A Single Injection of Recombinant Adeno-Associated Virus into the Lumbar Cistern Delivers Transgene Expression Throughout the Whole Spinal Cord

A minimally invasive endovascular approach to the cerebellopontine angle cistern enables broad CNS biodistribution of scAAV9-CB-GFP

Neurological disorders pose a challenge for targeted therapy due to restricted access of therapeutic agents to the central nervous system (CNS). Current methods are limited by procedure-related risks, invasiveness, and insufficient CNS biodistribution. A novel percutaneous transvenous technology, currently in clinical trials for communicating hydrocephalus, offers a minimally invasive approach by providing endovascular access to the cerebrospinal fluid-filled cerebellopontine angle (CPA) cistern. We hypothesized that drug delivery to the CPA cistern could yield widespread CNS distribution. Using an ovine model, we compared the biodistribution of scAAV9-CB-GFP following CPA cistern infusion with previously reported cisterna magna (CM) administration. Targeting both the CPA cistern and CM in sheep, we employed a lumbar spine-inserted microcatheter under fluoroscopy. CPA delivery of AAV9 demonstrated biodistribution and transduction in the cerebral cortices, striatum, thalamus, midbrain, cerebellum, and spinal cord, with minor liver distribution comparable to CM. The favorable safety profile in humans with hydrocephalus suggests that percutaneous endovascular injection into the CPA could offer a clinically safer and minimally invasive delivery system for CNS gene and cell-based therapies.

Adeno-associated virus vector delivery to the brain: Technology advancements and clinical applications

Adeno-associated virus (AAV) vectors have emerged as a promising tool in the development of gene therapies for various neurological diseases, including Alzheimer's disease and Parkinson's disease. However, the blood-brain barrier (BBB) poses a significant challenge to successfully delivering AAV vectors to the brain. Strategies that can overcome the BBB to improve the AAV delivery efficiency to the brain are essential to successful brain-targeted gene therapy. This review provides an overview of existing strategies employed for AAV delivery to the brain, including direct intraparenchymal injection, intra-cerebral spinal fluid injection, intranasal delivery, and intravenous injection of BBB-permeable AAVs. Focused ultrasound has emerged as a promising technology for the noninvasive and spatially targeted delivery of AAV administered by intravenous injection. This review also summarizes each strategy's current preclinical and clinical applications in treating neurological diseases. Moreover, this review includes a detailed discussion of the recent advances in the emerging focused ultrasound-mediated AAV delivery. Understanding the state-of-the-art of these gene delivery approaches is critical for future technology development to fulfill the great promise of AAV in neurological disease treatment.

Adeno-Associated Viral Vectors as Versatile Tools for Neurological Disorders: Focus on Delivery Routes and Therapeutic Perspectives

It is without doubt that the gene therapy field is currently in the spotlight for the development of new therapeutics targeting unmet medical needs. Thus, considering the gene therapy scenario, neurological diseases in general and neurodegenerative disorders in particular are emerging as the most appealing choices for new therapeutic arrivals intended to slow down, stop, or even revert the natural progressive course that characterizes most of these devastating neurodegenerative processes. Since an extensive coverage of all available literature is not feasible in practical terms, here emphasis was made in providing some advice to beginners in the field with a narrow focus on elucidating the best delivery route available for fulfilling any given AAV-based therapeutic approach. Furthermore, it is worth nothing that the number of ongoing clinical trials is increasing at a breath-taking speed. Accordingly, a landscape view of preclinical and clinical initiatives is also provided here in an attempt to best illustrate what is ongoing in this quickly expanding field.

Gene Therapy for Rare Neurological Disorders

There are over 7 000 diseases that are individually rare, but collectively affect missions of people worldwide. They are very commonly neurologic single-gene disorders. Recent advances in recombinant adeno-associated virus (rAAV) vectors have enabled breakthroughs, including FDA-approved gene therapies for Inherited Retinal Dystrophy due to RPE65 mutation and spinal muscular atrophy. A range of other gene therapies for rare neurologic diseases are at various stages of development. Future development of gene editing technologies promises further to broaden the potential for more patients with these disorders to benefit from innovative therapies.

