A novel SV40-based vector successfully transduces and expresses an alpha 1-antitrypsin ribozyme in a human hepatoma-derived cell line

Cre Recombinase Mediates the Removal of Bacterial Backbone to Efficiently Generate rSV40

Gene therapy has been shown to be a feasible approach to treat inherited disorders in vivo. Among the currently used viral vector systems, adeno-associated virus (AAV) vectors are the most advanced and have been applied in patients successfully. An important drawback of non-integrating AAV vectors is their loss of expression upon cell division, while repeating systemic administration lacks efficacy due to the induction of neutralizing antibodies. In addition, a significant percentage of the general population is not eligible for AAV-mediated gene therapy due to pre-existing immunity. Development of additional viral vectors may overcome this hurdle. Simian virus 40 (SV40)-derived vectors have been reported to transduce different tissues, including the liver, and prevalence of neutralizing antibodies in the general population is very low. This renders recombinant SV40 (rSV40) vector an interesting candidate for effective (re-)administration. Clinical use of SV40 vectors is in part hampered by less advanced production methods compared to AAVs. To optimize the production of rSV40 and make it better suitable for clinical practice, we developed a production system that relies on Cre recombinase-mediated removal of the bacterial plasmid backbone.

Therapeutics: Gene Therapy for Alpha-1 Antitrypsin Deficiency

This review seeks to give an overview of alpha-1 antitrypsin deficiency, including the different disease phenotypes that it encompasses. We then describe the different therapeutic endeavors that have been undertaken to address these different phenotypes. Lastly we discuss future potential therapeutics, such as genome editing, and how they may play a role in treating alpha-1 antitrypsin deficiency.

Challenges and Prospects for Alpha-1 Antitrypsin Deficiency Gene Therapy

Alpha-1 antitrypsin (AAT) is a protease inhibitor belonging to the serpin family. A number of identified mutations in the SERPINA1 gene encoding this protein result in alpha-1 antitrypsin deficiency (AATD). A decrease in AAT serum concentration or reduced biological activity causes considerable risk of chronic respiratory and liver disorders. As a monogenic disease, AATD appears to be an attractive target for gene therapy, particularly for patients with pulmonary dysfunction, where augmentation of functional AAT levels in plasma might slow down respiratory disease development. The short AAT coding sequence and its activity in the extracellular matrix would enable an increase in systemic serum AAT production by cellular secretion. In vitro and in vivo experimental AAT gene transfer with gamma-retroviral, lentiviral, adenoviral, and adeno-associated viral (AAV) vectors has resulted in enhanced AAT serum levels and a promising safety profile. Human clinical trials using intramuscular viral transfer with AAV1 and AAV2 vectors of the AAT gene demonstrated its safety, but did not achieve a protective level of AAT >11 μM in serum. This review provides an in-depth critical analysis of current progress in AATD gene therapy based on viral gene transfer. The factors affecting transgene expression levels, such as site of administration, dose and type of vector, and activity of the immune system, are discussed further as crucial variables for optimizing the clinical effectiveness of gene therapy in AATD subjects.

Cell and gene therapy for genetic diseases: inherited disorders affecting the lung and those mimicking sudden infant death syndrome

Some of the first human gene therapy trials targeted diseases of the lung and provided important information that will continue to help shape future trials. Here we describe both cell and gene therapies for lung diseases such as cystic fibrosis and alpha-1 antitrypsin disorder as well as fatty acid oxidation disorders that mimic sudden infant death syndrome (SIDS). Human clinical gene therapy trials for cystic fibrosis and alpha-1 antitrypsin have been performed using a variety of vectors including adenovirus, adeno-associated virus, and nonviral vectors. No human clinical gene therapy trials have been performed for disorders of fatty acid oxidation; however, important proof-of-principle studies have been completed for multiple fatty acid oxidation disorders. Important achievements have been made and have yet to come for cell and gene therapies for disorders of the lung and those mimicking SIDS.

Sustained miRNA-mediated knockdown of mutant AAT with simultaneous augmentation of wild-type AAT has minimal effect on global liver miRNA profiles

α-1 antitrypsin (AAT) deficiency can exhibit two pathologic states: a lung disease that is primarily due to the loss of AAT's antiprotease function, and a liver disease resulting from a toxic gain-of-function of the PiZ-AAT (Z-AAT) mutant protein. We have developed several recombinant adeno-associated virus (rAAV) vectors that incorporate microRNA (miRNA) sequences targeting the AAT gene while also driving the expression of miRNA-resistant wild-type AAT-PiM (M-AAT) gene, thus achieving concomitant Z-AAT knockdown in the liver and increased expression of M-AAT. Transgenic mice expressing the human PiZ allele treated with dual-function rAAV9 vectors showed that serum PiZ was stably and persistently reduced by an average of 80%. Treated animals showed knockdown of Z-AAT in liver and serum with concomitant increased serum M-AAT as determined by allele-specific enzyme-linked immunosorbent assays (ELISAs). In addition, decreased globular accumulation of misfolded Z-AAT in hepatocytes and a reduction in inflammatory infiltrates in the liver was observed. Results from microarray studies demonstrate that endogenous miRNAs were minimally affected by this treatment. These data suggests that miRNA mediated knockdown does not saturate the miRNA pathway as has been seen with viral vector expression of short hairpin RNAs (shRNAs). This safe dual-therapy approach can be applied to other disorders such as amyotrophic lateral sclerosis, Huntington disease, cerebral ataxia, and optic atrophies.

