Baculovirus-mediated gene transfer into pancreatic islet cells

Improved Baculovirus Vectors for Transduction and Gene Expression in Human Pancreatic Islet Cells

Pancreatic islet transplantation is a promising treatment for type 1 diabetes mellitus offering improved glycaemic control by restoring insulin production. Improved human pancreatic islet isolation has led to higher islet transplantation success. However, as many as 50% of islets are lost after transplantation due to immune responses and cellular injury, gene therapy presents a novel strategy to protect pancreatic islets for improved survival post-transplantation. To date, most of the vectors used in clinical trials and gene therapy studies have been derived from mammalian viruses such as adeno-associated or retrovirus. However, baculovirus BacMam vectors provide an attractive and safe alternative. Here, a novel BacMam was constructed containing a frameshift mutation within fp25, which results in virus stocks with higher infectious titres. This improved in vitro transduction when compared to control BacMams. Additionally, incorporating a truncated vesicular stomatitis virus G protein increased transduction efficacy and production of EGFP and BCL2 in human kidney (HK-2) and pancreatic islet β cells (EndoC βH3). Lastly, we have shown that our optimized BacMam vector can deliver and express egfp in intact pancreatic islet cells from human cadaveric donors. These results confirm that BacMam vectors are a viable choice for providing delivery of transgenes to pancreatic islet cells.

Gene Transfection and Expression of Transforming Growth Factor-β1 in Nonobese Diabetic Mouse Islets Protects β-Cells in Syngeneic Islet Grafts from Autoimmune Destruction

Nonobese diabetic (NOD) mice develop diabetes and destroy syngeneic islet grafts through an autoimmune response. Because transforming growth factor (TGF)-β1 downregulates immune responses, we tested whether overexpression of TGF-β1 by gene transfection of NOD mouse islets could protect β-cells in islet grafts from autoimmune destruction. NOD mouse islet cells were transfected with an adenoviral DNA expression vector encoding porcine latent TGF-β1 (Ad TGF- β1) or the adenoviral vector alone (control Ad vector). The frequency of total islet cells expressing TGF-1 protein was increased from 12±1% in control Ad vector-transfected cells to 89 ± 4% in Ad TGF-β1-transfected islet cells, and the frequency of β-cells that expressed TGF-β1 was increased from 12 ± 1% to 60 ± 7%. Also, secretion of TGF-β1 was significantly increased in islets that overexpressed TGF-β1. Ad TGF-β1-transfected NOD mouse islets that overexpressed TGF-β1 prevented diabetes recurrence after transplantation into diabetic NOD mice for a median of 22 days compared with only 7 days for control Ad vector-transfected islets (p = 0.001). Immunohistochemical examination of the islet grafts revealed significantly more TGF-β1+ cells and insulin+ cells and significantly fewer CD45+ leukocytes in Ad TGF-β1-transfected islet grafts. Also, islet β-cell apoptosis was significantly decreased whereas apoptosis of graft-infiltrating leukocytes was significantly increased in Ad TGF-β1-transfected islet grafts. These observations demonstrate that overexpression of TGF-β1, by gene transfection of NOD mouse islets, protects islet β-cells from apoptosis and autoimmune destruction and delays diabetes recurrence after islet transplantation.

Bone Marrow Mesenchymal Stem Cells Expressing Baculovirus-Engineered Bone Morphogenetic Protein-7 Enhance Rabbit Posterolateral Fusion

