Retroviral-mediated gene transfer into hepatocytes in vivo

Cell therapy in congenital inherited hepatic disorders

Congenital inherited hepatic disorders (CIHDs) are a set of diverse and heterogeneous group of genetic disorders leading to a defect in an enzyme or transporter. Most of these disorders are currently treated by liver transplantation as standard of care. Improved surgical techniques and post-operative care has led to a wider availability and success of liver transplantation program worldwide. However liver transplantation has its own limitations due to invasive surgery and lifelong use of immunosuppressive agents. Our experience from auxiliary liver transplantation (where right or the left lobe of the patient liver is replaced with a healthy liver donor) demonstrated successful treatment of the underlying defect of noncirrhotic metabolic disorder suggesting that whole liver replacement may not be necessary to achieve a change in phenotype. Large number of animal studies in human models of CIHD have shown success of hepatocyte transplantation leading to its human use. This review addresses the current state of human hepatocyte transplantation in the management of CIHDs with bottlenecks to its wider application and future perspectives.

Novel vectors and approaches for gene therapy in liver diseases

Gene therapy is becoming an increasingly valuable tool to treat many genetic diseases with no or limited treatment options. This is the case for hundreds of monogenic metabolic disorders of hepatic origin, for which liver transplantation remains the only cure. Furthermore, the liver contains 10-15% of the body's total blood volume, making it ideal for use as a factory to secrete proteins into the circulation. In recent decades, an expanding toolbox has become available for liver-directed gene delivery. Although viral vectors have long been the preferred approach to target hepatocytes, an increasing number of non-viral vectors are emerging as highly efficient vehicles for the delivery of genetic material. Herein, we review advances in gene delivery vectors targeting the liver and more specifically hepatocytes, covering strategies based on gene addition and gene editing, as well as the exciting results obtained with the use of RNA as a therapeutic molecule. Moreover, we will briefly summarise some of the limitations of current liver-directed gene therapy approaches and potential ways of overcoming them.

Polybrene induces neural degeneration by bidirectional Ca2+ influx-dependent mitochondrial and ER-mitochondrial dynamics

Hexadimethrine bromide (Polybrene) was once used clinically as a heparin neutralizer and has recently found use as a promoter in virus-mediated gene therapy trials and gene transfer in research. However, the potential for tissue-specific toxicity of polybrene at low doses has been ignored so far. Here, we found that after intracerebroventricular (ICV) polybrene injection, mice showed disability of movement accompanied neural death and gliosis in brain, and in human neurons, polybrene induces concentration-dependent neuritic beading and fragmentation. Mechanistically, polybrene induces a rapid voltage-dependent calcium channel (VDCC)-mediated influx of extracellular Ca²⁺. The elevated cytoplasmic Ca²⁺ activates DRP1, which leads to mitochondrial fragmentation and metabolic dysfunction. At the same time, Ca²⁺ influx induces endoplasmic reticulum (ER) fragmentation and tightened associations between ER and mitochondria, which makes mitochondria prone to Ca²⁺ overloading and ensuing permeability transition. These results reveal an unexpected neuronal toxicity of polybrene, wherein Ca²⁺ influx serves as a regulator for both mitochondrial dynamics and ER–mitochondrial remodeling.

Upgrading HepG2 cells with adenoviral vectors that encode drug-metabolizing enzymes: application for drug hepatotoxicity testing

INTRODUCTION

Drug attrition rates due to hepatotoxicity are an important safety issue considered in drug development. The HepG2 hepatoma cell line is currently being used for drug-induced hepatotoxicity evaluations, but its expression of drug-metabolizing enzymes is poor compared with hepatocytes. Different approaches have been proposed to upgrade HepG2 cells for more reliable drug-induced liver injury predictions. Areas covered: We describe the advantages and limitations of HepG2 cells transduced with adenoviral vectors that encode drug-metabolizing enzymes for safety risk assessments of bioactivable compounds. Adenoviral transduction facilitates efficient and controlled delivery of multiple drug-metabolizing activities to HepG2 cells at comparable levels to primary human hepatocytes by generating an 'artificial hepatocyte'. Furthermore, adenoviral transduction enables the design of tailored cells expressing particular metabolic capacities. Expert opinion: Upgraded HepG2 cells that recreate known inter-individual variations in hepatic CYP and conjugating activities due to both genetic (e.g., polymorphisms) or environmental (e.g., induction, inhibition) factors seems a suitable model to identify bioactivable drug and conduct hepatotoxicity risk assessments. This strategy should enable the generation of customized cells by reproducing human pheno- and genotypic CYP variability to represent a valuable human hepatic cell model to develop new safer drugs and to improve existing predictive toxicity assays.

Comparison between S+L- assay and LacZ marker rescue assay for detecting replication-competent gammaretroviruses

To avoid contamination of adventitious gammaretroviruses in biological products such as vaccines, it is necessary to check the master seed cells for manufacturing. There are several assays to detect infectious gammaretroviruses. Among these, sarcoma-positive, leukemia-negative (S+L-) assay is a classical infectivity assay, which is often recommended in governmental guidelines. The S+L- cells used in S+L- assay generate unique focus upon the infection of replication-competent gammaretroviruses. Although S+L- assay is well recognized for the detection, their applicability is questionable in some cases. On the other hand, LacZ marker rescue (LMR) assay detects infectious gammaretroviruses by transducing LacZ marker gene to the target cells, which shows lacZ-positive foci if the infectious virus is present. In this study, we compared LMR and S+L- assays for detection of a variety of endogenous and exogenous gammaretroviruses. As results, LMR assay could detect all gammaretroviruses examined. On the other hand, S+L- assay using feline S+L- cells, termed QN10S, could not detect porcine endogenous retrovirus (PERV) subgroups A/B. Further, S+L- mink cells could not detect feline leukemia virus subgroups B in addition to PERV-A/B. These data indicate that LMR assay is better suited to detect wider range of gammaretroviruses.

Gene therapies for hepatitis C virus

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis and infects approximately three to four million people per year, about 170 million infected people in total, making it one of the major global health problems. In a minority of cases HCV is cleared spontaneously, but in most of the infected individuals infection progresses to a chronic state associated with high risk to develop liver cirrhosis, hepatocellular cancer, or liver failure. The treatment of HCV infection has evolved over the years. Interferon (IFN)-α in combination with ribavirin has been used for decades as standard therapy. More recently, a new standard-of-care treatment has been approved based on a triple combination with either HCV protease inhibitor telaprevir or boceprevir. In addition, various options for all-oral, IFN-free regimens are currently being evaluated. Despite substantial improvement of sustained virological response rates, some intrinsic limitations of these new direct-acting antivirals, including serious side effects, the risk of resistance development and high cost, urge the development of alternative or additional therapeutic strategies. Gene therapy represents a feasible alternative treatment. Small RNA technology, including RNA interference (RNAi) techniques and antisense approaches, is one of the potentially promising ways to investigate viral and host cell factors that are involved in HCV infection and replication. With this, newly developed gene therapy regimens will be provided to treat HCV. In this chapter, a comprehensive overview guides you through the current developments and applications of RNAi and microRNA-based gene therapy strategies in HCV treatment.

