In situ retrovirus-mediated gene transfer into dog liver

Hydrodynamic plasmid DNA gene therapy model in liver transplantation

BACKGROUND

There is great interest in the field of transplantation to genetically modify grafts to decrease preservation injury or allograft rejection. Although adenoviral gene transfer has been effective in experimental liver transplantation, viral toxicity and safety concerns limit potential use in clinical trials. Therefore, the purpose of this study was to develop a model of nonviral gene transfer in the liver transplant setting, allowing for efficient transgene expression.

MATERIALS AND METHODS

Orthotopic syngeneic rat liver transplantation was performed with 3 h cold ischemia using University of Wisconsin (UW) preservation. A hydrodynamic gene transfer technique was developed where plasmid DNA was delivered to the liver graft by ex vivo rapid infusion of DNA in UW via the IVC with other vessels clamped. Expression plasmids for the marker genes luciferase and secreted human alpha1-antitrypsin (alpha1-AT) were used. Hepatic injury was assessed by graft histology and liver transaminases. Transgene expression was determined by hepatic luciferase relative light units activity (RLU) and serum alpha1-AT protein levels. Variables examined included the effect of (a) volume injected on the intravenous pressure in the liver graft; (b) injury to the liver, as measured by hepatic enzymes and histopathology; (c) variable expression between lobes; (d) volume of UW that the plasmid is administered in; (e) amount of DNA plasmid; (f) type of the promoter used; (g) clamp time; as well as (h) the time course of the marker gene expression.

RESULTS

Control rats underwent standard orthotopic syngeneic rat liver transplantation and had no detectable hepatic luciferase activity or serum human alpha1-AT. The optimal DNA plasmid dose was found to be 400 mug/liver graft, as there was no increase in the luciferase expression by increasing the dose. Furthermore, cytomegalovirus promoter yielded greater expression than Rous sarcoma virus. A high injection pressure gradient allowed for more efficient transgene expression, but produced greater liver injury shown by elevated transaminases and centrilobular necrosis. Lowering injection volume from 75 to 50% of graft weight decreased liver injury by 4.5-fold. Although higher UW injection volumes were associated with increased expression, volumes of only 50% led to luciferase expression up to 10,000,000 RLU/mg; this expression was homogeneous between the different liver lobes. Human alpha1-AT was detected in recipient blood as early as 6 h, peaked at 24 h, and remained high for 5 days.

CONCLUSIONS

We have developed a nonviral gene transfer technique where hydrostatic pressure across the cold-preserved liver vascular bed allows for efficient plasmid DNA delivery. This simple strategy should prove useful to genetically modify liver grafts in the transplantation setting.

Enhancement of ultrasound-mediated gene transfection by membrane modification

BACKGROUND

Ultrasound-mediated gene transfection (USMGT) with an echo contrast agent could be a new promising physical method of triggering localized gene delivery, but the effect is still modest. The aim of this study is to devise a method to improve efficiency of USMGT. We examined the effect of lidocaine and different temperatures on USMGT, each of which is a known membrane modifier, since the plasma membrane can be considered a site of action in USMGT.

METHODS

We observed the effect of lidocaine (0.01, 0.1 or 1.0 mM) and different temperatures (7, 20, 37, 42 or 44 degrees C) on USMGT (1 MHz, 3.6 W/cm(2) (I(SATA)) and 20 s exposure) in the presence of Levovist (10 mg/ml). At 20 h after sonication, transfection efficiency was evaluated by luciferase assay. Membrane fluidity was examined by fluorescence polarization measurement. Cavitational activity was measured by ESR spin trapping with 5,5-dimethyl-1-pyrroline N-oxide. The number of cells transfected with the GFP gene was counted under a fluorescence microscope.

RESULTS

Lidocaine (1 mM) and heat (42-44 degrees C) significantly increased luciferase expression approximately 18-fold and 19-fold higher than Levovist only. Both treatments were shown to increase membrane fluidity; in addition, heat enhanced a cavitational effect. It was confirmed by an experiment using the GFP gene that increase in luciferase expression was due to the increase in number of cells.

CONCLUSIONS

This enhancement could be useful for ultrasound-mediated gene therapy in the future since both treatments for membrane modification could be directly applied to the living body.

