Systemic gene expression after intravenous DNA delivery into adult mice

Gene therapy in pediatric oncology

An increased understanding of the molecular mechanisms of cancer and the ability to introduce exogenous genes into mammalian cells has led to the development of oncologic treatment strategies based upon gene transfer. Preclinical animal models have suggested a variety of approaches which are now being tested in pediatric trials. Studies using marker genes to trace cell origin have already generated important information regarding autologous bone marrow transplantation for pediatric cancers. A variety of therapeutic genes are also being clinically tested. Trials are underway to determine if introduction of immunostimulatory genes into cancer cells can be used to enhance host antitumor immunity. Treatment of primary brain tumors with insertion of drug sensitization genes is a promising new therapy that is also being clinically evaluated. Other strategies such as insertion of drug resistance genes into hematopoietic cells, anti-oncogene therapy, and tumor suppressor gene replacement are being tested in adults and may find use in pediatric cancer treatment. Although gene transfer offers promising new approaches for the therapy of pediatric cancer, many technical problems remain which limit efficacy and widespread use. Further basic research in the molecular biology of cancer and in vector development will be required to realize the full potential of gene therapy strategies.

Gene expression and active virus replication in the liver after injection of duck hepatitis B virus DNA into the peripheral vein of ducklings

BACKGROUND/AIMS

Duck hepatitis B virus is a member of the hepadnavirus family, which possesses strong hepatotropism. Duck hepatitis B virus DNA serves as a replicative template for producing biologically active virus particles after transfection into cell lines established from human hepatocellular carcinoma or into duck liver by direct injection of calcium phosphate-precipitated DNA. Our aim was to develop a new method of liver-specific gene expression after intravenous DNA delivery.

METHODS/RESULTS

We inoculated duck hepatitis B virus DNA with and without cationic liposomes, Lipofectin or LipofectAMINE, as DNA carries. Two weeks after a single intravenous injection of 10 or 50 micrograms of plasmid DNA containing a head-to-tail dimer of duck hepatitis B virus DNA into 25 one-day old ducklings, duck hepatitis B virus RNA transcripts including the pregenome replicative intermediate were detected by Northern blot in the liver of eight ducks (100%) of the Lipofectin group, five ducks (63%) of the LipofectAMINE group, and three ducks (50%) of the group which received DNA without carrier. Duck hepatitis B virus RNA transcription was almost exclusively liver specific, even though the liposomes had no tissue specificity. Replicative forms of duck hepatitis B virus DNA were detected in the liver and DHBsAg was observed in the cytoplasm of the hepatocytes by immunostaining. The serum of transfected ducklings contained virus particles which were infectious in other ducklings.

CONCLUSION

The efficient and liver-specific expression of inoculated DNA was due to the amplification of nucleic acids by active virus replication process under the control of hepatocyte specific regulation.

Double long-chain amidine liposome-mediated self replicating RNA transfection

We present experimental evidence that a complex made of a double long chain cationic amphiphile and recombinant mRNA facilitates the entry and expression of genetic material into cells. Combining the properties of the self replicating recombinant mRNA driven by the Semliki Forest Virus (SFV) replicon and the transfection potentialities of a new cationic amphiphile (N-t-butyl-N'-tetradecyl-3-tetradecylaminopropionamidine) yields a highly efficient mRNA transfection system conferring up to 100% infectivity. The preparation and characterization of the long chain amidine cationic amphiphile-mRNA complex as well as the influence of the diC14-amidine/RNA ratio on the infective activity are described.

Targeting of transgene expression to the vascular endothelium of mice by homologous recombination at the thrombomodulin locus

We describe a straightforward gene-targeting technique to achieve uniform, stable, and genetically invariant expression of a transgene in the vascular endothelium of mice. To demonstrate the feasibility of this approach, the reporter gene bacterial beta-galactosidase was inserted via homologous recombination into the intronless thrombomodulin locus of murine embryonic stem cells. In this fashion, the lacZ gene is placed under the regulatory control of the endogenous thrombomodulin promoter. The expression of the transgene in adult mice recapitulated the widespread, stable, and high-level expression of the thrombomodulin gene in vascular endothelium. These data indicate that targeting of cDNAs into the thrombomodulin locus serves as a viable strategy to express transgenes in endothelial cells. Analysis of reporter gene expression revealed a heterogeneous pattern of thrombomodulin gene activity in the endothelium of the aorta and its tributaries. We also show that embryonic stem cells with a targeted thrombomodulin locus contribute in a mosaic fashion to the vascular endothelium of chimeric mice. This method for generating animals with a functionally heterogeneous cardiovascular system should provide an experimental technique for studying how localized genetic abnormalities in endothelial cell function lead to the development of vascular diseases.

Gene therapy for donor hearts: ex vivo liposome-mediated transfection

OBJECTIVE

Liposomes may be an appropriate transfection vehicle for transplanted hearts, avoiding the use of viruses in immunosuppressed hosts and allowing transfection of nondividing cells. To study whether liposome-mediated transfection could be accomplished during transplantation, we used a liposome-reporter gene system in a rabbit model of allograft cardiac transplantation.

