Comparison of high-dose intracisterna magna and lumbar puncture intrathecal delivery of AAV9 in mice to treat neuropathies

Rescue of myocytes and locomotion through AAV2/9-2YF intracisternal gene therapy in a rat model of creatine transporter deficiency

Creatine deficiency syndromes (CDS), caused by mutations in GATM (AGAT), GAMT, and SLC6A8, mainly affect the central nervous system (CNS). CDS show brain creatine (Cr) deficiency, intellectual disability with severe speech delay, behavioral troubles, epilepsy, and motor dysfunction. AGAT/GAMT-deficient patients lack brain Cr synthesis but express the Cr transporter SLC6A8 at the blood-brain barrier and are thus treatable by oral supplementation of Cr. In contrast, no satisfactory treatment has been identified for Cr transporter deficiency (CTD), the most frequent of CDS. We used our Slc6a8Y389C CTD rat model to develop a new AAV2/9-2YF-driven gene therapy re-establishing the functional Slc6a8 transporter in rat CNS. We show, after intra-cisterna magna AAV2/9-2YF-Slc6a8-FLAG vector injection of postnatal day 11 pups, the transduction of Slc6a8-FLAG in cerebellum, medulla oblongata, and spinal cord as well as a partial recovery of Cr in these brain regions, together with full prevention of locomotion defaults and impairment of myocyte development observed in Slc6a8Y389 C/y male rats. While more work is needed to correct those CTD phenotypes more associated with forebrain structures, this study is the first demonstrating positive effects of an AAV-driven gene therapy on CTD and thus represents a very encouraging approach to treat the so-far untreatable CTD.

In vivo selection in non-human primates identifies AAV capsids for on-target CSF delivery to spinal cord

Systemic administration of adeno-associated virus (AAV) vectors for spinal cord gene therapy has challenges including toxicity at high doses and pre-existing immunity that reduces efficacy. Intrathecal (IT) delivery of AAV vectors into cerebral spinal fluid can avoid many issues, although distribution of the vector throughout the spinal cord is limited, and vector entry to the periphery sometimes initiates hepatotoxicity. Here we performed biopanning in non-human primates (NHPs) with an IT injected AAV9 peptide display library. We identified top candidates by sequencing inserts of AAV DNA isolated from whole tissue, nuclei, or nuclei from transgene-expressing cells. These barcoded candidates were pooled with AAV9 and compared for biodistribution and transgene expression in spinal cord and liver of IT injected NHPs. Most candidates displayed increased retention in spinal cord compared with AAV9. Greater spread from the lumbar to the thoracic and cervical regions was observed for several capsids. Furthermore, several capsids displayed decreased biodistribution to the liver compared with AAV9, providing a high on-target/low off-target biodistribution. Finally, we tested top candidates in human spinal cord organoids and found them to outperform AAV9 in efficiency of transgene expression in neurons and astrocytes. These capsids have potential to serve as leading-edge delivery vehicles for spinal cord-directed gene therapies.

Small G-Protein Rheb Gates Mammalian Target of Rapamycin Signaling to Regulate Morphine Tolerance in Mice

BACKGROUND

Analgesic tolerance due to long-term use of morphine remains a challenge for pain management. Morphine acts on μ-opioid receptors and downstream of the phosphatidylinositol 3-kinase signaling pathway to activate the mammalian target of rapamycin (mTOR) pathway. Rheb is an important regulator of growth and cell-cycle progression in the central nervous system owing to its critical role in the activation of mTOR. The hypothesis was that signaling via the GTP-binding protein Rheb in the dorsal horn of the spinal cord is involved in morphine-induced tolerance.

METHODS

Male and female wild-type C57BL/6J mice or transgenic mice (6 to 8 weeks old) were injected intrathecally with saline or morphine twice daily at 12-h intervals for 5 consecutive days to establish a tolerance model. Analgesia was assessed 60 min later using the tail-flick assay. After 5 days, the spine was harvested for Western blot or immunofluorescence analysis.

RESULTS

Chronic morphine administration resulted in the upregulation of spinal Rheb by 4.27 ± 0.195-fold (P = 0.0036, n = 6), in turn activating mTOR by targeting rapamycin complex 1 (mTORC1). Genetic overexpression of Rheb impaired morphine analgesia, resulting in a tail-flick latency of 4.65 ± 1.10 s (P < 0.0001, n = 7) in Rheb knock-in mice compared to 10 s in control mice (10 ± 0 s). Additionally, Rheb overexpression in spinal excitatory neurons led to mTORC1 signaling overactivation. Genetic knockout of Rheb or inhibition of mTORC1 signaling by rapamycin potentiated morphine-induced tolerance (maximum possible effect, 52.60 ± 9.56% in the morphine + rapamycin group vs. 16.60 ± 8.54% in the morphine group; P < 0.0001). Moreover, activation of endogenous adenosine 5'-monophosphate-activated protein kinase inhibited Rheb upregulation and retarded the development of morphine-dependent tolerance (maximum possible effect, 39.51 ± 7.40% in morphine + metformin group vs. 15.58 ± 5.79% in morphine group; P < 0.0001).

CONCLUSIONS

This study suggests spinal Rheb as a key molecular factor for regulating mammalian target of rapamycin signaling.

EDITOR’S PERSPECTIVE

Intrathecal delivery of a bicistronic AAV9 vector expressing β-hexosaminidase A corrects Sandhoff disease in a murine model: A dosage study

The pathological accumulation of GM2 ganglioside associated with Tay-Sachs disease (TSD) and Sandhoff disease (SD) occurs in individuals who possess mutant forms of the heterodimer β-hexosaminidase A (Hex A) because of mutation of the HEXA and HEXB genes, respectively. With a lack of approved therapies, patients experience rapid neurological decline resulting in early death. A novel bicistronic vector carrying both HEXA and HEXB previously demonstrated promising results in mouse models of SD following neonatal intravenous administration, including significant reduction in GM2 accumulation, increased levels of Hex A, and a 2-fold extension of survival. The aim of the present study was to identify an optimal dose of the bicistronic vector in 6-week-old SD mice by an intrathecal route of administration along with transient immunosuppression, to inform possible clinical translation. Three doses of the bicistronic vector were tested: 2.5e11, 1.25e11, and 0.625e11 vector genomes per mouse. The highest dose provided the greatest increase in biochemical and behavioral parameters, such that treated mice lived to a median age of 56 weeks (>3 times the lifespan of the SD controls). These results have direct implications in deciding a human equivalent dose for TSD/SD and have informed the approval of a clinical trial application (NCT04798235).

