RH10 provides superior transgene expression in mice when compared with natural AAV serotypes for neonatal gene therapy

Current and Emerging Issues in Adeno-Associated Virus Vector-Mediated Liver-Directed Gene Therapy

Adeno-associated virus (AAV) vectors have demonstrated safety and efficacy for gene transfer to hepatocytes in preclinical models, in various clinical trials and from a clinical experience with a growing number of approved gene therapy products. Although the exact duration is unknown, the expression of therapeutic genes in hepatocytes remains stable for several years after a single administration of the vector at clinically relevant doses in adult patients with hemophilia and other inherited metabolic disorders. However, clinical applications, especially for diseases requiring high AAV vector doses by intravenous administrations, have raised several concerns. These include the high prevalence of pre-existing immunity against the vector capsid, activation of the complement and the innate immunity with serious life-threatening complications, elevation of liver transaminases, liver growth associated with loss of transgene expression, underlying conditions negatively affecting AAV vector safety and efficacy. Despite these issues, the field is rapidly advancing with a better understanding of vector-host interactions and the development of new strategies to improve liver-directed gene therapy. This review provides an overview of the current and emerging challenges for AAV-mediated liver-directed gene therapy.

AAV Capsid Screening for Translational Pig Research Using a Mouse Xenograft Liver Model

In gene therapy, delivery vectors are a key component for successful gene delivery and safety, based on which adeno-associated viruses (AAVs) gained popularity in particular for the liver, but also for other organs. Traditionally, rodents have been used as animal models to develop and optimize treatments, but species and organ specific tropism of AAV desire large animal models more closely related to humans for preclinical in-depth studies. Relevant AAV variants with the potential for clinical translation in liver gene therapy were previously evolved in vivo in a xenogeneic mouse model transplanted with human hepatocytes. Here, we selected and evaluated efficient AAV capsids using chimeric mice with a >90% xenografted pig hepatocytes. The pig is a valuable preclinical model for therapy studies due to its anatomic and immunological similarities to humans. Using a DNA-barcoded recombinant AAV library containing 47 different capsids and subsequent Illumina sequencing of barcodes in the AAV vector genome DNA and transcripts in the porcine hepatocytes, we found the AAVLK03 and AAVrh20 capsid to be the most efficient delivery vectors regarding transgene expression in porcine hepatocytes. In attempting to validate these findings with primary porcine hepatocytes, we observed capsid-specific differences in cell entry and transgene expression efficiency where the AAV2, AAVAnc80, and AAVDJ capsids showed superior efficiency to AAVLK03 and AAVrh20. This work highlights intricacies of in vitro testing with primary hepatocytes and the requirements for suitable pre-clinical animal models but suggests the chimeric mouse to be a valuable model to predict AAV capsids to transduce porcine hepatocytes efficiently.

AAV-Mediated Restoration of Dystrophin-Dp71 in the Brain of Dp71-Null Mice: Molecular, Cellular and Behavioral Outcomes

A deficiency in the shortest dystrophin-gene product, Dp71, is a pivotal aggravating factor for intellectual disabilities in Duchenne muscular dystrophy (DMD). Recent advances in preclinical research have achieved some success in compensating both muscle and brain dysfunctions associated with DMD, notably using exon skipping strategies. However, this has not been studied for distal mutations in the DMD gene leading to Dp71 loss. In this study, we aimed to restore brain Dp71 expression in the Dp71-null transgenic mouse using an adeno-associated virus (AAV) administrated either by intracardiac injections at P4 (ICP4) or by bilateral intracerebroventricular (ICV) injections in adults. ICP4 delivery of the AAV9-Dp71 vector enabled the expression of 2 to 14% of brain Dp71, while ICV delivery enabled the overexpression of Dp71 in the hippocampus and cortex of adult mice, with anecdotal expression in the cerebellum. The restoration of Dp71 was mostly located in the glial endfeet that surround capillaries, and it was associated with partial localization of Dp71-associated proteins, α1-syntrophin and AQP4 water channels, suggesting proper restoration of a scaffold of proteins involved in blood-brain barrier function and water homeostasis. However, this did not result in significant improvements in behavioral disturbances displayed by Dp71-null mice. The potential and limitations of this AAV-mediated strategy are discussed. This proof-of-concept study identifies key molecular markers to estimate the efficiencies of Dp71 rescue strategies and opens new avenues for enhancing gene therapy targeting cognitive disorders associated with a subgroup of severely affected DMD patients.

Liver directed adeno-associated viral vectors to treat metabolic disease

The liver is the metabolic center of the body and an ideal target for gene therapy of inherited metabolic disorders (IMDs). Adeno-associated viral (AAV) vectors can deliver transgenes to the liver with high efficiency and specificity and a favorable safety profile. Recombinant AAV vectors contain only the transgene cassette, and their payload is converted to non-integrating circular double-stranded DNA episomes, which can provide stable expression from months to years. Insights from cellular studies and preclinical animal models have provided valuable information about AAV capsid serotypes with a high liver tropism. These vectors have been applied successfully in the clinic, particularly in trials for hemophilia, resulting in the first approved liver-directed gene therapy. Lessons from ongoing clinical trials have identified key factors affecting efficacy and safety that were not readily apparent in animal models. Circumventing pre-existing neutralizing antibodies to the AAV capsid, and mitigating adaptive immune responses to transduced cells are critical to achieving therapeutic benefit. Combining the high efficiency of AAV delivery with genome editing is a promising path to achieve more precise control of gene expression. The primary safety concern for liver gene therapy with AAV continues to be the small risk of tumorigenesis from rare vector integrations. Hepatotoxicity is a key consideration in the safety of neuromuscular gene therapies which are applied at substantially higher doses. The current knowledge base and toolkit for AAV is well developed, and poised to correct some of the most severe IMDs with liver-directed gene therapy.

In vivo lentiviral vector gene therapy to cure hereditary tyrosinemia type 1 and prevent development of precancerous and cancerous lesions

Conventional therapy for hereditary tyrosinemia type-1 (HT1) with 2-(2-nitro-4-trifluoromethylbenzoyl)−1,3-cyclohexanedione (NTBC) delays and in some cases fails to prevent disease progression to liver fibrosis, liver failure, and activation of tumorigenic pathways. Here we demonstrate cure of HT1 by direct, in vivo administration of a therapeutic lentiviral vector targeting the expression of a human fumarylacetoacetate hydrolase (FAH) transgene in the porcine model of HT1. This therapy is well tolerated and provides stable long-term expression of FAH in pigs with HT1. Genomic integration displays a benign profile, with subsequent fibrosis and tumorigenicity gene expression patterns similar to wild-type animals as compared to NTBC-treated or diseased untreated animals. Indeed, the phenotypic and genomic data following in vivo lentiviral vector administration demonstrate comparative superiority over other therapies including ex vivo cell therapy and therefore support clinical application of this approach.

Hereditary tyrosinemia type 1 (HT1) is an inborn error of metabolism caused by a deficiency in fumarylacetoacetate hydrolase (FAH). Here, the authors show in an animal model that HT1 can be treated via in vivo portal vein administration of a lentiviral vector carrying the human FAH transgene.

Intermittent lipid nanoparticle mRNA administration prevents cortical dysmyelination associated with arginase deficiency

Arginase deficiency is associated with prominent neuromotor features, including spastic diplegia, clonus, and hyperreflexia; intellectual disability and progressive neurological decline are other signs. In a constitutive murine model, we recently described leukodystrophy as a significant component of the central nervous system features of arginase deficiency. In the present studies, we sought to examine if the administration of a lipid nanoparticle carrying human ARG1 mRNA to constitutive knockout mice could prevent abnormalities in myelination associated with arginase deficiency. Imaging of the cingulum, striatum, and cervical segments of the corticospinal tract revealed a drastic reduction of myelinated axons; signs of degenerating axons were also present with thin myelin layers. Lipid nanoparticle/ARG1 mRNA administration resulted in both light and electron microscopic evidence of a dramatic recovery of myelin density compared with age-matched controls; oligodendrocytes were seen to be extending processes to wrap many axons. Abnormally thin myelin layers, when myelination was present, were resolved with intermittent mRNA administration, indicative of not only a greater density of myelinated axons but also an increase in the thickness of the myelin sheath. In conclusion, lipid nanoparticle/ARG1 mRNA administration in arginase deficiency prevents the associated leukodystrophy and restores normal oligodendrocyte function.