Intrathecal Delivery of Therapeutic Oligonucleotides for Potent Modulation of Gene Expression in the Central Nervous System

Therapeutic oligonucleotides hold tremendous potential for treating central nervous system (CNS) disorders. The route of administration of oligonucleotides significantly impacts both distribution and silencing efficiency. Here, we describe a technically simple, clinically relevant method to administer oligonucleotide compounds into the CNS via direct intrathecal injections. This method achieves distribution throughout the CNS rapidly and permits high-throughput testing of oligonucleotide efficacy and potency in mammals.

BDNF-overexpressing human umbilical cord mesenchymal stem cell-derived motor neurons improve motor function and prolong survival in amyotrophic lateral sclerosis mice

OBJECTIVE

To investigate the beneficial effect of brain-derived neurotrophic factor (BDNF) -overexpressing human umbilical cord mesenchymal stem cell (hUC-MSC)-derived motor neurons in the human Cu, Zn-superoxide dismutase1 (hSOD1)^G93A amyotrophic lateral sclerosis (ALS) mice.

METHODS

The BDNF gene was transfected into hUC-MSC-derived motor neurons by the lentivirus-mediated method. hSOD1^G93A mice were assigned to the ALS, ALS/MN, and ALS/MN-BDNF groups, and intrathecally administrated phosphate-buffered saline (PBS), motor neurons, or motor neurons overexpressing BDNF, respectively. The control group included non-transgenic wild-type littermates administrated PBS. One month after transplantation, the motor function of the mice was assessed by the rotarod test, and the lumbar enlargements were then isolated to detect the expression of hSOD1 and BDNF by western blotting, and the expression of choline acetyltransferase (ChAT), homeobox protein 9 (HB9), major histocompatibility complex I (MHCI) and microtubule-associated protein-2 (MAP-2) by immunofluorescence assay.

RESULTS

After transplantation, mice in the ALS/MN-BDNF and ALS/MN groups both exhibited longer latency to fall and longer survival than those in the ALS group (P < 0.01 vs. P < 0.05), and the improvement was more significant in the former than in the latter. However, cell transplantation did not delay disease onset. In the lumbar enlargements of the ALS/MN-BDNF and ALS/MN groups, the expression of hSOD1 was slightly reduced without statistical significance (P > 0.05), but the expression of BDNF, ChAT and HB9, and the co-expression of MHCI and MAP-2 were significantly greater than in the ALS group (P < 0.01), with the differences also being more prominent in the former group than in the latter.

CONCLUSIONS

Transplantation of BDNF-overexpressing hUC-MSC-derived motor neurons can improve motor performance and prolong the survival of hSOD1^G93A mice. Combining stem cell-derived motor neurons with BDNF might provide a new therapeutic strategy for ALS.

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.

Preoperative anxiety-induced glucocorticoid signaling reduces GABAergic markers in spinal cord and promotes postoperative hyperalgesia by affecting neuronal PAS domain protein 4

Preoperative anxiety is common in patients undergoing elective surgery and is closely related to postoperative hyperalgesia. In this study, a single prolonged stress model was used to induce preoperative anxiety-like behavior in rats 24 h before the surgery. We found that single prolonged stress exacerbated the postoperative pain and elevated the level of serum corticosterone. Previous studies have shown that glucocorticoid is associated with synaptic plasticity, and decreased spinal GABAergic activity can cause hyperalgesia in rodents. Here, single prolonged stress rats’ lumbar spinal cord showed reduced glutamic acid decarboxylase-65, glutamic acid decarboxylase-67, GABA type A receptor alpha 1 subunit, and GABA type A receptor gamma 2 subunit, indicating an impairment of GABAergic system. Furthermore, neuronal PAS domain protein 4 was also reduced in rats after single prolonged stress stimulation, which has been reported to promote GABAergic synapse development. Then, intraperitoneal injection of RU486 (a glucocorticoid receptor antagonist) rather than spironolactone (a mineralocorticoid receptor antagonist) was found to relieve single prolonged stress-induced hyperalgesia and reverse neuronal PAS domain protein 4 reduction and the impairment of GABAergic system. Furthermore, overexpressing neuronal PAS domain protein 4 could also restore the damage of GABAergic system caused by single prolonged stress while interfering with neuronal PAS domain protein 4 caused an opposite effect. Finally, after stimulation of rat primary spinal cord neurons with exogenous corticosterone in vitro, neuronal PAS domain protein 4 and GABAergic markers were also downregulated, and RU486 reversed that. Together, our results demonstrated that preoperative anxiety led to GABAergic system impairment in spinal cord and thus caused hyperalgesia due to glucocorticoid-induced downregulation of neuronal PAS domain protein 4.

