CNS-restricted Transduction and CRISPR/Cas9-mediated Gene Deletion with an Engineered AAV Vector

CRISPR/Cas9 Genome Editing for Tissue-Specific In Vivo Targeting: Nanomaterials and Translational Perspective

Clustered randomly interspaced short palindromic repeats (CRISPRs) and its associated endonuclease protein, i.e., Cas9, have been discovered as an immune system in bacteria and archaea; nevertheless, they are now being adopted as mainstream biotechnological/molecular scissors that can modulate ample genetic and nongenetic diseases via insertion/deletion, epigenome editing, messenger RNA editing, CRISPR interference, etc. Many Food and Drug Administration-approved and ongoing clinical trials on CRISPR adopt ex vivo strategies, wherein the gene editing is performed ex vivo, followed by reimplantation to the patients. However, the in vivo delivery of the CRISPR components is still under preclinical surveillance. This review has summarized the nonviral nanodelivery strategies for gene editing using CRISPR/Cas9 and its recent advancements, strategic points of view, challenges, and future aspects for tissue-specific in vivo delivery of CRISPR/Cas9 components using nanomaterials.

Gene Therapy for Neuropsychiatric Disorders: Potential Targets and Tools

Neuropsychiatric disorders that affect the central nervous system cause considerable pressures on the health care system and have a substantial economic burden on modern societies. The present treatments based on available drugs are mostly ineffective and often costly. The molecular process of neuropsychiatric disorders is closely connected to modifying the genetic structures inherited or caused by damage, toxic chemicals, and some current diseases. Gene therapy is presently an experimental concept for neurological disorders. Clinical applications endeavor to alleviate the symptoms, reduce disease progression, and repair defective genes. Implementing gene therapy in inherited and acquired neurological illnesses entails the integration of several scientific disciplines, including virology, neurology, neurosurgery, molecular genetics, and immunology. Genetic manipulation has the power to minimize or cure illness by inducing genetic alterations at endogenous loci. Gene therapy that involves treating the disease by deleting, silencing, or editing defective genes and delivering genetic material to produce therapeutic molecules has excellent potential as a novel approach for treating neuropsychiatric disorders. With the recent advances in gene selection and vector design quality in targeted treatments, gene therapy could be an effective approach. This review article will investigate and report the newest and the most critical molecules and factors in neuropsychiatric disorder gene therapy. Different genome editing techniques available will be evaluated, and the review will highlight preclinical research of genome editing for neuropsychiatric disorders while also evaluating current limitations and potential strategies to overcome genome editing advancements.

AAV vectors: The Rubik's cube of human gene therapy

Defective genes account for ∼80% of the total of more than 7,000 diseases known to date. Gene therapy brings the promise of a one-time treatment option that will fix the errors in patient genetic coding. Recombinant viruses are highly efficient vehicles for in vivo gene delivery. Adeno-associated virus (AAV) vectors offer unique advantages, such as tissue tropism, specificity in transduction, eliciting of a relatively low immune responses, no incorporation into the host chromosome, and long-lasting delivered gene expression, making them the most popular viral gene delivery system in clinical trials, with three AAV-based gene therapy drugs already approved by the US Food and Drug Administration (FDA) or European Medicines Agency (EMA). Despite the success of AAV vectors, their usage in particular scenarios is still limited due to remaining challenges, such as poor transduction efficiency in certain tissues, low organ specificity, pre-existing humoral immunity to AAV capsids, and vector dose-dependent toxicity in patients. In the present review, we address the different approaches to improve AAV vectors for gene therapy with a focus on AAV capsid selection and engineering, strategies to overcome anti-AAV immune response, and vector genome design, ending with a glimpse at vector production methods and the current state of recombinant AAV (rAAV) at the clinical level.

CRISPR-Cas9-Based Technology and Its Relevance to Gene Editing in Parkinson's Disease

Parkinson’s disease (PD) and other chronic and debilitating neurodegenerative diseases (NDs) impose a substantial medical, emotional, and financial burden on individuals and society. The origin of PD is unknown due to a complex combination of hereditary and environmental risk factors. However, over the last several decades, a significant amount of available data from clinical and experimental studies has implicated neuroinflammation, oxidative stress, dysregulated protein degradation, and mitochondrial dysfunction as the primary causes of PD neurodegeneration. The new gene-editing techniques hold great promise for research and therapy of NDs, such as PD, for which there are currently no effective disease-modifying treatments. As a result, gene therapy may offer new treatment options, transforming our ability to treat this disease. We present a detailed overview of novel gene-editing delivery vehicles, which is essential for their successful implementation in both cutting-edge research and prospective therapeutics. Moreover, we review the most recent advancements in CRISPR-based applications and gene therapies for a better understanding of treating PD. We explore the benefits and drawbacks of using them for a range of gene-editing applications in the brain, emphasizing some fascinating possibilities.

In vivo targeting of a variant causing vanishing white matter using CRISPR/Cas9

Vanishing white matter (VWM) is a leukodystrophy caused by recessive variants in subunits of eIF2B. At present, no curative treatment is available and patients often die at young age. Due to its monogenic nature, VWM is a promising candidate for the development of CRISPR/Cas9-mediated gene therapy. Here we tested a dual-AAV approach in VWM mice encoding CRISPR/Cas9 and a DNA donor template to correct a pathogenic variant in Eif2b5. We performed sequencing analysis to assess gene correction rates and examined effects on the VWM phenotype, including motor behavior. Sequence analysis demonstrated that over 90% of CRISPR/Cas9-induced edits at the targeted locus are insertion or deletion (indel) mutations, rather than precise corrections from the DNA donor template by homology-directed repair. Around half of the CRISPR/Cas9-treated animals died prematurely. VWM mice showed no improvement in motor skills, weight, or neurological scores at 7 months of age, and CRISPR/Cas9-treated controls displayed an induced VWM phenotype. In conclusion, CRISPR/Cas9-induced DNA double-strand breaks (DSBs) at the Eif2b5 locus did not lead to sufficient correction of the VWM variant. Moreover, indel formation in Eif2b5 induced an exacerbated VWM phenotype. Therefore, DSB-independent strategies like base- or prime editing might better suited for VWM correction.

Onasemnogene abeparvovec for the treatment of spinal muscular atrophy

INTRODUCTION

Gene therapy for spinal muscular atrophy (SMA) represents a significant milestone in the treatment of neurologic diseases. SMA is a neurodegenerative disease that results in motor neuron loss because of mutations of the survival motor neuron 1 gene, which directs survival motor neuron (SMN) protein production. Onasemnogene abeparvovec, a one-time gene replacement therapy, delivers a functional transgene to restore SMN protein expression. Onasemnogene abeparvovec has demonstrated improved survival and motor milestone achievements for presymptomatic infants and patients with SMA type 1.

