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

RGD motifs on the surface of baculovirus enhance transduction of human lung carcinoma cells

Baculovirus vectors have been shown to enter a variety of mammalian cell lines and gene transfer with wild-type baculovirus (WT) has been demonstrated both in vitro and in vivo. Different protein motifs have been displayed on the viral surface to serve as ligands for cell-specific receptor molecules. We have generated recombinant baculovirus vectors displaying an RGD-motif, recognized by alphaV integrin, on the viral surface. The RGD motifs within the C-terminus of coxsackie virus A9 and human parechovirus 1 VP1 proteins were fused to the N-terminus of the major envelope glycoprotein, gp64, of Autographa californica multiple nucleopolyhedrovirus. The recombinant RGD-presenting viruses bound more efficiently to the surface of human lung carcinoma cells (A549), known to contain alphaV integrins, as compared to WT baculovirus. In addition, the binding pattern of the RGD-displaying baculovirus showed extensive clustering. This most likely represents clustering of the integrin molecules on the cell surface, induced by binding of the RGD-displaying baculovirus. Finally, the transduction efficiency of an RGD-representing virus increased by almost three-fold as monitored by light emission measurements. In conclusion, these results suggest that the RGD-motif is functional on the surface of baculovirus and thereby these tropism-modified viruses bind more efficiently as well as enhance the transduction efficiency of human cancer cells expressing alphaV integrins.

Expression of Autographa californica multiple nucleopolyhedrovirus genes in mammalian cells and upregulation of the host beta-actin gene

The gene expression of Autographa californica multiple nucleopolyhedrovirus (AcMNPV) was examined in two types of mammalian cells, human HeLa14 and hamster BHK cells. DNA microarray analysis followed by reverse transcription-PCR identified at least 12 viral genes transcribed in both HeLa14 cells and BHK cells inoculated with AcMNPV. 5' rapid amplification of cDNA ends was carried out to examine the transcriptional fidelity of these genes in HeLa14 cells. The transcription of ie-1, ie-0 and gp64 was initiated at a baculovirus early gene motif, CAGT, accompanied by a TATA motif. In addition, the same splicing observed for ie-0 mRNA in Sf9 cells occurred in HeLa14 cells. While the transcription initiation sites for pe38 and p6.9 were not located in the CAGT motif, most of them were in a typical eukaryotic RNA polymerase II promoter structure (a conventional TATA motif and/or an initiator). Interestingly, the expression of beta-actin was upregulated in the mammalian cells inoculated with AcMNPV. Subsequent experiments using UV-inactivated virus confirmed the upregulation, suggesting that de novo synthesis of viral products is not required for the event. These results indicated that the AcMNPV genome acts as a template for transcription in mammalian cells through the usual infection pathway, though there is no evidence for the functional expression of viral genes at present.

Using gene delivery to protect HIV-susceptible CNS cells: inhibiting HIV replication in microglia

Antiretroviral chemotherapy penetrates the CNS poorly. CNS HIV, thus sheltered, may injure the brain and complicate control of systemic HIV infection. Microglial cells play a major role in HIV persistence in the CNS but are rarely targeted for gene delivery. Because recombinant SV40 vectors (rSV40s) transduce other phagocytic cells efficiently, we tested rSV40 delivery of anti-HIV genetic therapy to microglial cells. Microglia prepared as enriched cultures from human fetal brain, were transduced with marker vectors, SV(RFP) and SV(Nef/FLAG), respectively, carrying DsRed and HIV-1 Nef bearing a FLAG epitope. By immunostaining and FACS, 95% of unselected cells expressed the transgenes, without detectable toxicity. Microglia were transduced with SV(AT), carrying human alpha1-antitrypsin (alpha1AT), which blocks Env and Gag processing. SV(AT)-treated microglia strongly resisted challenge with HIV-1BaL, even when microglia were transduced with SV(AT) following HIV challenge. Thus, rSV40s effectively transduce microglia and protect them from HIV.

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.

