Systemic Gene Delivery in Large Species for Targeting Spinal Cord, Brain, and Peripheral Tissues for Pediatric Disorders

Abstract

Adeno-associated virus type 9 (AAV9) is a powerful tool for delivering genes throughout the central nervous system (CNS) following intravenous injection. Preclinical results in pediatric models of spinal muscular atrophy (SMA) and lysosomal storage disorders provide a compelling case for advancing AAV9 to the clinic. An important translational step is to demonstrate efficient CNS targeting in large animals at various ages. In the present study, we tested systemically injected AAV9 in cynomolgus macaques, administered at birth through 3 years of age for targeting CNS and peripheral tissues. We show that AAV9 was efficient at crossing the blood–brain barrier (BBB) at all time points investigated. Transgene expression was detected primarily in glial cells throughout the brain, dorsal root ganglia neurons and motor neurons within the spinal cord, providing confidence for translation to SMA patients. Systemic injection also efficiently targeted skeletal muscle and peripheral organs. To specifically target the CNS, we explored AAV9 delivery to cerebrospinal fluid (CSF). CSF injection efficiently targeted motor neurons, and restricted gene expression to the CNS, providing an alternate delivery route and potentially lower manufacturing requirements for older, larger patients. Our findings support the use of AAV9 for gene transfer to the CNS for disorders in pediatric populations.

Intrathecal gene therapy rescues a model of demyelinating peripheral neuropathy

“…However, none of those previous studies focused specifically on myelinating Schwann cells, because ubiquitous promoters were used. Widespread expression was reported in some cases after AAV injection from the spinal cord to the brain in both adults and neonates (26,33), and even after AAV9 injection in large animal models (27,34). This is the first demonstration, to our knowledge, of a successful intrathecal approach to treating peripheral neuropathy by delivering a myelin-related gene and achieving widespread Schwann cell-specific expression.…”

CNS-directed gene therapy for the treatment of neurologic and somatic mucopolysaccharidosis type II (Hunter syndrome)

“…There is considerable variability in the literature regarding the main CNS cell type targeted by AAV9. Several factors have been held accountable for the differences observed, including the route of delivery (73,74), the age at administration (75), the animal species (73,(76)(77)(78), the doses used, the promoter included in the expression cassette (74,79), and even the single-or double-stranded nature of the AAV (80). Alternatively, the quality of vector preparations could play an important role in determining vector tropism (81).…”

Gene therapy for the neurological manifestations in lysosomal storage disorders

“…Additionally, this approach exploits the property of the tropism for neural cells of select AAV serotypes and their ability to undergo axonal transport, thereby potentially distributing ( 86 ). Nevertheless, given the encouraging preclinical results in certain LSDs and the recent regulatory approval of systemic gene therapy using AAV9 to potentially address the CNS aspects of spinal muscular atrophy patients ( 87 ), this line of research will likely continue in earnest over the next several years.…”