Strong promoters are the key to highly efficient, noninflammatory and noncytotoxic adenoviral-mediated transgene delivery into the brain in vivo

Evaluation of Baculoviruses as Gene Therapy Vectors for Brain Cancer

We aimed to assess the potential of baculoviral vectors (BV) for brain cancer gene therapy. We compared them with adenoviral vectors (AdV), which are used in neuro-oncology, but for which there is pre-existing immunity. We constructed BVs and AdVs encoding fluorescent reporter proteins and evaluated their transduction efficiency in glioma cells and astrocytes. Naïve and glioma-bearing mice were intracranially injected with BVs to assess transduction and neuropathology. Transgene expression was also assessed in the brain of BV-preimmunized mice. While the expression of BVs was weaker than AdVs in murine and human glioma cell lines, BV-mediated transgene expression in patient-derived glioma cells was similar to AdV-mediated transduction and showed strong correlation with clathrin expression, a protein that interacts with the baculovirus glycoprotein GP64, mediating BV endocytosis. BVs efficiently transduced normal and neoplastic astrocytes in vivo, without apparent neurotoxicity. BV-mediated transgene expression was stable for at least 21 days in the brain of naïve mice, but it was significantly reduced after 7 days in mice systemically preimmunized with BVs. Our findings indicate that BVs efficiently transduce glioma cells and astrocytes without apparent neurotoxicity. Since humans do not present pre-existing immunity against BVs, these vectors may constitute a valuable tool for the delivery of therapeutic genes into the brain.

Down-Regulation of MHC Class I Expression in Human Keratinocytes Using Viral Vectors Containing US11 Gene of Human Cytomegalovirus and Cultivation on Bovine Collagen-Elastin Matrix (Matriderm®): Potential Approach for an Immune-Privileged Skin Substitute

Skin transplantation, especially in burn patients, is still challenging because surgeons are faced with limited disposability of autologous donor side material. The in vitro culture of keratinocytes has become an important reconstructive option. However, only non-immunogenic allogenic keratinocytes offer the opportunity to develop a skin graft that can overcome rejection. The purpose of the study was to develop targeted gene modification of keratinocytes in order to reduce immunogenicity for the use as allogenic transplantable skin graft by decreasing the expression of MHC class I. To reduce MHC class I expression, viral vectors containing the US11 gene of human cytomegalovirus were generated and tested on their functionality using Western blotting, indirect immunofluorescence staining, and flow cytometry. Transfected keratinocytes were seeded on commercially available bovine collagen-elastin matrices and further cultured for histological and cell survival assays. Results showed transient down-regulation of MHC class I after 24 h post-transfection, with recovery of MHC class I expression after 48 h. Histological assessments showed long-term cell survival as well as histological patterns comparable to epidermal layers of healthy human skin. The data postulates the potential application of US11 transfected keratinocytes as an approach towards an immune-privileged skin substitute. Nevertheless, further studies and data are needed.

An insight into non-integrative gene delivery approaches to generate transgene-free induced pluripotent stem cells

Over a decade ago, a landmark study that reported derivation of induced Pluripotent Stem Cells (iPSCs) by reprogramming fibroblasts has transformed stem cell research attracting the interest of the scientific community worldwide. These cells circumvent the ethical and immunological concerns associated with embryonic stem cells, and the limited self-renewal ability and restricted differentiation potential linked to adult stem cells. iPSCs hold great potential for understanding basic human biology, in vitro disease modeling, high-throughput drug testing and discovery, and personalized regenerative medicine. The conventional reprogramming methods involving retro- and lenti-viral vectors to deliver reprogramming factors in somatic cells to generate iPSCs nullify the clinical applicability of these cells. Although these gene delivery systems are efficient and robust, they carry an enormous risk of permanent genetic modifications and are potentially tumorigenic. To evade these safety concerns and derive iPSCs for human therapy, tremendous technological advancements have resulted in the development of non-integrating viral- and non-viral approaches. These gene delivery techniques curtail or eliminate the risk of any genomic alteration and enhance the prospects of iPSCs from bench-to-bedside. The present review provides a comprehensive overview of non-integrating viral (adenoviral vectors, adeno-associated viral vectors, and Sendai virus vectors) and DNA-based, non-viral (plasmid transfection, minicircle vectors, transposon vectors, episomal vectors, and liposomal magnetofection) approaches that have the potential to generate transgene-free iPSCs. The understanding of these techniques could pave the way for the use of iPSCs for various biomedical applications.

Evolutionary basis of a new gene- and immune-therapeutic approach for the treatment of malignant brain tumors: from mice to clinical trials for glioma patients

Glioma cells are one of the most aggressive and malignant tumors. Following initial surgery, and radio-chemotherapy they progress rapidly, so that patients' median survival remains under two years. They invade throughout the brain, which makes them difficult to treat, and are universally lethal. Though total resection is always attempted it is not curative. Standard of care in 2016 comprises surgical resection, radiotherapy and chemotherapy (temozolomide). Median survival is currently ~14-20months post-diagnosis though it can be higher in high complexity medical university centers, or during clinical trials. Why the immune system fails to recognize the growing brain tumor is not completely understood. We believe that one reason for this failure is that the brain lacks cells that perform the role that dendritic cells serve in other organs. The lack of functional dendritic cells from the brain causes the brain to be deficient in priming systemic immune responses to glioma antigens. To overcome this drawback we reconstituted the brain immune system for it to initiate and prime anti-glioma immune responses from within the brain. To achieve brain immune reconstitution adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1 derived thymidine kinase which converts ganciclovir into phospho-ganciclovir which becomes cytotoxic to dividing cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine for dendritic cells. This results in HSV-1/ganciclovir killing of tumor cells, and the release of tumor antigens, which are then taken up by dendritic cells recruited to the brain tumor microenvironment by Flt3L. Concomitant release of HMGB1, a TLR2 agonist that activates dendritic cells, stimulates dendritic cells loaded with glioma antigens to migrate to the cervical lymph nodes to prime a systemic CD8+ T cytotoxic killing of brain tumor cells. This induced immune response causes glioma-specific cytotoxicity, induces immunological memory, and does not cause brain toxicity or autoimmunity. A Phase I Clinical Trial, to test our hypothesis in human patients, was opened in December 2013 (see: NCT01811992, Combined Cytotoxic and Immune-Stimulatory Therapy for Glioma, at ClinicalTrials.gov). This trial is a first in human trial to test whether the re-engineering of the brain immune system can serve to treat malignant brain tumors. The long and winding road from the laboratory to the clinical trial follows below.