Gene technology based therapies in the brain

Gene therapy potentially represents one of the most important developments in modern medicine. Gene therapy, especially of cancer, has created exciting and elusive areas of therapeutic research in the past decade. In fact, the first gene therapy performed in a human was not against cancer but was performed to a 14 year old child suffering from adenosine deaminase (ADA) deficiency. In addition to cancer gene therapy there are many other diseases and disorders where gene therapy holds exciting and promising opportunities. These include amongst others gene therapy within the central nervous system and the cardiovascular system. Improvements of the efficiency and safety of gene therapy is the major goal of gene therapy development. After the death of Jesse Gelsinger, the first patient in whom death could be directly linked to the viral vector used for the treatment, ethical doubts were raised about the feasibility of gene therapy in humans. Therefore, the ability to direct gene transfer vectors to specific target cells is also a crucial task to be solved and will be important not only to achieve a therapeutic effect but also to limit potential adverse effects.

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.

Truncated vesicular stomatitis virus G protein improves baculovirus transduction efficiency in vitro and in vivo

Pseudotyping of viral vectors has been widely used to enhance viral transduction efficiency. One of the most popular pseudotyping proteins has been the G-protein of the vesicular stomatitis virus, VSV-G. In the present study, we show that the 21-amino-acid ectodomain with transmembrane and cytoplasmic tail domains of VSV-G (VSV-GED) augments baculovirus-mediated gene delivery in vertebrate cells by aiding viral entry. The VSV-GED pseudotyped virus replicated efficiently in insect cells yielding high titers. Five out of six studied cell lines showed improved transduction, as measured by a number of transduced cells or transgene expression level. Nearly 15-fold increase in the transduction efficiency was detected in rat malignant glioma cells as compared to the control virus. In the rat brain, transgene expression could be detected in the walls of lateral ventricles and in subarachnoid membranes. Increased transduction efficiency was also observed in the rabbit muscle. Our results suggest that VSV-GED enhances baculoviral gene transfer by augmenting gp64-mediated endosomal release. Moreover, no cytotoxicity was associated with improved gene transfer efficiency. Thus, VSV-GED pseudotyping provides a simple means to enhance baculovirus-mediated gene transfer in vitro and in vivo.

Gene Transfer to Dorsal Root Ganglia by Intrathecal Injection: Effects on Regeneration of Peripheral Nerves

Gene delivery to sensory neurons of the dorsal root ganglion (DRG) offers the prospect of developing new clinical interventions against peripheral nerve diseases and disorders. Here we show that genes can be transferred to rat DRG through lumbar intrathecal injection of delivery vectors into the cerebrospinal fluid. Genes could be transferred to DRG using polyethylenimine (PEI)/DNA complexes, Lipofectamine 2000/DNA complexes, adeno-associated virus vectors, or baculovirus vectors. We also show that nerve growth factor cDNA, delivered through lumbar intrathecal injection of PEI complexes, was able to improve regeneration of transected rat sciatic nerves. These data demonstrate the viability of using an intrathecal gene delivery approach for treating peripheral neuropathies.

Baculovirus as versatile vectors for protein expression in insect and mammalian cells

Today, many thousands of recombinant proteins, ranging from cytosolic enzymes to membrane-bound proteins, have been successfully produced in baculovirus-infected insect cells. Yet, in addition to its value in producing recombinant proteins in insect cells and larvae, this viral vector system continues to evolve in new and unexpected ways. This is exemplified by the development of engineered insect cell lines to mimic mammalian cell glycosylation of expressed proteins, baculovirus display strategies and the application of the virus as a mammalian-cell gene delivery vector. Novel vector design and cell engineering approaches will serve to further enhance the value of baculovirus technology.

Enhanced Prospects for Drug Delivery and Brain Targeting by the Choroid Plexus–CSF Route

