Adeno-associated Virus Vectors For Gene Therapy Research Articles

Transduction and Genome Editing of the Heart with Adeno-Associated Viral Vectors Loaded onto Electrospun Polydioxanone Nonwoven Fabrics.

In this study, we introduce electrospun polydioxanone (PDO) nonwoven fabrics as a platform for the delivery of adeno-associated virus (AAV) vectors for transduction and genome editing by adhering them to organ surfaces, including the heart. AAV vectors were loaded onto the PDO fabrics by soaking the fabrics in a solution containing AAV vectors. In vitro, the amount of AAV vectors loaded onto the fabrics could be adjusted by changing their concentration in the solution, and the number of cells expressing the green fluorescent protein (GFP) encoded by the AAV vectors increased in correlation with the increasing amount of loaded AAV vectors. In vivo, both transduction and genome editing resulted in the observation of GFP expression around AAV vector-loaded PDO fabrics attached to the surfaces of mouse hearts, indicating effective transduction and expression at the target site. These results demonstrate the great potential of electrospun PDO nonwoven fabrics carrying therapeutic AAV vectors for gene therapy.

Protein phosphatase 2A anchoring disruptor gene therapy for familial dilated cardiomyopathy

Familial Dilated Cardiomyopathy is a prevalent cause of heart failure that results from the mutation of genes encoding proteins of diverse function. Despite modern therapy, Dilated Cardiomyopathy typically has a poor outcome and is the leading cause of cardiac transplantation. The phosphatase PP2A at cardiomyocyte perinuclear mAKAPβ signalosomes promotes pathological eccentric cardiac remodeling, as is characteristic of Dilated Cardiomyopathy. Displacement of PP2A from mAKAPβ, inhibiting PP2A function in that intracellular compartment, can be achieved by expression of a mAKAPβ-derived PP2A binding domain-derived peptide. To test whether PP2A anchoring disruption would be effective at preventing Dilated Cardiomyopathy-associated cardiac dysfunction, the adeno-associated virus gene therapy vector AAV9sc.PBD was devised to express the disrupting peptide in cardiomyocytes in vivo. Proof-of-concept is now provided that AAV9sc.PBD improves the cardiac structure and function of a cardiomyopathy mouse model involving transgenic expression of a mutant α-tropomyosin E54K Tpm1 allele, while AAV9sc.PBD has no effect on normal non-transgenic mice. At the cellular level, AAV9sc.PBD restores cardiomyocyte morphology and gene expression in the mutant Tpm1 mouse. As the mechanism of AAV9sc.PBD action suggests potential efficacy in Dilated Cardiomyopathy regardless of the underlying etiology, these data support the further testing of AAV9sc.PBD as a broad-based treatment for Dilated Cardiomyopathy.

Safety and Efficacy of Adeno-Associated Viral Gene Therapy in Patients With Retinal Degeneration: A Systematic Review and Meta-Analysis.

This systematic review evaluates the safety and efficacy of ocular gene therapy using adeno-associated virus (AAV). MEDLINE, Embase, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov were searched systematically for controlled or non-controlled interventional gene therapy studies using key words related to retinal diseases, gene therapy, and AAV vectors. The primary outcome measure was safety, based on ocular severe adverse events (SAEs). Secondary outcome measures evaluated efficacy of the therapy based on best corrected visual acuity (BCVA) and improvements in visual sensitivity and systemic involvement following ocular delivery. Pooling was done using a DerSimonian Laird random effects model. Risk of bias was assessed using the Cochrane Risk of Bias Tool, version 1. Our search identified 3548 records. Of these, 80 publications met eligibility criteria, representing 28 registered clinical trials and 5 postmarket surveillance studies involving AAV gene therapy for Leber congenital amaurosis (LCA), choroideremia, Leber hereditary optic neuropathy (LHON), age-related macular degeneration (AMD), retinitis pigmentosa (RP), X-linked retinoschisis, and achromatopsia. Overall, AAV therapy vectors were associated with a cumulative incidence of at least one SAE of 8% (95% confidence intervals [CIs] of 5% to 12%). SAEs were often associated with the surgical procedure rather than the therapeutic vector itself. Poor or inconsistent reporting of adverse events (AEs) were a limitation for the meta-analysis. The proportion of patients with any improvement in BCVA and visual sensitivity was 41% (95% CIs of 31% to 51%) and 51% (95% CIs of 31% to 70%), respectively. Systemic immune involvement was associated with a cumulative incidence of 31% (95% CI = 21% to 42%). AAV gene therapy vectors appear to be safe but the surgical procedure required to deliver them is associated with some risk. The large variability in efficacy can be attributed to the small number of patients treated, the heterogeneity of the population and the variability in dosage, volume, and follow-up. This systematic review will help to inform and guide future clinical trials.

Readministration of high-dose adeno-associated virus gene therapy vectors enabled by ImmTOR nanoparticles combined with B cell-targeted agents.

Tolerogenic ImmTOR nanoparticles encapsulating rapamycin have been demonstrated to mitigate immunogenicity of adeno-associated virus (AAV) gene therapy vectors, enhance levels of transgene expression, and enable redosing of AAV at moderate vector doses of 2 to 5E12 vg/kg. However, recent clinical trials have often pushed AAV vector doses 10-fold to 50-fold higher, with serious adverse events observed at the upper range. Here, we assessed combination therapy of ImmTOR with B cell-targeting drugs for the ability to increase the efficiency of redosing at high vector doses. The combination of ImmTOR with a monoclonal antibody against B cell activation factor (aBAFF) exhibited strong synergy leading to more than a 5-fold to 10-fold reduction of splenic mature B cells and plasmablasts while increasing the fraction of pre-/pro-B cells. In addition, this combination dramatically reduced anti-AAV IgM and IgG antibodies, thus enabling four successive AAV administrations at doses up to 5E12 vg/kg and at least two AAV doses at 5E13 vg/kg, with the transgene expression level in the latter case being equal to that observed in control animals receiving a single vector dose of 1E14 vg/kg. Similar synergistic effects were seen with a combination of ImmTOR and a Bruton's tyrosine kinase inhibitor, ibrutinib. These results suggest that ImmTOR could be combined with B cell-targeting agents to enable repeated vector administrations as a potential strategy to avoid toxicities associated with vector doses above 1E14 vg/kg.