Adenovirus-Mediated CTLA4Ig or CD40Ig Gene Transfer Delays Pancreatic Islet Rejection in a Rat-to-Mouse Xenotransplantation Model after Systemic but Not Local Expression

Transient costimulation signal blockade of either CD28/CD80–86 interactions and/or CD40/CD154 interactions can prevent islet rejection in some models of both allo- and xenotransplantation. We have used adenoviruses coding for CTLA4Ig or CD40Ig and compared the efficacy of genetic modification of islets to systemic production through either intramuscular (IM) or intravenous (IV) injection of these vectors in a rat-to-mouse islet transplantation model. When gene transfer was performed into islets, a high level of primary nonfunction was induced. Furthermore, transduced functional grafts were rejected with the same kinetics as nontransduced islets. In contrast, IM AdCTLA4Ig and IV AdCD40Ig significantly delayed rejection (mean survival time of 54 ± 26.9 and 67.6 ± 44.9 days, respectively, vs. 24.3 ± 9.7 days for unmodified islets, p < 0.05). Combination of ex vivo AdCTLA4Ig islet transduction and IV AdCD40Ig did not improve graft survival further. In conclusion, islet graft transduction with adenoviruses coding for costimulation inhibitors resulted in local expression with low serum concentrations of CTLA4Ig or CD40Ig and was unable to protect islet xenografts from rejection. In contrast, IM or IV gene transfer resulted in high serum concentrations of these molecules and was highly efficient in prolonging xenograft survival. These results contrast with the efficacy of AdCTLA4Ig we observed in a rat islet allotransplantation model and suggest that islet xenograft rejection might be more difficult to control.

Destination Brain: the Past, Present, and Future of Therapeutic Gene Delivery

Neurological diseases and disorders (NDDs) present a significant societal burden and currently available drug- and biological-based therapeutic strategies have proven inadequate to alleviate it. Gene therapy is a suitable alternative to treat NDDs compared to conventional systems since it can be tailored to specifically alter select gene expression, reverse disease phenotype and restore normal function. The scope of gene therapy has broadened over the years with the advent of RNA interference and genome editing technologies. Consequently, encouraging results from central nervous system (CNS)-targeted gene delivery studies have led to their transition from preclinical to clinical trials. As we shift to an exciting gene therapy era, a retrospective of available literature on CNS-associated gene delivery is in order. This review is timely in this regard, since it analyzes key challenges and major findings from the last two decades and evaluates future prospects of brain gene delivery. We emphasize major areas consisting of physiological and pharmacological challenges in gene therapy, function-based selection of a ideal cellular target(s), available therapy modalities, and diversity of viral vectors and nanoparticles as vehicle systems. Further, we present plausible answers to key questions such as strategies to circumvent low blood-brain barrier permeability and most suitable CNS cell types for targeting. We compare and contrast pros and cons of the tested viral vectors in the context of delivery systems used in past and current clinical trials. Gene vector design challenges are also evaluated in the context of cell-specific promoters. Key challenges and findings reported for recent gene therapy clinical trials, assessing viral vectors and nanoparticles are discussed from the perspective of bench to bedside gene therapy translation. We conclude this review by tying together gene delivery challenges, available vehicle systems and comprehensive analyses of neuropathogenesis to outline future prospects of CNS-targeted gene therapies.

The Long and Winding Road: From the High-Affinity Choline Uptake Site to Clinical Trials for Malignant Brain Tumors

Malignant brain tumors are one of the most lethal cancers. They originate from glial cells which infiltrate throughout the brain. Current standard of care involves surgical resection, radiotherapy, and chemotherapy; median survival is currently ~14-20 months postdiagnosis. Given that the brain immune system is deficient in priming systemic immune responses to glioma antigens, we proposed to reconstitute the brain immune system to achieve immunological priming from within the brain. Two adenoviral vectors are injected into the resection cavity or remaining tumor. One adenoviral vector expresses the HSV-1-derived thymidine kinase which converts ganciclovir into a compound only cytotoxic to dividing glioma cells. The second adenovirus expresses the cytokine fms-like tyrosine kinase 3 ligand (Flt3L). Flt3L differentiates precursors into dendritic cells and acts as a chemokine that attracts dendritic cells to the brain. HSV-1/ganciclovir killing of tumor cells releases tumor antigens that are taken up by dendritic cells within the brain tumor microenvironment. Tumor killing also releases HMGB1, an endogenous TLR2 agonist that activates dendritic cells. HMGB1-activated dendritic cells, loaded with glioma antigens, migrate to cervical lymph nodes to stimulate a systemic CD8+ T cells cytotoxic immune response against glioma. This immune response is specific to glioma tumors, induces immunological memory, and does neither cause brain toxicity nor autoimmune responses. An IND was granted by the FDA on 4/7/2011. A Phase I, first in person trial, to test whether reengineering the brain immune system is potentially therapeutic is ongoing.

Tomato SlRbohB, a member of the NADPH oxidase family, is required for disease resistance against Botrytis cinerea and tolerance to drought stress

NADPH oxidases (also known as respiratory burst oxidase homologs, Rbohs) are key enzymes that catalyze the generation of reactive oxygen species (ROS) in plants. In the present study, eight SlRboh genes were identified in tomato and their possible involvement in resistance to Botrytis cinerea and drought tolerance was examined. Expression of SlRbohs was induced by B. cinerea and Pseudomonas syringae pv. tomato but displayed distinct patterns. Virus-induced gene silencing based silencing of SlRbohB resulted in reduced resistance to B. cinerea but silencing of other SlRbohs did not affect the resistance. Compared to non-silenced plants, the SlRbohB-silenced plants accumulated more ROS and displayed attenuated expression of defense genes after infection with B. cinerea. Silencing of SlRbohB also suppressed flg22-induced ROS burst and the expression of SlLrr22, a marker gene related to PAMP-triggered immunity (PTI). Transient expression of SlRbohB in Nicotiana benthamiana led to enhanced resistance to B. cinerea. Furthermore, silencing of SlRbohB resulted in decreased drought tolerance, accelerated water loss in leaves and the altered expression of drought-responsive genes. Our data demonstrate that SlRbohB positively regulates the resistance to B. cinerea, flg22-induced PTI, and drought tolerance in tomato.

Plasmacytoid dendritic cells in the tumor microenvironment: immune targets for glioma therapeutics

Adenovirus-mediated delivery of the immune-stimulatory cytokine Flt3L and the conditionally cytotoxic thymidine kinase (TK) induces tumor regression and long-term survival in preclinical glioma (glioblastoma multiforme [GBM]) models. Flt3L induces expansion and recruitment of plasmacytoid dendritic cells (pDCs) into the brain. Although pDCs can present antigen and produce powerful inflammatory cytokines, that is, interferon α (IFN-α), their role in tumor immunology remains debated. Thus, we studied the role of pDCs and IFN-α in Ad.TK/GCV+ Ad.Flt3L-mediated anti-GBM therapeutic efficacy. Our data indicate that the combined gene therapy induced recruitment of plasmacytoid DCs (pDCs) into the tumor mass; which were capable of in vivo phagocytosis, IFN-α release, and T-cell priming. Thus, we next used either pDCs or an Ad vector encoding IFN-α delivered within the tumor microenvironment. When rats were treated with Ad.TK/GCV in combination with pDCs or Ad-IFN-α, they exhibited 35% and 50% survival, respectively. However, whereas intracranial administration of Ad.TK/GCV + Ad.Flt3L exhibited a high safety profile, Ad-IFN-α led to severe local inflammation, with neurologic and systemic adverse effects. To elucidate whether the efficacy of the immunotherapy was dependent on IFN-α-secreting pDCs, we administered an Ad vector encoding B18R, an IFN-α antagonist, which abrogated the antitumoral effect of Ad.TK/GCV + Ad.Flt3L. Our data suggest that IFN-α release by activated pDCs plays a critical role in the antitumor effect mediated by Ad.TK/GCV + Ad.Flt3L. In summary, taken together, our results demonstrate that pDCs mediate anti-GBM therapeutic efficacy through the production of IFN-α, thus manipulation of pDCs constitutes an attractive new therapeutic target for the treatment of GBM.