AREAS COVERED

This expert review describes the current state of gene therapy for SMA, reviews the mechanism of and clinical experience with onasemnogene abeparvovec, explains future efforts to expand applications of gene therapy for SMA, and provides context for developing gene therapy for other conditions.

EXPERT OPINION

Onasemnogene abeparvovec has demonstrated efficacy in clinical trials and, because of this, is a valuable treatment option for patients with symptomatic infantile SMA and those identified by newborn screening. Gene therapy is still in its infancy, and challenges and uncertainties associated with transgene delivery must be addressed. With ongoing development of vector technology, more specific tissue tropism, reduced "off-target" effects, and an enhanced safety profile will continue to evolve.

Anti-Inflammatory Gene Therapy Improves Spatial Memory Performance in a Mouse Model of Alzheimer's Disease

The immune system plays a critical role in neurodegenerative processes involved in Alzheimer’s disease (AD). In this study, a gene-based immunotherapeutic method examined the effects of anti-inflammatory cellular immune response elements (CIREs) in the amyloid-β protein precursor (AβPP) mouse model. Bi-monthly intramuscular administration, beginning at either 4 or 6 months, and examined at 7.5 through 16 months, with plasmids encoding Interleukin (IL)-10, IL-4, TGF-β polynucleotides, or a combination thereof, into AβPP mice improved spatial memory performance. This work demonstrates an efficient gene therapy strategy to downregulate neuroinflammation, and possibly prevent or delay cognitive decline in AD.

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3′-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.

Clustered regularly interspaced short palindromic repeats as an advanced treatment for Parkinson's disease

Recently, genome-editing technology like clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 has improved the translational gap in the treatments mediated through gene therapy. The advantages of the CRISPR system, such as, work in the living cells and tissues, candidate this technique for the employing in experiments and the therapy of central nervous system diseases. Parkinson's disease (PD) is a widespread, disabling, neurodegenerative disease induced by dopaminergic neuron loss and linked to progressive motor impairment. Pathophysiological basis knowledge of PD has modified the PD classification model and expresses in the sporadic and familial types. Analyses of the earliest genetic linkage have shown in PD the inclusion of synuclein alpha (SNCA) genomic duplication and SNCA mutations in the familial types of PD pathogenesis. This review analyzes the structure, development, and function in genome editing regulated through the CRISPR/Cas9. Also, it explains the genes associated with PD pathogenesis and the appropriate modifications to favor PD. This study follows the direction by understanding the PD linking analyses in which the CRISPR technique is applied. Finally, this study explains the limitations and future trends of CRISPR service in relation to the genome-editing process in PD patients' induced pluripotent stem cells.

Genetic Variants and Oxidative Stress in Alzheimer's Disease

In an aging society, the number of people suffering from Alzheimer's Disease (AD) is still growing. Currently, intensive research is being carried out on the pathogenesis of AD. The results of these studies indicated that oxidative stress plays an important role in the onset and development of this disease. Moreover, in AD oxidative stress is generated by both genetic and biochemical factors as well as the functioning of the systems responsible for their formation and removal. The genetic factors associated with the regulation of the redox system include TOMM40, APOE, LPR, MAPT, APP, PSEN1 and PSEN2 genes. The most important biochemical parameters related to the formation of oxidative species in AD are p53, Homocysteine (Hcy) and a number of others. The formation of Reactive Oxygen Species (ROS) is also related to the efficiency of the DNA repair system, the effectiveness of the apoptosis, autophagy and mitophagy processes as well as the antioxidant potential. However, these factors are responsible for the development of many disorders, often with similar clinical symptoms, especially in the early stages of the disease. The discovery of markers of the early diagnosis of AD may contribute to the introduction of pharmacotherapy and slow down the progression of this disease.

In vivo genome editing in single mammalian brain neurons through CRISPR-Cas9 and cytosine base editors

Gene manipulation is a useful approach for understanding functions of genes and is important for investigating basic mechanisms of brain function on the level of single neurons and circuits. Despite the development and the wide range of applications of CRISPR-Cas9 and base editors (BEs), their implementation for an analysis of individual neurons in vivo remained limited. In fact, conventional gene manipulations are generally achieved only on the population level. Here, we combined either CRISPR-Cas9 or BEs with the targeted single-cell electroporation technique as a proof-of-concept test for gene manipulation in single neurons in vivo. Our assay consisted of CRISPR-Cas9- or BEs-induced gene knockout in single Purkinje cells in the cerebellum. Our results demonstrate the feasibility of both gene editing and base editing in single cells in the intact brain, providing a tool through which molecular perturbations of individual neurons can be used for analysis of circuits and, ultimately, behaviors.

BBB-crossing adeno-associated virus vector: An excellent gene delivery tool for CNS disease treatment

The presence of the blood-brain barrier (BBB) remains a challenge in the treatment of central nervous system (CNS) diseases, as it hinders the infiltration of many therapeutic drugs into the brain parenchyma. Therefore, developing efficacious pharmacological agents that can traverse the BBB is crucial for optimal treatment of diseases of the CNS such as neurodegenerative conditions and brain tumors. Adeno-associated virus (AAV), one of the most promising gene therapy vectors, has been shown to cross the BBB safely and is non-pathogenic in nature and therefore has been utilized for numerous diseases of the CNS. Along with the development of protein engineering techniques such as directed evolution including DNA shuffling, a great number of BBB-crossing AAVs have been developed, that could be systemically injected for therapeutic benefit. In this review, we discuss several feasible approaches to improve transportation of therapeutic agents to the CNS. We also discuss the advantages of using BBB-crossing AAVs, their role as a gene delivery agent and highlight the different types of BBB-AAV vectors that have been developed in order to provide a greater insight into how they can be used in diseases of the CNS.

Approach for in vivo delivery of CRISPR/Cas system: a recent update and future prospect

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) system provides a groundbreaking genetic technology that allows scientists to modify genes by targeting specific genomic sites. Due to the relative simplicity and versatility of the CRISPR/Cas system, it has been extensively applied in human genetic research as well as in agricultural applications, such as improving crops. Since the gene editing activity of the CRISPR/Cas system largely depends on the efficiency of introducing the system into cells or tissues, an efficient and specific delivery system is critical for applying CRISPR/Cas technology. However, there are still some hurdles remaining for the translatability of CRISPR/Cas system. In this review, we summarized the approaches used for the delivery of the CRISPR/Cas system in mammals, plants, and aquacultures. We further discussed the aspects of delivery that can be improved to elevate the potential for CRISPR/Cas translatability.