Lot-to-Lot Variation in Adeno-Associated Virus Serotype 9 (AAV9) Preparations

Viral vectors are complex drugs that pose a particular challenge for manufacturing. Previous studies have shown that, unlike small-molecule drugs, vector preparations do not yield a collection of identical particles. Instead, a mixture of particles that vary in capsid stoichiometry and impurities is created, which may differ from lot to lot. The consequences of this are unclear, but conflicting reports regarding the biological properties of vectors, including transduction patterns, suggest that this variability may have an effect. However, other variables, including differences in animal strains and techniques, make it difficult to identify a cause. Here, we report lot-to-lot variation in spinal cord gray matter transduction following intrathecal delivery of self-complementary adeno-associated virus serotype 9 vectors. Eleven lots of vector were evaluated from six vector cores, including one preclinical/Good Laboratory Practice lot. Eight of the lots, including the preclinical lot, failed to transduce the gray matter, whereas the other three provided robust transduction. The cause for this variation is unknown, but it did not correlate with vector titer, buffer, or purification method. These results highlight the need to identify the cause of this variation and to develop improved production and quality control methods to ensure lot-to-lot consistency of vector potency.

A Safe and Reliable Technique for CNS Delivery of AAV Vectors in the Cisterna Magna

Global gene delivery to the CNS has therapeutic importance for the treatment of neurological disorders that affect the entire CNS. Due to direct contact with the CNS, cerebrospinal fluid (CSF) is an attractive route for CNS gene delivery. A safe and effective route to achieve global gene distribution in the CNS is needed, and administration of genes through the cisterna magna (CM) via a suboccipital puncture results in broad distribution in the brain and spinal cord. However, translation of this technique to clinical practice is challenging due to the risk of serious and potentially fatal complications in patients. Herein, we report development of a gene therapy delivery method to the CM through adaptation of an intravascular microcatheter, which can be safely navigated intrathecally under fluoroscopic guidance. We examined the safety, reproducibility, and distribution/transduction of this method in sheep using a self-complementary adeno-associated virus 9 (scAAV9)-GFP vector. This technique was used to treat two Tay-Sachs disease patients (30 months old and 7 months old) with AAV gene therapy. No adverse effects were observed during infusion or post-treatment. This delivery technique is a safe and minimally invasive alternative to direct infusion into the CM, achieving broad distribution of AAV gene transfer to the CNS.

Fetal Gene Therapy Using a Single Injection of Recombinant AAV9 Rescued SMA Phenotype in Mice

Symptoms of spinal muscular atrophy (SMA) disease typically begin in the late prenatal or the early postnatal period of life. The intrauterine (IU) correction of gene expression, fetal gene therapy, could offer effective gene therapy approach for early onset diseases. Hence, the overall goal of this study was to investigate the efficacy of human survival motor neuron (hSMN) gene expression after IU delivery in SMA mouse embryos. First, we found that IU-intracerebroventricular (i.c.v.) injection of adeno-associated virus serotype-9 (AAV9)-EGFP led to extensive expression of EGFP protein in different parts of the CNS with a great number of transduced neural stem cells. Then, to implement the fetal gene therapy, mouse fetuses received a single i.c.v. injection of a single-stranded (ss) or self-complementary (sc) AAV9-SMN vector that led to a lifespan of 93 (median of 63) or 171 (median 105) days for SMA mice. The muscle pathology and number of the motor neurons also improved in both study groups, with slightly better results coming from scAAV treatment. Consequently, fetal gene therapy may provide an alternative therapeutic approach for treating inherited diseases such as SMA that lead to prenatal death or lifelong irreversible damage.