Previous studies have suggested that bone marrow-derived mesenchymal stem cells (BMDMSCs) genetically modified with baculoviral bone morphogenetic protein-2 (Bac-BMP-2) vectors could achieve successful fusion in a femur defect model or in a spinal fusion model. In this study, BMDMSCs expressing BMP-7 (Bac-BMP-7-BMDMSCs) were generated. We hypothesized that Bac-BMP-7-BMDMSCs could secrete more BMP-7 than untransduced BMDMSCs in vitro and achieve spinal posterolateral fusion in a rabbit model. Eighteen rabbits underwent posterolateral fusion at L4-5. Group I (n = 6) was implanted with collagen-β-tricalcium phosphate (TCP)-hydroxyapatite (HA), Group II (n = 6) was implanted with collagen-β-TCP-HA plus BMDMSCs, and Group III (n = 6) was implanted with collagen-β-TCP-HA plus Bac-BMP-7-BMDMSCs. In vitro production of BMP-7 was quantified with an enzyme-linked immunosorbent assay (ELISA). Spinal fusion was examined using computed tomography (CT), manual palpation, and histological analysis. ELISA demonstrated that Bac-BMP-7-BMDMSCs produced four-fold to five-fold more BMP-7 than did BMDMSCs. In the CT results, 6 fused segments were observed in Group I (50%, 6/12), 8 in Group II (67%, 8/12), and 12 in Group III (100%, 12/12). The fusion rate, determined by manual palpation, was 0% (0/6) in Group I, 0% (0/6) in Group II, and 83% (5/6) in Group III. Histology showed that Group III had more new bone and matured marrow formation. In conclusion, BMDMSCs genetically transduced with the Bac-BMP-7 vector could express more BMP-7 than untransduced BMDMSCs. These Bac-BMP-7-BMDMSCs on collagen-β-TCP-HA scaffolds were able to induce successful spinal fusion in rabbits.

Cell Therapy Using Bone Marrow-Derived Stem Cell Overexpressing BMP-7 for Degenerative Discs in a Rat Tail Disc Model

Degenerative discs can cause low back pain. Cell-based transplantation or growth factors therapy have been suggested as a strategy to stimulate disc regeneration. Bone marrow-derived mesenchymal stem cells (BMDMSC) containing bone morphogenetic protein-7 (BMP-7) gene were constructed. We evaluated the effectiveness of these BMP-7 overexpressing cells on degenerative discs in rat tails. In vitro and in vivo studies were designed. In the first stage, the rats were divided into two group according to discs punctured by different needle gauges (18 gauge and 22 gauge). In the second stage, the ideal size of needle was used to induce rat tail disc degeneration. These animals are divided into three groups according to timing of treatment (zero-week, two-week, four-week). Each group was divided into three treating subgroups: control group, BMDMSC group, and Baculo-BMP-7-BMDMSC group. Each rat undergoes radiography examination every two weeks. After eight weeks, the discs were histologically examined with hematoxylin and eosin stain and Alcian blue stain. The 18-gauge group exhibited significant decrease in disc height index (%) than 22-gauge group at eight weeks at both Co6-7 (58.1% ± 2.8% vs. 63.7% ± 1.0%, p = 0.020) and Co8-9 discs (62.7% ± 2.8% vs. 62.8% ± 1.5%, p = 0.010). Baculo-BMP-7-BMDMSCs group showed significant difference in disc height index compared to the BMDMSCs group at both Co6-7 (93.7% ± 1.5% vs. 84.8% ± 1.0%, p = 0.011) and Co8-9 (86.0% ± 2.1% vs. 81.8% ± 1.7%, p = 0.012). In Baculo-BMP-7-BMDMSCs group, the zero-week treatment subgroup showed significant better in disc height index compared to two-week treatment group (p = 0.044), and four-week treatment group (p = 0.011). The zero-week treatment subgroup in Baculo-BMP-7-BMDMSCs group also had significant lower histology score than two-week treatment (4.3 vs. 5.7, p = 0.045) and four-week treatment (4.3 vs. 6.0, p = 0.031). In conclusion, Baculo-BMP-7-BMDMSC can slow down the progression of disc degeneration, but could not provide evidence of regeneration. Early treatment might obtain more distinct results.

Feasibility of baculovirus-mediated reporter gene delivery for efficient monitoring of islet transplantation in vivo

OBJECTIVE

The objective of this study was to explore the feasibility of baculovirus vector-mediated sodium iodide symporter (NIS) gene delivery to monitor islet transplantation.