Postnatal therapeutic approaches in genetic neurodevelopmental disorders

Genetic neurodevelopmental disorders are characterized by abnormal neurophysiological and behavioral phenotypes, affecting individuals worldwide. While the subject has been heavily researched, current treatment options relate mostly to alleviating symptoms, rather than targeting the altered genome itself. In this review, we address the neurogenetic basis of neurodevelopmental disorders, genetic tools that are enabling precision research of these disorders in animal models, and postnatal gene-therapy approaches for neurodevelopmental disorders derived from preclinical studies in the laboratory.

Application of CRISPR-Cas systems in neuroscience

CRISPR-Cas systems have, over the years, emerged as indispensable tools for Genetic interrogation in contexts of clinical interventions, elucidation of genetic pathways and metabolic engineering and have pervaded almost every aspect of modern biology. Within this repertoire, the nervous system comes with its own set of perplexities and mysteries. Scientists have, over the years, tried to draw up a clearer genetic picture of the neuron and how it functions in a network, mainly in an endeavor to mitigate diseases of the human nervous system like Alzheimer's, Parkinson's, Huntington's, Autism Spectrum Disorder (ASD), etc. With most being progressive in nature, these diseases have plagued mankind for centuries. In spite of our immense progress in modern biology, we are yet to get a grasp over these diseases and unraveling their mechanisms is of utmost importance. Before CRISPR-Cas systems came along, the elucidation of the complex interactome of the mammalian nervous system was attempted with erstwhile existing electrophysiological, histological and pharmacological techniques coupled with Next Generation Sequencing and cell-specific targeting technologies. Zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), imparted excellent sequence specific DNA targeting capabilities but came with their huge baggage of extensive protein engineering requirements, which practically rendered them unsuitable for high throughput exercises. With the discovery of Clustered Regularly Interspaced Palindromic Repeats (CRISPR) and CRISPR Associated proteins(CAS) systems by Ishino (1987)¹, the era of extensive custom made endonuclease targeting was ushered in. For the first time in 2012, Jinek et al. (2012)² repurposed the CRISPR-Cas mediated bacterial immune system for customizable mammalian gene editing. The CRISPR-Cas technology made it possible to easily customize Cas9 endonucleases to cleave near specifically targeted sequences, thereby facilitating knock-ins or knock-outs, silencing or activating or editing any gene, at any locus of the genome, both at the base-pair level or at the epigenetic level. With this enhanced degree of freedom, decrypting the nervous system and therapeutic interventions for neuropathies became significantly less cumbersome an exercise. Here we take a brisk walk through the several endeavors of research that show how the humble bacteria's CRISPR-Cas system gave us the "nerves" to "talk" to our nerves with ease.

Challenges in adeno-associated virus-based treatment of central nervous system diseases through systemic injection

Adeno-associated virus (AAV) vector, an excellent gene therapy vector, has been widely used in the treatment of various central nervous system (CNS) diseases. Due to the presence of the blood-brain barrier (BBB), early attempts at AAV-based CNS diseases treatment were mainly performed through intracranial injections. Subsequently, systemic injections of AAV9, the first AAV that was shown to have BBB-crossing ability in newborn and adult mice, were assessed in clinical trials for multiple CNS diseases. However, the development of systemic AAV injections to treat CNS diseases is still associated with many challenges, such as the efficiency of AAV in crossing the BBB, the peripheral toxicity caused by the expression of AAV-delivered genes, and the immune barrier against AAV in the blood. In this review, we will introduce the biology of the AAV vector and the advantages of systemic AAV injections to treat CNS diseases. Most importantly, we will introduce the challenges associated with systemic injection of therapeutic AAV in treating CNS diseases and suggest feasible solutions.

Revisiting gene delivery to the brain: silencing and editing

Neurodegenerative disorders, ischemic brain diseases, and brain tumors are debilitating diseases that severely impact a person's life and could possibly lead to their demise if left untreated. Many of these diseases do not respond to small molecule therapeutics and have no effective long-term therapy. Gene therapy offers the promise of treatment or even a cure for both genetic and acquired brain diseases, mediated by either silencing or editing disease-specific genes. Indeed, in the last 5 years, significant progress has been made in the delivery of non-coding RNAs as well as gene-editing formulations to the brain. Unfortunately, the delivery is a major limiting factor for the success of gene therapies. Both viral and non-viral vectors have been used to deliver genetic information into a target cell, but they have limitations. Viral vectors provide excellent transduction efficiency but are associated with toxic effects and have limited packaging capacity; however, non-viral vectors are less toxic and show a high packaging capacity at the price of low transfection efficiency. Herein, we review the progress made in the field of brain gene therapy, particularly in the design of non-toxic and trackable non-viral vectors, capable of controlled release of genes in response to internal/external triggers, and in the delivery of formulations for gene editing. The application of these systems in the context of various brain diseases in pre-clinical and clinical tests will be discussed. Such promising approaches could potentially pave the way for clinical realization of brain gene therapies.

The Golgi Calcium ATPase Pump Plays an Essential Role in Adeno-associated Virus Trafficking and Transduction

Adeno-associated viruses (AAVs) have proven to be effective gene transfer vectors. However, our understanding of how the host cell environment influences AAV transduction is still evolving. In the present study, we investigated the role of ATP2C1, which encodes a membrane calcium transport pump, SPCA1, essential for maintaining cellular calcium homeostasis on AAV transduction. Our results indicate that cellular calcium is essential for efficient intracellular trafficking and conformational changes in the AAV capsid that support efficient genome transcription. Further, we show that pharmacological modulation of cellular calcium levels can potentially be applied to improve the AAV gene transfer efficiency.

Adeno-associated viruses (AAVs) are dependoparvoviruses that have proven useful for therapeutic gene transfer; however, our understanding of host factors that influence AAV trafficking and transduction is still evolving. Here, we investigated the role of cellular calcium in the AAV infectious pathway. First, we demonstrated a critical role for the host Golgi compartment-resident ATP-powered calcium pump (secretory pathway calcium ATPase 1 [SPCA1]) encoded by the ATP2C1 gene in AAV infection. CRISPR-based knockout (KO) of ATP2C1 decreases transduction by different AAV serotypes. ATP2C1 KO does not appear to inhibit AAV binding, cellular uptake, or nuclear entry; however, capsids within ATP2C1 KO cells demonstrate dispersed and punctate trafficking distinct from the perinuclear, trans-Golgi pattern observed in normal cells. In addition, we observed a defect in the ability of AAV capsids to undergo conformational changes and support efficient vector genome transcription in ATP2C1 KO cells. The calcium chelator BAPTA-AM, which reduces cytosolic calcium, rescues the defective ATP2C1 KO phenotype and AAV transduction in vitro. Conversely, the calcium ionophore ionomycin, which disrupts calcium gradients, blocks AAV transduction. Further, we demonstrated that modulating calcium in the murine brain using BAPTA-AM augments AAV gene expression in vivo. Taking these data together, we postulate that the maintenance of an intracellular calcium gradient by the calcium ATPase and processing within the Golgi compartment are essential for priming the capsid to support efficient AAV genome transcription.