METHODS

After aortic crossclamping, Stauffland donor hearts were injected with 10 ml Stanford cardioplegic solution; then a 1.3 to 2.0 mg/kg dose of chloramphenicol acetyl transferase in 1:1 deoxyribonucleic acid-liposome complexes was injected proximal to the aortic crossclamp for coronary artery perfusion. The hearts were transplanted into New Zealand White rabbit recipients in the heterotopic cervical position (n = 11 transplants). Recipients were sacrificed at 24 hours. Myocardial specimens (right and left ventricles) and vascular specimens (epicardial coronary artery, aortic root, and coronary sinus) from both the transplanted and native hearts were analyzed for chloramphenicol acetyl transferase protein by means of the enzymatic liquid scintillation assay (counts per minute per milligram of total protein).

RESULTS

In the recipient, myocardial chloramphenicol acetyl transferase activity was significantly greater in treated donor hearts (mean 4.6 x 10(5) cpm/mg +/- 1.1 x 10(5) [standard error]) than in native hearts (mean 4.1 x 10(2) cpm/mg +/- 72 [standard error], p < 0.01, Mann-Whitney U test). In treated donor hearts, right and left ventricular specimens, as well as apical and basal myocardial specimens, were transfected equally. Chloramphenicol acetyl transferase activity in vascular specimens also indicated transfection (mean 5.4 x 10(5) cpm/mg +/- 2.5 x 10(5) [standard error]). Chloramphenicol acetyl transferase activity in the coronary sinus was comparable with that in the coronary arteries, which suggests that liposomes can transverse the coronary capillary beds.

CONCLUSIONS

These findings demonstrate that ex vivo transfection of donor hearts with a liposome-reporter gene system results in significant in vivo expression of the transfected gene product after cardiac transplantation. Genetic alteration of myocardium and cardiac vasculature has potential clinical applications in the prevention of posttransplantation rejection, ischemia-reperfusion injury, and both transplant and nontransplant coronary artery disease.

Intracellular, genetic or congenital immunisation--transgenic approaches to increase disease resistance of farm animals

Novel approaches to modify disease resistance or susceptibility in livestock are justified not only by economical reasons and with respect to animal welfare but also by recent advancements in molecular genetics. The control or elimination of infectious pathogens in farm animals is historically achieved by the use of vaccines and drugs and by quarantine safeguards and eradication. Currently, research on the improvement of disease resistance based on nucleic acid technology focuses on two main issues: additive gene transfer and the development of nucleic acid vaccines. The strategies aim at the stable or transient expression of components known to influence non-specific or specific host defence mechanisms against infectious pathogens. Thus, candidates for gene transfer experiments include all genes inducing or conferring innate and acquired immunity as well as specific disease resistance genes. Referring to the site and mode of action and the source of the effective agent the strategies are termed 'intracellular', 'genetic' and 'congenital' immunisation. The targeted disruption (deletive gene transfer) of disease susceptibility genes awaits the establishment of totipotential embryonic cell lineages in farm animals. The cytokine network regulates cellular viability, growth and differentiation in physiological and pathophysiological states. The identification of the JAK-STAT pathway used by many cytokines for their intracellular signal propagation has provided not only new target molecules for modulating the immune response but will also permit the further elucidation of host-pathogen interactions and resistance mechanisms.

Development of drug targeting based on recombinant expression of the chicken avidin gene

The chemistry required for covalent biotinylation of drugs, radiopharmaceuticals and other ligands is highly developed, and a large number of biotinylated reagents can be readily synthesized. In order to investigate whether expression of avidin cDNA in mammalian cells might be useful as part of a drug targeting strategy, we transiently expressed the avidin gene in two human tumor cell lines (the cervical carcinoma cell line, HeLa, and the liver derived line, Hep G2). Avidin protein as detected by either immunohistochemistry or binding of streptavidin-biotin complexes was present and functional following transient expression. This result indicated that the mechanisms underlying avidin oligomerization which are necessary for proper protein folding are present within mammalian carcinoma cell lines. Next, we generated a producer cell line (derived from psi2) capable of releasing a recombinant retrovirus encoding chicken avidin, and a tumorigenic murine breast cancer cell line (16/C) with stable avidin expression. We show that these cell lines are suitable for conferring functional expression of avidin in vitro. These experiments establish a means by which avidin gene expression can be explored as a mechanism for targeted gene delivery of biotin-derivitized drugs in vitro, and have important implications for utilization of this strategy in vivo.

High yield incorporation of plasmid DNA within liposomes: effect on DNA integrity and transfection efficiency

Effective use of liposomes in gene therapy requires high yield incorporation of nucleic acids within vesicles which protect their content from nuclease attack and facilitate transfection: To that end, pGL2 plasmid DNA (3.99 x 10(6) Daltons) expressing the luciferase reporter gene was incorporated quantitatively (40-92% of the DNA used) by a mild procedure into neutral and negatively or positively charged multilamellar liposomes which offered considerable protection from deoxyribonuclease attack. Smaller vesicles (210-383 nm diameter) produced from such liposomes, retained much of the original content of DNA which was still significantly inaccessible to the enzyme. Liposomal plasmid DNA was found to retain its structural integrity and to transfect cells in vitro in relation to the size and surface charge of the vesicles. Such DNA-incorporating liposome constructs could prove effective for plasmid DNA expression in vivo.