Preclinical Development and Characterization of Novel Adeno-Associated Viral Vectors for the Treatment of Lipoprotein Lipase Deficiency.

Lipoprotein lipase deficiency (LPLD) results from mutations within the lipoprotein lipase (LPL) gene that lead to a complete lack of catalytically active LPL protein. Glybera was one of the first adeno-associated virus (AAV) gene replacement therapy to receive European Medicines Agency regulatory approval for the treatment of LPLD. However, Glybera is no longer marketed potentially due to a combination of economical, manufacturing, and vector-related issues. The aim of this study was to develop a more efficacious AAV gene therapy vector for LPLD. Following preclinical biodistribution, efficacy and non-Good Laboratory Practice toxicity studies with novel AAV1 and AAV8-based vectors in mice, we identified AAV8 pVR59. AAV8 pVR59 delivered a codon-optimized, human gain-of-function hLPLS447X transgene driven by a CAG promoter in an AAV8 capsid. AAV8 pVR59 was significantly more efficacious, at 10- to 100-fold lower doses, compared with an AAV1 vector based on Glybera, when delivered intramuscularly or intravenously, respectively, in mice with LPLD. Efficient gene transfer was observed within the injected skeletal muscle and liver following delivery of AAV8 pVR59, with long-term correction of LPLD phenotypes, including normalization of plasma triglycerides and lipid tolerance, for up to 6 months post-treatment. While intramuscular delivery of AAV8 pVR59 was well tolerated, intravenous administration augmented liver pathology. These results highlight the feasibility of developing a superior AAV vector for the treatment of LPLD and provide critical insight for initiating studies in larger animal models. The identification of an AAV gene therapy vector that is more efficacious at lower doses, when paired with recent advances in production and manufacturing technologies, will ultimately translate to increased safety and accessibility for patients.

Every little bit helps: A single-residue switch in a vascular AAV enables blood-brain barrier penetration

