Adeno-associated Virus as a Mammalian DNA Vector

AAV vector transduction restriction and attenuated toxicity in hESCs via a rationally designed inverted terminal repeat

Adeno-associated virus (AAV) inverted terminal repeats (ITRs) induce p53-dependent apoptosis in human embryonic stem cells (hESCs). To interrogate this phenomenon, a synthetic ITR (SynITR), harboring substitutions in putative p53 binding sites was generated and evaluated for vector production and gene delivery. Replication of SynITR flanked transgenic genome was similar compared to wild type (wt) ITR, with a modest increase in vector titers. Packaged in the AAV2 capsid, wtITR and SynITR vectors demonstrated similar transduction efficiencies of human cells without toxicity. Following AAV2-wtITR vector infection of hESCs, rapid apoptosis was observed as reported. In contrast, infection by AAV2 vectors packaged with SynITRs attenuated the wtITR-induced hESC toxicity. While hESC particle entry and the abundance of double stranded circular episomes was similar for the ITR contexts, reporter expression was inhibited from transduced SynITR genomes. Mechanistically, infection of hESCs induced γH2AX in an ITR-independent manner, however, canonical activation of p53α was uncoupled using AAV-SynITR. Further investigations in hESCs revealed additional novel findings: (i) p53β is uniquely and constitutively active and (ii) AAV vector infection, independent of the ITR sequence, induces activation of p53ψ. The data herein reveal an ITR-dependent AAV vector transduction restriction specific to hESCs and manipulation of the DNA damage response via ITR engineering.

Adeno-Associated Viral Vectors in the Treatment of Epilepsy

Epilepsy is a brain disorder characterized by a persistent predisposition to epileptic seizures. With various etiologies of epilepsy, a significant proportion of patients develop pharmacoresistance to antiepileptic drugs, which necessitates the search for new therapeutic methods, in particular, using gene therapy. This review discusses the use of adeno-associated viral (AAV) vectors in gene therapy for epilepsy, emphasizing their advantages, such as high efficiency of neuronal tissue transduction and low immunogenicity/cytotoxicity. AAV vectors provide the possibility of personalized therapy due to the diversity of serotypes and genomic constructs, which allows for increasing the specificity and effectiveness of treatment. Promising orientations include the modulation of the expression of neuropeptides, ion channels, transcription, and neurotrophic factors, as well as the use of antisense oligonucleotides to regulate seizure activity, which can reduce the severity of epileptic disorders. This review summarizes the current advances in the use of AAV vectors for the treatment of epilepsy of various etiologies, demonstrating the significant potential of AAV vectors for the development of personalized and more effective approaches to reducing seizure activity and improving patient prognosis.

Sustained and Efficient Delivery of Antivascular Endothelial Growth Factor by the Adeno-associated Virus for the Treatment of Corneal Neovascularization: An Outlook for Its Clinical Translation

Corneal diseases represent 5.1% of all eye defects and are the fourth leading cause of blindness globally. Corneal neovascularization can arise from all conditions of chronic irritation or hypoxia, which disrupts the immune-privileged state of the healthy cornea, increases the risk of rejection after keratoplasty, and leads to opacity. In the past decades, significant progress has been made for neovascular diseases of the retina and choroid, with plenty of drugs getting commercialized. In addition, to overcome the barriers of the short duration and inadequate penetration of conventional formulations of antivascular endothelial growth factor (VEGF), multiple novel drug delivery systems, including adeno-associated virus (AAV)-mediated transfer have gone through the full process of bench-to-bedside translation. Like retina neovascular diseases, corneal neovascularization also suffers from chronicity and a high risk of recurrence, necessitating sustained and efficient delivery across the epithelial barrier to reach deep layers of the corneal stroma. Among the explored methods, adeno-associated virus-mediated delivery of anti-VEGF to treat corneal neovascularization is the most extensively researched and most promising strategy for clinical translation although currently although, it remains predominantly at the preclinical stage. This review comprehensively examines the necessity, benefits, and risks of applying AAV vectors for anti-VEGF drug delivery in corneal vascularization, including its current progress and challenges in clinical translation.

Optogenetic Vision Restoration

Optogenetics has emerged over the past 20 years as a powerful tool to investigate the various circuits underlying numerous functions, especially in neuroscience. The ability to control by light the activity of neurons has enabled the development of therapeutic strategies aimed at restoring some level of vision in blinding retinal conditions. Promising preclinical and initial clinical data support such expectations. Numerous challenges remain to be tackled (e.g., confirmation of safety, cell and circuit specificity, patterns, intensity and mode of stimulation, rehabilitation programs) on the path toward useful vision restoration.

Optogenetics 2.0: challenges and solutions towards a quantitative probing of neural circuits

To exploit the full potential of optogenetics, we need to titrate and tailor optogenetic methods to emulate naturalistic circuit function. For that, the following prerequisites need to be met: first, we need to target opsin expression not only to genetically defined neurons per se, but to specifically target a functional node. Second, we need to assess the scope of optogenetic modulation, i.e. the fraction of optogenetically modulated neurons. Third, we need to integrate optogenetic control in a closed loop setting. Fourth, we need to further safe and stable gene expression and light delivery to bring optogenetics to the clinics. Here, we review these concepts for the human and rodent brain.

Production and Purification of Adeno-Associated Viral Vectors (AAVs) Using Orbitally Shaken HEK293 Cells

Here, we describe methods for the production of adeno-associated viral (AAV) vectors by transient transfection of HEK293 cells grown in serum-free medium using orbital shaken bioreactors and the subsequent purification of vector particles. The protocol for expression of AAV components is based on polyethyleneimine (PEI)-mediated transfection of a three-plasmid system and is specified for production in milliliter-to-liter scales. After PEI and plasmid DNA (pDNA) complex formation, the diluted cell culture is transfected without a prior concentration step or medium exchange. Following a 7-day batch process, cell cultures are further processed using a set of methods for cell lysis and vector recovery. Methods for the purification of viral particles are described, including immunoaffinity and anion-exchange chromatography, ultrafiltration, as well as digital PCR to quantify the concentration of vector particles.

Novel Therapeutic Targets for Fibrodysplasia Ossificans Progressiva: Emerging Strategies and Future Directions

Fibrodysplasia ossificans progressiva (FOP), also known as Stoneman syndrome, is a rare genetic disorder characterized by abnormal bone development caused by activating mutations of the ACVR1 gene. FOP affects both the developmental and postnatal stages, resulting in musculoskeletal abnormalities and heterotopic ossification. Current treatment options for FOP are limited, emphasizing the need for innovative therapeutic approaches. Challenges in the development of management criteria for FOP include difficulties in recruitment due to the rarity of FOP, disease variability, the absence of reliable biomarkers, and ethical considerations regarding placebo-controlled trials. This narrative review provides an overview of the disease and explores emerging strategies for FOP treatment. Gene therapy, particularly the CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9) system, holds promise in treating FOP by specifically targeting the ACVR1 gene mutation. Another gene therapy approach being investigated is RNA interference, which aims to silence the mutant ACVR1 gene. Small molecule inhibitors targeting glycogen synthase kinase-3β and modulation of the bone morphogenetic protein signaling pathway are also being explored as potential therapies for FOP. Stem cell-based approaches, such as mesenchymal stem cells and induced pluripotent stem cells, show potential in tissue regeneration and inhibiting abnormal bone formation in FOP. Immunotherapy and nanoparticle delivery systems provide alternative avenues for FOP treatment.

