cell doublings) under the influence of retrorsine/partial hepatectomy, and both repopulation and continued transgene expression in individual cells were documented by dual expression of a cell transplantation marker, dipeptidyl peptidase IV (DPPIV), and GFP. In this system, maintenance or expansion of the transplanted cells did not depend on expression of the transgene, establishing that positive selection is not required to maintain transgene expression following multiple divisions of transplanted, lentivirus-transduced hepatic cells. In conclusion, fetal hepatoblasts (liver stem/progenitor cells) can serve as efficient vehicles for ex vivo gene therapy and suggest that liver-based genetic disorders that do not shorten hepatocyte longevity or cause liver damage, such as phenylketonuria, hyperbilirubinemias, familial hypercholesterolemia, primary oxalosis, and factor IX deficiency, among others, might be amenable to treatment by this approach.

Vectors for the treatment of autoimmune disease

Gene therapy has been applied in a variety of experimental models of autoimmunity with some success. In this article, we outline recent developments in gene therapy vectors, discuss advantages and disadvantages of each, and highlight their recent applications in autoimmune models. We also consider progress in vector targeting and components for regulating transgene expression, which will both improve gene therapy safety and empower gene therapy to fullfil its potential as a therapeutic modality. In conclusion, we consider candidate vectors that satisfy requirements for application in the principal therapeutic strategies in which gene therapy will be applied to autoimmune conditions.

Progress and problems with the use of viral vectors for gene therapy

Gene therapy has a history of controversy. Encouraging results are starting to emerge from the clinic, but questions are still being asked about the safety of this new molecular medicine. With the development of a leukaemia-like syndrome in two of the small number of patients that have been cured of a disease by gene therapy, it is timely to contemplate how far this technology has come, and how far it still has to go.

Induction of protective immunity to Listeria monocytogenes with dendritic cells retrovirally transduced with a cytotoxic T lymphocyte epitope minigene

In the present study, we developed a cytotoxic T lymphocyte (CTL) epitope minigene-transduced dendritic cell (DC)-based vaccine against Listeria monocytogenes. Murine bone marrow-derived DCs were retrovirally transduced with a minigene for listeriolysin O (LLO) 91-99, a dominant CTL epitope of L. monocytogenes, and were injected into BALB/c mice intravenously. We found that the DC vaccine was capable of generating peptide-specific CD8+ T cells exhibiting LLO 91-99-specific cytotoxic activity and gamma interferon production, leading to induction of protective immunity to the bacterium. Furthermore, we demonstrated that the retrovirally transduced DC vaccine was more effective than a CTL epitope peptide-pulsed DC vaccine and a minigene DNA vaccine for eliciting antilisterial immunity. These results provide an alternative strategy in which retrovirally transduced DCs are used to design vaccines against intracellular pathogens.

'Advanced' generation lentiviruses as efficient vectors for cardiomyocyte gene transduction in vitro and in vivo

Efficient gene transduction in cardiomyocytes is a task that can be accomplished only by viral vectors. Up to now, the most commonly used vectors for this purpose have been adenoviral-derived ones. Recently, it has been demonstrated that lentiviral vectors can transduce growth-arrested cells, such as hematopoietic stem cells. Moreover, a modified form of lentiviral vector (the 'advanced' generation), containing an mRNA-stabilizer sequence and a nuclear import sequence, has been shown to significantly improve gene transduction in growth-arrested cells as compared to the third-generation vector. Therefore, we tested whether the 'advanced' generation lentivirus is capable of infecting and transducing cardiomyocytes both in vitro and in vivo, comparing efficacy in vitro against the third-generation of the same vector. Here we report that 'advanced' generation lentiviral vectors infected most (>80%) cardiomyocytes in culture, as demonstrated by immunofluorescence and FACS analyses: in contrast the percentage of cardiomyocytes infected by third-generation lentivirus was three- to four-fold lower. Moreover, 'advanced' generation lentivirus was also capable of infecting and inducing stable gene expression in adult myocardium in vivo. Thus, 'advanced' generation lentiviral vectors can be used for both in vitro and in vivo gene expression studies in the cardiomyocyte.

