Prevalence Study of Cellular Capsid-Specific Immune Responses to AAV2, 4, 5, 8, 9, and rh10 in Healthy Donors.

Recombinant adeno-associated virus (rAAV) vectors appear, more than ever, to be efficient viral vectors for in vivo gene transfer as illustrated by the approvals of 7 drugs across Europe and the United States. Nevertheless, preexisting immunity to AAV capsid in humans remains one of the major limits for a successful clinical translation. Whereas a preexisting humoral response to AAV capsid is well documented, the prevalence of preexisting capsid-specific T cell responses still needs to be studied and characterized. In this study, we investigated the prevalence of AAV-specific circulating T cells toward AAV2, 4, 5, 8, 9, and rh10 in a large cohort of healthy donors using the standard IFNγ ELISpot assay. We observed the highest prevalence of preexisting cellular immunity to AAV9 serotype followed by AAV8, AAV4, AAV2, AAVrh10, and AAV5 independently of the donors' serological status. An in-depth analysis of T cell responses toward the 2 most prevalent serotypes 8 and 9 shows that IFNγ secretion is mainly mediated by CD8 T cells for both serotypes. A polyfunctional analysis reveals different cytokine profiles between AAV8 and AAV9. Surprisingly, no IL-2 secretion was mediated by anti-AAV9 immune cells suggesting that these cells may rather be exhausted or terminally differentiated than cytotoxic T cells. Altogether, these results suggest that preexisting immunity to AAV may vary depending on the serotype and support the necessity of using multiparametric monitoring methods to better characterize anticapsid cellular immunity and foresee its impact in rAAV-mediated clinical trials.

Biodistribution and safety of a single rAAV3B-AAT vector for silencing and replacement of alpha-1 antitrypsin in Cynomolgus macaques.

Alpha-1 antitrypsin deficiency (AATD) is characterized by both chronic lung disease due to loss of wild-type AAT (M-AAT) antiprotease function and liver disease due to toxicity from delayed secretion, polymerization, and aggregation of misfolded mutant AAT (Z-AAT). The ideal gene therapy for AATD should therefore comprise both endogenous Z-AAT suppression and M-AAT overexpression. We designed a dual-function rAAV3B (df-rAAV3B) construct, which was effective at transducing hepatocytes, resulting in a considerable decrease of Z-AAT levels and safe M-AAT augmentation in mice. We optimized df-rAAV3B and created two variants, AAV3B-E12 and AAV3B-G3, to simultaneously enhance the concentration of M-AAT in the bloodstream to therapeutic levels and silence endogenous AAT liver expression in cynomolgus monkeys. Our results demonstrate that AAV3b-WT, AAV3B-E12, and AAV3B-G3 were able to transduce the monkey livers and achieve high M-AAT serum levels efficiently and safely. In this nondeficient model, we did not find downregulation of endogenous AAT. However, the dual-function vector did serve as a potentially "liver-sparing" alternative for high-dose liver-mediated AAT gene replacement in the context of underlying liver disease.

Transcriptomic Analysis Reveals the Inability of Recombinant AAV8 to Activate Human Monocyte-Derived Dendritic Cells.

Recombinant Adeno-Associated Virus (rAAV) is considered as one of the most successful and widely used viral vectors for in vivo gene therapy. However, host immune responses to the vector and/or the transgene product remain a major hurdle to successful AAV gene transfer. In contrast to antivector adaptive immunity, the initiation of the innate immunity towards rAAV is still poorly understood but is directly dependent on the interaction between the viral vector and innate immune cells. Here, we used a quantitative transcriptomic-based approach to determine the activation of inflammatory and anti-viral pathways after rAAV8-based infection of monocyte-derived dendritic cells (moDCs) obtained from 12 healthy human donors. We have shown that rAAV8 particles are efficiently internalized, but that this uptake does not induce any detectable transcriptomic change in moDCs in contrast to an adenoviral infection, which upregulates anti-viral pathways. These findings suggest an immunologically favorable profile for rAAV8 serotype with regard to in vitro activation of moDC model. Transcriptomic analysis of rAAV-infected innate immune cells is a powerful method to determine the ability of the viral vector to be seen by these sensor cells, which remains of great importance to better understand the immunogenicity of rAAV vectors and to design immune-stealth products.