Intracranial Gene Delivery Mediated by Albumin-Based Nanobubbles and Low-Frequency Ultrasound

Research in the field of high-intensity focused ultrasound (HIFU) for intracranial gene therapy has greatly progressed over the years. However, limitations of conventional HIFU still remain. That is, genes are required to cross the blood-brain barrier (BBB) in order to reach the neurological disordered lesion. In this study, we introduce a novel direct intracranial gene delivery method, bypassing the BBB using human serum albumin-based nanobubbles (NBs) injected through a less invasive intrathecal route via lumbar puncture, followed by intracranial irradiation with low-frequency ultrasound (LoFreqUS). Focusing on both plasmid DNA (pDNA) and messenger RNA (mRNA), our approach utilizes LoFreqUS for deeper tissue acoustic penetration and enhancing gene transfer efficiency. This drug delivery method could be dubbed as the "Spinal Back-Door Approach", an alternative to the "front door" BBB opening method. Experiments showed that NBs effectively responded to LoFreqUS, significantly improving gene transfer in vitro using U-87 MG cell lines. In vivo experiments in mice demonstrated significantly increased gene expression with pDNA; however, we were unable to obtain conclusive results using mRNA. This novel technique, combining albumin-based NBs and LoFreqUS offers a promising, efficient, targeted, and non-invasive solution for central nervous system gene therapy, potentially transforming the treatment landscape for neurological disorders.

Gene therapy for neurotransmitter-related disorders

Inborn errors of neurotransmitter (NT) metabolism are a group of rare, heterogenous diseases with predominant neurological features, such as movement disorders, autonomic dysfunction, and developmental delay. Clinical overlap with other disorders has led to delayed diagnosis and treatment, and some conditions are refractory to oral pharmacotherapies. Gene therapies have been developed and translated to clinics for paediatric inborn errors of metabolism, with 38 interventional clinical trials ongoing to date. Furthermore, efforts in restoring dopamine synthesis and neurotransmission through viral gene therapy have been developed for Parkinson's disease. Along with the recent European Medicines Agency (EMA) and Medicines and Healthcare Products Regulatory Agency (MHRA) approval of an AAV2 gene supplementation therapy for AADC deficiency, promising efficacy and safety profiles can be achieved in this group of diseases. In this review, we present preclinical and clinical advances to address NT-related diseases, and summarise potential challenges that require careful considerations for NT gene therapy studies.

Pharmacokinetics of AAV9 Mediated Trastuzumab Expression in Rat Brain Following Systemic and Local Administration

INTRODUCTION

Recombinant adeno-associated viruses(rAAVs) are an attractive tool to ensure long-term expression monoclonal antibody(mAb) in the central nervous system(CNS). It is still unclear whether systemic injection or local CNS administration of AAV9 is more beneficial for the exposure of the expressed mAb in the brain. Hence, we compared the biodistribution and transgene expression following AAV9-Trastuzumab administration through different routes.

METHODS AND RESULT

In-house generated AAV9-Trastuzumab vectors were administered at 5E+11 Vgs/rat through intravenous(IV), intracerebroventricular(ICV), intra-cisterna magna(ICM) and intrastriatal(IST) routes. Vector and trastuzumab blood/plasma concentrations were assessed at different time points up to the terminal time point of 21 days. Different brain regions in addition to the spinal cord, cerebrospinal fluid(CSF) and interstitial fluid(ISF), were also analyzed at the terminal time point. Our results show that vector biodistribution and Trastuzumab expression in the brain could the ranked as follows: IST>ICM>ICV>IV. Rapid clearance of vector was observed after administration via the ICM and ICV routes. The ICV route produced similar expression levels across different brain regions, while the ICM route had better expression in the hindbrain and spinal cord region. The IST route had higher expression in the forebrain region compared to the hindbrain region. A sharp decline in trastuzumab plasma concentration was observed across all routes of administration due to anti-trastuzumab antibody response.

CONCLUSION

In this study we have characterized vector biodistribution and transgene mAb expression after AAV9 vector administration through different routes in rats. IST and ICM represent the best administration routes to deliver antibody genes to the brain.

Gene therapy of adeno-associated virus (AAV) vectors in preclinical models of ischemic stroke

Stroke has been associated with devastating clinical outcomes, with current treatment strategies proving largely ineffective. Therefore, there is a need to explore alternative treatment options for addressing post-stroke functional deficits. Gene therapy utilizing adeno-associated viruses (AAVs) as a critical gene vector delivering genes to the central nervous system (CNS) gene delivery has emerged as a promising approach for treating various CNS diseases. This review aims to provide an overview of the biological characteristics of AAV vectors and the therapeutic advancements observed in preclinical models of ischemic stroke. The study further investigates the potential of manipulating AAV vectors in preclinical applications, emphasizing the challenges and prospects in the selection of viral vectors, drug delivery strategies, immune reactions, and clinical translation.

In vivo selection in non-human primates identifies superior AAV capsids for on-target CSF delivery to spinal cord

Systemic administration of adeno-associated virus (AAV) vectors for spinal cord gene therapy has challenges including toxicity at high doses and pre-existing immunity that reduces efficacy. Intrathecal delivery of AAV vectors into the cerebral spinal fluid (CSF) can avoid many of the issues of systemic delivery, although achieving broad distribution of the vector and transgene expression throughout the spinal cord is challenging and vector entry to the periphery occurs, sometimes initiating hepatotoxicity. Here we performed two rounds of in vivo biopanning in non-human primates (NHPs) with an AAV9 peptide display library injected intrathecally and performed insert sequencing on DNA isolated from either whole tissue (conventional selection), isolated nuclei, or nuclei from transgene-expressing cells. A subsequent barcoded pool of candidates and AAV9 was compared at the DNA (biodistribution) and RNA (expression) level in spinal cord and liver of intrathecally injected NHPs. Most of the candidates displayed enhanced biodistribution compared to AAV9 at all levels of spinal cord ranging from 2 to 265-fold. Nuclear isolation or expression-based selection yielded 4 of 7 candidate capsids with enhanced transgene expression in spinal cord (up to 2.4-fold), while no capsid obtained by conventional selection achieved that level. Furthermore, several capsids displayed lower biodistribution to the liver of up to 1,250-fold, compared to AAV9, providing a remarkable on target/off target biodistribution ratio. These capsids may have potential for gene therapy programs directed at the spinal cord and the selection method described here should be useful in clinically relevant large animal models.

