Abstract: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-anal… Show more
“…We found no sign of cellular degeneration that is commonly observed when the AAV vector is administrated via blood or cerebrospinal fluid. 40 Therefore, we concluded that the AAV vectors applied via the intra-nerve route at the current titer (1.2 × 10 12 gc/6 μL/animal) did not have their own toxic effects on DRG neurons. Figure 3 H&E-stained DRG sections Hematoxylin and eosin (H&E)-stained DRG sections stained 4 weeks after the sciatic nerve injections of AAV9-GFP (A–C), AAV6-GFP (D–F) vectors, and control (G and H) in the marmoset (A, B, D, E, and G) or rat (C, F, and H).…”
Section: Resultsmentioning
confidence: 72%
“…To confirm whether these observations might be influenced by potential immune cell infiltration, 33 , 39 , 40 we examined the immune responses of DRG cells by histological examination of hematoxylin and eosin (H&E)-stained DRG sections in both the rat and marmoset ( Figure 3 ).We found little sign of cellular infiltration in the AAV-9 injected (A–C), the AAV-6 injected (D–F), and the control animals (G and H). We found satellite cells or lymphocytes in every section, but they were not at the level of differentiating into macrophages, and we found no significant difference between the AAV-injected and control DRGs.…”
Adeno-associated virus 6 (AAV6) has been proposed as a potential vector candidate for specific gene expression in pain-related dorsal root ganglion (DRG) neurons, but this has not been confirmed in nonhuman primates. The aim of our study was to analyze the transduction efficiency and target specificity of this viral vector in the common marmoset by comparing it with those in the rat. When green fluorescent protein-expressing serotype-6 vector was injected into the sciatic nerve, the efficiency of gene expression in DRG neurons was comparable in both species. We found that the serotype-6 vector was largely specific to the pain-related ganglion neurons in the marmoset, as well as in the rat, whereas the serotype-9 vector resulted in contrasting effects in the two species. Neither AAV6 nor AAV9 resulted in DRG toxicity when administered via the sciatic nerve, suggesting this as a safer route of sensory nerve transduction than the currently used intrathecal or intravenous administrative routes. Furthermore, the AAV6 vector could be an optimal serotype for gene therapy for human chronic pain that has a minimal effect on other somatosensory functions of DRG neurons.
“…We found no sign of cellular degeneration that is commonly observed when the AAV vector is administrated via blood or cerebrospinal fluid. 40 Therefore, we concluded that the AAV vectors applied via the intra-nerve route at the current titer (1.2 × 10 12 gc/6 μL/animal) did not have their own toxic effects on DRG neurons. Figure 3 H&E-stained DRG sections Hematoxylin and eosin (H&E)-stained DRG sections stained 4 weeks after the sciatic nerve injections of AAV9-GFP (A–C), AAV6-GFP (D–F) vectors, and control (G and H) in the marmoset (A, B, D, E, and G) or rat (C, F, and H).…”
Section: Resultsmentioning
confidence: 72%
“…To confirm whether these observations might be influenced by potential immune cell infiltration, 33 , 39 , 40 we examined the immune responses of DRG cells by histological examination of hematoxylin and eosin (H&E)-stained DRG sections in both the rat and marmoset ( Figure 3 ).We found little sign of cellular infiltration in the AAV-9 injected (A–C), the AAV-6 injected (D–F), and the control animals (G and H). We found satellite cells or lymphocytes in every section, but they were not at the level of differentiating into macrophages, and we found no significant difference between the AAV-injected and control DRGs.…”
Adeno-associated virus 6 (AAV6) has been proposed as a potential vector candidate for specific gene expression in pain-related dorsal root ganglion (DRG) neurons, but this has not been confirmed in nonhuman primates. The aim of our study was to analyze the transduction efficiency and target specificity of this viral vector in the common marmoset by comparing it with those in the rat. When green fluorescent protein-expressing serotype-6 vector was injected into the sciatic nerve, the efficiency of gene expression in DRG neurons was comparable in both species. We found that the serotype-6 vector was largely specific to the pain-related ganglion neurons in the marmoset, as well as in the rat, whereas the serotype-9 vector resulted in contrasting effects in the two species. Neither AAV6 nor AAV9 resulted in DRG toxicity when administered via the sciatic nerve, suggesting this as a safer route of sensory nerve transduction than the currently used intrathecal or intravenous administrative routes. Furthermore, the AAV6 vector could be an optimal serotype for gene therapy for human chronic pain that has a minimal effect on other somatosensory functions of DRG neurons.
“…The microscopic findings in the DRG, spinal cord, and peripheral nerve were associated with proprioceptive deficiencies in piglets, but in NHP, CNS clinical signs are very rarely observed. Using aggregate data from 33 monkey studies that evaluated five different capsids, five different promoters, and 20 different transgenes, Hordeaux et al (2020a) were able to demonstrate that following rAAVbased gene therapies, DRG toxicity occurred more frequently when given via the cerebral spinal fluid (vs IV route), and severity increased with IV dose, and was more severe when administered to adult (vs juvenile) animals.…”
Section: Toxicity To Dorsal Root Gangliamentioning
The number of gene therapies in development continues to increase, as they represent a novel method to treat, and potentially cure, many diseases. Gene therapies can be conducted with an in vivo or ex vivo approach, to cause gene augmentation, gene suppression, or genomic editing. Adeno-associated viruses are commonly used to deliver gene therapies, but their use is associated with several manufacturing, nonclinical and clinical challenges. As these challenges emerge, regulatory agency expectations continue to evolve. Following administration of rAAV-based gene therapies, nonclinical toxicities may occur, which includes immunogenicity, hepatotoxicity, neurotoxicity, and the potential risks for insertional mutagenesis and subsequent tumorgenicity. The mechanism for these findings and translation into the clinical setting are unclear at this time but have influenced the nonclinical studies that regulatory agencies are increasingly requesting to support clinical trials and marketing authorizations. These evolving regulatory expectations and toxicities, as well as future nonclinical considerations, are discussed herein.
“…Therefore, to perform and deeply analyze immunotoxicity studies is essential to succeed in gene therapy studies. For instance, toxicity has been recently reported in the dorsal root ganglion (DRG) sensory neurons [69] after AAV injection in non-human primates. According to this study, DRG pathology was more severe when higher dose vector or older animals were injected.…”
Section: In Vivo Gene Therapy and Aav Vectorsmentioning
Friedreich’s ataxia is an autosomal recessive neurogenetic disease that is mainly associated with atrophy of the spinal cord and progressive neurodegeneration in the cerebellum. The disease is caused by a GAA-expansion in the first intron of the frataxin gene leading to a decreased level of frataxin protein, which results in mitochondrial dysfunction. Currently, there is no effective treatment to delay neurodegeneration in Friedreich’s ataxia. A plausible therapeutic approach is gene therapy. Indeed, Friedreich’s ataxia mouse models have been treated with viral vectors en-coding for either FXN or neurotrophins, such as brain-derived neurotrophic factor showing promising results. Thus, gene therapy is increasingly consolidating as one of the most promising therapies. However, several hurdles have to be overcome, including immunotoxicity and pheno-toxicity. We review the state of the art of gene therapy in Friedreich’s ataxia, addressing the main challenges and the most feasible solutions for them.
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