The adeno-associated virus rh10 vector is an effective gene transfer system for chronic spinal cord injury

Treatment options for chronic spinal cord injury (SCI) remain limited due to unfavourable changes in the microenvironment. Gene therapy can overcome these barriers through continuous delivery of therapeutic gene products to the target tissue. In particular, adeno-associated virus (AAV) vectors are potential candidates for use in chronic SCI, considering their safety and stable gene expression in vivo. Given that different AAV serotypes display different cellular tropisms, it is extremely important to select an optimal serotype for establishing a gene transfer system during the chronic phase of SCI. Therefore, we generated multiple AAV serotypes expressing ffLuc-cp156, a fusion protein of firefly luciferase and Venus, a variant of yellow fluorescent protein with fast and efficient maturation, as a reporter, and we performed intraparenchymal injection in a chronic SCI mouse model. Among the various serotypes tested, AAVrh10 displayed the highest photon count on bioluminescence imaging. Immunohistological analysis revealed that AAVrh10 showed favourable tropism for neurons, astrocytes, and oligodendrocytes. Additionally, with AAVrh10, the area expressing Venus was larger in the injury epicentre and extended to the surrounding tissue. Furthermore, the fluorescence intensity was significantly higher with AAVrh10 than with the other vectors. These results indicate that AAVrh10 may be an appropriate serotype for gene delivery to the chronically injured spinal cord. This promising tool may be applied for research and development related to the treatment of chronic SCI.

Intrathecal Adeno-Associated Viral Vector-Mediated Gene Delivery for Adrenomyeloneuropathy

Mutations in the gene encoding the peroxisomal ATP-binding cassette transporter (ABCD1) cause elevations in very long-chain fatty acids (VLCFAs) and the neurodegenerative disease adrenoleukodystrophy (ALD). In most adults, this manifests as the spinal cord axonopathy adrenomyeloneuropathy (AMN). A challenge in virus-based gene therapy in AMN is how to achieve functional gene correction to the entire spinal cord while minimizing leakage into the systemic circulation, which could contribute to toxicity. In the present study, we used an osmotic pump to deliver adeno-associated viral (AAV) vector into the lumbar cerebrospinal fluid space in mice. We report that slow intrathecal delivery of recombinant AAV serotype 9 (rAAV9) achieves efficient gene transfer across the spinal cord and dorsal root ganglia as demonstrated with two different transgenes, GFP and ABCD1. In the Abcd1^-/- mouse, gene correction after continuous rAAV9-CBA-hABCD1 delivery led to a 20% decrease in VLCFA levels in spinal cord compared with controls. The major cell types transduced were astrocytes, vascular endothelial cells, and neurons. Importantly, rAAV9 delivered intrathecally by osmotic pump, in contrast to bolus injection, reduced systemic leakage into peripheral organs, particularly liver and heart tissue.

Slow Infusion of Recombinant Adeno-Associated Viruses into the Mouse Cerebrospinal Fluid Space

Recombinant adeno-associated viruses (rAAVs) are the leading in vivo gene delivery platform, and have been extensively studied in gene therapy targeting various tissues, including the central nervous system (CNS). A single-bolus rAAV injection to the cerebrospinal fluid (CSF) space has been widely used to target the CNS, but it suffers from several drawbacks, such as leakage to peripheral tissues. Here, a protocol is described using an osmotic pump to infuse rAAV slowly into the mouse CSF space. Compared to the single-bolus injection technique, pump infusion can lead to higher CNS transduction and lower transduction in the peripheral tissues.

Intrathecal Injection of scAAV9-hIGF1 Prolongs the Survival of ALS Model Mice by Inhibiting the NF-kB Pathway

Amyotrophic lateral sclerosis (ALS) is a chronic, fatal neurodegenerative disorder characterized by the progressive loss of upper and lower motor neurons. Currently, there is no effective drug for ALS. Recent studies in ALS model mice have shown that insulin-like growth factor-1 (IGF1) may be a promising therapeutic drug. We demonstrate that self-complementary adeno-associated virus serum type 9 encoding the human IGF1 (scAAV9-hIGF1) could significantly postpone the onset and slow down the progression of the disease owning to inhibiting the NF-κB signaling pathway. Furthermore, the results were supported by experiments in which the CRISPR/Cas9 system was used to knock-down IGF1 in ALS mice (mIGF1). Our data indicate that IGF1-mediated suppression of NF-κB activation in microglia is a novel molecular mechanism underlying MN death in ALS. It provides new insight into IGF1 and points toward novel therapeutic targets of IGF1 in ALS.