The choroid plexus (CP), i.e., the blood-cerebrospinal fluid barrier (BCSFB) interface, is an epithelial boundary exploitable for drug delivery to brain. Agents transported from blood to lateral ventricles are convected by CSF volume transmission (bulk flow) to many periventricular targets. These include the caudate, hippocampus, specialized circumventricular organs, hypothalamus, and the downstream pia-glia and arachnoid membranes. The CSF circulatory system normally provides micronutrients, neurotrophins, hormones, neuropeptides, and growth factors extensively to neuronal networks. Therefore, drugs directed to CSF can modulate a variety of endocrine, immunologic, and behavioral phenomema; and can help to restore brain interstitial and cellular homeostasis disrupted by disease and trauma. This review integrates information from animal models that demonstrates marked physiologic effects of substances introduced into the ventricular system. It also recapitulates how pharmacologic agents administered into the CSF system prevent disease or enhance the brain's ability to recover from chemical and physical insults. In regard to drug distribution in the CNS, the BCSFB interaction with the blood-brain barrier is discussed. With a view toward translational CSF pharmacotherapy, there are several promising innovations in progress: bone marrow cell infusions, CP encapsulation and transplants, neural stem cell augmentation, phage display of peptide ligands for CP epithelium, CSF gene transfer, regulation of leukocyte and cytokine trafficking at the BCSFB, and the purification of neurotoxic CSF in degenerative states. The progressively increasing pharmacological significance of the CP-CSF nexus is analyzed in light of treating AIDS, multiple sclerosis, stroke, hydrocephalus, and Alzheimer's disease.

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.

Improvement in nuclear entry and transgene expression of baculoviruses by disintegration of microtubules in human hepatocytes

Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), a potent virus for mammalian cell gene delivery, possesses an ability to transduce mammalian cells without viral replication. We examined the role of the cellular cytoskeleton in the cytoplasmic trafficking of viral particles toward the nucleus in human hepatic cells. Microscopic studies showed that capsids were found in the nucleus after either viral inoculation or cytoplasmic microinjection of nucleocapsids. The presence of microtubule (MT) depolymerizing agents caused the amount of nuclear capsids to increase. Overexpression of p50/dynamitin, an inhibitor of dynein-dependent endocytic trafficking from peripheral endosomes along MTs toward late endosomes, did not significantly affect the amount of nuclear accumulation of nucleocapsids in the inoculated cells, suggesting that viral nucleocapsids are released into the cytosol during the early stages of the endocytic pathway. Moreover, studies with recombinant viruses containing the nuclear-targeted expression beta-galactosidase gene (beta-gal) showed a markedly increased level in the cellular expression of beta-galactosidase in the presence of MT-disintegrating drugs. The maximal increase in expression at 10 h postinoculation was observed in the presence of 80 muM nocodazole or 10 muM vinblastine. Together, these data suggest that the intact MTs constitute a barrier to baculovirus transport toward the nucleus.

Involvement of the Toll-like receptor 9 signaling pathway in the induction of innate immunity by baculovirus

We have previously shown that mice inoculated intranasally with a wild-type baculovirus (Autographa californica nuclear polyhedrosis virus [AcNPV]) are protected from a lethal challenge by influenza virus. However, the precise mechanism of induction of this protective immune response by the AcNPV treatment remained unclear. Here we show that AcNPV activates immune cells via the Toll-like receptor 9 (TLR9)/MyD88-dependent signaling pathway. The production of inflammatory cytokines was severely reduced in peritoneal macrophages (PECs) and splenic CD11c(+) dendritic cells (DCs) derived from mice deficient in MyD88 or TLR9 after cultivation with AcNPV. In contrast, a significant amount of alpha interferon (IFN-alpha) was still detectable in the PECs and DCs of these mice after stimulation with AcNPV, suggesting that a TLR9/MyD88-independent signaling pathway might also participate in the production of IFN-alpha by AcNPV. Since previous work showed that TLR9 ligands include bacterial DNA and certain oligonucleotides containing unmethylated CpG dinucleotides, we also examined the effect of baculoviral DNA on the induction of innate immunity. Transfection of the murine macrophage cell line RAW264.7 with baculoviral DNA resulted in the production of the inflammatory cytokine, while the removal of envelope glycoproteins from viral particles, UV irradiation of the virus, and pretreatment with purified baculovirus envelope proteins or endosomal maturation inhibitors diminished the induction of the immune response by AcNPV. Together, these results indicate that the internalization of viral DNA via membrane fusion mediated by the viral envelope glycoprotein, as well as endosomal maturation, which releases the viral genome into TLR9-expressing cellular compartments, is necessary for the induction of the innate immune response by AcNPV.

