Transient transfection methods for clinical adeno-associated viral vector production

Navigating the CRISPR/Cas Landscape for Enhanced Diagnosis and Treatment of Wilson's Disease

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein (Cas) system continues to evolve, thereby enabling more precise detection and repair of mutagenesis. The development of CRISPR/Cas-based diagnosis holds promise for high-throughput, cost-effective, and portable nucleic acid screening and genetic disease diagnosis. In addition, advancements in transportation strategies such as adeno-associated virus (AAV), lentiviral vectors, nanoparticles, and virus-like vectors (VLPs) offer synergistic insights for gene therapeutics in vivo. Wilson's disease (WD), a copper metabolism disorder, is primarily caused by mutations in the ATPase copper transporting beta (ATP7B) gene. The condition is associated with the accumulation of copper in the body, leading to irreversible damage to various organs, including the liver, nervous system, kidneys, and eyes. However, the heterogeneous nature and individualized presentation of physical and neurological symptoms in WD patients pose significant challenges to accurate diagnosis. Furthermore, patients must consume copper-chelating medication throughout their lifetime. Herein, we provide a detailed description of WD and review the application of novel CRISPR-based strategies for its diagnosis and treatment, along with the challenges that need to be overcome.

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

Extracellular vesicle depletion and UGCG overexpression mitigate the cell density effect in HEK293 cell culture transfection

The hitherto unexplained reduction of cell-specific productivity in transient gene expression (TGE) at high cell density (HCD) is known as the cell density effect (CDE). It currently represents a major challenge in TGE-based bioprocess intensification. This phenomenon has been largely reported, but the molecular principles governing it are still unclear. The CDE is currently understood to be caused by the combination of an unknown inhibitory compound in the extracellular medium and an uncharacterized cellular change at HCD. This study investigates the role of extracellular vesicles (EVs) as extracellular inhibitors for transfection through the production of HIV-1 Gag virus-like particles (VLPs) via transient transfection in HEK293 cells. EV depletion from the extracellular medium restored transfection efficiency in conditions that suffer from the CDE, also enhancing VLP budding and improving production by 60%. Moreover, an alteration in endosomal formation was observed at HCD, sequestering polyplexes and preventing transfection. Overexpression of UDP-glucose ceramide glucosyltransferase (UGCG) enzyme removed intracellular polyplex sequestration, improving transfection efficiency. Combining EV depletion and UGCG overexpression improved transfection efficiency by ∼45% at 12 × 106 cells/mL. These results suggest that the interaction between polyplexes and extracellular and intracellular vesicles plays a crucial role in the CDE, providing insights for the development of strategies to mitigate its impact.

Distinct regions within SAP25 recruit O-linked glycosylation, DNA demethylation, and ubiquitin ligase and hydrolase activities to the Sin3/HDAC complex

Epigenetic control of gene expression is crucial for maintaining gene regulation. Sin3 is an evolutionarily conserved repressor protein complex mainly associated with histone deacetylase (HDAC) activity. A large number of proteins are part of Sin3/HDAC complexes, and the function of most of these members remains poorly understood. SAP25, a previously identified Sin3A associated protein of 25 kDa, has been proposed to participate in regulating gene expression programs involved in the immune response but the exact mechanism of this regulation is unclear. SAP25 is not expressed in HEK293 cells, which hence serve as a natural knockout system to decipher the molecular functions uniquely carried out by this Sin3/HDAC subunit. Using molecular, proteomic, protein engineering, and interaction network approaches, we show that SAP25 interacts with distinct enzymatic and regulatory protein complexes in addition to Sin3/HDAC. While the O-GlcNAc transferase (OGT) and the TET1 /TET2/TET3 methylcytosine dioxygenases have been previously linked to Sin3/HDAC, in HEK293 cells, these interactions were only observed in the affinity purification in which an exogenously expressed SAP25 was the bait. Additional proteins uniquely recovered from the Halo-SAP25 pull-downs included the SCF E3 ubiquitin ligase complex SKP1/FBXO3/CUL1 and the ubiquitin carboxyl-terminal hydrolase 11 (USP11), which have not been previously associated with Sin3/HDAC. Finally, we use mutational analysis to demonstrate that distinct regions of SAP25 participate in its interaction with USP11, OGT/TETs, and SCF(FBXO3).) These results suggest that SAP25 may function as an adaptor protein to coordinate the assembly of different enzymatic complexes to control Sin3/HDAC-mediated gene expression.