IMPORTANCE Adeno-associated viruses (AAVs) have proven to be effective gene transfer vectors. However, our understanding of how the host cell environment influences AAV transduction is still evolving. In the present study, we investigated the role of ATP2C1, which encodes a membrane calcium transport pump, SPCA1, essential for maintaining cellular calcium homeostasis on AAV transduction. Our results indicate that cellular calcium is essential for efficient intracellular trafficking and conformational changes in the AAV capsid that support efficient genome transcription. Further, we show that pharmacological modulation of cellular calcium levels can potentially be applied to improve the AAV gene transfer efficiency.

Gene and Cell-Based Therapies for Parkinson's Disease: Where Are We?

Parkinson's disease (PD) is a neurodegenerative disorder that carries large health and socioeconomic burdens. Current therapies for PD are ultimately inadequate, both in terms of symptom control and in modification of disease progression. Deep brain stimulation and infusion therapies are the current mainstay for treatment of motor complications of advanced disease, but these have very significant drawbacks and offer no element of disease modification. In fact, there are currently no agents that are established to modify the course of the disease in clinical use for PD. Gene and cell therapies for PD are now being trialled in the clinic. These treatments are diverse and may have a range of niches in the management of PD. They hold great promise for improved treatment of symptoms as well as possibly slowing progression of the disease in the right patient group. Here, we review the current state of the art for these therapies and look to future strategies in this fast-moving field.

Coevolution of Adeno-associated Virus Capsid Antigenicity and Tropism through a Structure-Guided Approach

Adeno-associated viruses (AAV) are composed of nonenveloped, icosahedral protein shells that can be adapted to package and deliver recombinant therapeutic DNA. Approaches to engineer recombinant capsids for gene therapy applications have focused on rational design or library-based approaches that can address one or two desirable attributes; however, there is an unmet need to comprehensively improve AAV vector properties. Such cannot be achieved by utilizing sequence data alone but requires harnessing the three-dimensional (3D) structural properties of AAV capsids. Here, we solve the structures of a natural AAV isolate complexed with antibodies using cryo-electron microscopy and harness this structural information to engineer AAV capsid libraries through saturation mutagenesis of different antigenic footprints. Each surface loop was evolved by infectious cycling in the presence of a helper adenovirus to yield a new AAV variant that then serves as a template for evolving the next surface loop. This stepwise process yielded a humanized AAV8 capsid (AAVhum.8) displaying nonnatural surface loops that simultaneously display tropism for human hepatocytes, increased gene transfer efficiency, and neutralizing antibody evasion. Specifically, AAVhum.8 can better evade neutralizing antisera from multiple species than AAV8. Further, AAVhum.8 displays robust transduction in a human liver xenograft mouse model with expanded tropism for both murine and human hepatocytes. This work supports the hypothesis that critical properties, such as AAV capsid antibody evasion and tropism, can be coevolved by combining rational design and library-based evolution for clinical gene therapy.IMPORTANCE Clinical gene therapy with recombinant AAV vectors has largely relied on natural capsid isolates. There is an unmet need to comprehensively improve AAV tissue tropism, transduction efficiency, and antibody evasion. Such cannot be achieved by utilizing capsid sequence data alone but requires harnessing the 3D structural properties of AAV capsids. Here, we combine rational design and library-based evolution to coevolve multiple, desirable properties onto AAV by harnessing 3D structural information.

Promoter Orientation within an AAV-CRISPR Vector Affects Cas9 Expression and Gene Editing Efficiency

Adeno-associated virus (AAV) vectors have been widely adopted for delivery of CRISPR-Cas components, especially for therapeutic gene editing. For a single vector system, both the Cas9 and guide RNA (gRNA) are encoded within a single transgene, usually from separate promoters. Careful design of this bi-cistronic construct is required due to the minimal packaging capacity of AAV. We investigated how placement of the U6 promoter expressing the gRNA on the reverse strand to SaCas9 driven by a cytomegalovirus promoter affected gene editing rates compared to placement on the forward strand. We show that orientation in the reverse direction reduces editing rates from an AAV vector due to reduced transcription of both SaCas9 and guide RNA. This effect was observed only following AAV transduction; it was not seen following plasmid transfection. These results have implications for the design of AAV-CRISPR vectors, and suggest that results from optimizing plasmid transgenes may not translate when delivered via AAV.

The Impact of CRISPR-Cas9 on Age-related Disorders: From Pathology to Therapy

With advances in medical technology, the number of people over the age of 60 is on the rise, and thus, increasing the prevalence of age-related pathologies within the aging population. Neurodegenerative disorders, cancers, metabolic and inflammatory diseases are some of the most prevalent age-related pathologies affecting the growing population. It is imperative that a new treatment to combat these pathologies be developed. Although, still in its infancy, the CRISPR-Cas9 system has become a potent gene-editing tool capable of correcting gene-mediated age-related pathology, and therefore ameliorating or eliminating disease symptoms. Deleting target genes using the CRISPR-Cas9 system or correcting for gene mutations may ameliorate many different neurodegenerative disorders detected in the aging population. Cancer cells targeted by the CRISPR-Cas9 system may result in an increased sensitivity to chemotherapeutics, lower proliferation, and higher cancer cell death. Finally, reducing gene targeting inflammatory molecules production through microRNA knockout holds promise as a therapeutic strategy for both arthritis and inflammation. Here we present a review based on how the expanding world of genome editing can be applied to disorders and diseases affecting the aging population.

Utilization of the CRISPR-Cas9 Gene Editing System to Dissect Neuroinflammatory and Neuropharmacological Mechanisms in Parkinson's Disease

Chronic and debilitating neurodegenerative diseases, such as Parkinson's disease (PD), impose an immense medical, emotional, and economic burden on patients and society. Due to a complex interaction between genetic and environmental risk factors, the etiology of PD remains elusive. However, the cumulative evidence emerging from clinical and experimental research over the last several decades has identified mitochondrial dysfunction, oxidative stress, neuroinflammation, and dysregulated protein degradation as the main drivers of PD neurodegeneration. The genome-editing system CRISPR (clustered regularly interspaced short palindromic repeats) has recently transformed the field of biotechnology and biomedical discovery and is poised to accelerate neurodegenerative disease research. It has been leveraged to generate PD animal models, such as Parkin, DJ-1, and PINK1 triple knockout miniature pigs. CRISPR has also allowed the deeper understanding of various PD gene interactions, as well as the identification of novel apoptotic pathways associated with neurodegenerative processes in PD. Furthermore, its application has been used to dissect neuroinflammatory pathways involved in PD pathogenesis, such as the PKCδ signaling pathway, as well as the roles of novel compensatory or protective pathways, such as Prokineticin-2 signaling. This review aims to highlight the historical milestones in the evolution of this technology and attempts to illustrate its transformative potential in unraveling disease mechanisms as well as in the development of innovative treatment strategies for PD. Graphical Abstract.