Specific organ gene transfer in vivo by regional organ perfusion with herpes viral amplicon vectors: implications for local gene therapy

BACKGROUND

Many gene therapy strategies would benefit from efficient, regional organ delivery of therapeutic genes.

METHODS

Regional perfusions of lung, liver, or bladder were performed to determine if rapid and efficient gene transfer can be accomplished in vivo, and to determine if in vivo gene transfer can be limited to the organ of interest. In addition, herpes simplex virus tumor necrosis factor (HSVtnf), carrying the human tumor necrosis factoralpha gene was used as a treatment for methylcholanthrene sarcoma in a syngeneic lung metastases model in Fisher rats.

RESULTS

A 20-minute perfusion using HSV carrying beta-galactosidase (HSVlac) produced significant expression of this marker gene isolated to the target organs, without organ-specific tissue injury or inflammation. Regional perfusion of organs with HSV carrying the cytokine gene tumor necrosis factor alpha also resulted in high-level local organ production of this cytokine (2851 +/- 53 pg/g tissue in perfused lung versus 0 for the contralateral lung). For the current vector construct, expression of the gene of interest peaked between 2 and 4 days and was undetectable by 2 weeks after perfusion. In animals undergoing perfusion as treatment for pulmonary sarcoma, there was no difference between tumor counts in lungs perfused with HSVlac (17 +/- 6) or HSVtnf (22 +/- 8), but either treatment resulted in lower tumor counts than controls (111 +/- 24 nodules per lung, P <.02).

CONCLUSIONS

Regional organ perfusion using herpes viral vectors is an effective and well-tolerated in vivo method of transiently delivering potentially toxic gene products to target organs in directing gene therapy. Regional lung perfusion with HSV amplicons reduces tumor burden in a rat model of pulmonary metastases, though HSVtnf cannot be demonstrated to augment the cytopathic effect of the HSV amplicon alone in the current model.

A preclinical model of hepatocyte gene transfer: the in vivo, in situ perfused rat liver

Delivering retroviruses targeted to hepatocytes in vivo involves the injection of retroviruses directly into the portal vein. The aim of this work was to establish a clinically relevant system for retrovirus-mediated gene transfer in a new model of in vivo, in situ perfused rat liver and to study the transgene expression. At 24 h after partial hepatectomy, the liver was completely excluded from the splanchnic circulation using an extracorporeal shunt. Two independent normothermal, oxygenated perfusion systems were used. First, liver perfusion was carried out with a recirculating system (1 h). Culture supernatant containing retroviruses (1.5 x 10(8) ffu/ml, beta-galactosidase gene) was used as perfusate. Then the liver perfusion was maintained for more 30 min in a single liver passage system using culture medium without retroviruses as perfusate. High hepatocyte transduction rates (up to 34.4%) were obtained. PCR analysis showed no provirus in extrahepatic organs. Viral titrations performed simultaneously (inflow and outflow liver lines) showed that after 1 h of perfusion (up to 30 successive liver passages) retroviruses were still detected in the liver outflow perfusate (up to 2.0 x 10(7) ffu/ml). Washing the liver for 30 min dramatically decreased the leakage of retroviruses in the outflow. In order to be of clinical use, the injection of retroviruses targeted to hepatocytes in vivo should be done while the liver is completely excluded from the splanchnic circulation to avoid any extrahepatic retrovirus diffusion.

Inclusion of the hepatic locus control region, an intron, and untranslated region increases and stabilizes hepatic factor IX gene expression in vivo but not in vitro

We systematically compared human factor IX gene expression from a variety of plasmids containing different cis-regulatory sequences after transfection into different hepatocyte cell lines, or in vivo, after their injection into the livers of mice. Although there was a 1.5- to 2.0-fold variation in gene expression from cultured cells, a 65-fold variation was observed in the in vivo studies. We found that a plasmid containing the apolipoprotein E locus control region (HCR), human alpha1-antitrypsin (hAAT) promoter, hFIX minigene (hFIXmg) sequence including a portion of the first intron (intron A), 3'-untranslated region (3'-UTR), and a bovine growth hormone polyadenylation signal (bpA) produced the highest serum level of human factor IX, reaching 18 microg/ml (normal = 5 microg/ml) 1 day after injection. Although most of the plasmid DNAs resulted in transient gene expression, inclusion of an intron, a polyadenylation signal from either the 1.7-kb 3'-UTR or the 0.3-kb bpA, and the HCR resulted in persistent and therapeutic levels of hFIX gene expression, ranging from 0.5 to 2 microg/ml (10 to 40% of normal) for 225 days (length of experiment). These data underscore the importance of cis sequences for enhancing in vivo hepatic gene expression and reemphasize the lack of correlation of gene expression in tissue culture and in vivo studies.