Development of Stable Packaging and Producer Cell Lines for the Production of AAV Vectors

Today, recombinant adeno-associated virus (rAAV) vectors represent the vector systems which are mostly used for in vivo gene therapy for the treatment of rare and less-rare diseases. Although most of the past developments have been performed by using a transfection-based method and more than half of the authorized rAAV-based treatments are based on transfection process, the tendency is towards the use of stable inducible packaging and producer cell lines because their use is much more straightforward and leads in parallel to reduction in the overall manufacturing costs. This article presents the development of HeLa cell-based packaging/producer cell lines up to their use for large-scale rAAV vector production, the more recent development of HEK293-based packaging and producer cell lines, as well as of packaging cell lines based on the use of Sf9 cells. The production features are presented in brief (where available), including vector titer, specific productivity, and full-to-empty particle ratio.

Recent advances in upstream process development for production of recombinant adeno-associated virus

Recombinant adeno-associated virus (rAAV) is rapidly emerging as the preferred delivery vehicle for gene therapies, with promising advantages in safety and efficacy. Key challenges in systemic in-vivo rAAV gene therapy applications are the gap in production capabilities versus potential market demand and complex production process. This review summarizes current available information on rAAV upstream manufacturing processes and proposed optimizations for production. The advancements in rAAV production media were reviewed with proposals to speed up the cell culture process development. Furthermore, major methods for genetic element delivery to host cells were summarized with their advantages, limitations, and future directions for optimization. In addition, culture vessel selection criteria were listed based on production cell system, scale, and development stage. Process control at the production step was also outlined with an in-depth understanding of production kinetics and quality control.

Production of adeno-associated viral vector serotype 6 by triple transfection of suspension HEK293 cells at higher cell densities

In recent years, the use of adeno-associated viruses (AAVs) as vectors for gene and cell therapy has increased, leading to a rise in the amount of AAV vectors required during pre-clinical and clinical trials. AAV serotype 6 (AAV6) has been found to be efficient in transducing different cell types and has been successfully used in gene and cell therapy protocols. However, the number of vectors required to effectively deliver the transgene to one single cell has been estimated at 106 viral genomes (VG), making large-scale production of AAV6 necessary. Suspension cell-based platforms are currently limited to low cell density productions due to the widely reported cell density effect (CDE), which results in diminished production at high cell densities and decreased cell-specific productivity. This limitation hinders the potential of the suspension cell-based production process to increase yields. In this study, we investigated the improvement of the production of AAV6 at higher cell densities by transiently transfecting HEK293SF cells. The results showed that when the plasmid DNA was provided on a cell basis, the production could be carried out at medium cell density (MCD, 4 × 106  cells mL-1 ) resulting in titers above 1010  VG mL-1 . No detrimental effects on cell-specific virus yield or cell-specific functional titer were observed at MCD production. Furthermore, while medium supplementation alleviated the CDE in terms of VG/cell at high cell density (HCD, 10 × 106  cells mL-1 ) productions, the cell-specific functional titer was not maintained, and further studies are necessary to understand the observed limitations for AAV production in HCD processes. The MCD production method reported here lays the foundation for large-scale process operations, potentially solving the current vector shortage in AAV manufacturing.

Non-equilibrium virus particle dynamics: Microsecond MD simulations of the complete Flock House virus capsid under different conditions

Flock House virus (FHV) is an animal virus and considered a model system for non-enveloped viruses. It has a small, icosahedral capsid (T=3) and a bipartite positive-sense RNA genome. We present an extensive study of the FHV capsid dynamics from all-atom molecular dynamics simulations of the complete capsid. The simulations explore different biologically relevant conditions (neutral/low pH, with/without RNA in the capsid) using the CHARMM force field. The results show that low pH destabilizes the capsid, causing radial expansion, and RNA stabilizes the capsid. The finding of low pH destabilization is biologically relevant because the capsid is exposed to low pH in the endosome, where conformational changes occur leading to genome release. We also observe structural changes at the fivefold and twofold symmetry axes that likely relate to the externalization of membrane active γ peptides through the fivefold vertex and extrusion of RNA at the twofold axis. Simulations using the Amber force field at neutral pH are also performed and display similar characteristics to the CHARMM simulations.