Intramuscular Delivery of scAAV9-hIGF1 Prolongs Survival in the hSOD1G93A ALS Mouse Model via Upregulation of D-Amino Acid Oxidase

Self-complementary adeno-associated viral vector 9 (scAAV9) has been confirmed to be an efficient AAV serotype for gene transfer to the central nervous system (CNS). Neurotrophic factors have been considered to be therapeutic targets for amyotrophic lateral sclerosis (ALS). In the present study, we intramuscularly injected scAAV9 encoding human insulin-like growth factor 1 (hIGF1) into an hSOD1G93A ALS mouse model. We observed that scAAV9-hIGF1 significantly reduced the loss of motor neurons of the anterior horn in the lumbar spinal cord and delayed muscle atrophy in ALS mice. Importantly, IGF1 significantly delayed disease onset and prolonged the life span of ALS mice. In addition, scAAV9-hIGF1 protected motor neurons from apoptosis through upregulation of D-amino acid oxidase (DAO), which controls the level of D-serine. Moreover, to further verify these results, we used CRISPR-Cas9 system to target the central nervous system knockdown of IGF1. This experiment supported the continued investigation of neurotrophic factor gene therapies targeting the central nervous system as a potential treatment for ALS.

AAV gene delivery to the spinal cord: serotypes, methods, candidate diseases, and clinical trials

INTRODUCTION

Adeno-associated viral (AAV) vector-mediated gene delivery to the spinal cord has finally entered the pathway towards regulatory approval. Phase 1 clinical trials using AAV gene therapy for pediatric disorders - spinal muscular atrophy (SMA) and giant axonal neuropathy (GAN) - are now underway.

AREAS COVERED

This review addresses the latest progress in the field of AAV gene delivery to the spinal cord, particularly focusing on the most prominent AAV serotypes and delivery methodologies to the spinal cord. Candidate diseases and scaling up experiments in large animals are also discussed.

EXPERT OPINION

Intravenous (IV) and intrathecal (IT) deliveries seem to undoubtedly be the preferred routes of administration for diffuse spinal cord delivery of therapeutic AAV vectors that can cross the blood-brain barrier (BBB) and correct inherited genetic disorders. Conversely, intraparenchymal delivery is still an undervalued but very viable approach for segmental therapy in afflictions such as ALS or Pompe Disease as a means to prevent respiratory dysfunction.

Slow Intrathecal Injection of rAAVrh10 Enhances its Transduction of Spinal Cord and Therapeutic Efficacy in a Mutant SOD1 Model of ALS

Mutant SOD1 causes amyotrophic lateral sclerosis (ALS) by a dominant gain of toxicity. Previous studies have demonstrated therapeutic potential of mutant SOD1-RNAi delivered by intrathecal (IT) injection of recombinant adeno-associated virus (rAAV). However, optimization of delivery is needed to overcome the high degree of variation in the transduction efficiency and therapeutic efficacy. Here, on the basis of our previously defined, efficient IT injection method, we investigated the influence of injection speed on transduction efficiency in the central nervous system (CNS). We demonstrate that slow IT injection results in higher transduction of spinal cord and dorsal root ganglia (DRG) while fast IT injection leads to higher transduction of brain and peripheral organs. To test how these effects influence the outcome of RNAi therapy, we used slow and fast IT injection to deliver rAAVrh10-GFP-amiR-SOD1, a rAAV vector that expresses GFP and an artificial miRNA targeting SOD1, in SOD1-G93A mice. Both slow and fast IT injection produced therapeutic efficacy but the slow injection trended slightly toward a better outcome than the fast injection. These results demonstrate that IT injection speed influences the predominance of gene delivery at different CNS sites and should be taken into consideration in future therapeutic trials involving IT injection.