METHODS

Baculovirus vectors expressing green fluorescent protein (GFP) or NIS (Bac-GFP and Bac-NIS) were established using the Bac-to-Bac baculovirus expression system. The GFP expression of Bac-GFP-infected rat islets was observed in vitro by fluorescence microscopy. Iodine uptake and inhibition of iodine uptake by NaClO4 in Bac-NIS-infected islets were dynamically monitored in vitro. Bac-GFP- or Bac-NIS-infected islets were implanted into the left axillary cavity of NOD-SCID mice, and fluorescence imaging and (125)I NanoSPECT/CT imaging were subsequently performed in vivo.

RESULTS

Bac-GFP efficiently infected rat islets (over 95% infected at MOI=40), and the expression of GFP lasted approximately two weeks. NaClO4 could inhibit iodine uptake by Bac-NIS-infected islets. In vivo imaging revealed that the fluorescence intensity of the transplant sites in Bac-GFP-infected groups was significantly higher than in the non-infected group. Grafts could be clearly observed by (125)I NanoSPECT/CT imaging for up to 8 h.

CONCLUSION

Baculovirus vectors are powerful vehicles for studying rat islets in gene delivery. It is feasible to use a baculovirus vector to delivery an NIS gene for non-invasive monitoring transplanted islets in vivo by the expression of the target gene.

Seamless replacement of Autographa californica multiple nucleopolyhedrovirus gp64 with each of five novel type II alphabaculovirus fusion sequences generates pseudotyped virus that fails to transduce mammalian cells

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a member of the type I alphabaculoviruses, is able to transduce and deliver a functional gene to a range of non-host cells, including many mammalian lines and primary cells, a property mediated by the envelope fusion protein GP64. AcMNPV is non-cytopathic and inherently replication deficient in non-host cells. As such, AcMNPV represents a possible new class of gene therapy vector with potential future clinical utility. Whilst not a problem for in vitro gene delivery, the broad tropism displayed for non-host cells is less desirable in a gene therapy vector. The fusion protein F of type II alphabaculoviruses can substitute functionally for GP64, and such pseudotyped viruses display a severely impaired capacity for non-host-cell transduction. Thus, surface decoration of such an F-pseudotyped AcMNPV with cell-binding ligands may restore transduction competence and generate vectors with desirable cell-targeting characteristics. By seamlessly swapping the native gp64 coding sequence with each of five sequences encoding different F proteins, a set of F-pseudotyped AcMNPV was generated. This report details their relative abilities both to functionally replace GP64 in viral growth and to transduce human Saos-2 and HeLa cells. All five supported viable infections in insect cell cultures and one, the Mamestra configurata NPV (MacoNPV) F pseudotype, could be amplified to titres close to those of native AcMNPV. In contrast, none was able to transduce the Saos-2 and HeLa cell lines. The robust support provided by MacoNPV F in virus production makes the corresponding pseudotype a viable scaffold to display surface ligands to direct selective mammalian cell targeting.

Genetic modification of baculovirus expression vectors

As a protein expression vector, the baculovirus demonstrates many advantages over other vectors. With the development of biotechnology, baculoviral vectors have been genetically modified to facilitate high level expression of heterologous proteins in both insect and mammalian cells. These modifications include utilization of different promoters and signal peptides, deletion or replacement of viral genes for increasing protein secretion, integration of polycistronic expression cassette for producing protein complexes, and baculovirus pseudotyping, promoter accommodation or surface display for enhancing mammalian cell targeting gene delivery. This review summarizes the development and the current state of art of the baculovirus expression system. Further development of baculovirus expression systems will make them even more feasible and accessible for advanced applications.

Expression of a secreted protein in mammalian cells using baculovirus particles

There are many methods presently available to produce recombinant proteins in mammalian systems. The BacMam system is a simple straightforward method which overlaps two well-established technologies, namely the BEVS insect cell system and the transduction of mammalian cells in vitro. This chapter describes a method for the study of gene expression in mammalian cells in a series of simple steps. Protocols outlined include the design and construction of the recombinant baculovirus, cell culture techniques required to maintain both insect and mammalian cells, generation of baculovirus stocks, and methods to obtain maximal and reproducible gene expression in mammalian cells. Currently available statistical techniques using factorial design of experiment to optimize conditions for recombinant protein in vitro are outlined. Then details with respect to process scale-up in disposable bioreactors are included.