The clinical potential of adeno-associated virus (AAV) vectors as gene delivery tools for neurological diseases is constrained by the low capacity of natural AAV capsids to cross the blood-brain barrier (BBB). As a result, delivery of AAV vectors to the central nervous system (CNS) requires high vector doses or invasive local delivery, both associated with significant risks of vector-induced toxicity. To overcome this limitation, multiple groups have attempted to generate engineered AAV capsids with improved BBB penetration and CNS transduction. A previous study from Körbelin et al. performed directed evolution of an AAV2 peptide display library in mouse brain and identified AAV2-BR1, a capsid showing strong and highly specific transduction of the brain vasculature.1Körbelin J. Dogbevia G. Michelfelder S. Ridder D.A. Hunger A. Wenzel J. Seismann H. Lampe M. Bannach J. Pasparakis M. et al.A brain microvasculature endothelial cell-specific viral vector with the potential to treat neurovascular and neurological diseases.EMBO Mol. Med. 2016; 8: 609-625Crossref PubMed Scopus (96) Google Scholar In this issue of Molecular Therapy – Methods and Clinical Development, Hayato Kawabata and colleagues build on this body of work and show that a single mutation in the AAV2-BR1 capsid increases BBB penetration and causes a dramatic shift of vector tropism from the vasculature toward neurons.2Kawabata H. Konno A. Matsuzaki Y. Hirai H. A blood-brain barrier-penetrating AAV2 mutant created by a brain microvasculature endothelial cell-targeted AAV2 variant.Mol. Ther. Methods Clin. Dev. 2023; 29: 81-92Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar The authors later demonstrate that a similar shift in tropism can be achieved by generating mosaic capsids combining unmodified AAV2-BR1 and AAV9 subunits. These findings have important implications for AAV vector engineering, and they contribute to a better understanding of the molecular mechanisms controlling AAV tropism, endocytosis, vascular transcytosis (i.e., AAV transport from the bloodstream to the surrounding tissue through endothelial cells) and eventually transduction. The idea of using directed evolution to engineer AAV capsids with enhanced tropism for specific tissues was first proposed in 20033Müller O.J. Kaul F. Weitzman M.D. Pasqualini R. Arap W. Kleinschmidt J.A. Trepel M. Random peptide libraries displayed on adeno-associated virus to select for targeted gene therapy vectors.Nat. Biotechnol. 2003; 21: 1040-1046Crossref PubMed Scopus (315) Google Scholar,4Perabo L. Büning H. Kofler D.M. Ried M.U. Girod A. Wendtner C.M. Enssle J. Hallek M. In vitro selection of viral vectors with modified tropism: the adeno-associated virus display.Mol. Ther. 2003; 8: 151-157Abstract Full Text Full Text PDF PubMed Scopus (173) Google Scholar and since has led to the discovery of multiple designer capsids with improved properties (reviewed in Becker et al.5Becker J. Fakhiri J. Grimm D. Fantastic AAV gene therapy vectors and how to find them—random diversification, rational design and machine learning.Pathogens. 2022; 11: 756Crossref Scopus (8) Google Scholar). This evolution process is generally empirical, relying on the enrichment of certain mutants in cultured cells or animal tissues from large libraries of capsids harboring random mutations, chimeric sequences, or insertions. In most cases, the mechanisms leading to capsid phenotypic changes are yet to be discovered. Recent studies, however, have started to shed light on those molecular mechanisms by identifying receptors used by natural AAV capsids, such as KIAA0319L/AAV receptor (AAVR)6Pillay S. Meyer N.L. Puschnik A.S. Davulcu O. Diep J. Ishikawa Y. Jae L.T. Wosen J.E. Nagamine C.M. Chapman M.S. Carette J.E. An essential receptor for adeno-associated virus infection.Nature. 2016; 530: 108-112Crossref PubMed Scopus (261) Google Scholar or by engineered variants such as the highly neurotrophic capsid PHP.B.7Huang Q. Chan K.Y. Tobey I.G. Chan Y.A. Poterba T. Boutros C.L. Balazs A.B. Daneman R. Bloom J.M. Seed C. Deverman B.E. Delivering genes across the blood-brain barrier: LY6A, a novel cellular receptor for AAV-PHP.B capsids.PLoS One. 2019; 14: e0225206Crossref PubMed Scopus (96) Google Scholar In this latter case, the receptor was identified as Ly6A/SCA-1, a protein expressed on the surface of endothelial cells and essential for transcytosis of the capsid across the BBB. The receptor used by AAV2-BR1 to target the brain vasculature remains unknown, but the results obtained by Kawabata et al. provide important insight into the mechanisms of receptor-mediated transcytosis and transduction used by AAV capsids. AAV2-BR1 was isolated from an AAV2 peptide display constructed according to the method published by Müller et al. in 2003.1Körbelin J. Dogbevia G. Michelfelder S. Ridder D.A. Hunger A. Wenzel J. Seismann H. Lampe M. Bannach J. Pasparakis M. et al.A brain microvasculature endothelial cell-specific viral vector with the potential to treat neurovascular and neurological diseases.EMBO Mol. Med. 2016; 8: 609-625Crossref PubMed Scopus (96) Google Scholar,3Müller O.J. Kaul F. Weitzman M.D. Pasqualini R. Arap W. Kleinschmidt J.A. Trepel M. Random peptide libraries displayed on adeno-associated virus to select for targeted gene therapy vectors.Nat. Biotechnol. 2003; 21: 1040-1046Crossref PubMed Scopus (315) Google Scholar The constructs in this library contain a N587Q mutation adjacent to the randomized peptides, initially incorporated to facilitate the insertion of library-encoding oligonucleotide pools. In the present study, Kawabata et al. reverted this mutation to the parental N587 residue to generate the AAV2-BR1N capsid. This single-residue modification caused a profound change in tropism by allowing the capsid to undergo transcytosis across the BBB and transduce cells of the brain parenchyma instead of being “trapped” in the endothelial cells. This transduction-to-transcytosis switch suggests that the N587 residue participates in an essential interaction of the capsid with one or more cellular factors implicated in endosomal trafficking. Several models could account for these findings. In the first “single receptor” model, the Q587N reversion adjacent to the peptide presented on the AAV2-BR1 surface would modulate the affinity of the ensuing AAV2-BR1N capsid for its endothelial receptor. This change in capsid-receptor interaction could impact the release of the viral capsid from the receptor in the endocytic system, shifting the fate of the capsid from endosomal escape (and endothelial cell transduction) to transcytosis and egress from the basolateral membrane. In an alternative “receptor switch” model, the Q587N reversion would restore the binding of the capsid to a secondary receptor involved in cell-surface attachment and/or endosomal trafficking, such as heparan sulfate proteoglycan (HSPG) or AAVR. In this model, the original AAV2-BR1 capsid would be able to transduce vascular cells via its endothelial receptor but would be defective in extravasation or transduction of non-vascular cells due to impaired interaction with a secondary receptor caused by the N587Q mutation. This loss-of function would be rescued either by Q587N reversion in AAV2-BR1N or by the incorporation of AAV9 capsid subunits in mosaic AAV2-BR1/AAV9 capsids. The N587 residue lies between two arginines involved in HSPG binding (R585 and R588) but also in the vicinity of Q589, which directly contributes to the interaction with AAVR.8Meyer N.L. Hu G. Davulcu O. Xie Q. Noble A.J. Yoshioka C. Gingerich D.S. Trzynka A. David L. Stagg S.M. Chapman M.S. Structure of the gene therapy vector, adeno-associated virus with its cell receptor.Elife. 2019; 8: e44707Crossref PubMed Scopus (0) Google Scholar Several observations suggest that AAVR, rather than HSPG, may be involved in the phenotypic switch observed by Kawabata and colleagues. First, the transcytosis phenotype is rescued by the incorporation of capsid subunits from AAV9, which utilizes galactose and not HSPG as an attachment glycan.9Shen S. Bryant K.D. Brown S.M. Randell S.H. Asokan A. Terminal n-linked galactose is the primary receptor for adeno-associated virus.J. Biol. Chem. 2011; 286: 13532-13540Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar Second, N587 mutation has no measurable impact on AAV2 affinity for HSPG but can impair transduction at a post-binding stage,10Lochrie M.A. Tatsuno G.P. Christie B. McDonnell J.W. Zhou S. Surosky R. Pierce G.F. Colosi P. Mutations on the external surfaces of adeno-associated virus type 2 capsids that affect transduction and neutralization.J. Virol. 2006; 80: 821-834Crossref PubMed Scopus (159) Google Scholar more consistent with the involvement of AAVR. Lastly, the observations from the present study are strikingly reminiscent of findings from the Deverman group with PHP.eB showing that the depletion of AAVR leads to a dramatic shift of tropism from neurons to endothelial cells.7Huang Q. Chan K.Y. Tobey I.G. Chan Y.A. Poterba T. Boutros C.L. Balazs A.B. Daneman R. Bloom J.M. Seed C. Deverman B.E. Delivering genes across the blood-brain barrier: LY6A, a novel cellular receptor for AAV-PHP.B capsids.PLoS One. 2019; 14: e0225206Crossref PubMed Scopus (96) Google Scholar It is possible that the results from Deverman and from the present study converge toward the same phenomenon, in which an engineered capsid could utilize its de novo vascular receptor to transduce endothelial cells but would be defective in transcytosis and/or neuronal transduction when capsid-AAVR interaction is impaired. A comparison of AAV2-BR1 and AAV2-BR1N affinity for AAVR could provide further support to the receptor switch hypothesis. AAV2-BR1N did not show improved brain transduction in a primate model, which questions the clinical relevance of the findings. Nevertheless, this study represents an important step in the understanding of the complex, multistep binding-transcytosis-transduction process that is required for efficient brain transduction with AAV via intravenous dosing. The present study examined the impact of a single point mutation, but there is no doubt that the vast sequence space of AAV holds many more surprises and opportunities that could be harnessed for iterative vector improvement. The findings of Kawabata et al. have pivotal implications for the engineering of novel capsids, the understanding of combined action of multiple receptors, and eventually the semi-rational engineering of second- or third-generation variants with enhanced properties. The authors declare no financial interest.