Research progress of engineered mesenchymal stem cells and their derived exosomes and their application in autoimmune/inflammatory diseases

Autoimmune/inflammatory diseases affect many people and are an important cause of global incidence and mortality. Mesenchymal stem cells (MSCs) have low immunogenicity, immune regulation, multidifferentiation and other biological characteristics, play an important role in tissue repair and immune regulation and are widely used in the research and treatment of autoimmune/inflammatory diseases. In addition, MSCs can secrete extracellular vesicles with lipid bilayer structures under resting or activated conditions, including exosomes, microparticles and apoptotic bodies. Among them, exosomes, as the most important component of extracellular vesicles, can function as parent MSCs. Although MSCs and their exosomes have the characteristics of immune regulation and homing, engineering these cells or vesicles through various technical means, such as genetic engineering, surface modification and tissue engineering, can further improve their homing and other congenital characteristics, make them specifically target specific tissues or organs, and improve their therapeutic effect. This article reviews the advanced technology of engineering MSCs or MSC-derived exosomes and its application in some autoimmune/inflammatory diseases by searching the literature published in recent years at home and abroad.

Microfluidic production of nanogels as alternative triple transfection reagents for the manufacture of adeno-associated virus vectors

Adeno-associated viral vectors (AAVs) have proved a mainstay in gene therapy, owing to their remarkable transduction efficiency and safety profile. Their production, however, remains challenging in terms of yield, the cost-effectiveness of manufacturing procedures and large-scale production. In this work, we present nanogels produced by microfluidics as a novel alternative to standard transfection reagents such as polyethylenimine-MAX (PEI-MAX) for the production of AAV vectors with comparable yields. Nanogels were formed at pDNA weight ratios of 1 : 1 : 2 and 1 : 1 : 3, of pAAV cis-plasmid, pDG9 capsid trans-plasmid and pHGTI helper plasmid respectively, where vector yields at a small scale showed no significant difference to those of PEI-MAX. Weight ratios of 1 : 1 : 2 showed overall higher titers than 1 : 1 : 3, where nanogels with nitrogen/phosphate ratios of 5 and 10 produced yields of ≈8.8 × 10⁸ vg mL^-1 and ≈8.1 × 10⁸ vg mL^-1 respectively compared to ≈1.1 × 10⁹ vg mL^-1 for PEI-MAX. In larger scale production, optimised nanogels produced AAV at a titer of ≈7.4 × 10¹¹ vg mL^-1, showing no statistical difference from that of PEI-MAX at ≈1.2 × 10¹² vg mL^-1, indicating that equivalent titers can be achieved with easy-to-implement microfluidic technology at comparably lower costs than traditional reagents.

Genome concentration, characterization, and integrity analysis of recombinant adeno-associated viral vectors using droplet digital PCR

Precise, reproducible characterization of AAV is critical for comparing preclinical results between laboratories and determining a safe and effective clinical dose for gene therapy applications. In this study, we systematically evaluated numerous parameters to produce a simple and robust ddPCR protocol for AAV characterization. The protocol uses a low ionic strength buffer containing Pluronic-F68 and polyadenylic acid to dilute the AAV into the ddPCR concentration range and a 10-minute thermal capsid lysis prior to assembling ddPCR reactions containing MspI. A critical finding is that the buffer composition affected the ITR concentration of AAV but not the ITR concentration of a double stranded plasmid, which has implications when using a theoretical, stoichiometric conversion factor to obtain the titer based on the ITR concentration. Using this protocol, a more comprehensive analysis of an AAV vector formulation was demonstrated with multiple ddPCR assays distributed throughout the AAV vector genome. These assays amplify the ITR, regulatory elements, and eGFP transgene to provide a more confident estimate of the vector genome concentration and a high-resolution characterization of the vector genome identity. Additionally, we compared two methods of genome integrity analysis for three control sample types at eight different concentrations for each sample. The genome integrity was independent of sample concentration and the expected values were obtained when integrity was determined based on the excess number of positive droplets relative to the number of double positive droplets expected by chance co-encapsulation of two DNA targets. The genome integrity was highly variable and produced unexpected values when the double positive droplet percentage was used to calculate the genome integrity. A protocol using a one-minute thermal capsid lysis prior to assembling ddPCR reactions lacking a restriction enzyme used the non-ITR assays in a duplex ddPCR milepost experiment to determine the genome integrity using linkage analysis.