Recent advances in developing nucleic acid-based HBV therapy

Chronic HBV infection remains an important public health problem and currently licensed therapies rarely prevent complications of viral persistence. Silencing HBV gene expression using gene therapy, particularly with exogenous activators of RNAi, holds promise for developing an HBV gene therapy. However, immune stimulation, off-targeting effects and inefficient delivery of RNAi activators remain problematic. Several new approaches have recently been employed to address these issues. Chemical modifications to anti-HBV synthetic siRNAs have been investigated and a variety of vectors are being developed for delivery of RNAi effectors. In this article, we review the potential utility of gene therapy for treating HBV infection.

Therapeutic effects of hepatocyte growth factor-overexpressing human umbilical cord blood-derived mesenchymal stem cells on liver fibrosis in rats

Fibrosis is a common end stage for a variety of liver diseases, including most chronic liver diseases, and results from an imbalance between collagen deposition and degradation. Mesenchymal stem cells (MSCs) have the ability to migrate into fibrotic livers and differentiate into hepatocytes. Hepatocyte growth factor (HGF) has potent anti-apoptotic and mitogenic effects on hepatocytes during liver injury and plays an essential role in the development and regeneration of the liver. In this study, human HGF-overexpressing human umbilical cord blood-derived MSCs (hHGF-HUCB-MSCs) were prepared using the pMEX Expression System, and the upregulation of hHGF expression was confirmed by RT-PCR and ELISA. HGF expressed by hHGF-HUCB-MSCs exerted a stimulatory effect on hepatocyte proliferation in vitro. hHGF-HUCB-MSCs were transplanted to investigate the therapeutic effects of these cells on carbon tetrachloride (CCL4)-induced liver fibrosis in a rat model. After 4 weeks of cell treatment once per week with 2 × 10(6) cells, biochemical analysis of the serum and histopathological analysis of the liver tissue were performed. The results of the biochemical analysis of the serum show that the hHGF-HUCB-MSC-treated group had higher levels of alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase, indicating the improvement of liver function. Histopathology showed that the hHGF-HUCB-MSC-treated group had reduction in the density of collagen fibres. Thus hHGF-HUCB-MSCs can enhance liver regeneration and could be useful for the treatment of patients with liver fibrosis or cirrhosis.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Improvement of hydrodynamics-based gene transfer of nonviral DNA targeted to murine hepatocytes

The liver is an important organ for supporting the life of an individual. Gene transfer toward this organ has been attempted in many laboratories to date; however, there have been few reports on improved liver-targeted gene delivery by using a nonviral vector. In this study, we examined the effect of various types of gene delivery carriers on enhancing the uptake and gene expression of exogenous DNA in murine hepatocytes when a hydrodynamics-based gene delivery (HGD) is performed via tail-vein injection. Mice were singly injected with a large amount of phosphate-buffered saline containing reporter plasmid DNA and/or with a gene delivery carrier. One day after the gene delivery, the animals' livers were dissected and subjected to biochemical, histochemical, and molecular biological analyses. The strongest signal from the reporter plasmid DNA was observed when the DNA was mixed with a polyethylenimine- (PEI-) based reagent. Coinjection with pCRTEIL (a loxP-floxed reporter construct) and pTR/NCre (a liver-specific Cre expression vector) resulted in the liver-specific recombination of pCRTEIL. The combination of PEI with HGD would thus be a valuable tool for liver-specific manipulation to examine the function of a gene of interest in the liver and for creating liver disease models.

A new extensively characterised conditionally immortal muscle cell-line for investigating therapeutic strategies in muscular dystrophies

A new conditionally immortal satellite cell-derived cell-line, H2K 2B4, was generated from the H2K^b-tsA58 immortomouse. Under permissive conditions H2K 2B4 cells terminally differentiate in vitro to form uniform myotubes with a myogenic protein profile comparable with freshly isolated satellite cells. Following engraftment into immunodeficient dystrophin-deficient mice, H2K 2B4 cells regenerated host muscle with donor derived myofibres that persisted for at least 24 weeks, without forming tumours. These cells were readily transfectable using both retrovirus and the non-viral transfection methods and importantly upon transplantation, were able to reconstitute the satellite cell niche with functional donor derived satellite cells. Finally using the Class II DNA transposon, Sleeping Beauty, we successfully integrated a reporter plasmid into the genome of H2K 2B4 cells without hindering the myogenic differentiation. Overall, these data suggest that H2K 2B4 cells represent a readily transfectable stable cell-line in which to investigate future stem cell based therapies for muscle disease.

A robust lentiviral pseudotype neutralisation assay for in-field serosurveillance of rabies and lyssaviruses in Africa

The inflexibility of existing serological techniques for detection of rabies in surveillance constrains the benefit to be gained from many current control strategies. We analysed 304 serum samples from Tanzanian dogs for the detection of rabies antibodies in a pseudotype assay using lentiviral vectors bearing the CVS-11 envelope glycoprotein. Compared with the widely used gold standard fluorescent antibody virus neutralisation assay, a specificity of 100% and sensitivity of 94.4% with a strong correlation of antibody titres (r=0.915) were observed with the pseudotype assay. To increase the assay's surveillance specificity in Africa we incorporated the envelope glycoprotein of local viruses, Lagos bat virus, Duvenhage virus or Mokola virus and also cloned the lacZ gene to provide a reporter element. Neutralisation assays using pseudotypes bearing these glycoproteins reveal that they provide a greater sensitivity compared to similar live virus assays and will therefore allow a more accurate determination of the distribution of these highly pathogenic infections and the threat they pose to human health. Importantly, the CVS-11 pseudotypes were highly stable during freeze-thaw cycles and storage at room temperature. These results suggest the proposed pseudotype assay is a suitable option for undertaking lyssavirus serosurveillance in areas most affected by these infections.

Identification of a feline leukemia virus variant that can use THTR1, FLVCR1, and FLVCR2 for infection

The pathogenic subgroup C feline leukemia virus (FeLV-C) arises in infected cats as a result of mutations in the envelope (Env) of the subgroup A FeLV (FeLV-A). To better understand emergence of FeLV-C and potential FeLV intermediates that may arise, we characterized FeLV Env sequences from the primary FY981 FeLV isolate previously derived from an anemic cat. Here, we report the characterization of the novel FY981 FeLV Env that is highly related to FeLV-A Env but whose variable region A (VRA) receptor recognition sequence partially resembles the VRA sequence from the prototypical FeLV-C/Sarma Env. Pseudotype viruses bearing FY981 Env were capable of infecting feline, human, and guinea pig cells, suggestive of a subgroup C phenotype, but also infected porcine ST-IOWA cells that are normally resistant to FeLV-C and to FeLV-A. Analysis of the host receptor used by FY981 suggests that FY981 can use both the FeLV-C receptor FLVCR1 and the feline FeLV-A receptor THTR1 for infection. However, our results suggest that FY981 infection of ST-IOWA cells is not mediated by the porcine homologue of FLVCR1 and THTR1 but by an alternative receptor, which we have now identified as the FLVCR1-related protein FLVCR2. Together, our results suggest that FY981 FeLV uses FLVCR1, FLVCR2, and THTR1 as receptors. Our findings suggest the possibility that pathogenic FeLV-C arises in FeLV-infected cats through intermediates that are multitropic in their receptor use.

