Intravenous immunoglobulin prevents peripheral liver transduction of intrathecally delivered AAV vectors.

Gene therapy using neurotropic adeno-associated virus vectors represents an emerging solution for genetic disorders affecting the central nervous system. The first approved central nervous system-targeting adeno-associated virus gene therapy, Zolgensma®, for treating spinal muscular atrophy is administered intravenously at high doses that cause liver-associated adverse events in 20%-30% of patients. Intrathecal routes of vector administration, such as the intra-cisterna magna route, provide efficient gene transduction to central nervous system cells while reducing off-target liver transduction. However, significant levels of liver transduction often occur upon intra-cisterna magna vector delivery in preclinical studies. Using vectors expressing monoclonal antibody transgenes, we examined whether passive transfer of adeno-associated virus-neutralizing antibodies as intravenous immunoglobulin before intrathecal adeno-associated virus delivery improved the safety of viral gene therapy targeting the central nervous system in mice and nonhuman primates. We used intracerebroventricular and intra-cisterna magna routes for vector administration to mice and nonhuman primates, respectively, and evaluated transgene expression and vector genome distribution. Our data indicate that pretreatment with intravenous immunoglobulin significantly reduced gene transduction to the liver and other peripheral organs but not to the central nervous system in both species. With further refinement, this method may improve the safety of adeno-associated virus-based, central nervous system-targeting gene therapies in clinical settings.

Erratum: Intravenous immunoglobulin prevents peripheral liver transduction of intrathecally delivered AAV vectors.

[This corrects the article DOI: 10.1016/j.omtm.2022.09.017.].

Determining the Minimally Effective Dose of a Clinical Candidate Adeno-Associated Virus Vector in a Mouse Model of Hemophilia A.

Hemophilia A, a bleeding disorder, affects 1:5,000 males and is caused by a deficiency of human blood coagulation factor VIII (hFVIII). Studies in mice and macaques identified AAVhu37.E03.TTR.hFVIIIco-SQ.PA75 as a clinical candidate gene therapy vector to treat hemophilia A. In this study, we sought to determine the minimally effective dose (MED) of this vector in a hemophilia A mouse model. Mice received one of four vector doses (3 × 1011-1 × 1013 genome copies [GCs]/kg) via intravenous tail vein injection; one cohort received vehicle as a control. Animals were monitored daily after vector/vehicle administration. Blood samples were collected to evaluate hFVIII activity levels and anti-hFVIII antibodies. Animals were sacrificed and necropsied on days 28 and 56; tissues were harvested for histopathological examination and blood was collected for serum chemistry panel analysis. We found no significant differences in liver transaminase levels in mice administered any vector dose compared to those administered vehicle (except for one group administered 3 × 1011 GC/kg). Total bilirubin levels were significantly elevated compared to the vehicle group following two vector doses at day 56 (1 × 1012 and 1 × 1013 GC/kg). We observed no vector-related gross or histological findings. Most microscopic findings were in the vehicle group and considered secondary to blood loss, an expected phenotype of this mouse model. Since we observed no dose-limiting safety markers, we determined that the maximally tolerated dose was greater than or equal to the highest dose tested (1 × 1013 GC/kg). Since we detected hFVIII activity in all cohorts administered vector, we conclude that the MED is 3 × 1011 GC/kg-the lowest dose evaluated in this study.

Adeno-Associated Virus-Induced Dorsal Root Ganglion Pathology.