CRISPR System: A High-throughput Toolbox for Research and Treatment of Parkinson's Disease

In recent years, the innovation of gene-editing tools such as the CRISPR/Cas9 system improves the translational gap of treatments mediated by gene therapy. The privileges of CRISPR/Cas9 such as working in living cells and organs candidate this technology for using in research and treatment of the central nervous system (CNS) disorders. Parkinson's disease (PD) is a common, debilitating, neurodegenerative disorder which occurs due to loss of dopaminergic neurons and is associated with progressive motor dysfunction. Knowledge about the pathophysiological basis of PD has altered the classification system of PD, which manifests in familial and sporadic forms. The first genetic linkage studies in PD demonstrated the involvement of Synuclein alpha (SNCA) mutations and SNCA genomic duplications in the pathogenesis of PD familial forms. Subsequent studies have also insinuated mutations in leucine repeat kinase-2 (LRRK2), Parkin, PTEN-induced putative kinase 1 (PINK1), as well as DJ-1 causing familial forms of PD. This review will attempt to discuss the structure, function, and development in genome editing mediated by CRISP/Cas9 system. Further, it describes the genes involved in the pathogenesis of PD and the pertinent alterations to them. We will pursue this line by delineating the PD linkage studies in which CRISPR system was employed. Finally, we will discuss the pros and cons of CRISPR employment vis-à-vis the process of genome editing in PD patients' iPSCs.

Rare Opportunities: CRISPR/Cas-Based Therapy Development for Rare Genetic Diseases

Rare diseases pose a global challenge, in that their collective impact on health systems is considerable, whereas their individually rare occurrence impedes research and development of efficient therapies. In consequence, patients and their families are often unable to find an expert for their affliction, let alone a cure. The tide is turning as pharmaceutical companies embrace gene therapy development and as serviceable tools for the repair of primary mutations separate the ability to create cures from underlying disease expertise. Whereas gene therapy by gene addition took decades to reach the clinic by incremental disease-specific refinements of vectors and methods, gene therapy by genome editing in its basic form merely requires certainty about the causative mutation. Suddenly we move from concept to trial in 3 years instead of 30: therapy development in the fast lane, with all the positive and negative implications of the phrase. Since their first application to eukaryotic cells in 2013, the proliferation and refinement in particular of tools based on clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) prokaryotic RNA-guided nucleases has prompted a landslide of therapy-development studies for rare diseases. An estimated thousands of orphan diseases are up for adoption, and legislative, entrepreneurial, and research initiatives may finally conspire to find many of them a good home. Here we summarize the most significant recent achievements and remaining hurdles in the application of CRISPR/Cas technology to rare diseases and take a glimpse at the exciting road ahead.

Cas9 Ribonucleoprotein Complex Delivery: Methods and Applications for Neuroinflammation

The CRISPR/Cas9 system is a revolutionary gene editing technology that combines simplicity of use and efficiency of mutagenesis. As this technology progresses toward human therapies, valid concerns including off-target mutations and immunogenicity must be addressed. One approach to address these issues is to minimize the presence of the CRISPR/Cas9 components by maintaining a tighter temporal control of Cas9 endonuclease and reducing the time period of activity. This has been achieved to some degree by delivering the CRISPR/Cas9 system via pre-formed Cas9 + gRNA ribonucleoprotein (RNP) complexes. In this review, we first discuss the molecular modifications that can be made using CRISPR/Cas9 and provide an overview of current methods for delivering Cas9 RNP complexes both in vitro and in vivo. We conclude with examples of how Cas9 RNP delivery may be used to target neuroinflammatory processes, namely in regard to viral infections of the central nervous system and neurodegenerative diseases. We propose that Cas9 RNP delivery is a viable approach when considering the CRISPR/Cas9 system for both experimentation and the treatment of disease. Graphical Abstract.

Editing the Central Nervous System Through CRISPR/Cas9 Systems

The translational gap to treatments based on gene therapy has been reduced in recent years because of improvements in gene editing tools, such as the CRISPR/Cas9 system and its variations. This has allowed the development of more precise therapies for neurodegenerative diseases, where access is privileged. As a result, engineering of complexes that can access the central nervous system (CNS) with the least potential inconvenience is fundamental. In this review article, we describe current alternatives to generate systems based on CRISPR/Cas9 that can cross the blood-brain barrier (BBB) and may be used further clinically to improve treatment for neurodegeneration in Parkinson's and Alzheimer's disease (AD).

Adeno-associated virus-based Alzheimer's disease mouse models and potential new therapeutic avenues

Alzheimer's disease (AD) is a highly prevalent neurodegenerative condition that presents with cognitive decline. The current understanding of underlying disease mechanisms remains incomplete. Genetically modified mouse models have been instrumental in deciphering pathomechanisms in AD. While these models were typically generated by classical transgenesis and genome editing, the use of adeno-associated viruses (AAVs) to model and investigate AD in mice, as well as to develop novel gene-therapy approaches, is emerging. Here, we reviewed literature that used AAVs to study and model AD and discuss potential gene therapy strategies. LINKED ARTICLES: This article is part of a themed section on Therapeutics for Dementia and Alzheimer's Disease: New Directions for Precision Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.18/issuetoc.

Basic and Clinical Application of Adeno-Associated Virus-Mediated Genome Editing

Traditional gene therapy (gene replacement) has made a breakthrough in treating inherited diseases. Adeno-associated virus (AAV) has emerged as a highly promising vector with innate ability, boosting the development of gene replacement and gene targeting. With the recent advance of engineered nucleases that work efficiently in human cells, AAV mediated-genome editing with nucleases has raised hopes for in situ gene therapy of inherited and non-inherited diseases. Here, the applications of AAV-mediated genome editing are highlighted, and the prospect of AAV and nucleases that will render extension of such success in clinical gene therapy is discussed.