Gene Therapy for Pediatric Cancer: State of the Art and Future Perspectives

While modern treatments have led to a dramatic improvement in survival for pediatric malignancy, toxicities are high and a significant proportion of patients remain resistant. Gene transfer offers the prospect of highly specific therapies for childhood cancer. "Corrective" genes may be transferred to overcome the genetic abnormalities present in the precancerous cell. Alternatively, genes can be introduced to render the malignant cell sensitive to therapeutic drugs. The tumor can also be attacked by decreasing its blood supply with genes that inhibit vascular growth. Another possible approach is to modify normal tissues with genes that make them more resistant to conventional drugs and/or radiation, thereby increasing the therapeutic index. Finally, it may be possible to attack the tumor indirectly by using genes that modify the behavior of the immune system, either by making the tumor more immunogenic, or by rendering host effector cells more efficient. Several gene therapy applications have already been reported for pediatric cancer patients in preliminary Phase 1 studies. Although no major clinical success has yet been achieved, improvements in gene delivery technologies and a better understanding of mechanisms of tumor progression and immune escape have opened new perspectives for the cure of pediatric cancer by combining gene therapy with standard therapeutic available treatments.

Side effects of retroviral gene transfer into hematopoietic stem cells

Recent conceptual and technical improvements have resulted in clinically meaningful levels of gene transfer into repopulating hematopoietic stem cells. At the same time, evidence is accumulating that gene therapy may induce several kinds of unexpected side effects, based on preclinical and clinical data. To assess the therapeutic potential of genetic interventions in hematopoietic cells, it will be important to derive a classification of side effects, to obtain insights into their underlying mechanisms, and to use rigorous statistical approaches in comparing data. We here review side effects related to target cell manipulation; vector production; transgene insertion and expression; selection procedures for transgenic cells; and immune surveillance. We also address some inherent differences between hematopoiesis in the most commonly used animal model, the laboratory mouse, and in humans. It is our intention to emphasize the need for a critical and hypothesis-driven analysis of "transgene toxicology," in order to improve safety, efficiency, and prognosis for the yet small but expanding group of patients that could benefit from gene therapy.

Expression of the coxsackie and adenovirus receptor in human astrocytic tumors and xenografts

The sensitivity of human tissues and tumors to infection with type C adenoviruses correlates with the expression of the human coxsackie B- and adenovirus receptor, hCAR. HCAR is heterogeneously expressed in various tissues and types of human cancer cells, which has implications for the use of adenoviruses as vectors in cancer gene therapy. Using immunoblotting, real-time PCR, FACS-analysis and sensitivity to infection with adenovirus-lacZ, we analyzed the expression level of hCAR in glioma Grade IV cell lines. With real-time PCR, we also analyzed hCAR expression in primary human astrocytomas of different malignancy grades, as well as in their xenograft derivatives. Analysis of a set of 10 cell lines showed great variation in hCAR expression. Susceptibility to Ad5lacZ correlated well with hCAR expression, whereas no correlation was observed with the expression of alphavbeta3/alphavbeta5 integrins, proposed to function as co-receptors for adenoviruses. A great variation of CAR expression was also observed in primary astrocytomas of different malignancy grades. The mean value of CAR expression was significantly lower in 22 Grade IV tumors as compared to the values for 6 Grade II (p = 0.01) and 6 Grade III (p = 0.01) tumors. When the hCAR expression in 11 xenografts derived from Grade IV gliomas were compared to the levels detected in the original parental tumors, a mean 12-fold higher expression was seen in the xenografts (P = 0.01). Two xenografts with low hCAR expression grew considerably faster than the hCAR-expressing cells. Our results have relevance for the use of adenoviruses in gene therapy against astrocytomas.

Latest development in viral vectors for gene therapy

Gene therapy includes the application of various viral vectors, which represent most types and families of viruses, suitable for infection of mammalian host cells. Both hereditary diseases and acquired illnesses, such as cancer, can be targeted. Because of the various properties of each viral vector, the definition of their application range depends on factors such as packaging capacity, host range, cell- or tissue-specific targeting, replication competency, genome integration and duration of transgene expression. Recent engineering of modified viral vectors has contributed to improved gene delivery efficacy.

