Efficient and sustained gene expression in primary T lymphocytes and primary and cultured tumor cells mediated by adeno-associated virus plasmid DNA complexed to cationic liposomes

Synthetically Engineered Adeno-Associated Virus for Efficient, Safe, and Versatile Gene Therapy Applications

Gene therapy directly targets mutations causing disease, allowing for a specific treatment at a molecular level. Adeno-associated virus (AAV) has been of increasing interest as a gene delivery vehicle, as AAV vectors are safe, effective, and capable of eliciting a relatively contained immune response. With the recent FDA approval of two AAV drugs for treating rare genetic diseases, AAV vectors are now on the market and are being further explored for other therapies. While showing promise in immune privileged tissue, the use of AAV for systemic delivery is still limited due to the high prevalence of neutralizing antibodies (nAbs). To avoid nAb-mediated inactivation, engineered AAV vectors with modified protein capsids, materials tethered to the capsid surface, or fully encapsulated in a second, larger carrier have been explored. Many of these engineered AAVs have added benefits, including avoided immune response, overcoming the genome size limit, targeted and stimuli-responsive delivery, and multimodal therapy of two or more therapeutic modalities in one platform. Native and engineered AAV vectors have been tested to treat a broad range of diseases, including spinal muscular atrophy, retinal diseases, cancers, and tissue damage. This review will cover the benefits of AAV as a promising gene vector by itself, the progress and advantages of engineered AAV vectors, particularly synthetically engineered ones, and the current state of their clinical translation in therapy.

Optimization of eGFP expression using a modified baculovirus expression system

The baculovirus gene expression system is an efficient and safe protein expression system, since baculoviruses cannot replicate in mammalian cells. In order to improve the transduction efficiency and increase the reporter gene expression levels delivered by baculoviruses, we tested in the baculovirus expression cassette the Woodchuck hepatitis virus response element (WPRE), and AAV-derived inverted terminal repeats (ITRs) and the truncated vesicular stomatitis virus G protein (VSV-GED). The results showed that WPRE and VSV-GED have synergistic effects and could enhance the expression efficiency of enhanced green fluorescence protein (eGFP), and that ITRs effectively extended the duration of eGFP expression. We also demonstrated that the efficiency of eGFP expression varied under the control of the CMV, CBA, EF1-α or WSSV ie1 promoters in different cell lines.

Large-scale recombinant adeno-associated virus production

Since recombinant adeno-associated virus (rAAV) was first described as a potential mammalian cell transducing system, frequent reports purportedly solving the problems of scalable production have appeared. Yet few of these processes have enabled the development of robust and economical rAAV production. Two production platforms have emerged that have gained broad support for producing both research and clinical grade vectors. These processes differ fundamentally in several aspects. One approach is based on adherent mammalian cells and uses optimized chemical transient transfection for introducing the essential genetic components into the cells. The other approach utilizes suspension cultures of invertebrate cells. Baculovirus expression vectors are used for introducing the AAV genes into the cells. In addition, the baculovirus provides the helper functions necessary for efficient AAV DNA replication. The use of suspension cell culture provides an intrinsically more scalable platform system than using adherent cells. The upstream processes for suspension cultures are amenable for automation and are easily monitored and regulated to maintain optimum conditions that produce consistent yields of rAAV. Issues relating to developing new and improving existing rAAV production methods are discussed.

Transcriptional targeting to brain cells: Engineering cell type-specific promoter containing cassettes for enhanced transgene expression

Transcriptional targeting using a mammalian cellular promoter to restrict transgene expression to target cells is often desirable for gene therapy. This strategy is, however, hindered by relatively weak activity of some cellular promoters, which may lead to low levels of gene expression, thus declining therapeutic efficacy. Here we outline the advances accomplished in the area of transcriptional targeting to brain cells, with a particular focus on engineering gene cassettes to augment cell type-specific expression. Among the effective approaches that improve gene expression while retaining promoter specificity are promoter engineering to change authentic sequences of a cellular promoter and the combined use of a native cellular promoter and other cis-acting elements. Success in achieving high level and sustained transgene expression only in the cell types of interest would be of importance in allowing gene therapy to have its impact on patient treatment.

Repeated intrathecal injections of plasmid DNA encoding interleukin-10 produce prolonged reversal of neuropathic pain

Neuropathic pain is a major clinical problem unresolved by available therapeutics. Spinal cord glia play a pivotal role in neuropathic pain, via the release of proinflammatory cytokines. Anti-inflammatory cytokines, like interleukin-10 (IL-10), suppress proinflammatory cytokines. Thus, IL-10 may provide a means for controlling glial amplification of pain. We recently documented that intrathecal IL-10 protein resolves neuropathic pain, albeit briefly (approximately 2-3 h), given its short half-life. Intrathecal gene therapy using viruses encoding IL-10 can also resolve neuropathic pain, but for only approximately 2 weeks. Here, we report a novel approach that dramatically increases the efficacy of intrathecal IL-10 gene therapy. Repeated intrathecal delivery of plasmid DNA vectors encoding IL-10 (pDNA-IL-10) abolished neuropathic pain for greater than 40 days. Naked pDNA-IL-10 reversed chronic constriction injury (CCI)-induced allodynia both shortly after nerve injury as well as 2 months later. This supports that spinal proinflammatory cytokines are important in both the initiation and maintenance of neuropathic pain. Importantly, pDNA-IL-10 gene therapy reversed mechanical allodynia induced by CCI, returning rats to normal pain responsiveness, without additional analgesia. Together, these data suggest that intrathecal IL-10 gene therapy may provide a novel approach for prolonged clinical pain control.

Astrocytic expression of transgene in the rat brain mediated by baculovirus vectors containing an astrocyte-specific promoter

Therapeutic gene expression in glial cells has been tested for the treatment of neurological diseases in animal models. Many of such studies used the promoter of the glial fibrillary acidic protein (GFAP) to restrict gene expression to astrocytes. We have investigated in the current study whether it is possible to improve the transcriptional activity of the cellular promoter, while maintaining its cell-type specificity. We constructed an expression cassette containing a hybrid cytomegalovirus (CMV) enhancer/GFAP promoter and placed it into baculovirus vectors, a type of viral vectors capable of transducing astrocytes. In another vector design, we used inverted terminal repeats (ITRs) from adeno-associated virus (AAV) to flank the expression cassette. The recombinant baculoviruses with the hybrid promoter improved gene expression levels over two orders of magnitude in glial cell lines and by 10-fold in the rat brain when compared to the baculoviruses with the GFAP promoter alone. The expression was further improved by ITR flanking, reaching levels higher than that mediated by the baculovirus vectors with the CMV immediate-early enhancer/promoter (CMV promoter). Using these recombinant baculoviruses, we observed extended in vivo transgene expression in the rat brain at 90 days postinjection, by which time the gene expression from baculovirus vectors with the GFAP or CMV promoter had already become undetectable. The astrocyte specificity of the GFAP promoter was preserved in the engineered expression cassette with the CMV enhancer and the AAV ITRs, as demonstrated by immunohistological analysis of brain samples and an axonal retrograde transport assay. Taken together, our findings suggest that these baculovirus vectors may serve as useful tools for astrocyte-specific gene expression in the brain.