The Use of Adeno-associated virus (AAV) in Vaccine Development

 
 Adeno-associated virus (AAV) is a very tiny (20-26 nm) icosahedral and non-enveloped virus, and it belongs to the Parvoviridae family. AAV vectors are the most widely used option for gene therapy and delivery of therapeutic antibodies due to their relatively low immunogenicity, high safety profile, broad tropism, and their tendency to maintain long-term gene expression [1]. AVV vectors are developed by transfection of human embryonic kidney (HEK) 293 T cells with transgene, packaging and helper plasmids [2]. Several clinical studies have investigated the use of AAV vectors for gene therapy in treating of Parkinson’s disease, Alzheimer’s disease, heart disease, and prostate cancer [3]. AAV vectors have previously been used to treat muscular diseases, but in recent years, their usage as vaccine vectors to cure or prevent infectious diseases including HIV, HPV, and influenza has expanded [4].
  
 Here, we discuss the advantages and disadvantages of the use of AAV in vaccine development, and future approaches in improving the drawbacks caused by AAV-based vaccines. Numerous animal investigations have been conducted to explore vaccine vectors against various illnesses, suggesting a possibility for AAV-based vaccinations. Clinical studies on humans are, however, uncommon because, in contrast to other viral vectors, AAV induces a poor humoral and cellular immune response. Additionally, infectious vaccinations often target a large group of healthy individuals across a variety of ages, including children and teenagers. Therefore, compared to AAV-based gene therapies, vaccinations based on AAV vectors need to be more cost-effective and need more robust safety control.
  
 According to several research, AAV vector vaccines have been shown to induce a stronger or longer lasting antibody response in comparison to other vaccination approaches, such as DNA, recombinant proteins, inactivated viruses, or virus-like particles (VLPs) [5]. However, AAV vectors are thought to have a low immunogenic profile in comparison to other viral vectors. The main limitations of AAV vectors are their low transgenic capacity and widespread pre-existing immunity in humans [6]. Currently, strategies for improving AAV immunogenicity and circumventing pre-existing immunity are actively being investigated. The research undertaken so far have highlighted numerous significant benefits of AAV vectors for immunisation. Despite all the advantages, there are still a variety of challenges that limit the use of these vectors as a vaccine in humans. Thus, it is necessary to overcome these challenges in order to make AAV-based vaccines effective.

Fantastic AAV Gene Therapy Vectors and How to Find Them—Random Diversification, Rational Design and Machine Learning

Parvoviruses are a diverse family of small, non-enveloped DNA viruses that infect a wide variety of species, tissues and cell types. For over half a century, their intriguing biology and pathophysiology has fueled intensive research aimed at dissecting the underlying viral and cellular mechanisms. Concurrently, their broad host specificity (tropism) has motivated efforts to develop parvoviruses as gene delivery vectors for human cancer or gene therapy applications. While the sum of preclinical and clinical data consistently demonstrates the great potential of these vectors, these findings also illustrate the importance of enhancing and restricting in vivo transgene expression in desired cell types. To this end, major progress has been made especially with vectors based on Adeno-associated virus (AAV), whose capsid is highly amenable to bioengineering, repurposing and expansion of its natural tropism. Here, we provide an overview of the state-of-the-art approaches to create new AAV variants with higher specificity and efficiency of gene transfer in on-target cells. We first review traditional and novel directed evolution approaches, including high-throughput screening of AAV capsid libraries. Next, we discuss programmable receptor-mediated targeting with a focus on two recent technologies that utilize high-affinity binders. Finally, we highlight one of the latest stratagems for rational AAV vector characterization and optimization, namely, machine learning, which promises to facilitate and accelerate the identification of next-generation, safe and precise gene delivery vehicles.

Targeting mAKAPβ expression as a therapeutic approach for ischemic cardiomyopathy.