The administration of adeno-associated virus (AAV) vectors to nonhuman primates (NHP) via the blood or cerebrospinal fluid (CSF) can lead to dorsal root ganglion (DRG) pathology. The pathology is minimal to moderate in most cases; clinically silent in affected animals; and characterized by mononuclear cell infiltrates, neuronal degeneration, and secondary axonopathy of central and peripheral axons on histopathological analysis. We aggregated data from 33 nonclinical studies in 256 NHP and performed a meta-analysis of the severity of DRG pathology to compare different routes of administration, dose, time course, study conduct, age of the animals, sex, capsid, promoter, capsid purification method, and transgene. DRG pathology was observed in 83% of NHP that were administered AAV through the CSF, and 32% of NHP that received an intravenous (IV) injection. We show that dose and age at injection significantly affected the severity whereas sex had no impact. DRG pathology was minimal at acute time points (i.e., <14 days), similar from one to 5 months post-injection, and was less severe after 6 months. Vector purification method had no impact, and all capsids and promoters that we tested resulted in some DRG pathology. The data presented here from five different capsids, five different promoters, and 20 different transgenes suggest that DRG pathology is almost universal after AAV gene therapy in nonclinical studies using NHP. None of the animals receiving a therapeutic transgene displayed any clinical signs. Incorporation of sensitive techniques such as nerve-conduction velocity testing can show alterations in a minority of animals that correlate with the severity of peripheral nerve axonopathy. Monitoring sensory neuropathies in human central nervous system and high-dose IV clinical studies seems prudent to determine the functional consequences of DRG pathology.

Translational Feasibility of Lumbar Puncture for Intrathecal AAV Administration.

Preclinical studies have demonstrated that a single injection of an adeno-associated virus (AAV) vector into the cerebrospinal fluid (CSF) can achieve widespread gene transfer throughout the central nervous system. Successfully translating this approach to humans requires identifying factors that influence AAV distribution in the CSF so that optimal parameters can be replicated in the clinic. In the context of developing a motor neuron-targeted gene therapy for spinal muscular atrophy, we conducted studies in nonhuman primates to evaluate the impact of injection volume on spinal cord transduction after AAV delivery via lumbar puncture. Lumbar injection of an AAVhu68 vector targeted motor neurons throughout the spinal cord, but only in juvenile nonhuman primates administered large injection volumes, equivalent to about half of the total CSF volume. Upon repeating this study with clinically relevant injection volumes and larger animals, we found that lumbar puncture failed to achieve significant transduction of the spinal cord. In contrast, vector administered into the cisterna magna distributed reproducibly throughout the spinal cord in both juvenile and adult animals. These findings highlight the challenges of translating AAV delivery via lumbar puncture to humans and suggest that delivery into the cisterna magna may represent a more feasible alternative.

Adeno-associated virus-mediated expression of human butyrylcholinesterase to treat organophosphate poisoning.

Rare diseases defined by genetic mutations are classic targets for gene therapy. More recently, researchers expanded the use of gene therapy in non-clinical studies to infectious diseases through the delivery of vectorized antibodies to well-defined antigens. Here, we further extend the utility of gene therapy beyond the "accepted" indications to include organophosphate poisoning. There are no approved preventives for the multi-organ damage resulting from acute or chronic exposure to organophosphates. We show that a single intramuscular injection of adeno-associated virus vector produces peak expression (~0.5 mg/ml) of active human butyrylcholinesterase (hBChE) in mice serum within 3-4 weeks post-treatment. This expression is sustained for up to 140 days post-injection with no silencing. Sustained expression of hBChE provided dose-dependent protection against VX in male and female mice despite detectable antibodies to hBChE in some mice, thereby demonstrating that expression of hBChE in vivo in mouse muscle is an effective prophylactic against organophosphate poisoning.

AAV8 Gene Therapy for Crigler-Najjar Syndrome in Macaques Elicited Transgene T Cell Responses That Are Resident to the Liver.

Systemic delivery of adeno-associated viral (AAV) vectors has been evaluated for the treatment of several liver diseases, including homozygous familial hypercholesterolemia, ornithine transcarbamylase deficiency, and hemophilia. Here, we evaluated this approach for the treatment of Crigler-Najjar syndrome. We administered wild-type rhesus macaques with 1.0 × 1013 or 2.5 × 1013 genome copies/kg of an AAV serotype 8 vector expressing a codon-optimized version of human uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) from a liver-specific promoter. We extensively studied vector biodistribution, transgene expression, and immune responses following vector administration. All rhesus macaques survived until their scheduled necropsy at day 56 and showed no clinical abnormalities during the course of the study. Macaques administered with either vector dose developed a T cell response to the AAV capsid and/or transgene. We mapped the immunodominant epitope in the human UGT1A1 sequence, and we found no correlation between peripheral and tissue-resident lymphocyte responses. Upon further investigation, we characterized CD107a+, granzyme B+, CD4+, and CD8+ transgene-specific cellular responses that were restricted to tissue-resident T cells. This study highlights the importance of studying immune responses at the vector transduction site and the limited usefulness of blood as a surrogate to evaluate tissue-restricted T cell responses.