Efficiency of adenovirus-mediated gene transfer into hepatocytes by liver asanguineous perfusion method

Efficient targeted gene delivery is essential for successful gene therapy. In this study, we examined the liver asanguineous perfusion method (LAP) for adenovirus-mediated gene transfer to the liver from the standpoints of efficiency, tissue-specificity and safety. The adenoviral vector containing the E. coli LacZ gene driven by the CAG promoter was delivered to the livers of rats by LAP. This method involves selective in situ perfusion, with the liver isolated by clamping of the afferent and efferent blood vessels to prevent adenoviral vector dissemination and genetic modification of nonhepatic organs. We demonstrated that gene transfer to the liver by LAP was not uniform, but more efficient than by intravenous (i.v.) or intraportal (i.p.) infusion, and caused no obvious liver damage or high mortality. As determined by specific histochemical staining and polymerase chain reaction, the amount of vector DNA transferred to the nonhepatic organs by LAP was significantly less than that transferred by the other two methods. Our data suggest that LAP is clearly superior to i.v. or i.p. infusion in terms of efficiency, specificity and safety of gene delivery to the liver. Further reduction in surgical risk is needed for the clinical application of gene therapy.

[Effect of portal branch ligation on liver regeneration in the rat]

GOAL

The aim of this study was to assess liver regeneration after partial portal ligation.

METHODS

70% partial portal occlusion was obtained by ligation of the left portal vein branch. Total liver weight ratio were measured 96 hours after partial portal occlusion and in sham operated animals. The kinetics of hepatocytes division was evaluated by measuring the incorporation of 5-bromo-21-deoxyuridine into replicating cells at various time points by immunohistochemistry.

RESULTS

Partial portal occlusion did not alter the total liver weight 96 hours after surgery. It resulted in atrophy of the ligated lobes and hypertrophy of the lobes with preserved portal flow. Hypertrophy was associated to an increase of the percentage of replicating hepatocytes. The replication rate was maximum at 28 hours with a peak at 12.5% and was prolonged beyond the 48th hour.

CONCLUSIONS

Partial portal occlusion results in major and prolonged regeneration process in the liver lobes with preserved portal flow.

In vivo retrovirus-mediated gene transfer to the liver of dogs results in transient expression and induction of a cytotoxic immune response

Gene transfer in regenerating dog liver using high-titer recombinant retroviral vectors carrying the E. coli beta-galactosidase gene was studied. Supernatants containing amphotropic or gibbon ape pseudotyped recombinant retroviruses were infused into a peripheral vein in beagle dogs after partial hepatectomy. The kinetics of liver regeneration were determined in the animals and daily infusions were carried out for 4 or 5 days during the regeneration period. Up to 2.8% of hepatocytes were beta-galactosidase positive at the end of the procedure. However, the number of positive cells declined rapidly and few positive hepatocytes were detected after 3 weeks. PCR demonstrated the disappearance of the provirus. Histologically, inflammatory lesions were observed in the transduced livers. Finally, we demonstrated the presence of a cytotoxic T lymphocyte immune response directed against beta-galactosidase-expressing cells, which could explain the disappearance of the transgene. This work suggests that the efficiency of in vivo gene delivery using high-titer retroviral vectors directly infused into the circulation may be hampered by a cytotoxic immune response against the infected cells.

In vivo hepatocyte retrovirus-mediated gene transfer through the rat biliary tract