Targeted Gene Editing of Glia Maturation Factor in Microglia: a Novel Alzheimer's Disease Therapeutic Target

Alzheimer's disease (AD) is a devastating, progressive neurodegenerative disorder that leads to severe cognitive impairment in elderly patients. Chronic neuroinflammation plays an important role in the AD pathogenesis. Glia maturation factor (GMF), a proinflammatory molecule discovered in our laboratory, is significantly upregulated in various regions of AD brains. We have previously reported that GMF is predominantly expressed in the reactive glial cells surrounding the amyloid plaques (APs) in the mouse and human AD brain. Microglia are the major source of proinflammatory cytokines and chemokines including GMF. Recently clustered regularly interspaced short palindromic repeats (CRISPR) based genome editing has been recognized to study the functions of genes that are implicated in various diseases. Here, we investigated if CRISPR-Cas9-mediated GMF gene editing leads to inhibition of GMF expression and suppression of microglial activation. Confocal microscopy of murine BV2 microglial cell line transduced with an adeno-associated virus (AAV) coexpressing Staphylococcus aureus (Sa) Cas9 and a GMF-specific guide RNA (GMF-sgRNA) revealed few cells expressing SaCas9 while lacking GMF expression, thereby confirming successful GMF gene editing. To further improve GMF gene editing efficiency, we developed lentiviral vectors (LVs) expressing either Streptococcus pyogenes (Sp) Cas9 or GMF-sgRNAs. BV2 cells cotransduced with LVs expressing SpCas9 and GMF-sgRNAs revealed reduced GMF expression and the presence of indels in the exons 2 and 3 of the GMF coding sequence. Lipopolysaccharide (LPS) treatment of GMF-edited cells led to reduced microglial activation as shown by reduced p38 MAPK phosphorylation. We believe that targeted in vivo GMF gene editing has a significant potential for developing a unique and novel AD therapy.

A Self-Deleting AAV-CRISPR System for In Vivo Genome Editing

Adeno-associated viral (AAV) vectors packaging the CRISPR-Cas9 system (AAV-CRISPR) can efficiently modify disease-relevant genes in somatic tissues with high efficiency. AAV vectors are a preferred delivery vehicle for tissue-directed gene therapy because of their ability to achieve sustained expression from largely non-integrating episomal genomes. However, for genome editizng applications, permanent expression of non-human proteins such as the bacterially derived Cas9 nuclease is undesirable. Methods are needed to achieve efficient genome editing in vivo, with controlled transient expression of CRISPR-Cas9. Here, we report a self-deleting AAV-CRISPR system that introduces insertion and deletion mutations into AAV episomes. We demonstrate that this system dramatically reduces the level of Staphylococcus aureus Cas9 protein, often greater than 79%, while achieving high rates of on-target editing in the liver. Off-target mutagenesis was not observed for the self-deleting Cas9 guide RNA at any of the predicted potential off-target sites examined. This system is efficient and versatile, as demonstrated by robust knockdown of liver-expressed proteins in vivo. This self-deleting AAV-CRISPR system is an important proof of concept that will help enable translation of liver-directed genome editing in humans.

Adeno-associated virus-mediated delivery of CRISPR-Cas9 for genome editing in the central nervous system

The emergence of CRISPR-Cas9 as a powerful genome editing tool has led to several studies exploring its potential to treat neurological disorders. Cas9 and its sgRNA can be readily engineered to target any gene and can be multiplexed to target several genes at once. Furthermore, the use of adeno-associated virus (AAV) to deliver with Cas9 and its sgRNA is a promising therapeutic combination with strong potential to reach the clinic. Here we discuss how Cas9 editing has been utilized for gene insertion, knockout, and deletion in vivo for applications in the central nervous system (CNS). Furthermore, we highlight major challenges that remain for AAV-Cas9-sgRNA clinical translation.

Engineered viral vectors for functional interrogation, deconvolution, and manipulation of neural circuits

Optimization of traditional replication-competent viral tracers has granted access to immediate synaptic partners of target neuronal populations, enabling the dissection of complex brain circuits into functional neural pathways. The excessive virulence of most conventional tracers, however, impedes their utility in revealing and genetically perturbing cellular function on long time scales. As a promising alternative, the natural capacity of adeno-associated viral (AAV) vectors to safely mediate persistent and robust gene expression has stimulated strong interest in adapting them for sparse neuronal labeling and physiological studies. Furthermore, increasingly refined engineering strategies have yielded novel AAV variants with enhanced target specificity, transduction, and retrograde trafficking in the CNS. These potent vectors offer new opportunities for characterizing the identity and connectivity of single neurons within immense networks and modulating their activity via robust delivery of functional genetic tools.

Are Tanycytes the Missing Link Between Type 2 Diabetes and Alzheimer's Disease?

Tanycytes are highly specialized bipolar ependymal cells that line the ventrolateral wall and the floor of the third ventricle in the brain and form a blood-cerebrospinal fluid barrier at the level of the median eminence. They play a pivotal role in regulating metabolic networks that control body weight and energy homeostasis. Due to the glucosensing function of tanycytes, they could be considered as a critical player in the pathogenesis of type 2 diabetes. Genetic fate mapping studies have established the role of tanycytes for the newly detected adult hypothalamic neurogenesis with important implications for metabolism as well as pathophysiology of various neurodegenerative diseases. We believe that a comprehensive understanding of the physiological mechanisms underlying their neuroplasticity, glucosensing, and cross talk with endothelial cells will enable us to achieve metabolic homeostasis in type 2 diabetes patients and possibly delay the progression of Alzheimer's disease and hopefully improve cognitive function.

Gene Therapy Strategies to Restore ER Proteostasis in Disease

Proteostasis alterations are proposed as a transversal hallmark of several pathological conditions, including metabolic disorders, mechanical injury, cardiac malfunction, neurodegeneration, and cancer. Strategies to improve proteostasis aim to reduce the accumulation of specific disease-related misfolded proteins or bolster the endogenous mechanisms to fold and degrade abnormal proteins. Endoplasmic reticulum (ER) stress is a common pathological signature of a variety of diseases, which engages the unfolded protein response (UPR) as a cellular reaction to mitigate ER stress. Pharmacological modulation of the UPR is challenging considering the physiological importance of the pathway in various organs. However, local targeting of ER stress responses in the affected tissue using gene therapy is emerging as a possible solution to overcome side effects. The delivery of ER chaperones or active UPR components using adeno-associated virus (AAV) has demonstrated outstanding beneficial effects in several disease models (e.g., neurodegenerative conditions, eye disorders, and metabolic diseases). Here, we discuss current efforts to design and optimize gene therapy strategies to improve ER proteostasis in different disease contexts.

Slow Infusion of Recombinant Adeno-Associated Viruses into the Mouse Cerebrospinal Fluid Space

Recombinant adeno-associated viruses (rAAVs) are the leading in vivo gene delivery platform, and have been extensively studied in gene therapy targeting various tissues, including the central nervous system (CNS). A single-bolus rAAV injection to the cerebrospinal fluid (CSF) space has been widely used to target the CNS, but it suffers from several drawbacks, such as leakage to peripheral tissues. Here, a protocol is described using an osmotic pump to infuse rAAV slowly into the mouse CSF space. Compared to the single-bolus injection technique, pump infusion can lead to higher CNS transduction and lower transduction in the peripheral tissues.