A multipurpose vector system for the screening of libraries in bacteria, insect and mammalian cells and expression in vivo

We have constructed a novel tetra-promoter vector (pBVboostFG) system that enables screening of gene/cDNA libraries for functional genomic studies. The vector enables an all-in-one strategy for gene expression in mammalian, bacterial and insect cells and is also suitable for direct use in vivo. Virus preparation is based on an improved mini Tn7 transpositional system allowing easy and fast production of recombinant baculoviruses with high diversity and negligible background. Cloning of the desired DNA fragments or libraries is based on the recombination system of bacteriophage lambda. As an example of the utility of the vector, genes or cDNAs of 18 different proteins were cloned into pBVboostFG and expressed in different hosts. As a proof-of-principle of using the vector for library screening, a chromophoric Thr⁶⁵-Tyr-Gly⁶⁷-stretch of enhanced green fluorescent protein was destroyed and subsequently restored by novel PCR strategy and library screening. The pBVboostFG enables screening of genome-wide libraries, thus making it an efficient new platform technology for functional genomics.

Lentiviral transduction of microglial cells

Microglial cells are the resident immune cells of the central nervous system. Their function resembles that of tissue macrophages and, as such, they share many properties with both peripheral macrophages and monocytes. One striking similarity is the difficulty with which these cells can be genetically manipulated via transfection or transduction. We have sought to overcome this challenge and generate stably transduced microglial cell lines. Based on encouraging results from macrophages, we hypothesized that lentiviral vectors might provide a valuable tool in the transduction of microglial cells. Using a lentiviral-based vector system expressing enhanced green fluorescent protein (eGFP) under the control of the murine stem cell virus promoter (MSCV), we found that multiplicities of infection (MOIs) of 1, 10, and 100 transduce >70%, >88%, and >95% of the cells, respectively. From the pool of transduced cells, we established lines of N9 and BV-2 microglial cells with distinct fluorescence intensities. Using real time-polymerase chain reaction (PCR), we correlated the integrated eGFP copy numbers to eGFP fluorescence measured by flow cytometry. When mixed, up to three lines with different eGFP intensities could be separated by flow cytometry and fluorescence microscopy. Neither infection nor transgene expression influenced microglial activation as assessed by nitric oxide (NO) production, cytokine release, and surface antigen expression. Our findings that microglial cells are easily transduced by lentiviral based vectors will facilitate research depending on genetic manipulation and help generate transgenic cell lines. In addition, the availability of microglial cell lines with defined fluorescence properties could replace elaborate staining procedures for microglial identification in co-culture experiments.

Homeostatic capabilities of the choroid plexus epithelium in Alzheimer's disease

As the secretory source of vitamins, peptides and hormones for neurons, the choroid plexus (CP) epithelium critically provides substances for brain homeostasis. This distributive process of cerebrospinal fluid (CSF) volume transmission reaches many cellular targets in the CNS. In ageing and ageing-related dementias, the CP-CSF system is less able to regulate brain interstitial fluid. CP primarily generates CSF bulk flow, and so its malfunctioning exacerbates Alzheimers disease (AD). Considerable attention has been devoted to the blood-brain barrier in AD, but more insight is needed on regulatory systems at the human blood-CSF barrier in order to improve epithelial function in severe disease. Using autopsied CP specimens from AD patients, we immunocytochemically examined expression of heat shock proteins (HSP90 and GRP94), fibroblast growth factor receptors (FGFr) and a fluid-regulatory protein (NaK2Cl cotransporter isoform 1 or NKCC1). CP upregulated HSP90, FGFr and NKCC1, even in end-stage AD. These CP adjustments involve growth factors and neuropeptides that help to buffer perturbations in CNS water balance and metabolism. They shed light on CP-CSF system responses to ventriculomegaly and the altered intracranial pressure that occurs in AD and normal pressure hydrocephalus. The ability of injured CP to express key regulatory proteins even at Braak stage V/VI, points to plasticity and function that may be boosted by drug treatment to expedite CSF dynamics. The enhanced expression of human CP 'homeostatic proteins' in AD dementia is discussed in relation to brain deficits and pharmacology.