Safety profile of gutless adenovirus vectors delivered into the normal brain parenchyma: implications for a glioma phase 1 clinical trial

Adenoviral vectors (Ads) have been evaluated in clinical trials for glioma. However, systemic immunity against the vectors can hamper therapeutic efficacy. We demonstrated that combined immunostimulation and cytotoxic gene therapy provides long-term survival in preclinical glioma models. Because helper-dependent high-capacity Ads (HC-Ads) elicit sustained transgene expression, in the presence of antiadenoviral immunity, we engineered HC-Ads encoding conditional cytotoxic herpes simplex type 1 thymidine kinase and immunostimulatory cytokine Fms-like tyrosine kinase ligand-3 under the control of the TetOn system. Escalating doses of combined HC-Ads (1×10(8), 1×10(9), and 1×10(10) viral particles [VP]) were delivered into the rat brain. We assessed neuropathology, biodistribution, transgene expression, systemic toxicity, and behavioral impact at acute and chronic time points after vector delivery. Histopathological analysis did not reveal any evidence of toxicity or long-term inflammation at the lower doses tested. Vector genomes were restricted to the injection site. Serum chemistry did not uncover adverse systemic side effects at any of the doses tested. Taken together, our data indicate that doses of up to 1×10(9) VP of each HC-Ad can be safely administered into the normal brain. This comprehensive toxicity and biodistribution study will lay the foundations for implementation of a phase 1 clinical trial for GBM using HC-Ads.

pUNISHER: a high-level expression cassette for use with recombinant viral vectors for rapid and long term in vivo neuronal expression in the CNS

Fast onset and high-level neurospecific transgene expression in vivo is of importance for many areas in neuroscience, from basic to translational, and can significantly reduce the amount of vector load required to maintain transgene expression in vivo. In this study, we tested various cis elements to optimize transgene expression at transcriptional, posttranscriptional, and posttranslational levels and combined them together to create the high-level neuronal transgene expression cassette pUNISHER. Using a second-generation adenoviral vector system in combination with the pUNISHER cassette, we characterized its rate of onset of detectable expression and levels of expression compared with a neurospecific expression cassette driven by the 470-bp human synapsin promoter in vitro and in vivo. Our results demonstrate in primary neurons that the pUNISHER cassette, in a recombinant adenovirus type 5 background, led to a faster rate of onset of detectable transgene expression and higher level of transgene expression. More importantly, this cassette led to highly correlated neuronal expression in vivo and to stable transgene expression up to 30 days in the auditory brain stem with no toxicity on the characteristics of synaptic transmission and plasticity at the calyx of Held synapse. Thus the pUNISHER cassette is an ideal high-level neuronal expression cassette for use in vivo for neuroscience applications.

Gene therapy for brain cancer: combination therapies provide enhanced efficacy and safety

Glioblastoma multiforme (GBM) is the most common primary brain cancer in adults. Despite significant advances in treatment and intensive research, the prognosis for patients with GBM remains poor. Therapeutic challenges for GBM include its invasive nature, the proximity of the tumor to vital brain structures often preventing total resection, and the resistance of recurrent GBM to conventional radiotherapy and chemotherapy. Gene therapy has been proposed as a useful adjuvant for GBM, to be used in conjunction with current treatment. Work from our laboratory has shown that combination of conditional cytotoxic with immunotherapeutic approaches for the treatment of GBM elicits regression of large intracranial tumor masses and anti-tumor immunological memory in syngeneic rodent models of GBM. In this review we examined the currently available animal models for GBM, including rodent transplantable models, endogenous rodent tumor models and spontaneous GBM in dogs. We discuss non-invasive surrogate end points to assess tumor progression and therapeutic efficacy, such as behavioral tests and circulating biomarkers. Growing preclinical and clinical data contradict the old dogma that cytotoxic anti-cancer therapy would lead to an immune-suppression that would impair the ability of the immune system to mount an anti-tumor response. The implications of the findings reviewed indicate that combination of cytotoxic therapy with immunotherapy will lead to synergistic antitumor efficacy with reduced neurotoxicity and supports the clinical implementation of combined cytotoxic-immunotherapeutic strategies for the treatment of patients with GBM.

Gene transfer into rat brain using adenoviral vectors

Viral vector-mediated gene delivery is an attractive procedure for introducing genes into the brain, both for purposes of basic neuroscience research and to develop gene therapy for neurological diseases. Replication-defective adenoviruses possess many features which make them ideal vectors for this purpose-efficiently transducing terminally differentiated cells such as neurons and glial cells, resulting in high levels of transgene expression in vivo. Also, in the absence of anti-adenovirus immunity, these vectors can sustain very long-term transgene expression within the brain parenchyma. This unit provides protocols for the stereotactic injection of adenoviral vectors into the brain, followed by protocols to detect transgene expression or infiltrates of immune cells by immunocytochemistry or immunofluorescence. ELISPOT and neutralizing antibody assay methodologies are provided to quantitate the levels of cellular and humoral immune responses against adenoviruses. Quantitation of adenoviral vector genomes within the rat brain using qPCR is also described.

Release of HMGB1 in response to proapoptotic glioma killing strategies: efficacy and neurotoxicity

PURPOSE

In preparation for a phase I clinical trial using a combined cytotoxic/immunotherapeutic strategy with adenoviruses (Ad) expressing Flt3L (Ad-Flt3L) and thymidine kinase (Ad-TK) to treat glioblastoma (GBM), we tested the hypothesis that Ad-TK+GCV would be the optimal tumor-killing agent in relation to efficacy and safety when compared with other proapoptotic approaches.

EXPERIMENTAL DESIGN

The efficacy and neurotoxicity of Ad-TK+GCV was compared with Ads encoding the proapoptotic cytokines [tumor necrosis factor-alpha, tumor necrosis factor-related apoptosis-inducing factor (TRAIL), and Fas ligand (FasL)], alone or in combination with Ad-Flt3L. In rats bearing small GBMs (day 4), only Ad-TK+GCV or Ad-FasL improved survival.