Toxicology Study of Intra-Cisterna Magna Adeno-Associated Virus 9 Expressing Iduronate-2-Sulfatase in Rhesus Macaques.

Hunter syndrome is an X-linked recessive disease caused by deficiency of the lysosomal enzyme iduronate-2-sulfatase. The severe form of this progressive, systemic, and neurodegenerative disease results in loss of cognitive skills and early death. Several clinical trials are evaluating adeno-associated virus 9 for the treatment of neurodegenerative diseases using systemic or intrathecal lumbar administration. In large animals, administration via suboccipital puncture gives better brain transduction than lumbar administration. Here, we conducted a good laboratory practice-compliant investigational new drug-enabling study to determine the safety of suboccipital adeno-associated virus 9 gene transfer of human iduronate-2-sulfatase into nonhuman primates. Thirteen rhesus macaques received vehicle or one of two doses of vector with or without immunosuppression. We assessed in-life safety and immune responses. Animals were euthanized 90 days post-administration and sampled for histopathology and biodistribution. The procedure was well tolerated in all animals. Minimal mononuclear cerebrospinal fluid pleocytosis occurred in some animals. Asymptomatic minimal-to-moderate toxicity to some dorsal root ganglia sensory neurons and their associated axons occurred in all vector-treated animals. This study supports the clinical development of suboccipital adeno-associated virus 9 delivery for severe Hunter syndrome and highlights a potential toxicity that warrants monitoring in first-in-human studies.

Toxicology Study of Intra-Cisterna Magna Adeno-Associated Virus 9 Expressing Human Alpha-L-Iduronidase in Rhesus Macaques.

Mucopolysaccharidosis type I is a recessive genetic disease caused by deficiency of the lysosomal enzyme α-L-iduronidase, which leads to a neurodegenerative and systemic disease called Hurler syndrome in its most severe form. Several clinical trials are evaluating adeno-associated virus serotype 9 (AAV9) for the treatment of neurodegenerative diseases. Although these trials focus on systemic or lumbar administration, intrathecal administration via suboccipital puncture into the cisterna magna has demonstrated remarkable efficacy in large animals. We, therefore, conducted a good laboratory practice-compliant non-clinical study to investigate the safety of suboccipital AAV9 gene transfer of human α-L-iduronidase into nonhuman primates. We dosed 22 rhesus macaques, including three immunosuppressed animals, with vehicle or one of two doses of vector. We assessed in-life safety and immune responses. Animals were euthanized 14, 90, or 180 days post-vector administration and evaluated for histopathology and biodistribution. No procedure-related lesions or adverse events occurred. All vector-treated animals showed a dose-dependent mononuclear pleocytosis in the cerebrospinal fluid and minimal to moderate asymptomatic degeneration of dorsal root ganglia neurons and associated axons. These studies support the clinical development of suboccipital AAV delivery for Hurler syndrome and highlight a potential sensory neuron toxicity that warrants careful monitoring in first-in-human studies.

Standardized Method for Intra-Cisterna Magna Delivery Under Fluoroscopic Guidance in Nonhuman Primates.

Intrathecal delivery of adeno-associated virus vectors and other therapeutics are currently being evaluated for the treatment of central nervous system sequelae of lysosomal storage diseases, motor neuron diseases, and neurodegenerative diseases. As products transition from preclinical to clinical studies, a standardized and clinically relevant method of intrathecal delivery is increasingly germane. Here, we describe a method of intrathecal delivery via suboccipital puncture into the cisterna magna under fluoroscopic guidance in nonhuman primates. This procedure is suitable for use in good laboratory practice compliant studies, has an excellent safety profile, and is highly similar to the procedure currently being explored for use in humans.