Delivering retroviruses targeted to hepatocytes in vivo involves the injection of retroviruses directly into the blood stream of the portal vein. The aim of this work was to delineate the conditions for delivering retroviruses in vivo by perfusing in situ the bile duct of the regenerating rat liver, and to study the hepatocyte transgene expression. At 24 hr after partial hepatectomy, during the S phase of the cell cycle, regenerating livers were perfused for 2.8+/-0.5 hr through the bile duct with 36.2+/-6.8 ml (0.3+/-01 ml/min) of fresh culture supernatant containing amphotropic recombinant retroviruses encoding the beta-galactosidase gene. The virus total titer was 1.5 x 10(8) ffu (group I) or 6.5 x 10(8) ffu (groups II and III). The hepatic artery blood flow was either maintained (groups I and II) or interrupted (group III) during bile duct perfusion. Liver biopsies taken 7 days later showed that 31.4+/-24.2% (group I), 58.7+/-23.6% (group II), and 45.1+/-21.4% (group III) of hepatocytes expressed beta-galactosidase activity, predominantly in the periportal and mediolobular zones. This study demonstrates that hepatocytes of regenerating rat livers that have entered the S phase of the cell cycle as a result of partial hepatectomy can be transduced in vivo by retroviral vectors delivered in situ by bile duct perfusion. Furthermore, the number of transduced hepatocytes closely correlated with the viral total titer and was diminished by hepatic artery blood flow occlusion during perfusion.

Liver-directed gene transfer vectors

The ultimate goal of liver-directed gene therapy for genetic diseases is the stable expression of a therapeutic transgene in a significant proportion of hepatocytes. This article considers the various liver-directed gene transfer procedures studied so far. Performances and limitations of currently available vector systems are discussed with respect to their clinical relevance. Although some improvements have been reported, naked DNA and nonviral gene transfer vectors induce transient expression in only a limited number of cells. Clinical applications of retrovirus-mediated gene transfer are hampered by the need to induce hepatocyte division. First-generation adenovirus vectors are highly efficient; however, they induce an immune response leading to the rapid rejection of transduced cells. Promising new vector systems have emerged, including gutless adenovirus vectors, adeno-associated vectors, and lentivirus vectors. However, these systems are still poorly documented and their relevance to liver-directed gene therapy must be confirmed.

Hepatic regeneration in the isolated perfused rat liver followed by liver transplantation

Controlling the S phase of the hepatocyte cell cycle would be of considerable help for stable retroviral foreign gene transfer. The aim of this article is to study hepatocyte regeneration during S phase in isolated, perfused rat liver followed by liver transplantation. Normal livers (G I: n = 7) were perfused with blood from normal rats for 6.1+/-0.3 hours. Regenerating livers (G II; n = 7) obtained 18 hours after partial hepatectomy were perfused for 6.0+/-0.3 hours with blood from rats partially hepatectomized 18 hours before. Regenerating livers (G III; n = 7) obtained 22 hours after partial hepatectomy were perfused for 2.4+/-0.1 hours with blood from normal rats. In the normothermal perfusion system, a bolus of 25 mg of 5-bromo-2'-deoxyuridine (BrdU) was added to the perfusate. Liver biopsies were taken at the end of each experiment. In group II, a biopsy was also taken 1 hour after BrdU introduction. At the end of each experiment, livers were orthotopically transplanted. The percentage of BrdU positive hepatocyte nuclei was 0.2% in G I; 14.8% and 38.4% after 1 hour and 6.1 hours, respectively, in G II; and 46.5% after 2.4 hours in G III. In G I, five rats died at day 1, 5, 6, 7, and 48 and two rats were still alive after 17 months. In G II, all the rats died before day five. In G III, two rats died at day one, one at day six, and four were still alive after 12 months. This study shows that, after 6 hours of normothermal perfusion, organ viability allows successful liver transplantation and that rat hepatocyte regeneration during cell cycle S phase in isolated normothermal conditions progresses in a similar way-quantity and timing-to liver regeneration found in vivo after partial hepatectomy.

Highly efficient retrovirus-mediated gene transfer into rat hepatocytes in vivo

We have used high-titer (10(8) ffu/ml) recombinant retroviral vectors to transfer the beta-galactosidase (beta-Gal) gene to rat hepatocytes in vivo. In animals injected twice in the portal blood stream the next day after partial hepatectomy, half of the hepatocytes (46 +/- 17%) expressed the marker at the end of liver regeneration. The number of positive cells closely correlated with the viral titer as well as with beta-Gal enzymatic activity present in the whole liver. Because genes transferred via retroviral vectors in the liver are known to be expressed permanently, our present results open new possibilities for the development of gene therapy protocols for hereditary liver diseases using recombinant retroviral vectors.