CRISPR/Cas9: the Jedi against the dark empire of diseases

Advances in Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated system (CRISPR/Cas9) has dramatically reshaped our ability to edit genomes. The scientific community is using CRISPR/Cas9 for various biotechnological and medical purposes. One of its most important uses is developing potential therapeutic strategies against diseases. CRISPR/Cas9 based approaches have been increasingly applied to the treatment of human diseases like cancer, genetic, immunological and neurological disorders and viral diseases. These strategies using CRISPR/Cas9 are not only therapy oriented but can also be used for disease modeling as well, which in turn can lead to the improved understanding of mechanisms of various infectious and genetic diseases. In addition, CRISPR/Cas9 system can also be used as programmable antibiotics to kill the bacteria sequence specifically and therefore can bypass multidrug resistance. Furthermore, CRISPR/Cas9 based gene drive may also hold the potential to limit the spread of vector borne diseases. This bacterial and archaeal adaptive immune system might be a therapeutic answer to previous incurable diseases, of course rigorous testing is required to corroborate these claims. In this review, we provide an insight about the recent developments using CRISPR/Cas9 against various diseases with respect to disease modeling and treatment, and what future perspectives should be noted while using this technology.

Genome engineering for CNS injury and disease

Recent developments in genome engineering methods have advanced our knowledge of central nervous system (CNS) function in both normal health and following disease or injury. This review discusses current literature using gene editing tools in CNS disease and injury research, such as improving viral-mediated targeting of cell populations, generating new methods for genome editing, reprogramming cells into CNS cell types, and using organoids as models of development and disease. Readers may gain inspiration for continuing research into new genome engineering methods and for therapies for CNS applications.

A comprehensive review of the genetic and biological evidence supports a role for MicroRNA-137 in the etiology of schizophrenia

Since it was first associated with schizophrenia (SCZ) in a 2011 genome-wide association study (GWAS), there have been over 100 publications focused on MIR137, the gene encoding microRNA-137. These studies have examined everything from its fundamental role in the development of mice, flies, and fish to the intriguing enrichment of its target gene network in SCZ. Indeed, much of the excitement surrounding MIR137 is due to the distinct possibility that it could regulate a gene network involved in SCZ etiology, a disease which we now recognize is highly polygenic. Here we comprehensively review, to the best of our ability, all published genetic and biological evidence that could support or refute a role for MIR137 in the etiology of SCZ. Through a careful consideration of the literature, we conclude that the data gathered to date continues to strongly support the involvement of MIR137 and its target gene network in neuropsychiatric traits, including SCZ risk. There remain, however, more unanswered than answered questions regarding the mechanisms linking MIR137 genetic variation with behavior. These questions need answers before we can determine whether there are opportunities for diagnostic or therapeutic interventions based on MIR137. We conclude with a number of suggestions for future research on MIR137 that could help to provide answers and hope for a greater understanding of this devastating disorder.

Neuro-Immuno-Gene- and Genome-Editing-Therapy for Alzheimer's Disease: Are We There Yet?

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder and the current treatment strategies are largely ineffective thereby leading to irreversible and progressive cognitive decline in AD patients. AD continues to defy successful treatment despite significant advancements in the field of molecular medicine. Repeatedly, early promising preclinical and clinical results have catapulted into devastating setbacks leading to multi-billion dollar losses not only to the top pharmaceutical companies but also to the AD patients and their families. Thus, it is very timely to review the progress in the emerging fields of gene therapy and stem cell-based precision medicine. Here, we have made sincere efforts to feature the ongoing progress especially in the field of AD gene therapy and stem cell-based regenerative medicine. Further, we also provide highlights in elucidating the molecular mechanisms underlying AD pathogenesis and describe novel AD therapeutic targets and strategies for the new drug discovery. We hope that the quantum leap in the scientific advancements and improved funding will bolster novel concepts that will propel the momentum toward a trajectory leading to a robust AD patient-specific next generation precision medicine with improved cognitive function and excellent life quality.

In vivo genome editing in animals using AAV-CRISPR system: applications to translational research of human disease

Adeno-associated virus (AAV) has shown promising therapeutic efficacy with a good safety profile in a wide range of animal models and human clinical trials. With the advent of clustered regulatory interspaced short palindromic repeat (CRISPR)-based genome-editing technologies, AAV provides one of the most suitable viral vectors to package, deliver, and express CRISPR components for targeted gene editing. Recent discoveries of smaller Cas9 orthologues have enabled the packaging of Cas9 nuclease and its chimeric guide RNA into a single AAV delivery vehicle for robust in vivo genome editing. Here, we discuss how the combined use of small Cas9 orthologues, tissue-specific minimal promoters, AAV serotypes, and different routes of administration has advanced the development of efficient and precise in vivo genome editing and comprehensively review the various AAV-CRISPR systems that have been effectively used in animals. We then discuss the clinical implications and potential strategies to overcome off-target effects, immunogenicity, and toxicity associated with CRISPR components and AAV delivery vehicles. Finally, we discuss ongoing non-viral-based ex vivo gene therapy clinical trials to underscore the current challenges and future prospects of CRISPR/Cas9 delivery for human therapeutics.

Mapping the Structural Determinants Required for AAVrh.10 Transport across the Blood-Brain Barrier

Effective gene delivery to the CNS by intravenously administered adeno-associated virus (AAV) vectors requires crossing the blood-brain barrier (BBB). To achieve therapeutic CNS transgene expression, high systemic vector doses are often required, which poses challenges such as scale-up costs and dose-dependent hepatotoxicity. To improve the specificity and efficiency of CNS gene transfer, a better understanding of the structural features that enable AAV transit across the BBB is needed. We generated a combinatorial domain swap library using AAV1, a serotype that does not traverse the vasculature, and AAVrh.10, which crosses the BBB in mice. We then screened individual variants by phylogenetic and structural analyses and subsequently conducted systemic characterization in mice. Using this approach, we identified key clusters of residues on the AAVrh.10 capsid that enabled transport across the brain vasculature and widespread neuronal transduction in mice. Through rational design, we mapped a minimal footprint from AAVrh.10, which, when grafted onto AAV1, confers the aforementioned CNS phenotype while diminishing vascular and hepatic transduction through an unknown mechanism. Functional mapping of this capsid surface footprint provides a roadmap for engineering synthetic AAV capsids for efficient CNS gene transfer with an improved safety profile.