Liver-directed SERPINA1 gene therapy attenuates progression of spontaneous and tobacco smoke-induced emphysema in α1-antitrypsin null mice.

α1-antitrypsin deficiency is a rare genetic condition that can cause liver and/or lung disease. There is currently no cure for this disorder, although repeated infusions of plasma-purified protein may slow down emphysema progression. Gene therapy in which a single recombinant adeno-associated viral vector (rAAV) administration would lead to sustained protein expression could therefore similarly affect disease progression, and provide the added benefits of reducing treatment burden and thereby improving the patient's quality of life. The study presented here tests whether treating the Serpina1a-e knockout mouse model of α1-antitrypsin-deficiency lung disease with gene therapy would have an impact on the disease course, either on spontaneous disease caused by aging or on accelerated disease caused by exposure to cigarette smoke. Liver-directed gene therapy led to dose-dependent levels of biologically active human α1-antitrypsin protein. Furthermore, decreased lung compliance and increased elastic recoil indicate that treated mice had largely preserved lung tissue elasticity and alveolar wall integrity compared with untreated mice. rAAV-mediated gene augmentation is therefore able to compensate for the loss of function and restore a beneficial lung protease-antiprotease balance. This work constitutes a preclinical study report of a disease-modifying treatment in the Serpina1a-e knockout mouse model using a liver-specific rAAV serotype 8 capsid.

AAV gene therapy for Tay-Sachs disease.

Tay-Sachs disease (TSD) is an inherited neurological disorder caused by deficiency of hexosaminidase A (HexA). Here, we describe an adeno-associated virus (AAV) gene therapy expanded-access trial in two patients with infantile TSD (IND 18225) with safety as the primary endpoint and no secondary endpoints. Patient TSD-001 was treated at 30 months with an equimolar mix of AAVrh8-HEXA and AAVrh8-HEXB administered intrathecally (i.t.), with 75% of the total dose (1 × 1014 vector genomes (vg)) in the cisterna magna and 25% at the thoracolumbar junction. Patient TSD-002 was treated at 7 months by combined bilateral thalamic (1.5 × 1012 vg per thalamus) and i.t. infusion (3.9 × 1013 vg). Both patients were immunosuppressed. Injection procedures were well tolerated, with no vector-related adverse events (AEs) to date. Cerebrospinal fluid (CSF) HexA activity increased from baseline and remained stable in both patients. TSD-002 showed disease stabilization by 3 months after injection with ongoing myelination, a temporary deviation from the natural history of infantile TSD, but disease progression was evident at 6 months after treatment. TSD-001 remains seizure-free at 5 years of age on the same anticonvulsant therapy as before therapy. TSD-002 developed anticonvulsant-responsive seizures at 2 years of age. This study provides early safety and proof-of-concept data in humans for treatment of patients with TSD by AAV gene therapy.

AAV8 locoregional delivery induces long-term expression of an immunogenic transgene in macaques despite persisting local inflammation.