Ischemic cardiomyopathy is a leading cause of death and an unmet clinical need. Adeno-associated virus (AAV) gene-based therapies hold great promise for treating and preventing heart failure. Previously we showed that muscle A-kinase Anchoring Protein β (mAKAPβ, AKAP6β), a scaffold protein that organizes perinuclear signalosomes in the cardiomyocyte, is a critical regulator of pathological cardiac hypertrophy. Here, we show that inhibition of mAKAPβ expression in stressed adult cardiomyocytes in vitro was cardioprotective, while conditional cardiomyocyte-specific mAKAP gene deletion in mice prevented pathological cardiac remodeling due to myocardial infarction. We developed a new self-complementary serotype 9 AAV gene therapy vector expressing a short hairpin RNA for mAKAPβ under the control of a cardiomyocyte-specific promoter (AAV9sc.shmAKAP). This vector efficiently downregulated mAKAPβ expression in the mouse heart in vivo. Expression of the shRNA also inhibited mAKAPβ expression in human induced cardiomyocytes in vitro. Following myocardial infarction, systemic administration of AAV9sc.shmAKAP prevented the development of pathological cardiac remodeling and heart failure, providing long-term restoration of left ventricular ejection fraction. Our findings provide proof-of-concept for mAKAPβ as a therapeutic target for ischemic cardiomyopathy and support the development of a translational pipeline for AAV9sc.shmAKAP for the treatment of heart failure.

Quantitation of Trace Levels of DNA Released from Disrupted Adeno-Associated Virus Gene Therapy Vectors.

Adeno-associated virus (AAV) vectors for gene therapy have potential to provide a durable treatment response for a number of diseases with unmet need. DNA is released from AAV capsids at high temperatures. Less is known about DNA release that may occur under conditions relevant to clinical and commercial manufacturing, storage, and distribution. In this work we developed and applied a sensitive fluorescent dye-based method to quantitate trace levels of DNA released from AAV capsids. The method was used to characterize the impact of manufacturing process steps on the increase (up to 1.5%) and removal (down to 0.2%) of free DNA. Free DNA increased by 0.3% per day at 37°C and by 0.4% per freeze/thaw cycle in a phosphate-buffered saline formulation. When stored for 2 years at different temperatures, free DNA remained low (<0.6%) at both ≤ -60°C and at 2-8°C but was higher (2.6%) when the same sample was stored at -20°C. The dye-based method may be used to further characterize release of free DNA for different processes, formulations, and stress conditions. Overall, release of free DNA was a relatively minor degradation pathway under the conditions studied in this work.

Improved systemic AAV gene therapy with a neurotrophic capsid in Niemann-Pick disease type C1 mice.

Niemann-Pick C1 disease (NPC1) is a rare, fatal neurodegenerative disease caused by mutations in NPC1, which encodes the lysosomal cholesterol transport protein NPC1. Disease pathology involves lysosomal accumulation of cholesterol and lipids, leading to neurological and visceral complications. Targeting the central nervous system (CNS) from systemic circulation complicates treatment of neurological diseases with gene transfer techniques. Selected and engineered capsids, for example, adeno-associated virus (AAV)-PHP.B facilitate peripheral-to-CNS transfer and hence greater CNS transduction than parental predecessors. We report that systemic delivery to Npc1 m1N/m1N mice using an AAV-PHP.B vector ubiquitously expressing NPC1 led to greater disease amelioration than an otherwise identical AAV9 vector. In addition, viral copy number and biodistribution of GFP-expressing reporters showed that AAV-PHP.B achieved more efficient, albeit variable, CNS transduction than AAV9 in Npc1 m1N/m1N mice. This variability was associated with segregation of two alleles of the putative AAV-PHP.B receptor Ly6a in Npc1 m1N/m1N mice. Our data suggest that robust improvements in NPC1 disease phenotypes occur even with modest CNS transduction and that improved neurotrophic capsids have the potential for superior NPC1 AAV gene therapy vectors.

Overcoming innate immune barriers that impede AAV gene therapy vectors.

The field of gene therapy has made considerable progress over the past several years. Adeno-associated virus (AAV) vectors have emerged as promising and attractive tools for in vivo gene therapy. Despite the recent clinical successes achieved with recombinant AAVs (rAAVs) for therapeutics, host immune responses against the vector and transgene product have been observed in numerous preclinical and clinical studies. These outcomes have hampered the advancement of AAV gene therapies, preventing them from becoming fully viable and safe medicines. The human immune system is multidimensional and complex. Both the innate and adaptive arms of the immune system seem to play a concerted role in the response against rAAVs. While most efforts have been focused on the role of adaptive immunity and developing ways to overcome it, the innate immune system has also been found to have a critical function. Innate immunity not only mediates the initial response to the vector, but also primes the adaptive immune system to launch a more deleterious attack against the foreign vector. This Review highlights what is known about innate immune responses against rAAVs and discusses potential strategies to circumvent these pathways.

Targeted epigenetic repression by CRISPR/dSaCas9 suppresses pathogenic DUX4-fl expression in FSHD

Facioscapulohumeral muscular dystrophy (FSHD) is caused by incomplete silencing of the disease locus, leading to pathogenic misexpression of DUX4 in skeletal muscle. Previously, we showed that CRISPR inhibition could successfully target and repress DUX4 in FSHD myocytes. However, an effective therapy will require both efficient delivery of therapeutic components to skeletal muscles and long-term repression of the disease locus. Thus, we re-engineered our platform to allow in vivo delivery of more potent epigenetic repressors. We designed an FSHD-optimized regulatory cassette to drive skeletal muscle-specific expression of dCas9 from Staphylococcus aureus fused to HP1α, HP1γ, the MeCP2 transcriptional repression domain, or the SUV39H1 SET domain. Targeting each regulator to the DUX4 promoter/exon 1 increased chromatin repression at the locus, specifically suppressing DUX4 and its target genes in FSHD myocytes and in a mouse model of the disease. Importantly, minimizing the regulatory cassette and using the smaller Cas9 ortholog allowed our therapeutic cassettes to be effectively packaged into adeno-associated virus (AAV) vectors for in vivo delivery. By engineering a muscle-specific epigenetic CRISPR platform compatible with AAV vectors for gene therapy, we have laid the groundwork for clinical use of dCas9-based chromatin effectors in skeletal muscle disorders.