Gene Therapy for Acquired and Genetic Cholestasis

Cholestatic diseases can be caused by the dysfunction of transporters involved in hepatobiliary circulation. Although pharmacological treatments constitute the current standard of care for these diseases, none are curative, with liver transplantation being the only long-term solution for severe cholestasis, albeit with many disadvantages. Liver-directed gene therapy has shown promising results in clinical trials for genetic diseases, and it could constitute a potential new therapeutic approach for cholestatic diseases. Many preclinical gene therapy studies have shown positive results in animal models of both acquired and genetic cholestasis. The delivery of genes that reduce apoptosis or fibrosis or improve bile flow has shown therapeutic effects in rodents in which cholestasis was induced by drugs or bile duct ligation. Most studies targeting inherited cholestasis, such as progressive familial intrahepatic cholestasis (PFIC), have focused on supplementing a correct version of a mutated gene to the liver using viral or non-viral vectors in order to achieve expression of the therapeutic protein. These strategies have generated promising results in treating PFIC3 in mouse models of the disease. However, important challenges remain in translating this therapy to the clinic, as well as in developing gene therapy strategies for other types of acquired and genetic cholestasis.

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.

Long-term functional correction of cystathionine β-synthase deficiency in mice by adeno-associated viral gene therapy

Cystathionine β-synthase (CBS) deficiency is a recessive inborn error of sulfur metabolism characterized by elevated blood levels of total homocysteine (tHcy). Patients diagnosed with CBS deficiency are currently treated by a combination of vitamin supplementation and restriction of foods containing the homocysteine precursor methionine, but the effectiveness of this therapy is limited due to poor compliance. A mouse model for CBS deficiency (Tg-I278T Cbs^-/- ) was used to evaluate a potential gene therapy approach to treat CBS deficiency utilizing an AAVrh.10-based vector containing the human CBS cDNA downstream of the constitutive, strong CAG promoter (AAVrh.10hCBS). Mice were administered a single dose of virus and followed for up to 1 year. The data demonstrated a dose-dependent increase in liver CBS activity and a dose-dependent decrease in serum tHcy. Liver CBS enzyme activity at 1 year was similar to Cbs^+/- control mice. Mice given the highest dose (5.6 × 10¹¹ genomes/mouse) had mean serum tHcy decrease of 97% 1 week after injection and an 81% reduction 1 year after injection. Treated mice had either full- or substantial correction of alopecia, bone loss, and fat mass phenotypes associated with Cbs deficiency in mice. Our findings show that AAVrh.10-based gene therapy is highly effective in treating CBS deficiency in mice and supports additional pre-clinical testing for eventual use human trials.

Targeted deletion of PAC1 receptors in retinal neurons enhances neuron loss and axonopathy in a model of multiple sclerosis and optic neuritis

Chronic inflammation drives synaptic loss in multiple sclerosis (MS) and is also commonly observed in other neurodegenerative diseases. Clinically approved treatments for MS provide symptomatic relief but fail to halt neurodegeneration and neurological decline. Studies in animal disease models have demonstrated that the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP, ADCYAP1) exhibits anti-inflammatory, neuroprotective and regenerative properties. Anti-inflammatory actions appear to be mediated primarily by two receptors, VPAC1 and VPAC2, which also bind vasoactive intestinal peptide (VIP). Pharmacological experiments indicate that another receptor, PAC1 (ADCYAP1R1), which is highly selective for PACAP, provides protection to neurons, although genetic evidence and other mechanistic information is lacking. To determine if PAC1 receptors protect neurons in a cell-autonomous manner, we used adeno-associated virus (AAV2) to deliver Cre recombinase to the retina of mice harboring floxed PAC1 alleles. Mice were then subjected to chronic experimental autoimmune encephalomyelitis (EAE), a disease model that recapitulates major clinical and pathological features of MS and associated optic neuritis. Unexpectedly, deletion of PAC1 in naïve mice resulted in a deficit of retinal ganglionic neurons (RGNs) and their dendrites, suggesting a homeostatic role of PAC1. Moreover, deletion of PAC1 resulted in increased EAE-induced loss of a subpopulation of RGNs purported to be vulnerable in animal models of glaucoma. Increased axonal pathology and increased secondary presence of microglia/macrophages was also prominently seen in the optic nerve. These findings demonstrate that neuronal PAC1 receptors play a homeostatic role in protecting RGNs and directly protects neurons and their axons against neuroinflammatory challenge. SIGNIFICANCE STATEMENT: Chronic inflammation is a major component of neurodegenerative diseases and plays a central role in multiple sclerosis (MS). Current treatments for MS do not prevent neurodegeneration and/or neurological decline. The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to have anti-inflammatory, neuroprotective and regenerative properties but the cell type- and receptor-specific mechanisms are not clear. To test whether the protective effects of PACAP are direct on the PAC1 receptor subtype on neurons, we delete PAC1 receptors from neurons and investigate neuropathologigical changes in an animal model of MS. The findings demonstrate that PAC1 receptors on neurons play a homeostatic role in maintaining neuron health and can directly protect neurons and their axons during neuroinflammatory disease.

Overexpression of human BAG3P209L in mice causes restrictive cardiomyopathy

An amino acid exchange (P209L) in the HSPB8 binding site of the human co-chaperone BAG3 gives rise to severe childhood cardiomyopathy. To phenocopy the disease in mice and gain insight into its mechanisms, we generated humanized transgenic mouse models. Expression of human BAG3^P209L-eGFP in mice caused Z-disc disintegration and formation of protein aggregates. This was accompanied by massive fibrosis resulting in early-onset restrictive cardiomyopathy with increased mortality as observed in patients. RNA-Seq and proteomics revealed changes in the protein quality control system and increased autophagy in hearts from hBAG3^P209L-eGFP mice. The mutation renders hBAG3^P209L less soluble in vivo and induces protein aggregation, but does not abrogate hBAG3 binding properties. In conclusion, we report a mouse model mimicking the human disease. Our data suggest that the disease mechanism is due to accumulation of hBAG3^P209L and mouse Bag3, causing sequestering of components of the protein quality control system and autophagy machinery leading to sarcomere disruption.

An amino acid exchange (P209L) in the human co-chaperone BAG3 gives rise to severe childhood restrictive cardiomyopathy. Here the authors describe humanized transgenic mouse models which phenocopy the disease and provide insight into the pathogenic mechanisms.

In vivo Dominant-Negative Effect of an SCN5A Brugada Syndrome Variant

Loss-of-function mutations in the cardiac Na⁺ channel α-subunit Na_v1.5, encoded by SCN5A, cause Brugada syndrome (BrS), a hereditary disease characterized by sudden cardiac death due to ventricular fibrillation. We previously evidenced in vitro the dominant-negative effect of the BrS Na_v1.5-R104W variant, inducing retention of wild-type (WT) channels and leading to a drastic reduction of the resulting Na⁺ current (I_Na). To explore this dominant-negative effect in vivo, we created a murine model using adeno-associated viruses (AAVs).

High Levels of Frataxin Overexpression Lead to Mitochondrial and Cardiac Toxicity in Mouse Models

Friedreich ataxia (FA) is currently an incurable inherited mitochondrial disease caused by reduced levels of frataxin (FXN). Cardiac dysfunction is the main cause of premature death in FA. Adeno-associated virus (AAV)-mediated gene therapy constitutes a promising approach for FA, as demonstrated in cardiac and neurological mouse models. While the minimal therapeutic level of FXN protein to be restored and biodistribution have recently been defined for the heart, it is unclear if FXN overexpression could be harmful. Indeed, depending on the vector delivery route and dose administered, the resulting FXN protein level could reach very high levels in the heart, cerebellum, or off-target organs such as the liver. The present study demonstrates safety of FXN cardiac overexpression up to 9-fold the normal endogenous level but significant toxicity to the mitochondria and heart above 20-fold. We show gradual severity with increasing FXN overexpression, ranging from subclinical cardiotoxicity to left ventricle dysfunction. This appears to be driven by impairment of the mitochondria respiratory chain and ultrastructure, which leads to cardiomyocyte subcellular disorganization, cell death, and fibrosis. Overall, this study underlines the need, during the development of gene therapy approaches, to consider appropriate vector expression level, long-term safety, and biomarkers to monitor such events.