Proliferation induced by keratinocyte growth factor enhances in vivo retroviral-mediated gene transfer to mouse hepatocytes

Retroviral gene transfer to liver without prior injury has not yet been accomplished. We hypothesized that recombinant human keratinocyte growth factor would stimulate proliferation of hepatocytes and allow for efficient in vivo gene transfer with high titer murine Moloney retroviral vectors. This report shows that 48 h after intravenous injection of keratinocyte growth factor, hepatocyte proliferation increased approximately 40-fold compared to non-stimulated livers. When keratinocyte growth factor treatment was followed by intravenous injection of high titer (1 x 10(8) colony forming units/ml) retrovirus coding for the Escherichia Coli beta-galactosidase gene, there was a 600-fold increase in beta-galactosidase expression, with 2% of hepatocytes transduced. Thus, by exploiting the mitogenic properties of keratinocyte growth factor, retrovirus-mediated gene transfer to liver may be accomplished in vivo without the use of partial hepatectomy or pretreatment with other toxins to induce hepatocyte cell division.

Portal branch occlusion safely facilitates in vivo retroviral vector transduction of rat liver

Hepatic gene therapy might correct the clinical manifestations of several genetic disorders in patients. Although retroviral vectors with a strong liver-specific promoter can result in stable and therapeutic levels of expression of genes from the liver, application of these techniques in humans is limited by the need to perform one or more invasive procedures to achieve ex vivo or in vivo transduction of hepatocytes. In vivo delivery involves injection of retrovirus into the portal vein during liver regeneration. Although transduction is efficient and specific for the liver, induction of hepatocyte replication requires a 70% partial hepatectomy or administration of a liver toxin. An alternative method for inducing hepatocyte replication is to occlude branches of the portal vein. This results in apoptosis of hepatocytes in the occluded lobes and compensatory replication of the hepatocytes in the nonoccluded lobes. We demonstrate here that portal branch occlusion is nearly as effective as partial hepatectomy at facilitating retroviral vector transduction in vivo and has a lower morbidity. Portal branch occlusion could be performed in larger animals by minimally invasive techniques and has been used safely to treat human patients with liver cancer. Portal branch occlusion might ultimately be used in humans to facilitate retroviral vector transduction in vivo for the treatment of genetic diseases.

Gene transfer into hepatocytes and human liver tissue by baculovirus vectors

Gene therapy of liver diseases requires the development of efficient vectors for gene transfer in vivo. Retroviral and adenoviral vectors have been shown to deliver genes efficiently into hepatocytes in vitro and in vivo. However, these vectors do not allow for exclusive infection of the liver which would be highly advantageous for in vivo gene therapy strategies. We have recently demonstrated that genetically modified baculoviruses (Autographa californica nuclear polyhedrosis virus) efficiently deliver genes into cultured cells and have a strong preference for hepatocytes of different origin. Baculoviral gene transduction efficiency into human hepatocytes was determined to approach 100% and expression levels are high, provided that gene expression is controlled by mammalian promoters. In this report, we present further properties of baculoviruses regarding their use for hepatocyte gene transfer. Baculovirus-mediated gene expression declines rapidly in the hepatocellular carcinoma cell line Huh7 and more slowly in primary cultures of mouse hepatocytes. Direct application of baculoviruses for gene delivery to the liver in vivo is hampered by serum components, presumably by complement. However, we demonstrate here that baculoviral gene transfer is feasible in ex vivo perfused human liver tissue. This result suggests the development of a strategy using baculoviral vectors for liver-directed gene therapy.

Generation of recombinant adenovirus vectors with modified fibers for altering viral tropism

To expand the utility of recombinant adenovirus vectors for gene therapy applications, methods to alter native viral tropism to achieve cell-specific transduction would be beneficial. To this end, we are pursuing genetic methods to alter the cell recognition domain of the adenovirus fiber. To incorporate these modified fibers into mature virions, we have developed a method based on homologous DNA recombination between two plasmids. A fiber-deleted, propagation-defective rescue plasmid has been designed for recombination with a shuttle plasmid encoding a variant fiber gene. Recombination between the two plasmids results in the derivation of recombinant viruses containing the variant fiber gene. To establish the utility of this method, we constructed a recombinant adenovirus containing a fiber gene with a silent mutation. In addition, we generated an adenovirus vector containing chimeric fibers composed of the tail and shaft domains of adenovirus serotype 5 and the knob domain of serotype 3. This modification was shown to alter the receptor recognition profile of the virus containing the fiber chimera. Thus, this two-plasmid system allows for the generation of adenovirus vectors containing variant fibers. This method provides a rapid and facile means of generating fiber-modified recombinant adenoviruses. In addition, it should be possible to use this system in the development of adenovirus vectors with modified tropism to allow cell-specific targeting.