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.

Gene therapy approaches for equine osteoarthritis

With an intrinsically low ability for self-repair, articular cartilage injuries often progress to cartilage loss and joint degeneration resulting in osteoarthritis (OA). Osteoarthritis and the associated articular cartilage changes can be debilitating, resulting in lameness and functional disability both in human and equine patients. While articular cartilage damage plays a central role in the pathogenesis of OA, the contribution of other joint tissues to the pathogenesis of OA has increasingly been recognized thus prompting a whole organ approach for therapeutic strategies. Gene therapy methods have generated significant interest in OA therapy in recent years. These utilize viral or non-viral vectors to deliver therapeutic molecules directly into the joint space with the goal of reprogramming the cells' machinery to secrete high levels of the target protein at the site of injection. Several viral vector-based approaches have demonstrated successful gene transfer with persistent therapeutic levels of transgene expression in the equine joint. As an experimental model, horses represent the pathology of human OA more accurately compared to other animal models. The anatomical and biomechanical similarities between equine and human joints also allow for the use of similar imaging and diagnostic methods as used in humans. In addition, horses experience naturally occurring OA and undergo similar therapies as human patients and, therefore, are a clinically relevant patient population. Thus, further studies utilizing this equine model would not only help advance the field of human OA therapy but also benefit the clinical equine patients with naturally occurring joint disease. In this review, we discuss the advancements in gene therapeutic approaches for the treatment of OA with the horse as a relevant patient population as well as an effective and commonly utilized species as a translational model.

Genetically modified immunomodulatory cell-based biomaterials in tissue regeneration and engineering

To date, the wide application of cell-based biomaterials in tissue engineering and regeneration is remarkably hampered by immune rejection. Reducing the immunogenicity of cell-based biomaterials has become the latest direction in biomaterial research. Recently, genetically modified cell-based biomaterials with immunomodulatory genes have become a feasible solution to the immunogenicity problem. In this review, recent advances and future challenges of genetically modified immunomodulatory cell-based biomaterials are elaborated, including fabrication approaches, mechanisms of common immunomodulatory genes, application and, more importantly, current preclinical and clinical advances. The fabrication approaches can be categorized into commonly used (e.g., virus transfection) and newly developed approaches. The immunomodulatory mechanisms of representative genes involve complicated cell signaling pathways and metabolic activities. Wide application in curing multiple end-term diseases and replacing lifelong immunosuppressive therapy in multiple cell and organ transplantation models is demonstrated. Most significantly, practices of genetically modified organ transplantation have been conducted on brain-dead human decedent and even on living patients after a series of experiments on nonhuman primates. Nevertheless, uncertain biosecurity, nonspecific effects and overlooked personalization of current genetically modified immunomodulatory cell-based biomaterials are shortcomings that remain to be overcome.

High-efficiency nonviral CRISPR/Cas9-mediated gene editing of human T cells using plasmid donor DNA

Genome engineering of T lymphocytes, the main effectors of antitumor adaptive immune responses, has the potential to uncover unique insights into their functions and enable the development of next-generation adoptive T cell therapies. Viral gene delivery into T cells, which is currently used to generate CAR T cells, has limitations in regard to targeting precision, cargo flexibility, and reagent production. Nonviral methods for effective CRISPR/Cas9-mediated gene knock-out in primary human T cells have been developed, but complementary techniques for nonviral gene knock-in can be cumbersome and inefficient. Here, we report a convenient and scalable nonviral method that allows precise gene edits and transgene integration in primary human T cells, using plasmid donor DNA template and Cas9-RNP. This method is highly efficient for single and multiplex gene manipulation, without compromising T cell function, and is thus valuable for use in basic and translational research.

Therapeutic homology-independent targeted integration in retina and liver

Challenges to the widespread application of gene therapy with adeno-associated viral (AAV) vectors include dominant conditions due to gain-of-function mutations which require allele-specific knockout, as well as long-term transgene expression from proliferating tissues, which is hampered by AAV DNA episomal status. To overcome these challenges, we used CRISPR/Cas9-mediated homology-independent targeted integration (HITI) in retina and liver as paradigmatic target tissues. We show that AAV-HITI targets photoreceptors of both mouse and pig retina, and this results in significant improvements to retinal morphology and function in mice with autosomal dominant retinitis pigmentosa. In addition, we show that neonatal systemic AAV-HITI delivery achieves stable liver transgene expression and phenotypic improvement in a mouse model of a severe lysosomal storage disease. We also show that HITI applications predominantly result in on-target editing. These results lay the groundwork for the application of AAV-HITI for the treatment of diseases affecting various organs.

Comparison of highly pure rAAV9 vector stocks produced in suspension by PEI transfection or HSV infection reveals striking quantitative and qualitative differences

Recent clinical successes have propelled recombinant adeno-associated virus vectors (rAAV) to the center stage for human gene therapy applications. However, the exploding demand for high titers of highly pure rAAV vectors for clinical applications and market needs remains hindered by challenges met at the manufacturing stage. The production of rAAV by transfection in suspension cells remains one of the most commonly used production platforms. In this study, we describe our optimized protocol to produce rAAV by polyethyleneimine (PEI)-mediated transfection in suspension HEK293 cells, along with a side-by-side comparison to our high-performing system using the herpes simplex virus (HSV). Further, we detail a new, robust, and highly efficient downstream purification protocol compatible with both transfection and infection-based harvests that generated rAAV9 stocks of high purity. Our in-depth comparison revealed quantitative, qualitative, and biological differences between PEI-mediated transfection and HSV infection. The HSV production system yielded to higher rAAV vector titers, higher specific yields, and a higher percentage of full capsids than transfection. Furthermore, HSV-produced stocks had a significantly lower concentration of residual host cell proteins and helper DNA impurities, but contained detectable levels of HSV DNA. Importantly, the potency of PEI-produced and HSV-produced rAAV stocks were identical. Analyses of AAV Rep and Cap expression levels and replication showed that HSV-mediated production led to a lower expression of Rep and Cap, but increased levels of AAV genome replication. Our methodology enables high-yield, high purity rAAV production and a biological framework to improve transfection quality and yields by mimicking HSV-induced biological outcomes.

