Transduction profiles in minipig following MRI guided delivery of AAV-5 into thalamic and corona radiata areas

BACKGROUND

As a step towards clinical use of AAV-mediated gene therapy, brains of large animals are used to settle delivery parameters as most brain connections, and relative sizes in large animals and primates, are reasonably common. Prior to application in the clinic, approaches that have shown to be successful in rodent models are tested in larger animal species, such as dogs, non-human primates, and in this case, minipigs.

NEW METHOD

We evaluated alternate delivery routes to target the basal ganglia by injections into the more superficial corona radiata, and, deeper into the brain, the thalamus. Anatomically known connections can be used to predict the expression of the transgene following infusion of AAV5. For optimal control over delivery of the vector with regards to anatomical location in the brain and spread in the tissue, we have used magnetic resonance image-guided convection-enhanced diffusion delivery.

RESULTS

While the transduction of the cortex was observed, only partial transduction of the basal ganglia was achieved via the corona radiata. Thalamic administration, on the other hand, resulted in widespread transduction from the midbrain to the frontal cortex COMPARISON WITH EXISTING METHODS: Compared to other methods, such as delivery directly to the striatum, thalamic injection may provide an alternative when for instance, injection into the basal ganglia directly is not feasible.

CONCLUSIONS

The study results suggest that thalamic administration of AAV5 has significant potential for indications where the transduction of specific areas of the brain is required.

Transduction patterns in the CNS following various routes of AAV-5-mediated gene delivery

Various administration routes of adeno-associated virus (AAV)-based gene therapy have been examined to target the central nervous system to answer the question what the most optimal delivery route is for treatment of the brain with certain indications. In this study, we evaluated AAV5 vector system for its capability to target the central nervous system via intrastriatal, intrathalamic or intracerebroventricular delivery routes in rats. AAV5 is an ideal candidate for gene therapy because of its relatively low level of existing neutralizing antibodies compared to other serotypes, and its broad tissue and cell tropism. Intrastriatal administration of AAV5-GFP resulted in centralized localized vector distribution and expression in the frontal part of the brain. Intrathalamic injection showed transduction and gradient expression from the rostral brain into lumbar spinal cord, while intracerebroventricular administration led to a more evenly, albeit relatively superficially distributed, transduction and expression throughout the central nervous system. To visualize the differences between localized and intra-cerebral spinal fluid administration routes, we compared intrastriatal to intracerebroventricular and intrathecal administration of AAV5-GFP. Together, our results demonstrate that for efficient transgene expression, various administration routes can be applied.

MR-guided parenchymal delivery of adeno-associated viral vector serotype 5 in non-human primate brain

The present study was designed to characterize transduction of non-human primate brain and spinal cord with AAV5 viral vector after parenchymal delivery. AAV5-CAG-GFP (1 × 10¹³ vector genomes per milliliter (vg ml⁻¹)) was bilaterally infused either into putamen, thalamus or with the combination left putamen and right thalamus. Robust expression of GFP was seen throughout infusion sites and also in other distal nuclei. Interestingly, thalamic infusion of AAV5 resulted in the transduction of the entire corticospinal axis, indicating transport of AAV5 over long distances. Regardless of site of injection, AAV5 transduced both neurons and astrocytes equally. Our data demonstrate that AAV5 is a very powerful vector for the central nervous system and has potential for treatment of a wide range of neurological pathologies with cortical, subcortical and/or spinal cord affection.

Early passage bone marrow stromal cells express genes involved in nervous system development supporting their relevance for neural repair

PURPOSE

The assessment of the capacity of bone marrow stromal cells (BMSC) to repair the nervous system using gene expression profiling. The evaluation of effects of long-term culturing on the gene expression profile of BMSC.

METHODS

Fourty four k whole genome rat microarrays were used to study gene expression of cultured BMSC at passage (P)3 and to compare expression profiles between P3 and P14 BMSC. Quantitative PCR was employed to validate the microarray results.

RESULTS

P3 BMSC expressed genes involved in neural developmental events such as glial differentiation, neuron proliferation, and neurite formation. They also express genes encoding for growth factors and for proteins involved in growth factor signaling. A total of 6687 genes were co-expressed in P3 and P14 BMSC. Of these co-expressed genes, 3% (202 genes) was differentially expressed with 159 genes higher in P3 BMSC and 43 genes higher in P14 BMSC. The gene expression patterns were independently validated using quantitative PCR. Functional data mining by Gene Ontology (GO)-analysis revealed that 85/159 and 22/43 genes were annotated in the GO database. In P3 BMSC, 53 GO-classes were overrepresented with several involved in organ development, cell proliferation, and neural repair. In P14 BMSC, three GO-classes were overrepresented with one involved in organ development.