8-chloroadenosine induced HL-60 cell growth inhibition, differentiation, and G(0)/G(1) arrest involves attenuated cyclin D1 and telomerase and up-regulated p21(WAF1/CIP1)

8-Chloroadenosine, an active dephosphorylated metabolite of the antineoplastic agent 8-chloroadenosine 3',5'-monophosphate (8-Cl-cAMP), induces growth inhibition in multiple carcinomas. Here we report that 8-chloroadenosine inhibits growth in human promyelocytic leukemia HL-60 cells by a G(0)/G(1) phase arrest and terminates cell differentiation along the granulocytic lineage. The mechanism of 8-chloroadenosine-induced G(0)/G(1) arrest is independent of apoptosis. The expressions of cyclin D1 and c-myc in HL-60 are suppressed by 8-chloroadenosine, whereas the cyclin-dependent kinases inhibitor p21(WAF1/CIP1) is up-regulated. 8-Chloroadenosine has less effect on the expressions of cyclin-dependent kinase (cdk)2 and cdk4, G(1) phase cyclin-dependent kinases, and only moderately induces the expression of transforming growth factor beta1 (TGFbeta1) and the mitotic inhibitor p27(KIP1). Telomerase activity is reduced in extracts of 8-chloroadenosine treated HL-60 cells, but 8-chloroadenosine does not directly inhibit the catalytic activity of telomerase in vitro. Therefore, anti-proliferation of HL-60 cells by 8-chloroadenosine involves coordination of cyclin D1 suppression, reduction of telomerase activity, and up-regulation of p21(WAF1/CIP1) that arrest cell-cycle progression at G(0)/G(1) phase and terminate cell differentiation.

Adeno-associated virus inverted terminal repeats improve neuronal transgene expression mediated by baculoviral vectors in rat brain

Baculoviral vectors can transduce neurons in the CNS but mediate only transient expression of transgenes. We have developed a new baculoviral vector in which the inverted terminal repeats (ITRs) of adeno-associated virus are used to flank a luciferase reporter gene cassette harboring a neuron-specific promoter. When tested in rat brain, the new viral vector was able to provide transgene expression for at least 90 days. Immunohistological analysis demonstrated that ITR flanking did not affect the cellular preference of the neuronal promoter in the context of baculovirus. These findings establish an effective way to engineer baculoviral vectors in order to achieve sustained expression of a functional gene for gene therapy for neurodegenerative disorders and physiological studies of neurons.

Improved neuronal transgene expression from an AAV-2 vector with a hybrid CMV enhancer/PDGF-beta promoter

BACKGROUND

Adeno-associated virus type 2 (AAV-2) vectors are highly promising tools for gene therapy of neurological disorders. After accommodating a cellular promoter, AAV-2 vectors are able to drive sustained expression of transgene in the brain. This study aimed to develop AAV-2 vectors that also facilitate a high level of neuronal expression by enhancing the strength of a neuron-specific promoter, the human platelet-derived growth factor beta-chain (PDGF) promoter.

METHODS AND RESULTS

A hybrid promoter approach was adopted to fuse the enhancer of human cytomegalovirus immediately early (CMV) promoter to the PDGF promoter. In cultured cortex neurons, AAV-2 vectors containing the hybrid promoter augmented transgene expression up to 20-fold over that mediated by titer-matched AAV-2 vectors with the PDGF promoter alone and 4-fold over the CMV enhancer/promoter. Injection of AAV-2 vectors with the hybrid promoter into the rat striatum resulted in neuron-specific transgene expression, the level of which was about 10-fold higher than those provided by the two control AAV-2 expression cassettes at 4 weeks post-injection and maintained for at least 12 weeks. Gene expression in the substantia nigra through possible retrograde transport of the AAV-2 vectors injected into the striatum was not obvious. After direct injection of AAV-2 vectors into the substantia nigra, transgene expression driven by the hybrid promoter was observed specifically in dopaminergic neurons and its level was about 3 and 17 times higher than that provided by the PDGF promoter alone and the CMV enhancer/promoter, respectively.

CONCLUSIONS

Enhanced transgene capacity plus neuron-specificity of the AAV-2 vectors developed in this study might prove valuable for gene therapy of Parkinson's disease.

Effective Suppression of Class I Major Histocompatibility Complex Expression by the US11 or ICP47 Genes Can Be Limited by Cell Type or Interferon-γExposure

An impediment encountered in many viral-based gene therapy clinical trials has been the rapid destruction of the transgene by the host's immune response. The processing and presentation of antigens through the class I major histocompatibility complex (MHC) pathway is the initial specific response to viral infection. Disruption of the class I MHC pathway by herpes simplex virus (HSV) or the human cytomegalovirus (HCMV) results in a decrease of the CD8(+) cytotoxic T lymphocyte (CTL) response and prolongs survival of infected cells in the host. Two viral immune suppression genes that interfere with the class I MHC presentation pathway, the HSV type I ICP47 gene and HCMV US11 gene, were cloned and each incorporated into a retroviral vector. HSV ICP47 and HCMV US11 transgenes were expressed in multiple cells lines and compared for their abilities to reduce antigen presentation on the cell surface by class I MHC. Retroviral supernatants were used to transduce human, canine, and rat cell lines. Fluorescence-activated cell sorter (FACS) analysis of US11- and ICP47-transduced cell lines demonstrated substantial reductions in class I MHC cell surface expression in most cell lines except in rodent cells where ICP47 is nonfunctional. The decrease in the level of class I MHC expression for ICP47 transduced cell lines ranged from 31-98% relative to negative controls. US11 decreased class I cell surface MHC by 67-96%. When both ICP47 and US11 are expressed in human cells, a further reduction of class I MHC was observed. Next, human A375 melanoma cells were tested to determine if the resulting reduction in cell surface class I MHC would reduce in vitro cytotoxicity by CTL. A375 cells expressing either ICP47 or US11 demonstrated a twofold to threefold reduction of specific lysis by primed CD8(+) CTL. These data clearly establish an ability to convey immune protection to human cells by viral genes. However, further analysis demonstrated that interferon (IFN)-gamma could reverse part or all of the downregulation of class I MHC induced by the ICP47 or US11 genes. The ICP47 and US11 genes, when expressed in target cells, decrease class I MHC presentation and as such might be used in strategies to create local immunosuppression against transgenes or allografts.

Reversal of diabetes in the rat by injection of hematopoietic stem cells infected with recombinant adeno-associated virus containing the preproinsulin II gene

AIM

To study the effect of injecting hematopoietic stem cells containing the preproinsulin gene II (rI2) via recombinant adeno-associated virus (rAAV) into normal and streptozotocin-diabetic rats.

METHODS

rI2 was transfected into rat hematopoietic stem cells using rAAV vector. Stem cells were injected by intravenous route into normal and STZ-induced diabetic rats to study blood sugar and expression of rI2 in various tissues. The pLP-1 recombinant plasmid containing rI2 (vLP-1) was engineered as previously described. Bone marrow from female Wistar-Furth rats was enriched for stem cells by using plastic adherence and monoclonal antirat CD3 and CD45 RA to deplete T and B cells. The remaining cells were exposed to vLP-1 (multiplicity of infection MOI =50:1 or 100:1) for 2 h. Approximately ten million exposed stem cells were injected by intravenous route into each animal; there were four groups: normal animals at MOI 50:1 (group 1) or MOI 100:1 (group 2); group 3 animals (n = 9) were streptozotocin-induced diabetic animals at MOI 100:1. Animals that showed reversal of diabetes from group 3 were sacrificed for study of gene expression at weeks 1, 2, and 6, respectively. Control diabetic animals did not receive stem cells or virus constituted group 4. Expression of rI2 was analyzed by RT-PCR and Southern analyses.

RESULTS

Despite introduction of insulin gene, groups 1 and 2 had blood sugar concentrations that remained within normal levels, while 3 of 9 animals in group 3 showed reversal of diabetes; using RT-PCR,group 1 expressed rI2 in liver, spleen, thymus, brain, and heart at week 1 only. In group 2, rI2 was seen in the thymus up to 6 weeks; in diabetic animals (group 3) rI2 was seen in liver, bone marrow, spleen, thymus, and peripheral blood lymphocytes at week 2 and in thymus and lymphocytes at week 6.