Towards translational optogenetics

Optogenetics is widely used to interrogate the neural circuits underlying disease and has most recently been harnessed for therapeutic applications. The optogenetic toolkit consists of light-responsive proteins that modulate specific cellular functions, vectors for the delivery of the transgenes that encode the light-responsive proteins to targeted cellular populations, and devices for the delivery of light of suitable wavelengths at effective fluence rates. A refined toolkit with a focus towards translational uses would include efficient and safer viral and non-viral gene-delivery vectors, increasingly red-shifted photoresponsive proteins, nanomaterials that efficiently transduce near-infrared light deep into tissue, and wireless implantable light-delivery devices that allow for spatiotemporally precise interventions at clinically relevant tissue depths. In this Review, we examine the current optogenetics toolkit and the most notable preclinical and translational uses of optogenetics, and discuss future methodological and translational developments and bottlenecks.

Current trends in gene therapy for retinal diseases (Review)

The eye is considered an effective target for genetic therapy, as it has a privileged immune status, it is easily accessed for medication delivery and it is affected by a number of inherited disorders. In particular, the retina is considered for gene therapy due to the fact that it can be visualized with ease, it does not have lymphatic vessels, nor a direct blood network for the outer layers and its cells do not divide after birth, and thus transgene expression is not affected. As gene therapy is currently on a continuously progressive development trend, this emerging field of gene manipulation techniques has yielded promising results. This involves the development of treatments for a number of debilitating and blinding diseases, which were to date considered intractable. However, numerous unanswered questions remain as regards the long-term efficacy and safety profile of these treatments. The present review article discusses the current research status regarding genetic manipulation techniques aimed at addressing visual impairment related to retinal disorders, both inherited and degenerative.

Current and Future Prospects for Gene Therapy for Rare Genetic Diseases Affecting the Brain and Spinal Cord

In recent years, gene therapy has been raising hopes toward viable treatment strategies for rare genetic diseases for which there has been almost exclusively supportive treatment. We here review this progress at the pre-clinical and clinical trial levels as well as market approvals within diseases that specifically affect the brain and spinal cord, including degenerative, developmental, lysosomal storage, and metabolic disorders. The field reached an unprecedented milestone when Zolgensma® (onasemnogene abeparvovec) was approved by the FDA and EMA for in vivo adeno-associated virus-mediated gene replacement therapy for spinal muscular atrophy. Shortly after EMA approved Libmeldy®, an ex vivo gene therapy with lentivirus vector-transduced autologous CD34-positive stem cells, for treatment of metachromatic leukodystrophy. These successes could be the first of many more new gene therapies in development that mostly target loss-of-function mutation diseases with gene replacement (e.g., Batten disease, mucopolysaccharidoses, gangliosidoses) or, less frequently, gain-of-toxic-function mutation diseases by gene therapeutic silencing of pathologic genes (e.g., amyotrophic lateral sclerosis, Huntington's disease). In addition, the use of genome editing as a gene therapy is being explored for some diseases, but this has so far only reached clinical testing in the treatment of mucopolysaccharidoses. Based on the large number of planned, ongoing, and completed clinical trials for rare genetic central nervous system diseases, it can be expected that several novel gene therapies will be approved and become available within the near future. Essential for this to happen is the in depth characterization of short- and long-term effects, safety aspects, and pharmacodynamics of the applied gene therapy platforms.

An AAV-based, room-temperature-stable, single-dose COVID-19 vaccine provides durable immunogenicity and protection in non-human primates

The SARS-CoV-2 pandemic has affected more than 185 million people worldwide resulting in over 4 million deaths. To contain the pandemic, there is a continued need for safe vaccines that provide durable protection at low and scalable doses and can be deployed easily. Here, AAVCOVID-1, an adeno-associated viral (AAV), spike-gene-based vaccine candidate demonstrates potent immunogenicity in mouse and non-human primates following a single injection and confers complete protection from SARS-CoV-2 challenge in macaques. Peak neutralizing antibody titers are sustained at 1 year and complemented by functional memory T cell responses. The AAVCOVID vector has no relevant pre-existing immunity in humans and does not elicit cross-reactivity to common AAVs used in gene therapy. Vector genome persistence and expression wanes following injection. The single low-dose requirement, high-yield manufacturability, and 1-month stability for storage at room temperature may make this technology well suited to support effective immunization campaigns for emerging pathogens on a global scale.

In vivo Pooled Screening: A Scalable Tool to Study the Complexity of Aging and Age-Related Disease

Biological aging, and the diseases of aging, occur in a complex in vivo environment, driven by multiple interacting processes. A convergence of recently developed technologies has enabled in vivo pooled screening: direct administration of a library of different perturbations to a living animal, with a subsequent readout that distinguishes the identity of each perturbation and its effect on individual cells within the animal. Such screens hold promise for efficiently applying functional genomics to aging processes in the full richness of the in vivo setting. In this review, we describe the technologies behind in vivo pooled screening, including a range of options for delivery, perturbation and readout methods, and outline their potential application to aging and age-related disease. We then suggest how in vivo pooled screening, together with emerging innovations in each of its technological underpinnings, could be extended to shed light on key open questions in aging biology, including the mechanisms and limits of epigenetic reprogramming and identifying cellular mediators of systemic signals in aging.

Adeno-Associated Viral Vectors as Versatile Tools for Parkinson's Research, Both for Disease Modeling Purposes and for Therapeutic Uses

It is without any doubt that precision medicine therapeutic strategies targeting neurodegenerative disorders are currently witnessing the spectacular rise of newly designed approaches based on the use of viral vectors as Trojan horses for the controlled release of a given genetic payload. Among the different types of viral vectors, adeno-associated viruses (AAVs) rank as the ones most commonly used for the purposes of either disease modeling or for therapeutic strategies. Here, we reviewed the current literature dealing with the use of AAVs within the field of Parkinson’s disease with the aim to provide neuroscientists with the advice and background required when facing a choice on which AAV might be best suited for addressing a given experimental challenge. Accordingly, here we will be summarizing some insights on different AAV serotypes, and which would be the most appropriate AAV delivery route. Next, the use of AAVs for modeling synucleinopathies is highlighted, providing potential readers with a landscape view of ongoing pre-clinical and clinical initiatives pushing forward AAV-based therapeutic approaches for Parkinson’s disease and related synucleinopathies.