CONCLUSIONS

Our gene profiling results suggested a decreased plasticity and repair aptitude of long-term cultured BMSC. Our data indicated the use of early passage BMSC for neural repair approaches.

AAV-mediated in vivo knockdown of luciferase using combinatorial RNAi and U1i

RNA interference (RNAi) has been successfully employed for specific inhibition of gene expression; however, safety and delivery of RNAi remain critical issues. We investigated the combinatorial use of RNAi and U1 interference (U1i). U1i is a gene-silencing technique that acts on the pre-mRNA by preventing polyadenylation. RNAi and U1i have distinct mechanisms of action in different cellular compartments and their combined effect allows usage of minimal doses, thereby avoiding toxicity while retaining high target inhibition. As a proof of concept, we investigated knockdown of the firefly luciferase reporter gene by combinatorial use of RNAi and U1i, and evaluated their inhibitory potential both in vitro and in vivo. Co-transfection of RNAi and U1i constructs showed additive reduction of luciferase expression up to 95% in vitro. We attained similar knockdown when RNAi and U1i constructs were hydrodynamically transfected into murine liver, demonstrating for the first time successful in vivo application of U1i. Moreover, we demonstrated long-term gene silencing by AAV-mediated transduction of murine muscle with RNAi/U1i constructs targeting firefly luciferase. In conclusion, these results provide a proof of principle for the combinatorial use of RNAi and U1i to enhance target gene knockdown in vivo.

Anti-inflammatory effect by lentiviral-mediated overexpression of IL-10 or IL-1 receptor antagonist in rat glial cells and macrophages

Neuroinflammation, as defined by activation of local glial cells and production of various inflammatory mediators, is an important feature of many neurological disorders. Expression of pro-inflammatory mediators produced by glial cells in the central nervous system (CNS) is considered to contribute to the neuropathology observed in those diseases. To diminish the production or action of pro-inflammatory mediators, we have used lentiviral (LV) vector-mediated encoding rat interleukin-10 (rIL-10) or rat interleukin-1 receptor antagonist (rIL-1ra) to direct the local, long-term expression of these anti-inflammatory cytokines in the CNS. We have shown that cultured macrophages or astroglia transduced with LV-rIL-10 or LV-rIL-1ra produced far less tumor necrosis factor (TNF)alpha or IL-6, respectively in response to pro-inflammatory stimuli. Moreover, intracerebroventricular (i.c.v.) administration of LV-rIL-10 or LV-rIL-1ra resulted in transduction of glial cells and macrophages and, subsequently reduced TNFalpha, IL-6 and inducible nitric oxide synthase (iNOS) expression in various brain regions induced by inflammatory stimuli, whereas peripheral expression of these mediators remained unaffected. In addition, expression levels of the anti-inflammatory cytokines IL-4 and transforming growth factor-beta were not altered in either brain or pituitary gland. Furthermore, i.c.v. administration of LV-rIL-10 or LV-rIL-1ra given during the remission phase of chronic-relapsing experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis, improved the clinical outcome of the relapse phase. Thus, local application of LV vectors expressing anti-inflammatory cytokines could be of therapeutic interest to counteract pro-inflammatory processes in the brain without interfering with the peripheral production of inflammatory mediators.

Adeno-associated viral vector-mediated neurotrophin gene transfer in the injured adult rat spinal cord improves hind-limb function

To foster axonal growth from a Schwann cell bridge into the caudal spinal cord, spinal cells caudal to the implant were transduced with adeno-associated viral (AAV) vectors encoding for brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (AAV-NT-3). Control rats received AAV vectors encoding for green fluorescent protein or saline. AAV-BDNF- and AAV-NT-3-transduced 293 human kidney cells produced and secreted BDNF or NT-3, respectively, in vitro. The secreted neurotrophins were biologically active; they both promoted outgrowth of sensory neurites in vitro. In vivo, transgene expression was observed predominantly in neurons for at least 16 weeks after injection. Compared with controls, a modest though significant improvement in hind-limb function was found in rats that received AAV-BDNF and AAV-NT-3. Retrograde tracing demonstrated that twice as many neurons with processes extending toward the Schwann cell graft were present in the second lumbar cord segment of AAV-BDNF- and AAV-NT-3-injected animals compared with controls. We found no evidence, however, for growth of regenerated axons from the Schwann cell implant into the caudal cord. Our results suggest that AAV vector-mediated overexpression of BDNF and NT-3 in the cord caudal to a Schwann cell bridge modified the local lumbar axonal circuitry, which was beneficial for locomotor function.