Recombinant baculovirus as a highly potent vector for gene therapy of human colorectal carcinoma: molecular cloning, expression, and in vitro characterization

Present therapeutic strategies for most cancers are restricted mainly to the primary tumors and are also not very effective in controlling metastatic states. Alternatively, gene therapy can be a potential option for treating such cancers. Currently mammalian viral-based cancer gene therapy is the most popular approach, but the efficacy has been shown to be quite low in clinical trials. In this study, for the first time, the insect cell-specific baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) has been evaluated as a vector for gene delivery to colorectal cancer cells. Experiments involving factorial design were employed to study the individual and combined effects of different parameters such as multiplicity of infection (MOI), viral incubation time and epigenetic factors on transduction efficiency. The results demonstrate that baculovirus gene delivery system holds immense potential for development of a new generation of highly effective virotherapy for colorectal, as well as other major carcinomas (breast, pancreas, and brain), and offers significant benefits to traditional animal virus-based vectors with respect to safety concerns.

In vivo transcriptional targeting into the retinal vasculature using recombinant baculovirus carrying the human flt-1 promoter

Background

Endothelial cells are a target for gene therapy because they are implicated in a number of vascular diseases. Recombinant baculovirus have emerged as novel gene delivery vectors. However, there is no information available concerning the use of endothelial-specific promoters in the context of the baculovirus genome. In the present study, we have generated a recombinant baculovirus containing the human flt-1 promoter (BacFLT-GFP) driving the expression of the green fluorescent protein. Transcriptional gene targeting was analyzed in vitro in different mammalian cell lines and in vivo in adult rat retinal vasculature.

Results

BacFLT-GFP evoked the highest levels of expression in the endothelial cell line BUVEC-E6E7-1, similar to those reached by recombinant baculovirus carrying the CMV promoter (112% relative to BacCMV-GFP, n = 4). Interestingly, BacFLT-GFP directed high levels of expression in rat glioma C6 and in human glioblastoma CH235 cells (34.78% and 47.86% relative to BacCMV-GFP, respectively). Histone deacetylase inhibitors such as butyrate or trichostatin A enhanced the transcriptional activity of both BacCMV-GFP and BacFLT-GFP. Thus, in this study histone deacetylation appears to be a central mechanism for the silencing of baculovirus, independently of the promoter utilized. In vivo transcriptional targeting was demonstrated in adult rat retinal vasculature by intravitreal delivery of BacFLT-GFP and immunohistochemical staining with von Willebrand factor (vWF). Analysis by fluorescence microscopy and deconvolved three-dimensional confocal microscopy of retinal whole mounts obtained after 3 days of baculovirus injection showed that most GFP-expressing cells localized to the inner limiting membrane (ILM) and ganglion cell layer (GCL) and colocalize with vWF (70%, n = 10) in blood vessels, confirming the endothelial phenotype of the transduced cells.

Conclusion

Taken together, our results indicate that the restricted expression in endothelial cells mediated by the flt-1 promoter is not affected by the context of the baculovirus genome and demonstrate the potential of using recombinant baculovirus for transcriptional targeted gene expression into the eye vasculature.

The application of BacMam technology in nuclear receptor drug discovery

The nuclear receptor (NR) superfamily represents a major class of drug targets for the pharmaceutical industry. Strategies for the development of novel, more selective and safer compounds aimed at these receptors are now emerging. Reporter assays have been used routinely for the identification and characterisation of NR ligands. As the NR drug development process evolves, the increase in screening demand in terms of both capacity and complexity has necessitated the development of novel assay formats with increased throughput and flexibility. BacMam technology, a modified baculovirus system for over-expressing genes of interest in mammalian cells has helped answer this requirement. BacMam has many advantages over traditional gene delivery systems including high transduction efficiencies, broad cell host range, speed, cost and ease of generation and use. As outlined in this review, the technology has shown itself to be robust and efficient in various NR assay formats including transactivation (ER alpha/beta, MR, PR and PXR) and transrepression (GR-NFkappaB). In addition, the flexibility of this system will allow greater multiplexing of receptor, reporter, and cell host combinations as NR assays become more complex in order to relate better to relevant cellular and biological systems.