Calcineurin Aβ-Specific Anchoring Confers Isoform-Specific Compartmentation and Function in Pathological Cardiac Myocyte Hypertrophy.

The Ca2+/calmodulin-dependent phosphatase calcineurin is a key regulator of cardiac myocyte hypertrophy in disease. An unexplained paradox is how the β isoform of the calcineurin catalytic A-subunit (CaNAβ) is required for induction of pathological myocyte hypertrophy, despite calcineurin Aα expression in the same cells. It is unclear how the pleiotropic second messenger Ca2+ drives excitation-contraction coupling while not stimulating hypertrophy by calcineurin in the normal heart. Elucidation of the mechanisms conferring this selectivity in calcineurin signaling should reveal new strategies for targeting the phosphatase in disease. Primary adult rat ventricular myocytes were studied for morphology and intracellular signaling. New Förster resonance energy transfer reporters were used to assay Ca2+ and calcineurin activity in living cells. Conditional gene deletion and adeno-associated virus-mediated gene delivery in the mouse were used to study calcineurin signaling after transverse aortic constriction in vivo. CIP4 (Cdc42-interacting protein 4)/TRIP10 (thyroid hormone receptor interactor 10) was identified as a new polyproline domain-dependent scaffold for CaNAβ2 by yeast 2-hybrid screen. Cardiac myocyte-specific CIP4 gene deletion in mice attenuated pressure overload-induced pathological cardiac remodeling and heart failure. Blockade of CaNAβ polyproline-dependent anchoring using a competing peptide inhibited concentric hypertrophy in cultured myocytes; disruption of anchoring in vivo using an adeno-associated virus gene therapy vector inhibited cardiac hypertrophy and improved systolic function after pressure overload. Live cell Förster resonance energy transfer biosensor imaging of cultured myocytes revealed that Ca2+ levels and calcineurin activity associated with the CIP4 compartment were increased by neurohormonal stimulation, but minimally by pacing. Conversely, Ca2+ levels and calcineurin activity detected by nonlocalized Förster resonance energy transfer sensors were induced by pacing and minimally by neurohormonal stimulation, providing functional evidence for differential intracellular compartmentation of Ca2+ and calcineurin signal transduction. These results support a structural model for Ca2+ and CaNAβ compartmentation in cells based on an isoform-specific mechanism for calcineurin protein-protein interaction and localization. This mechanism provides an explanation for the specific role of CaNAβ in hypertrophy and its selective activation under conditions of pathologic stress. Disruption of CaNAβ polyproline-dependent anchoring constitutes a rational strategy for therapeutic targeting of CaNAβ-specific signaling responsible for pathological cardiac remodeling in cardiovascular disease deserving of further preclinical investigation.

GPR108 Is a Highly Conserved AAV Entry Factor.

Adeno-associated virus (AAV) is a highly promising gene transfer vector, yet major cellular requirements for AAV entry are poorly understood. Using a genome-wide CRISPR screen for entry of evolutionarily divergent serotype AAVrh32.33, we identified GPR108, a member of the G protein-coupled receptor superfamily, as an AAV entry factor. Of greater than 20 divergent AAVs across all AAV clades tested in human cell lines, only AAV5 transduction was unaffected in the GPR108 knockout (KO). GPR108 dependency was further shown in murine and primary cells invitro. These findings are further validated invivo, as the Gpr108 KO mouse demonstrates 10- to 100-fold reduced expression for AAV8 and rh32.33 but not AAV5. Mechanistically, both GPR108 N- and C-terminal domains are required for transduction, and on the capsid, a VP1 unique domain that is not conserved on AAV5 can be transferred to confer GPR108 independence onto AAV2 chimeras. Invitro binding and fractionation studies indicate reduced nuclear import and cytosolic accumulation in the absence of GPR108. We thus have identified the second of two AAV entry factors that is conserved between mice and humans relevant both invitro and invivo, further providing a mechanistic understanding to the tropism of AAV gene therapy vectors.

Efficacy and Safety in 15 Hemophilia B Patients Treated with the AAV Gene Therapy Vector Fidanacogene Elaparvovec and Followed for at Least 1 Year