Adeno-associated virus (AAV) vectors are considered efficient vectors for gene transfer, as illustrated by recent successful clinical trials targeting retinal or neurodegenerative disorders. However, limitations as host immune responses to AAV capsid or transduction of limited regions must still be overcome. Here, we focused on locoregional (LR) intravenous perfusion vector delivery that allows transduction of large muscular areas and is considered to be less immunogenic than intramuscular (IM) injection. To confirm this hypothesis, we injected 6 cynomolgus monkeys with an AAV serotype 8 (AAV8) vector encoding for the highly immunogenic GFP driven by either a muscle-specific promoter (n = 3) or a cytomegalovirus (CMV) promoter (n = 3). We report that LR delivery allows long-term GFP expression in the perfused limb (up to 1 year) despite the initiation of a peripheral transgene-specific immune response. The analysis of the immune status of the perfused limb shows that LR delivery induces persisting inflammation. However, this inflammation is not sufficient to result in transgene clearance and is balanced by resident regulatory T cells. Overall, our results suggest that LR delivery promotes persisting transgene expression by induction of Treg cells in situ and might be a safe alternative to IM route to target large muscle territories for the expression of secreted therapeutic factors.

CHOP and c-JUN up-regulate the mutant Z α1-antitrypsin, exacerbating its aggregation and liver proteotoxicity.

α1-Antitrypsin (AAT) encoded by the SERPINA1 gene is an acute-phase protein synthesized in the liver and secreted into the circulation. Its primary role is to protect lung tissue by inhibiting neutrophil elastase. The Z allele of SERPINA1 encodes a mutant AAT, named ATZ, that changes the protein structure and leads to its misfolding and polymerization, which cause endoplasmic reticulum (ER) stress and liver disease through a gain-of-function toxic mechanism. Hepatic retention of ATZ results in deficiency of one of the most important circulating proteinase inhibitors and predisposes to early-onset emphysema through a loss-of-function mechanism. The pathogenetic mechanisms underlying the liver disease are not completely understood. C/EBP-homologous protein (CHOP), a transcription factor induced by ER stress, was found among the most up-regulated genes in livers of PiZ mice that express ATZ and in human livers of patients homozygous for the Z allele. Compared with controls, juvenile PiZ/Chop-/- mice showed reduced hepatic ATZ and a transcriptional response indicative of decreased ER stress by RNA-Seq analysis. Livers of PiZ/Chop-/- mice also showed reduced SERPINA1 mRNA levels. By chromatin immunoprecipitations and luciferase reporter-based transfection assays, CHOP was found to up-regulate SERPINA1 cooperating with c-JUN, which was previously shown to up-regulate SERPINA1, thus aggravating hepatic accumulation of ATZ. Increased CHOP levels were detected in diseased livers of children homozygous for the Z allele. In summary, CHOP and c-JUN up-regulate SERPINA1 transcription and play an important role in hepatic disease by increasing the burden of proteotoxic ATZ, particularly in the pediatric population.

SOD1 Suppression with Adeno-Associated Virus and MicroRNA in Familial ALS.

Two patients with familial amyotrophic lateral sclerosis (ALS) and mutations in the gene encoding superoxide dismutase 1 (SOD1) were treated with a single intrathecal infusion of adeno-associated virus encoding a microRNA targeting SOD1. In Patient 1, SOD1 levels in spinal cord tissue as analyzed on autopsy were lower than corresponding levels in untreated patients with SOD1-mediated ALS and in healthy controls. Levels of SOD1 in cerebrospinal fluid were transiently and only slightly lower in Patient 1 but were not affected in Patient 2. In Patient 1, meningoradiculitis developed after the infusion; Patient 2 was pretreated with immunosuppressive drugs and did not have this complication. Patient 1 had transient improvement in the strength of his right leg, a measure that had been relatively stable throughout his disease course, but there was no change in his vital capacity. Patient 2 had stable scores on a composite measure of ALS function and a stable vital capacity during a 12-month period. This study showed that intrathecal microRNA can be used as a potential treatment for SOD1-mediated ALS.

Engraftment of Human Hepatocytes in the PiZ-NSG Mouse Model.

We recently described the generation of a novel mouse strain that efficiently and readily engrafts human primary hepatocytes to create liver xenografts (Borel et al., Mol Ther, 25: 2477-89, 2017). A transgenic mouse strain expressing a human PiZ allele for the SerpinA1 gene was crossed with the NOD-SCID-gamma chain knockout (NSG) strain to create a recipient strain (PiZ-NSG) for human hepatocyte xenotransplantation. In this chapter we provide a description of the methods to achieve these liver xenografts in the PiZ-NSG mouse.