Variables and strategies in development of therapeutic post-transcriptional gene silencing agents

Post-transcriptional gene silencing (PTGS) agents such as ribozymes, RNAi and antisense have substantial potential for gene therapy of human retinal degenerations. These technologies are used to knockdown a specific target RNA and its cognate protein. The disease target mRNA may be a mutant mRNA causing an autosomal dominant retinal degeneration or a normal mRNA that is overexpressed in certain diseases. All PTGS technologies depend upon the initial critical annealing event of the PTGS ligand to the target RNA. This event requires that the PTGS agent is in a conformational state able to support hybridization and that the target have a large and accessible single-stranded platform to allow rapid annealing, although such platforms are rare. We address the biocomplexity that currently limits PTGS therapeutic development with particular emphasis on biophysical variables that influence cellular performance. We address the different strategies that can be used for development of PTGS agents intended for therapeutic translation. These issues apply generally to the development of PTGS agents for retinal, ocular, or systemic diseases. This review should assist the interested reader to rapidly appreciate critical variables in PTGS development and facilitate initial design and testing of such agents against new targets of clinical interest.

Gene therapy for alpha-1 antitrypsin deficiency

Alpha-1 antitrypsin (AAT) deficiency is a common single-gene disorder among Northern Europeans and North Americans. The carrier frequency for the common missense mutation (Z-AAT) ranges from 4% in the US to nearly 25% in the Republic of Ireland. Severe AAT deficiency (plasma levels below 11 μm) is most commonly associated with an adult-onset lung disease, with pan-acinar emphysema and airway inflammation, which is thought to be primarily owing to the loss of function of AAT in neutralizing neutrophil elastase and other pro-inflammatory enzymes. In 5-10% of patients, severe liver disease may develop. This may occur at any time from infancy to adulthood, and is thought to be owing to toxicity from the Z-AAT mutant protein that folds poorly and forms insoluble polymers within the hepatocyte, which is the primary site for AAT production. Thus, gene therapy for AAT lung disease is conceived of as augmentation of serum levels (a prolonged form of protein replacement, which is currently in use), while gene therapy for liver disease presents the problem of also having to downregulate the production of Z-AAT protein. Over the years, numerous strategies have been employed for the gene therapy of both AAT-deficient lung disease and liver disease. These will be reviewed with an emphasis on modalities that have reached clinical trials recently.

In vivo post-transcriptional gene silencing of alpha-1 antitrypsin by adeno-associated virus vectors expressing siRNA

alpha-1 Antitrypsin (AAT) deficiency is one of the most common genetic diseases in North America, with a carrier frequency of approximately 4% in the US population. Homozygosity for the most common mutation (Glu342Lys, PI(*)Z) leads to the synthesis of a mutant protein, which accumulates and polymerizes within hepatocytes rather than being efficiently secreted. This lack of secretion causes severe serum deficiency predisposing to chronic lung disease. Twelve to fifteen percent of patients with PI(*)ZZ also develop liver disease, which can be severe, even in infancy. This is thought to be due to toxic effects of the accumulated mutant Z-AAT within the hepatocyte. Thus, an approach to reduce AAT-deficient liver disease will likely require some mechanism to decrease the amount of Z-AAT within hepatocytes. In this report, we describe studies of small-interfering RNAs (siRNAs) designed to downregulate endogenous AAT within hepatocytes. Three different siRNA sequences were identified and cloned into a recombinant adeno-associated virus (rAAV) backbone, either singly or as a trifunctional (3X) construct. Each had activity independently, but the levels of AAT expression in cell culture models showed the greatest decrease with the 3X construct, resulting in levels that were five-fold lower than controls. The rAAV-3X-siRNA was then packaged into AAV8 capsids and used in vivo to transduce the livers of human Z-AAT overexpressing transgenic mice. Those studies showed a decrease in total human AAT, a clearing of Z-AAT accumulation by immunohistochemistry, and a decrease in monomer Z-AAT within the liver within 3 weeks after vector injection. The rAAV8-3X-siRNA vector may hold promise as a potential therapy for patients with AAT liver disease.

Phase I trial of intramuscular injection of a recombinant adeno-associated virus serotype 2 alphal-antitrypsin (AAT) vector in AAT-deficient adults

A phase I trial of intramuscular injection of a recombinant adeno-associated virus serotype 2 (rAAV2) alpha1-antitrypsin (AAT) vector was performed in 12 AAT-deficient adults, 10 of whom were male. All subjects were either homozygous for the most common AAT mutation (a missense mutation designated PI*Z) or compound heterozygous for PI*Z and another mutation known to cause disease. There were four dose cohorts, ranging from 2.1 x 10(12) vector genomes (VG) to 6.9 x 10(13) VG, with three subjects per cohort. Subjects were injected sequentially in a dose-escalating fashion with a minimum of 14 days between patients. Subjects who had been receiving AAT protein replacement discontinued that therapy 28 days before vector administration. There were no vector-related serious adverse events in any of the 12 participants. Vector DNA sequences were detected in the blood between 1 and 3 days after injection in nearly all patients receiving doses of 6.9 x 10(12) VG or higher. Anti-AAV2 capsid antibodies were present and rose after vector injection, but no other immune responses were detected. One subject who had not been receiving protein replacement exhibited low-level expression of wild-type M-AAT in the serum (82 nM), which was detectable 30 days after receiving an injection of 2.1 x 10(13) VG. Unfortunately, residual but declining M-AAT levels from the washout of the protein replacement elevated background levels sufficiently to obscure any possible vector expression in that range in most of the other individuals in the higher dose cohorts.