Treating liver cirrhosis in dogs with hepatocyte growth factor gene therapy via the hepatic artery

BACKGROUND/PURPOSE

Liver cirrhosis, an irreversible result of chronic liver disease, has had no effective therapy except liver transplantation. We previously reported successful therapy of liver cirrhosis in rats using the hepatocyte growth factor gene. We presently performed hepatocyte growth factor gene therapy in dogs with liver cirrhosis to examine the feasibility for clinical use.

METHODS

Liver cirrhosis was established in beagles by administrating dimethylnitrosamine. Naked human hepatocyte growth factor gene or naked LacZ gene was injected repeatedly into livers via the hepatic artery using a porter catheter in dogs with cirrhosis.

RESULTS

Human hepatocyte growth factor gene expression was detected in livers by immunohistochemical staining and an enzyme-linked immunosorbent assay. Serum liver function test results improved with hepatocyte growth factor gene therapy, which also inhibited hepatic transforming growth factor-beta1expression and reversed fibrosis in cirrhotic liver, improving survival of the dogs.

CONCLUSION

As naked hepatocyte growth factor gene therapy via the hepatic artery proved simple, safe, and effective in larger animals with cirrhosis, this therapy may be clinically applicable.

Gene therapy for inborn errors of liver metabolism: progress towards clinical applications

The treatment for inborn errors of liver metabolism is based on dietary, drug, and cell therapies (orthotopic liver transplantation). However, significant morbidity and mortality still remain, and alternative strategies are needed. Gene replacement therapy has the potential of providing a definitive cure for patients with these diseases. Significant progress has been made in the pre-clinical arena and achievement of efficacy in different animal models has been reported using multiple gene transfer technologies. This article summarizes the gene transfer strategies being investigated, the pre-clinical data, and the available early clinical results for inborn errors of liver metabolism.

Preservation of hepatic phenotype in lentiviral-transduced primary human hepatocytes

Lentiviral vectors effectively transduce both dividing and non-dividing cells and stably integrate into the genome of the host cell. In this study, we evaluated the usefulness of a lentiviral system for genetic modulation of primary human hepatocyte cultures. Infection with GFP-expressing lentivectors shows that Huh7 and HepG2 cell lines, as well as primary cultures of human hepatocytes, are efficiently transduced by lentiviral vectors. Real-time RT-PCR analyses demonstrate that infection with lentivectors does not alter hepatic hallmarks such as the expression of the nuclear receptors CAR, PXR, RXR alpha, or HNF4 alpha, or expression of the secretory protein, albumin. Additionally, infected hepatocytes retain the capacity for CYP3A4 induction in response to treatment with phenobarbital, a uniquely sensitive indicator of hepatic differentiation status. Lentivectors may be used for both over-expression and knockdown analyses in primary hepatocytes, as demonstrated in this study by >200-fold CAR over-expression and knockdown of CAR to less than 40% of endogenous levels, with corresponding effects on CYP2B6 expression. In summary, lentiviral vectors provide a novel methodology by which primary human hepatocytes may be stably genetically manipulated, with minimal effects on the differentiated hepatic phenotype. These approaches offer considerable advantage over current methodologies, providing a valuable alternative for use in pharmacological and toxicological investigations involving primary human hepatocyte models and potentially for cell-based therapeutics to treat hepatic dysfunction in vivo.

The GLN family of murine endogenous retroviruses contains an element competent for infectious viral particle formation

Several families of endogenous retroviruses (ERVs) have been identified in the mouse genome, in several instances by in silico searches, but for many of them it remains to be determined whether there are elements that can still encode functional retroviral particles. Here, we identify, within the GLN family of highly reiterated ERVs, one, and only one, copy that encodes retroviral particles prone to infection of mouse cells. We show that its envelope protein confers an ecotropic host range and recognizes a receptor different from mCAT1 and mSMIT1, the two previously identified receptors for other ecotropic mouse retroviruses. Electron microscopy disclosed viral particle assembly and budding at the cell membrane, as well as release of mature particles into the extracellular space. These particles are closely related to murine leukemia virus (MLV) particles, with which they have most probably been confused in the past. This study, therefore, identifies a new class of infectious mouse ERVs belonging to the family Gammaretroviridae, with one family member still functional today. This family is in addition to the two MLV and mouse mammary tumor virus families of active mouse ERVs with an extracellular life cycle.

In vivo imaging of transplanted hepatocytes with a 1.5-T clinical MRI system--initial experience in mice

The feasibility of in vitro mature mouse hepatocyte labeling with a novel iron oxide particle was assessed and the ability of 1.5-T magnetic resonance imaging (MRI) to track labeled mouse hepatocytes in syngenic recipient livers following intraportal cell transplantation was tested. Mouse hepatocytes were incubated with anionic iron oxide nanoparticles at various iron concentrations. Cell viability was assessed and iron oxide particle uptake quantified. Labeled hepatocytes were intraportally injected into 20 mice, while unlabeled hepatocytes were injected into two mice. Liver T2 values, spleen-to-muscle relative signal intensity (RI( spleen/muscle )), and liver-to-muscle relative signal intensity (RI( liver/muscle )) on gradient-echo T2-weighted imaging after injection of either labeled or unlabeled hepatocytes were compared with an ANOVA test followed by Fisher's a posteriori PLSD test. Livers, spleens and lungs were collected for histological analysis. Iron oxide particle uptake was saturable with a maximum iron content of 20 pg per cell and without viability alteration after 3 days of culture. Following labeled-cell transplantation, recipient livers showed well-defined nodular foci of low signal intensity on MRI--consistent with clusters of labeled hepatocytes on pathological analysis--combined with a significant decrease in both liver T2 values and liver-to-muscle RI( liver/muscle ) (P = 0.01) with minimal T2 values demonstrated 8 days after transplantation. Conventional MRI can demonstrate the presence of transplanted iron-labeled mature hepatocytes in mouse liver.

Gene therapy for liver enzyme deficiencies: what have we learned from models for Crigler-Najjar and tyrosinemia?

The liver is the site of numerous metabolic inherited diseases. It has unique features that make it compliant to various gene therapy approaches. Many vector types and gene delivery strategies have been evaluated during the past 20 years in a number of animal models of metabolic liver diseases. However, the complete cure of inherited liver deficiencies by gene therapy in relevant animal models were only reported recently. These successes were achieved thanks to major advances in vector technology. In this review, we will focus on Crigler-Najjar disease and hereditary tyrosinemia, two paradigmatic examples of the two categories of enzymatic liver deficiencies: type I, in which the genetic defect does not affect liver histology; and type II, in which liver lesions are present.