Liver-directed gene transfer and application to therapy

The liver is an important and attractive target for the development of gene therapy strategies. Many genetic diseases are manifested in the liver, and both infectious and malignant diseases affect this organ. Retroviral and adenoviral vectors have been shown to infect hepatocytes with varying efficiently in vitro and in vivo. The presence of unique receptors at the cellular membrane of hepatocytes has stimulated the development of transfer strategies based on receptor targeting of vectors. The results of a first clinical trial for gene therapy in the liver based on ex vivo gene delivery has shown both the feasibility and the limits of current technology. This review discusses both existing vectors and strategies and prospective developments towards liver-directed gene therapy of genetic and malignant diseases.

Liver-directed gene therapy: a retroviral vector with a complete LTR and the ApoE enhancer-alpha 1-antitrypsin promoter dramatically increases expression of human alpha 1-antitrypsin in vivo

Hepatic gene therapy could improve the treatment of many inherited disorders. Although retroviral vectors result in long-term expression in hepatocytes in vivo, their low level of expression currently precludes most clinical applications. Four copies of the liver-specific apolipoprotein E (ApoE) enhancer were placed upstream of the human alpha 1-antitrypsin (hAAT) promoter in either orientation into a retroviral vector with a complete long terminal repeat (LTR) and the hAAT cDNA to generate ApoE(+)hAAT-LTR and ApoE(-)hAAT-LTR. In addition, the ApoAI promoter was placed upstream of the hAAT cDNA in a similar retroviral vector backbone. Amphotropic retroviral vectors were transferred into regenerating rat liver cells in vivo by intraportal injection. ApoE(-)hAAT-LTR and ApoE(+)hAAT-LTR led to average hAAT levels of 5 micrograms/ml (0.5% of normal levels of a very abundant protein), and 2.5 micrograms/ml, respectively, which was stable for at least 10 months after transduction. This level of serum hAAT was > 25-fold higher than what was observed from the ApoAI promoter used in this study. Serum levels of hAAT were > 15-fold higher than what was observed from retroviral vectors containing the hAAT cDNA that were analyzed previously by this lab. In some cases, improved expression was due to the promoter chosen. In other cases, the increase in expression was primarily due to the higher titers obtained by using a retroviral backbone with an intact LTR as opposed to a vector with a deletion in the LTR. The increased expression levels observed from this enhancer/promoter combination in an intact retroviral backbone may enable one to achieve therapeutic levels of clinically important genes from a retroviral vector in liver cells of animals.

Retroviral vector producer cell killing in human serum is mediated by natural antibody and complement: strategies for evading the humoral immune response

The introduction of retroviral vector producer cells (VPC) into tumors as a means of increasing transduction efficiency has recently been employed in human gene therapy trials. However, the fate of these xenogeneic cells in humans is not well understood. In the present study, we used an in vitro model to examine the survival of commonly used VPC lines in serum from humans and various other species. VPC derived from the murine NIH-3T3 cell line, including PA317, Psi CRIP, and GP + E-86, were effectively killed in sera from Old World primates, including human and baboon. Conversely, the same murine cell lines survived exposure to sera from dog, rabbit, rat, and mouse. This pattern of serum killing parallels the occurrence of the anti-alpha-galactosyl natural antibody (Ab) found exclusively in Old World primates. The anti-alpha-galactosyl Ab targets the terminal glycosidic structure Gal alpha 1-3Gal beta 1-4GlcNAc-R (alpha-galactosyl epitope) found on the surface of mammalian cells, excluding Old World primates. All murine-derived VPC tested expressed high levels of the alpha-galactosyl epitope as determined by FACS analysis. VPC killing was complement-mediated, because preincubation of human serum with a functionally blocking anti-C5 mAb completely abolished cell lysis. Furthermore, addition of soluble galactose(alpha 1-3)galactose (Gal alpha 1-3Gal) to human serum or down-regulation of the alpha-galactosyl epitope on the surface of VPC effectively reduced VPC killing, indicating that complement activation by these cells is primarily initiated by natural antibody recognition of the alpha-galactosyl epitope. Finally, VPC incubated with human serum for 8 hr in the presence of complement inhibition continued to produce viable retroviral particles, thus demonstrating a correlation between VPC and particle survival. Taken together, these data suggest that elimination of the alpha-galactosyl epitope or complement blockade may provide a strategy to prolong the survival of VPC and the particles that they produce in vivo.