RNAi-based suppression and replacement of rds-peripherin in retinal organotypic culture

Extensive mutational heterogeneity presents a significant barrier to the development of therapeutics for RDS-peripherin-linked autosomal-dominant retinitis pigmentosa (RP), for which more than 50 disease-related mutations have been identified to date. Mutation-independent suppression, using RNA interference (RNAi), together with simultaneous expression of a replacement rds gene (r-rds, which has been altered to escape suppression but nevertheless encodes wild-type protein) has been explored in COS-7 cells and mouse retinal explants. The efficacy of small interfering and short hairpin RNAs (si/shRNAs) silencing mouse rds, and the function of r-rds (containing degenerate substitutions in the RNAi target sequence) were analyzed at transcript (RT-PCR) and protein (ELISA) levels in COS-7 cells. "Dual-" and "triple-expression" constructs carrying the shRNA suppressor and the marker EGFP with or without the r-rds cassette were electroporated in vitro into retinal explants from 1-day-old pups. The retinae were dissociated at day 14, and transduced cells were FACS-sorted using the coexpressed EGFP marker and analyzed by RT-PCR. si/shRNAs decreased rds mRNA and protein expression by up to 82%, while r-rds was protected from suppression in COS-7 cells. Similarly, efficient RNAi-mediated suppression of endogenous rds was detected in retinal explants, while concomitant rescue of r-rds was also achieved. These data validate the concept of RNAi-based suppression coupled with replacement technology for the development of therapies targeting RDS-linked autosomal-dominant RP, and suggest that such approaches could potentially be used for other autosomal-dominant diseases with similarly extensive intragenic heterogeneity.

Using gene delivery to protect HIV-susceptible CNS cells: inhibiting HIV replication in microglia

Antiretroviral chemotherapy penetrates the CNS poorly. CNS HIV, thus sheltered, may injure the brain and complicate control of systemic HIV infection. Microglial cells play a major role in HIV persistence in the CNS but are rarely targeted for gene delivery. Because recombinant SV40 vectors (rSV40s) transduce other phagocytic cells efficiently, we tested rSV40 delivery of anti-HIV genetic therapy to microglial cells. Microglia prepared as enriched cultures from human fetal brain, were transduced with marker vectors, SV(RFP) and SV(Nef/FLAG), respectively, carrying DsRed and HIV-1 Nef bearing a FLAG epitope. By immunostaining and FACS, 95% of unselected cells expressed the transgenes, without detectable toxicity. Microglia were transduced with SV(AT), carrying human alpha1-antitrypsin (alpha1AT), which blocks Env and Gag processing. SV(AT)-treated microglia strongly resisted challenge with HIV-1BaL, even when microglia were transduced with SV(AT) following HIV challenge. Thus, rSV40s effectively transduce microglia and protect them from HIV.

Inhibition of hepatitis viral replication by siRNA

Small interfering RNA (siRNA)-mediated sequence-specific gene silencing is a powerful tool to inhibit endogenous and exogenous gene expression, and it holds great potential to prevent and eradicate viral infection, for which existing therapy is inadequate, such as HIV, hepatitis B virus (HBV) and hepatitis C virus (HCV). A number of studies have documented the effectiveness of siRNA against HBV or HCV at various regions of the viral genome in infected human hepatoma cell lines. Selected siRNA may reduce the production of viral replicons, as well as structural or non-structural proteins by > 90%. Only a few in vivo studies that demonstrated the efficacy of siRNA in the suppression of HBV replication in mice are available. Thus, reliable models of HBV and HCV infection in small animals or non-human primates are needed to evaluate the delivery and efficacy of siRNA as a therapeutic modality for viral hepatitis.

Gene therapy for autosomal dominant disorders of keratin

Dominant mutations that interfere with the assembly of keratin filaments cause painful and disfiguring epidermal diseases like pachyonychia congenita and epidermolysis bullosa simplex. Genetic therapies for such diseases must either suppress the production of the toxic proteins or correct the genetic defect in the chromosome. Because epidermal skin cells may be genetically modified in tissue culture or in situ, gene correction is a legitimate goal for keratin diseases. In addition, recent innovations, such as RNA interference in animals, make an RNA knockdown approach plausible in the near future. Although agents of RNA reduction (small interfering RNA, ribozymes, triplex oligonucleotides, or antisense DNA) can be delivered as nucleotides, the impermeability of the skin to large charged molecules presents a serious impediment. Using viral vectors to deliver genes for selective inhibitors of gene expression presents an attractive alternative for long-term treatment of genetic disease in the skin.

Efficient hepatic delivery and expression from a recombinant adeno-associated virus 8 pseudotyped alpha1-antitrypsin vector

alpha1-Antitrypsin (AAT) deficiency is a single-gene disorder in which a mutation in the AAT (approved symbol SERPINA1) gene (PI*Z) leads to misfolding of the protein, loss of the protective antiprotease effect of AAT for the lungs, and a toxic effect on hepatocytes. Optimal therapy for AAT deficiency will require a high percentage of hepatocyte transduction to be effective for liver and lung disease. Recently, rAAV genomes pseudotyped with capsids from serotypes 7 and 8 showed efficient hepatic transduction. We hypothesized that upon portal vein injection to target hepatocytes, serotype 8 would better transduce target cells and therefore express hAAT in both a greater percentage of cells and greater amounts. AAV2 and pseudotyped vectors for serotypes 1, 5, and 8 carrying the human AAT transgene were injected at 1 x 10(10) particle doses into C57Bl/6 mice. Circulating hAAT from AAV2/8-injected animals showed a 2-log advantage over AAV2 and 3-log increase over AAV2/1 and 5 for the 24-week study. Most significantly, up to 40% of total liver cells stained positive for the transgene in AAV2/8 subjects while remaining primarily episomal. Therefore, pseudotyped AAV8 provides a vehicle to infect a high percentage of hepatocytes stably and thereby express therapeutic molecules to modify AAT PiZ transcripts.