Gene therapy for type 1 diabetes

The most intensively studied autoimmune disorder, type 1 diabetes mellitus (DM1), has attracted perhaps the greatest interest for gene-based therapeutic and prophylactic interventions. The final clinical manifestation of this immunologically and genetically complex disease, the absence of insulin, is the major starting point for almost all the gene therapy modalities attempted to date. Insulin replacement by transplantation of islets of Langerhans or surrogate beta cells is the obvious choice, but the allogeneic nature of the transplants activates potent antidonor immunoreactivity necessitating gene and cell-based immunosuppressive strategies as an alternative to the toxic pharmacologic immunosuppressives indicated for classic solid organ transplants. Accumulating knowledge of the cellular mechanisms involved in onset, however, have yielded promising tolerance induction prophylactic approaches using genes and cells. Despite the early successes in a number of animal models, the true test of efficacy in humans remains to be demonstrated.

Baculovirus vectors for gene therapy

Since the discovery that baculoviruses can efficiently transduce mammalian cells, baculoviruses have been extensively studied as potential vectors for both in vitro and in vivo gene therapy. This chapter reviews the history of this research area, cells permissive to baculovirus transduction, factors influencing transduction and transgene expression, efforts to improve transduction, mechanisms of virus entry and intracellular trafficking, applications for in vivo and ex vivo gene therapy, as well as advantages, limitations, and safety issues concerning use of baculoviruses as gene therapy vectors. Recent progress and efforts directed toward overcoming existing bottlenecks are emphasized.

Baculovirus entry into human hepatoma cells

Autographa californica multiple nucleopolyhedrovirus (AcMNPV), a prototype member of the Baculoviridae family, has gained increasing interest as a potential vector candidate for mammalian gene delivery applications. AcMNPV is known to enter both dividing and nondividing mammalian cell lines in vitro, but the mode and kinetics of entry as well as the intracellular transport of the virus in mammalian cells is poorly understood. The general objective of this study was to characterize the entry steps of AcMNPV- and green fluorescent protein-displaying recombinant baculoviruses in human hepatoma cells. The viruses were found to bind and transduce the cell line efficiently, and electron microscopy studies revealed that virions were located on the cell surface in pits with an electron-dense coating resembling clathrin. In addition, virus particles were found in larger noncoated plasma membrane invaginations and in intracellular vesicles resembling macropinosomes. In double-labeling experiments, virus particles were detected by confocal microscopy in early endosomes at 30 min and in late endosomes starting at 45 min posttransduction. Viruses were also seen in structures specific for early endosomal as well as late endosomal/lysosomal markers by nanogold preembedding immunoelectron microscopy. No indication of viral entry into recycling endosomes or the Golgi complex was observed by confocal microscopy. In conclusion, these results suggest that AcMNPV enters mammalian cells via clathrin-mediated endocytosis and possibly via macropinocytosis. Thus, the data presented here should enable future design of baculovirus vectors suitable for more specific and enhanced delivery of genetic material into mammalian cells.

Adenine nucleotide regulation in pancreatic beta-cells: modeling of ATP/ADP-Ca2+ interactions

Glucose metabolism stimulates insulin secretion in pancreatic beta-cells. A consequence of metabolism is an increase in the ratio of ATP to ADP ([ATP]/[ADP]) that contributes to depolarization of the plasma membrane via inhibition of ATP-sensitive K+ (K(ATP)) channels. The subsequent activation of calcium channels and increased intracellular calcium leads to insulin exocytosis. Here we evaluate new data and review the literature on nucleotide pool regulation to determine the utility and predictive value of a new mathematical model of ion and metabolic flux regulation in beta-cells. The model relates glucose consumption, nucleotide pool concentration, respiration, Ca2+ flux, and K(ATP) channel activity. The results support the hypothesis that beta-cells maintain a relatively high [ATP]/[ADP] value even in low glucose and that dramatically decreased free ADP with only modestly increased ATP follows from glucose metabolism. We suggest that the mechanism in beta-cells that leads to this result can simply involve keeping the total adenine nucleotide concentration unchanged during a glucose elevation if a high [ATP]/[ADP] ratio exits even at low glucose levels. Furthermore, modeling shows that independent glucose-induced oscillations of intracellular calcium can lead to slow oscillations in nucleotide concentrations, further predicting an influence of calcium flux on other metabolic oscillations. The results demonstrate the utility of comprehensive mathematical modeling in understanding the ramifications of potential defects in beta-cell function in diabetes.