Muscle-Directed Delivery of an AAV1 Vector Leads to Capsid-Specific T Cell Exhaustion in Nonhuman Primates and Humans.

With the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) approvals for Zolgensma, Luxturna, and Glybera, recombinant adeno-associated viruses (rAAVs) are considered efficient tools for gene transfer. However, studies in animals and humans demonstrate that intramuscular (IM) AAV delivery can trigger immune responses to AAV capsids and/or transgenes. IM delivery of rAAV1 in humans has also been described to induce tolerance to rAAV characterized by the presence of capsid-specific regulatory T cells (Tregs) in periphery. To understand mechanisms responsible for tolerance and parameters involved, we tested 3 muscle-directed administration routes in rhesus monkeys: IM delivery, venous limb perfusion, and the intra-arterial push and dwell method. These 3 methods were well tolerated and led to transgene expression. Interestingly, gene transfer in muscle led to Tregs and exhausted T cell infiltrates in situ at both day 21 and day 60 post-injection. In human samples, an in-depth analysis of the functionality of these cells demonstrates that capsid-specific exhausted T cells are detected after at least 5 years post-vector delivery and that the exhaustion can be reversed by blocking the checkpoint pathway. Overall, our study shows that persisting transgene expression after gene transfer in muscle is mediated by Tregs and exhausted T cells.

A divalent siRNA chemical scaffold for potent and sustained modulation of gene expression throughout the central nervous system.

Sustained silencing of gene expression throughout the brain using small interfering RNAs (siRNAs) has not been achieved. Here we describe an siRNA architecture, divalent siRNA (di-siRNA), that supports potent, sustained gene silencing in the central nervous system (CNS) of mice and nonhuman primates following a single injection into the cerebrospinal fluid. Di-siRNAs are composed of two fully chemically modified, phosphorothioate-containing siRNAs connected by a linker. In mice, di-siRNAs induced the potent silencing of huntingtin, the causative gene in Huntington's disease, reducing messenger RNA and protein throughout the brain. Silencing persisted for at least 6 months, with the degree of gene silencing correlating to levels of guide strand tissue accumulation. In cynomolgus macaques, a bolus injection of di-siRNA showed substantial distribution and robust silencing throughout the brain and spinal cord without detectable toxicity and with minimal off-target effects. This siRNA design may enable RNA interference-based gene silencing in the CNS for the treatment of neurological disorders.

Bridging from Intramuscular to Limb Perfusion Delivery of rAAV: Optimization in a Non-human Primate Study.

Phase 1 and phase 2 gene therapy trials using intramuscular (IM) administration of a recombinant adeno-associated virus serotype 1 (rAAV1) for replacement of serum alpha-1 antitrypsin (AAT) deficiency have shown long-term (5-year) stable transgene expression at approximately 2% to 3% of therapeutic levels, arguing for the long-term viability of this approach to gene replacement of secreted serum protein deficiencies. However, achieving these levels required 100 IM injections to deliver 135 mL of vector, and further dose escalation is limited by the scalability of direct IM injection. To further advance the dose escalation, we sought to bridge the rAAV-AAT clinical development program to regional limb perfusion, comparing two methods previously established for gene therapy, peripheral venous limb perfusion (VLP) and an intra-arterial push and dwell (IAPD) using rAAV1 and rAAV8 in a non-human primate (rhesus macaque) study. The rhesus AAT transgene was used with a c-myc tag to enable quantification of transgene expression. 5 cohorts of animals were treated with rAAV1-IM, rAAV1-VLP, rAAV1-IAPD, rAAV8-VLP, and rAAV8-IAPD (n = 2-3), with a dose of 6 × 1012 vg/kg. All methods were well tolerated clinically. Potency, as determined by serum levels of AAT, of rAAV1 by the VLP method was twice that observed with direct IM injection; 90 µg/mL with VLP versus 38 µg/mL with direct IM injection. There was an approximately 25-fold advantage in estimated vector genomes retained within the muscle tissue with VLP and a 5-fold improvement in the ratio of total vector genomes retained within muscle as compared with liver. The other methods were intermediate in the potency and retention of vector genomes. Examination of muscle enzyme (CK) levels indicated rAAV1-VLP to be equally safe as compared with IM injection, while the IAPD method showed significant CK elevation. Overall, rAAV1-VLP demonstrates higher potency per vector genome injected and a greater total vector retention within the muscle, as compared to IM injection, while enabling a much greater total dose to be delivered, with equivalent safety. These data provide the basis for continuation of the dose escalation of the rAAV1-AAT program in patients and bode well for rAAV-VLP as a platform for replacement of secreted proteins.