Adeno-Associated Virus Gene Therapy in a Sheep Model of Tay-Sachs Disease

Tay-Sachs disease (TSD) is a fatal neurodegenerative disorder caused by a deficiency of the enzyme hexosaminidase A (HexA). TSD also occurs in sheep, the only experimental model of TSD that has clinical signs of disease. The natural history of sheep TSD was characterized using serial neurological evaluations, 7 Tesla magnetic resonance imaging, echocardiograms, electrodiagnostics, and cerebrospinal fluid biomarkers. Intracranial gene therapy was also tested using AAVrh8 monocistronic vectors encoding the α-subunit of Hex (TSD α) or a mixture of two vectors encoding both the α and β subunits separately (TSD α + β) injected at high (1.3 × 10¹³ vector genomes) or low (4.2 × 10¹² vector genomes) dose. Delay of symptom onset and/or reduction of acquired symptoms were noted in all adeno-associated virus-treated sheep. Postmortem evaluation showed superior HexA and vector genome distribution in the brain of TSD α + β sheep compared to TSD α sheep, but spinal cord distribution was low in all groups. Isozyme analysis showed superior HexA formation after treatment with both vectors (TSD α + β), and ganglioside clearance was most widespread in the TSD α + β high-dose sheep. Microglial activation and proliferation in TSD sheep-most prominent in the cerebrum-were attenuated after gene therapy. This report demonstrates therapeutic efficacy for TSD in the sheep brain, which is on the same order of magnitude as a child's brain.

Improved gene delivery to adult mouse spinal cord through the use of engineered hybrid adeno-associated viral serotypes

Adeno-associated viral (AAV) vectors are often used in gene therapy for neurological disorders because of its safety profile and promising results in clinical trials. One challenge to AAV gene therapy is effective transduction of large numbers of the appropriate cell type, which can be overcome by modulating the viral capsid through DNA shuffling. Our previous study demonstrates that Rec2, among a family of novel engineered hybrid capsid serotypes (Rec1~4) transduces adipose tissue with far superior efficiency than naturally occurring AAV serotypes. Here we assessed the transduction of adult spinal cord at two different doses of AAV vectors expressing green fluorescent protein (2 × 10⁹ or 4 × 10⁸ viral particles) via intraparenchymal injection at the thoracic vertebral level T9. In comparison to an equal dose of the currently preferable AAV9 serotype, Rec3 serotype transduced a broader region of spinal cord up to approximately 1.5 cm longitudinally, and displayed higher transgene expression and increased maximal transduction rates of astrocytes at either dose and neurons at the lower dose. These novel engineered hybrid vectors could provide powerful tools at lower production costs to manipulate gene expression in spinal cord for mechanistic studies, or provide potent vehicles for gene therapy delivery, such as neurotrophins, to spinal cord.

Efficient CNS targeting in adult mice by intrathecal infusion of single-stranded AAV9-GFP for gene therapy of neurological disorders

Adeno-associated virus (AAV) gene therapy constitutes a powerful tool for the treatment of neurodegenerative diseases. While AAVs are generally administered systemically to newborns in preclinical studies of neurological disorders, in adults the maturity of the blood-brain barrier (BBB) must be considered when selecting the route of administration. Delivery of AAVs into the cerebrospinal fluid (CSF) represents an attractive approach to target the central nervous system (CNS) and bypass the BBB. In this study, we investigated the efficacy of intra-CSF delivery of a single-stranded (ss) AAV9-CAG-GFP vector in adult mice via intracisternal (iCist) or intralumbar (it-Lumb) administration. It-Lumb ssAAV9 delivery resulted in greater diffusion throughout the entire spinal cord and green fluorescent protein (GFP) expression mainly in the cerebellum, cortex and olfactory bulb. By contrast, iCist delivery led to strong GFP expression throughout the entire brain. Comparison of the transduction efficiency of ssAAV9-CAG-GFP versus ssAAV9-SYN1-GFP following it-Lumb administration revealed widespread and specific GFP expression in neurons and motoneurons of the spinal cord and brain when the neuron-specific synapsin 1 (SYN1) promoter was used. Our findings demonstrate that it-Lumb ssAAV9 delivery is a safe and highly efficient means of targeting the CNS in adult mice.

Redirecting N-acetylaspartate metabolism in the central nervous system normalizes myelination and rescues Canavan disease

Canavan disease (CD) is a debilitating and lethal leukodystrophy caused by mutations in the aspartoacylase (ASPA) gene and the resulting defect in N-acetylaspartate (NAA) metabolism in the CNS and peripheral tissues. Recombinant adeno-associated virus (rAAV) has the ability to cross the blood-brain barrier and widely transduce the CNS. We developed a rAAV-based and optimized gene replacement therapy, which achieves early, complete, and sustained rescue of the lethal disease phenotype in CD mice. Our treatment results in a super-mouse phenotype, increasing motor performance of treated CD mice beyond that of WT control mice. We demonstrate that this rescue is oligodendrocyte independent, and that gene correction in astrocytes is sufficient, suggesting that the establishment of an astrocyte-based alternative metabolic sink for NAA is a key mechanism for efficacious disease rescue and the super-mouse phenotype. Importantly, the use of clinically translatable high-field imaging tools enables the noninvasive monitoring and prediction of therapeutic outcomes for CD and might enable further investigation of NAA-related cognitive function.