RNA interference mediated in human primary cells via recombinant baculoviral vectors

The success of RNA interference (RNAi) in mammalian cells, mediated by siRNAs or shRNA-generating plasmids, is dependent, to an extent, upon transfection efficiency. This is a particular problem with primary cells, which are often difficult to transfect using cationic lipid vehicles. Effective RNAi in primary cells is thus best achieved with viral vectors, and retro-, adeno-, and lentivirus RNAi systems have been described. However, the use of such human viral vectors is inherently problematic, e.g., Class 2 status and requirement of secondary helper functions. Although insect cells are their natural host, baculoviruses also transduce a range of vertebrate cell lines and primary cells with high efficiency. The inability of baculoviral vectors to replicate in mammalian cells, their Class 1 status, and the simplicity of their construction make baculovirus an attractive alternative gene delivery vector. We have developed a baculoviral-based RNAi system designed to express shRNAs and GFP from U6 and CMV promoters, respectively. Transduction of Saos2, HepG2, Huh7, and primary human hepatic stellate cells with a baculoviral construct expressing shRNAs targeting lamin A/C resulted in effective knockdown of the corresponding mRNA and protein. Development of this baculoviral-based system provides an additional shRNA delivery option for RNAi-based investigations in mammalian cells.

Baculovirus as a highly efficient expression vector in insect and mammalian cells

Baculovirus has been widely used for the production of recombinant proteins in insect cells. Since the finding that baculovirus can efficiently transduce mammalian cells, the applications of baculovirus have been greatly expanded. The prospects and drawbacks of baculovirus-mediated gene expression, either in insect or in mammalian cells, are reviewed. Recent progresses in expanding the applications to studies of gene regulation, viral vector preparation, in vivo and ex vivo gene therapy studies, generation of vaccine vectors, etc are discussed and the efforts directed towards overcoming the existing bottlenecks are particularly emphasized.

Highly efficient baculovirus-mediated gene transfer into rat chondrocytes

To explore the potential of baculovirus serving as a gene delivery vector in tissue engineering of articular cartilage, the efficiencies of baculovirus-mediated gene delivery into primary rat chondrocytes were evaluated and the transduction protocol commonly employed by others (using concentrated virus at multiplicity of infection [MOI] 200 for 1 h) was found to be ineffective (<1%). Therefore, a modified protocol was adopted, which markedly enhanced the efficiency (68%). Optimization of the transduction parameters, such as incubation time (8 h), temperature (25 degrees C), and surrounding solutions (PBS), further increased the efficiency to 88% and prolonged the duration of expression to 21 days, suggesting that the cells previously considered nonpermissive to baculovirus transduction may be reexamined for their permissiveness using alternative transduction protocols. The elevated efficiency correlated well with increased virus uptake upon extended incubation time, as demonstrated by quantitative real-time polymerase chain reaction (Q-PCR). The Q-PCR also revealed the degradation of viral DNA over culture time. Although the virus transduction somewhat hindered the cell proliferation, growth rate could be restored in the long-term culture. More importantly, transduced cells could secrete articular cartilage-specific type II collagen and glycosaminoglycan as well as mock-transduced cells, confirming that normal differentiation state of rat chondrocytes is retained upon baculovirus transduction. Taken together, these data indicate that baculovirus is a safe and highly efficient gene delivery vehicle into rat chondrocytes.