Prevention of murine breast cancer by vaccination with tumor cells modified by cytokine-producing recombinant vaccinia viruses

BACKGROUND

Cancer gene therapy expressing specific levels of multiple genes has not been adequately tested. This study investigates the antitumor effects of recombinant vaccinia viruses (recVVs) that express predictable levels of single and multiple cytokines in a passive immunization murine breast cancer (C3HBA) model.

METHODS

Seventeen recVVs encoding different cytokine combinations under weak and strong VV promoters were constructed. Cytokine production was measured in vitro by enzyme-linked immunosorbent assay. Mice were immunized with infected C3HBA cells and rechallenged 10 days later with 10(6) parental tumor cells. Controls were treated with saline or recVVs not expressing cytokines. Tumors were measured for 24 days. Data were analyzed using Fisher's exact test and the Breslow-Gehan-Wilcoxon test.

RESULTS

recVVs encoding multiple cytokines induced secretion of each cytokine at predictable levels corresponding to VV promoter strength. Ten of 10 controls developed tumors by day 11 after rechallenge. recVVs producing large but not small amounts of murine granulocyte-macrophage colony-stimulating factor (GM-CSF) alone resulted in complete protection in all immunized mice (p = 0.0003) for 24 days and disease-free survival (DFS) was significantly prolonged versus controls (p < 0.001). GM-CSF under a weak promoter was also effective in combination with human interleukin-1 beta (hIL-1 beta; p = 0.0220; DFS, p = 0.031) or interferon-gamma (IFN-gamma; p = 0.0037; DFS, p = 0.003). Effectiveness of hIL-1 beta and IFN-gamma vaccines depended on cytokine combinations and not the amount of cytokine produced. IL-2 or tumor necrosis factor-alpha vaccines had no significant antitumor effect.

CONCLUSIONS

(a) recVVs can simultaneously express controllable levels of two cytokines; (b) tumor cells modified by recVVs generate systemic antitumor immunity; and (c) strength of immunity appears to be related to the amounts and specific cytokine(s) produced.

Gene Therapy and Inherited Dyslipidemia

OBJECTIVE

To explore the current status and future potential of gene therapy for the inherited dyslipidemias.

METHODS

A brief overview of the inherited dyslipidemias, a review of the currently available means of transferring genetic material in vivo, and a discussion of two examples of conditions in which gene therapy may be useful--familial hypercholesterolemia and reduced high-density lipoprotein cholesterol syndromes--are presented.

RESULTS

Although substantial progress has been made in the management of inherited dyslipidemia, optimal treatment regimens are not available in all cases. Gene therapy has recently emerged as a potential solution to some of these problems. For gene therapy to be successful, several factors are necessary: an efficient means of gene transfer, long-term transgene expression, and lack of toxicity. Although the feasibility of this approach has been demonstrated, currently available vectors have a number of technical and safety limitations.

CONCLUSION

Gene therapy for inherited dyslipidemias has many technical hurdles that must be overcome before it will have widespread clinical application.

Improved cationic lipid formulations for in vivo gene therapy

The problem of assessing in vivo activity of gene delivery systems is complex. The reporter gene must be carefully chosen depending on the application. Plasmids with strong promoters, enhancers and other elements that optimize transcription and translation should be employed, such as the CMVint and pCIS-CAT constructs. Formulation aspects of cationic lipid-DNA complexes are being studied in several laboratories, and the physical properties and molecular organization of the complexes are being elucidated. Likewise, studies on the mechanism of DNA delivery with cationic lipids are accumulating which support the basic concept that the complexes fuse with biological membranes leading to the entry of intact DNA into the cytoplasm. Naked plasmid DNA administered by various routes is expressed at significant levels in vivo. This observation is not restricted to skeletal and heart muscle, but has been observed in lung, dermis, and in undefined tissues following intravenous administration. Most of the widely available cationic lipids, including Lipofectin, Lipofectamine and DC-cholesterol have a very poor ability to enhance DNA expression above the baseline naked DNA level, at least in lung. In this report we have revealed a novel cationic lipid, DLRIE, which can significantly enhance CAT expression in mouse lung by 25-fold above the naked DNA level. Other compounds are currently being evaluated which can enhance the naked DNA expression even higher. Plasmid vector improvements have led to further increase in in vivo lung expression, so that the net improvement is > 5,000-fold. Results of this nature are advancing the pharmaceutical gene therapy opportunities for synthetic cationic lipid based gene delivery systems.

Introduction of murine Il-4 gene into B16(F10) melanoma tumors by direct gene transfer with DNA-liposome complexes

Il-4 is a highly pleiotropic cytokine which induces cytotoxic activity when present at the tumor site. Death of tumor cells probably depends on the appearance of an inflammatory infiltrate composed of eosinophils and macrophages. Regression of established tumor masses has been readily observed upon direct intratumor implantation of cells which constitutively produce high amounts of Il-4. We now report a similar potent anti-tumor effect achieved via direct gene transfer, i.e. by injecting Il-4 DNA complexed with cationic liposomes into B16(F10) melanoma tumor in vivo.