CONCLUSIONS

We have shown that (1) rAAV is a useful vector for transferring rI2 into rat hematopoietic stem cells; (2) normal animals remained euglycemic after injection of stem cells containing rI2 despite identification in various tissues suggesting autoregulation, and (3) short-term reversal of diabetes was achieved in some animals by injection of stem cells containing rI2.

Cationic lipids and cationic ligands induce DNA helix denaturation: detection of single stranded regions by KMnO4probing

Cationic lipids and cationic polymers are widely used in gene delivery. Using 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) as a cationic lipid, we have investigated the stability of the DNA in DOTAP:DNA complexes by probing with potassium permanganate (KMnO4). Interestingly, thymidines followed by a purine showed higher susceptibility to cationic ligand-mediated melting. Similar studies performed with other water-soluble cationic ligands such as polylysine, protamine sulfate and polyethyleneimine also demonstrated melting of the DNA but with variations. Small cations such as spermine and spermidine and a cationic detergent, cetyl trimethylammonium bromide, also rendered the DNA susceptible to modification by KMnO4. The data presented here provide direct proof for melting of DNA upon interaction with cationic lipids. Structural changes subsequent to binding of cationic lipids/ligands to DNA may lead to instability and formation of DNA bubbles in double-stranded DNA.

Immune responses to adeno-associated virus and its recombinant vectors

Recombinant adeno-associated virus (rAAV) vectors have emerged as highly promising for use in gene transfer for a variety of reasons, including lack of pathogenicity and wide host range. In addition, all virus-encoded genes have been removed from standard rAAV vectors, resulting in their comparatively low intrinsic immunogenicity. For gene replacement strategies, transgenes encoded by rAAV vectors may induce less robust host immune responses than other vectors in vivo. However, under appropriate conditions, host immune responses can be generated against rAAV-encoded transgenes, raising the potential for their use in vaccine development. In this review, we summarize current understanding of the generation of both undesirable and beneficial host immune responses directed against rAAV and encoded transgenes, and how they might be exploited for optimal use of this promising vector system.

A DNA vaccine containing inverted terminal repeats from adeno-associated virus increases immunity to HIV

BACKGROUND

DNA vaccines have been used to induce both humoral and cellular immune responses against infectious microorganisms. This study explores whether DNA vaccine immunogenicity can be improved by introducing inverted terminal repeats (ITRs) from adeno-associated virus (AAV) into the regulatory region of the DNA plasmid.

METHODS

CMV promoter-driven HIV Env expressing plasmid (pCMV-HIV) and the pCMV-HIV plasmid introduced ITRs (pITR/CMV-HIV) were transfected in HEK293 cells with LipofectAmine. The HIV Env expression was quantified with Western blot. Fifty micro g of pCMV-HIV or pITR/CMV-HIV plasmid with RIBI adjuvant were immunized to BALB/c mice on days 0, 14 and 28 by intramuscular route, and HIV-specific serum IgG titer was detected 2, 6, 10, 14 and 18 weeks after the first immunization. HIV-specific tetramer assay and HIV-specific IFN-gamma ELIspot assay were performed 1 week after the last immunization. The immune mice were intravenously challenged with a vaccinia virus expressing the HIV env gene 1 week after the last immunization.

RESULTS

Significantly higher level of HIV Env expression was achieved by pITR/CMV-HIV plasmid. BALB/c mice immunized with pITR/CMV-HIV plasmid generated significantly higher HIV-specific antibody, higher cellular immune responses and lower viral loading than animals immunized with pCMV-HIV plasmid.

CONCLUSIONS

AAV ITRs enhance CMV-dependent up-regulation of transgene expression and immunogenicity of DNA vaccine.

Gene delivery into primary T cells: overview and characterization of a transgenic model for efficient adenoviral transduction

Technologies for transfer of exogenous genes into primary T cells have been limited until recently. The introduction of new approaches for gene transfer via different viral vectors has expanded the options for genetic manipulation of primary T cells and has provided powerful tools for studies of T cell activation and differentiation. We provide a brief overview of the systems currently available and contrast the advantages and disadvantages of each. We also describe a new transgenic model that enables highly efficient gene delivery into primary T cells by nonreplicating adenoviral vectors.

Structural changes in DNA mediated by cationic lipids alter in vitro transcriptional activity at low charge ratios

Lipid/DNA complexes or Lipoplexes have been characterized by various biochemical and biophysical methods to understand the physical basis of transfection. Here we have addressed the effect of cationic liposomes, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), on transcription of DNA templates in vitro. Transcriptional activity of DNA-dependent RNA polymerase at DNA templates complexed with the cationic lipid varied as a function of charge ratio of lipid/DNA. At low charge ratios of 0.3:1 lipid/DNA and up to 1:1, we observed stimulation in transcription, while at higher charge ratios of lipid/DNA 3:1, complete inhibition in the activity occurred. Cetyl tri-methyl ammonium bromide (CTAB), a cationic detergent, and polyethylenimine (PEI), a cationic polymer, also bring about similar changes although to a lesser extent. The stimulation in transcription motivated us to probe into the molecular nature of the lipid/DNA interactions by absorbance spectroscopy and circular dichroism (CD). Upon interaction with lipids, hyperchromicity and susceptibility to micrococcal nuclease has increased, which suggests that the DNA was partially denatured. On complexation with the cationic lipid (DOTAP), the magnitude of the positive band in CD spectra decreased, accompanied with a red shift, as a function of charge ratio. Results from spectroscopic and enzyme assays suggest that at low charge ratios DNA may be partially unwound.

Dynamics of transgene expression in human glioblastoma cells mediated by herpes simplex virus/adeno-associated virus amplicon vectors

One of the challenges in gene therapy is to ensure stable transgene expression at the site of disease with a high degree of accuracy and safety. In this paper, we examine both viral and cellular elements that may affect the level of transgene expression mediated by herpes simplex virus type 1 (HSV-1) adeno-associated virus (AAV) amplicon vectors. These elements include the AAV inverted terminal repeats (ITRs), the AAV Rep proteins, and the allelic status of 19q in human glioma cell lines. The latter is of particular interest because the AAV integration site (AAVS1) is located on the long arm of chromosome 19 and 30-40% of human glioblastoma tumors are reported to have loss of heterozygosity in this region of chromosome 19q. Fluorescence-activated cell-sorting analysis results indicate that inclusion of minimal or full-length AAV ITRs in HSV-1 amplicon vectors markedly increases the efficiency of transgene expression. On the other hand, insertion of the AAV rep gene decreases the level of transgene expression, apparently because of the cytotoxic effects of Rep proteins. Further, the levels of transgene expression appear to be independent of 19q allelic status or the number of endogenous AAVS1 sequences in the various glioma cell lines studied. Taken together, these data support employing AAV ITRs, in the context of HSV-1 amplicon vectors, to enhance short-term levels of transgene expression.

In vivo transfection of the mouse vas deferens

To explore the possibility that specific characteristics of the epithelium of the male tract can be modified, transfections of the mouse vas deferens have been performed using in vivo injections of cationic DNA/liposome complexes. Gene transfer was done employing the reporter genes pEGFP-C1 encoding Green Fluorescent Protein (GFP) and pCMV-nls-beta encoding the nuclear beta-Galactosidase (beta-Gal). Foreign gene expression reached a maximum of 6.8% in the epithelial cells of the vas after treatment with the nuclear beta-Gal gene construction and of 13.3% after employing the GFP gene construction. Expression of the GFP gene appeared from one week up to three months following injection, and it appeared as patches of modified cells along the epithelium. Results from immunocytochemistry and Western Blotting support the conclusion that transfection of epithelial cells was achieved. We have also transfected the vas using gene constructions that express secretory proteins--specifically, the reporter system pSEAP-control that expresses a secretory form of human placental alkaline phosphatase, and the pGFP-Ctk-37 that expresses a secretion form of GFP. In both cases, the fluids expressed from the transfected vas showed a significant increase of alkaline phosphatase activity after pSEAP transfection and the presence of GFP protein when pGFP-Ctk-37 gene construction was employed. Our results indicate that the vas can be transfected in vivo using liposomes as vectors of foreign genes and that the vas fluid contents can be modified.