VWA3A-derived ependyma promoter drives increased therapeutic protein secretion into the CSF

Recombinant adeno-associated viral vectors (rAAVs) are a promising strategy to treat neurodegenerative diseases because of their ability to infect non-dividing cells and confer long-term transgene expression. Despite an ever-growing library of capsid variants, widespread delivery of AAVs in the adult central nervous system remains a challenge. We have previously demonstrated successful distribution of secreted proteins by infection of the ependyma, a layer of post-mitotic epithelial cells lining the ventricles of the brain and central column of the spinal cord, and subsequent protein delivery via the cerebrospinal fluid (CSF). Here we define a functional ependyma promoter to enhance expression from this cell type. Using RNA sequencing on human autopsy samples, we identified disease- and age-independent ependyma gene signatures. Associated promoters were cloned and screened as libraries in mouse and rhesus macaque to reveal cross-species function of a human DNA-derived von Willebrand factor domain containing 3A (VWA3A) promoter. When tested in mice, our VWA3A promoter drove strong, ependyma-localized expression of eGFP and increased secreted ApoE protein levels in the CSF by 2-12× over the ubiquitous iCAG promoter.

Toxicologic Pathology Forum: Opinion on Interpretive Challenges for Procedure-Related Effects Associated With Direct Central Nervous System Delivery of Oligonucleotides to Rodents, Dogs, and Nonhuman Primates

Direct delivery of therapeutics to the central nervous system (CNS) greatly expands opportunities to treat neurological diseases but is technically challenging. This opinion outlines principal technical aspects of direct CNS delivery via intracerebroventricular (ICV) or intrathecal (IT) injection to common nonclinical test species (rodents, dogs, and nonhuman primates) and describes procedure-related clinical and histopathological effects that confound interpretation of test article-related effects. Direct dosing is by ICV injection in mice due to their small body size, while other species are dosed IT in the lumbar cistern. The most frequent procedure-related functional effects are transient absence of lower spinal reflexes after IT injection or death soon after ICV dosing. Common procedure-related microscopic findings in all species include leukocyte infiltrates in CNS meninges or perivascular (Virchow-Robin) spaces; nerve fiber degeneration in the spinal cord white matter (especially dorsal and lateral tracts compressed by dosing needles or indwelling catheters), spinal nerve roots, and sciatic nerve; meningeal fibrosis at or near IT injection sites; hemorrhage; and gliosis. Findings typically are minimal to occasionally mild. Findings tend to be more severe and/or have a higher incidence in the spinal cord segments and spinal nerve roots at or close to the site of administration.

Safety and Efficacy of Intravenous and Intrathecal Delivery of AAV9-Mediated ARSA in Minipigs

Metachromatic leukodystrophy (MLD) is a hereditary neurodegenerative disease characterized by demyelination and motor and cognitive impairments due to deficiencies of the lysosomal enzyme arylsulfatase A (ARSA) or the saposin B activator protein (SapB). Current treatments are limited; however, gene therapy using adeno-associated virus (AAV) vectors for ARSA delivery has shown promising results. The main challenges for MLD gene therapy include optimizing the AAV dosage, selecting the most effective serotype, and determining the best route of administration for ARSA delivery into the central nervous system. This study aims to evaluate the safety and efficacy of AAV serotype 9 encoding ARSA (AAV9-ARSA) gene therapy when administered intravenously or intrathecally in minipigs, a large animal model with anatomical and physiological similarities to humans. By comparing these two administration methods, this study contributes to the understanding of how to improve the effectiveness of MLD gene therapy and offers valuable insights for future clinical applications.

Early postnatal administration of an AAV9 gene therapy is safe and efficacious in CLN3 disease

CLN3 disease, caused by biallelic mutations in the CLN3 gene, is a rare pediatric neurodegenerative disease that has no cure or disease modifying treatment. The development of effective treatments has been hindered by a lack of etiological knowledge, but gene replacement has emerged as a promising therapeutic platform for such disorders. Here, we utilize a mouse model of CLN3 disease to test the safety and efficacy of a cerebrospinal fluid-delivered AAV9 gene therapy with a study design optimized for translatability. In this model, postnatal day one administration of the gene therapy virus resulted in robust expression of human CLN3 throughout the CNS over the 24-month duration of the study. A range of histopathological and behavioral parameters were assayed, with the therapy consistently and persistently rescuing a number of hallmarks of disease while being safe and well-tolerated. Together, the results show great promise for translation of the therapy into the clinic, prompting the launch of a first-in-human clinical trial (NCT03770572).

Investigating the Impact of Delivery Routes for Exon Skipping Therapies in the CNS of DMD Mouse Models

Nucleic acid-based therapies have demonstrated great potential for the treatment of monogenetic diseases, including neurologic disorders. To date, regulatory approval has been received for a dozen antisense oligonucleotides (ASOs); however, these chemistries cannot readily cross the blood–brain barrier when administered systemically. Therefore, an investigation of their potential effects within the central nervous system (CNS) requires local delivery. Here, we studied the brain distribution and exon-skipping efficacy of two ASO chemistries, PMO and tcDNA, when delivered to the cerebrospinal fluid (CSF) of mice carrying a deletion in exon 52 of the dystrophin gene, a model of Duchenne muscular dystrophy (DMD). Following intracerebroventricular (ICV) delivery (unilateral, bilateral, bolus vs. slow rate, repeated via cannula or very slow via osmotic pumps), ASO levels were quantified across brain regions and exon 51 skipping was evaluated, revealing that tcDNA treatment invariably generates comparable or more skipping relative to that with PMO, even when the PMO was administered at higher doses. We also performed intra-cisterna magna (ICM) delivery as an alternative route for CSF delivery and found a biased distribution of the ASOs towards posterior brain regions, including the cerebellum, hindbrain, and the cervical part of the spinal cord. Finally, we combined both ICV and ICM injection methods to assess the potential of an additive effect of this methodology in inducing efficient exon skipping across different brain regions. Our results provide useful insights into the local delivery and associated efficacy of ASOs in the CNS in mouse models of DMD. These findings pave the way for further ASO-based therapy application to the CNS for neurological disease.