Paramagnetic polymerized liposomes as new recirculating MR contrast agents

We describe a well-tolerated blood pool contrast agent with extended recirculatory half-life based on paramagnetic polymerized liposomes (PPLs). PPLs were constructed from a new type of polymerizable lipid molecule that has a derivative of gadopentetate dimeglumine as the hydrophilic head group and diacetylene groups in the hydrophobic acyl chains, which cross-link when irradiated with ultraviolet (UV) light. Biodistribution, blood pool half-life, and MR image enhancement were determined for PPLs composed of 10% of the gadopentetate dimeglumine lipid and 90% of ditricosadiynoyl tricosadiynayl phosphatidylcholine (DAPC) at a dose of 0.015 mmol Gd+3/kg in rats. In T1-weighed MR images (TR/TE = 400/18 msec), an average signal enhancement of 34% in the kidneys and 20% in the liver was observed, which persisted for at least 90 minutes after administration of the PPLs. Biodistribution studies using radiolabeled PPLs confirmed that 80% of the injected dose remained in the blood pool after 2 hours. The half-life of elimination from the blood pool was 19 hours. The preparation was well tolerated in rats and produced similar MR contrast enhancement of the blood pool as produced by other liposome contrast agents. However, the half-life of PPL elimination from the blood pool was prolonged relative to other liposome systems.

Efficiency of in vivo gene transfection into transplanted rat heart by coronary infusion of HVJ liposome

BACKGROUND

Current methods of in vivo gene transfer into myocardium are limited by low efficiency. To improve in vivo gene transfer, a gene transfer method using hemagglutinating virus of Japan (HVJ) as a viral vector can be an alternative.

METHODS AND RESULTS

In vivo gene transfection of FITC-labeled oligonucleotide (F-ODN) and cDNA of beta-galactosidase (beta-gal) was examined with use of the HVJ liposome (H group) or without it (C group). In the H group, F-ODN or cDNA of beta-gal were complexed with liposomes, DNA binding nuclear protein (HMG1), and the viral protein coat of HVJ. After the harvest of donor rat hearts arrested by cardioplegia, the coronary artery was infused with the liposome gene complex. The hearts were transplanted into the abdomens of recipient rats and harvested 3 days after transplantation. Regarding F-ODN, the H group clearly showed FITC staining in the nuclei of the myocytes and endothelial cells in almost all layers of the myocardium as compared with the C group. Regarding the expression of beta-gal, the H group showed a clear expression of beta-gal on myocytes, whereas very low expression of beta-gal was seen in the C group.

CONCLUSIONS

The donor hearts were transfected with F-ODN and beta-gal gene in almost all layers of the myocardium as a result of coronary infusion of the HVJ liposome during cardioplegic arrest. Our method is seen as a novel in vivo gene transfer technique for the heart and may provide a new tool for both research and therapy of heart transplantation.

Cationic liposome-mediated intravenous gene delivery

Systemic gene transfer provides new opportunities for the analysis of gene function and gene regulation in vivo, as well as for human gene therapy. We used the chloramphenicol acetyltransferase reporter gene to examine several parameters important for the development of efficient, cationic liposome-mediated, intravenous (IV) gene transfer in mice. We then demonstrated that this approach can produce high level expression of biologically important genes. Specifically, we assessed the relationship of expression vector design to the level of systemic gene expression produced, and compared transfection levels produced by intravenously injecting DNA alone versus DNA-liposome complexes. We found that both the position of the heterologous intron, and the promoter element used in the expression plasmid, significantly affected the level of systemic gene expression produced. Although intravenous injection of plasmid DNA alone transfected every tissue analyzed, liposome-mediated delivery was much more efficient. We also established that repeated i.v. injection of DNA-liposome complexes produced high level systemic transfection. The second injection of DNA-liposome complexes produced levels of gene expression at least as high as those following a single i.v. injection. Thus, unlike some viral vectors, a neutralizing host-immune response does not limit re-expression, following reinjection of DNA-liposome complexes. Finally, we showed that the expression vectors which produced the highest levels of chloramphenicol acetyltransferase reporter gene expression could also produce high level expression of two colony stimulating factor genes in mice. Specifically, i.v. injection of liposomes complexed to expression vectors into which we had inserted either the murine granulocyte-macrophage-colony stimulating factor cDNA or the human granulocyte-CSF cDNA, produced circulating levels of the corresponding colony stimulating factor gene product comparable to levels which have been shown previously to be both biologically and therapeutically significant.

Interaction of cationic liposomes with cells of electrically active neuronal networks in culture

Incubation of rhodamine-labeled cationic liposomes with mature murine spinal cultures results in strong fluorescence that is evenly distributed on somata and neurites of neurons in 7 different cultures. Staining of the glial carpet is minimal. Rhodamine-labeled dextran, encapsulated in liposomes, also stains neurons. Electron microscope data show external attachment and intact internalization of liposomes. Spontaneous electrical bursting activity is altered but not lost after incubation.

Gene therapy in the central nervous system: direct versus indirect gene delivery

Over the last decade, the combination of molecular biology and cell transplantation techniques has given rise to a powerful method for gene therapy. The implantation of genetically modified cultured cells has been extensively used in the central nervous system (CNS) in various experimental models of neurologic disorders. More recently, viral and chemical methods have been developed to further efforts to shuttle transgenes into the relatively inaccessible brain. Adenoviral and liposomal synthetic vectors carry transgenes into neural tissue in situ and are beginning to show promise as new methods for CNS therapy.