A feasibility study of different commercially available serum-free mediums to enhance lentivirus and adeno-associated virus production in HEK 293 suspension cells

Lentivirus and adeno-associated viruses are invaluable tools for biotechnology applications due to their genetic material delivery abilities both in vitro and in vivo. However, their large-scale productions with Good Manufacturing Practices yield low efficiency when adherent and serum dependent HEK293 (Human Embryonic Kidney) cells are used as the host. To increase production efficiency, HEK293 cells are adapted to grow in suspension using commercially available and chemically defined serum-free mediums. Suspended cells can be transiently transfected for viral vector production; however, significant improvements are still needed to increase yield and thereby cost effectiveness. Here, we evaluated four most preferred commercially available mediums that are IVY, FreeStyle293, LV-MAX, and BalanCD HEK293 for the transient transfection feasibility of lentiviral (LV) and adeno-associated virus serotype 2 (AAV2) production in FlorabioHEK293 suspension cells. The highest transfection efficiency was over 90% and obtained by using polyethyleneimine (PEI) 25 K and by media adaptation in IVY without using any transfection enhancer. For the first time the feasibility of HEK293 cells, which were adapted to grow in suspension culture by Florabio and IVY media, were tested for virus production. This study demonstrates the best transfection medium for scalable and optimized production of Lentivirus and Adeno-Associated Virus in suspended HEK293 cell culture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00551-1.

Current Advances in Adeno-Associated Virus-Mediated Gene Therapy to Prevent Acquired Hearing Loss

Adeno-associated viruses (AAVs) are viral vectors that offer an excellent platform for gene therapy due to their safety profile, persistent gene expression in non-dividing cells, target cell specificity, lack of pathogenicity, and low immunogenicity. Recently, gene therapy for genetic hearing loss with AAV transduction has shown promise in animal models. However, AAV transduction for gene silencing or expression to prevent or manage acquired hearing loss is limited. This review provides an overview of AAV as a leading gene delivery vector for treating genetic hearing loss in animal models. We highlight the advantages and shortcomings of AAV for investigating the mechanisms and preventing acquired hearing loss. We predict that AAV-mediated gene manipulation will be able to prevent acquired hearing loss.

Robust AAV Genotyping Based on Genetic Distances in Rep Gene That Are Maintained by Ubiquitous Recombination

Adeno-associated viruses (AAVs) are a convenient tool for gene therapy delivery. According to the current classification, they are divided into the species AAV A and AAV B within the genus Dependoparvovirus. Historically AAVs were also subdivided on the intraspecies level into 13 serotypes, which differ in tissue tropism and targeted gene delivery capacity. Serotype, however, is not a universal taxonomic category, and their assignment is not always robust. Cross-reactivity has been shown, indicating that classification could not rely on the results of serological tests alone. Moreover, since the isolation of AAV4, all subsequent AAVs were subdivided into serotypes based primarily on genetic differences and phylogenetic reconstructions. An increased interest in the use of AAV as a gene delivery tool justifies the need to improve the existing classification. Here, we suggest genotype-based AAV classification below the species level based on the rep gene. A robust threshold was established as 10% nt differences within the 1248 nt genome fragment, with 4 distinct AAV genotypes identified. This distinct sub-species structure is maintained by ubiquitous recombination within, but not between, rep genes of the suggested genotypes.

Assessment of genome packaging in AAVs using Orbitrap-based charge-detection mass spectrometry

Adeno-associated viruses (AAVs) represent important gene therapy vectors with several approved clinical applications and numerous more in clinical trials. Genome packaging is an essential step in the bioprocessing of AAVs and needs to be tightly monitored to ensure the proper delivery of transgenes and the production of effective drugs. Current methods to monitor genome packaging have limited sensitivity, a high demand on labor, and struggle to distinguish between packaging of the intended genome or unwanted side-products. Here we show that Orbitrap-based charge-detection mass spectrometry allows the very sensitive quantification of all these different AAV bioprocessing products. A protocol is presented that allows the quantification of genome-packed AAV preparations in under half an hour, requiring only micro-liter quantities of typical AAV preparations with ∼1013 viral capsids per milliliter. The method quickly assesses the integrity and amount of genome packed AAV particles to support AAV bioprocessing and characterization of this rapidly emerging class of advanced drug therapies.

Self-attenuating adenovirus enables production of recombinant adeno-associated virus for high manufacturing yield without contamination

Recombinant adeno-associated virus (rAAV) shows great promise for gene therapy, however scalability, yield and quality remain significant issues. Here we describe an rAAV manufacturing strategy using a 'helper' adenovirus that self-inhibits its major late promoter (MLP) to truncate its own replication. Inserting a tetracycline repressor (TetR) binding site into the MLP and encoding the TetR under its transcriptional control allowed normal adenovirus replication in the presence of doxycycline but only genome amplification and early gene expression (the 'helper' functions) in its absence. Using this self-inhibiting adenovirus we demonstrate delivery of adenoviral helper functions, AAV rep and cap genes, and the rAAV genome to yield up to 30-fold more rAAV vectors compared to the helper-free plasmid approach and significant improvements in particle infectivity for a range of serotypes. This system allows significant improvements in the production of serotypes rAAV2, rAAV6, rAAV8 and rAAV9, and enables propagation of existing rAAV without transfection, a process that improves batch quality by depleting reverse packaged DNA contaminants. We propose this as a high-yielding, contaminant-free system suitable for scalable rAAV manufacture.