Stress-Induced Mouse Model of the Cardiac Manifestations of Friedreich's Ataxia Corrected by AAV-mediated Gene Therapy

Friedreich's ataxia (FA), an autosomal recessive disorder caused by a deficiency in the expression of frataxin (FXN), is characterized by progressive ataxia and hypertrophic cardiomyopathy. Although cardiac dysfunction is the most common cause of mortality in FA, the cardiac disease remains subclinical for most of the clinical course because the neurologic disease limits muscle oxygen demands. Previous FXN knockout mouse models exhibit fatal cardiomyopathy similar to human FA, but in contrast to the human condition, untreated mice become moribund by 2 months of age, unlike humans where the cardiac disease often does not manifest until the third decade. The study was designed to create a mouse model for early FA disease relevant to the time for which a gene therapy would likely be most effective. To generate a cardiac-specific mouse model of FA cardiomyopathy similar to the human disease, we used a cardiac promoter (αMyhc) driving CRE recombinase cardiac-specific excision of FXN exon 4 to generate a mild, cardiac-specific FA model that is normal at rest, but exhibits the cardiac phenotype with stress. The hearts of αMyhc mice had decreased levels of FXN and activity of the mitochondrial complex II/complex IV respiratory chain. At rest, αMyhc mice exhibited normal cardiac function as assessed by echocardiographic assessment of ejection fraction and fractional shortening, but when the heart was stressed chemically with dobutamine, αMyhc mice compared with littermate control mice had a 62% reduction in the stress ejection fraction (p < 2 × 10-4) and 71% reduction in stress-related fractional shortening (p < 10-5). When assessing functional cardiac performance using running on an inclined treadmill, αMyhc mice stayed above the midline threefold less than littermate controls (p < 0.02). A one-time intravenous administration of 1011 genome copies of AAVrh.10hFXN, an adeno-associated virus (AAV) serotype rh10 gene transfer vector expressing human FXN, corrected the stress-induced ejection fraction and fractional shortening phenotypes. Treated αMyhc mice exhibited exercise performance on a treadmill indistinguishable from littermate controls (p > 0.07). These αMyhc mice provide an ideal model to study long-term cardiac complications due to FA and AAV-mediated gene therapy correction of stress-induced cardiac phenotypes typical of human FA.

Intrathecal AAVrh10 corrects biochemical and histological hallmarks of mucopolysaccharidosis VII mice and improves behavior and survival

Mucopolysaccharidosis (MPS) type VII is a lysosomal storage disease caused by ß-glucuronidase deficiency, prompting glycosaminoglycan accumulation in enlarged vesicles, leading to peripheral and neuronal dysfunction. Here, we present a gene therapy strategy using lumbar puncture of AAVrh10 encoding human β-glucuronidase (AAVrh10-GUSB) to adult MPS VII mice. This minimally invasive technique efficiently delivers the recombinant vector to the cerebrospinal fluid (CSF) with a single intrathecal injection. We show that AAVrh10 delivery to the CSF allows global, stable transduction of CNS structures. In addition, drainage of AAVrh10-GUSB from the CSF to the bloodstream resulted in the transduction of somatic organs such as liver, which provided a systemic β-glucuronidase source sufficient to achieve serum enzyme activity comparable to wild type mice. ß-glucuronidase levels were enough to correct biochemical and histopathological hallmarks of the disease in the CNS and somatic organs at short and long term. Moreover, the progression of the bone pathology was also reduced. Importantly, the biochemical correction led to a significant improvement in the physical, cognitive and emotional characteristics of MPS VII mice, and doubling their life span. Our strategy may have implications for gene therapy in patients with lysosomal storage diseases.

Comparative Analysis of the Capsid Structures of AAVrh.10, AAVrh.39, and AAV8

Adeno-associated viruses (AAVs) from clade E are often used as vectors in gene delivery applications. This clade includes rhesus isolate 10 (AAVrh.10) and 39 (AAVrh.39) which, unlike representative AAV8, are capable of crossing the blood-brain barrier (BBB), thereby enabling the delivery of therapeutic genes to the central nervous system. Here, the capsid structures of AAV8, AAVrh.10 and AAVrh.39 have been determined by cryo-electron microscopy and three-dimensional image reconstruction to 3.08-, 2.75-, and 3.39-Å resolution, respectively, to enable a direct structural comparison. AAVrh.10 and AAVrh.39 are 98% identical in amino acid sequence but only ∼93.5% identical to AAV8. However, the capsid structures of all three viruses are similar, with only minor differences observed in the previously described surface variable regions, suggesting that specific residues S269 and N472, absent in AAV8, may confer the ability to cross the BBB in AAVrh.10 and AAVrh.39. Head-to-head comparison of empty and genome-containing particles showed DNA ordered in the previously described nucleotide-binding pocket, supporting the suggested role of this pocket in DNA packaging for the Dependoparvovirus The structural characterization of these viruses provides a platform for future vector engineering efforts toward improved gene delivery success with respect to specific tissue targeting, transduction efficiency, antigenicity, or receptor retargeting.IMPORTANCE Recombinant adeno-associated virus vectors (rAAVs), based on AAV8 and AAVrh.10, have been utilized in multiple clinical trials to treat different monogenetic diseases. The closely related AAVrh.39 has also shown promise in vivo As recently attained for other AAV biologics, e.g., Luxturna and Zolgensma, based on AAV2 and AAV9, respectively, the vectors in this study will likely gain U.S. Food and Drug Administration approval for commercialization in the near future. This study characterized the capsid structures of these clinical vectors at atomic resolution using cryo-electron microscopy and image reconstruction for comparative analysis. The analysis suggested two key residues, S269 and N472, as determinants of BBB crossing for AAVrh.10 and AAVrh.39, a feature utilized for central nervous system delivery of therapeutic genes. The structure information thus provides a platform for engineering to improve receptor retargeting or tissue specificity. These are important challenges in the field that need attention. Capsid structure information also provides knowledge potentially applicable for regulatory product approval.

High-Throughput In Vitro, Ex Vivo, and In Vivo Screen of Adeno-Associated Virus Vectors Based on Physical and Functional Transduction

Adeno-associated virus (AAV) vectors are quickly becoming the vectors of choice for therapeutic gene delivery. To date, hundreds of natural isolates and bioengineered variants have been reported. While factors such as high production titer and low immunoreactivity are important to consider, the ability to deliver the genetic payload (physical transduction) and to drive high transgene expression (functional transduction) remains the most important feature when selecting AAV variants for clinical applications. Reporter expression assays are the most commonly used methods for determining vector fitness. However, such approaches are time consuming and become impractical when evaluating a large number of variants. Limited access to primary human tissues or challenging model systems further complicates vector testing. To address this problem, convenient high-throughput methods based on next-generation sequencing (NGS) are being developed. To this end, we built an AAV Testing Kit that allows inherent flexibility in regard to number and type of AAV variants included, and is compatible with in vitro, ex vivo, and in vivo applications. The Testing Kit presented here consists of a mix of 30 known AAVs where each variant encodes a CMV-eGFP cassette and a unique barcode in the 3′-untranslated region of the eGFP gene, allowing NGS-barcode analysis at both the DNA and RNA/cDNA levels. To validate the AAV Testing Kit, individually packaged barcoded variants were mixed at an equal ratio and used to transduce cells/tissues of interest. DNA and RNA/cDNA were extracted and subsequently analyzed by NGS to determine the physical/functional transduction efficiencies. We were able to assess the transduction efficiencies of immortalized cells, primary cells, and induced pluripotent stem cells in vitro, as well as in vivo transduction in naïve mice and a xenograft liver model. Importantly, while our data validated previously reported transduction characteristics of individual capsids, we also identified novel previously unknown tropisms for some AAV variants.

Gene therapy for progressive familial intrahepatic cholestasis type 3 in a clinically relevant mouse model

Progressive familial intrahepatic cholestasis type 3 (PFIC3) is a rare monogenic disease caused by mutations in the ABCB4 gene, resulting in a reduction in biliary phosphatidylcholine. Reduced biliary phosphatidylcholine cannot counteract the detergent effects of bile salts, leading to cholestasis, cholangitis, cirrhosis and ultimately liver failure. Here, we report results from treating two- or five-week-old Abcb4-/- mice with an AAV vector expressing human ABCB4, resulting in significant decreases of PFIC3 disease biomarkers. All male mice achieved a sustained therapeutic effect up through 12 weeks, but the effect was achieved in only 50% of females. However, two-week-old females receiving a second inoculation three weeks later maintained the therapeutic effect. Upon sacrifice, markers of PFIC3 disease such as, hepatosplenomegaly, biliary phosphatidylcholine and liver histology were significantly improved. Thus, AAV-mediated gene therapy successfully prevented PFIC3 symptoms in a clinically relevant mouse model, representing a step forward in improving potential therapy options for PFIC3 patients.