Investigation of optimal transduction conditions for baculovirus-mediated gene delivery into mammalian cells

Although baculovirus-mediated gene delivery into mammalian cells has been documented in a wealth of the literature, systematic investigation of the optimal transduction conditions remains unavailable. In this work, a transduction protocol using unconcentrated baculovirus is proposed for simple and efficient gene delivery into HeLa cells. We found that approximately 75-85% of the cells could be readily transduced and express the reporter protein when virus transduction occurred for 4 h at 25 degrees C using Dulbecco's phosphate-buffered saline (D-PBS) as the surrounding solution. This method contrasts with previous protocols in which transduction occurs for 1 h at 37 degrees C using growth medium (e.g., DMEM) as the surrounding solution. Investigation of the physical parameters led to the findings that: 1) baculovirus uptake by HeLa cells continued for at least 4 h in the event of high virus dosage, which led to higher gene expression; 2) the half-life of baculovirus dramatically decreased at 37 degrees C; 3) EGTA pretreatment did not apparently facilitate the gene delivery when the cells grew to multilayers; and 4) lower transduction efficiency and gene expression were obtained when DMEM was used (in comparison with D-PBS and TNM-FH), suggesting that DMEM contains certain inhibitory factors for baculovirus transduction. Our data uncovered several aspects that were not investigated before and the optimized transduction conditions allowed for gene delivery as efficient as that by the protocols commonly employed by others, but eliminated the need for virus ultracentrifugation. The protocol not only represented a simpler approach, but also considerably reduced possible virus inactivation during ultracentrifugation, thus making it easier to convert the baculovirus/mammalian cell system to a tool for eukaryotic protein production on a larger scale.

Neuronal gene transfer by baculovirus-derived vectors accommodating a neurone-specific promoter

Recombinant baculoviruses have been employed as gene delivery vectors for mammalian cells, including neurones, during recent years. The aim of the current study was to develop a new recombinant baculovirus vector capable of enhancing gene expression in neurones. A hybrid promoter constructed by fusing the enhancer of human cytomegalovirus (CMV) immediately early promoter to the human platelet-derived growth factor (PDGF) beta-chain promoter was placed into a baculovirus expression cassette. In cultured neurones, baculovirus vectors containing the hybrid promoter augmented transgene expression up to 100-fold greater than that mediated by titre-matched baculovirus vectors with the PDGF promoter alone. Double immunostaining of tissue sections collected from the striatum and the retina injected with the new baculovirus vector demonstrated its specificity in driving gene expression almost exclusively in neurones, confirming the feasibility of using a tissue-specific promoter in the context of baculovirus vectors to provide cell type-specific transgene expression. The attributes of the new baculovirus vector might have practical implications for gene therapy in the nervous system.

Direct imaging shows that insulin granule exocytosis occurs by complete vesicle fusion

Confocal imaging of GFP-tagged secretory granules combined with the use of impermeant extracellular dyes permits direct observation of insulin packaged in secretory granules, trafficking of these granules to the plasma membrane, exocytotic fusion of granules with the plasma membrane, and eventually the retrieval of membranes by endocytosis. Most such studies have been done in tumor cell lines, using either confocal methods or total internal reflectance microscopy. Here we compared these methods by using GFP-syncollin or PC3-GFP plus rhodamine dextrans to study insulin granule dynamics in insulinoma cells, normal mouse islets, and primary pancreatic beta cells. We found that most apparently docked granules did not fuse with the plasma membrane after stimulation. Granules that did fuse typically fused completely, but a few dextran-filled granules lingered at the membrane. Direct recycling of granules occurred only rarely. Similar results were obtained with both confocal and total internal reflection microscopy, although each technique had advantages for particular aspects of the granule life cycle. We conclude that insulin exocytosis involves a prolonged interaction of secretory granules with the plasma membrane, and that the majority of exocytotic events occur by full, not partial, fusion.

Improved display of synthetic IgG-binding domains on the baculovirus surface

Improved display of foreign protein moieties in combination with beneficial alteration of the viral surface properties should be of value for targeted and enhanced gene delivery. Here, we describe a vector based on Autographa californica multiple nucleopolyhedrovirus (AcMNPV) displaying synthetic IgG-binding domains (ZZ) of protein A fused to the transmembrane anchor of vesicular stomatitis virus (VSV) G protein. This display vector was equipped with a GFP/EGFP expression cassette enabling fluorescent detection in both insect and mammalian cells. The virus construct displayed the biologically active fusion protein efficiently and showed increased binding capacity to IgG. As the display is carried out using a membrane anchor of foreign origin, gp64 is left intact for virus entry, which may increase gene expression in the transduced mammalian cells. In addition, the viral vector can be targeted to any desired cell type via binding of ZZ domains when an appropriate IgG antibody is available.