High-efficiency lentiviral vector-mediated gene transfer into murine macrophages and activated splenic B lymphocytes

The goal of the present report was to determine if lentiviral vectors could mediate gene transfer into murine terminally differentiated macrophages and mature B lymphocytes as a new strategy of gene delivery into professional antigen-presenting cells (APC). We demonstrated that nondividing tissue resident macrophages were efficiently transduced in vitro by lentiviral vectors. Gene transfer efficiencies of up to 90% were demonstrated using a green fluorescent protein (GFP) reporter gene-containing vector and expression was stable for the length of cell culture. Transduced macrophages were functionally competent, preserving their phagocytic activity, accessory cell function, interleukin (IL)-12 secretion, and nitric oxide (NO) production similar to control untransduced macrophages. Lentiviral vector mediated transduction of CD19(+) B cell blasts was demonstrated to be in the range of 60%-70% GFP-positive cells. These transduced cells retain the ability to upregulate CD80 and CD86 similar to control B cell cultures. In addition, we show that the human immunodeficiency virus type 1 (HIV-1) accessory proteins Nef, Vpr, Vif, and Vpu are not required for the transduction of both resident macrophages and activated B lymphoblasts. We conclude that HIV-1-based lentiviral vectors can mediate efficient gene transfer into primary murine macrophages and mature B lymphocytes.

NLS bioconjugates for targeting therapeutic genes to the nucleus

One of the major steps limiting non-viral gene transfer efficiency is the entry of plasmid DNA from the cytoplasm into the nucleus of transfected cells. Trafficking of nuclear proteins from the cytoplasm into the nucleus through nuclear pore complexes is mediated by the presence of nuclear localization sequences (NLS) on proteins. Viral DNA and RNA also require interaction with cellular machinery for efficient nuclear import. In this article, we review the various strategies used to provide plasmid DNA with nuclear localization sequences, and discuss the possibility of developing efficient gene delivery systems based on these strategies.

Negative-strand RNA viral vectors: intravenous application of Sendai virus vectors for the systemic delivery of therapeutic genes

Treatment by gene replacement is critical in the field of gene therapy. Suitable vectors for the delivery of therapeutic genes have to be generated and tested in preclinical settings. Recently, extraordinary features for a local gene delivery by Sendai virus vectors (SeVV) have been reported for different tissues. Here we show that direct intravenous application of SeVV in mice is not only feasible and safe, but it results in the secretion of therapeutic proteins to the circulation, for example, human clotting Factor IX (hFIX). In vitro characterization of first-generation SeVV demonstrated that secreted amounts of hFIX were at least comparable to published results for retroviral or adeno-associated viral vectors. Furthermore, as a consideration for application in humans, SeVV transduction led to efficient hFIX synthesis in primary human hepatocytes, and SeVV-encoded hFIX proteins could be shown to be functionally active in the human clotting cascade. In conclusion, our investigations demonstrate for the first time that intravenous administration of negative-strand RNA viral vectors may become a useful tool for the wide area of gene replacement requirements.

Inhibiting HIV-1 infection in human T cells by lentiviral-mediated delivery of small interfering RNA against CCR5

Double-stranded RNAs approximately 21 nucleotides long [small interfering RNA (siRNA)] are recognized as powerful reagents to reduce the expression of specific genes. To use them as reagents to protect cells against viral infection, effective methods for introducing siRNAs into primary cells are required. Here, we describe success in constructing a lentivirus-based vector to introduce siRNAs against the HIV-1 coreceptor, CCR5, into human peripheral blood T lymphocytes. With high-titer vector stocks, >40% of the peripheral blood T lymphocytes could be transduced, and the expression of a potent CCR5-siRNA resulted in up to 10-fold inhibition of CCR5 expression on the cell surface over a period of 2 weeks in the absence of selection. In contrast, the expression of another major HIV-1 coreceptor, CXCR4, was not affected. Importantly, blocking CCR5 expression by siRNAs provided a substantial protection for the lymphocyte populations from CCR5-tropic HIV-1 virus infection, dropping infected cells by 3- to 7-fold; only a minimal effect on infection by a CXCR4-tropic virus was observed. Thus, our studies demonstrate the feasibility and potential of lentiviral vector-mediated delivery of siRNAs as a general means of intracellular immunization for the treatment of HIV-1 and other viral diseases.