Axonal transport of recombinant baculovirus vectors

Targeted gene delivery to neurons is crucial to effective gene therapy of neurodegenerative diseases. Several types of viral gene vectors may target neurons through retrograde axonal transport to somas of projection neurons after viral internalization at axon terminal fields. In this report we demonstrate for the first time that recombinant baculovirus vectors could migrate by axonal transport to cell bodies, resulting in transgene expression in projection neurons. After stereotaxic injection of Cy3-labeled baculovirus vectors into the rat striatum, retrograde axonal transport of the baculovirus vectors was observed along the corticostriatal pathway and nigrostriatal pathway. Furthermore, after intra-vitreous body injection, anterograde axonal transport and transsynaptic transport of the virus particles were observed in defined connections of the visual system, from the retina to the optic nerve, the lateral geniculate body, the superior colliculus, and the primary visual cortex. PCR analysis confirmed the existence of transported viral DNA in the tissue samples collected from projection fields. Driven by a neuron-specific promoter, transgene expression from the recombinant baculovirus vectors was detectable in target regions remote from injection sites. The attributes of baculovirus vectors in the bidirectional axonal transport and transneuronal transport in neural circuits of the central nervous system could be utilized for targeted gene delivery.

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.

Gene transfer vector biodistribution: pivotal safety studies in clinical gene therapy development

Techniques allowing for gene transfer vectors biodistribution investigation, in the frame of preclinical gene therapy development, are exposed. Emphasis is given on validation and test performance assessment. In the second part, specific gene vector distribution properties are reviewed (adenovirus, AAV, plasmid, retroviruses, herpes-derived vectors, germline transmission risks). The rationale for biodistribution by quantitative PCR, animal study and result interpretation is discussed. The importance and pivotal role of biodistribution study in gene transfer medicine development is shown through the determination of target organs for toxicity, germline transmission assessment and determination of risks of shedding and spreading of vectors in the gene transfer recipient and the environment.

Effect of adenovirus serotype 5 fiber and penton modifications on in vivo tropism in rats

Sequestration of adenovirus serotype 5 (Ad5) in liver restricts its use for gene delivery to other target sites in vivo. To date, no studies have systematically assessed the impact of genetic capsid modifications on in vivo tropism in rats, an important preclinical model for many disease types. We evaluated a panel of Ad5 vectors with capsid mutations or pseudotyped with the short fiber from serotype 41 (Ad41s) for infectivity in Wistar Kyoto rats in vitro and systemically in vivo. In vitro studies demonstrated that both coxsackie and adenovirus receptor (CAR) and heparan sulfate proteoglycan (HSPG) binding were predominant predictors of Ad5 tropism. In vivo, neither CAR nor integrin mutations alone affected liver transduction. The HSPG-binding mutation alone moderately reduced rat liver transgene levels by 2-fold (P < 0.05). This was further substantially decreased by additional mutation of CAR binding (95-fold). Combining CAR and integrin mutations reduced transgene levels by >99% (509-fold, P < 0.01), an effect not observed in parallel experiments in mice and highly variable when studied further in an additional two strains of rat. Ad41s mediated very low liver transduction (58-fold lower than AdCTL). Moreover, CAR-binding mutants (KO1-containing) or pseudotyping 41s eliminated hemagglutination of rat and human red blood cells in vitro. This highlights some important potential species and strain differences dictating Ad5 tropism in vivo and identifies vectors that are substantially detargeted from rat liver in vivo.