Lipid nanoparticle-targeted mRNA therapy as a treatment for the inherited metabolic liver disorder arginase deficiency

Arginase deficiency is caused by biallelic mutations in arginase 1 (ARG1), the final step of the urea cycle, and results biochemically in hyperargininemia and the presence of guanidino compounds, while it is clinically notable for developmental delays, spastic diplegia, psychomotor function loss, and (uncommonly) death. There is currently no completely effective medical treatment available. While preclinical strategies have been demonstrated, disadvantages with viral-based episomal-expressing gene therapy vectors include the risk of insertional mutagenesis and limited efficacy due to hepatocellular division. Recent advances in messenger RNA (mRNA) codon optimization, synthesis, and encapsulation within biodegradable liver-targeted lipid nanoparticles (LNPs) have potentially enabled a new generation of safer, albeit temporary, treatments to restore liver metabolic function in patients with urea cycle disorders, including ARG1 deficiency. In this study, we applied such technologies to successfully treat an ARG1-deficient murine model. Mice were administered LNPs encapsulating human codon-optimized ARG1 mRNA every 3 d. Mice demonstrated 100% survival with no signs of hyperammonemia or weight loss to beyond 11 wk, compared with controls that perished by day 22. Plasma ammonia, arginine, and glutamine demonstrated good control without elevation of guanidinoacetic acid, a guanidino compound. Evidence of urea cycle activity restoration was demonstrated by the ability to fully metabolize an ammonium challenge and by achieving near-normal ureagenesis; liver arginase activity achieved 54% of wild type. Biochemical and microscopic data showed no evidence of hepatotoxicity. These results suggest that delivery of ARG1 mRNA by liver-targeted nanoparticles may be a viable gene-based therapeutic for the treatment of arginase deficiency.

rAAVrh74.MCK.GALGT2 Protects against Loss of Hemodynamic Function in the Aging mdx Mouse Heart

Dilated cardiomyopathy is a common cause of death in patients with Duchenne muscular dystrophy (DMD). Gene therapies for DMD must, therefore, have a therapeutic impact in cardiac as well as skeletal muscles. Our previous studies have shown that GALGT2 overexpression in mdx skeletal muscles can prevent muscle damage. Here we have tested whether rAAVrh74.MCK.GALGT2 gene therapy in mdx cardiac muscle can prevent the loss of heart function. Treatment of mdx hearts with rAAVrh74.MCK.GALGT2 1 day after birth did not negatively alter hemodynamic function, tested at 3 months of age, and it prevented early left ventricular remodeling and expression of fibrotic gene markers. Intravenous treatment of mdx mice with rAAVrh74.MCK.GALGT2 at 2 months of age significantly improved stroke volume and cardiac output compared to mock-treated mice analyzed at 17 months, both at rest and after stimulation with dobutamine. rAAVrh74.MCK.GALGT2 treatment of mdx heart correlated with increased glycosylation of α-dystroglycan with the CT glycan and increased utrophin protein expression. These data provide the first demonstration that GALGT2 overexpression can inhibit the loss of cardiac function in the dystrophin-deficient heart and, thus, may benefit both cardiac and skeletal muscles in DMD patients.

Efficient transduction of adeno-associated virus vectors into gerbil hippocampus with an appropriate combination of viral capsids and promoters

Adeno-associated virus (AAV) is an ideal vector for gene transduction into the central nervous system because of its safety and efficiency. While it is currently widely used for clinical trials and is expected to become more widespread, the appropriate combination of viral serotypes and promoters have not been fully investigated. In this study, we compared the transduced gene expression of AAVrh10 to AAV5 in gerbil hippocampus using three different promoters, including cytomegalovirus (CMV), chicken β-actin promoter with the CMV immediate-early enhancer (CAG), and the Synapsin 1 (Syn1) promoter. Four-week-old male gerbils underwent stereotaxic injection with 1 × 10¹⁰ viral genome of AAV carrying green fluorescent protein (GFP). Quantification of the GFP-positive areas 3 weeks after injection showed that AAVrh10-CMV and AAVrh10-CAG were the most efficient (p < 0.001, compared with the control) and AAVrh10-Syn1 and AAV5-CMV were the next most efficient (p < 0.05, compared with the control). On the other hand, AAV5-Syn1 showed little expression, which was only observed at the injected site. In conclusion, we should note that some combinations of viral capsids and promoters can result in failure of gene delivery, while most of them will work appropriately in the transgene expression in the brain.

In Vivo Potency Assay for Adeno-Associated Virus-Based Gene Therapy Vectors Using AAVrh.10 as an Example

The development of a drug product requires rigorous methods of characterization and quality control to assure drug potency. Gene therapy products, a relatively new strategy for drug design with very few licensed examples, represent a unique challenge for the measure of potency. Unlike traditional drugs, potency for a gene therapeutic is a tally of the measures of multiple steps, including infectivity, transcription, translation, protein modifications, proper localization of the protein product, and protein function. This is particularly challenging for products based on the adeno-associated virus (AAV) platform, which has poor in vitro infectivity, limiting the sensitivity and thus the usefulness of cell-based assays. A rigorous in vivo assay has been established that separately evaluates infection, transcription, and resulting protein levels with specifications for each based on real time polymerase chain reaction (DNA and RNA) and standard protein assays. For an acceptance criterion, an administered vector must have vector DNA, transgene mRNA, and transgene expressed protein each concurrently meet individual specifications or the production lot fails. Using the AAVrh.10 serotype as a model vector and three different transgenes as examples, the assay is based on intravenous administration of the vector to male mice. At 2 weeks, the harvested liver is homogenized and assessed for vector genome levels (to assess for vector delivery), mRNA (to assess vector infectivity and transcription), and protein in the liver or serum (to assess protein expression). For all AAV vectors, the assay is robust and reproducible: vector DNA (linearity 10²-10⁹ copies, coefficient of variation) intra-assay <0.8%, inter-assay <0.5%; mRNA intra-assay <3.3%, inter-assay <3.4%. The reproducibility of the assay for transgene expressed protein is product specific. This in vivo potency assay is a strategy for characterization and a quantitative lot release test, providing a path forward to meet regulatory drug requirements for any AAV gene therapy vectors.

Adeno-Associated Virus-Mediated Gene Transfer of Tissue Inhibitor of Metalloproteinases-1 Impairs Neutrophil Extracellular Trap Formation and Ameliorates Hepatic Ischemia and Reperfusion Injury

Matrix metalloproteinase-9 (MMP-9) is abundantly expressed by infiltrating leukocytes and contributes to the pathogenesis of hepatic ischemia and reperfusion injury (IRI). On the other hand, its physiological inhibitor, the tissue inhibitor of metalloproteinases-1 (TIMP-1), is available in insufficient levels to hamper MMP-9 activity during hepatic IRI. In this study, we generated recombinant adeno-associated virus type 8 vectors (rAAV8) encoding mouse TIMP-1 driven by a liver-specific thyroxine-binding globulin promoter as a strategy to increase the levels of TIMP-1 during liver IRI. Biodistribution analysis confirmed selective overexpression of TIMP-1 in livers of rAAV8-TIMP-1 vector treated C57BL/6 mice. rAAV8-TIMP-1-treated mice showed reduced MMP-9 activity, diminished leukocyte trafficking and activation, lowered transaminase levels, and improved histology after liver IRI. Moreover, the rAAV8-TIMP-1 vector therapy enhanced significantly the 7-day survival rate of TIMP-1^-/- mice subjected to hepatic IRI. Neutrophils are the first cells recruited to inflamed tissues and, once activated, they release nuclear DNA-forming web-like structures, known as neutrophil extracellular traps. It was found that TIMP-1 has the ability to reduce formation of neutrophil extracellular traps and, consequently, limit the impact of neutrophil extracellular trap-mediated cytotoxicity in hepatic IRI. This is the first report demonstrating that TIMP-1 overexpression is hepatoprotective in ischemia and reperfusion injury. Hence, TIMP-1 may represent a promising molecule for drug development to treat liver IRI.

Human hepatocyte transplantation corrects the inherited metabolic liver disorder arginase deficiency in mice

The transplantation, engraftment, and expansion of primary hepatocytes have the potential to be an effective therapy for metabolic disorders of the liver including those of nitrogen metabolism. To date, such methods for the treatment of urea cycle disorders in murine models has only been minimally explored. Arginase deficiency, an inherited disorder of nitrogen metabolism that presents in the first two years of life, has the potential to be treated by such methods. To explore the potential of this approach, we mated the conditional arginase deficient mouse with a mouse model deficient in fumarylacetoacetate hydrolase (FAH) and with Rag2 and IL2-Rγ mutations to give a selective advantage to transplanted (normal) human hepatocytes. On day -1, a uroplasminogen-expressing adenoviral vector was administered intravenously followed the next day with the transplantation of 1 × 106 human hepatocytes (or vehicle alone) by intrasplenic injection. As the initial number of administered hepatocytes would be too low to prevent hepatotoxicity-induced mortality, NTBC cycling was performed to allow for hepatocyte expansion and repopulation. While all control mice died, all except one human hepatocyte transplanted mice survived. Four months after hepatocyte transplantation, 2 × 1011 genome copies of AAV-TBG-Cre recombinase was administered IV to disrupt endogenous hepatic arginase expression. While all control mice died within the first month, human hepatocyte transplanted mice did well. Ammonia and amino acids, analyzed in both groups before and after disruption of endogenous arginase expression, while well-controlled in the transplanted group, were markedly abnormal in the controls. Ammonium challenging further demonstrated the durability and functionality of the human repopulated liver. In conclusion, these studies demonstrate that human hepatocyte repopulation in the murine liver can result in effective treatment of arginase deficiency.