Influence of disease stage on polyethylenimine-mediated plasmid DNA delivery in murine hepatitis

In order to determine the influence of hepatic disease-stage on polyethylenimine-mediated gene delivery, we investigated branched and linear polyethylenimine (B-PEI, L-PEI)-mediated plasmid DNA delivery with time in murine hepatitis induced by a subcutaneous injection of tetrachloro carbon (CCl(4)). Plasmid DNA (pDNA) encoding firefly luciferase was used as the model reporter gene. We determined luciferase activity in various organs of CCl(4)-treated mice and control mice after an intravenous administration of B-PEI and L-PEI/pDNA complexes. Both B-PEI and L-PEI/pDNA complexes showed significantly lower gene expression in the liver, spleen, and lung at the stage of severe hepatitis (18 h after CCl(4) injection), whereas the complexes induced gene expression in the liver at the liver regeneration stage (48 h after CCl(4) injection). Significant differences in gene expressions between CCl(4)-treated mice and control mice vanished in most organs at the hepatitis subsidence stage (168 h after CCl(4) injection), indicating that the influence of hepatitis induced by CCl(4) was reversible with PEI-mediated gene delivery. Our findings demonstrated that murine hepatitis induced by CCl(4) could influence polyethylenimine-mediated plasmid DNA delivery according to the disease stage. These results indicate the necessity of considering the timing and dose of gene therapy according to the disease stage.

Development of a Moloney murine leukemia virus-based pseudotype anti-HIV assay suitable for accurate and rapid evaluation of HIV entry inhibitors

There has been increasing interest in the identification of novel HIV entry inhibitors. For the discovery of these entry inhibitors, robust surrogate anti-HIV assays are highly desired. The authors report a novel anti-HIV assay system using Moloney murine leukemia viruses (MMLVs) pseudotyped with cytoplasmic tail-truncated HIV envelope protein gp140. These pseudotyped MMLV-HIVgp140 viral particles carry luciferase transcripts; therefore, robust luciferase signal can be detected in cells infected by these pseudotypes. Polycationic agent polybrene and spinoculation markedly enhanced the infection efficiency of these pseudotypes. It was demonstrated that the tropism of these pseudotypes is dependent on the pseudotyped HIV envelope proteins. MMLV viruses pseudotyped with gp140 from an R5 HIV virus specifically infect CCR5-expressing cells, and viruses pseudotyped with gp140 from an X4 HIV virus specifically infect CXCR4-expressing cells. Furthermore, CCR5 antagonists inhibited only MMLV-gp140(R5) infections, and CXCR4 antagonists inhibited only MMLV-gp140(X4) infections. A variety of known HIV entry inhibitors were tested in both R5- and X4-dependent pseudotype antiviral assays, and the IC50 values generated were consistent with published results. The pseudotype antiviral assay was also used in the characterization of hundreds of novel CCR5 antagonists. The IC50 values determined in this assay were compared with those determined in HIV antiviral and cell-cell fusion (CCF) assays, and good correlation was found between pseudotype antiviral assay and HIV antiviral assay (R2 = 0.9) or CCF assay (R2 = 0.8).

Partial Hepatectomy Enhances Polyethylenimine-Mediated Plasmid DNA Delivery

Polyethylenimine (PEI) is widely used for non-viral transfection in vitro and in vivo. Hepatectomy is an interesting and considerable factor modifying PEI-mediated gene expression. We investigated the gene expression in mice over time following partial hepatectomy after an intravenous injection of PEI/plasmid DNA (pDNA) complex. pDNA encoding firefly luciferase was used as the model reporter gene. The hepatectomized liver was rapidly regenerated until 72 h. After 168 h, the liver weight of hepatectomized mice was similar to that of control mice. Slight liver function impairment was only observed at 1-24 h after hepatectomy in alanine aminotransferase and aspartate aminotransferase levels. Luciferase activity in the liver of partial hepatectomized mice at 48 h after partial hepatectomy increased by 70 times compared with that of control mice; however, luciferase activities did not significantly differ between hepatectomized mice and control mice in the spleen, lung, kidney, and heart. Among the lobes, luciferase activity by gram of tissue was not significantly different, indicating that gene expression enhancement by partial hepatectomy occurred equally throughout the liver. In conclusion, our findings demonstrate that liver resection is an influencing factor on PEI-mediated gene delivery in mice. These results indicate the necessity of considering cell division in PEI-mediated pDNA delivery.

Mixed hematopoietic molecular chimerism results in permanent transgene expression from retrovirally transduced hepatocytes in mice

BACKGROUND

Cytotoxic immune elimination of transduced hepatocytes may limit gene therapy for inherited liver diseases. Using beta-galactosidase as a marker gene, we studied whether creation of mixed beta-galactosidase molecular hematopoietic chimerism could induce tolerance to beta-galactosidase-transduced hepatocytes.

METHODS

Molecular hematopoietic chimerism was established in irradiated recipient mice by transplantation of either a mixture of wild-type and beta-galactosidase-transgenic bone marrow or autologous bone marrow stem cells that were transduced with beta-galactosidase lentiviral vectors. After transplantation, mice were hepatectomized and injected with beta-galactosidase recombinant retroviruses to transduce regenerating hepatocytes. We monitored the presence of beta-galactosidase-expressing hepatocytes as well as the appearance of anti-beta-galactosidase antibodies during the time.

RESULTS

In control animals, anti-beta-galactosidase antibodies and cytotoxic T-lymphocyte (CTL) response developed as early as 3 weeks after gene transfer. Transduced hepatocytes disappeared concomitantly. In bone marrow transplanted mice, tolerance could be observed in a significant proportion of animals. Tolerance resulted in permanent liver transgene expression and was absent unless a chimerism above 1% was achieved, demonstrating a threshold effect.

CONCLUSIONS

Creation of a molecular hematopoietic chimerism can result in transgene tolerance and evade immune rejection of retrovirally transduced hepatocytes. This strategy may be useful for hepatic inherited diseases in which the transgene product behaves as a non-self protein.

Injection of skeletal muscle-derived cells into the penis improves erectile function

We investigated the effect of intrapenile injection of muscle-derived cells (MDC) on the erectile function in rats with bilateral cavernous nerve injury. Rat MDC were harvested and transduced with a retrovirus expressing the lacZ gene. Hanks' balanced salt solution (HBSS) (20 microl) or MDC (1 x 10(6) cells/side) were injected in each corpora cavernosa immediately before bilateral cavernous nerve transection. Intracavernous pressures (ICP) were measured 2 or 4 weeks after surgery with electrical stimulation of the pelvic nerves. Mean maximal ICP of sham group was significantly lower than that of control group both at 2 and 4 weeks after surgery. When MDC were injected into the penis, ICP improved over the sham-injected group at both 2 and 4 weeks after surgery. Percent area of PGP 9.5 staining was significantly greater in MDC-injected penis than in sham-injected at 2 and 4 weeks. Penile MDC injection can facilitate recovery of injured penile innervation and improve erectile function.

A tissue-engineered suburethral sling in an animal model of stress urinary incontinence

OBJECTIVE

To create and evaluate the functional effects of a tissue-engineered sling in an animal model of stress urinary incontinence (SUI).