Induction of chemosensitivity in nasopharyngeal carcinoma cells using a human papillomavirus regulatory sequence and the thymidine kinase gene

Nasopharyngeal carcinoma (NPC) is a human cancer of epithelial cell origin. Infection by Epstein-Barr virus has been shown to be closely associated with this tumor. Recent studies have indicated that another common epitheliotropic virus, human papillomavirus (HPV), is also found in a significant number of NPC cases. In this study, we evaluated the feasibility of using the HPV regulatory long control region (LCR) to drive the expression of the thymidine kinase (tk) gene to achieve chemosensitivity for gene therapeutic treatment of NPC. Testing HPV-11-LCR-tk constructs in NPC cell lines in the presence of ganciclovir (GCV) led to 50-60% cell death of transfected cells. The therapeutic efficacy was further tested in an in vivo model using nude mice transplanted with tumors derived from transfected NPC cells. Injection of 50 mg/kg body weight GCV twice daily for 14 days resulted in visually complete regression of the transplanted NPC tumor loads within 20 days after GCV treatment. Taken together, results from this pilot study indicate the feasibility of the development of a gene therapeutic protocol based on the chemosensitive gene constructs described in this paper.

Kinetics of efficient recombinant adeno-associated virus transduction in retinal pigment epithelial cells

The aim of this study was to investigate the premise that retinal pigment epithelial (RPE) cells are more permissive to recombinant adeno-associated virus (rAAV) transduction than other cells. We investigated the kinetics and mechanisms of rAAV transduction in RPE cells and found that the transduction efficiencies of cultured RPE cells HRPE51 and ARPE19 were significantly higher than those of 293 (P < 0.008) and HeLa (P < 0.025) cells. In addition, RPE cells reached maximum transduction efficiency at a much lower m.o.i. (m.o.i. 10) than 293 cells (m.o.i. 25). Competition experiments using 1 microg/ml heparin inhibited the high level of transduction in RPE cells by 30%, but additional heparin failed to reduce rAAV transduction further. Southern hybridization of low-molecular-weight DNA from transduced RPE cells indicated that 42% of single-stranded rAAV DNA was translocated into the nucleus by 2 h postinfection. By 6 h postinfection, double-stranded rAAV DNA was observed, which coincided with the onset of transgene expression. Southern and fluorescence in situ hybridization of total genomic DNA indicated that long-term transgene expression in RPE cells was maintained by the integration of rAAV into the cellular chromosome. Together, these results suggest that the high permissiveness of RPE cells is not related to the presence of heparan sulfate receptors or nuclear trafficking but may be due to an enhanced rate of second-strand synthesis and that integration in RPE cells is responsible for long-term transgene expression.

Gene therapy: principles and applications to hematopoietic cells

Ever since the development of technology allowing the transfer of new genes into eukaryotic cells, the hematopoietic system has been an obvious and desirable target for gene therapy. The last 10 years have witnessed an explosion of interest in this approach to treat human disease, both inherited and acquired, with the initiation of multiple clinical protocols. All gene therapy strategies have two essential technical requirements. These are: (1) the efficient introduction of the relevant genetic material into the target cell and (2) the expression of the transgene at therapeutic levels. Conceptual and technical hurdles involved with these requirements are still the objects of active research. To date, the most widely used and best understood vectors for gene transfer in hematopoietic cells are derived from retroviruses, although they suffer from several limitations. However, as gene transfer mechanisms become more efficient and long-term gene expression is enhanced, the variety of diseases that can be tackled by gene therapy will continue to expand. However, until the problem of delivery and subsequent expression is adequately resolved, gene therapy will not realize its full potential. The first part of this review gives an overview of the gene delivery technology available at present to transfer genetic sequences in human somatic cells. The relevance of the hematopoietic system to the development of gene therapy strategies as well as hematopoietic cell-based gene therapy is discussed in the second part.

DOTAP cationic liposomes prefer relaxed over supercoiled plasmids

Cationic liposomes and DNA interact electrostatically to form complexes called lipoplexes. The amounts of unbound (free) DNA in a mixture of cationic liposomes and DNA at different cationic lipid:DNA molar ratios can be used to describe DNA binding isotherms; these provide a measure of the binding efficiency of DNA to different cationic lipid formulations at various medium conditions. In order to quantify the ratio between the various forms of naked DNA and supercoiled, relaxed and single-stranded DNA, and the ratio between cationic lipid bound and unbound DNA of various forms we developed a simple, sensitive quantitative assay using agarose gel electrophoresis, followed by staining with the fluorescent cyanine DNA dyes SYBR Green I or SYBR Gold. This assay was compared with that based on the use of ethidium bromide (the most commonly used nucleic acid stain). Unlike ethidium bromide, SYBR Green I DNA sensitivity and concentration-dependent fluorescence intensity were identical for supercoiled and nicked-relaxed forms. DNA detection by SYBR Green I in solution is approximately 40-fold more sensitive than by ethidium bromide for double-stranded DNA and approximately 10-fold for single-stranded DNA, and in agarose gel it is 16-fold more sensitive for double-stranded DNA compared with ethidium bromide. SYBR Gold performs similarly to SYBR Green I. This study shows that: (a) there is no significant difference in DNA binding isotherms to the monocationic DOTAP (DOTAP/DOPE) liposomes and to the polycationic DOSPA (DOSPA/DOPE) liposomes, even when four DOSPA positive charges are involved in the electrostatic interaction with DNA; (b) the helper lipids affect DNA binding, as DOTAP/DOPE liposomes bind more DNA than DOTAP/cholesterol; (c) in the process of lipoplex formation, when the DNA is a mixture of two forms, supercoiled and nicked-relaxed (open circular), there is a preference for the binding to the cationic liposomes of plasmid DNA in the nicked-relaxed over the supercoiled form. This preference is much more pronounced when the cationic liposome formulation is based on the monocationic lipid DOTAP than on the polycationic lipid DOSPA. The preference of DOTAP formulations to bind to the relaxed DNA plasmid suggests that the binding of supercoiled DNA is weaker and easier to dissociate from the complex.

DNA/dendrimer complexes mediate gene transfer into murine cardiac transplants ex vivo

Starburst polyamidoamine dendrimers are synthetic polymers with unique structural and physical characteristics suitable for DNA gene transfer. Our previous studies demonstrated that Starburst dendrimers augment plasmid-mediated gene transfer efficiency in a nonvascularized, cardiac transplantation model. In this study, the fifth generation of ethylenediamine core dendrimer was investigated for its ability to enhance gene transfer and expression in a clinically relevant murine vascularized heart transplantation model. The plasmid pMP6A-beta-gal, encoding beta-galactosidase (beta-Gal), was incubated with dendrimers to form complexes. The complexes were perfused via the coronary arteries during donor graft harvesting, and reporter gene expression was determined by quantitative evaluation of X-Gal staining. The grafts infused with pMP6A-beta-gal/dendrimer complexes showed beta-Gal expression in myocytes from 7 to 14 days. A number of variables for transfer of the DNA/dendrimer complexes were tested, including DNA:dendrimer charge ratios, concentrations of DNA and dendrimer, preservation solutions, ischemic time, and enhancement of vascular permeability by serotonin, papaverine, and VEGF administration. The results showed that DNA/dendrimer complexes containing 20 microg of DNA and 260 microg of dendrimer (1:20 charge ratio) in a total volume of 200 microl resulted in highest gene expression in the grafts. The results also showed that prolonged incubation (cold ischemic time) to 2 h and pretreatment with serotonin further enhanced gene expression.