Adeno-associated virus serotype rh10 is a useful gene transfer vector for sensory nerves that innervate bone in immunodeficient mice

Adeno-associated virus (AAV) is frequently used to manipulate gene expression in the sensory nervous system for the study of pain mechanisms. Although some serotypes of AAV are known to have nerve tropism, whether AAV can distribute to sensory nerves that innervate the bone or skeletal tissue has not been shown. This information is crucial, since bone pain, including cancer-induced bone pain, is an area of high importance in pain biology. In this study, we found that AAVrh10 transduces neurons in the spinal cord and dorsal root ganglia of immunodeficient mice with higher efficacy than AAV2, 5, 6, 8, and 9 when injected intrathecally. Additionally, AAVrh10 has tropism towards sensory neurons in skeletal tissue, such as bone marrow and periosteum, while it occasionally reaches the sensory nerve fibers in the mouse footpad. Moreover, AAVrh10 has higher tropic affinity to large myelinated and small peptidergic sensory neurons that innervate bone, compared to small non-peptidergic sensory neurons that rarely innervate bone. Taken together, these results suggest that AAVrh10 is a useful gene delivery vector to target the sensory nerves innervating bone. This finding may lead to a greater understanding of the molecular mechanisms of chronic bone pain and cancer-induced bone pain.

Intrathecal administration of AAV/GALC vectors in 10-11-day-old twitcher mice improves survival and is enhanced by bone marrow transplant

Globoid cell leukodystrophy (GLD), or Krabbe disease, is an autosomal recessive neurodegenerative disease caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). Hematopoietic stem cell transplantation (HSCT) provides modest benefit in presymptomatic patients but is well short of a cure. Gene transfer experiments using viral vectors have shown some success in extending the survival in the mouse model of GLD, twitcher mice. The present study compares three single-stranded (ss) AAV serotypes, two natural and one engineered (with oligodendrocyte tropism), and a self-complementary (sc) AAV vector, all packaged with a codon-optimized murine GALC gene. The vectors were delivered via a lumbar intrathecal route for global CNS distribution on PND10-11 at a dose of 2 × 10(11) vector genomes (vg) per mouse. The results showed a similar significant extension of life span of the twitcher mice for all three serotypes (AAV9, AAVrh10, and AAV-Olig001) as well as the scAAV9 vector, compared to control cohorts. The rAAV gene transfer facilitated GALC biodistribution and detectable enzymatic activity throughout the CNS as well as in sciatic nerve and liver. When combined with BMT from syngeneic wild-type mice, there was significant improvement in survival for ssAAV9. Histopathological analysis of brain, spinal cord, and sciatic nerve showed significant improvement in preservation of myelin, with ssAAV9 providing the greatest benefit. In summary, we demonstrate that lumbar intrathecal delivery of rAAV/mGALCopt can significantly enhance the life span of twitcher mice treated at PND10-11 and that BMT synergizes with this treatment to improve the survival further. © 2016 Wiley Periodicals, Inc.

Spinal nociceptive circuit analysis with recombinant adeno-associated viruses: the impact of serotypes and promoters

Recombinant adeno-associated virus (rAAV) vector-mediated gene transfer into genetically defined neuron subtypes has become a powerful tool to study the neuroanatomy of neuronal circuits in the brain and to unravel their functions. More recently, this methodology has also become popular for the analysis of spinal cord circuits. To date, a variety of naturally occurring AAV serotypes and genetically modified capsid variants are available but transduction efficiency in spinal neurons, target selectivity, and the ability for retrograde tracing are only incompletely characterized. Here, we have compared the transduction efficiency of seven commonly used AAV serotypes after intraspinal injection. We specifically analyzed local transduction of different types of dorsal horn neurons, and retrograde transduction of dorsal root ganglia (DRG) neurons and of neurons in the rostral ventromedial medulla (RVM) and the somatosensory cortex (S1). Our results show that most of the tested rAAV vectors have similar transduction efficiency in spinal neurons. All serotypes analyzed were also able to transduce DRG neurons and descending RVM and S1 neurons via their spinal axon terminals. When comparing the commonly used rAAV serotypes to the recently developed serotype 2 capsid variant rAAV2retro, a > 20-fold increase in transduction efficiency of descending supraspinal neurons was observed. Conversely, transgene expression in retrogradely transduced neurons was strongly reduced when the human synapsin 1 (hSyn1) promoter was used instead of the strong ubiquitous hybrid cytomegalovirus enhancer/chicken β-actin promoter (CAG) or cytomegalovirus (CMV) promoter fragments. We conclude that the use of AAV2retro greatly increases transduction of neurons connected to the spinal cord via their axon terminals, while the hSyn1 promoter can be used to minimize transgene expression in retrogradely connected neurons of the DRG or brainstem. Cover Image for this issue: doi. 10.1111/jnc.13813.

Optimized AAV rh.10 Vectors That Partially Evade Neutralizing Antibodies during Hepatic Gene Transfer

Of the 12 common serotypes used for gene delivery applications, Adeno-associated virus (AAV)rh.10 serotype has shown sustained hepatic transduction and has the lowest seropositivity in humans. We have evaluated if further modifications to AAVrh.10 at its phosphodegron like regions or predicted immunogenic epitopes could improve its hepatic gene transfer and immune evasion potential. Mutant AAVrh.10 vectors were generated by site directed mutagenesis of the predicted targets. These mutant vectors were first tested for their transduction efficiency in HeLa and HEK293T cells. The optimal vector was further evaluated for their cellular uptake, entry, and intracellular trafficking by quantitative PCR and time-lapse confocal microscopy. To evaluate their potential during hepatic gene therapy, C57BL/6 mice were administered with wild-type or optimal mutant AAVrh.10 and the luciferase transgene expression was documented by serial bioluminescence imaging at 14, 30, 45, and 72 days post-gene transfer. Their hepatic transduction was further verified by a quantitative PCR analysis of AAV copy number in the liver tissue. The optimal AAVrh.10 vector was further evaluated for their immune escape potential, in animals pre-immunized with human intravenous immunoglobulin. Our results demonstrate that a modified AAVrh.10 S671A vector had enhanced cellular entry (3.6 fold), migrate rapidly to the perinuclear region (1 vs. >2 h for wild type vectors) in vitro, which further translates to modest increase in hepatic gene transfer efficiency in vivo. More importantly, the mutant AAVrh.10 vector was able to partially evade neutralizing antibodies (~27-64 fold) in pre-immunized animals. The development of an AAV vector system that can escape the circulating neutralizing antibodies in the host will substantially widen the scope of gene therapy applications in humans.

Rescue of the Functional Alterations of Motor Cortical Circuits in Arginase Deficiency by Neonatal Gene Therapy

Arginase 1 deficiency is a urea cycle disorder associated with hyperargininemia, spastic diplegia, loss of ambulation, intellectual disability, and seizures. To gain insight on how loss of arginase expression affects the excitability and synaptic connectivity of the cortical neurons in the developing brain, we used anatomical, ultrastructural, and electrophysiological techniques to determine how single-copy and double-copy arginase deletion affects cortical circuits in mice. We find that the loss of arginase 1 expression results in decreased dendritic complexity, decreased excitatory and inhibitory synapse numbers, decreased intrinsic excitability, and altered synaptic transmission in layer 5 motor cortical neurons. Hepatic arginase 1 gene therapy using adeno-associated virus rescued nearly all these abnormalities when administered to neonatal homozygous knock-out animals. Therefore, gene therapeutic strategies can reverse physiological and anatomical markers of arginase 1 deficiency and therefore may be of therapeutic benefit for the neurological disabilities in this syndrome.