Amelioration of chronic neuropathic pain after partial nerve injury by adeno-associated viral (AAV) vector-mediated over-expression of BDNF in the rat spinal cord

Changing the levels of neurotrophins in the spinal cord micro-environment after nervous system injury has been proposed to recover normal function, such that behavioral response to peripheral stimuli does not lead to chronic pain. We have investigated the effects of recombinant adeno-associated viral (rAAV)-mediated over-expression of brain-derived neurotrophic factor (BDNF) in the spinal cord on chronic neuropathic pain after unilateral chronic constriction injury (CCI) of the sciatic nerve. The rAAV-BDNF vector was injected into the dorsal horn at the thirteenth thoracic spinal cord vertebra (L(1) level) 1 week after CCI. Allodynia and hyperalgesia induced by CCI in the hindpaws were permanently reversed, beginning 1 week after vector injection, compared with a similar injection of a control rAAV-GFP vector (green fluorescent protein) or saline. In situ hybridization for BDNF demonstrated that both dorsal and ventral lumbar spinal neurons contained an intense signal for BDNF mRNA, at 1 to 8 weeks after vector injection. There was no similar BDNF mRNA over-expression associated with either injections of saline or rAAV-GFP. These data suggest that chronic neuropathic pain is sensitive to early spinal BDNF levels after partial nerve injury and that rAAV-mediated gene transfer could potentially be used to reverse chronic pain after nervous system injuries in humans.

Intravitreal injection of adeno-associated viral vectors results in the transduction of different types of retinal neurons in neonatal and adult rats: a comparison with lentiviral vectors

Replication-deficient viral vectors encoding the marker gene green fluorescent protein (GFP) were injected into the vitreous of newborn, juvenile (P14), and adult rats. We tested two different types of modified virus: adeno-associated viral-2-GFP (AAV-GFP) and lentiviral-GFP vectors (LV-GFP). The extent of retinal cell transduction in different-aged animals was compared 7, 21, and 70 days after eye injections. At all postinjection times, LV-GFP transduction was mostly limited to pigment epithelium and cells in sclera and choroid. In contrast, transduction of large numbers of neural retinal cells was seen 21 and 70 days after AAV-GFP injections. AAV-GFP predominantly transduced neurons, although GFP-positive Müller cells were seen. All neuronal classes were labeled, but the extent of transduction for a given class varied depending on injection age. After P0 injections about 50% of transduced cells were photoreceptors and 30-40% were amacrine or bipolar cells. After adult injections 60-70% of transduced cells were retinal ganglion cells. In adults many GFP-positive retinal axons were traced through the optic nerve/tract and terminal arbors were visualized in central targets.

Injury-induced class 3 semaphorin expression in the rat spinal cord

In this study we evaluate the expression of all members of the class 3 semaphorins and their receptor components following complete transection and contusion lesions of the adult rat spinal cord. Following both types of lesions the expression of all class 3 semaphorins is induced in fibroblast in the neural scar. The distribution of semaphorin-positive fibroblasts differs markedly in scars formed after transection or contusion lesion. In contusion lesions semaphorin expression is restricted to fibroblasts of the meningeal sheet surrounding the lesion, while after transection semaphorin-positive fibroblast penetrate deep into the center of the lesion. Two major descending spinal cord motor pathways, the cortico- and rubrospinal tract, continue to express receptor components for class 3 semaphorins following injury, rendering them potentially sensitive to scar-derived semaphorins. In line with this we observed that most descending spinal cord fibers were not able to penetrate the semaphorin positive portion of the neural scar formed at the lesion site. These results suggest that the full range of secreted semaphorins contributes to the inhibitory nature of the neural scar and thereby may inhibit successful regeneration in the injured spinal cord. Future studies will focus on the neutralization of class 3 semaphorins, in order to reveal whether this creates a more permissive environment for regeneration of injured spinal cord axons.

Viral vector-mediated gene expression in olfactory ensheathing glia implants in the lesioned rat spinal cord

Implantation of olfactory ensheathing glia (OEG) is a promising strategy to augment long-distance regeneration in the injured spinal cord. In this study, implantation of OEG following unilateral hemisection of the dorsal cervical spinal cord was combined with ex vivo gene transfer techniques. We report, to our knowledge for the first time, that purified cultures of primary OEG are capable of expressing a foreign gene following adenoviral (AdV) and lentiviral (LV) vector-mediated gene transfer. OEG implants subjected to AdV vector-mediated gene transfer expressed high levels of transgenic protein in both intact and lesioned spinal cord at 7 days after implantation. However, the levels of transgene expression gradually declined between 7 and 30 days after implantation in lesioned spinal cord. Infection with LV vectors resulted in stable transduction of primary OEG cultures and transgene expression persisted for at least 4 months after implantation. Genetic engineering of OEG opens the possibility of expressing additional neurotrophic genes and create optimal 'bridging' substrates to support spinal axon regeneration. Furthermore, stable transduction of OEG allows us to reliably study the behaviour of implanted cells and to obtain better understanding of their regeneration supporting properties.