Primary T lymphocytes as targets for gene therapy

Peripheral blood T lymphocytes have been considered an attractive target for gene therapy applications. They can be easily harvested and readily expanded ex vivo. The transduction efficiency of primary human lymphocytes with standard retroviral vectors approaches 50% or more using optimized methods of gene transfer. Other methods of gene transfer, including adenoviral, adeno-associated viral, and lentiviral vectors, or nonviral techniques, have also been used for gene transfer into primary lymphocytes. Despite encouraging results in vitro, human clinical trials using retroviral vectors to transduce primary lymphocytes have been hindered by low expression levels of transgenes and immune responses against transgene products. Strategies to overcome these problems need to be developed.

Liposome-mediated, nonviral gene transfer induces a systemic inflammatory response which can exacerbate pre-existing inflammation

Cationic liposome and plasmid-mediated gene transfer has emerged as a novel technique for the targeted delivery of protein-based therapies in acute inflammatory diseases. However, concerns have arisen that cationic liposomes and plasmid DNA have inherent proinflammatory properties which could exacerbate pre-existing inflammatory processes. In healthy mice, intraperitoneal administration of cationic liposomes (200 nmol) complexed to plasmid DNA (100 microg) induced a proinflammatory response characterized by the induction of tumor necrosis factor alpha and interleukin-1beta mRNA expression. The plasma concentrations of the hepatic acute phase proteins interleukin-6, amyloid A, amyloid P, and seromucoid were also increased (P<0.05), and this response was seen in endotoxin-resistant (C3H/HeJ) mice. The inflammatory response associated with gene transfer increased the mortality and severity of experimentally induced sterile inflammation (pancreatitis). We conclude that systemic administration of cationic liposomes and plasmid DNA is associated with induction of the innate immune response which may exacerbate pre-existing inflammatory processes.

Adeno-associated virus-based vectors in gene therapy

Adeno-associated virus (AAV) vectors were shown capable of high efficiency transduction of both dividing and nondividing cells and tissues. AAV-mediated transduction leads to stable, long-term transgene expression in the absence of apparent immune response. These properties and the broad host range of AAV vectors indicate that they constitute a powerful tool for gene therapy purposes. An additional potential benefit of AAV vectors is their ability to integrate site-specifically in the presence of Rep proteins which can be expressed transiently, thus limiting their suspected adverse effects. The major restrictions of AAV as vectors are their limited genetic capacity and strict packaging size constraint of less than 5 kb. Another difficulty is the labor-intensive and expensive procedure for the production and packaging of recombinant AAV vectors. The major benefits and drawbacks of AAV vectors and advances made in the past 3 years are discussed.

Aspartoacylase gene transfer to the mammalian central nervous system with therapeutic implications for Canavan disease

With the ultimate goal of developing safe and effective in vivo gene therapy for the treatment of Canavan disease and other neurological disorders, we developed a non-viral lipid-entrapped, polycation-condensed delivery system (LPD) for central nervous system gene transfer, in conjunction with adeno-associated virus (AAV)-based plasmids containing recombinant aspartoacylase (ASPA). The gene delivery system was tested in healthy rodents and primates, before proceeding to preliminary studies in 2 children with Canavan disease. Toxicity and expression testing was first carried out in human 293 cells, which demonstrated effective transduction of cells and high levels of functional ASPA activity. We performed in vivo toxicity and expression testing of LPD/pAAVaspa and LPD/pAAVlac in rodents, which demonstrated widespread gene expression for more than 10 months after intraventricular delivery, and local expression in deep brain nuclei and white matter tracts for more than 6 months after intraparenchymal injections, with no significant adverse effects. We also performed intraventricular delivery of LPD/pAAVaspa to 2 cynomologous monkeys, with 2 additional monkeys receiving LPD and saline controls. None of the monkeys demonstrated significant adverse effects, and at 1 month the 2 LPD/pAAVaspa monkeys were positive for human ASPA transcript by reverse transcriptase polymerase chain reaction of brain tissue punches. Finally, we performed the first in vivo gene transfer study for a human neurodegenerative disease in 2 children with Canavan disease to assess the in vivo toxicity and efficacy of ASPA gene delivery. Our results suggest that LPD/pAAVaspa is well tolerated in human subjects and is associated with biochemical, radiological, and clinical changes.

A novel N-acyl phosphatidylethanolamine-containing delivery vehicle for spermine-condensed plasmid DNA

A unique method for formulation of plasmid DNA with phospholipids has been devised for the purpose of producing vehicles that can mediate gene delivery and transfection of living cells. The polycation, spermine, was used to condense plasmid DNA within a water-in-chloroform emulsion stabilized by phospholipids. After organic solvent removal, the particles formed could be extruded to a number average size of about 200 nm and retained DNA that was protected from nuclease digestion. This resulted in a relatively high protected DNA-to-lipid ratio of approximately 1 microg DNA/micromol lipid. The size distribution of the preparation was relatively homogeneous as judged by light microscopy and quasi-elastic light scattering. Electron microscopic studies showed structural heterogeneity, but suggested that at least some of the plasmid DNA in this preparation was in the form of the previously observed spermine-condensed bent rods and toroids and was encapsulated within liposomal membranes. Preparations with the fusogenic phospholipid composition, 1, 2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-dodecanoyl/ 1, 2-dioleoyl-sn-glycero-3-phosphocholine, showed transfection activity for several cells lines, particularly OVCAR-3 cells. The transfection activity sedimented with the lipid during centrifugation, confirming the association of active plasmid DNA with phospholipids. Transfection efficiency in culture was found to be of the same order of magnitude as cationic lipoplexes but much less toxic to the cells. Significant transfection of OVCAR-3 cells in tissue culture could also be observed, even in the presence of the intraperitoneal fluid from a mouse with an OVCAR-3 ascites tumor. These data indicate a new type of liposomal gene delivery system devoid of cationic lipids, phosphatidylethanolamine, cationic polymers and viral components.

Gene transfer of virally encoded chemokine antagonists vMIP-II and MC148 prolongs cardiac allograft survival and inhibits donor-specific immunity

Introducing immunomodulatory molecules into allografts by gene transfer may avoid the side-effects of systemic immunosuppression. vMIP-II and MC148 are two recently identified chemokine homologues encoded by human herpes virus 8 and Molluscum contagiosum, respectively, that have antagonistic activities against multiple different CC and CXC chemokine receptors. We hypothesized that introduction of these molecules into cardiac allografts may block leukocyte infiltration into the grafts and prolong survival. Vascularized and nonvascularized cardiac allografts in mice were performed and plasmid DNA encoding vMIP-II, MC148 and/or vIL-10 was transferred into the allograft at the time of transplantation. Gene transfer of either vMIP-II or MC148 into cardiac allografts markedly prolonged graft survival. Combining gene transfer of either one of these chemokine antagonists with vIL-10 gene transfer, which has a mechanistically different immunosuppressive action, further enhanced graft survival. vMIP-II and MC148 gene transfer both resulted in a marked decrease of donor-specific cytotoxic T lymphocytes (CTL) infiltrating the grafts and inhibited alloantibody production. These results demonstrate that plasmid-mediated gene transfer of virally encoded chemokine antagonists vMIP-II and MC148 can block donor-specific lymphocyte immunity within cardiac allografts and prolong graft survival. This is a new mechanistic approach to analyze, treat, and prevent graft rejection. Delivery of these or related molecules by gene transfer or conventional pharmacologic means may represent a novel therapeutic modality for alloactivation.