Integration efficiency of a hybrid adenoretroviral vector

The frequency with which the hybrid vector AdLTR-luc mediates genomic integration [Nat. Biotech. 18 (2000) 176-180] is unknown. To address this, we constructed AdLTR-red, using the AdLTR-luc backbone and the enhanced red fluorescence protein cDNA. Kinetic studies showed that AdLTR-red and a conventional adenoviral vector, AdCMV-red, entered and transduced epithelial cells comparably. AdLTR-red integration frequency in vitro, i.e., the percentage of red clones after 10-12 doubling times from limiting dilutions, was 8.0% (36/450; at 67 particles/cell). With AdCMV-red, 0/549 clones were integration-positive. Seven days after AdLTR-luc or AdCMV-luc (10(11) particles) femoral vein administration to adult rats splenocytes were prepared, stimulated with concanavalin A, and examined by FISH. AdLTR-luc integration occurred in 5-11% of mitotic rat splenocytes, while no unequivocal integration was found with AdCMV-luc. These data provide the first quantitative evidence of the frequency for genomic integration with this hybrid vector.

Development of an adenovirus-shedding assay for the detection of adenoviral vector-based vaccine and gene therapy products in clinical specimens

Adenoviral vectors are used widely as gene therapy and vaccine delivery systems. An adenovirus-shedding assay may be performed in clinical trials to monitor the safety of the vector and to investigate the potential relation between clinical symptoms and shed vector virus. This report describes the development and statistical performance of the shedding assay. Live adenovirus was recovered from throat swab and urine samples spiked with E1-deleted adenovirus type 5 vector expressing HIV-1 gag [Ad5HIVgag], in the presence or absence of wild-type adenovirus (WT Ad5). Samples were cultured in 293 and A549 cells, and the DNA extracted from virus culture was tested by polymerase chain reaction (PCR) for sequence identity. The results showed that the frequency of Ad5HIVgag infectivity in 293 cells by cytopathic effect (CPE) or an immunofluorescence assay (IFA) was concentration-dependent (53% for 10(2), 94% for 10(4), and 100% for 10(6) viral particles). WT Ad5 virus did not interfere with Ad5HIVgag. PCR amplisets could specifically amplify target sequences in the background of nonspecific DNA matrices and could distinguish Ad5HIVgag from wild-type adenoviruses. This assay may be used for clinical trials using adenovirus vectors as vehicles for vaccines.

Current status of gene therapy for inherited lung diseases

Gene therapy as a treatment modality for pulmonary disorders has attracted significant interest over the past decade. Since the initiation of the first clinical trials for cystic fibrosis lung disease using recombinant adenovirus in the early 1990s, the field has encountered numerous obstacles including vector inflammation, inefficient delivery, and vector production. Despite these obstacles, enthusiasm for lung gene therapy remains high. In part, this enthusiasm is fueled through the diligence of numerous researchers whose studies continue to reveal great potential of new gene transfer vectors that demonstrate increased tropism for airway epithelia. Several newly identified serotypes of adeno-associated virus have demonstrated substantial promise in animal models and will likely surface soon in clinical trials. Furthermore, an increased understanding of vector biology has also led to the development of new technologies to enhance the efficiency and selectivity of gene delivery to the lung. Although the promise of gene therapy to the lung has yet to be realized, the recent concentrated efforts in the field that focus on the basic virology of vector development will undoubtedly reap great rewards over the next decade in treating lung diseases.