Targeted Therapy in Cardiovascular Disease: A Precision Therapy Era

Targeted therapy refers to exploiting the specific therapeutic drugs against the pathogenic molecules (a protein or a gene) or cells. The drug specifically binds to disease-causing molecules or cells without affecting normal tissue, thus enabling personalized and precision treatment. Initially, therapeutic drugs included antibodies and small molecules, (e.g. nucleic acid drugs). With the advancement of the biology technology and immunotherapy, the gene editing and cell editing techniques are utilized for the disease treatment. Currently, targeted therapies applied to treat cardiovascular diseases (CVDs) mainly include protein drugs, gene editing technologies, nucleic acid drugs and cell therapy. Although targeted therapy has demonstrated excellent efficacy in pre-clinical and clinical trials, several limitations need to be recognized and overcome in clinical application, (e.g. off-target events, gene mutations, etc.). This review introduces the mechanisms of different targeted therapies, and mainly describes the targeted therapy applied in the CVDs. Furthermore, we made comparative analysis to clarify the advantages and disadvantages of different targeted therapies. This overview is expected to provide a new concept to the treatment of the CVDs.

CARAMBA: a first-in-human clinical trial with SLAMF7 CAR-T cells prepared by virus-free Sleeping Beauty gene transfer to treat multiple myeloma

Clinical development of chimeric antigen receptor (CAR)-T-cell therapy has been enabled by advances in synthetic biology, genetic engineering, clinical-grade manufacturing, and complex logistics to distribute the drug product to treatment sites. A key ambition of the CARAMBA project is to provide clinical proof-of-concept for virus-free CAR gene transfer using advanced Sleeping Beauty (SB) transposon technology. SB transposition in CAR-T engineering is attractive due to the high rate of stable CAR gene transfer enabled by optimized hyperactive SB100X transposase and transposon combinations, encoded by mRNA and minicircle DNA, respectively, as preferred vector embodiments. This approach bears the potential to facilitate and expedite vector procurement, CAR-T manufacturing and distribution, and the promise to provide a safe, effective, and economically sustainable treatment. As an exemplary and novel target for SB-based CAR-T cells, the CARAMBA consortium has selected the SLAMF7 antigen in multiple myeloma. SLAMF7 CAR-T cells confer potent and consistent anti-myeloma activity in preclinical assays in vitro and in vivo. The CARAMBA clinical trial (Phase-I/IIA; EudraCT: 2019-001264-30) investigates the feasibility, safety, and anti-myeloma efficacy of autologous SLAMF7 CAR-T cells. CARAMBA is the first clinical trial with virus-free CAR-T cells in Europe, and the first clinical trial that uses advanced SB technology worldwide.

NaCl and KCl mediate log increase in AAV vector particles and infectious titers in a specific/timely manner with the HSV platform

The increasing demand for adeno-associated virus (AAV) vectors, a result from the surging interest for their potential to cure human genetic diseases by gene transfer, tumbled on low-performing production systems. Innovative improvements to increase both yield and quality of the vector produced have become a priority undertaking in the field. In a previous study, we showed that adding a specific concentration of sodium chloride (NaCl) to the production medium resulted in a dramatic increase of AAV vector particle and infectious titers when using the herpes simplex virus (HSV) production system, both in adherent or suspension platforms. In this work, we studied additional salts and their impact on AAV vector production. We found that potassium chloride (KCl), or a combination of KCl and NaCl, resulted in the highest increase in AAV vector production. We determined that the salt-mediated effect was the most impactful when the salt was present between 8 and approximately 16 h post-infection, with the highest rate increase occurring within the first 24 h of the production cycle. We showed that the AAV vector yield increase did not result from an increase in cell growth, size, or viability. Furthermore, we demonstrated that the impact on AAV vector production was specifically mediated by NaCl and KCl independently of their impact on the osmolality of the production media. Our findings convincingly showed that NaCl and KCl were uniquely efficacious to promote up to a 10-fold increase in the production of highly infectious AAV vectors when produced in the presence of HSV. We think that this study will provide unique and important new insights in AAV biology toward the establishment of more successful production protocols.

UnaG as a reporter in adeno-associated virus-mediated gene transfer for biomedical imaging

Adeno-associated virus (AAV) is one of the most common gene transfer vectors, but it has a limited capacity. A smaller fluorescent protein is urgently needed since it is more suitable to act as a reporter in AAV. In this study, a bilirubin-dependent reporter smaller than EGFP, termed UnaG, was found to have the ability to label the neurons of a mouse brain as clearly as EGFP without the addition of exogenous bilirubin. We also found that UnaG's pH tolerance is better than that of EGFP; however, its fluorescence recovery after protonated quenching is not as good as that of EGFP. In addition, UnaG preserved its fluorescence better than EGFP in SeeDB clearing. Taken together, this study demonstrates that UnaG can act as a small intrinsically fluorescent reporter in the mouse brain without an additional ligand, thus providing an alternative over EGFP for AAV-mediated neuron labeling in mammals.

Viral Vector Systems for Gene Therapy: A Comprehensive Literature Review of Progress and Biosafety Challenges

Introduction

National Institutes of Health (NIH) defines gene therapy as an experimental technique that uses genes to treat or prevent disease. Although gene therapy is a promising treatment option for a number of diseases (including inherited disorders, some types of cancer, and certain viral infections), the technique remains risky and is still under study to make sure that it will be effective and safe.

Methods

Applications of viral vectors and nonviral gene delivery systems have found an encouraging new beginning in gene therapy in recent years. Although several viral vectors and nonviral gene delivery systems have been developed in the past 3 decades, no one delivery system can be applied in gene therapy to all cell types in vitro and in vivo. Furthermore, the use of viral vector systems (both in vitro and in vivo) present unique occupational health and safety challenges. In this review article, we discuss the biosafety challenges and the current framework of risk assessment for working with the viral vector systems.

Discussion

The recent advances in the field of gene therapy is exciting, but it is important for scientists, institutional biosafety committees, and biosafety officers to safeguard public trust in the use of this technology in clinical trials and make conscious efforts to engage the public through ongoing forums and discussions.

Emerging technologies to study glial cells

Development, physiological functions, and pathologies of the brain depend on tight interactions between neurons and different types of glial cells, such as astrocytes, microglia, oligodendrocytes, and oligodendrocyte precursor cells. Assessing the relative contribution of different glial cell types is required for the full understanding of brain function and dysfunction. Over the recent years, several technological breakthroughs were achieved, allowing "glio-scientists" to address new challenging biological questions. These technical developments make it possible to study the roles of specific cell types with medium or high-content workflows and perform fine analysis of their mutual interactions in a preserved environment. This review illustrates the potency of several cutting-edge experimental approaches (advanced cell cultures, induced pluripotent stem cell (iPSC)-derived human glial cells, viral vectors, in situ glia imaging, opto- and chemogenetic approaches, and high-content molecular analysis) to unravel the role of glial cells in specific brain functions or diseases. It also illustrates the translation of some techniques to the clinics, to monitor glial cells in patients, through specific brain imaging methods. The advantages, pitfalls, and future developments are discussed for each technique, and selected examples are provided to illustrate how specific "gliobiological" questions can now be tackled.