Site-specific integration of adeno-associated virus-based plasmid vectors in lipofected HeLa cells

Adeno-associated virus (AAV) integrates specifically into a site (AAVS1) on human chromosome 19q13.3-qter. Similarly, there is accumulating evidence that this site-specific integration occurs by transfection of AAV-based plasmid vectors. In order to further define the process of plasmid integration events, we constructed some AAV plasmids, introduced them into HeLa cells by lipofection, and isolated chromosomal integrants. One of such plasmids, pTH-5, contained the rep and neomycin-resistant (neo(r)) genes flanked by the 5'- and 3'-inverted terminal repeats of AAV and the hygromycin-resistant (hyg(r)) gene located in the plasmid backbone. Southern blot analysis revealed that among 36 G418-resistant (G418(r)) clones isolated, 22 (61%) showed site-specific integration into AAVS1. Further structural and functional analyses on the expression of the hyg(r) gene in the site-specific clones and the LacZ gene in clones generated with plasmid pTH-2 indicated that, together with the AAV sequence, the plasmid backbone was integrated into the AAVS1 site and thus the neo(r) and hyg(r) genes remained linked at high frequencies in the targeted integrants compared with random integrants. Sequence analysis of integration junctions between pTH-5 and AAVS1 revealed that the junctions occurred in the p5 promoter region of the plasmid while mainly in the partial cDNA coding region of the AAVS1 site. We also found that plasmid pTH-1 linearized in the backbone before lipofection gave a significantly lower frequency of site-specific integration (26%) than the circular form (60%). This finding may support the involvement of the double-stranded, circular form of infected AAV in the integration process. Our results may help to understand the process and mechanism of site-specific integration of lipofected AAV plasmid vectors.

A single amino acid determines the immunostimulatory activity of interleukin 10

Cellular interleukin 10s (cIL-10s) of human and murine origin have extensive sequence and structural homology to the Epstein-Barr virus BCRF-I gene product, known as viral IL-10 (vIL-10). Although these cytokines share many immunosuppressive properties, vIL-10 lacks several of the immunostimulatory activities of cIL-10 on certain cell types. The molecular and cellular bases for this dichotomy are not currently defined. Here, we show that the single amino acid isoleucine at position 87 of cIL-10 is required for its immunostimulatory function. Substitution of isoleucine in cIL-10 with alanine, which corresponds to the vIL-10 residue, abrogates immunostimulatory activity for thymocytes, mast cells, and alloantigenic responses while preserving immunosuppressive activity for inhibition of interferon gamma production and prolongation of cardiac allograft survival. Conversely, substitution of alanine with isoleucine in vIL-10 converts it to a cIL-10-like molecule with immunostimulatory activity. This single conservative residue alteration significantly affects ligand affinity for receptor; however, affinity changes do not necessarily alter specific activities for biologic responses in a predictable fashion. These results suggest complex regulation of IL-10 receptor-ligand interactions and subsequent biological responses. These results demonstrate that vIL-10 may represent a captured and selectively mutated cIL-10 gene that benefits viral pathogenesis by leading to ineffective host immune responses. The ability to manipulate the activity of IL-10 in either a stimulatory or suppressive direction may be of practical value for regulating immune responses for disease therapy, and of theoretical value for determining what aspects of IL-10 activity are important for normal T cell responses.

Gene transfer of immunomodulatory peptides correlates with heme oxygenase-1 induction and enhanced allograft survival

BACKGROUND

Decapeptides derived from human HLA class I sequences have been shown to prolong allograft survival. The mechanism of action of these peptides has been uncertain, because they act in an MHC unrestricted manner. Recently, it was found that these peptides bind heme oxygenase 1 (HO-1). In the present study, we sought to determine whether local delivery of these peptides through gene transfer could extend allograft survival, and to explore the underlying mechanisms.

METHODS

C57BL/6 neonatal hearts were transplanted to CBA/J recipients and the peptide, or plasmid DNA encoding the peptide, was injected directly into the allograft at the time of the transplant.

RESULTS

Direct injection of 1 microg of the B2702 peptide into the allograft did not prolong survival (13.3+/-0.8 vs. 13.4+/-0.8 days for untreated controls), but injection of 400 microg of peptide did extend survival (22.0+/-0.6). Injection of plasmid DNA encoding the B2702 peptide was superior to peptide delivery, extending graft survival to 30.8+/-1.5 days. Similar results were obtained using another plasmid encoding the rationally designed peptide BC1 (28.5+/-1.7), whereas no significant prolongation was observed using a plasmid encoding the control peptide B2705 (16.5+/-1.0). To explore the hypothesis that these peptides exert their immunosuppressive effect by altering HO-1 activity, animals were treated with iron protoporphyrin, an inducer of HO-1 activity, or tin protoporphyrin, an inhibitor of HO-1. Treatment with iron protoporphyrin alone extended graft survival (24.5+/-1.6) and did not alter the benefit in survival seen with BC1 gene transfer (28.0+/-0.8). In contrast, treatment with tin protoporphyrin abolished the benefit of BC1 gene transfer (17.0+/-0.6).

CONCLUSIONS

These results demonstrate that plasmid mediated gene transfer is an effective means for delivering immunosuppressive peptides to extend allograft survival. The experiments suggest that these peptides may act by increasing HO-1 activity and support a role for HO-1 in immune regulation and allograft survival.

Intravenous angiotensinogen antisense in AAV-based vector decreases hypertension

Angiotensinogen (AGT) has been linked to hypertension. Because there are no direct inhibitors of AGT, we have developed antisense (AS) inhibition of AGT mRNA delivered in an adeno-associated virus (AAV)-based plasmid vector. This plasmid, driven by the cytomegalovirus promoter, contains a green fluorescent protein reporter gene and AS cDNA for rat AGT. Transfection of the plasmid into rat hepatoma cells brought a strong expression of the transgenes and a significant reduction in the level of AGT. In the in vivo study, naked plasmid DNA was intravenously injected into adult spontaneously hypertensive rats at different doses (0.6, 1.5, and 3 mg/kg). Expression of AGT AS mRNA was present in liver and heart, and it lasted longer in the liver. All three doses produced a significant decrease in blood pressure (BP). BP decreased for 2, 4, and 6 days, respectively. The lowest dose decreased BP by 12 +/- 3.0 mmHg, whereas the higher doses decreased BP by up to 22.5 +/- 5.2 mmHg compared with the control rats injected with saline (P < 0.01). The injection of the plasmid with liposomes produced a more profound and longer reduction (8 days) in BP. Consistent changes in plasma AGT level were observed. Sense plasmid had no effect. No liver toxicity was observed after injection of AS plasmid with or without liposomes. Our results suggest that the systemic delivery of AS against AGT mRNA by AAV-based plasmid vector, especially with liposomes, may have potential for gene therapy of hypertension and that further studies with the plasmid packaged into a recombinant AAV vector for a longer-lasting AS effect are warranted.

Endobronchial transfection of naked TGF-beta1 cDNA attenuates acute lung rejection

BACKGROUND

We investigated endobronchial transfection of CAT and TGF-beta1 cDNA selectively delivered to the lung graft with or without liposomes.

METHODS

Phase I: F344 rats received 130 microg of naked plasmid pCF1-CAT or complexed to liposome GL67 via left main bronchus instillation. Rats were awakened (pCF1-CAT, n = 4; GL67:pCF1-CAT, n = 4) or served as donors in an isogenic transplant (pCF1-CAT, n = 5; GL67:pCF1-CAT, n = 5). ELISA was performed on lungs, hearts, and livers on POD 2. Phase II: BN lungs received TGF-beta1 sense (n = 6); antisense (n = 5); GL67:TGF-beta1 sense (n = 10); or saline solution (n = 10). F344 recipients were sacrificed on POD 5. The arterial pO2 and rejection were assessed. RT-PCR for murine TGF-beta1 was performed.