Systemic gene therapy: biodistribution and long-term expression of a transgene in mice

We have investigated the in vivo efficacy of a systemic gene transfer method, which combines a liposomal delivery system (DLS liposomes) with episomally replicative DNA plasmids to effect long-term expression of a transgene in cells. A single i.v. injection of a plasmid DNA vector containing the luciferase gene as a marker was administered with the DLS liposomes in BALB/c mice. The luciferase gene and its product were found in all mouse tissues tested as determined by PCR analysis and immunohistochemistry. Luciferase activity was also detected in all tissues tested and was present in lung, liver, spleen, and heart up to 3 months postinjection. In contrast to the nonepisomal vectors tested (pRSV-luc and pCMVintlux), human papovavirus (BKV)-derived episomal vectors showed long-term transgene expression. We found that these episomal vectors replicated extrachromosomally in lung 2 weeks postinjection. Results indicated that transgene expression in specific tissues depended on the promoter element used, DNA/liposome formulation, dose of DNA per injection, and route of administration.

Non-viral gene therapy

Gene therapy is a medical/surgical intervention currently being developed, in which genes are introduced into cells in order to treat or cure a wide variety of human diseases. The field has evolved over the past four decades, with most experimental gene-therapy studies based on the use of viruses to deliver the genes of therapeutic interest. More recently, a large number of non-viral approaches to gene therapy have emerged, yielding promising pre-clinical results, and which are currently being evaluated in early stage clinical trials.

Gene transfer to the thymus. A means of abrogating the immune response to recombinant adenovirus

OBJECTIVE

The authors investigated whether adenoviral gene transfer to the thymus could be accomplished in vivo and whether immunologic unresponsiveness to recombinant adenovirus could be induced by intrathymic inoculation.

SUMMARY BACKGROUND DATA

A major barrier to the clinical application of adenovirus-mediated gene therapy for diseases requiring long-lasting gene expression is the immunogenicity of adenoviral vectors, which limits the duration of its effects. In other experimental models, intrathymic inoculation of foreign proteins or cells has proven to be an effective means to induce immunologic tolerance.

METHODS

The efficiency of gene transfer to the mouse thymus after direct inoculation of recombinant adenovirus was compared with that of several other vectors. Animals inoculated with adenovirus-infected pancreatic islets into the thymus were tested for unresponsiveness to the virus with a subsequent challenge of adenovirus administered into the liver by intravenous injection.

RESULTS

Adenovirus accomplished highly efficient gene transfer to the thymus, unlike plasmid DNA, DNA-liposome complexes, retrovirus, and adeno-associated virus. Adenoviral transgene expression was transient in the thymus of immunocompetent mice but persistent in CD8+ T-cell-deficient and severe combined immunodeficiency (SCID) mice, implicating the role of cytotoxic T lymphocytes in viral clearance. Intrathymic transplantation of syngeneic pancreatic islet cells infected with adenovirus impaired the normal antiviral cytotoxic T-lymphocyte response and prolonged hepatic transgene expression after an intravenous challenge with adenovirus.

CONCLUSIONS

Recombinant adenovirus accomplishes highly efficient gene transfer to the thymus in vivo. Intrathymic inoculation of adenovirus-infected islets can be used to induce immunologic unresponsiveness to the adenoviral vector and, potentially, to other proteins that it might be engineered to encode.

Nonviral gene therapy: the promise of genes as pharmaceutical products

Although most research on gene therapy has focused on the use of recombinant viruses to deliver genes to cells in vivo, progress also has been made toward developing nonviral, pharmaceutical formulations of genes for in vivo human therapy. Various methods for nonviral gene therapy have been proposed. Some approaches are aimed at developing "artificial viruses" that attempt to mimic the process of viral infection using synthetic materials. Others apply the theory and methods of advanced, particulate drug delivery to deliver DNA to select somatic targets. These approaches employ DNA complexes containing lipid, protein, peptide, or polymeric carriers as well as ligands capable of targeting the DNA complex to cell-surface receptors on the target cell and ligands for directing the intracellular trafficking of DNA to the nucleus. Nonviral systems have been used to deliver genes to the lung, liver, endothelium, epithelium, and tumor cells and have been shown to be generally safe. More than a dozen clinical trials are currently underway using nonviral systems for disease indications including cystic fibrosis and cancer. Future advances in nonviral systems will be based on an emerging appreciation of the biological constraints on the fate and function of DNA within the body and within the cell.

Liposome-encapsulated DNA-mediated gene transfer and synthesis of human factor IX in mice

Hemophilia B is an X-chromosome-linked recessive disorder that is caused by a deficiency of biologically active clotting factor IX (FIX). In this work, liposomes (Lip) were used for non-viral, in vivo gene transfer of the human FIX gene into mouse organs. Plasmid DNA, containing the human FIX cDNA under the control of the Moloney murine leukemia virus (MoMLV) long terminal repeat (LTR), was encapsulated in 1-2-microns multilamellar Lip composed of egg phosphatidylcholine (EPC). The percentage of Lip-associated DNA was 47%, and 72% of the Lip DNA was protected from DNase I digestion. The Lip-encapsulated (Len) DNA was injected intravenously into Balb/c mice, and at various times post-injection, various tissues were examined for the presence of the exogenous DNA. Plasmid DNA was detected by Southern blot analysis mainly in the liver and spleen, but small amounts were also detected in the lungs, heart and kidneys. The plasmid DNA was retained in mouse liver cells for at least 7 days post-injection, and remained in an episomal state. The levels of human FIX protein in the mouse plasma were 190-650 pg per ml for 2 to 7 days post-injection. Treatment of mice with chloroquine (Cq) and colchicine (Cc) prior to Lip injection significantly increased the amount of plasmid DNA found in the liver cells, as well as the level of human FIX in the plasma. These results demonstrate the potential use of Len DNA for gene transfer into liver and spleen, and for gene therapy of inherited and acquired disorders.