An optimal therapeutic expression level is crucial for suicide gene therapy for hepatic metastatic cancer in mice

The most serious problem in current gene therapy is discrepancies between experimental data and actual clinical outcomes, which may be due to insufficient analyses and/or inappropriate animal models. We have explored suicide gene therapy by using various clinically relevant animal models and doubt the clinical use of maximal suicide gene expression, which has been generally recommended. To explore this subject further, we studied what expression level of suicide gene and what promoter led to the maximal clinical benefit in the case of hepatic metastatic cancer in mice. Therapeutic and adverse side effects of 4 adenoviral vectors that express herpes simplex virus thymidine kinase (HSV-tk) under different promoters were scrupulously investigated in 2 mouse models of hepatic metastasis of gastric cancer that possess clinical characteristics. Surprisingly, increases in HSV-tk expression beyond a certain point, achieved by the Rous sarcoma virus long terminal repeat promoter, not only enhanced the adverse side effects of lethal hepatotoxicity and ganciclovir-independent cytotoxicity but also failed to further increase therapeutic potential. Moreover, the carcinoembryonic antigen (CEA) tumor-specific promoter, the therapeutic potential of which had been underestimated, was much more useful-even in the case of low CEA-producing cancer-than had been previously reported. In conclusion, the optimal therapeutic expression level of a suicide gene is a novel concept and a crucial factor for successful cancer gene therapy. The present results, which contradict those of previous studies, alert researchers about possible problems with ongoing and future clinical trials that lack this concept.

Avoiding proteasomal processing: the case of EBNA1

Ubiquitin/proteasome-dependent proteolysis is involved in the regulation of a large variety of cellular processes including cell cycle progression, tissue development and atrophy, flux of substrates through metabolic pathways, selective elimination of abnormal proteins and processing of intracellular antigens for major histocompatibility complex (MHC) class I-restricted T-cell responses. Many viruses tamper with this proteolytic machinery by encoding proteins that interact with various components of the pathway. A particularly interesting example of a viral protein that interferes with proteasomal processing is the Epstein-Barr virus (EBV) nuclear antigen-1 (EBNA1). EBNA1 contains an internal repeat exclusively composed of glycines and alanines that inhibits in cis the presentation of MHC class I-restricted T-cell epitopes and prevents ubiquitin/proteasome-dependent proteolysis in vitro and in vivo. The glycine-alanine repeat acts as a transferable element on a variety of proteasomal substrates and may therefore provide a new approach to the modification of cellular proteins for therapeutic purposes.

Lentiviruses in gene therapy clinical research

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

Gene therapy as an alternative to liver transplantation

Liver transplantation has become a well-recognized therapy for hepatic failure resulting from acute or chronic liver disease. It also plays a role in the treatment of certain inborn errors of metabolism that do not directly injure the liver. In fact, the liver maintains a central role in many inherited and acquired genetic disorders. There has been a considerable effort to develop new and more effective gene therapy approaches, in part, to overcome the need for transplantation as well as the shortage of donor livers. Traditional gene therapy involves the delivery of a piece of DNA to replace the faulty gene. More recently, there has been a growing interest in the use of gene repair to correct certain genetic defects. In fact, targeted gene repair has many advantages over conventional replacement strategies. In this review, we will describe a variety of viral and nonviral strategies that are now available to the liver. The ever-growing list includes viral vectors, antisense and ribozyme technology, and the Sleeping Beauty transposon system. In addition, targeted gene repair with RNA/DNA oligonucleotides, small-fragment homologous replacement, and triplex-forming and single-stranded oligonucleotides is a long-awaited and potentially exciting approach. Although each method uses different mechanisms for gene repair and therapy, they all share a basic requirement for the efficient delivery of DNA.