Baculoviruses as Vectors for Gene Therapy against Human Prostate Cancer

Current curative strategies for prostate cancer are restricted to the primary tumour, and the effect of treatments to control metastatic disease is not sustained. Therefore, the application of gene therapy to prostate cancer is an attractive alternative. Baculoviruses are highly restricted insect viruses, which can enter, but not replicate in mammalian cells. Baculoviruses can incorporate large amounts of extra genetic material, and will express transgenes in mammalian cells when under the control of a mammalian or strong viral promoter. Successful gene delivery has been achieved both in vitro and in vivo and into both dividing and nondividing cells, which is important since prostate cancers divide relatively slowly. In addition, the envelope protein gp64 is sufficiently mutable to allow targeted transduction of particular cell types. In this review, the advantages of using baculoviruses for prostate cancer gene therapy are explored, and the mechanisms of viral entry and transgene expression are described.

Baculoviruses exhibit restricted cell type specificity in rat brain: a comparison of baculovirus- and adenovirus-mediated intracerebral gene transfer in vivo

Baculoviruses have recently been shown to be effective gene transfer vectors in mammalian cells. However, very little information is available about their target cell tropism in the central nervous system. We studied transduction efficiency, tropism and biodistribution of baculoviruses after local delivery to rat brain and compared their properties to adenoviruses. It was found that baculoviruses specifically transduced cuboid epithelium of the choroid plexus in ventricles and that the transduction efficiency was as high as 76+/-14%, whereas adenoviruses showed preference to corpus callosum glial cells and ventricular ependymal lining. Only a modest microglia response was seen after the baculovirus transduction whereas the adenovirus gene transfer led to a strong microglia response. Sensitive nested RT-PCR revealed transgene expression in the hindbrain and in ectopic organs including spleen, heart and lung, which indicates that some escape of both vectors occurs to ectopic organs after local gene transfer to the brain. We conclude that both baculovirus and adenovirus vectors can be used for local intracerebral gene therapy. The knowledge of the cell type specificity of the vectors may offer a possibility to achieve targeted gene delivery to distinct brain areas. Baculoviruses seem to be especially useful for the targeting of choroid plexus cells.

Baculovirus as mammalian cell expression vector for gene therapy: an emerging strategy

The monopoly of insect cells to host baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) as a eukaryotic gene expression system has been shattered with the growing evidence that it also infects mammalian cells in culture. Although AcMNPV fails to replicate in vertebrate cells, it does express alien genes with levels of expression that are dependent on the strength of the promoter used to drive transcription of the foreign gene. It also has been reported that the recombinant AcMNPV enters human hepatic cells in culture preferentially and specifically in comparison with the other mammalian cells of different origin and sources. This has resulted in the use of AcMNPV as a potent mammalian cell delivery system as a xenovector for gene therapy, more precisely liver-specific gene delivery in vitro and in vivo.

Recombinant baculoviruses as mammalian cell gene-delivery vectors

The baculovirus expression system has been used extensively for the expression of recombinant proteins in insect cells. Recently, recombinant baculovirus vectors engineered to contain mammalian cell-active promoter elements, have been used successfully for transient and stable gene delivery in a broad spectrum of primary and established mammalian cells. The application of modified baculoviruses for in vivo gene delivery has also been demonstrated. In contrast to other commonly used viral vectors, baculoviruses have the unique property of replicating in insect cells while being incapable of initiating a replication cycle and producing infectious virus in mammalian cells. The viruses can be readily manipulated, accommodate large insertions of foreign DNA, initiate little to no microscopically observable cytopathic effect in mammalian cells and have a good biosafety profile. These attributes will undoubtedly lead to the increased application and continued development of this system for efficient gene delivery into mammalian cells. Who said you can't teach an old dog new tricks?