Comparison of analytical techniques to quantitate the capsid content of adeno-associated viral vectors

Adeno-associated virus (AAV) vectors, which contain a DNA transgene packaged into a protein capsid, have shown tremendous therapeutic potential in recent years. An inherent characteristic of the manufacturing process is production of empty capsids that lack the transgene and are therefore unable to provide the intended therapeutic benefit. The effect of empty capsids on clinical outcomes is not well understood, but there are immunogenicity and efficacy concerns, and these empty capsids are considered a product-related impurity. Therefore, empty capsids should be controlled during the manufacturing process and monitored through analytical testing, but there are limited techniques available that are capable of quantifying capsid content and even fewer that are amenable to validation and implementation as registered release tests in a regulated environment. In addition, there is currently not a widely accepted gold standard technique for quantifying capsid content, and the understanding of how the results compare between different orthogonal technologies is limited. The current study utilizes a comprehensive assessment to evaluate diverse analytical techniques for their ability to quantitate capsid content.

Exploring the design space of AAV transient-transfection in suspension cell lines

The safety and utility of adeno-associated virus (AAV) to modulate target gene expression has been well demonstrated, and AAV vectors are a leading gene therapy platform. However, manufacturing presents challenges in terms of productivity and scalability as compared to incumbent therapeutic modalities. In particular, a pivot from adherent cell- to suspension culture-based AAV manufacturing processes requires enhanced study of the transfection step. For the method proposed herein, a Response Surface Design of Experiments is suggested to explore the role of five transfection factors-cell density at transfection, DNA concentration, ratio of complexing reagent to DNA, and molar ratios of the transfecting plasmids-influencing viral genome titer and biological potency. Additionally, an AAV categorical factor matrix is presented for developing a workflow to interrogate the impact of AAV permutations for different capsid serotypes, harbored genes of interest, and inverted terminal repeat configurations on transfection process parameters.

Mechanistic model for production of recombinant adeno-associated virus via triple transfection of HEK293 cells

Manufacturing of recombinant adeno-associated virus (rAAV) viral vectors remains challenging, with low yields and low full:empty capsid ratios in the harvest. To elucidate the dynamics of recombinant viral production, we develop a mechanistic model for the synthesis of rAAV viral vectors by triple plasmid transfection based on the underlying biological processes derived from wild-type AAV. The model covers major steps starting from exogenous DNA delivery to the reaction cascade that forms viral proteins and DNA, which subsequently result in filled capsids, and the complex functions of the Rep protein as a regulator of the packaging plasmid gene expression and a catalyst for viral DNA packaging. We estimate kinetic parameters using dynamic data from literature and in-house triple transient transfection experiments. Model predictions of productivity changes as a result of the varied input plasmid ratio are benchmarked against transfection data from the literature. Sensitivity analysis suggests that (1) the poorly coordinated timeline of capsid synthesis and viral DNA replication results in a low ratio of full virions in harvest, and (2) repressive function of the Rep protein could be impeding capsid production at a later phase. The analyses from the mathematical model provide testable hypotheses for evaluation and reveal potential process bottlenecks that can be investigated.

Production of Recombinant Transmembrane Proteins from Mammalian Cells for Biochemical and Structural Analyses

Eukaryotic integral membrane proteins are key components of various biological processes. Because they are implicated in multiple diseases, it is important to understand their mechanism of action by elucidating their structure and function. Complex technical challenges associated with the generation of recombinant membrane proteins severely impair our ability to understand them using structural and biochemical methods. Here, we provide a detailed procedure to address and mitigate difficulties involved in the large-scale heterologous overexpression and purification of eukaryotic membrane proteins using HEK293S GnTi^- cells transduced with baculovirus. Two human proteins, hDHHC15 and hPORCN, are presented as examples, with step-by-step instructions for transient transfection and generation of baculoviruses, followed by overexpression and purification from HEK293S GnTi^- cells. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Small-scale protein expression in mammalian HEK293T cells Basic Protocol 2: Generation of baculovirus from Sf9 (insect) cells Alternate Protocol: Enumeration-free method for generating P₂ viral stock Support Protocol 1: Small-scale transduction of HEK293T cells with P₂ baculovirus Basic Protocol 3: Large-scale viral transduction of HEK293S GnTi^- cells Support Protocol 2: Large-scale membrane preparation from HEK293S GnTi^- cells Basic Protocol 4: Large-scale purification of membrane proteins from HEK293S GnTi^- cells.