Background: Adeno-Associated Virus (AAV) based liver transduction has emerged as a potentially viable gene therapy approach for the treatment of hemophilia patients. Fidanacogene elaparvovec (previously SPK-9001) is a hepatotropic bioengineered AAV based vector that delivers a high activity factor IX (FIX) transgene driven by a liver specific promoter. The Phase 1/2a development consists of a dosing study where patients are followed for 52 weeks post vector infusion followed by a long-term follow-up study for an additional 5 years. Data on the first 10 patients were previously published and demonstrated safe and sustained expression of a high activity FIX protein with an associated decreased requirement for exogenous factor administration and markedly reduced annualized bleeding rate. Here we present data on 15 patients infused with fidanacogene elaparvovec with ≥ 1 year of follow-up, which represents the largest cohort of Hemophilia B (HB) patients treated with the same vector at the same dose. Methods: Fifteen (15) adult HB patients were infused with 5 x 1011 vg/kg of fidanacogene elaparvovec and followed for at least 1 year as part of the Phase 1/2a dosing study. FIX activity (FIX:C) levels were measured using a one-stage assay. Endpoints include: Safety and tolerability, steady-state activity calculated as the geometric mean of all observed FIX:C activity levels from week 12 through week 52; annualized bleeding rate (ABR) prior to and 52 weeks after vector infusion; T cell response to fidanacogene elaparvovec capsid and transgene monitored post-infusion using an interferon-γ enzyme-linked immunospot (ELISpot) assay. Results: Three of fifteen patients were treated with corticosteroids for elevations in hepatic transaminases of which 2 were positive for capsid reactive T cells by interferon-γ ELISpot. There were otherwise no treatment related adverse events. The mean post-infusion steady-state FIX:C was 22.9%±9.9% at 1 year post vector infusion as measured in a central laboratory by one-stage assay utilizing Actin-FSL. Mean ABR during the first 52 weeks following fidanacogene elaparvovec infusion was 0.4±1.1 compared to 8.9±14.0 in the 52 weeks preceding infusion (p&lt;0.001). Twelve (12) out of 15 patients reported zero bleeds in the 52 weeks post-vector infusion. Five of 15 subjects infused factor for a total of 20 infusions. Additional follow-up data will be presented for all patients enrolled in the long-term follow-up study. Conclusions: Fidanacogene elaparvovec was well tolerated in 15 patients with no serious adverse events. Data for all patients at 52 weeks post-infusion demonstrated a marked reduction in bleeding frequency and exogenous FIX use. All hepatic transaminase elevations responded to treatment with corticosteroids. Collectively, to date, this represents the largest cohort of HB patients treated with the same AAV based gene therapy and at the lowest dose. Treatment has been efficacious for all patients with manageable immune responses when present. These data support progression to a pivotal Phase 3 study at the dose evaluated. Disclosures George: University of Pennyslvania: Employment; Avrobio: Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy. Sullivan:Octapharma: Consultancy, Other: Advisory Board. Rasko:bluebird bio: Honoraria; Celgene: Honoraria; Novartis: Honoraria; FSHD Global Research Foundation: Membership on an entity's Board of Directors or advisory committees; Rarecyte: Consultancy, Equity Ownership; Gene Technology Technical Advisory, Australian Government: Other: Advisory committee; GSK: Honoraria; Takeda: Honoraria; Cynata: Honoraria; Genea: Equity Ownership; Cure The Future Foundation: Membership on an entity's Board of Directors or advisory committees; Gilead: Honoraria; Pfizer: Honoraria; Spark: Honoraria; Imago: Consultancy; Advisory Committee on Biologics, Australian Government: Other: Advisory Committee; NHMRC Mitochondrial Donation Expert Working Committee: Other: Advisory Committee; Australian Cancer Research Scientific Advisory Board: Membership on an entity's Board of Directors or advisory committees. Giermasz:Genentech/Roche: Consultancy, Other: Research, Speakers Bureau; uniQure: Consultancy, Other: Research; Bioverativ/Sanofi: Consultancy, Speakers Bureau; BioMarin: Consultancy, Other: Research; Sangamo: Other: Research. Samelson-Jones:The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania: Employment. Ducore:Bayer: Consultancy, Honoraria, Other: speaker (not bureau); Spark Therapeutics: Research Funding; Shire: Consultancy, Honoraria; Octapharma: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; HEMA Biologics: Consultancy, Honoraria; BioMarin: Research Funding; Bioverativ: Research Funding. Teitel:BioMarin: Consultancy; Bayer: Consultancy, Research Funding; Shire: Consultancy; Pfizer: Consultancy, Research Funding; Novo Nordisk: Consultancy; Octapharma: Consultancy; CSL Behring: Consultancy. McGuinn:Biogen: Research Funding; Roche/Genetech: Research Funding; Spark: Research Funding; Shire/Baxalta: Consultancy, Research Funding. Wright:Solid Biosciences: Consultancy; Yposkesi: Other: Senior Advisor, SAB; LogicBio Therapeutics: Other: Member, SAB; Memorial Sloan Kettering Cancer Center: Consultancy; Agilis Biotherapeutics: Consultancy; Axovant Sciences: Other: Chief Technology Officer, Gene Therapies; Akous Therapeutics: Consultancy; National Institutes of Health: Consultancy; Leland Stanford Junior University: Consultancy; Wright Biologics: Other; Sanofi Genzyme: Consultancy; Spark Therapeutics: Consultancy, Other: co-founder, Chief Technology Advisor/Officer, Member, SAB; Adrenas Therapeutics: Other: Member, SAB; Ambys Medicines: Consultancy; CEVEC Pharmaceuticl: Other: Member, SAB. Anguela:Spark Therapeutics: Employment, Equity Ownership, Patents &amp; Royalties. High:Spark Therapeutics: Employment, Equity Ownership, Patents &amp; Royalties. Rybin:Pfizer: Employment. Murphy:Pfizer Inc.: Employment. Rupon:Pfizer: Employment.

Post-translational modifications in capsid proteins of recombinant adeno-associated virus (AAV) 1-rh10 serotypes.

