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Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator ( CFTR ) gene. Although many people with CF (pwCF) are treated using CFTR modulators, some are non-responsive due to their genotype or other uncharacterized reasons. Autologous airway stem cell therapies, in which the CFTR cDNA has been replaced, may enable a durable therapy for all pwCF. Previously, CRISPR-Cas9 with two AAVs was used to sequentially insert two-halves of the CFTR cDNA and an enrichment cassette into the CFTR locus. However, the editing efficiency was <10% and required enrichment to restore CFTR function. Further improvement in gene insertion may enhance cell therapy production. To improve CFTR cDNA insertion in human airway basal stem cells (ABCs), we evaluated the use of the small molecules AZD7648 and ART558, which inhibit non-homologous end-joining (NHEJ) and micro-homology mediated end-joining (MMEJ). Adding AZD7648 alone improved gene insertion by 2- to 3-fold. Adding both ART558 and AZD7648 improved gene insertion but induced toxicity. ABCs edited in the presence of AZD7648 produced differentiated airway epithelial sheets with restored CFTR function after enrichment. Adding AZD7648 did not increase off-target editing. Further studies are necessary to validate if AZD7648 treatment enriches cells with oncogenic mutations., Competing Interests: The authors declare no competing interests., (© 2024 The Author(s).)

Recent clinical studies of single gene replacement therapy for neuromuscular disorders have shown they can slow or stop disease progression, but such therapies have had little impact on reversing muscle disease that was already present. To reverse disease in patients with muscular dystrophy, new muscle mass and strength must be rebuilt at the same time that gene replacement prevents subsequent disease. Here, we show that treatment of FKRP P448L mice with a dual FKRP/FST gene therapy packaged into a single adeno-associated virus (AAV) vector can build muscle strength and mass that exceed levels found in wild-type mice and can induce normal ambulation endurance in a 1-h walk test. Dual FKRP/FST therapy also showed more even increases in muscle mass and amplified muscle expression of both genes relative to either single gene therapy alone. These data suggest that treatment with single AAV-bearing dual FKRP/FST gene therapies can overcome loss of ambulation by improving muscle strength at the same time it prevents subsequent muscle damage. This design platform could be used to create therapies for other forms of muscular dystrophy that may improve patient outcomes., Competing Interests: Declaration of interests P.T.M. has financial conflicts of interest with Sarepta Therapeutics and Genosera Inc. A patent has been filed on this technology., (Copyright © 2024 The American Society of Gene and Cell Therapy. Published by Elsevier Inc. All rights reserved.)

Neuroinflammation is a miscreant in accelerating progression of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). However, treatments targeting neuroinflammation alone have led to disappointing results in clinical trials. Both neuronal and non-neuronal cell types have been implicated in the pathogenesis of ALS, and multiple studies have shown correction of each cell type has beneficial effects on disease outcome. Previously, we shown that AAV9-mediated superoxide dismutase 1 (SOD1) suppression in motor neurons and astrocytes significantly improves motor function and extends survival in ALS mouse models. Despite neuron and astrocyte correction, ALS mice still succumb to death with microgliosis observed in endpoint tissue. Therefore, we hypothesized that the optimal therapeutic approach will target and simultaneously correct motor neurons, astrocytes, and microglia. Here, we developed a novel approach to indirectly target microglia with galectin-1 (Gal1) and combined this with our previously established AAV9.SOD1.short hairpin RNA treatment. We show Gal1 conditioning of SOD1 G93A microglia decreases inflammatory markers and rescues motor neuron death in vitro . When paired with SOD1 downregulation, we found a synergistic effect of combination treatment in vivo and show a significant extension of survival of SOD1 G93A mice over SOD1 suppression alone. These results highlight the importance of targeting inflammatory microglia as a critical component in future therapeutic development., Competing Interests: A patent on AAV gene therapy vectors that contain a therapeutic protein and additionally express an anti-inflammatory protein or peptide has been filed by The Research Institute at Nationwide Children’s Hospital with K.C.M. and S.B.L. as inventors., (© 2024 The Authors.)