AAV vectors applied to the treatment of CNS disorders: Clinical status and challenges

In recent years, adeno-associated virus (AAV) has become the most important vector for central nervous system (CNS) gene therapy. AAV has already shown promising results in the clinic, for several CNS diseases that cannot be treated with drugs, including neurodegenerative diseases, neuromuscular diseases, and lysosomal storage disorders. Currently, three of the four commercially available AAV-based drugs focus on neurological disorders, including Upstaza for aromatic l-amino acid decarboxylase deficiency, Luxturna for hereditary retinal dystrophy, and Zolgensma for spinal muscular atrophy. All these studies have provided paradigms for AAV-based therapeutic intervention platforms. AAV gene therapy, with its dual promise of targeting disease etiology and enabling 'long-term correction' of disease processes, has the advantages of immune privilege, high delivery efficiency, tissue specificity, and cell tropism in the CNS. Although AAV-based gene therapy has been shown to be effective in most CNS clinical trials, limitations have been observed in its clinical applications, which are often associated with side effects. In this review, we summarized the therapeutic progress, challenges, limitations, and solutions for AAV-based gene therapy in 14 types of CNS diseases. We focused on viral vector technologies, delivery routes, immunosuppression, and other relevant clinical factors. We also attempted to integrate several hurdles faced in clinical and preclinical studies with their solutions, to seek the best path forward for the application of AAV-based gene therapy in the context of CNS diseases. We hope that these thoughtful recommendations will contribute to the efficient translation of preclinical studies and wide application of clinical trials.

High-frequency ultrasound-guided intrathecal injections in a young mouse model: Targeting the central nervous system in drug delivery

BACKGROUND

Intrathecal injections provide important access to the central nervous system for delivery of anesthetic, analgesic or chemotherapeutic drugs that do not otherwise cross the blood-brain barrier. The administration of drugs via this route in animal models is challenging due to an inability to visualize the small target space during injection. Successful drug delivery therefore requires expertise in indirectly assessing vertebral and spinal cord anatomy and gaining advanced procedural skills. These factors are especially compounded in small animals such as mice (the most common mammalian model) and in investigations modeling pediatric drug delivery, where the animal is even smaller.

NEW METHOD

To address these issues, we have developed a method in which high-frequency ultrasound imaging is used to visualize and target the lumbar intrathecal space for injections. The technique is demonstrated in mice as young as postnatal day 16. To evaluate the method, a gadolinium-based magnetic resonance imaging (MRI) contrast agent was injected intrathecally, and subsequent brain delivery was verified post-injection by MRI.

RESULTS

Successful intrathecal injections of the MRI contrast agent showed distribution to the brain. In this study, we achieved a targeting success rate of 80% in 20 animals.

COMPARISON WITH EXISTING METHODS AND CONCLUSION

We expect that the new method will be convenient for drug delivery to the central nervous system in rodent research and provide higher reliability than unguided approaches, an essential contribution that will enable intrathecal delivery in pediatric mouse models.

Gene Therapy of Sphingolipid Metabolic Disorders

Sphingolipidoses are defined as a group of rare hereditary diseases resulting from mutations in the genes encoding lysosomal enzymes. This group of lysosomal storage diseases includes more than 10 genetic disorders, including GM1-gangliosidosis, Tay-Sachs disease, Sandhoff disease, the AB variant of GM2-gangliosidosis, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease, Farber disease, etc. Enzyme deficiency results in accumulation of sphingolipids in various cell types, and the nervous system is also usually affected. There are currently no known effective methods for the treatment of sphingolipidoses; however, gene therapy seems to be a promising therapeutic variant for this group of diseases. In this review, we discuss gene therapy approaches for sphingolipidoses that are currently being investigated in clinical trials, among which adeno-associated viral vector-based approaches and transplantation of hematopoietic stem cells genetically modified with lentiviral vectors seem to be the most effective.

Assessment of AAV9 distribution and transduction in rats after administration through Intrastriatal, Intracisterna magna and Lumbar Intrathecal routes

Challenges in obtaining efficient transduction of brain and spinal cord following systemic AAV delivery have led to alternative administration routes being used in clinical trials that directly infuse the virus into the CNS. However, data comparing different direct AAV injections into the brain remain limited making it difficult to choose optimal routes. Here we tested both AAV9-egfp and AAV9-fLuc delivery via intrastriatal (IST), intracisterna magna (ICM) and lumbar intrathecal (LIT) routes in adult rats and assessed vector distribution and transduction in brain, spinal cord and peripheral tissues. We find that IST infusion leads to robust transgene expression in the striatum, thalamus and cortex with lower peripheral tissue transduction and anti-AAV9 capsid titers compared to ICM or LIT. ICM delivery provided strong GFP and luciferase expression across more brain regions than the other routes and similar expression in the spinal cord to LIT injections, which itself largely failed to transduce the rat brain. Our data highlight the strengths and weaknesses of each direct CNS delivery route which will help with future clinical targeting.

Biodistribution of Adeno-Associated Virus Gene Therapy Following Cerebrospinal Fluid-Directed Administration

Adeno-associated virus (AAV)-based gene therapies, exemplified by the approved therapy for spinal muscular atrophy, have the potential to deliver disease-course-altering treatments for central nervous system (CNS) indications. However, several clinical trials have reported severe adverse events, including patient deaths following high-dose systemic administration for muscle-directed gene transfer, highlighting the need to explore approaches utilizing lower doses when targeting the CNS. Animal models of disease provide insight into the response to new AAV therapies. However, translation from small to larger animals and eventually to humans is hampered by anatomical and biological differences across the species and their impact on AAV delivery. We performed a literature review of preclinical studies of AAV gene therapy biodistribution following cerebrospinal fluid (CSF) delivery (intracerebroventricular, intra-cisterna magna, and intrathecal lumbar). The reviewed literature varies greatly in the reported biodistribution of AAV following administration into the CSF. Differences between studies, including animal model, vector serotype used, method used to assess biodistribution, and route of administration, among other variables, contribute to differing outcomes and difficulties in translating these preclinical results. For example, only half of the published AAV-based gene therapy studies report vector copy number, the most direct readout following administration of a vector; none of these studies reported details such as the empty:full capsid ratio and quality of encapsidated genome. Analysis of the last decade's literature focusing on AAV-based gene therapies targeting the CNS underscores limitations of the body of knowledge and room for continued research. In particular, there is a need to understand the biodistribution achieved by different CSF-directed routes of administration and determining if specific cell types/structures of interest will be transduced. Our findings point to a clear need for a more systematic approach across the field to align the assessments and elements reported in preclinical research to enable more reliable translation across animal models and into human studies.