RNA-based anti-HIV-1 gene therapeutic constructs in SCID-hu mouse model

Effective suppression of HIV-1 replication requires inhibition of critical viral target molecules. Tat and Rev are indispensable regulatory factors for HIV-1 replication, whereas Env mediates virus entry by direct interaction with surface receptor CD4 and coreceptor CCR5 or CXCR4. Anti-HIV-1 tat-rev and env ribozymes and Rev aptamers were previously demonstrated to provide relatively long-term protection against HIV-1 infection in vitro. However, further improvements in these constructs for clinical application in a stem-cell-based gene therapy setting requires in vivo characterization. Toward this end, we introduced these constructs into CD34(+) hematopoietic progenitor cells by retrovirus-mediated gene transduction. Ribozyme- and aptamer-transduced CD34(+) cells differentiated normally into multiple lineages of erythroid and myeloid progenies in a colony-forming unit assay. Macrophages that differentiated from the transduced CD34(+) cells expressed anti-tat-rev and -env ribozymes and Rev aptamers and displayed their normal characteristic surface markers CD14, CD4, and CCR5. Using the SCID-hu mouse in vivo human thymopoiesis model, we demonstrated that ribozyme- and aptamer-transduced CD34(+) cells retained their normal capacity to reconstitute human fetal thymus and liver tissue (thy/liv) grafts. Reconstitution by ribozyme- and aptamer-transduced CD34(+) cells reached levels of up to 87% based on HLA surface marker staining. Differentiated thymocytes derived from reconstituted grafts expressed anti-tat-rev and -env ribozymes and Rev aptamers and showed significant resistance to HIV-1 infection upon challenge. Analysis of reconstituted thymocytes by hybridization revealed an average of 0.4 to 2 copies of vector sequences per cell. Southern analysis of proviral integration junctions in progeny thymocytes demonstrated that the human thy/liv grafts were reconstituted by a few primitive hematopoietic stem cells. These results highlight the utility of RNA-based anti-HIV-1 gene therapeutic approaches and their preclinical testing in a surrogate animal model harboring human tissue.

Vascular growth factors for coronary angiogenesis

Coronary artery disease not amendable to conventional revascularization poses a significant medical problem. Advances in the understanding of blood vessel growth have given rise to efforts to develop novel therapeutic approaches for these "no-option" patients. Therapeutic angiogenesis makes use of the administration of angiogenic growth factor protein or gene to promote the development of endogenous collateral vessels in ischemic myocardium. Among the growth factors that play a role in blood vessel growth and development, vascular endothelial growth factors (VEGFs) and fibroblast growth factors have been the most extensively studied. Various methods of delivery have been used to enhance localization and persistence. Preliminary animal experiments have been promising with evidence of capillary formation at the target myocardium after growth factor administration. Initial phase I and II clinical trials have been undertaken. Preliminary information on efficacy is beginning to become available, raising hopes and questions about the future direction and potential success of therapeutic angiogenesis as a clinical approach to the treatment of myocardial ischemia. Although the initial clinical results are encouraging, real efficacy has still to be proven and the potential side-effects of these potent angiogenic growth factors remain a concern. Large-scale, randomized, and placebo-controlled studies will be required to demonstrate the true clinical benefit of this novel therapeutic treatment for ischemic heart disease.

In vivo correction of murine tyrosinemia type I by DNA-mediated transposition

Gene therapy applications of naked DNA constructs for genetic disorders have been limited because of lack of permanent transgene expression. This limitation, however, can be overcome by the Sleeping Beauty (SB) transposable element, which can achieve permanent transgene expression through genomic integration from plasmid DNA. To date, only one example of an in vivo gene therapy application of this system has been reported. In this report, we have further defined the activity of the SB transposon in vivo by analyzing the expression and integration of a fumarylacetoacetate hydrolase (FAH) transposon in FAH-deficient mice. In this model, stably corrected FAH(+) hepatocytes are clonally selected and stable integration events can therefore be quantified and characterized at the molecular level. Herein, we demonstrate that SB-transposon-transfected hepatocytes can support significant repopulation of the liver, resulting in long-lasting correction of the FAH-deficiency phenotype. A single, combined injection of an FAH-expressing transposon plasmid and a transposase expression construct resulted in stable FAH expression in approximately 1% of transfected hepatocytes. The average transposon copy number was determined to be approximately 1/diploid genome and expression was not silenced during serial transplantation. Molecular analysis indicated that high-efficiency DNA-mediated transposition into the mouse genome was strictly dependent on the expression of wild-type transposase.