Leukoencephalopathy with vanishing white matter (VWM) is a progressive incurable white matter disease that most commonly occurs in childhood and presents with ataxia, spasticity, neurological degeneration, seizures, and premature death. A distinctive feature is episodes of rapid neurological deterioration provoked by stressors such as infection, seizures, or trauma. VWM is caused by autosomal recessive mutations in one of five genes that encode the eukaryotic initiation factor 2B complex, which is necessary for protein translation and regulation of the integrated stress response. The majority of mutations are in EIF2B5. Astrocytic dysfunction is central to pathophysiology, thereby constituting a potential therapeutic target. Herein we characterize two VWM murine models and investigate astrocyte-targeted adeno-associated virus serotype 9 (AAV9)-mediated EIF2B5 gene supplementation therapy as a therapeutic option for VWM. Our results demonstrate significant rescue in body weight, motor function, gait normalization, life extension, and finally, evidence that gene supplementation attenuates demyelination. Last, the greatest rescue results from a vector using a modified glial fibrillary acidic protein (GFAP) promoter-AAV9-gfaABC(1)D-EIF2B5-thereby supporting that astrocytic targeting is critical for disease correction. In conclusion, we demonstrate safety and early efficacy through treatment with a translatable astrocyte-targeted gene supplementation therapy for a disease that has no cure., Competing Interests: Declaration of interests J.L.B. is on the board of wFluidx, Inc., owns stock in Orchard Therapeutics, and has consulted for Bluebird bio, Calico Life Sciences, Denali Therapeutics, Enzyvant, and Neurogene. A.M.B. is a beneficiary of a licensing agreement with Axovant Gene Therapies (royalties) and Neurogene (royalties) and has received income from Neurogene (consulting and honorarium). A.M.B., K.M.F., J.L.B., N.K.P., and J.A.H. are inventors on a provisional patent: Materials and Methods for the Treatment of EIF2B5 Mutations and Diseases Resulting Therefrom. Provisional Patent 63/316,241., (Copyright © 2024 The American Society of Gene and Cell Therapy. Published by Elsevier Inc. All rights reserved.)

Duchenne muscular dystrophy (DMD) is a progressive X-linked disease caused by mutations in the DMD gene that prevent the expression of a functional dystrophin protein. Exon duplications represent 6%-11% of mutations, and duplications of exon 2 (Dup2) are the most common (∼11%) of duplication mutations. An exon-skipping strategy for Dup2 mutations presents a large therapeutic window. Skipping one exon copy results in full-length dystrophin expression, whereas skipping of both copies (Del2) activates an internal ribosomal entry site (IRES) in exon 5, inducing the expression of a highly functional truncated dystrophin isoform. We have previously confirmed the therapeutic efficacy of AAV9.U7snRNA-mediated skipping in the Dup2 mouse model and showed the absence of off-target splicing effects and lack of toxicity in mice and nonhuman primates. Here, we report long-term dystrophin expression data following the treatment of 3-month-old Dup2 mice with the scAAV9.U7.ACCA vector. Significant exon 2 skipping and robust dystrophin expression in the muscles and hearts of treated mice persist at 18 months after treatment, along with the partial rescue of muscle function. These data extend our previous findings and show that scAAV9.U7.ACCA provides long-term protection by restoring the disrupted dystrophin reading frame in the context of exon 2 duplications., Competing Interests: NCH licensed the vector described herein to Audentes Therapeutics, which was subsequently acquired by Astellas Therapeutics. N.W. and K.M.F. have received royalty payments as a result of this license., (© 2023 The Authors.)

Duchenne muscular dystrophy is an X-linked disorder typically caused by out-of-frame mutations in the DMD gene. Most of these are deletions of one or more exons, which can theoretically be corrected through CRISPR-Cas9-mediated knockin. Homology-independent targeted integration is a mechanism for achieving such a knockin without reliance on homology-directed repair pathways, which are inactive in muscle. We designed a system based on insertion into intron 19 of a DNA fragment containing a pre-spliced mega-exon encoding DMD exons 1-19, along with the MHCK7 promoter, and delivered it via a pair of AAV9 vectors in mice carrying a Dmd exon 2 duplication. Maximal efficiency was achieved using a Cas9:donor adeno-associated virus (AAV) ratio of 1:5, with Cas9 under the control of the SPc5-12 promoter. This approach achieved editing of 1.4% of genomes in the heart, leading to 30% correction at the transcript level and restoration of 11% of normal dystrophin levels. Treatment efficacy was lower in skeletal muscles. Sequencing additionally revealed integration of fragmentary and recombined AAV genomes at the target site. These data provide proof of concept for a gene editing system that could restore full-length dystrophin in individuals carrying mutations upstream of intron 19, accounting for approximately 25% of Duchenne muscular dystrophy patients., Competing Interests: A.A.S. and K.M.F. are inventors on a pending patent application filed by Nationwide Children’s Hospital for the gene editing system presented in this work., (© 2023 The Authors.)