RESULTS

Phase I: CAT expression was 519+/-287 pg and 63+/-68 with pCF1-CAT and 104+/-67 and 37+/-45 with GL67:pCF1-CAT, respectively, in the non-transplant and in the transplant setting. No protein was detected in the hearts, livers, and in the native lung of the recipients. Phase II: RT-PCR confirmed murine TGF-beta1 transfection. pO2 was 362.7+/-110.2 (mean mm Hg +/- SD) for sense TGF-beta1; 146.88+/-85.5 for antisense; 241.5+/-181.5 for GL67-TGF-beta1 sense; and 88.4+/-38.7 for saline. TGF-beta1 sense versus all other groups, p<0.05, GL67-TGF-beta1 sense versus saline, p = 0.01. Rejection was significantly lower for TGF-beta1 sense versus saline, p = 0.04.

CONCLUSIONS

Endobronchial administration of naked plasmid achieves selective transfection of lung grafts. Using this strategy, TGF-beta1 reduces early lung allograft rejection.

Gene therapy for lung disease

Gene therapy is a new field of medical research that has great potential to influence the course of treatment of human disease. The lung has been a particularly attractive target organ for gene therapy due to its accessibility and the identification of genetic deficits for a number of lung diseases. Several clinical trials have shown evidence of low levels of gene transfer and expression, but without any benefit to the patients involved. Thus, current studies are focusing on further research and technological improvements to the vectors. Gene therapy is now beginning to benefit from a shift in emphasis from clinical trials to the development of better tools and procedures to deliver gene therapy to the bedside.

The challenge of vector development in gene therapy

Gene therapy is the treatment of diseases based on the transfer of genetic information. Agents that carry or deliver DNA to target cells are called vectors (Latin vector: carrier, deliverer). Ideally, a vector should accommodate an unlimited amount of inserted DNA, lack the ability of autonomous replication of its own DNA, be easily manufactured, and be available in concentrated form. Secondly, it should have the ability to target specific cell types or to limit its gene expression to specific cell types, and to achieve sustained gene expression in the long term or in a controlled fashion. Finally, it should not be toxic or immunogenic. Such a vector does not exist and none of the DNA delivery systems so far available for in vivo gene transfer is perfect with respect to any of these points. Gene therapy and the means to promote it depend heavily on the development and improvement of new gene vector systems.

Circular intermediates of recombinant adeno-associated virus have defined structural characteristics responsible for long-term episomal persistence in muscle tissue

Adeno-associated viral (AAV) vectors have demonstrated great utility for long-term gene expression in muscle tissue. However, the mechanisms by which recombinant AAV (rAAV) genomes persist in muscle tissue remain unclear. Using a recombinant shuttle vector, we have demonstrated that circularized rAAV intermediates impart episomal persistence to rAAV genomes in muscle tissue. The majority of circular intermediates had a consistent head-to-tail configuration consisting of monomer genomes which slowly converted to large multimers of >12 kbp by 80 days postinfection. Importantly, long-term transgene expression was associated with prolonged (80-day) episomal persistence of these circular intermediates. Structural features of these circular intermediates responsible for increased persistence included a DNA element encompassing two viral inverted terminal repeats (ITRs) in a head-to-tail orientation, which confers a 10-fold increase in the stability of DNA following incorporation into plasmid-based vectors and transfection into HeLa cells. These studies suggest that certain structural characteristics of AAV circular intermediates may explain long-term episomal persistence with this vector. Such information may also aid in the development of nonviral gene delivery systems with increased efficiency.

Targeted integration of adeno-associated virus-derived plasmids in transfected human cells

Adeno-associated virus (AAV) integrates its genomic DNA into a defined region of human chromosome 19 (AAVS1). The specificity of integration is dependent on the presence of the inverted terminal repeats (ITR) and on expression of the rep gene. To develop vectors capable of targeting the insertion of a selected DNA sequence into a specific location of human chromosome, we determined whether the rep gene can mediate site-specific integration when cloned outside of an ITR-flanked transgene cassette. HeLa and Huh-7 cells were transfected with a plasmid containing the rep gene, as well as the green fluorescent protein (GFP) and neomycin (neo) resistance gene inserted between the ITRs of AAV. Southern blot analysis of individual clones detected Rep-mediated site-specific integration of the ITR-flanked DNA in 25% and 12% of the HeLa and Huh-7 clones, respectively. The localization of the GFP-Neo sequence on chromosome 19 also was confirmed by fluorescent in situ hybridization analysis of the transfected HeLa clones. Sequence analysis of the ITR-AAVS1 junction of one of the transfected Huh-7 clones indicated that the insertion of the ITR DNA fragment had occurred at nucleotide 1003. These results have implications for the development of AAV-derived vectors capable of directing the site-specific integration of a gene of interest.

Tolerance Induction by Anti-CD2 Plus Anti-CD3 Monoclonal Antibodies: Evidence for an IL-4 Requirement

Anti-CD2 mAb plus anti-CD3 mAb induce alloantigen specific tolerance. We sought to determine whether Th2 cytokines are involved in the induction of tolerance in this model. Addition of anti-IL-4 mAb or anti-IL-10 mAb to anti-CD2 plus anti-CD3 treatment abrogated tolerance and resulted in graft survivals of 26 ± 4 and 25 ± 5 days, respectively. Splenocytes from the anti-IL-4 mAb and anti-IL-10 groups had greater proliferation in response to alloantigen than either tolerant or naive groups. Cytokine analysis of MLR supernatants showed increased IL-10 in the tolerant group and increased IFN-γ in the anti-IL-4 mAb treated group. Donor-specific alloantibody responses in untreated immune animals had a predominantly Th1 (IgG2a) alloantibody response, while the tolerogenic regimen reduced the ratio of IgG2a:IgG1 titers. The addition of anti-IL-4 mAb to the tolerogenic regimen partly restored the Th1-related IgG2a response. Tolerance did not develop in IL-4 knockout animals treated with anti-CD2 plus anti-CD3 (mean graft survival, 27 ± 5 days). Restoration of IL-4 to IL-4 knockout animals by gene transfer with plasmid DNA resulted in prolongation of survival to 46 ± 7 days, while adoptive transfer of wild-type splenocytes into IL-4 knockout recipients resulted in indefinite graft survival (&gt;60 days) and indefinite survival of second donor-type grafts. IL-10 gene transfer to IL-4 knockout recipients did not prolong graft survival (28 ± 4). These results demonstrate that tolerance in this model is mediated at least in part by Th2-type cells that secrete IL-4, promote IL-10 and IgG1 production, and inhibit alloantigen reactivity.