MATERIALS AND METHODS

Twenty female Sprague-Dawley rats were divided into four equal groups: a control group (C) had no intervention before the leak-point pressure (LPP) was measured; a denervated group (D) had bilateral proximal sciatic nerve transection (PSNT) and periurethral dissection with no sling placed; group S had concomitant bilateral PSNT and a suburethral sling of small intestinal submucosa (SIS) placed; and group (M) had concomitant bilateral PSNT with implantation of a tissue-engineered sling. The suburethral sling was placed via a transabdominal approach with the sling sutured to the pubic bone. Tissue-engineered slings were prepared with muscle-derived cells obtained via the pre-plate technique and subsequently seeded for 2 weeks on a SIS scaffold. Suburethral slings were implanted 2 weeks before LPP testing, using the vertical-tilt method.

RESULTS

Surgically placing a suburethral sling is feasible in the female rat, with few complications. LPPs from both sling groups (S and M) were not significantly different from untreated controls (C). The S, M and C groups all had significantly higher LPPs than group D. Importantly, no rat from either sling group (S and M) had signs of urinary retention.

CONCLUSIONS

Placing tissue-engineered slings in an animal model of SUI resulted in LPP values that were not significantly different from those in untreated control or SIS (S) groups. These data show that incorporating muscle stem cells into SIS slings does not adversely alter the advantageous mechanical properties of the SIS sling in a model of SUI, and provide the basis for future functional studies of tissue-engineered sling materials with long-term retention.

Ameliorating effect of hepatocyte growth factor on inflammatory bowel disease in a murine model

Hepatocyte growth factor (HGF), a multifunctional cytokine, accelerates intestinal epithelial proliferation. We studied the effects of HGF in mice with trinitrobenzene sulfonic acid-induced colitis, which shows clinical and molecular resemblance to Crohn's disease. Mice with colitis repeatedly were transfected intramuscularly with human HGF cDNA. Weight, survival, histopathology, proinflammatory cytokine mRNAs, and leukocyte infiltration were assessed. Treatment with HGF cDNA induced tyrosine phosphorylation of intestinal c-Met/HGF receptors, inhibited apoptosis, and promoted mitosis in intestinal epithelial cells, accelerating intestinal epithelial restoration and suppressing inflammation. Transfection with HGF cDNA markedly suppressed intestinal mRNA expression of T-helper 1 cytokines such as interleukin-12 and -1beta, interferon-gamma, and tumor necrosis factor-alpha. Numbers of total and CD4-positive T cells, neutrophils, and myloperoxidase activity in intestinal epithelium were diminished by HGF gene transfer, which also prevented weight loss, and improved survival. HGF might prove useful for controlling inflammatory bowel disease.

Adjuvant interleukin-12 gene therapy for the management of colorectal liver metastases

In humans, no efficient treatment exists not only against multifocal liver metastases (LM) but also against recurrent microscopic liver metastases within the liver remnant following curative liver resection. Furthermore, in nonmultifocal LM, partial liver resection could be performed, but in more than 50% of the patients, tumor recurrence within liver remnant is observed, partly due to the growth of dormant cancer cells in the setting of postoperative host immune dysfunction. We investigated the therapeutic potential of interleukin-12 (IL-12) immuno-gene therapies in these experimental models under total vascular exclusion (TVE) of the liver. In rats with multiple LM of DHDK12 colon cancer cells, we observed a significant reduction in tumor volume after retroviral-mediated gene transfer of either herpes simplex virus thymidine kinase (HSV1-TK) and ganciclovir (GCV) administration, or IL-12. Combined treatment with HSV1-TK/GCV and IL-12 resulted in improved tumor volume reduction and even survival. In rats with recurrent microscopic DHDK12 LM established after partial liver resection, we observed significantly decreased recurrent tumor volumes and increased survival after retroviral-mediated IL-12 gene transfer. In both settings, immunohistological analysis revealed that IL-12 immuno-gene therapy was accompanied by an infiltration of CD8+ T lymphocytes within the tumors. Altogether, our results suggest that IL-12 adjuvant gene therapy could improve the management of patients with either resectable or unresectable LM.

Naked DNA for Liver Gene Transfer

The majority of acquired and inherited genetic disorders, including most inborn errors of metabolism, are manifested in the liver. Therefore, it is hardly any surprise to see a large number of Medline reports describing gene therapy efforts in preclinical settings directed toward this organ (Inoue et al., 2004; Oka and Chen, 2004). Of late, non-viral vectors have garnered a lot of attention from the biomedical research community engaged in liver gene therapy (Gupta et al., 2004). However, the first initiative toward gene transfer to the liver using a non-viral approach was taken by Hickman et al. (1994), who applied the technique of naked DNA injection pioneered by Wolff (1990) for skeletal muscle. Direct injection of naked DNA resulted in low, variable and localized gene expression in the rat liver. Consequently, several developments reported in the literature since then aimed to improve hepatic gene expression by employing both surgical and nonsurgical methods. These developments include the exploitation of the unique vasculature of liver as well as the use of electric and mechanical force as an adjunct to the systemic administration of the naked plasmid gene. This chapter focuses on these developments reported from various laboratories, including ours. In addition, the underlying mechanism responsible for the dramatic increase in gene expression using these latest approaches for non-viral gene transfer to the liver is also discussed.

Liver gene therapy: advances and hurdles

Liver gene therapy is being developed as an alternative to orthotopic liver transplantation, which is the only effective therapy for many liver diseases. The liver has unique features that make it attractive for in vivo and ex vivo gene transfer. In vivo approach is far less invasive than ex vivo approach, although in most cases, host immune response directed against the transgene product and/or vector particles severely impairs the efficiency of gene transfer, and precludes long-term transgene expression after in vivo gene delivery. Ex vivo approach allows for an elective targeting of the hepatocytes, avoiding that the transgene be expressed in professional antigen-presenting, but is faced with the low in vitro proliferative ability of hepatocytes, and to the low in vivo liver repopulating ability of transplanted cells. In some specific situations where immune response was controlled or transplanted cells had a strong growth advantage over host hepatocytes, gene transfer resulted in long-term and complete correction of a liver genetic defect. In this review, we will outline the liver diseases that may benefit from gene therapy, the vector technology under investigation, the advances and the problems to be overcome.

Mature hepatocytes are the source of small hepatocyte-like progenitor cells in the retrorsine model of liver injury

BACKGROUND/AIMS

Mature hepatocytes divide to restore liver mass after injury. However, when hepatocyte division is impaired by retrorsine poisoning, regeneration proceeds from another cell type: the small hepatocyte-like progenitor cells (SHPCs). Our aim was to test whether SHPCs could originate from mature hepatocytes.

METHODS

Mature hepatocytes were genetically labeled using retroviral vectors harboring the beta-galactosidase gene. After labeling, retrorsine was administered to rats followed by a partial hepatectomy to trigger regeneration. A liver biopsy was performed one month after surgery and rats were sacrificed one month later.

RESULTS

We observed the proliferation of small hepatocytes arranged in clusters in liver biopsies. These cells expressed Ki67 antigen and displayed a high mitotic index. At sacrifice, regeneration was completed and clusters had merged. A significant proportion of clusters also expressed beta-galactosidase demonstrating their origin from labeled mature hepatocytes. Finally, the overall proportion of beta-galactosidase positive cells was identical at the time of hepatectomy as well as in liver biopsy and at sacrifice.