Anc80L65 is a synthetic, ancestral adeno-associated virus that has high tropism toward retinal photoreceptors after subretinal injection in mice and non-human primates. We characterized, for the first time, the post-intravitreal cell-specific transduction profile of Anc80L65 compared with AAV9. Here we use Anc80L65 and AAV9 to intravitreally deliver a copy of the gene encoding GFP into WT C57Bl/6J mice. GFP expression was driven by one of two clinically relevant promoters, chicken β actin (CB) or truncated MECP2 (P546). After qualitative assessment of relative GFP expression, we found Anc80L65 and AAV9 to have similar transduction profiles. Through the development of a novel method for quantifying GFP-positive retinal cells, we found Anc80L65 to have higher tropism in Müller glia and AAV9 to have higher tropism in horizontal cells. In addition, we found P546 to promote GFP expression at a more moderate level compared with the high levels seen under the CB promoter. Finally, for the first time, we characterized Anc80L65 cross-reactivity in human sera; 83% of patients with AAV2 pre-existing antibodies were found to be seropositive for Anc80L65. This study demonstrates the expanded therapeutic applications of Anc80L65 to treat retinal disease and provides the first insights to Anc80L65 pre-existing immunity in humans., Competing Interests: K.M. is receiving royalties from Gene Therapy programs licensed to Amicus Therapeutics and Kiadis. K.M. is a scientific advisor with compensation and stock options and has received research funding from Alcyone Therapeutics., (© 2023 The Authors.)

Duchenne muscular dystrophy (DMD) is a devastating muscle-wasting disease that arises due to the loss of dystrophin expression, leading to progressive loss of motor and cardiorespiratory function. Four exon-skipping approaches using antisense phosphorodiamidate morpholino oligomers (PMOs) have been approved by the FDA to restore a DMD open reading frame, resulting in expression of a functional but internally deleted dystrophin protein, but in patients with single-exon duplications, exon skipping has the potential to restore full-length dystrophin expression. Cell-penetrating peptide-conjugated PMOs (PPMOs) have demonstrated enhanced cellular uptake and more efficient dystrophin restoration than unconjugated PMOs. In the present study, we demonstrate widespread PPMO-mediated dystrophin restoration in the Dup2 mouse model of exon 2 duplication, representing the most common single-exon duplication among patients with DMD. In this proof-of-concept study, a single intravenous injection of PPMO targeting the exon 2 splice acceptor site induced 45% to 68% exon 2-skipped Dmd transcripts in Dup2 skeletal muscles 15 days post-injection. Muscle dystrophin restoration peaked at 77% to 87% average dystrophin-positive fibers and 41% to 51% of normal signal intensity by immunofluorescence, and 15.7% to 56.8% of normal by western blotting 15 to 30 days after treatment. These findings indicate that PPMO-mediated exon skipping is a promising therapeutic strategy for muscle dystrophin restoration in the context of exon 2 duplications., Competing Interests: K.M.F. has received research support for a clinical trial from Sarepta Therapeutics. K.M.F. and N.W. hold a patent related to therapeutic exon 2 skipping, and along with Nationwide Children’s Hospital receive royalties from Astellas Gene Therapy for that patent, which is not directly related to the data presented here., (© 2022 The Authors.)