High-brightness anterograde transneuronal HSV1 H129 tracer modified using a Trojan horse-like strategy

Neurotropic viral transsynaptic tracing is an increasingly powerful technique for dissecting the structure and function of neural circuits. Herpes simplex virus type 1 strain H129 has been widely used as an anterograde tracer. However, HSV tracers still have several shortcomings, including high toxicity, low sensitivity and non-specific retrograde labeling. Here, we aimed to construct high-brightness HSV anterograde tracers by increasing the expression of exogenous genes carried by H129 viruses. Using a Trojan horse-like strategy, a HSV/AAV (adeno-associated virus) chimaera termed H8 was generated to enhance the expression of a fluorescent marker. In vitro and in vivo assays showed that the exogenous gene was efficiently replicated and amplified by the synergism of the HSV vector and introduced AAV replication system. H8 reporting fluorescence was brighter than that of currently available H129 tracers, and H8 could be used for fast and effective anterograde tracing without additional immunostaining. These results indicated that foreign gene expression in HSV tracers could be enhanced by integrating HSV with AAV replication system. This approach may be useful as a general enhanced expression strategy for HSV-based tracing tools or gene delivery vectors.

AAV-mediated expression of HLA-G1/5 reduces severity of experimental autoimmune uveitis

Non-infectious uveitis (NIU) is an intractable, recurrent, and painful disease that is a common cause of vision loss. Available treatments of NIU, such as the use of topical corticosteroids, are non-specific and have serious side effects which limits them to short-term use; however, NIU requires long-term treatment to prevent vision loss. Therefore, a single dose therapeutic that mediates long-term immunosuppression with minimal side effects is desirable. In order to develop an effective long-term therapy for NIU, an adeno-associated virus (AAV) gene therapy approach was used to exploit a natural immune tolerance mechanism induced by the human leukocyte antigen G (HLA-G). To mimic the prevention of NIU, naïve Lewis rats received a single intravitreal injection of AAV particles harboring codon-optimized cDNAs encoding HLA-G1 and HLA-G5 isoforms one week prior to the induction of experimental autoimmune uveitis (EAU). AAV-mediated expression of the HLA-G-1 and -5 transgenes in the targeted ocular tissues following a single intravitreal injection of AAV-HLA-G1/5 significantly decreased clinical and histopathological inflammation scores compared to untreated EAU eyes (p < 0.04). Thus, localized ocular gene delivery of AAV-HLA-G1/5 may reduce the off-target risks and establish a long-term immunosuppressive effect that would serve as an effective and novel therapeutic strategy for NIU, with the potential for applications to additional ocular immune-mediated diseases.

Durable multitransgene expression in vivo using systemic, nonviral DNA delivery

Recombinant adeno-associated virus (AAV) vectors are transforming therapies for rare human monogenic deficiency diseases. However, adaptive immune responses to AAV and its limited DNA insert capacity, restrict their therapeutic potential. HEDGES (high-level extended duration gene expression system), a nonviral DNA- and liposome-based gene delivery platform, overcomes these limitations in immunocompetent mice. Specifically, one systemic HEDGES injection durably produces therapeutic levels of transgene-encoded human proteins, including FDA-approved cytokines and monoclonal antibodies, without detectable integration into genomic DNA. HEDGES also controls protein production duration from <3 weeks to >1.5 years, does not induce anti-vector immune responses, is reexpressed for prolonged periods following reinjection, and produces only transient minimal toxicity. HEDGES can produce extended therapeutic levels of multiple transgene-encoded therapeutic human proteins from DNA inserts >1.5-fold larger than AAV-based therapeutics, thus creating combinatorial interventions to effectively treat common polygenic diseases driven by multigenic abnormalities.

Internal Ribosome Entry Site Dramatically Reduces Transgene Expression in Hematopoietic Cells in a Position-Dependent Manner

Bicistronic transgene expression mediated by internal ribosome entry site (IRES) elements has been widely used. It co-expresses heterologous transgene products from a message RNA driven by a single promoter. Hematologic gene delivery is a promising treatment for both inherited and acquired diseases. A combined strategy was recently documented for potential genome editing in hematopoietic cells. A transduction efficiency exceeding ~90% can be achieved by capsid-optimized recombinant adeno-associated virus serotype 6 (rAAV6) vectors. In this study, to deliver an encephalomyocarditis virus (EMCV) IRES-containing rAAV6 genome into hematopoietic cells, we observed that EMCV IRES almost completely shut down the transgene expression during the process of mRNA–protein transition. In addition, position-dependent behavior was observed, in which only the EMCV IRES element located between a promoter and the transgenes had an inhibitory effect. Although further studies are warranted to evaluate the involvement of cellular translation machinery, our results propose the use of specific IRES elements or an alternative strategy, such as the 2A system, to achieve bicistronic transgene expression in hematopoietic cells.

Gene Delivery to Human Limbal Stem Cells Using Viral Vectors

Limbal stem cell (LSC) transplantation is a promising treatment for ocular surface diseases especially LSC deficiency. Genetic engineering represents an attractive strategy to increase the potential for success in LSC transplantations either by correcting autologous diseased LSCs or by decreasing the immunogenicity of allogeneic LSCs. Therefore, two popular viral vectors, adeno-associated viral (AAV) vector and lentiviral (LV) vector, were compared for gene delivery in human LSCs. Transduction efficiency was evaluated by flow cytometry, quantitation of viral genomes, and fluorescence microscopy after introducing eight self-complementary AAV serotypes or LV carrying a green fluorescent protein (GFP) cassette to fresh limbal epithelial cells, cultivated LSC colonies, or after corneal intrastromal injection into human explant tissue. For fresh limbal epithelial cells, AAV6 showed the highest transduction efficiency, followed by LV and AAV4 at 24 h after vector incubation, which did not directly correlate with internalized genome copy number. The colony formation efficiency, as well as colony size over time, showed no significant differences among AAV serotypes, LV, and nontreated controls. The percentage of GFP+ colonies at 14 days post-seeding was significantly higher in the LV group, which plateaued at 50% GFP+ upon serial passages. Interestingly, AAV6-treated colonies initially showed a variegated transduction phenotype with no GFP+ colonies in serial passages. Quantitative polymerase chain reaction and AAV6 capsid staining revealed that transduction was restricted to differentiated cells of LSC colonies at a post-entry step. Following central intrastromal injection of human corneas, both LV and AAV6 transduced the stroma and endothelial cells, and AAV6 also transduced cells of the epithelia. However, no transduction was observed in derived LSC colonies. The collective results demonstrate the effectiveness of LV for stable human LSC genetic engineering and an unreported phenomenon of AAV6 transduction restriction in multipotent cells derived from the human limbus.