Liver-targeted gene therapy by SV40-based vectors using the hydrodynamic injection method

Efficient reconstitution of defective genes in hepatocytes could be used to treat various liver and systemic diseases through gene therapy. To explore the potential of SV40-based vectors in liver gene therapy, we constructed SV/luc, an SV40 T-antigen replacement transduction vector, that was propagated on COS and COT cells, which supply the SV40 T-antigen in trans. For liver targeting, BALB/C mice were injected via the tail vein with SV/luc stocks containing 3 x 10(6) to 10(8) transducing units in a volume of 1-2 ml. Luciferase activity was monitored with a light-detection cooled charged-coupled device (CCCD) camera, which enables continuous in vivo measurement of luc expression. The SV40 vector proved to be efficient in gene delivery to the liver, leading to long-term (> or =107 days) transgene expression in hepatocytes. Optimal results were obtained with 3 x 10(6) to 3 x 10(7) transducing units. The hydrodynamic vector delivery method caused transient liver inflammatory changes, with full recovery within days. Low levels of SV40-neutralizing antibodies were detected in the sera of treated mice; however, there was no indication of vector or transgene-specific cellular immune responses. Vectors packaged in vitro, using recombinant capsid proteins and plasmid DNA, were also effective in liver transduction. These results suggest that SV40 vectors may be useful for liver gene therapy.

alpha1-Antitrypsin deficiency . 6: new and emerging treatments for alpha1-antitrypsin deficiency

Alpha-1-antitrypsin (AAT) deficiency is a genetic condition that increases the risk of developing lung and liver disease, as well as other associated conditions. Most treatment of affected individuals is not specifically directed at AAT deficiency but focuses on the resultant disease state. The only currently available specific therapeutic agent-namely, intravenous augmentation with plasma derived AAT protein-is marketed in a limited number of countries. Treatments aimed at correcting the underlying genetic abnormality, supplementing or modifying the gene product, and halting or reversing organ injury are now beginning to emerge. These innovative approaches may prove effective at modifying or eliminating diseases association with AAT deficiency.

Gene therapy for human alpha1-antitrypsin deficiency in an animal model using SV40-derived vectors

BACKGROUND & AIMS

In most genetic diseases, the goal of gene therapy is to deliver a particular transgene; however, sometimes a deleterious gene product must be eliminated. Because of the promise of recombinant simian virus 40 (rSV40) vectors, we tested their ability to deliver a transgene and to target a transcript for destruction by direct administration of the vectors to the liver of an animal model for human alpha1-antitrypsin (alpha1-AT) deficiency.

METHODS

Therapy of human alpha1-AT deficiency requires stable transduction of resting hepatocytes, both to deliver wild-type alpha1-AT and to inhibit production of mutant alpha1-AT. Transgenic mice carrying the mutant human alpha1-AT PiZ allele were treated through an indwelling portal vein catheter with a simian virus 40 (SV40)-derived vector carrying a ribozyme designed to target the human transcript.

RESULTS

Treated transgenic mice showed marked decreases of human alpha1-AT messenger RNA and the protein in the liver, and serum levels of human alpha1-AT were decreased to 50% +/- 5% of pretreatment values 3-16 weeks after transduction. Moreover, when normal mice were treated with an SV40-derived vector containing a modified human alpha1-AT complementary DNA engineered to be resistant to cleavage by the alpha1-AT ribozyme, they expressed human alpha1-AT messenger RNA and protein in their livers and serum levels of human alpha1-AT remained >1 microg/mL for 1 year.

CONCLUSIONS

These results represent the initial steps toward a novel approach to the gene therapy of alpha1-AT deficiency.

Simian Virus-40 as a Gene Therapy Vector

Simian virus-40 (SV40), an icosahedral papovavirus, has recently been modified to serve as a gene delivery vector. Recombinant SV40 vectors (rSV40) are good candidates for gene transfer, as they display some unique features: SV40 is a well-known virus, nonreplicative vectors are easy-to-make, and can be produced in titers of 10(12) IU/ml. They also efficiently transduce both resting and dividing cells, deliver persistent transgene expression to a wide range of cell types, and are nonimmunogenic. Present disadvantages of rSV40 vectors for gene therapy are a small cloning capacity and the possible risks related to random integration of the viral genome into the host genome. Considerable efforts have been devoted to modifing this virus and setting up protocols for viral production. Preliminary therapeutic results obtained both in tissue culture cells and in animal models for heritable and acquired diseases indicate that rSV40 vectors are promising gene transfer vehicles. This article reviews the work performed with SV40 viruses as recombinant vectors for gene transfer. A summary of the structure, genomic organization, and life cycle of wild-type SV40 viruses is presented. Furthermore, the strategies utilized for the development, production, and titering of rSV40 vectors are discussed. Last, the therapeutic applications developed to date are highlighted.

Hepatitis B virus enhances transduction of human hepatocytes by SV40-based vectors

BACKGROUND/AIMS

Chronic HBV infection, a world-wide epidemic, can lead to chronic hepatitis and eventually to cirrhosis and hepatocellular carcinoma. The liver poses obstacles for many available gene-transfer vectors. SV40-based vectors can transduce human hepatic and hematopoietic cells. We studied the effect of HBV on the transduction - efficiency of human hepatic cells by SV40 - based vectors.

METHODS

A SV40-vector carrying the luciferase gene, and wild-type SV40, were used to assess transduction efficiency of human HBV-positive and HBV-negative hepatic cells. Transduction efficiency was measured as luciferase activity or by T-antigen staining. To evaluate whether differences in transduction efficiency are due to cell recognition and/or nuclear transport, MHC-I receptors were measured by FACS analysis and SV40-DNA was extracted from the nuclei of transduced cells and quantified.