Engineered CRISPR Systems for Next Generation Gene Therapies

An ideal in vivo gene therapy platform provides safe, reprogrammable, and precise strategies which modulate cell and tissue gene regulatory networks with a high temporal and spatial resolution. Clustered regularly interspaced short palindromic repeats (CRISPR), a bacterial adoptive immune system, and its CRISPR-associated protein 9 (Cas9), have gained attention for the ability to target and modify DNA sequences on demand with unprecedented flexibility and precision. The precision and programmability of Cas9 is derived from its complexation with a guide-RNA (gRNA) that is complementary to a desired genomic sequence. CRISPR systems open-up widespread applications including genetic disease modeling, functional screens, and synthetic gene regulation. The plausibility of in vivo genetic engineering using CRISPR has garnered significant traction as a next generation in vivo therapeutic. However, there are hurdles that need to be addressed before CRISPR-based strategies are fully implemented. Some key issues center on the controllability of the CRISPR platform, including minimizing genomic-off target effects and maximizing in vivo gene editing efficiency, in vivo cellular delivery, and spatial-temporal regulation. The modifiable components of CRISPR systems: Cas9 protein, gRNA, delivery platform, and the form of CRISPR system delivered (DNA, RNA, or ribonucleoprotein) have recently been engineered independently to design a better genome engineering toolbox. This review focuses on evaluating CRISPR potential as a next generation in vivo gene therapy platform and discusses bioengineering advancements that can address challenges associated with clinical translation of this emerging technology.

Therapeutic gene editing: delivery and regulatory perspectives

Gene-editing technology is an emerging therapeutic modality for manipulating the eukaryotic genome by using target-sequence-specific engineered nucleases. Because of the exceptional advantages that gene-editing technology offers in facilitating the accurate correction of sequences in a genome, gene editing-based therapy is being aggressively developed as a next-generation therapeutic approach to treat a wide range of diseases. However, strategies for precise engineering and delivery of gene-editing nucleases, including zinc finger nucleases, transcription activator-like effector nuclease, and CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated nuclease Cas9), present major obstacles to the development of gene-editing therapies, as with other gene-targeting therapeutics. Currently, viral and non-viral vectors are being studied for the delivery of these nucleases into cells in the form of DNA, mRNA, or proteins. Clinical trials are already ongoing, and in vivo studies are actively investigating the applicability of CRISPR/Cas9 techniques. However, the concept of correcting the genome poses major concerns from a regulatory perspective, especially in terms of safety. This review addresses current research trends and delivery strategies for gene editing-based therapeutics in non-clinical and clinical settings and considers the associated regulatory issues.

Structure-guided evolution of antigenically distinct adeno-associated virus variants for immune evasion

Preexisting neutralizing antibodies (NAbs) against adeno-associated viruses (AAVs) pose a major, unresolved challenge that restricts patient enrollment in gene therapy clinical trials using recombinant AAV vectors. Structural studies suggest that despite a high degree of sequence variability, antibody recognition sites or antigenic hotspots on AAVs and other related parvoviruses might be evolutionarily conserved. To test this hypothesis, we developed a structure-guided evolution approach that does not require selective pressure exerted by NAbs. This strategy yielded highly divergent antigenic footprints that do not exist in natural AAV isolates. Specifically, synthetic variants obtained by evolving murine antigenic epitopes on an AAV serotype 1 capsid template can evade NAbs without compromising titer, transduction efficiency, or tissue tropism. One lead AAV variant generated by combining multiple evolved antigenic sites effectively evades polyclonal anti-AAV1 neutralizing sera from immunized mice and rhesus macaques. Furthermore, this variant displays robust immune evasion in nonhuman primate and human serum samples at dilution factors as high as 1:5, currently mandated by several clinical trials. Our results provide evidence that antibody recognition of AAV capsids is conserved across species. This approach can be applied to any AAV strain to evade NAbs in prospective patients for human gene therapy.

Gene therapy and editing: Novel potential treatments for neuronal channelopathies

Pharmaceutical treatment can be inadequate, non-effective, or intolerable for many people suffering from a neuronal channelopathy. Development of novel treatment options, particularly those with the potential to be curative is warranted. Gene therapy approaches can permit cell-specific modification of neuronal and circuit excitability and have been investigated experimentally as a therapy for numerous neurological disorders, with clinical trials for several neurodegenerative diseases ongoing. Channelopathies can arise from a wide array of gene mutations; however they usually result in periods of aberrant network excitability. Therefore gene therapy strategies based on up or downregulation of genes that modulate neuronal excitability may be effective therapy for a wide range of neuronal channelopathies. As many channelopathies are paroxysmal in nature, optogenetic or chemogenetic approaches may be well suited to treat the symptoms of these diseases. Recent advances in gene-editing technologies such as the CRISPR-Cas9 system could in the future result in entirely novel treatment for a channelopathy by repairing disease-causing channel mutations at the germline level. As the brain may develop and wire abnormally as a consequence of an inherited or de novo channelopathy, the choice of optimal gene therapy or gene editing strategy will depend on the time of intervention (germline, neonatal or adult). This article is part of the Special Issue entitled 'Channelopathies.'

Myotonic Dystrophies: State of the Art of New Therapeutic Developments for the CNS

Myotonic dystrophies are multisystemic diseases characterized not only by muscle and heart dysfunction but also by CNS alteration. They are now recognized as brain diseases affecting newborns and children for myotonic dystrophy type 1 and adults for both myotonic dystrophy type 1 and type 2. In the past two decades, much progress has been made in understanding the mechanisms underlying the DM symptoms allowing development of new molecular therapeutic tools with the ultimate aim of curing the disease. This review describes the state of the art for the characterization of CNS related symptoms, the development of molecular strategies to target the CNS as well as the available tools for screening and testing new possible treatments.

Future of rAAV Gene Therapy: Platform for RNAi, Gene Editing, and Beyond

The use of recombinant adeno-associated viruses (rAAVs) ushered in a new millennium of gene transfer for therapeutic treatment of a number of conditions, including congenital blindness, hemophilia, and spinal muscular atrophy. rAAV vectors have remarkable staying power from a therapeutic standpoint, withstanding several ebbs and flows. As new technologies such as clustered regularly interspaced short palindromic repeat genome editing emerge, it is now the delivery tool-the AAV vector-that is the stalwart. The long-standing safety of this vector in a multitude of clinical settings makes rAAV a selling point in the advancement of approaches for gene replacement, gene knockdown, gene editing, and genome modification/engineering. The research community is building on these advances to develop more tailored delivery approaches and to tweak the genome in new and unique ways. Intertwining these approaches with newly engineered rAAV vectors is greatly expanding the available tools to manipulate gene expression with a therapeutic intent.