Five Years of Successful Inducible Transgene Expression Following Locoregional Adeno-Associated Virus Delivery in Nonhuman Primates with No Detectable Immunity.

Anti-transgene immune responses elicited after intramuscular (i.m.) delivery of recombinant adeno-associated virus (rAAV) have been shown to hamper long-term transgene expression in large-animal models of rAAV-mediated gene transfer. To overcome this hurdle, an alternative mode of delivery of rAAV vectors in nonhuman primate muscles has been described: the locoregional (LR) intravenous route of administration. Using this injection mode, persistent inducible transgene expression for at least 1 year under the control of the tetracycline-inducible Tet-On system was previously reported in cynomolgus monkeys, with no immunity against the rtTA transgene product. The present study shows the long-term follow-up of these animals. It is reported that LR delivery of a rAAV2/1 vector allows long-term inducible expression up to at least 5 years post gene transfer, with no any detectable host immune response against the transactivator rtTA, despite its immunogenicity following i.m. gene transfer. This study shows for the first time a long-term regulation of muscle gene expression using a Tet-On-inducible system in a large-animal model. Moreover, these findings further confirm that the rAAV LR delivery route is efficient and immunologically safe, allowing long-term skeletal muscle gene transfer.

Safe and effective superoxide dismutase 1 silencing using artificial microRNA in macaques.

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease caused by degeneration of motor neurons leading to rapidly progressive paralysis. About 10% of cases are caused by gain-of-function mutations that are transmitted as dominant traits. A potential therapy for these cases is to suppress the expression of the mutant gene. Here, we investigated silencing of SOD1, a gene commonly mutated in familial ALS, using an adeno-associated virus (AAV) encoding an artificial microRNA (miRNA) that targeted SOD1 In a superoxide dismutase 1 (SOD1)-mediated mouse model of ALS, we have previously demonstrated that SOD1 silencing delayed disease onset, increased survival time, and reduced muscle loss and motor and respiratory impairments. Here, we describe the preclinical characterization of this approach in cynomolgus macaques (Macaca fascicularis) using an AAV serotype for delivery that has been shown to be safe in clinical trials. We optimized AAV delivery to the spinal cord by preimplantation of a catheter and placement of the subject with head down at 30° during intrathecal infusion. We compared different promoters for the expression of artificial miRNAs directed against mutant SOD1 Results demonstrated efficient delivery and effective silencing of the SOD1 gene in motor neurons. These results support the notion that gene therapy with an artificial miRNA targeting SOD1 is safe and merits further development for the treatment of mutant SOD1-linked ALS.

Artificial miRNAs Reduce Human Mutant Huntingtin Throughout the Striatum in a Transgenic Sheep Model of Huntington's Disease.