RESULTS

In rats bearing large GBMs (day 9), the combination of Ad-Flt3L with Ad-FasL did not improve survival over FasL alone, whereas Ad-Flt3L combined with Ad-TK+GCV led to 70% long-term survival. Expression of FasL and TRAIL caused severe neuropathology, which was not encountered when we used Ad-TK+/-Ad-Flt3L. In vitro, all treatments elicited release of high mobility group box 1 protein (HMGB1) from dying tumor cells. In vivo, the highest levels of circulating HMGB1 were observed after treatment with Ad-TK+GCV+Ad-Flt3L; HMGB1 was necessary for the therapeutic efficacy of AdTK+GCV+Ad-Flt3L because its blockade with glycyrrhizin completely blocked tumor regression. We also showed the killing efficacy of Ad-TK+GCV in human GBM cell lines and GBM primary cultures, which also elicited release of HMGB1.

CONCLUSIONS

Our results indicate that Ad-TK+GCV+Ad-Flt3L exhibit the highest efficacy and safety profile among the several proapoptotic approaches tested. The results reported further support the implementation of this combined approach in a phase I clinical trial for GBM.

Potential adenovirus-mediated gene therapy of glioma cancer

Malignant gliomas are typically characterized by rapid cell proliferation and a marked propensity to invade and damage surrounding tissues. They are the main brain tumors notoriously resistant to currently available therapies, since they fail to undergo apoptosis upon anticancer treatments. With recent advances in neuroscience and improved understanding of the molecular mechanisms of invasive migration, gene therapy provides a new strategy for treating glioma cancer. Brain tumor gene therapy using viral vectors and stem cells has shown promise in animal model and human patient studies. Here, we review recent studies on engineering adenoviral vectors that can be used as therapy for brain tumors. The new findings presented in this study are essential for the further exploration of this cancer and they represent an approach for developing a newer and more effective therapeutic approach in the clinical treatment of human glioma cancer.

Striatal readministration of rAAV vectors reveals an immune response against AAV2 capsids that can be circumvented

Recombinant adeno-associated virus (rAAV) expresses no viral genes after transduction. In addition, because the brain is relatively immunoprivileged, intracranial rAAV transduction may be immunologically benign due to a lack of antigen presentation. However, preexposure to AAV allows neutralizing antibodies (nAbs) to block brain transduction and rAAV readministration in the brain leads to an inflammatory response in the second-injection site. In this study, we replicate our striatal rAAV2/2-GDNF readministration results and extend this effect to a second transgene, green fluorescent protein (GFP). Unlike rAAV2/2-GDNF readministration, striatal rAAV2/2-GFP readministration leads to a loss of transgene in the second site in the absence of detectable circulating nAbs. In order to determine whether the transgene or the AAV2 capsid is the antigenic stimulus in brain for the immune response in the second site, we readministered rAAV2/2-GFP using two different rAAV serotypes (rAAV2/2 followed by rAAV2/5). In this case, there was no striatal inflammation or transgene loss detected in the second-injection site. In addition, striatal readministration of rAAV2/5-GFP also resulted in no detectable immune response. Furthermore, delaying rAAV2/2 striatal readministration to a 11-week interval abrogated the immune response in the second-injection site. Finally, while striatal readministration of rAAV2/2 leads to significant loss of transgene in the second-injection site, this effect is not due to loss of vector genomes as determined by quantitative real-time PCR. We conclude that intracellular processing of AAV capsids after transduction is the immunogenic antigen and capsid serotypes that are processed more quickly than rAAV2/2 are less immunogenic.

Herpes simplex virus type 1 thymidine kinase sequence fused to the lacz gene increases levels of {beta}-galactosidase activity per genome of high-capacity but not first-generation adenoviral vectors in vitro and in vivo

Increased transgene expression per vector genome is an important goal in the optimization of viral vectors for gene therapy. Herein we demonstrate that herpes simplex virus type 1 (HSV1) thymidine kinase (TK) gene sequences (1,131 bp) fused to the 3' end of lacZ increase transgene expression from high-capacity adenoviral vectors (HCAd), but not from first-generation (Ad) vectors. The woodchuck hepatitis virus posttranscriptional regulatory element (WPRE), in contrast, increased transgene expression levels from Ad but not HCAd vectors. The differential activity of the HSV1 TK gene and WPRE sequences was detected both in vitro and in vivo and suggests potentially different mechanisms of action or the interaction of these elements with vector genomic sequences.

Gene therapy to enhance allograft incorporation after host tissue irradiation

Structural bone allografts are used to reconstruct large skeletal defects after tumor surgery. Although allograft-related complications are declining, the use of perioperative radiation therapy is associated with a poorer outcome. Recently, BMP-2 levels in the host bed were reportedly diminished after exposure to radiation doses consistent with those used perioperatively to treat musculoskeletal sarcoma. Reintroduction of this osteogenic protein may circumvent the deleterious effects of preoperative radiation on allograft incorporation. We introduced a novel polymeric BMP-2 gene delivery system into the host-allograft junctions at the time of transplantation in an ovine tibial defect model with or without preoperative exposure to 50 Gy radiation. After 4 months, we noted no radiographic or histologic improvements in allograft incorporation after preoperative radiation and BMP-2 reintroduction; however, 50 Gy radiation was associated with increased porosity in the interface regions and poorer radiographic healing. We identified no BMP2-expressing cells or protein in the interface at the study end point, suggesting the polymeric gene delivery system was unable to promote extended expression of the protein or induce a healing response. Although gene therapy may hold promise as a novel technique to improve allograft incorporation, our data do not support that contention with the current approach.

Gene transfer into rat brain using adenoviral vectors

Recombinant adenovirus vectors are attractive vehicles to deliver genes into the brain for the purposes of neurobiological research and for gene therapy of neurological diseases. This unit provides a comprehensive set of protocols for adenovirus vector-mediated gene transfer to the brain, including introduction of the vector into the brain by stereotaxic injection and preparation and processing of brain tissue for the evaluation of gene transfer. The potential side-effects of administering adenovirus vectors to the brain are discussed in detail. The unit also provides protocols for evaluating these side-effects (e.g., demyelination, inflammation, vector-mediated cytotoxicity, etc.). Finally, critical parameters for obtaining optimal gene transfer with minimum side-effects are presented.

Affinity-based biosensors as promising tools for gene doping detection

Innovative bioanalytical approaches can be foreseen as interesting means for solving relevant emerging problems in anti-doping control. Sport authorities fear that the newer form of doping, so-called gene doping, based on a misuse of gene therapy, will be undetectable and thus much less preventable. The World Anti-Doping Agency has already asked scientists to assist in finding ways to prevent and detect this newest kind of doping. In this Opinion article we discuss the main aspects of gene doping, from the putative target analytes to suitable sampling strategies. Moreover, we discuss the potential application of affinity sensing in this field, which so far has been successfully applied to a variety of analytical problems, from clinical diagnostics to food and environmental analysis.