Post‐translational modifications in viral capsids are known to fine‐tune and regulate several aspects of the infective life cycle of several viruses in the host. Recombinant viruses that are generated in a specific producer cell line are likely to inherit unique post‐translational modifications during intra‐cellular maturation of its capsid proteins. Data on such post‐translational modifications in the capsid of recombinant adeno‐associated virus serotypes (AAV1‐rh10) is limited. We have employed liquid chromatography and mass spectrometry analysis to characterize post‐translational modifications in AAV1‐rh10 capsid protein. Our analysis revealed a total of 52 post‐translational modifications in AAV2‐AAVrh10 capsids, including ubiquitination (17%), glycosylation (36%), phosphorylation (21%), SUMOylation (13%) and acetylation (11%). While AAV1 had no detectable post‐translational modification, at least four AAV serotypes had >7 post‐translational modifications in their capsid protein. About 82% of these post‐translational modifications are novel. A limited validation of AAV2 capsids by MALDI‐TOF and western blot analysis demonstrated minimal glycosylation and ubiquitination of AAV2 capsids. To further validate this, we disrupted a glycosylation site identified in AAV2 capsid (AAV2‐N253Q), which severely compromised its packaging efficiency (~ 100‐fold vs. AAV2 wild‐type vectors). In order to confirm other post‐translational modifications detected such as SUMOylation, mutagenesis of a SUMOylation site(K258Q) in AAV2 was performed. This mutant vector demonstrated reduced levels of SUMO‐1/2/3 proteins and negligible transduction, 2 weeks after ocular gene transfer. Our study underscores the heterogeneity of post‐translational modifications in AAV vectors. The data presented here, should facilitate further studies to understand the biological relevance of post‐translational modifications in AAV life cycle and the development of novel bioengineered AAV vectors for gene therapy applications.EnzymesTrypsin, EC 3.4.21.4

Polarized AAVR expression determines infectivity by AAV gene therapy vectors.

Adeno-associated virus (AAV) has been investigated to transfer the cystic fibrosis transmembrane conductance regulator (CFTR) to airways. Inhaled AAV2-CFTR in people with cystic fibrosis (CF) is safe, but inefficient. In vitro, AAV2 transduction of human airway epithelia on the apical (luminal) side is inefficient, but efficient basolaterally. We previously selected AAV2.5T, a novel capsid that apically transduces CF human airway epithelia and efficiently restores CFTR function. We hypothesize the AAV receptor (AAVR) is basolaterally localized, and that AAV2.5T utilizes an alternative apical receptor. We found AAVR in human airway epithelia by western blot and RNA-Seq analyses. Using immunocytochemistry we did not find endogenous AAVR at membranes but overexpression localized AAVR to the basolateral membrane, where it preferentially increased transduction. Anti-AAVR antibodies blocked transduction by AAV2 from the basolateral side but not AAV2.5T from the apical side, suggesting a unique apical receptor. Finally, we found infection by AAV2 but not AAV2.5T was blocked by CRISPR knockout of AAVR in cell lines. Our data suggest the absence of apical AAVR is rate limiting for AAV2, and efficient transduction by AAV2.5T is accomplished using an AAVR independent pathway. Our findings inform the development of gene therapy for CF, and AAV vectors in general.

Adeno-associated virus 2 bound to its cellular receptor AAVR.

Adeno-associated virus (AAV) is a leading vector for virus-based gene therapy. The receptor for AAV (AAVR; also named KIAA0319L) was recently identified, and the precise characterization of AAV-AAVR recognition is in immediate demand. Taking advantage of a particle-filtering algorithm, we report here the cryo-electron microscopy structure of the AAV2-AAVR complex at 2.8 Å resolution. This structure reveals that of the five Ig-like polycystic kidney disease (PKD) domains in AAVR, PKD2 binds directly to the spike region of the AAV2 capsid adjacent to the icosahedral three-fold axis. Residues in strands B and E, and the BC loop of AAVR PKD2 interact directly with the AAV2 capsid. The interacting residues in the AAV2 capsid are mainly in AAV-featured variable regions. Mutagenesis of the amino acids at the AAV2-AAVR interface reduces binding activity and viral infectivity. Our findings provide insights into the biology of AAV entry with high-resolution details, providing opportunities for the development of new AAV vectors for gene therapy.

Impact of the Assembly-Activating Protein on Molecular Evolution of Synthetic Adeno-Associated Virus Capsids.

Over the last decade, the role of the assembly-activating protein (AAP) has begun to be dissected for the formation of adeno-associated virus (AAV) capsids based on different viral serotypes. Recently, the authors' group has specifically studied AAP's relevance during production of AAV gene therapy vectors in mammalian or insect cells, and AAP was found to be essential for capsid protein stabilization and generation of functional vector particles. Here, the lingering question is additionally addressed of whether molecular AAV evolution via DNA family shuffling of viral capsid genes would perturb AAP functionality due to concurrent and inadvertent recombination of the AAP open reading frame. To this end, a battery of complementary experiments was conducted in which: (1) the ability of chimeric AAP from AAVDJ, a hybrid of serotypes 2, 8, and 9, was tested to rescue AAP knockouts in the three parental serotypes; (2) the functionality of 60 chimeric AAPs extracted from five shuffled, unselected capsid libraries was measured; (3) whether production of different shuffled libraries, 10 wild-type serotypes or 25 individual chimeric capsids, can be enhanced by overexpression of AAP cocktails was assessed; and (4) the activity of 12 chimeric AAPs isolated from a shuffled library that was iteratively selected in vivo in mouse livers was studied. Collectively, the data demonstrate a remarkable tolerance of AAP for recombination via DNA family shuffling, evidenced by the findings that (1) all chimeric AAPs studied here retained at least partial activity, even in cases where the cognate hybrid capsid may be non-functional, and that (2) ectopic AAP overexpression did not enhance production of shuffled AAV chimeras or libraries, implying that the inherently encoded hybrid AAP variants are sufficiently active. Together, this work provides compelling evidence that AAP is not rate limiting during AAV capsid shuffling and thereby relieves a major concern in the field of AAV vector evolution.