Cellular pathways of recombinant adeno-associated virus production for gene therapy

Recombinant adeno-associated viruses (rAAVs) are among the most important vectors for in vivo gene therapies. With the rapid development of gene therapy, current rAAV manufacturing capacity faces a challenge to meet the emerging demand for these therapies in the future. To examine the bottlenecks in rAAV production during cell culture, we focus here on an analysis of cellular pathways of rAAV production, based on an overview of assembly mechanisms first in the wild-type (wt) AAV replication and then in the common methods of rAAV production. The differences analyzed between the wild-type and recombinant systems provide insights into the mechanistic differences that may correlate with viral productivity. Based on these analyses, we identify potential barriers to high productivity of rAAV and discuss future directions for improvement to meet the emerging needs set by the growth of rAAV-based therapy and the needs of patients.

Overexpression of LVRN impedes the invasion of trophoblasts by inhibiting epithelial-mesenchymal transition

Laeverin (LVRN) was first detected on the outer layer of the chorion laeve and migrating extravillous trophoblasts (EVTs). It is an enzyme that plays an important role in the placentation and pathophysiology of preeclampsia (PE). Previous studies have indicated that LVRN may be required for the invasion of human trophoblast cells. Paradoxically, LVRN was found to be highly expressed in the trophoblasts of PE patients with impaired invasive capacities. In this study, we detected the expression of LVRN in the placentas of PE patients (n=5) and normal term pregnancy women (n=5) as a control group by immunohistochemistry. LVRN was elevated in decidua (P=0.0083) and villi (P=0.0079) of PE patients. Next, LVRN was overexpressed via adeno-associated virus-mediated gene transfer in trophoblastic cell lines HTR8, Swan71, and JAR. Matrigel transwell assay and wound healing assay showed that overexpression of LVRN impeded the invasion of these three cell lines. Western blot analysis showed that LVRN overexpression caused downregulation of N-cadherin and vimentin and upregulation of E-cadherin, suggesting the inhibitory role of LVRN in epithelial-mesenchymal transition (EMT). Moreover, our data indicated that long noncoding RNA NONSTAT103348 (lnc10-7) was elevated in PE patients. Silencing lnc10-7 led to decreased LVRN expression. Taken together, although the basal level of LVRN may be crucial for cell invasion, overexpression of LVRN may abrogate the cell invasiveness, suggesting a multifaceted role of LVRN in the pathogenesis of PE.

Breaking the sound barrier: Towards next-generation AAV vectors for gene therapy of hearing disorders

Owing to the advances in transgenic animal technology and the advent of the next-generation sequencing era, over 120 genes causing hereditary hearing loss have been identified by now. In parallel, the field of human gene therapy continues to make exciting and rapid progress, culminating in the recent approval of several ex vivo and in vivo applications. Despite these encouraging developments and the growing interest in causative treatments for hearing disorders, gene therapeutic interventions in the inner ear remain in their infancy and await clinical translation. This review focuses on the adeno-associated virus (AAV), which nowadays represents one of the safest and most promising vectors in gene therapy. We first provide an overview of AAV biology and outline the principles of therapeutic gene transfer with recombinant AAV vectors, before pointing out major challenges and solutions for clinical translation including vector manufacturing and species translatability. Finally, we highlight seminal technologies for engineering and selection of next-generation "designer" AAV capsids, and illustrate their power and potential with recent examples of their application for inner ear gene transfer in animals.