Optimized Adeno-Associated Viral-Mediated Human Factor VIII Gene Therapy in Cynomolgus Macaques.

Hemophilia A is a common hereditary bleeding disorder that is characterized by a deficiency of human blood coagulation factor VIII (hFVIII). Previous studies with adeno-associated viral (AAV) vectors identified two liver-specific promoter and enhancer combinations (E03.TTR and E12.A1AT) that drove high level expression of a codon-optimized, B-domain-deleted hFVIII transgene in a mouse model of the disease. This study further evaluated these enhancer/promoter combinations in cynomolgus macaques using two different AAV capsids (AAVrh10 and AAVhu37). Each of the four vector combinations was administered intravenously at a dose of 1.2 × 1013 genome copy/kg into five macaques per group. Delivery of the hFVIII transgene via the AAVhu37 capsid resulted in a substantial increase in hFVIII expression compared to animals administered with AAVrh10 vectors. Two weeks after administration of E03.TTR packaged within the AAVhu37 capsid, average hFVIII expression was 20.2 ± 5.0% of normal, with one animal exhibiting peak expression of 37.1% of normal hFVIII levels. The majority of animals generated an anti-hFVIII antibody response by week 8-10 post vector delivery. However, two of the five macaques administered with AAVhu37.E03.TTR were free of a detectable antibody response for 30 weeks post vector administration. Overall, the study supports the continued development of AAV-based gene therapeutics for hemophilia A using the AAVhu37 capsid.

Severe Toxicity in Nonhuman Primates and Piglets Following High-Dose Intravenous Administration of an Adeno-Associated Virus Vector Expressing Human SMN.

Neurotropic adeno-associated virus (AAV) serotypes such as AAV9 have been demonstrated to transduce spinal alpha motor neurons when administered intravenously (i.v.) at high doses. This observation led to the recent successful application of i.v. AAV9 delivery to treat infants with spinal muscular atrophy, an inherited deficiency of the survival of motor neuron (SMN) protein characterized by selective death of lower motor neurons. To evaluate the efficiency of motor neuron transduction with an AAV9 variant (AAVhu68) using this approach, three juvenile nonhuman primates (NHPs; aged 14 months) and three piglets (aged 7-30 days) were treated with an i.v. injection of an AAVhu68 vector carrying a human SMN transgene at a dose similar to that employed in the spinal muscular atrophy clinical trial. Administration of 2 × 1014 genome copies per kilogram of body weight resulted in widespread transduction of spinal motor neurons in both species. However, severe toxicity occurred in both NHPs and piglets. All three NHPs exhibited marked transaminase elevations. In two NHPs, the transaminase elevations resolved without clinical sequelae, while one NHP developed acute liver failure and shock and was euthanized 4 days after vector injection. Degeneration of dorsal root ganglia sensory neurons was also observed, although NHPs exhibited no clinically apparent sensory deficits. There was no correlation between clinical findings and T-cell responses to the vector capsid or transgene product in NHPs. Piglets demonstrated no evidence of hepatic toxicity, but within 14 days of vector injection, all three animals exhibited proprioceptive deficits and ataxia, which profoundly impaired ambulation and necessitated euthanasia. These clinical findings correlated with more severe dorsal root ganglia sensory neuron lesions than those observed in NHPs. The liver and sensory neuron findings appear to be a direct consequence of AAV transduction independent of an immune response to the capsid or transgene product. The present results and those of another recent study utilizing a different AAV9 variant and transgene indicate that systemic and sensory neuron toxicity may be general properties of i.v. delivery of AAV vectors at high doses, irrespective of the capsid serotype or transgene. Preclinical and clinical studies involving high systemic doses of AAV vectors should include careful monitoring for similar toxicities.