Baculovirus vectors elicit antigen-specific immune responses in mice

To characterize the induction of antigen-specific immune response mediated by baculovirus, vectors expressing the E2 glycoprotein of hepatitis C virus or the carcinoembryonic antigen (CEA) under the control of the cytomegalovirus immediate-early promoter-enhancer were constructed. Additionally, a baculovirus vector encoding the E2 glycoprotein (Bac-G-E2) and expressing vesicular stomatitis virus glycoprotein (VSV-G) in the viral envelope was generated by inserting the VSV-G coding sequence downstream of the polyhedrin promoter. Mice were subjected to intramuscular, intranasal, or subcutaneous inoculations with Bac-E2 and the cellular immune response was monitored by ELISPOT and intracellular staining. Additionally, humoral response was monitored by titrating anti-E2 antibodies. Induction of a measurable anti-E2 T-cell response was observed only after intramuscular injection and was predominantly CD8(+) specific. The immunogenic properties of baculovirus as vaccine vector were not restricted to E2 because a CEA-specific CD4(+) T-cell response was observed upon intramuscular injection of Bac-CEA. Interestingly, the Bac-G-E2 vector was shown to be a more efficient immunogen than Bac-E2, in view of the 10-fold difference in the minimal dose required to elicit a measurable T-cell response upon intramuscular injection. Induction of inflammatory cytokines such as gamma interferon, tumor necrosis factor alpha, and interleukin-6 was detected as early as 6 h postinjection of Bac-G-E2. Most importantly, both vectors elicited CD8(+) T cells with effector function capable of lysing target cells loaded with a hepatitis C virus-specific epitope. Additionally, enhanced NK cytolytic activity was detected in immunized mice. Thus, these results further demonstrate that baculovirus may be considered a useful vector for gene therapy.

Viral and non-viral vectors in gene therapy: technology development and clinical trials

Gene therapy as part of modern molecular medicine holds great promise for the treatment of both acute and chronic diseases and has the potential to bring a revolutionary era to cancer treatment. Gene therapy has been named the medicine of the future. For the past 10 years various viral and non-viral vectors have been engineered for improved gene and drug delivery. Although various diseases have been targeted, cancer therapy has been addressed to a large extent because of the straight forward approach. Delivery of toxic or immunostimulatory genes by viral and non-viral vectors has been investigated and encouraging results have been obtained in animal models. A large number of clinical trials have been conducted with some highly promising outcome. We propose that combinations of viruses with liposomes or polymers will solve the problem of systemic viral delivery and tumor targeting, bringing a revolution in molecular medicine and in applications of gene therapy in humans.

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.

Baculovirus capsid display: a novel tool for transduction imaging

Baculoviruses are enveloped insect viruses that can carry large quantities of foreign DNA in their genome. Baculoviruses have proved to be very promising gene therapy vectors but little is known about their transduction mechanisms in mammalian cells. We show in this study that Autographa californica multiple nuclear polyhedrosis virus capsid is compatible with the incorporation of desired proteins in large quantities. Fusions can be made to the N-terminus or C-terminus of the major capsid protein vp39 without compromising the viral titer or functionality. As an example of the baculovirus capsid display we show a tracking of the baculovirus transduction in mammalian cells by an enhanced green fluorescent protein (EGFP)-displaying virus. Our confocal and electron microscopy results suggest that the transduction block in mammalian cells is not in the endosomal escape, as previously proposed, but rather in the cytoplasmic transport or nuclear entry of the virus capsid. Our results also suggest that the EGFP-tagged virus can be used for visualization of the virus biodistribution in vivo. Furthermore, capsid-modified baculoviruses hold great promise for the nuclear and subcellular targeting of transgenes and as a novel peptide display system for a variety of eukaryotic applications.

In vitro and in vivo gene delivery by recombinant baculoviruses

Although recombinant baculovirus vectors can be an efficient tool for gene transfer into mammalian cells in vitro, gene transduction in vivo has been hampered by the inactivation of baculoviruses by serum complement. Recombinant baculoviruses possessing excess envelope protein gp64 or other viral envelope proteins on the virion surface deliver foreign genes into a variety of mammalian cell lines more efficiently than the unmodified baculovirus. In this study, we examined the efficiency of gene transfer both in vitro and in vivo by recombinant baculoviruses possessing envelope proteins derived from either vesicular stomatitis virus (VSVG) or rabies virus. These recombinant viruses efficiently transferred reporter genes into neural cell lines, primary rat neural cells, and primary mouse osteal cells in vitro. The VSVG-modified baculovirus exhibited greater resistance to inactivation by animal sera than the unmodified baculovirus. A synthetic inhibitor of the complement activation pathway circumvented the serum inactivation of the unmodified baculovirus. Furthermore, the VSVG-modified baculovirus could transduce a reporter gene into the cerebral cortex and testis of mice by direct inoculation in vivo. These results suggest the possible use of the recombinant baculovirus vectors in combination with the administration of complement inhibitors for in vivo gene therapy.