Adeno-associated virus serotype 9 (AAV9) vectors have recently been shown to transduce cells throughout the central nervous system of nonhuman primates when injected into the cerebrospinal fluid (CSF), a finding which could lead to a minimally invasive approach to treat genetic and acquired diseases affecting the entire CNS. We characterized the transduction efficiency of two routes of vector administration into the CSF of cynomolgus macaques—lumbar puncture, which is typically used in clinical practice, and suboccipital puncture, which is more commonly used in veterinary medicine. We found that delivery of vector into the cisterna magna via suboccipital puncture is up to 100-fold more efficient for achieving gene transfer to the brain. In addition, we evaluated the inflammatory response to AAV9-mediated GFP expression in the nonhuman primate CNS. We found that while CSF lymphocyte counts increased following gene transfer, there were no clinical or histological signs of immune toxicity. Together these data indicate that delivery of AAV9 into the cisterna magna is an effective method for achieving gene transfer in the CNS, and suggest that adapting this uncommon injection method for human trials could vastly increase the efficiency of gene delivery.

Leber’s congenital amaurosis (LCA) is a group of severe inherited retinal degenerations that are symptomatic in infancy and lead to total blindness in adulthood. Recent clinical trials using recombinant adeno-associated virus serotype 2 (rAAV2) successfully reversed blindness in patients with LCA caused by RPE65 mutations after one subretinal injection. However, it was unclear whether treatment of the second eye in the same manner would be safe and efficacious, given the potential for a complicating immune response after the first injection. Here, we evaluated the immunological and functional consequences of readministration of rAAV2-hRPE65v2 to the contralateral eye using large animal models. Neither RPE65-mutant (affected; RPE65−/−) nor unaffected animals developed antibodies against the transgene product, but all developed neutralizing antibodies against the AAV2 capsid in sera and intraocular fluid after subretinal injection. Cell-mediated immune responses were benign, with only 1 of 10 animals in the study developing a persistent T cell immune response to AAV2, a response that was mediated by CD4+ T cells. Sequential bilateral injection caused minimal inflammation and improved visual function in affected animals. Thus, subretinal readministration of rAAV2 in animals is safe and effective, even in the setting of preexisting immunity to the vector, a parameter that has been used to exclude patients from gene therapy trials.

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.

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 × 10 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.

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.

The image shows a section of the lumbar spinal cord from a cynomolgus macaque that had received AAV9.CB.EGFP via the cisterna magna. Expression of GFP in multiple motor neurons is visible. Injection into the cerebrospinal fluid has been shown to be an effective route of vector administration for neuron transduction.

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.

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