Regulated expression of adenoviral vectors-based gene therapies: therapeutic expression of toxins and immune-modulators

Regulatable promoter systems allow gene expression to be tightly controlled in vivo. This is highly desirable for the development of safe, efficacious adenoviral vectors that can be used to treat human diseases in the clinic. Ideally, regulatable cassettes should have minimal gene expression in the "OFF" state, and expression should quickly reach therapeutic levels in the "ON" state. In addition, the components of regulatable cassettes should be non-toxic at physiological concentrations and should not be immunogenic, especially when treating chronic illness that requires long-lasting gene expression. In this chapter, we will describe in detail protocols to develop and validate first generation (Ad) and high-capacity adenoviral (HC-Ad) vectors that express therapeutic genes under the control of the TetON regulatable system. Our laboratory has successfully used these protocols to regulate the expression of marker genes, immune stimulatory genes, and toxins for cancer gene therapeutics, i.e., glioma that is a deadly form of brain cancer. We have shown that this third generation TetON regulatable system, incorporating a doxycycline (DOX)-sensitive rtTA(2)S-M2 inducer and tTS(Kid) silencer, is non-toxic, relatively non-immunogenic, and can tightly regulate reporter transgene expression downstream of a TRE promoter from adenoviral vectors in vitro and also in vivo.

Viral vectors for in vivo gene transfer in Parkinson's disease: properties and clinical grade production

Because Parkinson's disease is a progressive degenerative disorder that is mainly confined to the basal ganglia, gene transfer to deliver therapeutic molecules is an attractive treatment avenue. The present review focuses on direct in vivo gene transfer vectors that have been developed to a degree that they have been successfully used in animal model of Parkinson's disease. Accordingly, the properties of recombinant adenovirus, recombinant adeno-associated virus, herpes simplex virus, and lentivirus are described and contrasted. In order for viral vectors to be developed into clinical grade reagents, they must be manufactured and tested to precise regulatory standards. Indeed, clinical lots of viral vectors can be produced in compliance with current Good Manufacturing Practices (cGMPs) regulations using industry accepted manufacturing methodologies, manufacturing controls, and quality systems. The viral vector properties themselves combined with physiological product formulations facilitate long-term storage and direct in vivo administration.

One-year expression from high-capacity adenoviral vectors in the brains of animals with pre-existing anti-adenoviral immunity: clinical implications

The main challenge of gene therapy is to provide long-term, efficient transgene expression. Long-term transgene expression from first generation adenoviral vectors (Advs) delivered to the central nervous system (CNS) is elicited in animals not previously exposed to adenovirus (Ad). However, upon systemic immunization against Ad, transgene expression from a first generation Adv is abolished. High-capacity Advs (HC-Advs) provide sustained very long-term transgene expression in the brain, even in animals pre-immunized against Ad. In this study, we tested the hypothesis that a HC-Adv in the brain would allow for long-term transgene expression, for up to 1 year, in the brain of mice immunized against Ad prior to delivery of the vector to the striatum. In naïve animals, the expression of beta-galactosidase from Adv or HC-Adv was sustained for 1 year. In animals immunized prior to vector delivery, expression from a first generation Adv was abolished. These results point to a very long-term HC-Adv-mediated transgene expression in the brain, even in animals that had been immunized systemically against Ad before the delivery of HC-Adv into the brain. This study therefore indicates the utility of HC-Adv as a powerful gene therapy vector for chronic neurological disorders, even in patients who had been pre-exposed to Ad prior to gene therapy.

Time course of transgene expression after intrastriatal pseudotyped rAAV2/1, rAAV2/2, rAAV2/5, and rAAV2/8 transduction in the rat

In vivo recombinant adeno-associated viral vector (rAAV)-mediated transduction of various tissues including brain has been characterized by slow onset and gradual increase in gene expression before reaching stable long-term protein levels. The early time course of transgene expression has not been quantified using newly available rAAV capsid serotypes. In this experiment, the onset of expression of green fluorescent protein (GFP) after intrastriatal injection of rAAV2-based pseudotyped vectors (rAAV1, rAAV5, and rAAV8 capsids) was quantified. Native GFP fluorescence displayed a delayed onset of expression of at least 7 days for all the pseudotyped rAAV vectors. However, GFP immunohistochemical staining revealed significant transgene expression by 4 days after transduction for all serotypes and stable GFP(+) neuronal populations mediated by all serotypes within 14 days post transduction at the latest. rAAV2/1 and rAAV2/2 displayed no time-dependent increase of GFP(+) striatal neurons; reaching maximal striatal cell GFP(+) counts at 4 days after injection. All serotypes displayed peak transgene expression by 4 weeks post injection where native GFP(+) neurons were equal to immunostained striatal GFP(+) neurons. The inflammatory response to these rAAV vectors was present up to 4 weeks after transduction but was not apparent 9 months post injection. Thus, rAAV-mediated transgene expression begins earlier than previously thought.

Optimization of adenoviral vector-mediated transgene expression in the canine brain in vivo, and in canine glioma cells in vitro

Expression of the immune-stimulatory molecule Fms-like tyrosine kinase 3 ligand (Flt3L) and the conditional cytotoxic enzyme herpes simplex virus type 1 thymidine kinase (HSV1-TK) provides long-term immune-mediated survival of large glioblastoma multiforme (GBM) models in rodents. A limitation for predictive testing of novel antiglioma therapies has been the lack of a glioma model in a large animal. Dogs bearing spontaneous GBM may constitute an attractive large-animal model for GBM, which so far has remained underappreciated. In preparation for a clinical trial in dogs bearing spontaneous GBMs, we tested and optimized adenovirus-mediated transgene expression with negligible toxicity in the dog brain in vivo and in canine J3T glioma cells. Expression of the marker gene beta-galactosidase (beta-Gal) was higher when driven by the murine (m) than the human (h) cytomegalovirus (CMV) promoter in the dog brain in vivo, without enhanced inflammation. In the canine brain, beta-Gal was expressed mostly in astrocytes. beta-Gal activity in J3T cells was also higher with the mCMV than the hCMV promoter driving tetracycline-dependent (TetON) transgene expression within high-capacity adenovirus vectors (HC-Ads). Dog glioma cells were efficiently transduced by HC-Ads expressing mCMV-driven HSV1-TK, which induced 90% reduction in cell viability in the presence of ganciclovir. J3T cells were also effectively transduced with HC-Ads expressing Flt3L under the control of the regulatable TetON promoter system, and as predicted, Flt3L release was stringently inducer dependent. HC-Ads encoding therapeutic transgenes under the control of regulatory sequences driven by the mCMV promoter are excellent vectors for the treatment of spontaneous GBM in dogs, which constitute an ideal preclinical animal model.