RESULTS

Two HBV-positive cell-lines, HepG2.2.2.15 and FLC4-A10II, were transduced significantly more efficiently than their parental HBV-negative cell-lines. Transient transfection of HuH-7 cells with the HBV genome also increased transduction efficiency. The level of MHC-I, the cellular receptor for SV40, was comparable in all the cell-lines studied. However, soon after infection with SV40, the nuclei of HepG2.2.2.15 contained >6-fold more SV40-DNA than HepG2.

CONCLUSIONS

HBV increases transduction by SV40-vectors. This is due to enhanced vector entry and/or transport into the nucleus. SV40-vectors appear to have a potential for gene therapy for the treatment of HBV infections.

Conditional expression of α1-antitrypsin delivered by recombinant SV40 vectors protects lymphocytes against HIV

Constitutive expression of alpha(1)-antitrypsin (alpha(1)AT), a serine protease inhibitor, by a recombinant simian virus-40-based vector blocks both HIV gp160 and p55 processing, and so is a powerful inhibitor of HIV replication. To apply these findings more effectively in devising HIV therapies, we tested HIV LTR conditional promoter, to drive the expression of alpha(1)AT. SV[LTR](AT) was designed so that synthesis of human alpha(1)AT would be trans-activated by HIV infection. Cell lines and primary human lymphocytes were transduced with SV[LTR](AT) without selection and detectable toxicity. Responsiveness of alpha(1)AT expression to HIV Tat or HIV challenge was confirmed by Northern blotting, RT-PCR, cytofluorimetry and immunostaining. SV[LTR](AT)-transduced cells were protected from HIV-1(NL4-3) at a challenge dose of 0.04 MOI (T-cell lines) or 0.2 MOI (peripheral blood lymphocytes). Conditional expression of alpha(1)AT consistently protected T cells from HIV challenge as effectively as did constitutive expression. Combining the efficiency of rSV40 vectors with HIV-responsive expression of a highly effective anti-HIV therapeutic may be an effective approach to gene therapy of HIV replication.

Exploiting hepatitis C virus activation of NFkappaB to deliver HCV-responsive expression of interferons alpha and gamma

Chronic infection with hepatitis C virus (HCV) may lead to liver failure and hepatocellular carcinoma. Current treatment for HCV includes high systemic doses of interferonalpha (IFNalpha), which is effective in less than half of patients and may have severe side effects. We designed conditional IFNalpha and IFNgamma expression constructs to be triggered by HCV-induced activation of NFkappaB, and delivered these using highly efficient recombinant Tag-deleted SV40-derived vectors. NFkappaB activates the HIV-1NL4-3 long terminal repeat (HIVLTR) as a promoter, which accounts for the conditional transgene expression. Human hepatocyte lines and primary rat hepatocytes (PRH) were transduced with SV[HIVLTR](IFN) vectors, and transfected with HCV cDNA. Production of human and murine IFNalpha and IFNgamma in cytosol and culture supernatants was measured. HCV activated the HIVLTR to produce and secrete IFNs, and did so largely through the NFkappaB binding sites of the HIVLTR. Levels of IFNs secreted, and the magnitude of induction in response to HCV, were greater in hepatocyte lines than in primary cultured hepatocytes. However, even in the latter, supernatant IFNalpha concentrations achieved by this approach were similar to therapeutic serum concentrations sought in systemic IFNalpha-treated patients. In coculture studies, secreted IFNalpha activated its cognate response elements in untransduced cells, suggesting that its potential inhibitory effects on HCV may not be limited to transduced cells. Although HCV replication in culture is difficult to assess, HCV-induced IFNalpha production demonstrably reduced HCV transcription. Conditional expression of IFNs within the liver may represent an attractive approach to therapy of severe chronic HCV infection that could avoid the side effects of systemic treatment regimens.

Mechanisms of alpha1-antitrypsin inhibition of cellular serine proteases and HIV-1 protease that are essential for HIV-1 morphogenesis

Proprotein processing is essential for HIV infectivity. Cellular trans-Golgi network (TGN) serine proteases (e.g., furin) are required to cleave HIV envelope gp160 to gp120. In addition, HIV protease (PR), an aspartyl protease, cleaves p55(Gag) to p24, etc., in budding virions. alpha1-Antitrypsin (alpha(1)AT) is cleaved by serine proteases, causing a conformational change in alpha(1)AT that sequesters and so inactivates the protease. alpha(1)AT blocks both gp160 and p55 processing, and so is a powerful inhibitor of HIV replication. We hypothesized that alpha(1)AT inhibited gp160 and p55 processing via different mechanisms, and that in both cases, alpha(1)AT bound and was itself cleaved by the proteases whose activities were blocked. alpha(1)AT delivered by SV(AT), a recombinant, Tag-deleted SV40-derived vector, localized to the TGN, co-precipitated with furin, and depleted furin from the TGN. After SV(AT) transduction and HIV challenge, alpha(1)AT was detected in resulting nascent immature HIV-1 virions. alpha(1)AT also blocked incorporation of the enzymatically active dimeric form of PR into HIV virions. Western analysis using recombinant proteins showed that alpha(1)AT directly bound HIV PR, and was cleaved by it. The simultaneous inhibition of two different steps in HIV morphogenesis both increases alpha(1)AT antilentiviral activity and decreases the possibility that HIV mutations will allow escape from inhibition.