Intercostal nerve implants transduced with an adenoviral vector encoding neurotrophin-3 promote regrowth of injured rat corticospinal tract fibers and improve hindlimb function

Following injury to central nervous tissues, damaged neurons are unable to regenerate their axons spontaneously. Implantation of peripheral nerves into the CNS, however, does result in axonal regeneration into these transplants and is one of the most powerful strategies to promote CNS regeneration. In the present study implantation of peripheral nerve bridges following dorsal hemisection is combined with ex vivo gene transfer with adenoviral vectors encoding neurotrophin-3 (Ad-NT-3) to examine whether this would stimulate regeneration of one of the long descending tracts of the spinal cord, the corticospinal tract (CST), into and beyond the peripheral nerve implant. We chose to use an adenoviral vector encoding NT-3 because CST axons are sensitive to this neurotrophin and Schwann cells in peripheral nerve implants do not express this neurotrophin. At 16 weeks postimplantation of Ad-NT-3-transduced intercostal nerves, approximately three- to fourfold more of the anterogradely traced corticospinal tract fibers had regrown their axons through gray matter below the lesion site when compared to control animals. Regrowth of CST fibers occurred over more than 8 mm distal to the lesion site. No regenerating CST fibers were, however, observed into the transduced peripheral implant. Animals with a peripheral nerve transduced with Ad-NT-3 also exhibited improved function of the hindlimbs when compared to control animals treated with an adenoviral vector encoding LacZ. Thus, transient overexpression of NT-3 in peripheral nerve tissue bridges is apparently sufficient to stimulate regrowth of CST fibers and to promote recovery of hindlimb function, but does not result in regeneration of CST fibers into such transplants. Taken together, combining an established neurotransplantation approach with viral vector-gene transfer promotes the regrowth of injured CST fibers through gray matter and improves the recovery of hindlimb function.

The use of adenoviral vectors and ex vivo transduced neurotransplants: towards promotion of neuroregeneration

Regeneration of injured axons following injury depends on a delicate balance between growth-promoting and growth-inhibiting factors. Overexpression of neurotrophin genes seems a promising strategy to promote regeneration. Trophic genes can be overexpressed at the site of injury at the axonal stumps, or at the perikaryal level of the injured neuron. Transduction of the neural cells can be achieved by applying adenoviral vectors, either directly in vivo or-in the case of neurotransplantation as an ex vivo approach. In both cases it would create a more permissive environment for axonal growth and therefore in functional regeneration. In this article, the feasibility of the use of adenoviral vectors in several neuroregeneration models--in particularly in spinal cord lesion models and the biological clock transplantation model--is illustrated. The results show that the adenoviral vectors can be a powerful tool to study the effects of overexpression of genes in an in vivo paradigm of nerve regeneration or nerve outgrowth. The potential use of adenoviral vectors and ex vivo transduced neurotransplants is discussed.

Adenoviral vector-mediated expression of a foreign gene in peripheral nerve tissue bridges implanted in the injured peripheral and central nervous system

Axons of the CNS do normally not regenerate after injury, in contrast to axons of the PNS. This is due to a different microenvironment at the site of the lesion as well as a particular intrinsic program of axonal regrowth. Although transplantation of peripheral nerve tissue bridges is perhaps the most successful approach to promoting regeneration in the CNS, ingrowth of CNS nerve fibers with such transplants is limited. Genetic modification of peripheral nerve bridges to overexpress outgrowth-promoting proteins should, in principle, improve the permissive properties of peripheral nerve transplants. The present study shows that pieces of peripheral intercostal nerve, subjected to ex vivo adenoviral vector-mediated gene transfer and implanted as nerve bridges in transected sciatic nerve, avulsed ventral root, hemi-sected spinal cord and intact brain, are capable of expressing a foreign gene. In vitro studies showed expression of the reporter gene LacZ up to 30 days in Schwann cells. After implantation, LacZ expression could be detected at 7 days postimplantation, but had virtually disappeared at 14 days. Schwann cells of the transduced nerve bridges retained the capacity of guiding regenerative peripheral and central nerve fiber ingrowth. Transduction of intercostal nerve pieces prior to implantation should, in principle, enable enhanced local production of neurotrophic factors within the transplant and has the potential to improve the regeneration of injured axons into the graft.