Production, Processing, and Characterization of Synthetic AAV Gene Therapy Vectors

Over the last two decades, gene therapy vectors based on wild-type Adeno-associated viruses (AAV) are safe and efficacious in numerous clinical trials and are translated into three approved gene therapy products. Concomitantly, a large body of preclinical work has illustrated the power and potential of engineered synthetic AAV capsids that often excel in terms of an organ or cell specificity, the efficiency of in vitro or in vivo gene transfer, and/or reactivity with anti-AAV immune responses. In turn, this has created a demand for new, scalable, easy-to-implement, and plug-and-play platform processes that are compatible with the rapidly increasing range of AAV capsid variants. Here, the focus is on recent advances in methodologies for downstream processing and characterization of natural or synthetic AAV vectors, comprising different chromatography techniques and thermostability measurements. To illustrate the breadth of this portfolio, two chimeric capsids are used as representative examples that are derived through forward- or backwards-directed molecular evolution, namely, AAV-DJ and Anc80. Collectively, this ever-expanding arsenal of technologies promises to facilitate the development of the next AAV vector generation derived from synthetic capsids and to accelerate their manufacturing, and to thus boost the field of human gene therapy.

Micro-dystrophin AAV Vectors Made by Transient Transfection and Herpesvirus System Are Equally Potent in Treating mdx Mouse Muscle Disease

Vector production scale-up is a major barrier in systemic adeno-associated virus (AAV) gene therapy. Many scalable manufacturing methods have been developed. However, the potency of the vectors generated by these methods has rarely been compared with vectors made by transient transfection (TT), the most commonly used method in preclinical studies. In this study, we blindly compared therapeutic efficacy of an AAV9 micro-dystrophin vector generated by the TT method and scalable herpes simplex virus (HSV) system in a Duchenne muscular dystrophy mouse model. AAV was injected intravenously at 5 × 1014 (high), 5 × 1013 (medium), or 5 × 1012 (low) viral genomes (vg)/kg. Comparable levels of micro-dystrophin expression were observed at each dose in a dose-dependent manner irrespective of the manufacturing method. Vector biodistribution was similar in mice injected with either the TT or the HSV method AAV. Evaluation of muscle degeneration/regeneration showed equivalent protection by vectors made by either method in a dose-dependent manner. Muscle function was similarly improved in a dose-dependent manner irrespective of the vector production method. No apparent toxicity was observed in any mouse. Collectively, our results suggest that the biological potency of the AAV micro-dystrophin vector made by the scalable HSV method is comparable to that made by the TT method.

AAV-Mediated Combination Gene Therapy for Neuropathic Pain: GAD65, GDNF, and IL-10

Neuropathic pain is a chronic pain state characterized by nerve damage, inflammation, and nociceptive neuron hyperactivity. As the underlying pathophysiology is complex, a more effective therapy for neuropathic pain would be one that targets multiple elements. Here, we generated recombinant adeno-associated viruses (AAVs) encoding three therapeutic genes, namely, glutamate decarboxylase 65, glial cell-derived neurotrophic factor, and interleukin-10, with various combinations. The efficacy for pain relief was evaluated in a rat spared nerve injury model of neuropathic pain. The maximal analgesic effect was achieved when the AAVs expressing all three genes were administered to rats with neuropathic pain. The combination of two virus constructs expressing the three genes was named KLS-2031 and evaluated as a potential novel therapeutic for neuropathic pain. Single transforaminal epidural injections of KLS-2031 into the intervertebral foramen to target the appropriate dorsal root ganglion produced notable long-term analgesic effects in female and male rats. Furthermore, KLS-2031 mitigated the neuroinflammation, neuronal cell death, and dorsal root ganglion hyperexcitability induced by the spared nerve injury. These results suggest that KLS-2031 represents a promising therapeutic option for refractory neuropathic pain.

Identification of Key Coagulation Activity Determining Elements in Canine Factor VIII

It is well known that canine factor VIII (cFVIII) has a higher specific activity than does human FVIII (hFVIII), and it has been previously demonstrated that cFVIII light chain is able to enhance hFVIII activity. The goal of this study was to first determine which amino acids in cFVIII light chain were responsible for enhancing hFVIII activity, and second to use these amino acids to develop a hFVIII variant with enhanced functional activity. We systemically screened segments of cFVIII light chain by testing an array of human-canine light chain hybrids and found that canine amino acids 1857-2147 were key to this enhancement. Each canine amino acid within this span was screened individually using a negative selection method, which led to the identification of 12 aa (JF12) in the FVIII light chain that could enhance activity. Substitution of the corresponding 12 aa into hFVIII (hFVIIIJF12BDD) elevated the specific activity profile in vitro. Furthermore, hFVIIIJF12BDD expressed an in vivo-displayed increased coagulation activity compared to wild-type, while maintaining normal secretion efficiency. In conclusion, we identified the amino acids in cFVIII that are the key determinants for higher specific activity and may be the basis for future development of therapeutic treatments for hemophilia A.