Inhibiting AIDS in the central nervous system: gene delivery to protect neurons from HIV

Gene therapy to treat primary and secondary CNS diseases, including neuro-AIDS, has not yet been effective. New approaches to delivering therapeutic genes to the central nervous system are therefore required. Recombinant SV40 vectors (rSV40) transduce both dividing and quiescent cells efficiently, and so we tested them for their ability to deliver anti-HIV-1 transgenes to terminally differentiated human NT2-derived neurons (NT2-N). These vectors transduced >95% of immature as well as mature human neurons efficiently, without detectable toxicity and without requiring selection. rSV40 gene delivery was stable to retinoic acid-induced neuronal differentiation. The rSV40 vectors used in these studies, SV(RevM10) and SV(AT), respectively carried the cDNAs for RevM10, a trans-dominant mutant of HIV-1 Rev, and human alpha1-antitrypsin. As measured by HIV-1 p24 antigen assays and by immunostaining for gp120, NT2-N treated with these vectors strongly resisted challenge with different strains of HIV-1. Protection from HIV replication and HIV-induced cytotoxicity was conferred by SV(AT) and SV(RevM10) and remained constant throughout retinoic acid-induced neuronal differentiation and for the duration of these studies (> or =11 weeks). rSV40 transduction of human neurons might therefore be a practicable approach to gene delivery for the treatment of CNS diseases, including neuro-AIDS.

HIV-1 proprotein processing as a target for gene therapy

The central role of endoconvertases and HIV-1 protease (HIV-1 PR) in the processing of HIV proproteins makes the design of specific inhibitors important in anti-HIV gene therapy. Accordingly, we tested native alpha(1) antitrypsin (alpha(1)AT) delivered by a recombinant simian virus-40-based vector, SV(AT), as an inhibitor of HIV-1 proprotein maturation. Cell lines and primary human lymphocytes were transduced with SV(AT) without selection and detectable toxicity. Expression of alpha(1)AT was confirmed by Northern blotting, immunoprecipitation and immunostaining. SV(AT)-transduced cells showed no evidence of HIV-1-related cytopathic effects when challenged with high doses of HIV-1(NL4-3). As measured by HIV-1 p24 assay, SV(AT)-transduced cells were protected from HIV-1(NL4-3) at challenge dose of 40 000 TCID(50) (MOI = 0.04). In addition, peripheral blood lymphocytes treated with SV(AT) were protected from HIV doses challenge up to 40 000 TCID(50) (MOI = 0.04). By Western blot analyses, the delivered alpha(1)AT inhibited cellular processing of gp160 to gp120 and decreased HIV-1 virion gp120. SV(AT) inhibited processing of p55(Gag) as well. Furthermore, high levels of uncleaved p55(Gag) protein were detected in HIV virus particles recovered from SV(AT)-transduced cells lines and primary lymphocytes. Thus, delivering alpha(1)AT using SV(AT) to human lymphocytes strongly inhibits replication of HIV-1, most likely by inhibiting the activities both of the cellular serine proteases involved in processing gp160 and of the aspartyl protease, HIV-1 PR, which cleaves p55(Gag). alpha(1)AT delivered by SV(AT) may represent a novel and effective strategy for gene therapy to interfere with HIV replication, by blocking a stage in the virus replicative cycle that has until now been inaccessible to gene therapeutic intervention.

Prospects for cationic polymers in gene and oligonucleotide therapy against cancer

Gene and antisense/ribozyme therapy possesses tremendous potential for the successful treatment of genetically based diseases, such as cancer. Several cancer gene therapy strategies have already been realized in vitro, as well as in vivo. A few have even reached the stage of clinical trials, most of them phase I, while some antisense strategies have advanced to phase II and III studies. Despite this progress, a major problem in exploiting the full potential of cancer gene therapy is the lack of a safe and efficient delivery system for nucleic acids. As viral vectors possess toxicity and immunogenicity, non-viral strategies are becoming more and more attractive. They demonstrate adequate safety profiles, but their rather low transfection efficiency remains a major drawback. This review will introduce the most important cationic polymers used as non-viral vectors for gene and oligonucleotide delivery and will summarize strategies for the targeting of these agents to cancer tissues. Since the low efficiency of this group of vectors can be attributed to specific systemic and subcellular obstacles, these hurdles, as well as strategies to circumvent them, will be discussed. Local delivery approaches of vector/DNA complexes will be summarized and an overview of the principles of anticancer gene and antisense/ribozyme therapy as well as an outline of ongoing clinical trials will be presented.

Approach to establishing a liver targeting gene therapeutic vector using naturally occurring defective hepatitis B viruses devoid of immunogenic T cell epitope

The development of liver-directed virus vector may play a crucial role in hepatic gene therapy. Hepatitis B virus (HBV) is the only known DNA virus that has hepatocyte specificity. In order to construct an efficient HBV-based vector for targeting the liver, we studied the potential use of naturally occurring defective HBVs obtained from hepatitis patients. The enhanced green fluorescent protein (EGFP) gene or small tag sequences (Flag) were introduced in frame into the deleted sites of the defective HBVs. One HBV defective in site for putative T cell epitope and a part of the polymerase gene tolerated EGFP insertion and was successfully packaged. This defective recombinant HBV harboring 48 bp Flag tag sequence instead of EGFP (rHBV-7-Flag) replicated well. Human primary hepatocytes could uptake rHBV-7-Flag virions, though in a low frequency, when exposed to the virions at a high density in the culture medium, and also express Flag tag sequences. This defective HBV-based vector may have a potential application in liver targeting gene therapy.

Evidence for the involvement of Gi2 in activation of extracellular signal-regulated kinases in hepatocytes

BACKGROUND

Activation of the extracellular signal-regulated kinases ERK1 and ERK2 in hepatocytes by prostaglandin (PG)F2alpha was recently found to be inhibited by pertussis toxin (PTX) suggesting a role for Gi proteins.