Genetic Approaches for the Treatment of Giant Axonal Neuropathy

Giant axonal neuropathy (GAN) is a pediatric, hereditary, neurodegenerative disorder that affects both the central and peripheral nervous systems. It is caused by mutations in the GAN gene, which codes for the gigaxonin protein. Gigaxonin plays a role in intermediate filament (IF) turnover hence loss of function of this protein leads to IF aggregates in various types of cells. These aggregates can lead to abnormal cellular function that manifests as a diverse set of symptoms in persons with GAN including nerve degeneration, cognitive issues, skin diseases, vision loss, and muscle weakness. GAN has no cure at this time. Currently, an adeno-associated virus (AAV) 9-mediated gene replacement therapy is being tested in a phase I clinical trial for the treatment of GAN. This review paper aims to provide an overview of giant axonal neuropathy and the current efforts at developing a treatment for this devastating disease.

Transduction characteristics of alternative adeno-associated virus serotypes in the cat brain by intracisternal delivery

Multiple studies have examined the transduction characteristics of different AAV serotypes in the mouse brain, where they can exhibit significantly different patterns of transduction. The pattern of transduction also varies with the route of administration. Much less information exists for the transduction characteristics in large-brained animals. Large animal models have brains that are closer in size and organization to the human brain, such as being gyrencephalic compared to the lissencephalic rodent brains, pathway organization, and certain electrophysiologic properties. Large animal models are used as translational intermediates to develop gene therapies to treat human diseases. Various AAV serotypes and routes of delivery have been used to study the correction of pathology in the brain in lysosomal storage diseases. In this study, we evaluated the ability of selected AAV serotypes to transduce cells in the cat brain when delivered into the cerebrospinal fluid via the cisterna magna. We previously showed that AAV1 transduced significantly greater numbers of cells than AAV9 in the cat brain by this route. In the present study, we evaluated serotypes closely related to AAVs 1 and 9 (AAVs 6, AS, hu32) that may mediate more extensive transduction, as well as AAVs 4 and 5, which primarily transduce choroid plexus epithelial (CPE) and ependymal lining cells in the rodent brain. The related serotypes tended to have similar patterns of transduction but were divergent in some specific brain structures.

Intrathecal delivery and its applications in leptomeningeal disease

Intrathecal delivery (IT) of opiates into the cerebrospinal fluid (CSF) for anesthesia and pain relief has been used clinically for decades, but this relatively straightforward approach of bypassing the blood-brain barrier has been underutilized for other indications because of its lack of utility in delivering small lipid-soluble drugs. However, emerging evidence suggests that IT drug delivery be an efficacious strategy for the treatment of cancers in which there is leptomeningeal spread of disease. In this review, we discuss CSF flow dynamics and CSF clearance pathways in the context of intrathecal delivery. We discuss human and animal studies of several new classes of therapeutic agents-cellular, protein, nucleic acid, and nanoparticle-based small molecules-that may benefit from IT delivery. The complexity of the CSF compartment presents several key challenges in predicting biodistribution of IT-delivered drugs. New approaches and strategies are needed that can overcome the high rates of turnover in the CSF to reach specific tissues or cellular targets.

Sestrin2 overexpression attenuates osteoarthritis pain via induction of AMPK/PGC-1α-mediated mitochondrial biogenesis and suppression of neuroinflammation

BACKGROUND

Our previous study indicated that reactive oxygen species (ROS) are critically involved in chronic pain. Sestrin2 (Sesn2), a novel stress-inducible protein, is evidenced to reduce the generation of ROS. The study examined the role of Sesn2 in osteoarthritis (OA) pain and delineated the underlying molecular mechanisms.

METHODS

In the present study, we investigated the impact of Sesn2 on mitochondrial biogenesis in a rat model of OA pain. After adeno-associated viral (AAV)-Sesn2EGFP was injected for 14 days, OA was induced by intra-articular injection of monosodium iodoacetate (MIA). We assessed pain behaviors (weight-bearing asymmetry and paw withdrawal threshold) and explored possible mechanisms in the L4-6 spinal cord.

RESULTS

Our results showed that overexpression of Sesn2 in the spinal cord alleviated pain behaviors in OA rats. Moreover, overexpression of Sesn2 increased the activity of AMP-activated protein kinase (AMPK) signaling and significantly restored mitochondrial biogenesis. Besides, Sesn2 overexpression inhibited the activation of astrocytes and microglia, and decreased the production of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in the spinal cord of the OA pain rats. These effects were significantly reversed by an AMPK inhibitor.

CONCLUSIONS

Collectively, these results suggest that Sesn2 overexpression ameliorates mechanical allodynia and weight-bearing asymmetry in OA rats via activation of AMPK/PGC-1α-mediated mitochondrial biogenesis in the spinal cord. Moreover, Sesn2 overexpression attenuates OA-induced neuroinflammation at least partly by activating AMPK signaling. Sesn2 may become an encouraging therapeutic strategy for OA pain relief and other disorders.

AAV9/MFSD8 gene therapy is effective in preclinical models of neuronal ceroid lipofuscinosis type 7 disease

Neuronal ceroid lipofuscinosis type 7 (CLN7) disease is a lysosomal storage disease caused by mutations in the facilitator superfamily domain containing 8 (MFSD8) gene, which encodes a membrane-bound lysosomal protein, MFSD8. To test the effectiveness and safety of adeno-associated viral (AAV) gene therapy, an in vitro study demonstrated that AAV2/MFSD8 dose dependently rescued lysosomal function in fibroblasts from a CLN7 patient. An in vivo efficacy study using intrathecal administration of AAV9/MFSD8 to Mfsd8- /- mice at P7-P10 or P120 with high or low dose led to clear age- and dose-dependent effects. A high dose of AAV9/MFSD8 at P7-P10 resulted in widespread MFSD8 mRNA expression, tendency of amelioration of subunit c of mitochondrial ATP synthase accumulation and glial fibrillary acidic protein immunoreactivity, normalization of impaired behaviors, doubled median life span, and extended normal body weight gain. In vivo safety studies in rodents concluded that intrathecal administration of AAV9/MFSD8 was safe and well tolerated. In summary, these results demonstrated that the AAV9/MFSD8 vector is both effective and safe in preclinical models.