Huntington's disease (HD) is a fatal neurodegenerative disease caused by a genetic expansion of the CAG repeat region in the huntingtin (HTT) gene. Studies in HD mouse models have shown that artificial miRNAs can reduce mutant HTT, but evidence for their effectiveness and safety in larger animals is lacking. HD transgenic sheep express the full-length human HTT with 73 CAG repeats. AAV9 was used to deliver unilaterally to HD sheep striatum an artificial miRNA targeting exon 48 of the human HTT mRNA under control of two alternative promoters: U6 or CßA. The treatment reduced human mutant (m) HTT mRNA and protein 50-80% in the striatum at 1 and 6 months post injection. Silencing was detectable in both the caudate and putamen. Levels of endogenous sheep HTT protein were not affected. There was no significant loss of neurons labeled by DARPP32 or NeuN at 6 months after treatment, and Iba1-positive microglia were detected at control levels. It is concluded that safe and effective silencing of human mHTT protein can be achieved and sustained in a large-animal brain by direct delivery of an AAV carrying an artificial miRNA.

Survival Advantage of Both Human Hepatocyte Xenografts and Genome-Edited Hepatocytes for Treatment of α-1 Antitrypsin Deficiency.

Hepatocytes represent an important target for gene therapy and editing of single-gene disorders. In α-1 antitrypsin (AAT) deficiency, one missense mutation results in impaired secretion of AAT. In most patients, lung damage occurs due to a lack of AAT-mediated protection of lung elastin from neutrophil elastase. In some patients, accumulation of misfolded PiZ mutant AAT protein triggers hepatocyte injury, leading to inflammation and cirrhosis. We hypothesized that correcting the Z mutant defect in hepatocytes would confer a selective advantage for repopulation of hepatocytes within an intact liver. A human PiZ allele was crossed onto an immune-deficient (NSG) strain to create a recipient strain (NSG-PiZ) for human hepatocyte xenotransplantation. Results indicate that NSG-PiZ recipients support heightened engraftment of normal human primary hepatocytes as compared with NSG recipients. This model can therefore be used to test hepatocyte cell therapies for AATD, but more broadly it serves as a simple, highly reproducible liver xenograft model. Finally, a promoterless adeno-associated virus (AAV) vector, expressing a wild-type AAT and a synthetic miRNA to silence the endogenous allele, was integrated into the albumin locus. This gene-editing approach leads to a selective advantage of edited hepatocytes, by silencing the mutant protein and augmenting normal AAT production, and improvement of the liver pathology.

5 Year Expression and Neutrophil Defect Repair after Gene Therapy in Alpha-1 Antitrypsin Deficiency.

Alpha-1 antitrypsin deficiency is a monogenic disorder resulting in emphysema due principally to the unopposed effects of neutrophil elastase. We previously reported achieving plasma wild-type alpha-1 antitrypsin concentrations at 2.5%-3.8% of the purported therapeutic level at 1 year after a single intramuscular administration of recombinant adeno-associated virus serotype 1 alpha-1 antitrypsin vector in alpha-1 antitrypsin deficient patients. We analyzed blood and muscle for alpha-1 antitrypsin expression and immune cell response. We also assayed previously reported markers of neutrophil function known to be altered in alpha-1 antitrypsin deficient patients. Here, we report sustained expression at 2.0%-2.5% of the target level from years 1-5 in these same patients without any additional recombinant adeno-associated virus serotype-1 alpha-1 antitrypsin vector administration. In addition, we observed partial correction of disease-associated neutrophil defects, including neutrophil elastase inhibition, markers of degranulation, and membrane-bound anti-neutrophil antibodies. There was also evidence of an active T regulatory cell response (similar to the 1 year data) and an exhausted cytotoxic T cell response to adeno-associated virus serotype-1 capsid. These findings suggest that muscle-based alpha-1 antitrypsin gene replacement is tolerogenic and that stable levels of M-AAT may exert beneficial neutrophil effects at lower concentrations than previously anticipated.

Regulatory and Exhausted T Cell Responses to AAV Capsid.