Gene therapy research for kidney diseases

A resurgence in the development of newer gene therapy systems has led to recent successes in the treatment of B cell cancers, retinal degeneration and neuromuscular atrophy. Gene therapy offers the ability to treat the patient at the root cause of their malady by restoring normal gene function and arresting the pathological progression of their genetic disease. The current standard of care for most genetic diseases is based upon the symptomatic treatment with polypharmacy while minimizing any potential adverse effects attributed to the off-target and drug-drug interactions on the target or other organs. In the kidney, however, the development of gene therapy modifications to specific renal cells has lagged far behind those in other organ systems. Some positive strides in the past few years provide continued enthusiasm to invest the time and effort in the development of new gene therapy vectors for medical intervention to treat kidney diseases. This mini-review will systematically describe the pros and cons of the most commonly tested gene therapy vector systems derived from adenovirus, retrovirus, and adeno-associated virus and provide insight about their potential utility as a therapy for various types of genetic diseases in the kidney.

Standard screening methods underreport AAV-mediated transduction and gene editing

Conventional methods to discern adeno-associated virus (AAV) vector transduction patterns are based on high, stable expression of a reporter gene. As a consequence, conventionally described tropisms omit cell types that undergo transient transduction, or have low but undetectable levels of reporter expression. This creates a blind spot for AAV-based genome editing applications because only minimal transgene expression is required for activity. Here, we use editing-reporter mice to fill this void. Our approach sensitively captures both high and low transgene expression from AAV vectors. Using AAV8 and other serotypes, we demonstrate the superiority of the approach in a side-by-side comparison with traditional methods, demonstrate numerous, previously unknown sites of AAV targeting, and better predict the gene editing footprint after AAV-CRISPR delivery. We anticipate that this system, which captures the full spectrum of transduction patterns from AAV vectors in vivo, will be foundational to current and emerging AAV technologies.

Conventional methods to detect AAV vector transduction can miss transient or low levels of reporter expression. Here the authors use editing-reporter mice and discover numerous sites of AAV targeting along with better prediction of the gene editing footprint.

Attenuation of Inherited and Acquired Retinal Degeneration Progression with Gene-based Techniques

Inherited retinal dystrophies cause progressive vision loss and are major contributors to blindness worldwide. Advances in gene therapy have brought molecular approaches into the realm of clinical trials for these incurable illnesses. Select phase I, II and III trials are complete and provide some promise in terms of functional outcomes and safety, although questions do remain over the durability of their effects and the prevalence of inflammatory reactions. This article reviews gene therapy as it can be applied to inherited retinal dystrophies, provides an update of results from recent clinical trials, and discusses the future prospects of gene therapy and genome surgery.

Production and use of adeno-associated virus vectors as tools for cancer immunotherapy

Recombinant adeno-associated viruses (rAAVs) are attractive tools for research in cancer immunotherapy. A single administration of an AAV vector in tumor mouse models induces a progressive increase in transgene expression which reaches a plateau 1 or 2 weeks after administration. The rAAV is then able to maintain the expression of the immunostimulatory transgene. Thus, the use of these vectors obviates the need for frequent administrations of the therapeutic protein to achieve the antitumor effect. The long-term expression of AAV vectors can be exploited for the evaluation of the antitumor activity of immune-enhancing proteins. Most preclinical studies have focused on the expression of cytokines and on the induction of immune responses elicited by tumor-associated antigens expressed by rAAVs. Notwithstanding, rAAVs may not be suitable for immunostimulatory proteins that require high and/or immediate expression. In this chapter, we review a feasible, reliable and detailed protocol to produce and purify AAV vectors as a tool for cancer immunotherapy strategies.

Effects of gene therapy on cardiovascular symptoms of lysosomal storage diseases

Lysosomal storage diseases (LSDs) are inherited conditions caused by impaired lysosomal function and consequent substrate storage, leading to a range of clinical manifestations, including cardiovascular disease. This may lead to significant symptoms and even cardiac failure, which is an important cause of death among patients. Currently available treatments do not completely correct cardiac involvement in the LSDs. Gene therapy has been tested as a therapeutic alternative with promising results for the heart disease. In this review, we present the results of different approaches of gene therapy for LSDs, mainly in animal models, and its effects in the heart, focusing on protocols with cardiac functional analysis.

Adeno-Associated Viral Vectors as a Tool for Large Gene Delivery to the Retina

Gene therapy using adeno-associated viral (AAV) vectors currently represents the most promising approach for the treatment of many inherited retinal diseases (IRDs), given AAV's ability to efficiently deliver therapeutic genes to both photoreceptors and retinal pigment epithelium, and their excellent safety and efficacy profiles in humans. However, one of the main obstacles to widespread AAV application is their limited packaging capacity, which precludes their use from the treatment of IRDs which are caused by mutations in genes whose coding sequence exceeds 5 kb. Therefore, in recent years, considerable effort has been made to identify strategies to increase the transfer capacity of AAV vectors. This review will discuss these new developed strategies, highlighting the advancements as well as the limitations that the field has still to overcome to finally expand the applicability of AAV vectors to IRDs due to mutations in large genes.

Vector uncoating limits adeno-associated viral vector-mediated transduction of human dendritic cells and vector immunogenicity

AAV vectors poorly transduce Dendritic cells (DC), a feature invoked to explain AAV's low immunogenicity. However, the reason for this non-permissiveness remained elusive. Here, we performed an in-depth analysis using human monocyte-derived immature DC (iDC) as model. iDC internalized AAV vectors of various serotypes, but even the most efficient serotype failed to transduce iDC above background. Since AAV vectors reached the cell nucleus, we hypothesized that AAV's intracellular processing occurs suboptimal. On this basis, we screened an AAV peptide display library for capsid variants more suitable for DC transduction and identified the I/VSS family which transduced DC with efficiencies of up to 38%. This property correlated with an improved vector uncoating. To determine the consequence of this novel feature for AAV's in vivo performance, we engineered one of the lead candidates to express a cytoplasmic form of ovalbumin, a highly immunogenic model antigen, and assayed transduction efficiency as well as immunogenicity. The capsid variant clearly outperformed the parental serotype in muscle transduction and in inducing antigen-specific humoral and T cell responses as well as anti-capsid CD8+ T cells. Hence, vector uncoating represents a major barrier hampering AAV vector-mediated transduction of DC and impacts on its use as vaccine platform.

Current Progress on MicroRNA-Based Gene Delivery in the Treatment of Osteoporosis and Osteoporotic Fracture

Emerging evidence demonstrates that microRNAs, as important endogenous posttranscriptional regulators, are essential for bone remodeling and regeneration. Undoubtedly, microRNA-based gene therapies show great potential to become novel approaches against bone-related diseases, including osteoporosis and associated fractures. The major obstacles for continued advancement of microRNA-based therapies in clinical application include their poor in vivo stability, nonspecific biodistribution, and unwanted side effects. Appropriate chemical modifications and delivery vectors, which improve the biological performance and potency of microRNA-based drugs, hold the key to translating miRNA technologies into clinical practice. Thus, this review summarizes the current attempts and existing deficiencies of chemical modifications and delivery systems applied in microRNA-based therapies for osteoporosis and osteoporotic fractures to inform further explorations.