Long-term disease prevention with a gene therapy targeting oligodendrocytes in a mouse model of adrenomyeloneuropathy

Adrenomyeloneuropathy (AMN) is a late-onset axonopathy of spinal cord tracts caused by mutations of the ABCD1 gene that encodes ALDP, a peroxisomal transporter of very long chain fatty acids (VLCFA). Disturbed metabolic interaction between oligodendrocytes (OL) and axons is suspected to play a major role in AMN axonopathy. To develop a vector targeting OL, the human ABCD1 gene driven by a short 0.3 kb part of the human myelin-associated glycoprotein (MAG) promoter was packaged into an adeno-associated viral serotype 9 (rAAV9). An intravenous injection of this vector at postnatal day 10 (P10) in Abcd1-/- mice, a model of AMN, allowed a near normal motor performance to persist for 24 months, while age-matched untreated mice developed major defects of balance and motricity. Three weeks post vector, 50-54% of spinal cord white matter OL were expressing ALDP at the cervical level, and only 6-7% after 24 months. In addition, 29-32% of cervical spinal cord astrocytes at 3 weeks and 16-19% at 24 months also expressed ALDP. C26:0-lysoPC, a sensitive VLCFA marker of AMN, was lower by 41% and 50%, respectively in the spinal cord and brain of vector-treated compared with untreated mice. In a non-human primate (NHP), the intrathecal injection of the rAAV9-MAG vector induced abundant ALDP expression at 3 weeks in spinal cord OL (43%, 29%, 26% at cervical, thoracic and lumbar levels) and cerebellum OL (35%). In addition, 33-41 % of spinal cord astrocytes expressed hALDP, and 27% of cerebellar astrocytes. To our knowledge, OL targeting had not been obtained before in primates with other vectors or promoters. The current results thus provide a robust proof-of-concept not only for the gene therapy of AMN but for other CNS diseases where the targeting of OL with the rAAV9-MAG vector may be of interest.

Adeno-associated viral vector serotype 9-based gene replacement therapy for SURF1-related Leigh syndrome

SURF1 (surfeit locus protein 1)-related Leigh syndrome is an early-onset neurodegenerative disorder, characterized by reduction in complex IV activity, resulting in disrupted mitochondrial function. Currently, there are no treatment options available. To test our hypothesis that adeno-associated viral vector serotype 9 (AAV9)/human SURF1 (hSURF1) gene replacement therapy can provide a potentially meaningful and long-term therapeutic benefit, we conducted preclinical efficacy studies using SURF1 knockout mice and safety evaluations with wild-type (WT) mice. Our data indicate that with a single intrathecal (i.t.) administration, our treatment partially and significantly rescued complex IV activity in all tissues tested, including liver, brain, and muscle. Accordingly, complex IV content (examined via MT-CO1 protein expression level) also increased with our treatment. In a separate group of mice, AAV9/hSURF1 mitigated the blood lactic acidosis induced by exhaustive exercise at 9 months post-dosing. A toxicity study in WT mice showed no adverse effects in either the in-life portion or after microscopic examination of major tissues up to a year following the same treatment regimen. Taken together, our data suggest a single dose, i.t. administration of AAV9/hSURF1 is safe and effective in improving biochemical abnormalities induced by SURF1 deficiency with potential applicability for SURF1-related Leigh syndrome patients.

Efficacy of AAV serotypes to target Schwann cells after intrathecal and intravenous delivery

To optimize gene delivery to myelinating Schwann cells we compared clinically relevant AAV serotypes and injection routes. AAV9 and AAVrh10 vectors expressing either EGFP or the neuropathy-associated gene GJB1/Connexin32 (Cx32) under a myelin specific promoter were injected intrathecally or intravenously in wild type and Gjb1-null mice, respectively. Vector biodistribution in lumbar roots and sciatic nerves was higher in AAVrh10 injected mice while EGFP and Cx32 expression rates and levels were similar between the two serotypes. A gradient of biodistribution away from the injection site was seen with both intrathecal and intravenous delivery, while similar expression rates were achieved despite higher vector amounts injected intravenously. Quantified immune cells in relevant tissues were similar to non-injected littermates. Overall, AAV9 and AAVrh10 efficiently transduce Schwann cells throughout the peripheral nervous system with both clinically relevant routes of administration, although AAV9 and intrathecal injection may offer a more efficient approach for treating demyelinating neuropathies.

Delivery Platforms for CRISPR/Cas9 Genome Editing of Glial Cells in the Central Nervous System

Glial cells (astrocytes, oligodendrocytes, and microglia) are emerging as key players in several physiological and pathological processes of the central nervous system (CNS). Astrocytes and oligodendrocytes are not only supportive cells that release trophic factors or regulate energy metabolism, but they also actively modulate critical neuronal processes and functions in the tripartite synapse. Microglia are defined as CNS-resident cells that provide immune surveillance; however, they also actively contribute to shaping the neuronal microenvironment by scavenging cell debris or regulating synaptogenesis and pruning. Given the many interconnected processes coordinated by glial cells, it is not surprising that both acute and chronic CNS insults not only cause neuronal damage but also trigger complex multifaceted responses, including neuroinflammation, which can critically contribute to the disease progression and worsening of symptoms in several neurodegenerative diseases. Overall, this makes glial cells excellent candidates for targeted therapies to treat CNS disorders. In recent years, the application of gene editing technologies has redefined therapeutic strategies to treat genetic and age-related neurological diseases. In this review, we discuss the advantages and limitations of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-based gene editing in the treatment of neurodegenerative disorders, focusing on the development of viral- and nanoparticle-based delivery methods for in vivo glial cell targeting.

Treatment of adult metachromatic leukodystrophy model mice using intrathecal administration of type 9 AAV vector encoding arylsulfatase A

Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by an arylsulfatase A (ARSA) deficiency and characterized by severe neurological symptoms resulting from demyelination within the central and peripheral nervous systems. We investigated the feasibility and efficacy of intrathecal administration of a type 9 adeno-associated viral vector encoding ARSA (AAV9/ARSA) for the treatment of 6-week-old MLD model mice, which are presymptomatic, and 1-year-old mice, which exhibit neurological abnormalities. Immunohistochemical analysis following AAV9/ARSA administration showed ARSA expression within the brain, with highest activities in the cerebellum and olfactory bulbs. In mice treated at 1 year, alcian blue staining and quantitative analysis revealed significant decreases in stored sulfatide. Behaviorally, mice treated at 1 year showed no improvement in their ability to traverse narrow balance beams as compared to untreated mice. By contrast, MLD mice treated at 6 weeks showed significant decreases in stored sulfatide throughout the entire brain and improved ability to traverse narrow balance beams. These findings suggest intrathecal administration of an AAV9/ARSA vector is a promising approach to treating genetic diseases of the central nervous system, including MLD, though it may be essential to begin therapy before the onset of neurological symptoms.