CONCLUSIONS

The constant proportion of beta-galactosidase positive cells during the regeneration process demonstrates that mature hepatocytes are randomly recruited to proliferate and compensate parenchyma loss in this model. Furthermore, mature hepatocytes are the source of SHPC after retrorsine injury.

Characteristics of murine histidinaemia and its potential for genetic manipulation

BACKGROUND

Histidinaemia is an autosomal recessive disorder affecting the hepatic enzyme histidine ammonia lyase (histidase) resulting in elevated plasma and urinary histidine and is prototypic of a series of hepatic cytosolic enzyme defects.

AIMS

To characterise the physiology of murine histidinaemia with respect to histidine excretion and catabolism, and explore the potential for manipulating cellular and whole body histidase metabolism by gene transfer.

MATERIALS AND METHODS

We studied his/his mice which have a G to A substitution in the gene encoding histidase, using both in vitro transduction of isolated hepatocytes by lipofection with wild-type histidase cDNA, and in vivo transduction of whole liver using a retroviral construct.

RESULTS AND CONCLUSION

Histidase cDNA expression restored histidase activity in vivo and in vitro towards normal levels, demonstrated both at the cellular level and by whole body metabolic studies, establishing the potential of this model for the development of new gene therapeutic approaches.

Anti-cancer effect of adenovirus p53 on human cervical cancer cell growth in vitro and in vivo

To evaluate anti-tumor effects of recombinant adenovirus p53, time-course p53, E6 expression, and cell growth inhibition were investigated in vitro and in vivo using cervical cancer cell lines such as CaSki, SiHa, HeLa, HeLaS3, C33A, and HT3. The cell growth inhibition was studied via cell count assay, MTT assay and neutral red assay. After transfecting AdCMVp53 into SiHa cells-xenografted nude mice, the transduction efficiency and anti-tumor effect were investigated for a month. The results showed that adenoviral p53 expression induced significant growth suppression on the cancer cells, in which E6 transcript was strongly repressed, and that the expression of p53 and E6 were remarkably dependent on each cell type. The transduction efficiency was highly maintained in vivo as well as in vitro, and the size of tumor was remarkably decreased in comparison with AdCMVLacZ control. The results suggest that the adenovirus-mediated p53 gene transfection was done very effectively in vitro and in vivo experiment, and the cell growth was suppressed via p53-dependent apoptotic cell death, and that the anti-tumor effect could be related to E6 and p53 expression pattern.

Intraurethral muscle-derived cell injections increase leak point pressure in a rat model of intrinsic sphincter deficiency

OBJECTIVES

To determine whether allogenic muscle-derived cells (MDCs) could restore sphincter function in rats with intrinsic sphincter deficiency (ISD). ISD denotes a malfunction of the urethral sphincter.

METHODS

ISD was produced in 25 adult female Sprague-Dawley rats by cauterizing tissues lateral to the mid-urethra. One week after cauterization, 1.5 x 10(6) MDCs, genetically engineered for beta-galactosidase expression, was injected into the mid-urethra in 16 rats. Another 9 rats were injected with Hanks' balanced salt solution after cauterization. As a control, 9 normal rats underwent a sham operation. Sphincter function was studied using the vertical tilt table/intravesical pressure clamp technique to measure leak point pressures (LPPs). The fate of the MDCs was assessed using LacZ staining.

RESULTS

The injection of MDCs increased the LPP without affecting bladder function. The mean LPP of the control rats 2, 4, and 6 weeks after the sham operation was 49.8 +/- 1.3, 51.2 +/- 1.5, and 51.6 +/- 2.0 cm H2O, respectively. The mean LPP of the rats 2, 4, and 6 weeks after cauterization and Hanks' balanced salt solution injection was 17.2 +/- 1.4, 26.9 +/- 1.9, and 25.5 +/- 1.3 cm H2O, respectively. The mean LPP of the rats 2, 4, and 6 weeks after cauterization and MDC injection was 38.2 +/- 2.2, 43.1 +/- 2.6, and 51.5 +/- 0.9 cm H2O, respectively. LacZ staining confirmed that MDC had integrated within the striated muscle layer of the cauterized urethra.

CONCLUSIONS

The injection of intraurethral MDCs improved sphincter function in rats with ISD and may provide an attractive alternative to current treatments.

Regeneration of skeletal muscle from transplanted immortalised myoblasts is oligoclonal

Myoblasts transplanted into muscles of recipient mice mostly die, only a minor stem cell-like subpopulation surviving and participating in muscle regeneration. To investigate this phenomenon further, we used a retrovirus expressing beta-galactosidase to provide a unique marker for satellite-cell-derived muscle precursor cells, before transplanting them into myopathic mdx nu/nu mouse muscle. We employed inverse polymerase chain reaction to identify viral integrations, to follow the fate of clones present within the injected cells. Mass-infected cultures contained many marked clones, some of which contributed disproportionately to muscle regeneration. Although no particular clones showed overall predominance, some were present in more than one injected muscle, an eventuality unlikely to arise by chance. Conversely, in grafts of muscle precursor cells that had either been labelled as sparse satellite-cell derived cultures, or had been cloned, all clones were shown to be able to survive and form muscle in vivo. Moreover, all clones contributed to further generations of new-formed muscle fibres following a series of injuries administered to injected muscles, demonstrating that some cells of each clone had been retained as stem-cell-like muscle precursors. Furthermore, retrovirally marked satellite-cell-derived clones were derived from muscles that had been injected with marked muscle precursor cells. These cells formed muscle following their transplantation into a new host mouse, confirming their stem cell properties.

Recombinant adenovirus-p53 gene transfer and cell-specific growth suppression of human cervical cancer cells in vitro and in vivo

PURPOSE

We investigated the time-course expression patterns of p53 and E6 on cervical cancer cells to obtain a molecular level understanding of cell-dependent tumor growth suppression effects of recombinant adenovirus expressing p53 in vitro and in vivo.

METHODS

Four human papillomavirus (HPV)-infected human cervical cancer cell lines (HPV 16-positive cells, CaSki and SiHa cells; and HPV 18-positive cells, HeLa and HeLaS3 cells) were used. Also, HPV negative C33A and HT3 cell line that has a mutation on p53 gene were used. After infection with AdCMVp53, the cell growth inhibition was studied via cell count assay, MTT assay, and Neutral red assay. After transfecting AdCMVp53 and AdCMVLacZ into the cancer cells-xenografted nude mice, antitumor effects were investigated for 1 month, respectively.