RESULTS

Targeting the Gi2alpha expression by a specific ribozyme inhibited the PGF2alpha -induced ERK1/2 activation in hepatocytes. On the other hand a non-cleaving form of the Gi2alpha ribozyme did not significantly decrease the ERK1/2 activation. In ribozyme-treated cells the Gi2alpha protein level was reduced, while the Gqalpha level was not affected thus confirming the specificity of the ribozyme.

CONCLUSION

The present data suggest an important role of Gi2 in PGF2alpha -induced ERK1/2 signaling in hepatocytes.

Preparation and properties of an alpha-1-protease inhibitor concentrate with high specific activity

BACKGROUND AND OBJECTIVES

Because the current demand for alpha-1-protease inhibitor (A1PI) exceeds the available supply, we aimed to develop a process for purification of A1PI from plasma which would achieve the highest possible degree of purity, specific activity and yield.

MATERIALS AND METHODS

A1PI was purified from Cohn fraction IV-1,4 using ethanol precipitation and Q-Sepharose chromatography. Ceramic hydroxyapatite chromatography was used as a final purification step. Two independent virus-inactivation procedures (chemical and vapour heating) were applied.

RESULTS

The resulting A1PI had an unprecedented high specific activity. In addition, the process led to the discovery of a new isoform of A1PI in isoelectric focusing gels.

CONCLUSION

The high specific activity of the A1PI preparation achieved with this process should allow a reduction of the A1PI total protein load necessary to achieve clinically relevant effects.

SV40-derived vectors provide effective transgene expression and inhibition of HIV-1 using constitutive, conditional,and pol III promoters

Vectors based on recombinant SV40 viruses (rSV40) are highly effective in delivering transgene expression driven by constitutive promoters. We tested here whether these vectors could be used with conditional promoters and promoters using RNA polymerase III transcription, with inhibition of HIV-1 by Tat activation response (TAR) decoys as a functional measure of effective transgene delivery and activity. TAR decoys inhibit HIV-1 Tat, a trans-activator of HIV-1 transcription. Tat acts early in the viral replicative cycle and is essential for efficient viral replication. We evaluated rSV40 gene delivery using two different inhibitors of Tat. One was a dual function polyTAR gene encoding 25 sequential TAR elements (TAR(25)), plus an antisense tat, driven either by HIV-1 long terminal repeat (HIV-LTR) as a conditional promoter, or by cytomegalovirus immediate-early promoter (CMV-IEP) as a constitutive promoter. The other inhibitor was a single TAR decoy, driven by the U6 small nuclear RNA promoter (U6-P). These decoys were delivered to unselected cells in two different human T lymphocyte lines and to unstimulated primary human peripheral blood mononuclear cells (pbmc). Gene delivery was confirmed by PCR, and expression by RT-PCR. By in situ hybridization analysis, >95% of cells were transduced. These transgene constructs protected all cell types tested from HIV-1, as measured by syncytia formation and p24 antigen release. Somewhat better inhibition of HIV-1 replication was achieved with HIV-1 long terminal repeat (HIV-1 LTR) as a conditional promoter than with the constitutive CMV-IEP. The U6-P was also very effective, driving a TAR(1) transcript. Cell viability was not detectably affected by TAR decoy expression. Thus, rSV40 vectors effectively deliver HIV-1-inhibitory RNAs using either constitutive or conditional pol II promoters, or using a pol III promoter. The versatility of this gene delivery system may prove to be useful in anti-HIV-1 therapeutics.

Ribozyme gene therapy: applications for molecular medicine

RNA enzymes--ribozymes--are being developed as treatments for a variety of diseases ranging from inborn metabolic disorders to viral infections and acquired diseases such as cancer. Ribozymes can be used both to downregulate and to repair pathogenic genes. In some instances, short-term exogenous delivery of stabilized RNA is desirable, but many treatments will require viral-mediated delivery to provide long-term expression of the therapeutic catalyst. Current gene therapy applications employ variations on naturally occurring ribozymes, but in vitro selection has provided new RNA and DNA catalysts, and research on trans-splicing and RNase P has suggested ways to harness the endogenous ribozymes of the cell for therapeutic purposes.

Biotechnology: alternatives to human plasma-derived therapeutic proteins

Proteins derived from human plasma have become critically important therapeutic products since their introduction in the 1940s. In the last 20 years, the tools of molecular biology have provided alternatives to the administration of the natural products. Recombinant analogues of Factor VIII and Factor IX are commercially available, and recombinant forms of other plasma proteins are under development. Genetic engineering also provides the opportunity to modify a natural protein to improve the efficiency with which it can be produced in vitro, or to change its therapeutic profile. More efficient production systems, such as transgenic plants or animals, may yield less costly therapies and a wider availability of products that are now in limited supply. Finally, gene therapy offers the prospect of permanently correcting conditions arising from deficiencies in any one of several plasma proteins, freeing individuals from the need to undergo periodic treatments with exogenous proteins.

A replication-deficient rSV40 mediates liver-directed gene transfer and a long-term amelioration of jaundice in gunn rats

BACKGROUND & AIMS

In the quest for a recombinant viral vector for liver-directed gene therapy that would permit both prolonged and efficient transgene expression in quiescent hepatocytes in vivo and repeated administration, we evaluated a recombinant simian virus 40 (rSV40).

METHODS

The rSV40 was generated through replacement of the DNA encoding for the T antigens (Tag) by the coding region of human bilirubin-uridine 5'-diphosphate-glucuronosyl-transferase (BUGT) complementary DNA (SV-hBUGT). Helper-free rSV40 units were generated at infectious titers of 5 x 10(9) to 1 x 10(10) infectious units (IU)/mL in a Tag-producing packaging cell line (COS-7 cells).