Recombinant adeno-associated viruses (AAVs) are quickly becoming the preferred viral vector for viral gene delivery for the treatment of a wide variety of genetic disorders. However, since their use in a clinical trial targeting hemophilia B patients 10 years ago, immune responses to the AAV capsid appear to have hampered some of the early clinical gene transfer efficacy. Indeed, AAV-based gene transfer has been shown to reactivate capsid-specific memory T cells, which have correlated with a decline in AAV-transduced tissue in some patients. Importantly, clinical trials have also shown that this reactivation can be quelled by administering time-course taper of glucocorticoid steroids before or after dosing. More recently, two clinical studies have shown that AAV gene transfer is not only able to induce a deleterious immune response, but also can result in the initiation of a tolerance to the AAV capsid mediated by regulatory T cells and exhausted T cells. This article reviews clinical trials describing immune responses to AAV, as well as the mechanisms responsible for immune tolerance in chronic infections and how it could apply to AAV-based gene transfer. A better understanding of both cytotoxic and tolerogenic immune responses to recombinant AAV will lead to safer gene transfer protocols in patients.

Therapeutic rAAVrh10 Mediated SOD1 Silencing in Adult SOD1(G93A) Mice and Nonhuman Primates.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease; survival in ALS is typically 3-5 years. No treatment extends patient survival by more than three months. Approximately 20% of familial ALS and 1-3% of sporadic ALS patients carry a mutation in the gene encoding superoxide dismutase 1 (SOD1). In a transgenic ALS mouse model expressing the mutant SOD1(G93A) protein, silencing the SOD1 gene prolongs survival. One study reports a therapeutic effect of silencing the SOD1 gene in systemically treated adult ALS mice; this was achieved with a short hairpin RNA, a silencing molecule that has raised multiple safety concerns, and recombinant adeno-associated virus (rAAV) 9. We report here a silencing method based on an artificial microRNA termed miR-SOD1 systemically delivered using adeno-associated virus rAAVrh10, a serotype with a demonstrated safety profile in CNS clinical trials. Silencing of SOD1 in adult SOD1(G93A) transgenic mice with this construct profoundly delayed both disease onset and death in the SOD1(G93A) mice, and significantly preserved muscle strength and motor and respiratory functions. We also document that intrathecal delivery of the same rAAVrh10-miR-SOD1 in nonhuman primates significantly and safely silences SOD1 in lower motor neurons. This study supports the view that rAAVrh10-miR-SOD1 merits further development for the treatment of SOD1-linked ALS in humans.

Early interaction of adeno-associated virus serotype 8 vector with the host immune system following intramuscular delivery results in weak but detectable lymphocyte and dendritic cell transduction.

Following in vivo recombinant adeno-associated virus (rAAV)-based gene transfer, adaptive immune responses specific to the vector or the transgene product have emerged as a potential roadblock to successful clinical translation. The occurrence of such responses depends on several parameters, including the route of vector administration as well as the viral serotype and the genome configuration, either self-complementary (sc) or single-stranded (ss). These parameters influence rAAV vector-associated immunity by modulating the crosstalk between the vector and the host immune system, including vector ability to interact or even transduce lymphoid tissues in general and antigen-presenting cells (APCs) in particular. Little is known about immune cell populations that are targeted in vivo by rAAV vectors. Moreover, the transduction of dendritic cells is still controversial and not directly demonstrated. Here, we show that intramuscular administration of an sc rAAV8 vector in the mouse leads to a rapid distribution of viral genomes in the lymphoid tissues that is associated with transgene expression. Transduced cells were detected in follicular areas of the spleen and the draining lymph nodes. In addition to B and T lymphocytes, transduced professional APCs were detected although at very low frequency. In addition, viral genomes and transgene transcripts were also detected in these cell populations after ss rAAV8 vector administration. Although the functional significance of those observations needs further explorations, our results highlight an early and intricate interaction between the rAAV vector upon its in vivo delivery and the host immune system.