Emerging role of viral vectors for circuit-specific gene interrogation and manipulation in rodent brain

Over the past half century, novel tools have allowed the characterization of myriad molecular underpinnings of neural phenomena including synaptic function, neurogenesis and neurodegeneration, membrane excitability, and neurogenetics/epigenetics. More recently, transgenic mice have made possible cell type-specific explorations of these phenomena and have provided critical models of many neurological and psychiatric diseases. However, it has become clear that many critical areas of study require tools allowing the study and manipulation of individual neural circuits within the brain, and viral vectors have come to the forefront in driving these circuit-specific studies. Here, we present a surface-level review of the general classes of viral vectors used for study of the brain, along with their suitability for circuit-specific studies. We then cover in detail a new long-lasting, retrograde expressing form of herpes simplex virus termed LT-HSV that has become highly useful in circuit-based studies. We detail some of its current uses and propose a variety of future uses for this critical new tool, including circuit-based transgene overexpression, gene editing, and gene expression profiling.

Harnessing CRISPR/Cas 9 System for manipulation of DNA virus genome

The recent development of the Clustered Regularly Interspaced Palindromic Repeat (CRISPR)/CRISPR-associated protein 9 (Cas9) system, a genome editing system, has many potential applications in virology. The possibility of introducing site specific breaks has provided new possibilities to precisely manipulate viral genomics. Here, we provide diagrams to summarize the steps involved in the process. We also systematically review recent applications of the CRISPR/Cas9 system for manipulation of DNA virus genomics and discuss the therapeutic potential of the system to treat viral diseases.

Scalable Production and Purification of Adeno-Associated Viral Vectors (AAV)

Here we describe methods for the production of adeno-associated viral (AAV) vectors by transient transfection of HEK293 cells grown in serum-free medium in orbital shaken bioreactors and the subsequent purification of vector particles. The protocol for expression of AAV components is based on polyethyleneimine (PEI) mediated transfection of a 2-plasmid system and is specified for production in milliliter to liter scales. After PEI and plasmid DNA (pDNA) complex formation the diluted cell culture is transfected without a prior concentration step or medium exchange. Following a 3-day batch process, cell cultures are further processed using different methods for lysis and recovery. Methods for the purification of viral particles are described, including iodixanol gradient purification, immunoaffinity chromatography, and ultrafiltration, as well as quantitative PCR to quantify vector titer.

Serotype survey of AAV gene delivery via subconjunctival injection in mice

AAV gene therapy approaches in the posterior eye resulted in the first FDA-approved gene therapy-based drug. However, application of AAV vectorology to the anterior eye has yet to enter even a Phase I trial. Furthermore, the simple and safe subconjunctival injection has been relatively unexplored in regard to AAV vector transduction. To determine the utility of this route for the treatment of various ocular disorders, a survey of gene delivery via natural AAV serotypes was performed and correlated to reported cellular attachment factors. AAV serotypes packaged with a self-complementary reporter were administered via subconjunctival injection to WT mice. Subconjunctival injection of AAV vectors was without incidence; however, vector shedding in tears was noted weeks following administration. AAV transduction was serotype dependent in anterior segment tissues including the eye lid, conjunctiva, and cornea, as well as the periocular tissues including muscle. Transgene product in the cornea was highest for AAV6 and AAV8, however, their corneal restriction was remarkably different; AAV6 appeared restricted to the endothelium layer while AAV8 efficiently transduced the stromal layer. Reported AAV cellular receptors were not well correlated to vector transduction; although, in some cases they were conserved among mouse and human ocular tissues. Subconjunctival administration of particular AAV serotypes may be a simple and safe targeted gene delivery route for ocular surface, muscular, corneal, and optic nerve diseases.

Can an in vivo imaging system be used to determine localization and biodistribution of AAV5-mediated gene expression following subretinal and intravitreal delivery in mice?

Recombinant adeno associated viruses (AAV) are the most commonly used vectors in animal model studies of gene therapy for retinal diseases. The ability of a vector to localize and remain in the target tissue, and in this manner to avoid off-target effects beyond the site of delivery, is critical to the efficacy and safety of the treatment. The in vivo imaging system (IVIS) is a non-invasive imaging tool used for detection and quantification of bioluminescence activity in rodents. Our aim was to investigate whether IVIS can detect localization and biodistribution of AAV5 vector in mice following subretinal (SR) and intravitreal (IVT) injections. AAV5 carrying firefly luciferase DNA under control of the ubiquitous cytomegalovirus (CMV) promoter was injected unilaterally IVT or SR (in the central or peripheral retina) of forty-one mice. Luciferase activity was tracked for up to 60 weeks in the longest surviving animals, using repeated (up to 12 times) IVIS bioluminescence imaging. Luciferase presence was also confirmed immunohistochemically (IHC) and by PCR in representative animals. In the SR group, IVIS readings demonstrated luciferase activity in all (32/32) eyes, and luciferase presence was confirmed by IHC (4/4 eyes) and PCR (12/12 eyes). In the IVT group, IVIS readings demonstrated luciferase activity in 7/9 eyes, and luciferase presence was confirmed by PCR in 5/5 eyes and by IHC (2/2 eyes). In two SR-injected animals (one each from the central and peripheral injection sites), PCR detected luciferase presence in the ipsilateral optic nerves, a finding that was not detected by IVIS or IHC. Our results show that when evaluating SR delivery, IVIS has a sensitivity and specificity of 100% compared with the gold standard PCR. When evaluating IVT delivery, IVIS has a sensitivity of 78% and specificity of 100%. These finding confirm the ability of IVIS to detect in-vivo localized expression of AAV following SR delivery in the retina up to 60 weeks post-treatment, using repeated imaging for longitudinal evaluation, without fading of the biological signal, thereby replacing the need for post mortem processing in order to confirm vector expression. However, IVIS is probably not sensitive enough, compared with genome detection, to demonstrate biodistribution to the optic nerve, as it could not detect luciferase activity in ipsilateral optic nerves following SR delivery in mice.

Seeing the Light after 25 Years of Retinal Gene Therapy

The retina has been at the forefront of translational gene therapy. Proof-of-concept that gene therapy could restore vision in a large animal led to the initiation of the first successful clinical trials and, in turn, to the recent approval of the first gene therapy product for an ocular disease. As dozens of clinical trials of retinal gene therapy have begun, new challenges are identified, which include delivery of large genes, counteracting gain-of-function mutations, and safe and effective gene transfer to diseased retinas. Advancements in vector design, improvements of delivery routes, and selection of optimal timing for intervention will contribute to extend the initial success of retinal gene therapy to an increasing number of inherited blinding conditions.