Adeno-associated virus serotype rh.10 displays strong muscle tropism following intraperitoneal delivery

Recombinant adeno-associated virus (rAAV) is an attractive tool for basic science and translational medicine including gene therapy, due to the versatility in its cell and organ transduction. Previous work indicates that rAAV transduction patterns are highly dependent on route of administration. Based on this relationship, we hypothesized that intraperitoneal (IP) administration of rAAV produces unique patterns of tissue tropism. To test this hypothesis, we investigated the transduction efficiency of 12 rAAV serotypes carrying an enhanced green fluorescent protein (EGFP) reporter gene in a panel of 12 organs after IP injection. Our data suggest that IP administration emphasizes transduction patterns that are different from previously reported intravascular delivery methods. Using this approach, rAAV efficiently transduces the liver, pancreas, skeletal muscle, heart and diaphragm without causing significant histopathological changes. Of note, rAAVrh.10 showed excellent muscle transduction following IP administration, highlighting its potential as a new muscle-targeting vector.

Tailored transgene expression to specific cell types in the central nervous system after peripheral injection with AAV9

The capacity of certain adeno-associated virus (AAV) vectors to cross the blood–brain barrier after intravenous delivery offers a unique opportunity for noninvasive brain delivery. However, without a well-tailored system, the use of a peripheral route injection may lead to undesirable transgene expression in nontarget cells or organs. To refine this approach, the present study characterizes the transduction profiles of new self-complementary AAV9 (scAAV9) expressing the green fluorescent protein (GFP) either under an astrocyte (glial fibrillary acidic (GFA) protein) or neuronal (Synapsin (Syn)) promoter, after intravenous injection of adult mice (2 × 10¹³ vg/kg). ScAAV9-GFA-GFP and scAAV9-Syn-GFP robustly transduce astrocytes (11%) and neurons (17%), respectively, without aberrant expression leakage. Interestingly, while the percentages of GFP-positive astrocytes with scAAV9-GFA-GFP are similar to the performances observed with scAAV9-CBA-GFP (broadly active promoter), significant higher percentages of neurons express GFP with scAAV9-Syn-GFP. GFP-positive excitatory as well as inhibitory neurons are observed, as well as motor neurons in the spinal cord. Additionally, both activated (GFAP-positive) and resting astrocytes (GFAP-negative) express the reporter gene after scAAV9-GFA-GFP injection. These data thoroughly characterize the gene expression specificity of AAVs fitted with neuronal and astrocyte-selective promoters after intravenous delivery, which will prove useful for central nervous system (CNS) gene therapy approaches in which peripheral expression of transgene is a concern.

AAV9 supports wide-scale transduction of the CNS and TDP-43 disease modeling in adult rats

AAV9 has emerged as an efficient adeno-associated virus (AAV) serotype for gene transfer to the central nervous system. We have used this technique to study aspects of amyotrophic lateral sclerosis (ALS) by administering AAV encoding the ALS-related gene transactive response DNA binding protein of 43 kDa (TDP-43) to neonatal rats. However, inducing the expression in adult subjects would be preferable to mimic the adult onset of symptoms in ALS. We expressed either green fluorescent protein (GFP) or TDP-43 in adult rats after an intravenous (i.v.) route of administration to attempt wide-scale transduction of the spinal cord for disease modeling. In order to optimize the gene transfer, we made comparisons of efficiency by age, gender, and across several AAV serotypes (AAV1, AAV8, AAV9, and AAV10). The data indicate more efficient neuronal transduction in neonates, with little evidence of glial transduction at either age, no gender-related differences in transduction, and that AAV9 was efficient in adults relative to the other serotypes tested. Based on these data, AAV9 TDP-43 was expressed at three vector doses in adult female rats yielding highly consistent, dose-dependent motor deficits. AAV9 can be delivered i.v. to adult rats to achieve consistent pathophysiological changes and a relevant adult-onset system for disease modeling.