Evaluation of Intrathecal Routes of Administration for Adeno-Associated Viral Vectors in Large Animals.

Delivery of adeno-associated viral (AAV) vectors into the cerebrospinal fluid (CSF) can achieve gene transfer to cells throughout the brain and spinal cord, potentially making many neurological diseases tractable gene therapy targets. Identifying the optimal route of CSF access for intrathecal AAV delivery will be a critical step in translating this approach to clinical practice. We previously demonstrated that vector injection into the cisterna magna is a safe and effective method for intrathecal AAV delivery in nonhuman primates; however, this procedure is not commonly used in clinical practice. More routine methods of administration into the CSF are now being explored, including intracerebroventricular (ICV) injection and injection through a lumbar puncture. In this study, we compared ICV and intracisternal (IC) AAV administration in dogs. We also evaluated vector administration via lumbar puncture in nonhuman primates, with some animals placed in the Trendelenburg position after injection, a maneuver that has been suggested to improve cranial distribution of vector. In the dog study, ICV and IC vector administration resulted in similarly efficient transduction throughout the brain and spinal cord. However, animals in the ICV cohort developed encephalitis associated with a T-cell response to the transgene product, a phenomenon that was not observed in the IC cohort. In the nonhuman primate study, transduction efficiency was not improved by placing animals in the Trendelenburg position after injection. These findings illustrate important limitations of commonly used methods for CSF access in the context of AAV delivery, and will be important for informing the selection of a route of administration for first-in-human studies.

Impact of intravenous infusion time on AAV8 vector pharmacokinetics, safety, and liver transduction in cynomolgus macaques.

Systemically delivered adeno-associated viral (AAV) vectors are now in early-phase clinical trials for a variety of diseases. While there is a general consensus on inclusion and exclusion criteria for each of these trials, the conditions under which vectors are infused vary significantly. In this study, we evaluated the impact of intravenous infusion rate of AAV8 vector in cynomolgus macaques on transgene expression, vector clearance from the circulation, and potential activation of the innate immune system. The dose of AAV8 vector in terms of genome copies per kilogram body weight and its concentration were fixed, while the rate of infusion varied to deliver the entire dose over different time periods, including 1, 10, or 90 minutes. Analyses during the in-life phase of the experiment included sequential evaluation of whole blood for vector genomes and appearance of proinflammatory cytokines. Liver tissues were analyzed at the time of necropsy for enhanced green fluorescent protein (eGFP) expression and vector genomes. The data were remarkable with a relative absence of any statistically significant effect of infusion time on vector transduction, safety, and clearance. However, some interesting and unexpected trends did emerge.

Delivery of an Adeno-Associated Virus Vector into Cerebrospinal Fluid Attenuates Central Nervous System Disease in Mucopolysaccharidosis Type II Mice.

Mucopolysaccharidosis type II (MPS II) is a rare X-linked genetic disorder caused by deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS), leading to impaired catabolism of ubiquitous polysaccharides and abnormal accumulation of these undegraded substrates in the lysosome. Like many lysosomal storage diseases, MPS II is characterized by both somatic and central nervous system (CNS) involvement. Intravenous enzyme replacement therapy can improve somatic manifestations of MPS II, but systemic IDS does not cross the blood-brain barrier and therefore cannot address CNS disease. In this study, an adeno-associated virus serotype 9 vector carrying the IDS gene was injected into the cerebrospinal fluid (CSF) of IDS deficient mice, a model of MPS II. Treated mice exhibited dose-dependent IDS expression and resolution of brain storage lesions, as well as improvement in long-term memory in a novel object recognition test. These findings suggest that delivery of adeno-associated virus vectors into CSF could serve as a platform for efficient, long-term enzyme delivery to the CNS, potentially addressing this critical unmet need for patients with MPS II and many related lysosomal enzyme deficiencies.

Comparative Study of Liver Gene Transfer With AAV Vectors Based on Natural and Engineered AAV Capsids.