The fate of plasmid DNA after intravenous injection in mice: involvement of scavenger receptors in its hepatic uptake

PURPOSE

We examined the stability and disposition characteristics of a naked plasmid DNA pCAT as a model gene after intravenous injection in mice to construct the strategy of in vivo gene delivery systems.

METHODS

After the injection of pCAT to the mice, stability, tissue distribution, hepatic cellular localization, and effect of some polyanions on the hepatic uptake were studied.

RESULTS

The in vitro study demonstrated that the pCAT was rapidly degraded in mouse whole blood with a half-life of approximately 10 min at a concentration of 100 micrograms/ml. After intravenous injection, pCAT was degraded at a significantly faster rate than that observed in the whole blood, suggesting that pCAT in vivo was also degraded in other compartments. Following intravenous injection of [32P] pCAT, radioactivity was rapidly eliminated from the plasma due to extensive uptake by the liver. Hepatic accumulation occurred preferentially in the non-parenchymal cells. The hepatic uptake of radioactivity derived from [32P] pCAT was inhibited by preceding administration of polyanions such as polyinosinic acid, dextran sulfate, maleylated and succinylated bovine serum albumin but not by polycytidylic acid. These findings indicate that pCAT is taken up by the liver via scavenger receptors on the non-parenchymal cells. Pharmacokinetic analysis revealed that the apparent hepatic uptake clearance was fairly close to the liver plasma flow.

CONCLUSIONS

These findings provide useful information for the development of delivery systems for in vivo gene therapy.

Complexes between cationic liposomes and DNA visualized by cryo-TEM

The association structures formed by cationic liposomes and DNA-plasmids have been successfully employed as gene carriers in transfection assays. In the present study such complexes was studied by cryo-TEM (cryo-transmission electron microscopy). Cationic liposomes made up by DOPE (dioleoylphosphatidylethanolamine) and various amounts of three different cationic surfactants were investigated. The cryo-TEM analysis suggests that an excess of lipid in terms of charge, leads to entrapment of the DNA molecules between the lamellas in clusters of aggregated multilamellar structures. With increasing amounts of DNA free or loosely bound plasmids were found in the vicinity of the complexes. The importance of the choice of surfactant, as reported from many transfection assays, was not reflected in changes of the type of DNA-vesicle association. A tendency towards polymorphism of the lipid mixtures is reported and its possible implications are discussed.

Fusion of cationic liposomes with mammalian cells occurs after endocytosis

The interaction of cationic liposomes prepared using either dioleoyltrimethylammonium propane (DOTAP) or 3 beta-(N-(N',N'-dimethylaminoethane)carbamoyl)cholesterol (DC-CHOL) with model membranes and with cultured mammalian cells was examined using an assay developed for monitoring virus-cell fusion (Stegmann et al. (1993) Biochemistry 32, 11330-11337). Lipid mixing between cationic liposomes and liposomes composed of DOPE/dioleoylphosphatidylglycerol (DOPG) or dioleoylphosphatidylcholine (DOPC)/DOPG was insensitive to pH in the range of pH 4.5-7.0 and was not affected by sodium chloride concentration in the range of 0-150 mM. Lipid mixing was dependent on dioleoylphosphatidylethanolamine (DOPE), since cationic liposomes prepared using dioleoylphosphatidylcholine (DOPC) were incapable of lipid mixing with DOPC/DOPG liposomes. The interaction of cationic liposomes with Hep G-2 and CHO D- cells was also studied. For both cell types, liposome-cell lipid mixing was rapid at 37 degrees C, beginning within minutes and continuing for up to 1 hour after uptake. The extent of lipid mixing was decreased at 15 degrees C, especially at later (> or = 20 min) time points. This suggests that at least part of the observed lipid mixing occurred after reaching cellular lysosomes. No lipid mixing was seen at 4 degrees C. Monensin inhibited lipid mixing between cationic liposomes and the cells, despite having no effect on liposome uptake. Inhibition of endocytic uptake of liposomes, either by incubation in hypertonic media or by depletion of cellular ATP with sodium azide and 2-deoxyglucose abolished liposome-cell fusion in both cell types. These data demonstrate that binding to the cell surface is insufficient for cationic liposome-cell fusion and that uptake into the endocytic pathway is required for fusion to occur.