RESULTS

For each cervical cancer cell, IC50 was as follows; CaSki (68.5 multiplicity of infection, or MOI), SiHa (43.5 MOI), HeLa (31 MOI), HeLaS3 (42 MOI), C33A (21 MOI), and HT3 (62 MOI). In particular, complete inhibition of cell growth was observed at 125 MOI in both CaSki and SiHa cells. However, the complete inhibition was detected at 62.5 MOI in HeLa and HeLaS3. In contrast, at these MOI, no suppression of cell growth was observed when cells were infected with recombinant adenovirus expressing beta-gal as a negative control. The levels of p53 protein were notably expressed in CaSki and HeLa more than in SiHa and HeLaS3 on days 2 and 4. However, the p53 was only detected in HeLaS3 on day 6. In contrast, p53 expression was continually maintained in C33A and HT3 during the same periods. After transfection AdCMVp53 into CaSki- and SiHa-xenografted nude mice, the size of tumor was remarkably decreased in SiHa cells as compared to AdCMVLacZ transfection.

CONCLUSION

The adenovirus-mediated p53 gene transfection was done effectively in vitro and in vivo. Also, the antitumor effects were accomplished via differential role of p53-specific apoptotic cell death, which is dependent upon the cervical cancer cell line.

Comparison of serum sensitivities of pseudotype retroviruses produced from newly established packaging cell lines of human and feline origins

To apply retrovirus vectors for in vivo gene therapy in cats, it is necessary to develop vector systems that are not inactivated by cat serum. In this study, the retrovirus packaging cell lines 2SC-1 and AHCeB7 were newly established from human embryonic kidney (HEK) 293 and feline fibroblastic AH927 cells, respectively. Then the sensitivities of pseudotype viruses released from these cell lines to fresh sera from humans and cats were compared. Pseudotype viruses from the 2SC-1 cells were inactivated efficiently by cat serum but not by human serum. Pseudotype viruses from the AHCeB7 cells were also inactivated efficiently by human serum, however they were rather resistant to cat serum. When the xenoantigenicity of the cell lines was examined by flow cytometry, AH927 cells reacted with human serum, however, HEK293 cells did not react with cat serum. These results suggested that pseudotype viruses from 2SC-1 cells were inactivated by the fresh cat serum in an antibody-independent manner. Chelating experiments revealed that certain temperature-sensitive factor(s) other than complements might be involved in the inactivation. The usage of feline cells as packaging cells is suitable for in vivo gene therapy in cats.

Feline foamy virus genome and replication strategy

Crucial aspects of the foamy virus (FV) replication strategy have so far only been investigated for the prototypic FV (PFV) isolate, which is supposed to be derived from nonhuman primates. To study whether the unusual features of this replication pathway also apply to more-distantly related FVs, we constructed feline FV (FFV) infectious molecular clones and vectors. It is shown by quantitative RNA and DNA PCR analysis that FFV virions contain more RNA than DNA. Full-length linear DNA was found in extracellular FFV by Southern blot analysis. Similar to PFV, azidothymidine inhibition experiments and the transfection of nucleic acids extracted from extracellular FFV indicated that DNA is the functional relevant FFV genome. Unlike PFV, no evidence was found indicating that FFV recycles its DNA into the nucleus.

Hepatocyte growth factor gene transfer into the liver via the portal vein using electroporation attenuates rat liver cirrhosis

Although a variety of gene transfer methods to the liver have been designed, there are some problems such as the transfection efficiency and safety. In the present study, we developed a modified method of gene transfer into the liver by infusion of plasmid DNA via the portal vein followed by electroporation. After green fluorescence protein gene transfer, transgene expressions were detected in 24 h, and then maximally at 3 days, and persisted for 3 weeks. Histological analysis revealed that very mild tissue damage was induced in the liver to which electroporation was applied. In the second study, human hepatocyte growth factor (HGF) was more detected in the liver injected with 500 microg of human HGF gene than 100 microg of human HGF gene. However, serum HGF did not increase with 100 or 500 microg of human HGF gene. Moreover, 500 microg of HGF gene transfer into the liver by using this method could achieve the long survival of all dimethylnitrosamine-treated rats and attenuate the fibrous regions in the liver. These results suggest that HGF gene transfer into the liver via the portal vein using electroporation might be one of the useful methods for the treatment of various liver diseases.

Gene expression analysis of murine cells producing amphotropic mouse leukaemia virus at a cultivation temperature of 32 and 37 degrees C

Cultivation of retrovirus packaging cells at 32 degrees C represents a common procedure to achieve high titres in mouse retrovirus production. Gene expression profiling of mouse NIH 3T3 cells producing amphotropic mouse leukaemia virus 4070A revealed that 10 % of the 1176 cellular genes investigated were regulated by temperature shift (37/32 degrees C), while 5 % were affected by retrovirus infection. Strikingly, retrovirus production at 32 degrees C activated the cholesterol biosynthesis/transport pathway and caused an increase in plasma membrane cholesterol levels. Furthermore, these conditions resulted in transcriptional activation of smoothened (smo), patched (ptc) and gli-1; Smo, Ptc and Gli-1, as well as cholesterol, are components of the Sonic hedgehog (Shh) signalling pathway, which directs pattern formation, diversification and tumourigenesis in mammalian cells. These findings suggest a link between cultivation at 32 degrees C, production of MLV-A and the Shh signalling pathway.

Role of paracellular junction complexes in baculovirus-mediated gene transfer to nondividing rat hepatocytes

Gene delivery to differentiated hepatocytes is notoriously difficult. Hepatocytes plated on collagen-coated dishes and maintained in dimethyl sulfoxide (DMSO)-supplemented medium acquire paracellular junctions, arrange themselves in multicellular islands and are an excellent in vitro model for studying liver function. Baculovirus-mediated gene delivery to hepatocytes in this culture system is restricted to peripheral cells of the islands. However, this limitation can be overcome by transient calcium depletion of the cells prior to and during baculovirus infection. Examination of the mechanism underlying this process revealed that calcium depletion was accompanied by a transient loss of intercellular contacts and paracellular junction complex integrity, increased distance between adjoining cells, and internalization of the tight junction protein, zona occludens ZO-1. Internalization of ZO-1 was accompanied by baculovirus infection of internal cells of hepatocyte islands. When calcium levels were restored, paracellular junction complex integrity returned to normal by 12 h. No permanent alterations in hepatocyte ultrastructure and albumin mRNA, and protein expression were caused by this gene transfer method. Loss in paracellular junction complex integrity exposes the basolateral (sinusoidal) surface of hepatocytes resulting in homogeneous baculovirus-mediated gene delivery to approximately 75% of the cells in long-term DMSO culture. We conclude that the use of recombinant baculovirus as a vector in combination with transient calcium depletion is a highly efficient method for delivering exogenous genes to hepatocytes without loss of hepatic differentiation.