In a phase 1/2, open-label dose escalation trial, we delivered rAAVrh74.MCK. GALGT2 (also B4GALNT2 ) bilaterally to the legs of two boys with Duchenne muscular dystrophy using intravascular limb infusion. Subject 1 (age 8.9 years at dosing) received 2.5 × 10 13 vector genome (vg)/kg per leg (5 × 10 13 vg/kg total) and subject 2 (age 6.9 years at dosing) received 5 × 10 13 vg/kg per leg (1 × 10 14 vg/kg total). No serious adverse events were observed. Muscle biopsy evaluated 3 or 4 months post treatment versus baseline showed evidence of GALGT2 gene expression and GALGT2 -induced muscle cell glycosylation. Functionally, subject 1 showed a decline in 6-min walk test (6MWT) distance; an increase in time to run 100 m, and a decline in North Star Ambulatory Assessment (NSAA) score until ambulation was lost at 24 months. Subject 2, treated at a younger age and at a higher dose, demonstrated an improvement over 24 months in NSAA score (from 20 to 23 points), an increase in 6MWT distance (from 405 to 478 m), and only a minimal increase in 100 m time (45.6-48.4 s). These data suggest preliminary safety at a dose of 1 × 10 14 vg/kg and functional stabilization in one patient., Competing Interests: P.T.M. and Nationwide Children’s Hospital report a financial conflict of interest related to this study, as they both receive licensing fees from Sarepta Therapeutics for rAAVrh74.MCK.GALGT2. P.T.M. is also co-founder and President of Genosera Inc., (© 2022 The Authors.)

Duchenne muscular dystrophy (DMD) is typically caused by mutations that disrupt the DMD reading frame, but nonsense mutations in the 5' part of the gene induce utilization of an internal ribosomal entry site (IRES) in exon 5, driving expression of a highly functional N-truncated dystrophin. We have developed an AAV9 vector expressing U7 small nuclear RNAs targeting DMD exon 2 and have tested it in a mouse containing a duplication of exon 2, in which skipping of both exon 2 copies induces IRES-driven expression, and skipping of one copy leads to wild-type dystrophin expression. One-time intravascular injection either at postnatal days 0-1 or at 2 months results in efficient exon skipping and dystrophin expression, and significant protection from functional and pathologic deficits. Immunofluorescence quantification showed 33%-53% average dystrophin intensity and 55%-79% average dystrophin-positive fibers in mice treated in adulthood, with partial amelioration of DMD pathology and correction of DMD-associated alterations in gene expression. In mice treated neonatally, dystrophin immunofluorescence reached 49%-85% of normal intensity and 76%-99% dystrophin-positive fibers, with near-complete correction of dystrophic pathology, and these beneficial effects persisted for at least 6 months. Our results demonstrate the robustness, durability, and safety of exon 2 skipping using scAAV9.U7snRNA.ACCA, supporting its clinical use., Competing Interests: Since the performance of this work, Nationwide Children’s Hospital licensed the vector described herein to Audentes/Astellas Therapeutics. N.W., A.V., and K.M.F. have received royalty payments as a result of this license., (© 2022 The Authors.)

Duchenne muscular dystrophy (DMD) is an X-linked progressive disease characterized by loss of dystrophin protein that typically results from truncating mutations in the DMD gene. Current exon-skipping therapies have sought to treat deletion mutations that abolish an open reading frame (ORF) by skipping an adjacent exon, in order to restore an ORF that allows translation of an internally deleted yet partially functional protein, as is seen with many patients with the milder Becker muscular dystrophy (BMD) phenotype. In contrast to that approach, skipping of one copy of a duplicated exon would be expected to result in a full-length transcript and production of a wild-type protein. We have developed an adeno-associated virus (AAV)-based U7snRNA exon-skipping approach directed toward exon 2, duplications of which represent 10% of all DMD duplication mutations. Deletion of exon 2 results in utilization of an exon 5 internal ribosome entry site (IRES) that allows translation beginning in exon 6 of a highly protective dystrophin protein, providing a wide therapeutic window for treatment. Both intramuscular and systemic administration of this vector in the Dup2 mouse model results in robust dystrophin expression and correction of muscle physiologic defects, allowing dose escalation to establish a putative minimal efficacious dose for a human clinical trial., Competing Interests: Since the performance of this work, Nationwide Children’s Hospital has licensed the vector described herein to Audentes Therapeutics. N.W., A.V.C., and K.M.F. have received royalty payments as a result of this license., (© 2021 The Authors.)