SIGNIFICANCE STATEMENT

These studies are one of the few investigations to try to understand the underlying neurological dysfunction that occurs in urea cycle disorders and the only to examine arginase deficiency. We have demonstrated by multiple modalities that, in murine layer 5 cortical neurons, a gradation of abnormalities exists based on the functional copy number of arginase: intrinsic excitability is altered, there is decreased density in asymmetrical and perisomatic synapses, and analysis of the dendritic complexity is lowest in the homozygous knock-out. With neonatal administration of adeno-associated virus expressing arginase, there is near-total recovery of the abnormalities in neurons and cortical circuits, supporting the concept that neonatal gene therapy may prevent the functional abnormalities that occur in arginase deficiency.

The influence of rAAV2-mediated SOX2 delivery into neonatal and adult human RPE cells; a comparative study

Cell replacement is a promising therapy for degenerative diseases like age-related macular degeneration (AMD). Since the human retina lacks regeneration capacity, much attention has been directed toward persuading for cells that can differentiate into retinal neurons. In this report, we have investigated reprogramming of the human RPE cells and concerned the effect of donor age on the cellular fate as a critical determinant in reprogramming competence. We evaluated the effect of SOX2 over-expression in human neonatal and adult RPE cells in cultures. The coding region of human SOX2 gene was cloned into adeno-associated virus (AAV2) and primary culture of human neonatal/adult RPE cells were infected by recombinant virus. De-differentiation of RPE to neural/retinal progenitor cells was investigated by quantitative real-time PCR and ICC for neural/retinal progenitor cells' markers. Gene expression analysis showed 80-fold and 12-fold over-expression for SOX2 gene in infected neonatal and adult hRPE cells, respectively. The fold of increase for Nestin in neonatal and adult hRPE cells was 3.8-fold and 2.5-fold, respectively. PAX6 expression was increased threefold and 2.5-fold in neonatal/adult treated cultures. Howbeit, we could not detect rhodopsin, and CHX10 expression in neonatal hRPE cultures and expression of rhodopsin in adult hRPE cells. Results showed SOX2 induced human neonatal/adult RPE cells to de-differentiate toward retinal progenitor cells. However, the increased number of PAX6, CHX10, Thy1, and rhodopsin positive cells in adult hRPE treated cultures clearly indicated the considerable generation of neuro-retinal terminally differentiated cells.

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.

Structure of neurotropic adeno-associated virus AAVrh.8

Adeno-associated virus rhesus isolate 8 (AAVrh.8) is a leading vector for the treatment of neurological diseases due to its efficient transduction of neuronal cells and reduced peripheral tissue tropism. Toward identification of the capsid determinants for these properties, the structure of AAVrh.8 was determined by X-ray crystallography to 3.5 Å resolution and compared to those of other AAV isolates. The capsid viral protein (VP) structure consists of an αA helix and an eight-stranded anti-parallel β-barrel core conserved in parvoviruses, and large insertion loop regions between the β-strands form the capsid surface topology. The AAVrh.8 capsid exhibits the surface topology conserved in all AAVs: depressions at the icosahedral twofold axis and surrounding the cylindrical channel at the fivefold axis, and three protrusions around the threefold axis. A structural comparison to serotypes AAV2, AAV8, and AAV9, to which AAVrh.8 shares ∼ 84%, ∼ 91%, and ∼ 87% VP sequence identity, respectively, revealed differences in the surface loops known to affect receptor binding, transduction efficiency, and antigenicity. Consistent with this observation, biochemical assays showed that AAVrh.8 is unable to bind heparin and does not cross-react with conformational monoclonal antibodies and human donor serum directed against the other AAVs compared. This structure of AAVrh.8 thus identified capsid surface differences which can serve as template regions for rational design of vectors with enhanced transduction for specific tissues and escape pre-existing antibody recognition. These features are essential for the creation of an AAV vector toolkit that is amenable to personalized disease treatment.

Long-term Improvements in Lifespan and Pathology in CNS and PNS After BMT Plus One Intravenous Injection of AAVrh10-GALC in Twitcher Mice

Krabbe disease is an autosomal recessive disorder resulting from defects in the lysosomal enzyme galactocerebrosidase (GALC). GALC deficiency leads to severe neurological features. The only treatment for presymptomatic infantile patients and later-onset patients is hematopoietic stem cell transplantation (HSCT). This treatment is less than ideal with most patients eventually developing problems with gait and expressive language. Several naturally occurring animal models are available, including twitcher (twi) mice, which have been used for many treatment trials. Previous studies demonstrated that multiple injections of AAVrh10-GALC into the central nervous system (CNS) of neonatal twi mice resulted in significant improvements. Recently we showed that one i.v. injection of AAVrh10-GALC on PND10 resulted in normal GALC activity in the CNS and high activity in the peripheral nervous system (PNS). In the present study, a single i.v. injection of AAVrh10-GALC was given 1 day after bone marrow transplantation (BMT) on PND10. The mice show greatly extended lifespan and normal behavior with improved CNS and PNS findings. Since HSCT is the standard of care in human patients, adding this single i.v. injection of viral vector may greatly improve the treatment outcome.

Augmentation of transgene-encoded protein after neonatal injection of adeno-associated virus improves hepatic copy number without immune responses

BACKGROUND

Achieving persistent expression is a prerequisite for genetic therapies for inherited metabolic enzymopathies. Such disorders potentially could be treated with gene therapy shortly after birth to prevent pathology. However, rapid cell turnover leads to hepatic episomal vector loss, which diminishes effectiveness. The current studies assessed whether tolerance to transgene proteins expressed in the neonatal period is durable and if the expression may be augmented with subsequent adeno-associated virus (AAV) administration.

METHODS

AAV was administered to mice on day 2 with reinjection at 14 or at 14 and 42 d with examination of changes in hepatic copies and B and T cell-mediated immune responses.

RESULTS

Immune responses to the transgene protein and AAV were absent after neonatal administration. Reinjection at 14 or at 14 and 42 d resulted in augmented expression with greater hepatic genome copies. Unlike controls, immune responses to transgene proteins were not detected in animals injected as neonates and subsequently. However, while no immune response developed after neonatal administration, anticapsid immune responses developed with further injections suggesting immunological ignorance was the initial mechanism of unresponsiveness.

CONCLUSIONS

Persistence of transgene protein allows for tolerance induction permitting readministration of AAV to re-establish protein levels that decline with growth.

Adeno-associated virus serotypes for gene therapeutics

Gene transfer vectors based on adeno-associated virus (AAV) are showing exciting therapeutic promise in early phase clinical trials. The ability to cross-package the prototypic AAV2 vector genome into different capsids is a powerful way of conferring novel tropism and biology, with evolving capsid engineering technologies and directed evolution approaches further enhancing the utility and flexibility of these vectors. Novel properties of specific capsids show unpredictable species and cell-type specificity. Therefore, full realisation of the therapeutic potential of AAV vectors requires the development of more therapeutically predictive preclinical methods for evaluating capsid performance. This will strongly complement an iterative approach to the evaluation of capsid variants in the clinic and, should wherever possible, include the determination of gene transfer efficiencies.

Development of operational immunologic tolerance with neonatal gene transfer in nonhuman primates: preliminary studies

Achieving persistent expression is a prerequisite for effective genetic therapies for inherited disorders. These proof-of-concept studies focused on adeno-associated virus (AAV) administration to newborn monkeys. Serotype rh10 AAV expressing ovalbumin and green fluorescent protein (GFP) was administered intravenously at birth and compared with vehicle controls. At 4 months postnatal age, a second injection was administered intramuscularly, followed by vaccination at 1 year of age with ovalbumin and GFP. Ovalbumin was highest 2 weeks post administration in the treated monkey, which declined but remained detectable thereafter; controls demonstrated no expression. Long-term AAV genome copies were present in myocytes. At 4 weeks, neutralizing antibodies to rh10 were present in the experimental animal only. With AAV9 administration at 4 months, controls showed transient ovalbumin expression that disappeared with the development of strong anti-ovalbumin and anti-GFP antibodies. In contrast, increased and maintained ovalbumin expression was noted in the monkey administered AAV at birth, without antibody development. After vaccination, the experimental monkey maintained levels of ovalbumin without antibodies, whereas controls demonstrated high levels of antibodies. These preliminary studies suggest that newborn AAV administration expressing secreted and intracellular xenogenic proteins may result in persistent expression in muscle, and subsequent vector administration can result in augmented expression without humoral immune responses.