Cancer gene therapy using plasmid DNA: pharmacokinetic study of DNA following injection in mice

The fate of plasmid DNA complexed with cationic lipids delivered intravenously in mice was evaluated at selected timepoints up to 6 months postinjection. Blood half-life and tissue distribution of plasmid DNA and potential expression in tissues were examined. Southern blot analyses of blood indicated that intact plasmid DNA was rapidly degraded, with a half-life of less than 5 min for intact plasmid, and was no longer detectable at 1 hr postinjection. Southern analyses of tissue demonstrated that intact DNA was differentially retained in the lung, spleen, liver, heart, kidney, marrow, and muscle up to 24 hr postinjection. After 7 days, no intact plasmid DNA was detectable by Southern blot analysis; however, the plasmid was detectable by the polymerase chain reaction (PCR) in all tissues examined at 7 and 28 days postinjection. At 6 months postinjection, femtogram levels of plasmid were detected only in muscle. Immunohistochemical analyses did not detect encoded protein in the tissues harboring residual plasmid at 1 or 7 days postinjection.

Transgenic animals as models for human disease

Since its first description in 1981 (1), transgenic technology has greatly influenced the focus and direction pace of biomedical research. Introduction of foreign DNA into the genome of animals by microinjection into fertilized oocytes is now used in almost every field of research spanning from oncology, immunology and neurology to cardiovascular medicine. The ability to integrate genes in the germline and their successful expression in the host provides an opportunity to study the role of a certain gene in the initiation and propagation of disease. Transgenic methodology serves as the link between molecular biology, introducing in vitro a defined genetic modification and whole animal physiology, with the resulting in vivo alteration of body function. This potential has been exploited to study the pathophysiological role of human genes. Transgenic animals have been used to study aspects of tumor development, immune regulation, cardiovascular development and atherosclerosis. These studies have provided new insights into the genetic origin of certain diseases and have improved our understanding of pathological processes on the cellular level. As a future goal, these studies may also serve the development of new diagnostic tools or novel therapeutic strategies such as gene therapy.

DNA vaccination against persistent viral infection

This study shows that DNA vaccination can confer protection against a persistent viral infection by priming CD8+ cytotoxic T lymphocytes (CTL). Adult BALB/c (H-2d) mice were injected intramuscularly with a plasmid expressing the nucleoprotein (NP) gene of lymphocytic choriomeningitis virus (LCMV) under the control of the cytomegalovirus promoter. The LCMV NP contains the immunodominant CTL epitope (amino acids 118 to 126) recognized by mice of the H-2d haplotype. After three injections with 200 micrograms of NP DNA, the vaccinated mice were challenged with LCMV variants (clones 13 and 28b) that establish persistent infection in naive adult mice. Fifty percent of the DNA-vaccinated mice were protected, as evidenced by decreased levels of infectious virus in the blood and tissues, eventual clearance of viral antigen from all organs tested, the presence of an enhanced LCMV-specific CD8+ CTL response, and maintenance of memory CTL after clearance of virus infection. However, it should be noted that protection was seen in only half of the vaccinated mice, and we were unable to directly measure virus-specific immune responses in any of the DNA-vaccinated mice prior to LCMV challenge. Thus, at least in the system that we have used, gene immunization was a suboptimal method of inducing protective immunity and was several orders of magnitude less efficient than vaccination with live virus. In conclusion, our results show that DNA immunization works against a persistent viral infection but that efforts should be directed towards improving this novel method of vaccination.

Systemic gene therapy with p53 reduces growth and metastases of a malignant human breast cancer in nude mice

We report on an in vivo delivery system that attenuates the growth, in nude mice, of a malignant human breast cancer cell line containing a p53 mutation. Nude mice, inoculated with breast carcinoma cells, were injected every 10-12 days with a liposome-p53 complex via the tail vein. A significant reduction of greater than 60% in primary tumor volume was observed as compared to the control groups. Furthermore, when individual growth patterns of the tumors were assessed, we found that primary tumor size regressed in the majority of p53-treated animals (8/15), whereas only one tumor in the control groups (1/22) regressed. The eight tumors that regressed with the liposome-p53 complex showed no evidence of relapse for 1 month after the cessation of treatment. We also determined that the administration of the liposome-p53 complex reduced the incidence of metastases. The MDA-MB-435 tumor cells, transduced with the lacZ gene, facilitated quantitation of beta-galactosidase activity and tumor burden in the lungs. The number of metastatic cells in the lung was significantly lower in the p53-treated group (0.53 +/- 0.43 x 10(6), p < 0.01) than in either the vector-treated (8.1 +/- 3.7 x 10(6)) or untreated control groups (15.8 +/- 5.9 x 10(6)). Thus, systemic administration of the liposome-p53 complex reduced not only the size of the primary tumors but, more importantly, prevented the relapse and metastases of these tumors.

DNA immunization confers protection against lethal lymphocytic choriomeningitis virus infection

DNA vaccination has been evaluated with the lymphocytic choriomeningitis virus (LCMV) model system. Plasmid DNA encoding the LCMV nucleoprotein, when injected intramuscularly, induces both antiviral antibodies and cytotoxic T lymphocytes. Injection of DNA encoding the nucleoprotein or the viral glycoprotein confers protection against normally lethal LCMV challenge in a major histocompatibility complex-dependent manner. The protection conferred is incomplete, but it is most probably mediated by the induced cytotoxic T lymphocytes.

