Evaluation of biolistic gene transfer methods in vivo using non-invasive bioluminescent imaging techniques

Systems to regulate gene expression from an Adeno-associated viral (AAV) vector are widely used. In most cases, the transgene expression has to be switched on by applying a drug. In terms of safety of gene therapy, a shut-off system for AAV vectors would be beneficial to silence gene expression in case of side-effects, ideally by destruction of the vector genome. Therefore, the aim of the present study was to develop a system for elimination of gene expression from an AAV vector after systemic injection using an inducible Cre recombinase. In presence of tamoxifen, the inducible Cre recombinase is activated which should result in excision of DNA fragments flanked by loxP sites within the vector.
\nBefore evaluating the final shut-off system, several experiments were performed to analyze the background activity of the induced CreERT2 recombinase, the best suited positions of the loxP sites within the AAV genome and the influence of the loxP sites on the transgene expression. Moreover, a co-transduction of an AAV vector encoding the CreERT2 and a second AAV vector expressing the reporter gene flanked by loxP sites was tested.
\nAAV vectors of serotype 9 were used for packaging the final shut-off system consisting of the inducible CreERT2 recombinase, a luciferase reporter gene, and different positions of loxP sites to investigate the effect of loxP localization within the vector genome. To drive reporter gene and CreERT2 expression, the CMV promoter was used. All vectors were first tested in vitro. Afterwards, the vectors which showed a significant down-regulation of transgene expression after tamoxifen administration were also analyzed in vivo. Here, a significant reduction in reporter gene activity could be detected in animals receiving AAV vectors containing loxP sites one week upon tamoxifen administration. Another finding was that the insertion of loxP sites has a negative influence on the expression levels of the transgene. Thereby, the vector expressing the reporter gene flanked by loxP sites showed the lowest expression but also the highest extent of down-regulation after tamoxifen treatment. Finally, the shut-off system used was improved in terms of coding capacity of the AAV genome used. Therefore, the “self-cleaving” peptide P2A of the Porcine Teschovirus-1 was used to replace the promoter driving CreERT2 expression to increase the limiting coding capacity for the gene of interest. Again, these AAV9 vectors were tested in vitro and in vivo, also showing a significant reduction in reporter gene expression after tamoxifen administration.
\nTaken together, expression of an inducible Cre recombinase allows efficient inactivation of AAV-mediated gene expression on the expense of reduced overall expression efficiency due to insertion of loxP sites. These results contribute to the generation of a novel shut-off system for AAV-mediated gene transfer applicable for the use in combination with various promoters and AAV serotypes to target cell types or tissues of choice.

Stable genetic transformation of high oleic Helianthus annuus L. genotypes with high efficiency

Phase I Study of Noninvasive Imaging of Adenovirus-mediated Gene Expression in the Human Prostate

Valproic acid enhances gene expression from viral gene transfer vectors

The surface epithelium of mid-gestational murine embryos is thought to be an attractive target for gene therapy in vivo, due to its visibility and accessibility from the external surface of the maternal uterus. Almost all studies of in utero gene transfer have adopted viral vectors for infection of fetal epithelium, and depended on intraamniotic introduction and simple incubation of vectors, leading to only infection of the surface layer (periderm) of fetal skin. Here we report a simple and convenient method of gene transfer of plasmid DNA into the deeper portion of surface skin of murine mid-gestational fetus. One to two microlitres of a solution containing a lacZ expression plasmid (0.5-1 microg) and trypan blue (0.05%) were placed onto the surface of a fetus (E 14.5) near the eye by a micropipette attached to a mouthpiece. This fetus was immediately electroporated by placing it between tweezer-type electrodes attached to a square-pulse generator. At 1 and 4 days after gene transfer, fetuses were subjected to histochemical staining for lacZ activity in the presence of X-Gal, a substrate for lacZ. Focal reactions were observed in the skin epidermal layers including periderm and basal layer 1 day after DNA introduction. However, lacZ-positive cells were limited to a skin surface layer, the stratum corneum, in the samples obtained 4 days after gene transfer. Similar observation was also made in the transgenic fetuses (carrying a lacZ gene placed immediately downstream of the loxP-flanked sequence) injected with Cre expression vector. These findings suggest rapid movement of fetal epidermal cells toward the surface during late developmental stages. This local gene transfer approach appears to be effective as a method for skin-targeted gene transfer, enabling study of the role of genes of interest and tracing of cell lineage during fetal skin development.

Successful Compensation for Dystrophin Deficiency by a Helper-dependent Adenovirus Expressing Full-length Utrophin

Stem cell therapies offer the potential for repair and regeneration of cardiac tissue. To facilitate evaluation of stem cell activity in vivo, we created novel dual-reporter mouse embryonic stem (mES) cell lines that express the firefly luciferase (LUC) reporter gene under the control of the cardiac sodium-calcium exchanger-1 (Ncx-1) promoter in the background of the 7AC5-EYFP mES cell line that constitutively expresses the enhanced yellow fluorescent protein (EYFP). We compared the ability of recombinant clonal cell lines to express LUC before and after induction of cardiac differentiation in vitro. In particular, one of the clonal cell lines (Ncx-1-43LUC mES cells) showed markedly enhanced LUC expression (45-fold increase) upon induction of cardiac differentiation in vitro. Further, cardiac differentiation in these cells was perpetuated over a period of 2-4 weeks after transplantation in a neonatal mouse heart model, as monitored by noninvasive bioluminescence imaging (BLI) and confirmed via postmortem immunofluorescence and histological assessments. In contrast, transplantation of undifferentiated pluripotent Ncx-1-43LUC mES cells in neonatal hearts did not result in detectable levels of cardiac differentiation in these cells in vivo. These results suggest that prior induction of cardiac differentiation in vitro enhances development and maintenance of a cardiomyocyte-like phenotype for mES cells following transplantation into neonatal mouse hearts in vivo. We conclude that the Ncx-1-43LUC mES cell line is a novel tool for monitoring early cardiac differentiation in vivo using noninvasive BLI.