Addition of fibronectin to alginate matrix improves peripheral nerve regeneration in tissue-engineered conduits

Schwann cell (SC) transplantation has been proposed to encourage peripheral nerve regeneration, but an optimal SC-carrying matrix would be needed. The aim of this study was to characterize how the addition of fibronectin to alginate would affect the outcome of nerve regeneration promoted by Schwann cells embedded in this matrix. Genetically labeled rat SCs were obtained by lacZ gene transduction. SCs were suspended in alginate hydrogel matrix with/without addition of liquid fibronectin, and their viability and growth in the different types of matrices were assessed in vitro by AlamarBlue assay. In vivo assessment of SC transplantation in the matrix was carried out with poly-3-hydroxybutyrate (PHB) conduits to bridge a sciatic nerve gap. The grafted conduits were harvested at 2, 3, and 6 weeks and assessed for the presence of labeled SCs in relation to regrowing axons. The amount and rate of axonal regeneration were assessed by quantitative immunohistochemistry. Addition of fibronectin to alginate hydrogel improved SC viability and growth profile in vitro. X-Gal staining confirmed that SCs transplanted in PHB conduits were viable throughout the time course, and that the labeled SCs were clearly associated with regenerating axons. The regeneration rate was enhanced when liquid fibronectin was added to the alginate matrix. Furthermore, the presence of SCs also enhanced regeneration and there was an additive effect when both SCs and fibronectin were combined with alginate. In conclusion, the addition of fibronectin to alginate hydrogel matrix contributed to improve nerve regeneration, supporting SC viability and augmenting their effect on axonal growth when transplanted in a bioengineered nerve conduit.

The temperature stability of mouse retroviruses depends on the cholesterol levels of viral lipid shell and cellular plasma membrane

To delineate parameters contributing to the extracellular lifetime of retroviral vectors, we carried out stability tests of retroviruses derived from cell lines of different origin and kept under different cultivation conditions. Results show that amphotropic mouse retroviruses (MLV-A) derived from human and hamster cells exhibit 2- to 3-fold higher half-lives compared to retroviruses from mouse cells. Cultivation at 32 degrees C has been reported to yield high virus titers. However, the benefit of virus production in mouse cells at 32 degrees C is controversial. In our hands the cultivation temperature affected, hitherto not noticed, the half-life time of MLV-A. The 37/32 degrees C shift resulted in a 3-fold decrease of viral half-lifes compared to MLV-A released from mouse cells at 37 degrees C. Thus, MLV-A released at 37 degrees C is phenotypically different from MLV-A synthesized at 32 degrees C. Increased virus stability was inversely correlated with the level of cholesterol in the viral membrane. Finally, depletion of viral cholesterol in vitro resulted in intact virus with increased thermal stability. Thus, retrovirus lability depends on the host cell and parallels the cholesterol amount in the viral lipid shell.

Immune-mediated loss of transgene expression in skin: implications for cutaneous gene therapy

A clearer understanding of the immune-mediated loss of transgene from cutaneous epithelium is necessary for development of effective clinical gene therapy protocols for patients who carry null mutations in the target gene. We have used retrovirus-mediated transfer of lacZ to mouse skin as a model to investigate the mechanism of immune-mediated transgene loss in skin. Transduction of C57Bl/6 mouse skin resulted in elicitation of both humoral and cellular immune responses. Antibody responses did not play a major role in the loss of transgene. Infiltration of the transduced skin with CD4(+) and CD8(+) cells and induction of transgene-specific cytotoxic T lymphocytes implied a role for T-cell-mediated responses. Transduction of mice deficient in either major histocompatibility complex (MHC) class I or class II molecules resulted in transient transgene expression. Only in MHC(-/-) mice lacking expression of both class I and class II MHC molecules was persistent transgene expression seen. These data indicate a primary role for T-cell-mediated responses in the immune-mediated loss of transgene expression. Furthermore, CD4 and CD8 T cells have overlapping roles and either population can effectively eliminate transduced cells. Therefore, long-term cutaneous gene therapy may require development of strategies to interfere with activation or function of both T cell populations.

Displaying epidermal growth factor on spleen necrosis virus-derived targeting vectors

Targeted gene transfer into human cells has previously been achieved with spleen necrosis virus (SNV)-derived vector particles harboring envelope (Env) proteins which carry single chain Fv (scFv) domains derived from antibodies. Such cell targeting vectors have been found to directly transduce human cells expressing the cell surface molecules recognized by the respective scFv. In an attempt to achieve targeted gene transfer into epidermal growth factor receptor (EGFR)-positive human cells, SNV vector particles carrying a surface (SU) envelope protein N-terminally modified with the EGF domain and the wildtype transmembrane protein were generated. However, direct transduction of EGFR-positive cells was not detected. Canine D17 cells, which can be infected by wildtype SNV, were also not transduced. Infectivity of D17 cells was restored by removal of the EGF modification via cleavage of a factor Xa site located between the EGF domain and the SU protein or by blocking the EGFRs on the cell surface by EGF treatment. The properties of SNV-EGF vector particles as described here are similar to those of murine leukemia virus-derived vector particles harboring envelope proteins modified with a growth factor-derived domain. It seems therefore that, although scFv-modified SNV allows direct cell targeting, EGF-modified SNV allows only indirect cell targeting.

Coreceptor Switch of [MLV(SIVagm)] pseudotype vectors by V3-loop exchange

Retroviral vectors derived from murine leukemia virus (MLV) have been pseudotyped with a variant of the envelope glycoprotein (Env) of nonpathogenic simian immunodeficiency virus from African green monkeys (SIVagm) to result in [MLV(SIVagm-wt)] vector particles. The variant env gene encodes a full-length surface envelope glycoprotein (SU) and a C-terminally truncated transmembrane protein (TM). To change the coreceptor usage of this vector from CCR5 to CXCR4, which is predominant on human CD4-positive lymphocytes, the putative V3-loop of SIVagm SU was replaced by that of the T cell tropic HIV-1 variant BH10. The resulting [MLV(SIVagm-X4)] vectors were shown to specifically transduce CD4/CXCR4-positive cell lines, demonstrating the equivalent function in cell entry and choice of coreceptor usage of the V3-loops of SIVagm and HIV-1. These modified vectors were able to transduce primary human lymphocytes and were resistant to neutralization by sera from HIV-1-infected individuals. The [MLV(SIVagm-X4)] pseudotype vector generated is thus a promising candidate vector, e.g., for in vivo gene therapy of HIV-1 infection.

Demonstration of direct lineage between hepatocytes and hepatocellular carcinoma in diethylnitrosamine-treated rats

The question whether hepatocellular carcinoma (HCC) arises from dedifferentiation of mature hepatocytes or from proliferation of liver stem cells is still debated. In the present study, we used retroviral-mediated genetic labeling to investigate the fate of mature hepatocytes in rats after administration of diethylnitrosamine (DEN). Mature hepatocytes were genetically labeled by intravenous injection of retroviral vectors containing the Escherichia coli beta-galactosidase gene coupled to a nuclear localization signal (nls-LacZ) 1 day after partial hepatectomy. Liver biopsies performed after completion of hepatic regeneration showed that 18.3% of hepatocytes expressed the nls-LacZ transgene. Rats were then treated with DEN in drinking water for 12 weeks and sacrificed between 98 and 151 days after the onset of DEN administration. Clones of beta-galactosidase positive cells were observed, half of which (53%) also expressed the placental form of glutathione-S-transferase (GSTp), a marker of preneoplastic cells. HCCs of various sizes expressing GSTp were present in all animals. Careful examination of 90 HCCs revealed that 16 (17.7%) also expressed nls-LacZ. This figure precisely matched the proportion of labeled hepatocytes before DEN treatment (18.3%). In conclusion, a random clonal origin of HCC from mature hepatocytes is seen in the DEN model of hepatocarcinogenesis.