A human immunodeficiency virus type 1 pol gene-derived sequence (cPPT/CTS) increases the efficiency of transduction of human nondividing monocytes and T lymphocytes by lentiviral vectors

We have investigated the capacity of two human immunodeficiency virus type 1-derived lentivectors, differing in the presence of a 118-bp pol fragment containing the cPPT/CTS element, to transduce human normal primary cells of different hematopoietic lineages. Infection of resting monocytes with a high multiplicity of infection (MOI > 10) revealed that the lentivirus carrying the pol fragment (cPPT) is effective, transducing 75% of cells compared with 36% for the no-cPPT vector. Even at low MOIs (< or =1) the cPPT vector still shows a better transduction efficiency than the no-cPPT vector. Moreover, transduction does not require dendritic cell differentiation. In contrast, infection of nonactivated T lymphocytes showed that both vectors, tested at high MOIs, can transduce a small, although measurable, percentage of cells (up to 10%), which may correspond to G(1a) "activated" cells as detected by simultaneous staining of DNA and RNA, in our cultures in the presence of medium alone. Furthermore, we show that the sole addition of interleukin 2 or interleukin 15 represents a full proliferative signal under our conditions and permits high transduction efficiency (up to 30% with the cPPT vector and 15% with the no-cPPT vector). Still higher transduction of T lymphocytes can be achieved after stimulation with phytohemagglutinin and interleukin 2 (up to 78% with the cPPT vector vs. 42% with the no-cPPT vector). Finally, both viruses do not transduce either resting or proliferating tonsillar B lymphocytes.

Intact microtubules support adenovirus and herpes simplex virus infections

Capsids and the enclosed DNA of adenoviruses, including the species C viruses adenovirus type 2 (Ad2) and Ad5, and herpesviruses, such as herpes simplex virus type 1 (HSV-1), are targeted to the nuclei of epithelial, endothelial, fibroblastic, and neuronal cells. Cytoplasmic transport of fluorophore-tagged Ad2 and immunologically detected HSV-1 capsids required intact microtubules and the microtubule-dependent minus-end-directed motor complex dynein-dynactin. A recent study with epithelial cells suggested that Ad5 was transported to the nucleus and expressed its genes independently of a microtubule network. To clarify the mechanisms by which Ad2 and, as an independent control, HSV-1 were targeted to the nucleus, we treated epithelial cells with nocodazole (NOC) to depolymerize microtubules and measured viral gene expression at different times and multiplicities of infections. Our results indicate that in NOC-treated cells, viral transgene expression was significantly reduced at up to 48 h postinfection (p.i.). A quantitative analysis of subcellular capsid localization indicated that NOC blocked the nuclear targeting of Ad2 and also HSV-1 by more than 90% at up to 7 h p.i. About 10% of the incoming Texas Red-coupled Ad2 (Ad2-TR) was enriched at the nucleus in microtubule-depleted cells at 5 h p.i. This result is consistent with earlier observations that Ad2-TR capsids move randomly in NOC-treated cells at less than 0.1 micro m/s and over distances of less than 5 micro m, characteristic of Brownian motion. We conclude that fluorophore-tagged Ad2 and HSV-1 particles are infectious and that microtubules play a prominent role in efficient nuclear targeting during entry and gene expression of species C Ads and HSV-1.

Electrotransfer of gene encoding endostatin into normal and neoplastic mouse tissues: inhibition of primary tumor growth and metastatic spread

Electroporation-mediated gene transfer relies upon direct delivery of plasmids into cells permeabilized by electric fields, a method more efficient than transfer using nonviral vectors, although neither approaches the transfer efficiency of viral vectors. Here we studied electrotransfer of a gene encoding an angiogenesis inhibitor (endostatin) into primary tumors and muscle tissues, which would serve as a site of synthesis and secretion into the bloodstream of a therapeutic antimetastatic protein with systemic effects. Optimum electroporation conditions (voltage, number and duration of impulses, separation of caliper electrodes) were first established to maximize expression of a reporter gene transferred into murine Renca kidney carcinoma, B16(F10) melanoma, or skeletal muscle tissues. In neoplastic tissues, electrotransfer of plasmid DNA was far more efficient than electroporation with lipoplexes, but no differences between naked DNA and lipoplexes were found in case of electroporated muscles. We then studied the electrotransfer of plasmid DNA carrying the endostatin gene into pre-established experimental Renca tumors. A significant inhibition of tumor growth was observed in animals electroporated with this construct. Electrotransfer of the endostatin gene into muscle tissues resulted in reduced numbers of experimental B16(F10) metastases in the lungs. This study clearly shows that electroporation may be used to efficiently transfer antiangiogenic genes into both normal and neoplastic tissues.