Systemic AAVrh10 provides higher transgene expression than AAV9 in the brain and the spinal cord of neonatal mice

Systemic delivery of self-complementary (sc) adeno-associated-virus vector of serotype 9 (AAV9) was recently shown to provide robust and widespread gene transfer to the central nervous system (CNS), opening new avenues for practical, and non-invasive gene therapy of neurological diseases. More recently, AAV of serotype rh10 (AAVrh10) was also found highly efficient to mediate CNS transduction after intravenous administration in mice. However, only a few studies compared AAV9 and AAVrh10 efficiencies, particularly in the spinal cord. In this study, we compared the transduction capabilities of AAV9 and AAVrh10 in the brain, the spinal cord, and the peripheral nervous system (PNS) after intravenous delivery in neonatal mice. As reported in previous studies, AAVrh10 achieved either similar or higher transduction than AAV9 in all the examined brain regions. The superiority of AAVrh10 over AAV9 appeared statistically significant only in the medulla and the cerebellum, but a clear trend was also observed in other structures like the hippocampus or the cortex. In contrast to previous studies, we found that AAVrh10 was more efficient than AAV9 for transduction of the dorsal spinal cord and the lower motor neurons (MNs). However, differences between the two serotypes appeared mainly significant at low dose, and surprisingly, increasing the dose did not improve AAVrh10 distribution in the spinal cord, in contrary to AAV9. Similar dose-related differences between transduction efficiency of the two serotypes were also observed in the sciatic nerve. These findings suggest differences in the transduction mechanisms of these two serotypes, which both hold great promise for gene therapy of neurological diseases.

Mechanism-based combination treatment dramatically increases therapeutic efficacy in murine globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD, Krabbe disease) is a lysosomal storage disease (LSD) caused by a deficiency in galactocerebrosidase (GALC) activity. In the absence of GALC activity, the cytotoxic lipid, galactosylsphingosine (psychosine), accumulates in the CNS and peripheral nervous system. Oligodendrocytes and Schwann cells are particularly sensitive to psychosine, thus leading to a demyelinating phenotype. Although hematopoietic stem-cell transplantation provides modest benefit in both presymptomatic children and the murine model (Twitcher), there is no cure for GLD. In addition, GLD has been relatively refractory to virtually every experimental therapy attempted. Here, Twitcher mice were simultaneously treated with CNS-directed gene therapy, substrate reduction therapy, and bone marrow transplantation to target the primary pathogenic mechanism (GALC deficiency) and two secondary consequences of GALC deficiency (psychosine accumulation and neuroinflammation). Simultaneously treating multiple pathogenic targets resulted in an unprecedented increase in life span with improved motor function, persistent GALC expression, nearly normal psychosine levels, and decreased neuroinflammation. Treating the primary pathogenic mechanism and secondary targets will likely improve therapeutic efficacy for other LSDs with complex pathological and clinical presentations.

Efficient gene delivery to photoreceptors using AAV2/rh10 and rescue of the Rho(-/-) mouse

As gene therapies for various forms of retinal degeneration progress toward human clinical trial, it will be essential to have a repertoire of safe and efficient vectors for gene delivery to the target cells. Recombinant adeno-associated virus (AAV) serotype 2/2 has been shown to be well tolerated in the human retina and has provided efficacy in human patients for some inherited retinal degenerations. In this study, the AAV2/8 and AAV2/rh10 serotypes have been compared as a means of gene delivery to mammalian photoreceptor cells using a photoreceptor specific promoter for transgene expression. Both AAV2/8 and AAV2/rh10 provided rescue of the retinal degeneration present in the rhodopsin knockout mouse, with similar levels of benefit as evaluated by molecular, histological, and functional readouts. Transgene expression levels were significantly higher (fivefold) 1 week postsubretinal injection when employing AAV2/8 for rhodopsin gene delivery compared to AAV2/rh10, and were indistinguishable by 6 weeks postadministration of vector. This study reports the use of the AAV2/rh10 serotype to provide rescue in a degenerating retina and provides a comparative evaluation of AAV2/rh10 with respect to AAV2/8, a serotype regarded as providing efficient delivery to photoreceptors.

Amand T, Si J, Goossens S, Haenebalcke L, Haigh JJ, Kyriakopoulou L, Schulze A, Funk CD. Strategies to rescue the consequences of inducible arginase-1 deficiency in mice

Arginase-1 catalyzes the conversion of arginine to ornithine and urea, which is the final step of the urea cycle used to remove excess ammonia from the body. Arginase-1 deficiency leads to hyperargininemia in mice and man with severe lethal consequences in the former and progressive neurological impairment to varying degrees in the latter. In a tamoxifen-induced arginase-1 deficient mouse model, mice succumb to the enzyme deficiency within 2 weeks after inducing the knockout and retain <2 % enzyme in the liver. Standard clinical care regimens for arginase-1 deficiency (low-protein diet, the nitrogen-scavenging drug sodium phenylbutyrate, ornithine supplementation) either failed to extend lifespan (ornithine) or only minimally prolonged lifespan (maximum 8 days with low-protein diet and drug). A conditional, tamoxifen-inducible arginase-1 transgenic mouse strain expressing the enzyme from the Rosa26 locus modestly extended lifespan of neonatal mice, but not that of 4-week old mice, when crossed to the inducible arginase-1 knockout mouse strain. Delivery of an arginase-1/enhanced green fluorescent fusion construct by adeno-associated viral delivery (rh10 serotype with a strong cytomegalovirus-chicken β-actin hybrid promoter) rescued about 30% of male mice with lifespan prolongation to at least 6 months, extensive hepatic expression and restoration of significant enzyme activity in liver. In contrast, a vector of the AAV8 serotype driven by the thyroxine-binding globulin promoter led to weaker liver expression and did not rescue arginase-1 deficient mice to any great extent. Since the induced arginase-1 deficient mouse model displays a much more severe phenotype when compared to human arginase-1 deficiency, these studies reveal that it may be feasible with gene therapy strategies to correct the various manifestations of the disorder and they provide optimism for future clinical studies.

Intravenous injection of AAVrh10-GALC after the neonatal period in twitcher mice results in significant expression in the central and peripheral nervous systems and improvement of clinical features

Globoid cell leukodystrophy (GLD) or Krabbe disease is an autosomal recessive disorder resulting from the defective lysosomal enzyme galactocerebrosidase (GALC). The lack of GALC enzyme leads to severe neurological symptoms. While most human patients are infants who do not survive beyond 2 years of age, older patients are also diagnosed. In addition to human patients, several naturally occurring animal models, including dog, mouse, and monkey, have also been identified. The mouse model of Krabbe disease, twitcher (twi) mouse has been used for many treatment trials including gene therapy. Using the combination of intracerebroventricular, intracerebellar, and intravenous (iv) injection of the adeno-associated virus serotype rh10 (AAVrh10) expressing mouse GALC in neonate twi mice we previously have demonstrated a significantly extended normal life and exhibition of normal behavior in treated mice. In spite of the prolonged healthy life of these treated mice and improved myelination, it is unlikely that using multiple injection sites for viral administration will be approved for treatment of human patients. In this study, we have explored the outcome of the single iv injection of viral vector at post-natal day 10 (PND10). This has resulted in increased GALC activity in the central nervous system (CNS) and high GALC activity in the peripheral nervous system (PNS). As we have shown previously, an iv injection of AAVrh10 at PND2 results in a small extension of life beyond the typical lifespan of the untreated twi mice (~40 days). In this study, we report that mice receiving a single iv injection at PND10 had no tremor and continued to gain weight until a few weeks before they died. On average, they lived 20-25 days longer than untreated mice. We anticipate that this strategy in combination with other therapeutic options may be beneficial and applicable to treatment of human patients.

Minimal ureagenesis is necessary for survival in the murine model of hyperargininemia treated by AAV-based gene therapy

Hyperammonemia is less severe in arginase 1 deficiency compared with other urea cycle defects. Affected patients manifest hyperargininemia and infrequent episodes of hyperammonemia. Patients typically suffer from neurological impairment with cortical and pyramidal tract deterioration, spasticity, loss of ambulation, seizures and intellectual disability; death is less common than with other urea cycle disorders. In a mouse model of arginase I deficiency, the onset of symptoms begins with weight loss and gait instability, which progresses toward development of tail tremor with seizure-like activity; death typically occurs at about 2 weeks of life. Adeno-associated viral vector gene replacement strategies result in long-term survival of mice with this disorder. With neonatal administration of vector, the viral copy number in the liver greatly declines with hepatocyte proliferation in the first 5 weeks of life. Although the animals do survive, it is not known from a functional standpoint how well the urea cycle is functioning in the adult animals that receive adeno-associated virus. In these studies, we administered [1-13C] acetate to both littermate controls and adeno-associated virus-treated arginase 1 knockout animals and examined flux through the urea cycle. Circulating ammonia levels were mildly elevated in treated animals. Arginine and glutamine also had perturbations. Assessment 30 min after acetate administration demonstrated that ureagenesis was present in the treated knockout liver at levels as low at 3.3% of control animals. These studies demonstrate that only minimal levels of hepatic arginase activity are necessary for survival and ureagenesis in arginase-deficient mice and that this level of activity results in control of circulating ammonia. These results may have implications for potential therapy in humans with arginase deficiency.