A Multifaceted Approach to Optimizing AAV Delivery to the Brain for the Treatment of Neurodegenerative Diseases

Despite major advancements in gene therapy technologies, there are no approved gene therapies for diseases which predominantly effect the brain. Adeno-associated virus (AAV) vectors have emerged as the most effective delivery vector for gene therapy owing to their simplicity, wide spread transduction and low immunogenicity. Unfortunately, the blood-brain barrier (BBB) makes IV delivery of AAVs, to the brain highly inefficient. At IV doses capable of widespread expression in the brain, there is a significant risk of severe immune-mediated toxicity. Direct intracerebral injection of vectors is being attempted. However, this method is invasive, and only provides localized delivery for diseases known to afflict the brain globally. More advanced methods for AAV delivery will likely be required for safe and effective gene therapy to the brain. Each step in AAV delivery, including delivery route, BBB transduction, cellular tropism and transgene expression provide opportunities for innovative solutions to optimize delivery efficiency. Intra-arterial delivery with mannitol, focused ultrasound, optimized AAV capsid evolution with machine learning algorithms, synthetic promotors are all examples of advanced strategies which have been developed in pre-clinical models, yet none are being investigated in clinical trials. This manuscript seeks to review these technological advancements, and others, to improve AAV delivery to the brain, and to propose novel strategies to build upon this research. Ultimately, it is hoped that the optimization of AAV delivery will allow for the human translation of many gene therapies for neurodegenerative and other neurologic diseases.

Reprogramming astrocytes to motor neurons by activation of endogenous Ngn2 and Isl1

Central nervous system injury and neurodegenerative diseases cause irreversible loss of neurons. Overexpression of exogenous specific transcription factors can reprogram somatic cells into functional neurons for regeneration and functional reconstruction. However, these practices are potentially problematic due to the integration of vectors into the host genome. Here, we showed that the activation of endogenous genes Ngn2 and Isl1 by CRISPRa enabled reprogramming of mouse spinal astrocytes and embryonic fibroblasts to motor neurons. These induced neurons showed motor neuronal morphology and exhibited electrophysiological activities. Furthermore, astrocytes in the spinal cord of the adult mouse can be converted into motor neurons by this approach with high efficiency. These results demonstrate that the activation of endogenous genes is sufficient to induce astrocytes into functional motor neurons in vitro and in vivo. This direct neuronal reprogramming approach may provide a novel potential therapeutic strategy for treating neurodegenerative diseases and spinal cord injury.

AAV9-mediated FIG4 delivery prolongs life span in Charcot-Marie-Tooth disease type 4J mouse model

Charcot-Marie-Tooth disease type 4J (CMT4J) is caused by recessive, loss-of-function mutations in FIG4, encoding a phosphoinositol(3,5)P2-phosphatase. CMT4J patients have both neuron loss and demyelination in the peripheral nervous system, with vacuolization indicative of endosome/lysosome trafficking defects. Although the disease is highly variable, the onset is often in childhood and FIG4 mutations can dramatically shorten life span. There is currently no treatment for CMT4J. Here, we present the results of preclinical studies testing a gene-therapy approach to restoring FIG4 expression. A mouse model of CMT4J, the Fig4-pale tremor (plt) allele, was dosed with a single-stranded adeno-associated virus serotype 9 (AAV9) to deliver a codon-optimized human FIG4 sequence. Untreated, Fig4plt/plt mice have a median survival of approximately 5 weeks. When treated with the AAV9-FIG4 vector at P1 or P4, mice survived at least 1 year, with largely normal gross motor performance and little sign of neuropathy by neurophysiological or histopathological evaluation. When mice were treated at P7 or P11, life span was still significantly prolonged and peripheral nerve function was improved, but rescue was less complete. No unanticipated adverse effects were observed. Therefore, AAV9-mediated delivery of FIG4 is a well-tolerated and efficacious strategy in a mouse model of CMT4J.

Intra-cisterna magna delivery of an AAV vector with the GLUT1 promoter in a pig recapitulates the physiological expression of SLC2A1

Glucose transporter 1 deficiency syndrome (GLUT1DS) is caused by haplo-insufficiency of SLC2A1, which encodes GLUT1, resulting in impaired hexose transport into the brain. Previously, we generated a tyrosine-mutant AAV9/3 vector in which SLC2A1 was expressed under the control of the endogenous GLUT1 promoter (AAV-GLUT1), and confirmed the improved motor function and cerebrospinal fluid glucose levels of Glut1-deficient mice after cerebroventricular injection of AAV-GLUT1. In preparation for clinical application, we examined the expression of transgenes after intra-cisterna magna injection of AAV-GFP (tyrosine-mutant AAV9/3-GFP with the CMV promoter) and AAV-GLUT1. We injected AAV-GFP or AAV-GLUT1 (1.63 × 10¹² vector genomes/kg) into the cisterna magna of pigs to compare differential promoter activity. After AAV-GFP injection, exogenous GFP was expressed in broad areas of the brain and peripheral organs. After AAV-GLUT1 injection, exogenous GLUT1 was expressed predominantly in the brain. At the cellular level, exogenous GLUT1 was mainly expressed in the endothelium, followed by glia and neurons, which was contrasted with the neuronal-predominant expression of GFP by the CMV promotor. We consider intra-cisterna magna injection of AAV-GLUT1 to be a feasible approach for gene therapy of GLUT1DS.

MCOLN1 gene therapy corrects neurologic dysfunction in the mouse model of mucolipidosis IV

Mucolipidosis IV (MLIV) is an orphan disease leading to debilitating psychomotor deficits and vision loss. It is caused by loss-of-function mutations in the MCOLN1 gene that encodes the lysosomal transient receptor potential channel mucolipin1, or TRPML1. With no existing therapy, the unmet need in this disease is very high. Here, we showed that AAV-mediated CNS-targeted gene transfer of the human MCOLN1 gene rescued motor function and alleviated brain pathology in the MLIV mouse model. Using the AAV-PHP.b vector in symptomatic mice, we showed long-term reversal of declined motor function and significant delay of paralysis. Next, using self-complementary AAV9 clinical candidate vector, we showed that its intracerebroventricular administration in post-natal day 1 mice significantly improved motor function, myelination and reduced lysosomal storage load in the MLIV mouse brain. Based on our data and general advancements in the gene therapy field, we propose scAAV9-mediated CSF-targeted MCOLN1 gene transfer as a therapeutic strategy in MLIV.

