Intramuscular Delivery of Gene Therapy for Targeting the Nervous System

Abstract

Virus-mediated gene therapy has the potential to deliver exogenous genetic material into specific cell types to promote survival and counteract disease. This is particularly enticing for neuronal conditions, as the nervous system is renowned for its intransigence to therapeutic targeting. Administration of gene therapy viruses into skeletal muscle, where distal terminals of motor and sensory neurons reside, has been shown to result in extensive transduction of cells within the spinal cord, brainstem, and sensory ganglia. This route is minimally invasive and therefore clinically relevant for gene therapy targeting to peripheral nerve soma. For successful transgene expression, viruses administered into muscle must undergo a series of processes, including host cell interaction and internalization, intracellular sorting, long-range retrograde axonal transport, endosomal liberation, and nuclear import. In this review article, we outline key characteristics of major gene therapy viruses—adenovirus, adeno-associated virus (AAV), and lentivirus—and summarize the mechanisms regulating important steps in the virus journey from binding at peripheral nerve terminals to nuclear delivery. Additionally, we describe how neuropathology can negatively influence these pathways, and conclude by discussing opportunities to optimize the intramuscular administration route to maximize gene delivery and thus therapeutic potential.

Conditional RAC1 knockout in motor neurons restores H-reflex rate-dependent depression after spinal cord injury

“…As a result, we observed close-to-none GFAP-positive cells expressing tdTomato (data not shown). Similarly, in agreement with other work, we observed no overlap between tdTomato expression and IBA1, demonstrating that AAV9CMVCre did not have affinity for microglia 44 , 45 .

Figure 4 Conditional Rac1 KO in alpha-motor neurons did not alter microglia or astrocyte reactivity in the ventral horn.

…”

Recombinant adeno-associated virus mediated gene delivery in the extracranial nervous system of adult mice by direct nerve immersion

“…The advantage of intraparenchymal delivery is that the transduction is predominantly localized at the site of injection, which limits potential undesirable effects in other tissues/regions that may present as confounding factors in data interpretation. However, this approach involves invasive procedures and is potentially limited in certain delivery aspects such that widespread transduction in peripheral nervous system is a significant challenge ( Bedbrook et al., 2018 ; Hocquemiller et al., 2016 ; Tosolini and Sleigh, 2020 ; Yu et al., 2016 ). For example, direct nerve, DRG or intra-spinal injections are usually performed using 1–2 μL AAV load with the aim to achieve local transduction in neurons or glial cells ( Homs et al., 2011 ), and specificity can be increased by AAV design incorporating cell-specific regulatory elements ( Yu et al., 2016 ).…”

“…In comparison, AAV mediated gene delivery in adult nervous system using peripheral routes remains an evolving field ( Bedbrook et al., 2018 ; Hoyng et al., 2015 ). Since the focus of this manuscript is an experimental protocol, we are unable to provide a detailed discussion on advantages and efficacy of different peripheral routes of AAV delivery into rodents- e.g., intramuscular ( Towne et al., 2009 ), intraperitoneal ( Dane et al., 2013 ), intravenous ( Gessler et al., 2019 ), intra-nerve ( Homs et al., 2011 ) and into dorsal root ganglia (DRG) ( Yu et al., 2016 ), and the reader is encouraged to consult some recent review articles elsewhere for in-depth discussion and specific research studies ( Tosolini and Sleigh, 2020 ; Hoyng et al., 2015 ; Wang et al., 2019 ; Gessler et al., 2019 ; Naso et al., 2017 ; Mason et al., 2011 ; Bedbrook et al., 2018 ; Hocquemiller et al., 2016 ; Samulski and Muzyczka, 2014 ). In summary, the above cited examples show that peripheral routes of AAV delivery can be utilized for achieving optimal levels of transgene expression in the nervous system, either within the local neuroanatomical structures (e.g., in peripheral nerve terminals and neurons within the DRG or spinal cord following intramuscular injection ( Jan et al., 2019 ; Towne et al., 2009 ; Tosolini and Sleigh, 2020 )) or more distally (e.g., spinal cord or brain following intravenous ( Gessler et al., 2019 ; Stoica et al., 2013 )).…”

Current knowledge and challenges associated with targeted delivery of neurotrophic factors into the central nervous system: focus on available approaches

“…In the latter phase, viral vectors internalize into the nerve axons and reach soma and nucleus. Inside the nucleus, the gene expression is initiated which follows by the production of NTFs in the cytoplasm [ 169 ]. Like the IV route, the IM route is a repeatable and slightly invasive way for viral vector administration while in this approach the possibility of gene expression in other non-specific sites is low.…”