Efficient central nervous system AAVrh10-mediated intrathecal gene transfer in adult and neonate rats

Intracerebral administration of recombinant adeno-associated vector (AAV) has been performed in several clinical trials. However, delivery into the brain requires multiple injections and is not efficient to target the spinal cord, thus limiting its applications. To assess widespread and less invasive strategies, we tested intravenous (IV) or intrathecal (that is, in the cerebrospinal fluid (CSF)) delivery of a rAAVrh10-egfp vector in adult and neonate rats and studied the effect of the age at injection on neurotropism. IV delivery is more efficient in neonates and targets predominantly Purkinje cells of the cerebellum and sensory neurons of the spinal cord and dorsal root ganglia. A single intra-CSF administration of AAVrh10, single strand or oversized self-complementary, is efficient for the targeting of neurons in the cerebral hemispheres, cerebellum, brainstem and spinal cord. Green fluorescent protein (GFP) expression is more widespread in neonates when compared with adults. More than 50% of motor neurons express GFP in the three segments of the spinal cord in neonates and in the cervical and thoracic regions in adults. Neurons are almost exclusively transduced in neonates, whereas neurons, astrocytes and rare oligodendrocytes are targeted in adults. These results expand the possible routes of delivery of AAVrh10, a serotype that has shown efficacy and safety in clinical trials concerning neurodegenerative diseases.

Experimental therapies in the murine model of globoid cell leukodystrophy

BACKGROUND

Globoid cell leukodystrophy or Krabbe disease, is a rapidly progressive childhood lysosomal storage disorder caused by a deficiency in galactocerebrosidase. Galactocerebrosidase deficiency leads to the accumulation of galactosylsphingosine (psychosine), a cytotoxic lipid especially damaging to oligodendrocytes and Schwann cells. The progressive loss of cells involved in myelination results in a dysmyelinating phenotype affecting both the central and peripheral nervous systems. Current treatment for globoid cell leukodystrophy is limited to bone marrow or umbilical cord blood transplantation. However, these therapies are not curative and simply slow the progression of the disease. The Twitcher mouse is a naturally occurring biochemically faithful model of human globoid cell leukodystrophy that has been used extensively to study globoid cell leukodystrophy pathophysiology and experimental treatments. In this review, we present the major single and combination experimental therapies targeting specific aspects of murine globoid cell leukodystrophy.

METHODS

Literature review and analysis.

RESULTS

The evidence suggests that even with the best available therapies, targeting a single pathogenic mechanism provides minimal clinical benefit. More recently, combination therapies have demonstrated the potential to further advance globoid cell leukodystrophy treatment by synergistically increasing life span. However, such therapies must be designed and evaluated carefully because not all combination therapies yield such positive results.

CONCLUSIONS

A more complete understanding of the underlying pathophysiology and the interplay between various therapies holds the key to the discovery of more effective treatments for globoid cell leukodystrophy.

Myocyte-mediated arginase expression controls hyperargininemia but not hyperammonemia in arginase-deficient mice

Human arginase deficiency is characterized by hyperargininemia and infrequent episodes of hyperammonemia that cause neurological impairment and growth retardation. We previously developed a neonatal mouse adeno-associated viral vector (AAV) rh10-mediated therapeutic approach with arginase expressed by a chicken β-actin promoter that controlled plasma ammonia and arginine, but hepatic arginase declined rapidly. This study tested a codon-optimized arginase cDNA and compared the chicken β-actin promoter to liver- and muscle-specific promoters. ARG1(-/-) mice treated with AAVrh10 carrying the liver-specific promoter also exhibited long-term survival and declining hepatic arginase accompanied by the loss of AAV episomes during subsequent liver growth. Although arginase expression in striated muscle was not expected to counteract hyperammonemia, due to muscle's lack of other urea cycle enzymes, we hypothesized that the postmitotic phenotype in muscle would allow vector genomes to persist, and hence contribute to decreased plasma arginine. As anticipated, ARG1(-/-) neonatal mice treated with AAVrh10 carrying a modified creatine kinase-based muscle-specific promoter did not survive longer than controls; however, their plasma arginine levels remained normal when animals were hyperammonemic. These data imply that plasma arginine can be controlled in arginase deficiency by muscle-specific expression, thus suggesting an alternative approach to utilizing the liver for treating hyperargininemia.

Prevention and reversal of severe mitochondrial cardiomyopathy by gene therapy in a mouse model of Friedreich's ataxia

Cardiac failure is the most common cause of mortality in Friedreich's ataxia (FRDA), a mitochondrial disease characterized by neurodegeneration, hypertrophic cardiomyopathy and diabetes. FRDA is caused by reduced levels of frataxin (FXN), an essential mitochondrial protein involved in the biosynthesis of iron-sulfur (Fe-S) clusters. Impaired mitochondrial oxidative phosphorylation, bioenergetics imbalance, deficit of Fe-S cluster enzymes and mitochondrial iron overload occur in the myocardium of individuals with FRDA. No treatment exists as yet for FRDA cardiomyopathy. A conditional mouse model with complete frataxin deletion in cardiac and skeletal muscle (Mck-Cre-Fxn(L3/L-) mice) recapitulates most features of FRDA cardiomyopathy, albeit with a more rapid and severe course. Here we show that adeno-associated virus rh10 vector expressing human FXN injected intravenously in these mice fully prevented the onset of cardiac disease. Moreover, later administration of the frataxin-expressing vector, after the onset of heart failure, was able to completely reverse the cardiomyopathy of these mice at the functional, cellular and molecular levels within a few days. Our results demonstrate that cardiomyocytes with severe energy failure and ultrastructure disorganization can be rapidly rescued and remodeled by gene therapy and establish the preclinical proof of concept for the potential of gene therapy in treating FRDA cardiomyopathy.

Long-term correction of biochemical and neurological abnormalities in MLD mice model by neonatal systemic injection of an AAV serotype 9 vector

As both the immune system and the blood-brain barrier (BBB) are likely to be developmentally immature in the perinatal period, neonatal gene transfer may be useful for the treatment of lysosomal storage disease (LSD) with neurological involvements such as metachromatic leukodystrophy (MLD). In this experiment, we examined the feasibility of single-strand adeno-associated viral serotype-9 (ssAAV9)-mediated systemic neonatal gene therapy of MLD mice. ssAAV9 vector expressing human arylsulfatase A (ASA) and green fluorescent protein (GFP) (ssAAV9/ASA) was injected into the jugular vein of newborn MLD mice. High levels of ASA expression were observed in the muscle and heart for at least 15 months. ASA was continuously secreted into plasma without development of antibodies against ASA. Global gene transfer into the brain and spinal cord (SC), across the BBB, and long-term ASA expression in the central nervous system were detected in treated mice. Significant inhibition of the accumulation of sulfatide (Sulf) in the brain and cervical SC was confirmed by Alcian blue staining and biochemical analysis of the Sulf content. In a behavior test, treated mice showed a greater ability to traverse narrow balance beams than untreated mice. These data clearly demonstrate that MLD mice model can be effectively treated through neonatal systemic injection of ssAAV9/ASA.

Intrathecal administration of IGF-I by AAVrh10 improves sensory and motor deficits in a mouse model of diabetic neuropathy

Different adeno-associated virus (AAV) serotypes efficiently transduce neurons from central and peripheral nervous systems through various administration routes. Direct administration of the vectors to the cerebrospinal fluid (CSF) could be an efficient and safe strategy. Here, we show that lumbar puncture of a nonhuman AAV leads to wide and stable distribution of the vector along the spinal cord in adult mice. AAVrh10 efficiently and specifically infects neurons, both in dorsal root ganglia (60% total sensory neurons) and in the spinal cord (up to one-third of α-motor neurons). As a proof of concept, we demonstrate the efficacy of AAVrh10 in a mouse model of diabetic neuropathy, in which intrathecal delivery of the vector coding for insulin-like growth factor (IGF-I) favored the release of the therapeutic protein into the CSF through its expression by sensory and motor neurons. IGF-I-treated diabetic animals showed increased vascular endothelial growth factor expression, activation of Akt/PI3K pathway, and stimulated nerve regeneration and myelination in injured limbs. Moreover, we achieved restoration of nerve conduction velocities in both sensory and motor nerves by AAVrh10, whereas we reached only sensory nerve improvement with AAV1. Our results indicate that intrathecal injection of AAVrh10 is a promising tool to design gene therapy approaches for sensorimotor diseases.