Regulatable gutless adenovirus vectors sustain inducible transgene expression in the brain in the presence of an immune response against adenoviruses

In view of recent serious adverse events and advances in gene therapy technologies, the use of regulatable expression systems is becoming recognized as indispensable adjuncts to successful clinical gene therapy. In the present work we optimized high-capacity adenoviral (HC-Ad) vectors encoding the novel tetracycline-dependent (TetOn)-regulatory elements for efficient and regulatable gene expression in the rat brain in vivo. We constructed two HC-Ad vectors encoding beta-galactosidase (beta-gal) driven by a TetOn system containing the rtTAS(s)M2 transactivator and the tTS(Kid) repressor under the control of the murine cytomegalovirus (mCMV) (HC-Ad-mTetON-beta-Gal) or the human CMV (hCMV) promoter (HC-Ad-hTetON-beta-Gal). Expression was tightly regulatable by doxycycline (Dox), reaching maximum expression in vivo at 6 days and returning to basal levels at 10 days following the addition or removal of Dox, respectively. Both vectors achieved higher transgene expression levels compared to the expression from vectors encoding the constitutive mCMV or hCMV promoter. HC-Ad-mTetON-beta-Gal yielded the highest transgene expression levels and expressed in both neurons and astrocytes. Antivector immune responses continue to limit the clinical use of vectors. We thus tested the inducibility and longevity of HC-Ad-mediated transgene expression in the brain of rats immunized against adenovirus by prior intradermal injections of RAds. Regulated transgene expression from HC-Ad-mTetON-beta-Gal remained active even in the presence of a significant systemic immune response. Therefore, these vectors display two coveted characteristics of clinically useful vectors, namely their regulation and effectiveness even in the presence of prior immunization against adenovirus.

Regulatable gene expression systems for gene therapy

It is feasible to restrict transgene expression to a tissue or region in need of therapy by using promoters that respond to focusable physical stimuli. The most extensively investigated promoters of this type are radiation-inducible promoters and heat shock protein gene promoters that can be activated by directed, transient heat. Temporal regulation of transgenes can be achieved by various two- or three-component gene switches that are triggered by an appropriate small molecule inducer. The most commonly considered gene switches that are reviewed herein are based on small molecule-responsive transactivators derived from bacterial tetracycline repressor, insect or mammalian steroid receptors, or mammalian FKBP12/FRAP. A new generation of gene switches combines a heat shock protein gene promoter and a small molecule-responsive gene switch and can provide for both spatial and temporal regulation of transgene activity.

An investigation of the problem of two-layered immunohistochemical staining in paraformaldehyde fixed sections

In sections of paraformaldehyde fixed brain tissue, stained using immunohistochemical methods, the distribution of staining within the sections is not uniform. Whilst stained cells are seen at the top and bottom surfaces, the central thicknesses of the sections contain little or no immunoreactivity. This presents a major problem for quantification, as each section contains a population of cells that is not visualized by the staining method. Following extensive investigation of this phenomenon, we report that the failure of full thickness, immunohistochemical staining is not a failure of the immunohistochemical methodology per se, nor is it related directly to the thickness of the sections used. Rather, the problem lies in the chemistry of the tissue itself, and originates during fixation of the tissues using paraformaldehyde-based perfusion methods, which render the cell membranes impermeable to one or more components of the staining protocol. We show that this impermeability is affected by addition of membrane-disrupting agents to the fixative, and by a reduction of exposure to paraformaldehyde during fixation. The present investigation contributes to the development of new fixation protocols, optimised for use in both immunohistochemical methods and morphometric analyses.

Immunological thresholds in neurological gene therapy: highly efficient elimination of transduced cells might be related to the specific formation of immunological synapses between T cells and virus-infected brain cells

First-generation adenovirus can be engineered with powerful promoters to drive expression of therapeutic transgenes. Numerous clinical trials for glioblastoma multiforme using first generation adenoviral vectors have either been performed or are ongoing, including an ongoing, Phase III, multicenter trial in Europe and Israel (Ark Therapeutics, Inc.). Although in the absence of anti-adenovirus immune responses expression in the brain lasts 6-18 months, systemic infection with adenovirus induces immune responses that inhibit dramatically therapeutic transgene expression from first generation adenoviral vectors, thus, potentially compromising therapeutic efficacy. Here, we show evidence of an immunization threshold for the dose that generates an immune response strong enough to eliminate transgene expression from the CNS. For the systemic immunization to eliminate transgene expression from the brain, > or = 1 x 10(7) infectious units (iu) of adenovirus need to be used as immunogen. Furthermore, this immune response eliminates >90% of transgene expression from 1 x 10(7)-1 x 10(3) iu of vector injected into the striatum 60 days earlier. Importantly, elimination of transgene expression is independent of the nature of the promoter that drives transgene expression and is accompanied by brain infiltration of CD8(+) T cells and macrophages. In conclusion, once the threshold for systemic immunization (i.e. 1 x 10(7) iu) is crossed, the immune response eliminates transgene expression by >90% even from brains that receive as little as 1000 iu of adenoviral vectors, independently of the type of promoter that drives expression.

Improved high-capacity adenoviral vectors for high-level neuron-restricted gene transfer to the CNS

Adenovirus-based (Ad) vectors are used widely for experimental gene transfer to the CNS. Ad transduce many cell types including postmitotic neurons. However, their use for CNS gene transfer is limited due to the host immune response elicited. Furthermore, the extensive distribution of the primary cellular receptor for Ad, the coxsackievirus and adenovirus receptor (CAR), allows adenoviral vectors to infect a broad range of host cells which may be disadvantageous in tissues with various different cell types, like the CNS. The use of tissue-specific promoters allows for neuron-restricted gene expression, even though gene expression driven by these promoters is often very weak. Accordingly, increased transgene expression levels from viral transcription units are needed in order to improve the overall performance of Ad vectors. We designed a high-capacity Ad vector (HC-Ad) that allows for high-level, neuron-restricted transgene expression and shows no obvious signs of immunogenicity or toxicity in the mouse brain.

Quantification of high-capacity helper-dependent adenoviral vector genomes in vitro and in vivo, using quantitative TaqMan real-time polymerase chain reaction

First-generation adenoviral (Ad) and high-capacity adenoviral (HC-Ad) vectors are efficient delivery vehicles for transferring therapeutic transgenes in vivo into tissues/organs. The initial successes reported with adenoviral vectors in preclinical trials have been limited by immune-related adverse side effects. This has been, in part, attributed to the use of poorly characterized preparations of adenoviral vectors and also to the untoward immune adverse side effects elicited when high doses of these vectors were used. HC-Ads have several advantages over Ads, including the lack of viral coding sequences, which after infection and uncoating, makes them invisible to the host's immune system. Another advantage is their large cloning capacity (up to approximately 35 kb). However, accurate characterization of HC-Ad vectors, and of contaminating replication-competent adenovirus (RCA) or helper virus, is necessary before these preparations can be used safely in clinical trials. Consequently, the development of accurate, simple, and reproducible methods to standardize and validate adenoviral preparations for the presence of contaminant genomes is required. By using a molecular method that allows accurate, reproducible, and simultaneous determination of HC-Ad, contaminating helper virus, and RCA genome copy numbers based on real-time quantitative PCR, we demonstrate accurate detection of these three genomic entities, within CsCl-purified vector stocks, total DNA isolated from cells transduced in vitro, and from brain tissue infected in vivo. This approach will allow accurate assessment of the levels and biodistribution of HC-Ad and improve the safety and efficacy of clinical trials.