Adeno-associated virus 2/9 delivery of Cre recombinase in mouse primary afferents

Genetically-modified animal models have significantly increased our understanding of the complex central nervous system circuits. Among these models, inducible transgenic mice whose specific gene expression can be modulated through a Cre recombinase/LoxP system are useful to study the role of specific peptides and proteins in a given population of cells. In the present study, we describe an efficient approach to selectively deliver a Cre-GFP to dorsal root ganglia (DRG) neurons. First, mice of different ages were injected in both hindpaws with a recombinant adeno-associated virus (rAAV2/9-CBA-Cre-GFP). Using this route of injection in mice at 5 days of age, we report that approximately 20% of all DRG neurons express GFP, 6 to 8 weeks after the infection. The level of infection was reduced by 50% when the virus was administered at 2 weeks of age. Additionally, the virus-mediated delivery of the Cre-GFP was also investigated via the intrathecal route. When injected intrathecally, the rAAV2/9-CBA-Cre-GFP virus infected a much higher proportion of DRG neurons than the intraplantar injection, with up to 51.6% of infected lumbar DRG neurons. Noteworthy, both routes of injection predominantly transduced DRG neurons over spinal and brain neurons.

Dopaminergic dysfunction in neurodevelopmental disorders: recent advances and synergistic technologies to aid basic research

Neurodevelopmental disorders (NDDs) represent a diverse group of syndromes characterized by abnormal development of the central nervous system and whose symptomatology includes cognitive, emotional, sensory, and motor impairments. The identification of causative genetic defects has allowed for creation of transgenic NDD mouse models that have revealed pathophysiological mechanisms of disease phenotypes in a neural circuit- and cell type-specific manner. Mouse models of several syndromes, including Rett syndrome, Fragile X syndrome, Angelman syndrome, Neurofibromatosis type 1, etc., exhibit abnormalities in the structure and function of dopaminergic circuitry, which regulates motivation, motor behavior, sociability, attention, and executive function. Recent advances in technologies for functional circuit mapping, including tissue clearing, viral vector-based tracing methods, and optical readouts of neural activity, have refined our knowledge of dopaminergic circuits in unperturbed states, yet these tools have not been widely applied to NDD research. Here, we will review recent findings exploring dopaminergic function in NDD models and discuss the promise of new tools to probe NDD pathophysiology in these circuits.

AAV vector-meditated expression of HLA-G reduces injury-induced corneal vascularization, immune cell infiltration, and fibrosis

Over 1.5 million individuals suffer from cornea vascularization due to genetic and/or environmental factors, compromising visual acuity and often resulting in blindness. Current treatments of corneal vascularization are limited in efficacy and elicit undesirable effects including, ironically, vision loss. To develop a safe and effective therapy for corneal vascularization, adeno-associated virus (AAV) gene therapy, exploiting a natural immune tolerance mechanism induced by human leukocyte antigen G (HLA-G), was investigated. Self-complementary AAV cassettes containing codon optimized HLA-G1 (transmembrane) or HLA-G5 (soluble) isoforms were validated in vitro. Then, following a corneal intrastromal injection, AAV vector transduction kinetics, using a chimeric AAV capsid, were determined in rabbits. One week following corneal trauma, a single intrastromal injection of scAAV8G9-optHLA-G1 + G5 prevented corneal vascularization, inhibited trauma-induced T-lymphocyte infiltration (some of which were CD8⁺), and dramatically reduced myofibroblast formation compared to control treated eyes. Biodistribution analyses suggested AAV vectors persisted only in the trauma-induced corneas; however, a neutralizing antibody response to the vector capsid was observed inconsistently. The collective data demonstrate the clinical potential of scAAV8G9-optHLA-G to safely and effectively treat corneal vascularization and inhibit fibrosis while alluding to broader roles in ocular surface immunity and allogenic organ transplantation.

Gene Therapy with the Sleeping Beauty Transposon System

The widespread clinical implementation of gene therapy requires the ability to stably integrate genetic information through gene transfer vectors in a safe, effective, and economical manner. The latest generation of Sleeping Beauty (SB) transposon vectors fulfills these requirements, and may overcome limitations associated with viral gene transfer vectors and transient nonviral gene delivery approaches that are prevalent in ongoing clinical trials. The SB system enables high-level stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, thereby representing a highly attractive gene transfer strategy for clinical use. Here, we review the most important aspects of using SB for gene therapy, including vectorization as well as genomic integration features. We also illustrate the path to successful clinical implementation by highlighting the application of chimeric antigen receptor (CAR)-modified T cells in cancer immunotherapy.

Virus-Derived Peptides for Clinical Applications

Novel affinity agents with high specificity are needed to make progress in disease diagnosis and therapy. Over the last several years, peptides have been considered to have fundamental benefits over other affinity agents, such as antibodies, due to their fast blood clearance, low immunogenicity, rapid tissue penetration, and reproducible chemical synthesis. These features make peptides ideal affinity agents for applications in disease diagnostics and therapeutics for a wide variety of afflictions. Virus-derived peptide techniques provide a rapid, robust, and high-throughput way to identify organism-targeting peptides with high affinity and selectivity. Here, we will review viral peptide display techniques, how these techniques have been utilized to select new organism-targeting peptides, and their numerous biomedical applications with an emphasis on targeted imaging, diagnosis, and therapeutic techniques. In the future, these virus-derived peptides may be used as common diagnosis and therapeutics tools in local clinics.

Strategies to optimize capsid protein expression and single-stranded DNA formation of adeno-associated virus in Saccharomyces cerevisiae

AIMS

Adeno-associated virus type 2 (AAV) is a nonpathogenic parvovirus that is a promising tool for gene therapy. We aimed to construct plasmids for optimal expression and assembly of capsid proteins and evaluate adenovirus (Ad) protein effect on AAV single-stranded DNA (ssDNA) formation in Saccharomyces cerevisiae.

METHODS AND RESULTS

Yeast expression plasmids have been developed in which the transcription of AAV capsid proteins (VP1,2,3) is driven by the constitutive ADH1 promoter or galactose-inducible promoters. Optimal VP1,2,3 expression was obtained from GAL1/10 bidirectional promoter. Moreover, we demonstrated that AAP is expressed in yeast and virus-like particles (VLPs) assembled inside the cell. Finally, the expression of two Ad proteins, E4orf6 and E1b55k, had no effect on AAV ssDNA formation.

CONCLUSIONS

This study confirms that yeast is able to form AAV VLPs; however, capsid assembly and ssDNA formation are less efficient in yeast than in human cells. Moreover, the expression of Ad proteins did not affect AAV ssDNA formation.

SIGNIFICANCE AND IMPACT OF THE STUDY

New manufacturing strategies for AAV-based gene therapy vectors (rAAV) are needed to reduce costs and time of production. Our study explores the feasibility of yeast as alternative system for rAAV production.