Pseudotyped adeno-associated viral vectors for gene transfer in dermal fibroblasts: implications for wound-healing applications

Different delivery mechanisms have been proposed in the literature for targeted therapies in the treatment of lymphedema. They vary from simple and direct injection to sophisticated induction of gene expression in a targeted tissue. We conducted a systematic review of publications assessing the use of viral vectors for gene transfer in lymphedema treatment. We hypothesized that viral vectors are an effective way to deliver targeted therapy in lymphedema treatment. We conducted a comprehensive systematic review of the published literature on targeted therapies associated with lymphedema surgery using the PubMed database. Eligibility criteria excluded papers that reported use of viral vectors for other medical conditions. s, presentations, reviews, meta-analyses, and non-English language articles were also excluded. From 21 potential articles found in the literature, fourteen fulfilled study eligibility criteria. Positive outcomes in terms of lymphangiogenesis were seen. The viral vectors used included adenovirus and recombinant adeno-associated virus. Most of the genes expressed were growth factors, but expression of dominant-negative transforming growth factor-β1 receptor-II or Prox1 was also proposed. Five studies targeted genetic expression on lymphedema tissue, five on transplanted lymph nodes, two on skeletal muscle, and one on adipose-derived stem cells. Publications assessing use of viral vectors for gene transfer in lymphedema treatment demonstrated that it is an effective mechanism of delivering targeted therapies. However, to date, all studies were experimental and further studies must be performed before translating these therapies into clinical practice.

We have demonstrated that tracheal insufflation of recombinant plasmid DNA results in transfection of rat lungs to the same extent as insufflation of plasmid-cationic liposome complex. To understand this observation better, we investigated the in vitro gene transfer of plasmid DNA in the presence and absence of cationic liposome and the effect of surfactant on gene transfer. The chloramphenicol acetyltransferase (CAT) expression plasmids pBL-CAT and pSV-CAT were studied in three cell types: rat fetal lung fibroblast (RFL-6), calf pulmonary artery endothelial cell (CPAE), and rat type II alveolar epithelial cell (type II AE). Three cationic liposomes were tested: DDAB (dimethyl-dioctadecyl ammonium bromide)-liposome, DOTAP (dioleoyltrimethyl ammonium propane)-liposome, and lipofectin. The results revealed that (i) plasmid DNA alone caused a dose-dependent, low-level transfection, most efficiently in RFL-6 followed by CPAE and type II AE, (ii) DDAB-liposome markedly enhanced gene transfer, most efficiently in RFL-6 followed by CPAE and type II AE, (iii) Survanta, a naturally derived surfactant preparation, and Exosurf, a synthetic surfactant, while having no effect on in vitro gene transfer by plasmid DNA alone, markedly inhibited cationic liposome-mediated gene transfer, (iv) dipalmitoyl phosphatidylcholine was responsible for the inhibitory effect of Exosurf, and (v) inhibition of cationic liposome-mediated gene transfer by Exosurf was not due to inhibition of plasmid DNA-cationic liposome complex uptake or interference with the promoter and enhancer. The observed inhibition of cationic liposome-mediated gene transfer by surfactant may in part explain our previous observation that tracheal insufflation of plasmid DNA and plasmid-cationic liposome complex results in equal lung gene transfer.

The particle bombardment (gene gun) method for gene transfer provides a new and efficient means for transfection of various cell types in culture. In this study we evaluate its application to human prostate tumor cells. Transient expression of the firefly luciferase gene driven by five viral and five cellular promoters was assessed after in vitro gene transfer using the gene gun method. The relative strengths of these promoters were quantitatively determined in four different human prostate tumor cell lines: DU145, PC-3, LNCaP, and CWR22Rv1 cells. In situ histochemical staining of cells, transfected with bacterial beta-galactosidase cDNA as a reporter gene, was also performed to evaluate the transfection efficiency. Time course of gene expression was determined using the luciferase reporter gene. The peak levels of transient expression of firefly luciferase are observed within 24 hr after gene transfer. Sustained but reduced luciferase levels were also detected as long as 5 days post transfection. Up to 35% of bombarded cells in vitro were found to express transgenic beta-galactosidase activity. Among tested viral promoters, cytomegalovirus early enhancer/promoter activity was observed to confer consistently the highest activity in each test cell line, whereas phosphoglycerate kinase gene promoter possessed the highest activity among the cellular promoters tested. The particle bombardment gene-transfer technology can be effectively employed as an efficient method for in vitro gene-transfer into prostate tumor cells. The characterization of relative promoter strength and preference may be useful for future studies of cancer gene therapy approaches.

Editorial: Intracoronary adenovirus-mediated transfer of immunosuppressive cytokine genes prolongs allograft survival

Strategies to Modulate Immune Responses: A New Frontier for Gene Therapy

Optimized protocol for biolistic transfection of brain slices and dissociated cultured neurons with a hand-held gene gun

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future.