Effective high-capacity gutless adenoviral vectors mediate transgene expression in human glioma cells

Glioblastoma multiforme (GBM) is the most common subtype of primary malignant brain tumor. Although serotype 5 adenoviral vectors (Ads) have been used successfully in clinical trials for GBM, the capacity of Ads to infect human glioma cells and the expression of adenoviral receptors in GBM cells have been challenged. In this report, we studied the expression of three molecules that have been shown to mediate adenoviral entry into cells, i.e., coxsackie and adenovirus receptor (CAR), integrin alphavbeta3 (INT), and major histocompatibility complex class I (MHCI), in rodent glioma cell lines and low-passage primary cultures and cell lines from human GBM. We correlated levels of expression of CAR, INT, and MHCI with transduction efficiency elicited by several high-capacity helper-dependent adenoviral vectors (HC-Ads). Expression levels of adenoviral receptors were variable among the different GBM cells studied. HC-Ad-mediated therapeutic gene expression was efficient, ranging between 20 and 80% of the total target cells expressing the encoded transgenes. Our results show no correlation between the levels of CAR, INT, or MHCI molecules and the levels of transgene expression or the number of GBM cells transduced. We conclude that expression levels of adenoviral receptors do not predict their transduction efficiency or biological function.

Coordinate enhancement of transgene transcription and translation in a lentiviral vector

BACKGROUND

Coordinate enhancement of transgene transcription and translation would be a potent approach to significantly improve protein output in a broad array of viral vectors and nonviral expression systems. Many vector transgenes are complementary DNA (cDNA). The lack of splicing can significantly reduce the efficiency of their translation. Some retroviruses contain a 5' terminal post-transcriptional control element (PCE) that facilitates translation of unspliced mRNA. Here we evaluated the potential for spleen necrosis virus PCE to stimulate protein production from HIV-1 based lentiviral vector by: 1) improving translation of the internal transgene transcript; and 2) functionally synergizing with a transcriptional enhancer to achieve coordinate increases in RNA synthesis and translation.

RESULTS

Derivatives of HIV-1 SIN self-inactivating lentiviral vector were created that contain PCE and cytomegalovirus immediate early enhancer (CMV IE). Results from transfected cells and four different transduced cell types indicate that: 1) PCE enhanced transgene protein synthesis; 2) transcription from the internal promoter is enhanced by CMV IE; 3) PCE and CMV IE functioned synergistically to significantly increase transgene protein yield; 4) the magnitude of translation enhancement by PCE was similar in transfected and transduced cells; 5) differences were observed in steady state level of PCE vector RNA in transfected and transduced cells; 6) the lower steady state was not attributable to reduced RNA stability, but to lower cytoplasmic accumulation in transduced cells.

CONCLUSION

PCE is a useful tool to improve post-transcriptional expression of lentiviral vector transgene. Coordinate enhancement of transcription and translation is conferred by the combination of PCE with CMV IE transcriptional enhancer and increased protein yield up to 11 to 17-fold in transfected cells. The incorporation of the vector provirus into chromatin correlated with reduced cytoplasmic accumulation of PCE transgene RNA. We speculate that epigenetic modulation of promoter activity altered cotranscriptional recruitment of RNA processing factors and reduced the availability of fully processed transcript or the efficiency of export from the nucleus. Our results provide an example of the dynamic interplay between the transcription and post-transcription steps of gene expression and document that introduction of heterologous gene expression signals can yield disparate effects in transfected versus transduced cells.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.

Regulatable gene expression systems for gene therapy applications: progress and future challenges

Gene therapy aims to revert diseased phenotypes by the use of both viral and nonviral gene delivery systems. Substantial progress has been made in making gene transfer vehicles more efficient, less toxic, and nonimmunogenic and in allowing long-term transgene expression. One of the key issues in successfully implementing gene therapies in the clinical setting is to be able to regulate gene expression very tightly and consistently as and when it is needed. The regulation ought to be achievable using a compound that should be nontoxic, be able to penetrate into the desired target tissue or organ, and have a half-life of a few hours (as opposed to minutes or days) so that when withdrawn or added (depending on the regulatable system used) gene expression can be turned "on" or "off" quickly and effectively. Also, the genetic switches employed should ideally be nonimmunogenic in the host. The ability to switch transgenes on and off would be of paramount importance not only when the therapy is no longer needed, but also in the case of the development of adverse side effects to the therapy. Many regulatable systems are currently under development and some, i.e., the tetracycline-dependent transcriptional switch, have been used successfully for in vivo preclinical applications. Despite this, there are no examples of switches that have been employed in a human clinical trial. In this review, we aim to highlight the main regulatable systems currently under development, the gene transfer systems employed for their expression, and also the preclinical models in which they have been used successfully. We also discuss the substantial challenges that still remain before these regulatable switches can be employed in the clinical setting.

Versatility of gene therapy vectors through viruses

Several viruses have been engineered for gene therapy applications, and the specific properties of each viral vector have been exploited to target a variety of inherited and acquired diseases. Preclinical and clinical studies demonstrated that viral vectors are highly versatile tools capable of efficient transfer of foreign genetic information into almost all cell types and tissues. Gene therapy applications depend on vector characteristics, such as host range, cell- or tissue-specific targeting, genome integration, efficiency and duration of transgene expression, packaging capacity, and suitability for scale-up production. This review discusses the advances in the development of viral vectors, with particular emphasis on how knowledge of virus biology has been exploited to design a variety of vectors with improved safety characteristics and efficiency, potentially suitable for a large number of gene therapy applications.

Gene therapy for spinal fusion

Spinal fusion will continue to be an important part of the surgical treatment of spinal pathology for the foreseeable future. Traditional challenges to successful spinal fusion surgery include autograft donor site morbidity and pseudoarthrosis. Recent advances in the understanding of the biology of bone formation have allowed the development of therapeutic biologics. Although recombinant bone morphogenetic proteins delivered to the arthrodesis site will stimulate fusion, these proteins have been less successful in more challenging fusion situations (posterolateral), require supraphysiologic doses to promote fusion in humans, and are quite expensive. Gene therapy may represent the easiest method for the application of bone-forming biologic agents to promote spinal fusion. Both in vivo and ex vivo techniques of delivery of therapeutic genes have been used effectively to promote fusion in lower animals. Considerable research is required to identify gene therapy techniques and vectors with acceptable safety profiles and high fusion rates.

Increased utility in the CNS of a powerful neuron-specific tetracycline-regulatable adenoviral system developed using a post-transcriptional enhancer

BACKGROUND

In previous studies we have found that the tetracycline (Tet)-regulatable system functions best in recombinant adenoviral (Ad) vectors when the Tet transactivators and the Tet-regulatable element (TRE) are incorporated into separate viral vectors. However, such a dual vector system is disadvantaged by the need to use relatively high titres that may elicit an immune response. Therefore, to develop a system that could be used at low titres while mediating strong, tightly regulatable gene expression in the central nervous system (CNS), we incorporated the woodchuck hepatitis virus post-transcriptional enhancer (WPRE) into a neuron-specific Tet-regulatable Ad system.