RESULTS

After 1, 3, or 7 daily infusions of 3 x 10(9) IU of SV-hBUGT through an indwelling portal vein catheter in bilirubin-UGT-deficient jaundiced Gunn rats, mean serum bilirubin concentrations decreased by 40%, 60% and 70%, respectively, in 3 weeks and remained at those levels throughout the duration of the study (40 days). Results of liver biopsies from SV-hBUGT-treated Gunn rats, but not from controls, were positive for human BUGT DNA, messenger RNA, and protein. Bilirubin-UGT activity in liver homogenates was 8%-12% of normal, and bilirubin glucuronides were excreted in bile. Immunostaining showed that >50%-60% of hepatocytes stably expressed the transgene. Portal vein infusion of an rSV40 expressing hepatitis B surface antigen (HBsAg) in a naive Gunn rat and a Gunn rat that had received 7 injections of SV-BUGT resulted in approximately equal levels of hepatic expression of HBsAg, indicating that multiple inoculations of SV-BUGT did not elicit neutralizing antibodies. Plasma alanine aminotransferase levels and liver histology remained normal despite repeated injections of rSV40.

CONCLUSIONS

rSV40 vectors may represent a significant advance toward gene therapy for metabolic diseases.

Ribozyme uses in retinal gene therapy

In this chapter we discuss the design, delivery and preclinical testing of mutation-specific ribozymes for the treatment of dominantly inherited retinal disease. We focus particular attention on the initial screening of ribozymes in vitro, because the activity of RNA enzymes in cell-free systems can be used to predict their suitability for animal experiments. Current techniques for delivering genes of interest to cells of the retina using viral vectors are then briefly surveyed emphasizing vector properties that best match to the needs of a ribozyme-based therapy. Using these considerations, analysis of ribozyme gene therapy for an autosomal dominant RP-like disease in a rodent model is outlined emphasizing the desirability of combining biochemical, morphological and electrophysiological measures of therapy. Finally, we describe alternative, perhaps more general, ribozyme approaches that have yet to be tested in the context of retinal disease.

Construction of HBV-specific ribozyme and its recombinant with HDV and their cleavage activity in vitro

AIM: To construct the recombinant of HDV cDNA and HBV-specific ribozyme gene by recombinant PCR in order to use HDV as a transporting vector carrying HBV-specific ribozyme into liver cells for inhibiting the replication of HBV.

METHODS: We separately cloned the ribozyme (RZ) gene and recombinant DVRZ (comprising HDV cDNA and HBV-specific ribozyme gene) into the downstream of T7 promoter of pTAdv-T vector and studied the in vitro cleavage activity of their transcripts (rRZ, rDVRZ) on target RNA (rBVCF) from in vitro transcription of HBV C gene fragment(BVCF).

RESULTS: Both the simple (rRZ) and the recombinant ribozyme rDVRZ could efficiently catalyze the cleavage of target RNA (rBVCF) under different temperatures (37 °C, 42 °C and 55 °C) and Mg²⁺ concentrations (10 mmol/L, 15 mmol/L and 20 mmol/L) and their catalytic activity tended to increase as the temperature was rising. But the activity of rRZ was evidently higher than that of rDVRZ.

CONCLUSION: The recombinant of HDV cDNA and ribozyme gene had the potential of being further explored and used in gene therapy of HBV infection.

Gene therapy using SV40-derived vectors: what does the future hold?

Effective genetic therapy requires both a fragment of genetic material to be used therapeutically and a means to deliver it. We began to study simian virus-40 (SV40) as a vector for gene transfer because available gene delivery vehicles did not provide for the full range of therapeutic uses. Other vectors are variably limited by immunogenicity, difficulties in production, restricted specificity, low titers, poor transduction efficiency, etc. In theory recombinant viral vectors based on SV40 (rSV40) should not, on the other hand, be similarly constrained. rSV40 vectors are easily manipulated and produced at very high titer, stable, lacking in immunogenicity, and capable of providing sustained high levels of transgene expression in both resting and dividing cells. The principle limitation of SV40-derived vectors is the size of the packageable insert (</=5 kb). The rationale for developing SV40 as a gene therapy vector is reviewed. Our studies with rSV40 gene transfer have focused mostly on hematopoietic progenitor cells (CD34+) and their derivatives, and on gene delivery to the liver. In both settings, in vitro and in vivo, SV40 has proven to be very effective. It is thus a promising gene delivery vehicle that can complement others currently in use or under development.

Participation of the melanocortin-1 receptor in the UV control of pigmentation

The cloning of the melanocortin-1 receptor (MC1R) gene from human melanocytes and the demonstration that these cells respond to the melanocortins alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) with increased proliferation and melanogenesis have renewed the interest in investigation the physiological role of these hormones in regulating human pigmentation. Alpha-melanocyte stimulating hormone and ACTH are both synthesized in the human epidermis, and their synthesis is upregulated by exposure to ultraviolet radiation (UVR). Activation of the MC1R by ligand binding results in stimulation of cAMP formation, which is a principal mechanism for inducing melanogenesis. The increase in cAMP is required for the pigmentary response of human melanocytes to UVR, and for allowing them to overcome the UVR-induced G1 arrest. Treatment of human melanocytes with alpha-MSH increases eumelanin synthesis, an effect that is expected to enhance photoprotection of the skin. Population studies have revealed more than 20 allelic variants of the MC1R gene. Some of these variants are overexpressed in individuals with skin type I or II, red hair, and poor tanning ability. Future studies will aim at further exploration of the role of these variants in MC1R function, and in determining constitutive human pigmentation, the response to sun exposure, and possibly the susceptibility to skin cancer.