Enhanced CNS transduction from AAV.PHP.eB infusion into the cisterna magna of older adult rats compared to AAV9

The development of high efficiency, central nervous system (CNS) targeting AAV-based gene therapies is necessary to address challenges in both pre-clinical and clinical investigations. The engineered capsids, AAV.PHP.B and AAV.PHP.eB, show vastly improved blood-brain barrier penetration compared to their parent serotype, AAV9, but with variable effect depending on animal system, strain, and delivery route. As most characterizations of AAV.PHP variants have been performed in mice, it is currently unknown whether AAV.PHP variants improve CNS targeting when delivered intrathecally in rats. We evaluated the comparative transduction efficiencies of equititer doses (6 × 10¹¹vg) of AAV.PHP.eB-CAG-GFP and AAV9-CAG-GFP when delivered into the cisterna magna of 6–9-month old rats. Using both quantitative and qualitative assessments, we observed consistently superior biodistribution of GFP+ cells and fibers in animals treated with AAV.PHP.eB compared to those treated with AAV9. Enhanced GFP signal was uniformly observed throughout rostrocaudal brain regions in AAV.PHP.eB-treated animals with matching GFP protein expression detected in the forebrain, midbrain, and cerebellum. Collectively, these data illustrate the benefit of intracisternal infusions of AAV.PHP.eB as an optimal system to distribute CNS gene therapies in preclinical investigations of rats, and may have important translational implications for the clinical CNS targeting.

Future Prospects of Gene Therapy for Friedreich's Ataxia

Friedreich's ataxia is an autosomal recessive neurogenetic disease that is mainly associated with atrophy of the spinal cord and progressive neurodegeneration in the cerebellum. The disease is caused by a GAA-expansion in the first intron of the frataxin gene leading to a decreased level of frataxin protein, which results in mitochondrial dysfunction. Currently, there is no effective treatment to delay neurodegeneration in Friedreich's ataxia. A plausible therapeutic approach is gene therapy. Indeed, Friedreich's ataxia mouse models have been treated with viral vectors en-coding for either FXN or neurotrophins, such as brain-derived neurotrophic factor showing promising results. Thus, gene therapy is increasingly consolidating as one of the most promising therapies. However, several hurdles have to be overcome, including immunotoxicity and pheno-toxicity. We review the state of the art of gene therapy in Friedreich's ataxia, addressing the main challenges and the most feasible solutions for them.

AAV9-mediated Schwann cell-targeted gene therapy rescues a model of demyelinating neuropathy

Mutations in the GJB1 gene, encoding the gap junction (GJ) protein connexin32 (Cx32), cause X-linked Charcot-Marie-Tooth disease (CMT1X), an inherited demyelinating neuropathy. We developed a gene therapy approach for CMT1X using an AAV9 vector to deliver the GJB1/Cx32 gene under the myelin protein zero (Mpz) promoter for targeted expression in Schwann cells. Lumbar intrathecal injection of the AAV9-Mpz.GJB1 resulted in widespread biodistribution in the peripheral nervous system including lumbar roots, sciatic and femoral nerves, as well as in Cx32 expression in the paranodal non-compact myelin areas of myelinated fibers. A pre-, as well as post-onset treatment trial in Gjb1-null mice, demonstrated improved motor performance and sciatic nerve conduction velocities along with improved myelination and reduced inflammation in peripheral nerve tissues. Blood biomarker levels were also significantly ameliorated in treated mice. This study provides evidence that a clinically translatable AAV9-mediated gene therapy approach targeting Schwann cells could potentially treat CMT1X.

Current Clinical Applications of In Vivo Gene Therapy with AAVs

Hereditary diseases are caused by mutations in genes, and more than 7,000 rare diseases affect over 30 million Americans. For more than 30 years, hundreds of researchers have maintained that genetic modifications would provide effective treatments for many inherited human diseases, offering durable and possibly curative clinical benefit with a single treatment. This review is limited to gene therapy using adeno-associated virus (AAV) because the gene delivered by this vector does not integrate into the patient genome and has a low immunogenicity. There are now five treatments approved for commercialization and currently available, i.e., Luxturna, Zolgensma, the two chimeric antigen receptor T cell (CAR-T) therapies (Yescarta and Kymriah), and Strimvelis (the gammaretrovirus approved for adenosine deaminase-severe combined immunodeficiency [ADA-SCID] in Europe). Dozens of other treatments are under clinical trials. The review article presents a broad overview of the field of therapy by in vivo gene transfer. We review gene therapy for neuromuscular disorders (spinal muscular atrophy [SMA]; Duchenne muscular dystrophy [DMD]; X-linked myotubular myopathy [XLMTM]; and diseases of the central nervous system, including Alzheimer’s disease, Parkinson’s disease, Canavan disease, aromatic l-amino acid decarboxylase [AADC] deficiency, and giant axonal neuropathy), ocular disorders (Leber congenital amaurosis, age-related macular degeneration [AMD], choroideremia, achromatopsia, retinitis pigmentosa, and X-linked retinoschisis), the bleeding disorder hemophilia, and lysosomal storage disorders.

A comparison of in vivo viral targeting systems identifies adeno-associated virus serotype 9 (AAV9) as an effective vector for genetic manipulation of Leydig cells in adult mice

BACKGROUND

Despite the increasing popularity of deliverable transgenics, a robust and fully validated method for targeting Leydig cells, capable of delivering long-term transgene expression, is yet to be defined.

OBJECTIVES

We compared three viral vector systems in terms of their cell targeting specificity, longevity of gene expression and impact on targeted cell types when delivered to the interstitial compartment of the mouse testis.

MATERIALS & METHODS

We delivered lentiviral, adenoviral and adeno-associated (AAV) viral particles to the interstitial compartment of adult mouse testis. Immunolocalization and stereology were performed to characterize ability of vectors to target and deliver transgenes to Leydig cells.

RESULTS

Viral vectors utilized in this study were found to specifically target Leydig cells when delivered interstitially. Transgene expression in lentiviral-targeted Leydig cells was detected for 7 days post-injection before Leydig cells underwent apoptosis. Adenoviral-delivered transgene expression was detected for 10 days post-injection with no evidence of targeted cell apoptosis. We found serotype differences in AAV injected testis with AAV serotype 9 targeting a significant proportion of Leydig cells. Targeting efficiency increased to an average of 59.63% (and a maximum of 80%) of Leydig cells with the addition of neuraminidase during injection. In AAV injected testis sections, transgene expression was detectable for up to 50 days post-injection.

DISCUSSION & CONCLUSION

Lentivirus, Adenovirus and Adeno-Associated virus delivery to the testis resulted in key variances in targeting efficiency of Leydig cells and in longevity of transgene expression, but identified AAV9 + Neuraminidase as an efficient vector system for transgene delivery and long-term expression. Simple viral delivery procedures and the commercial availability of viral vectors suggests AAV9 + Neuraminidase will be of significant utility to researchers investigating the genetics underpinning Leydig cell function and holds promise to inform the development of novel therapeutics for the treatment of male reproductive disorders.