METHODS

The WPRE was incorporated into Ad vectors encoding the Tet-Off (tTA) transactivator driven by the synapsin-1 and CMV promoters and encoding the TRE driving EGFP expression (TRE)-EGFP.

RESULTS

The addition of the WPRE to the neuron-specific Tet-regulatable system mediated a greater than three-fold increase in transgene expression in primary hippocampal neurons with no loss of gene regulation. The results also showed that the addition of the WPRE enhanced transgene expression in the CNS without the loss of neuron specificity and without affecting the ability to regulate transgene expression.

CONCLUSIONS

We have further developed a tetracycline-regulatable neuron-specific expression system such that it can now be used at low titres with no loss of transgene expression or ability to regulate transgene expression. It should therefore be of significant value to studies investigating neuronal gene function and to those seeking to develop effective neuronal gene therapy strategies.

cAMP responsive element-binding protein phosphorylation is necessary for perirhinal long-term potentiation and recognition memory

We established the importance of phosphorylation of cAMP responsive element-binding protein (CREB) to both the familiarity discrimination component of long-term recognition memory and plasticity within the perirhinal cortex of the temporal lobe. Adenoviral transduction of perirhinal cortex (and adjacent visual association cortex) with a dominant-negative inhibitor of CREB impaired the preferential exploration of novel over familiar objects at a long (24 h) but not a short (15 min) delay, disrupted the normal reduced activation of perirhinal neurons to familiar compared with novel pictures, and impaired long-term potentiation of synaptic transmission in perirhinal slices. The consistency of these effects across the behavioral, systems, and cellular levels of analysis provides strong evidence for involvement of CREB phosphorylation in synaptic plastic processes within perirhinal cortex necessary for long-term recognition memory.

Inflammatory and anti-glioma effects of an adenovirus expressing human soluble Fms-like tyrosine kinase 3 ligand (hsFlt3L): treatment with hsFlt3L inhibits intracranial glioma progression

Glioblastoma multiforme is an intracranial tumor that has very poor prognosis. Patients usually succumb to their disease 6 to 12 months after they are diagnosed despite very aggressive treatment modalities. We tested the efficacy of a potent differentiation and proliferation factor for the professional antigen-presenting dendritic cells (DCs), i.e., Flt3L, for its potential role as a novel therapy for gliomas. We investigated the ability of recombinant adenoviral vectors encoding human soluble Flt3L (hsFlt3L) to improve the survival of Lewis rats bearing intracranial syngeneic CNS-1 gliomas. We show that RAdhsFlt3L can improve survival in a dose-dependent manner. Seventy percent of rats survive when treated with 8 x 10(7) pfu RAdhsFlt3L (P < 0.0005). In addition we demonstrate in both naive Lewis rats and C57BL/6 mice the presence of increased numbers of cells bearing DC markers (OX62 and MHCII, in rats, or CD11C, 33D1, MHCII, and F4/80, but not DEC205, in mice) in sites of brain delivery of RAdhsFlt3L. These results show that expression of hsFlt3L in the brain leads to the presence of cells displaying DC markers. We demonstrate that treatment with hsFlt3L leads to inhibition of tumor growth and significantly increased life span of animals implanted with syngeneic CNS-1 glioma cells. Animals that had survived for long periods, i.e., 6 months, had eliminated the implanted tumors after neuropathological analysis; on the other hand, some of the 3-month survivors still appeared to harbor brain tumors. Our results have profound implications for immune-mediated brain tumor therapy and also suggest the ability to recruit DC-like cells within the brain parenchyma in response to the local expression of Flt3L from adenoviral vectors.

The future of flexor tendon surgery

Clinical outcomes following flexor tendon repair have made significant improvements in the last 50 years. In that time standard treatment has evolved from secondary grafting to primary repair with postoperative rehabilitation protocols. Unfortunately, excellent results are not yet attained universally following treatment. Improving understanding of tendon healing at the cellular, molecular, and genetic levels will likely enable surgeons to modulate the normal repair process. We now look toward biologic augmentation of flexor tendon repairs to address the problems of increasing tensile strength while reducing adhesion formation following injury and operative repair.

Approaches to improving the kinetics of adenovirus-delivered genes and gene products

Adenovirus (Ad) vectors have been expected to play a great role in gene therapy because of their extremely high transduction efficiency and wide tropism. However, due to the intrinsic deficiency of their immunogenic toxicities, Ad vectors are rapidly cleared from the host, transgene expression is transient, and readministration of the same serotype Ad vectors is problematic. As a result, Ad vectors are continually undergoing refinement to realize their potential for gene therapy application. Even after 1999, when a patient fatally succumbed to the toxicity associated with Ad vector administration at a University of Pennsylvania (U.S.) experimental clinic, enthusiasm of gene therapists for Ad vectors has not waned. With great efforts from various research groups, significant advances have been achieved through comprehensive approaches to improving the kinetics of Ad vector-delivered genes and gene products.

Neuronal expression of the transcription factor Gli1 using the Talpha1 alpha-tubulin promoter is neuroprotective in an experimental model of Parkinson's disease

Nigrostriatal neurons degenerate during Parkinson's disease. Experimentally, neurotoxins such as 6-hydroxydopamine (6-OHDA) in rodents, and MPTP in mice and non-human primates, are used to model the disease-induced degeneration of midbrain dopaminergic neurons. Glial-cell-derived neurotrophic factor (GDNF) is a very powerful neuroprotector of dopaminergic neurons in all species examined. However, recent reports have indicated the possibility that GDNF may, in the long term and if expressed in an unregulated manner, exert untoward effects on midbrain dopaminergic neuronal structure and function. Although GDNF remains a powerful neurotrophin, the search for alternative therapies based on alternative and complementary mechanisms of action to GDNF is warranted. Recently, recombinant adenovirus-derived vectors encoding the differentiation factor Sonic Hedgehog (Shh) and its downstream transcriptional activator (Gli1) were shown to protect dopaminergic neurons in the substantia nigra pars compacta from 6-OHDA-induced neurotoxicity in rats in vivo. A pancellular human CMV (hCMV) promoter was used to drive the expression of both Shh and Gli1. Since Gli1 is a transcription factor and therefore exerts its actions intracellularly, we decided to test whether expression of Gli1 within neurons would be effective for neuroprotection. We demonstrate that neuronal-specific expression of Gli1 using the neuron-specific Talpha1 alpha-tubulin (Talpha1) promoter was neuroprotective, and its efficiency was comparable to the pancellular strong viral hCMV promoter. These results suggest that expression of the transcription factor Gli1 solely within neurons is neuroprotective for dopaminergic neurons in vivo and, furthermore, that neuronal-specific promoters are effective within the context of adenovirus-mediated gene therapy-induced neuroprotection of dopaminergic midbrain neurons. Since cell-type specific promoters are known to be weaker than the viral hCMV promoter, our data demonstrate that neuronal-specific expression of transcription factors is an effective, specific, and sufficient targeted approach for neurological gene therapy applications, potentially minimizing side effects due to unrestricted promiscuous gene expression within target tissues.