Vectors based on the clade E family member adeno-associated virus (AAV) serotype 8 have shown promise in patients with hemophilia B and have emerged as best in class for human liver gene therapies. We conducted a thorough evaluation of liver-directed gene therapy using vectors based on several natural and engineered capsids including the clade E AAVrh10 and the largely uncharacterized and phylogenically distinct AAV3B. Included in this study was a putatively superior hepatotropic capsid, AAVLK03, which is very similar to AAV3B. Vectors based on these capsids were benchmarked against AAV8 and AAV2 in a number of in vitro and in vivo model systems including C57BL/6 mice, immune-deficient mice that are partially repopulated with human hepatocytes, and nonhuman primates. Our studies in nonhuman primates and human hepatocytes demonstrated high level transduction of the clade E-derived vectors and equally high transduction with vectors based on AAV3B. In contrast to previous reports, AAVLK03 vectors are not superior to either AAV3B or AAV8. Vectors based on AAV3B should be considered for liver-directed gene therapy when administered following, or before, treatment with the serologically distinct clade E vectors.

Adenosine antagonists reverse the cataleptic effects of haloperidol: implications for the treatment of Parkinson's disease.

The effects of adenosine antagonists were compared in two rodent models of Parkinsonian symptoms. In the first experiment the dopamine D2 antagonist, haloperidol, was used to induce catalepsy. It was found that treatment with the non-selective adenosine antagonist caffeine significantly reduced catalepsy at each dose. Treatment with the selective A1 antagonist CPT also produced a significant reduction in catalepsy, as did treatment with the selective A2A antagonist SCH58261. In the second experiment haloperidol was used to suppress locomotor activity in an open field test. Treatment with caffeine significantly increased locomotion reduced by haloperidol, but not at all doses tested. Treatment with CPT also increased haloperidol-suppressed locomotor activity in dose-dependent manner. Surprisingly, treatment with SCH58261 did not significantly increase locomotor activity in animals treated with haloperidol at any dose tested. While some of these results were unexpected, the overall pattern suggests that adenosine antagonists would be useful as therapies for Parkinsonian patients as they appear to increase movement. The results also suggest that in acute timelines A1 antagonists may be more beneficial than previously supposed.

Miniaturization: an overview of biotechnologies for monitoring the physiology and pathophysiology of rodent animal models.

Recent advances in bioengineering technologies have made it possible to collect high-quality reproducible data quantitatively in a wide range of laboratory animal species, including rodents. Several of these technologies are incorporated into a plan called Miniaturization, which aims to design, develop, and maintain rodent animal models to study the pathophysiology and therapy of human diseases. Laser Doppler flowmetry, digital sonomicrometry, bioelectrical impedance, and microdialysis are some of the most widely used methods under the plan because they cause minimal pain and distress, reduce the number of animals used in biomedical research, and allow chronic, nonterminal assessment of physiological parameters in rodents. An overview of each of these technologies and their major applications in rodents used for biomedical research is provided.

Use of three infusion pumps for postoperative administration of buprenorphine or morphine in dogs.

Results of using an implantable osmotic pump, a preset disposable infusion pump, or a reusable programmable infusion pump for postoperative administration of buprenorphine or morphine in dogs undergoing abdominal surgery are described. Ten dogs underwent abdominal surgery for implantation of vascular access ports. Dogs were given buprenorphine s.c. by use of an implantable osmotic pump (4 dogs), morphine s.c. by use of a preset infusion pump (4), or buprenorphine intra-arterially by use of a programmable infusion pump (2). Dogs were monitored, and serum buprenorphine or morphine concentration was measured for 72 hours after surgery; pumps were removed 48 hours after surgery. Severity of pain was determined by assigning a pain score. The preset infusion pump and the programmable infusion pump resulted in comparable pain relief and sustained serum analgesic concentrations throughout the recovery period. However, the cost of the pumps and other associated factors may limit their use to dogs undergoing invasive surgical procedures expected to result in substantial postoperative pain. The level of analgesia obtained with the implantable osmotic pumps was inconsistent.