Delivery of an anti-HIV-1 ribozyme into HIV-infected cells via cationic liposomes

Cationic liposome-mediated intracellular delivery of a fluorescein-labeled chimeric DNA-RNA ribozyme targeted to the HIV-1 5' LTR was investigated, using THP-1, THP-1/HIV-1IIIB or HeLa/LAV cells. Different fluorescence patterns were observed when the cells were exposed to Lipofectamine, Lipofectin or DMRIE:DOPE (1:1) complexed to the ribozyme. With Lipofectamine intense cell-associated fluorescence was found. Incubation with Lipofectin resulted in less intense diffuse fluorescence, while with DMRIE an intense but sporadic fluorescence was observed. Differentiated THP-1/HIV-1IIIB cells were more susceptible to killing by liposome-ribozyme complexes than THP-1 cells. Under non-cytotoxic conditions (a 4-h treatment) complexes of 5, 10 or 15 microM Lipofectin or DOTAP:DOPE (1:1) and ribozyme, at lipid:ribozyme ratios of 8:1 or 4:1, did not affect p24 production in THP-1/HIV-1IIIB cells in spite of the intracellular accumulation of the ribozyme. A 24-h exposure of THP-1/HIV-1IIIB cells to 5 microM Lipofectin or DOTAP:DOPE (1:1) complexed with either the functional or a modified control ribozyme reduced virus production by approximately 30%. Thus, the antiviral effect of the liposome-complexed ribozyme was not sequence-specific. In contrast, the free ribozyme at a relatively high concentration inhibited virus production by 30%, while the control ribozyme was ineffective, indicating a sequence-specific effect. Both Lipofectin and DOTAP complexed with ribozyme were toxic at 10 and 15 microM after a 24-h treatment. A 4-h treatment of HeLa/LAV cells with Lipofectin at 5, 10 or 15 microM was not toxic to the cells, but also did not inhibit p24 production. In contrast, treatment of HeLa CD4+ cells immediately after infection with HIV-1IIIB at the same lipid concentrations and lipid:ribozyme ratios was cytotoxic. Our results indicate that the delivery of functional ribozyme into cells by cationic liposomes is an inefficient process and needs extensive improvement before it can be used in ex vivo and in vivo applications.

Transient human gene therapy: a novel cytokine regulatory strategy for experimental pancreatitis

OBJECTIVE

The purpose of this study was to evaluate the ability to transfect a murine pancreas with a human cytokine regulatory gene (interleukin-10 [IL-10]) and examine the duration of transgene expression, its effect on the normal pancreas, and its antiinflammatory effect during acute pancreatitis.

SUMMARY BACKGROUND DATA

Interleukin-1beta and tumor necrosis factor-alpha are known detrimental mediators during the progression of acute pancreatitis, and blockade of either cytokine results in decreased severity of pancreatitis and improved survival. Although gene therapy has been proposed as a method to deliver protein-based therapy during a number of conditions, no means of effectively transfecting the pancreas without inducing injury has been developed.

METHODS

A plasmid-human IL-10 construct (pMP6-hIL-10) complexed with cationic liposomes was administered by single intraperitoneal injection to healthy mice. Effective transfection (reverse transcriptase-polymerase chain reaction for hIL-10 mRNA), transfected cell type (in situ polymerase chain reaction for hIL-10 DNA), and the effect on the normal pancreas were determined. Additional animals were transfected to determine the effects of this regulatory gene on the severity of pancreatitis.

RESULTS

Nearly 80% of all pancreatic cells expressed human DNA that was subsequently transcribed into mRNA through day 14. The transfection event had no effect on amylase, lipase, or pancreatic histologic appearance. Successful transfection could attenuate subsequently induced pancreatitis (all parameters p < 0.05).

CONCLUSIONS

Transient transfection of a human IL-10 gene can be accomplished into all cell types of murine pancreata using a plasmid/ liposome vector. The DNA is effectively transcribed into intact mRNA and does not cause inflammation or acinar cell damage. Transfer of this cytokine regulatory gene decreases the severity of pancreatitis, demonstrating a benefit of gene therapy during this acute inflammatory process.

Enhanced collagen accumulation following direct transfection of the inducible nitric oxide synthase gene in cutaneous wounds

Inducible nitric oxide synthase (iNOS) is expressed during cutaneous wound repair. Mounting evidence suggests that wound nitric oxide (NO) augments collagen accumulation. We hypothesized that in vivo transfection of wound cells with the iNOS gene would increase physiological wound NO levels and thus augment collagen accumulation. Polyvinyl alcohol sponges were instilled with a mammalian expression plasmid (pMP6) containing either the chloramphenicol acetyl transferase (CAT) reporter or murine iNOS gene driven by a CMV immediate-early promoter. Plasmid DNA was injected alone or in complex with cationic liposomes, and the sponges were placed subcutaneously in male Sprague-Dawley rats which had received a longitudinal dorsal midline incision. Animals were sacrificed at different time points post-wounding and the sponges assayed for CAT activity, transfected iNOS mRNA, total nitrate and nitrite concentration (NOx) (as an index of wound NO synthesis), and hydroxyproline content (as an index of sponge collagen accumulation). The results demonstrate that wound cells were more efficiently transfected by naked DNA than by liposome mediated transfection and that maximal expression of both iNOS and CAT occurred at 48 hrs with a rapid decline after this time point. After 7 days, iNOS transfected sponges had accumulated significantly more collagen than those transfected with CAT. We conclude that cutaneous wounds can be successfully transfected by direct injection of naked DNA and that increased iNOS expression precedes an increase in collagen synthesis.

Recombinant adeno-associated virus for the generation of autologous, gene-modified tumor vaccines: evidence for a high transduction efficiency into primary epithelial cancer cells

To explore the potential of recombinant vectors based on recombinant adeno-associated virus (rAAV) for cancer vaccination, we investigated the transduction efficiency of rAAV into cancer cells ex vivo. Infection of human epithelial cancer cell lines with rAAV carrying reporter genes encoding beta-galactosidase (rAAV/LacZ) or luciferase (rAAV/Luc) resulted in high levels of reporter gene expression (>90% positive cells). In marked contrast, rAAV poorly transduced all murine tumor cell lines, as well as human hematopoietic cell lines. Either irradiation or adenovirus infection of tumor cells prior to rAAV infection induced a 10- to 100-fold increase of reporter gene expression. To determine the transduction efficiency of rAAV into primary cancer cells, freshly isolated, irradiated tumor cells from malignant melanoma and ovarian carcinoma patients were infected with rAAV/Luc, resulting in up to 6.9-fold higher levels of gene expression than in a HeLa tumor cell line. Time course experiments with freshly isolated tumor cells infected with rAAV/Luc showed maximal levels of luciferase expression between days 3 and 9 posttransduction. Simultaneous infection of primary tumor cells with up to three rAAV vectors containing genes encoding the immunostimulatory proteins B7-2 (CD86), p35 subunit of IL-12, and p40 subunit of IL-12 resulted in high expression of B7-2 in more than 90% of the tumor cells and in the secretion of high levels of IL-12. Taken together, our results demonstrate that rAAV efficiently transduces freshly isolated human, epithelial tumor cells and might therefore be a potent tool to produce improved, gene-modified cancer vaccines.

Improvement of transduction efficiency of recombinant adeno-associated virus vector by entrapment in multilamellar liposomes

Recombinant adeno-associated virus (AAV) has attracted considerable interest as a potential vector for human gene therapy, but its transduction efficiency is quite low. The present study demonstrated AAV vector-associated liposomes to be more effective for in vitro gene transfer to human glioma cells than are liposomes containing plasmid DNA. Using vector-associated liposomes increased the transduction efficiency more than 10-fold compared to liposomes containing plasmid DNA and more than 6-fold compared to AAV alone. From these results, AAV vector-associated liposomes appear to be a good candidate for in vivo gene delivery to human gliomas.

Viral sequences enable efficient and tissue-specific expression of transgenes in Xenopus

Expression of transgenes within a single generation by direct DNA injection into vertebrate embryos has been plagued by inefficient and nonuniform gene expression. We report a novel strategy for efficient and stable expression of transgenes driven by both ubiquitous and tissue-specific promoters by direct DNA injection into developing Xenopus laevis embryos. This strategy involves flanking expression cassettes of interest with inverted terminal repeat sequences (ITRs) from adeno-associated virus. Our results suggest that the ITR strategy may be generally applicable to other systems, such as zebra fish and embryonic stem cells, and may enable tissue-specific expression of transgenes in problematic contexts.