Transgenic mice expressing the human heat shock protein 70 have improved post-ischemic myocardial recovery

Heat shock treatment induces expression of several heat shock proteins and subsequent post-ischemic myocardial protection. Correlations exist between the degree of stress used to induce the heat shock proteins, the amount of the inducible heat shock protein 70 (HSP70) and the level of myocardial protection. The inducible HSP70 has also been shown to be protective in transfected myogenic cells. Here we examined the role of human inducible HSP70 in transgenic mouse hearts. Overexpression of the human HSP70 does not appear to affect normal protein synthesis or the stress response in transgenic mice compared with nontransgenic mice. After 30 min of ischemia, upon reperfusion, transgenic hearts versus nontransgenic hearts showed significantly improved recovery of contractile force (0.35 +/- 0.08 versus 0.16 +/- 0.05 g, respectively, P < 0.05), rate of contraction, and rate of relaxation. Creatine kinase, an indicator of cellular injury, was released at a high level (67.7 +/- 23.0 U/ml) upon reperfusion from nontransgenic hearts, but not transgenic hearts (1.6 +/- 0.8 U/ml). We conclude that high level constitutive expression of the human inducible HSP70 plays a direct role in the protection of the myocardium from ischemia and reperfusion injury.

Direct gene delivery of human tissue kallikrein reduces blood pressure in spontaneously hypertensive rats

Hypertension is a multigene and multifactorial disorder affecting approximately 25% of the population. To demonstrate potential therapeutic effects of human tissue kallikrein in hypertension, spontaneously hypertensive rats were subjected to somatic gene therapy. Two human tissue kallikrein DNA constructs, one under the promoter control of the metallothionein metal response element and the other under the control of the Rous sarcoma virus 3'-LTR, were generated. We delivered naked DNA constructs into spontaneously hypertensive rats via intravenous injection. The expression of human tissue kallikrein in rats was identified in the heart, lung, and kidney by reverse transcription polymerase chain reaction followed by Southern blot analysis and an ELISA specific for human tissue kallikrein. A single injection of both human kallikrein plasmid DNA constructs caused a sustained reduction of blood pressure which began 1 wk after injection and continued for 6 wk. A maximal effect of blood pressure reduction of 46 mmHg in rats was observed 2-3 wk after injection with kallikrein DNA as compared to rats with vector DNA (n = 6, P < 0.05). The hypotensive effect caused by somatic gene delivery of human tissue kallikrein in hypertensive rats is reversed by subcutaneous injection of aprotinin, a potent tissue kallikrein inhibitor. No antibodies to either human tissue kallikrein or kallikrein DNA were detected in rat sera after injection of the human kallikrein gene. These results show that direct gene delivery of human tissue kallikrein causes a sustained reduction in systolic blood pressure in genetically hypertensive rats and indicate that the feasibility of kallikrein gene therapy for treating human hypertension should be studied.

The spinal cord as an alternative model for nerve tissue graft

The spinal cord provides an alternative model for nerve tissue grafting experiments. Anatomo-functional correlations are easier to make here than in any other region of the CNS because of a direct implication of spinal cord neurons in sensorimotor activities. Lesions can be easily performed to isolate spinal cord neurons from descending inputs. The anatomy of descending monoaminergic systems is well defined and these systems offer a favourable paradigm for lesion-graft experiments.

Multiple obstacles to gene therapy in the brain

Neuwelt et al. have proposed gene-transfer experiments utilizing an animal model that offers many important advantages for investigating the feasibility of gene therapy in the human brain. A variety of tissues concerning the viral vector and mode of delivery of the corrective genes need to be resolved, however, before such therapy is scientifically supportable.

Principles of brain tissue engineering

It is often presumed that effects of neural tissue transplants are due to release of neurotransmitter. In many cases, however, effects attributed to transplants may be related to phenomena such as trophic effects mediated by glial cells or even tissue reactions to injury. Any conclusion regarding causation of graft effects must be based on the control groups or other comparisons used. In human clinical studies, for example, comparing the same subject before and after transplantation allows for many interpretations of the causes of clinical changes.

Lessons on transplant survival from a successful model system

Studies on the snailMelampusreveal that connectivity is crucial to the survival of transplanted ganglia. Transplanted CNS ganglia can innervate targets or induce supernumerary structures. Neuron survival is optimized by the neural incorporation that occurs when a transplanted ganglion is substituted for an excised ganglion. Better provision for the trophic requirements of neurons will improve the success of mammalian fetal transplants.

Repairing the brain: Trophic factor or transplant?

Three experiments on neural grafting with adult rat hosts are described. Working memory impairments were produced by lesioning the hippocampus or severing its connections with the septum by ablating the fimbria-fornix. The results suggest that the survival and growth of a neural graft, whether an autograft or a xenograft, is not a necessary condition for functional recovery on a task tapping working memory.

Will brain tissue grafts become an important therapy to restore visual function in cerebrally blind patients?

Grafting embryonic brain tissue into the brain of patients with visual field loss due to cerebral lesions may become a method to restore visual function. This method is not without risk, however, and will only be considered in cases of complete blindness after bilateral occipital lesions, when other, risk-free neuropsychological methods fail.

Difficulties inherent in the restoration of dynamically reactive brain systems

The responses displayed by an injured or diseased nervous system are complex. Some of the responses may effect a functional reorganization of the affected neural circuitry. Strategies aimed at the restoration of function, whether or not these involve transplantation, need to recognize the innate reactive capacity of the nervous system to damage. More successful strategies will probably incorporate, rather than ignore, the adaptive responses of the compromised neural systems.