Use of sodium butyrate to enhance production of retroviral vectors expressing CFTR cDNA

Previously, we constructed a retrovirus vector (LCFSN) for transduction and expression of the cDNA encoding the normal human cystic fibrosis transmembrane conductance regulator (CFTR). The titer of virus from amphotropic packaging cells producing the LCFSN vector was low (10(3)-10(4) infectious units/ml). In an attempt to increase virus production, we used sodium butyrate (NaB) to treat murine retrovirus packaging cells producing this vector. NaB treatment increased the production of LCFSN from between 20-fold to greater than 1,000-fold, depending upon the producer clone, thereby resulting in virus titers up to about 1 x 10(7) infectious units/ml. This induction of virus titer could be accounted for, at least in part, by an increase in steady-state levels of full-length vector RNA within the producer cells. With some clonal producer cell lines, lowering the temperature of the virus harvest in combination with NaB treatment resulted in an apparent synergistic increase in virus production. The production of retrovirus vectors containing genes other than CFTR could also be increased by NaB treatment, although the enhancement in titer was modest (2-fold to 10-fold). The increase in virus production was not accompanied by an induction of replication-competent helper virus. NaB treatment also increased the transient production of retroviral vectors following DNA-mediated transfection into packaging cells such that virus titers of greater than 10(6) infectious units/ml could be readily attained.

Adenovirus-mediated urokinase gene transfer induces liver regeneration and allows for efficient retrovirus transduction of hepatocytes in vivo

Retrovirus-mediated gene transfer into hepatocytes in vivo results in long-term gene expression. Limitations include the need to remove two-thirds of the liver and the relatively low frequency of gene transfer. To increase gene transfer without surgical hepatectomy, mouse hepatocytes were transduced in vivo with a recombinant adenovirus that transiently expressed urokinase, resulting in high rates of asynchronous liver regeneration. During the regenerative phase, in vivo retroviral-mediated gene transfer in hepatocytes resulted in 5- to 10-fold greater transduction efficiencies than that obtained by conventional partial hepatectomy. In 3-4 weeks, the architecture and microscopic structure of the recipient livers were normal. The two-viral system of achieving permanent transgene expression from hepatocytes in vivo offers an alternative approach to current ex vivo and in vivo gene-transfer models.

Glucose responsiveness of a reporter gene transduced into hepatocytic cells using a retroviral vector

An MMLV-based retroviral vector containing the chloramphenicol acetyl transferase reporter gene under the control of a glucose-dependent internal promoter derived from the L-type pyruvate kinase gene was constructed. After transfection into psi-CRIP packaging cells, clones producing recombinant retrovirus were selected. These retroviruses were used to infect cultured established hepatocytic cells whose endogenous L-type pyruvate kinase gene is transcriptionally regulated by glucose. In the infected cells, the reporter gene was as responsive to glucose as the endogenous L-type pyruvate kinase gene, and the glucose gene activation was time- and concentration-dependent. The possibility to confer a glucose responsiveness on a transgene carried by a retroviral vector provides a powerful tool in the prospect of gene therapy for diabetes mellitus.

Long-term delivery of a lysosomal enzyme by genetically modified fibroblasts in dogs

We have evaluated the feasibility and efficacy of intraperitoneal implants (neo-organs) for protein delivery in large animals. Skin biopsies were taken from four healthy dogs. Primary fibroblast cultures were transduced with a retroviral vector coding for the human beta-glucuronidase. One to six lattices each containing 10(9) skin fibroblasts were implanted into the omentum of the donor animal. Laparotomies performed at regular intervals showed vascularized neo-organs without local inflammation. Human beta-glucuronidase levels equivalent to 0.8 to 3.1% of the endogenous canine activity were detected for up to 340 days on liver biopsy samples. These results indicate that neo-organs can be considered for the long-term delivery of therapeutic proteins or enzymes in humans.

Protection of retroviral vector particles in human blood through complement inhibition

The rapid inactivation of murine-derived retroviral vectors in human or nonhuman primate sera is largely attributed to the activity of complement mediated through the classical pathway. In this study, we have further investigated the relationship between the human complement cascade and retrovirus inactivation. Preincubation in normal human serum effectively inactivated LXSN retroviral vector particles, whereas the vector maintained the ability to transduce cells following incubation in sera deficient in either the C1, C2, C3, C5, C6, C8, or C9 human complement proteins. Preincubation of serum with monoclonal antibodies (mAbs) that functionally block specific complement components, including C5, C6, C8, and C9, successfully protected the LXSN vector from complement-mediated inactivation. Treatment of serum with cobra venom factor, which consumes terminal complement, also effectively protected the vector from inactivation. LXSN vector survival in serum corresponded inversely to the level of complement activity following treatment of serum with anti-C5 mAb as assessed in an erythrocyte hemolytic assay. Additionally, pretreatment of human whole blood with anti-C5 mAb effectively inhibited inactivation of the LXSN vector. Taken together, these data demonstrate that formation of the membrane attack complex (MAC, C5b-9) is required for the inactivation of the murine-based LXSN retroviral vector in human blood and that this process can be abrogated with the use of soluble complement inhibitors.

Retroviral delivery of DNA into the livers of transgenic mice bearing premalignant and malignant hepatocellular carcinomas

To develop gene therapy for hepatocellular carcinoma (HCC), we infused mice through the portal vein with retrovirus carrying the Escherichia coli beta-galactosidase reporter gene under the transcriptional control of the viral long terminal repeat (LTR) and the promoter from the mouse multidrug resistance gene mdr1b. Two transgenic mouse HCC models were used, one bearing the human hepatitis B viral envelope protein and the other SV40 T antigen. These animals develop HCC with predictable pathological manifestations. The viral transduction efficiency appeared to depend upon the stage of the disease in the animals. The most efficient transduction occurred when the livers had developed microscopic nodular hyperplasia; in some cases as many as 0.01-0.1 copies/cell were transduced. The transduction efficiency was lower in the late stage of the disease when livers had a heavy tumor burden and in the early stage when no lesion was evident. Low viral transduction efficacy was also seen in nontransgenic animals but was significantly increased by partial hepatectomy. The expression of the reporter gene in these animals was very low, as determined by histological staining. These results suggest that hepatocarcinogenesis can enhance retroviral delivery of foreign genes into the liver. Further development by increasing the viral transducing efficiency and the level of expression of transduced gene is required.

Factors influencing retroviral-mediated gene transfer into hepatocytes in vivo

Direct gene transfer into hepatocytes represents an attractive alternative to organ transplantation for the treatment of genetic liver diseases. This approach is hampered either by the difficulty to obtain, cultivate, and reimplant hepatocytes or by the poor stability of the expression of the transgene. In the present report, we show that direct in vivo infection of hepatocytes with a retroviral vector following partial hepatectomy results in a life-long expression of the transgene in adult rats and mice. We demonstrate that the kinetics of hepatocyte susceptibility to infection is closely associated with the kinetics of cell division. We also present evidence that a complete vascular exclusion of the organ allows better gene transfer as compared to simple portal infusion of the viral particles, presumably through a higher volume of retrovirus-containing medium delivered to the liver.

Recombinant retroviral vector delivered intramuscularly localizes to the site of injection in mice

A murine retroviral vector encoding the human immunodeficiency virus type 1 (HIV-1) env and rev genes can be used to induce cytotoxic T lymphocyte responses. Immune responses can be induced by an ex vivo treatment, in which autologous cells are transduced in vitro and re-introduced to the donor, or by direct administration of retroviral vector via intramuscular injection. In this study we have used polymerase chain reaction (PCR) analysis to examine the distribution of recombinant murine retrovirus directly administered to mice. Mice were injected intramuscularly with HIV-IT(V), an amphotropic murine leukemia virus (MLV)-based retroviral vector carrying the HIV-1 env/rev genes and a neomycin resistance marker gene. Detection of the HIV-1 env gene in DNA isolated from injection sites demonstrated in vivo transduction. No evidence of transduction was observed in the testes, spleen, kidney, or thymus. Retroviral DNA was detected in the liver of one animal in the study. These data suggest that retroviral vector administered intramuscularly to mice localizes primarily to the site of injection and that measurable transduction in the testes does not occur.