A Simple, Two-Step, Small-Scale Purification of Recombinant Adeno-Associated Viruses

Recombinant adeno-associated viruses (rAAVs) are robust and versatile tools for in vivo gene delivery. Natural and designer capsid variations in rAAVs allow for targeted gene delivery to specific cell types. Low immunogenicity and lack of pathogenesis also add to the popularity of this virus as an innocuous gene delivery vector for gene therapy. rAAVs are routinely used to express recombinases, sensors, detectors, CRISPR-Cas9 components, or to simply overexpress a gene of interest for functional studies. High production demand has given rise to multiple platforms for the production and purification of rAAVs. However, most platforms rely heavily on large amounts of starting material and multiple purification steps to produce highly purified viral particles. Often, researchers require several small-scale purified rAAVs. Here, we describe a simple and efficient technique for purification of recombinant rAAVs from small amounts of starting material in a two-step purification method. In this method, rAAVs are released into the packaging cell medium using high salt concentration, pelleted by ultracentrifugation to remove soluble impurities. Then, the resuspended pellet is purified using a protein spin-concentrator. In this protocol, we modify the conventional rAAV purification methods to eliminate the need for fraction collection and the labor-intensive steps for evaluating the titer and purity of individual fractions. The resulting rAAV preparations are comparable in titer and purity to commercially available samples. This simplified process can be used to generate highly purified rAAV particles on a small scale, thereby saving resources, generating less waste, and reducing a laboratory's environmental footprint.

Development of new self-assembled cationic amino liposomes for efficient gene delivery

A library of 83 structurally diverse cationic amino liposomes is rationally designed and parallelly synthesized for the transfection of plasmid DNA and siRNA. Our designed self-assembled liposomes not only exhibit excellent transfection efficiency in HEK 293T cells and mouse embryonic stem cells, but also show low cytotoxicity.

Carboxylated nanodiamond-mediated CRISPR-Cas9 delivery of human retinoschisis mutation into human iPSCs and mouse retina

Nanodiamonds (NDs) are considered to be relatively safe carbon nanomaterials used for the transmission of DNA, proteins and drugs. The feasibility of utilizing the NDs to deliver CRISPR-Cas9 system for gene editing has not been clearly studied. Therefore, in this study, we aimed to use NDs as the carriers of CRISPR-Cas9 components designed to introduce the mutation in RS1 gene associated with X-linked retinoschisis (XLRS). ND particles with a diameter of 3 nm were functionalized by carboxylation of the surface and covalently conjugated with fluorescent mCherry protein. Two linear DNA constructs were attached to the conjugated mCherry: one encoded Cas9 endonuclease and GFP reporter, another encoded sgRNA and contained insert of HDR template designed to introduce RS1 c.625C>T mutation. Such nanoparticles were successfully delivered and internalized by human iPSCs and mouse retinas, the efficiency of internalization was significantly improved by mixing with BSA. The delivery of ND particles led to introduction of RS1 c.625C>T mutation in both human iPSCs and mouse retinas. Rs1 gene editing in mouse retinas resulted in several pathological features typical for XLRS, such as aberrant photoreceptor structure. To conclude, our ND-based CRISPR-Cas9 delivery system can be utilized as a tool for creating in vitro and in vivo disease models of XLRS. STATEMENT OF SIGNIFICANCE: X-linked retinoschisis (XLRS) is a prevalent hereditary retinal disease, which is caused by mutations in RS1 gene, whose product is important for structural organization of the retina. The recent development of genome editing techniques such as CRISPR-Cas9 significantly improved the prospects for better understanding the pathology and development of treatment for this disease. Firstly, gene editing can allow development of appropriate in vitro and in vivo disease models; secondly, CRISPR-Cas9 can be applied for gene therapy by removing the disease-causative mutation in vivo. The major prerequisite for these approaches is to develop safe and efficient CRISPR-Cas9 delivery system. In this study, we tested specifically modified nanodiamonds for such a delivery system. We were able to introduce Rs1 mutation into the mouse retina and, importantly, observed several XLRS-specific effects.

Production of adeno-associated virus vectors for in vitro and in vivo applications

Delivering and expressing a gene of interest in cells or living animals has become a pivotal technique in biomedical research and gene therapy. Among viral delivery systems, adeno-associated viruses (AAVs) are relatively safe and demonstrate high gene transfer efficiency, low immunogenicity, stable long-term expression, and selective tissue tropism. Combined with modern gene technologies, such as cell-specific promoters, the Cre/lox system, and genome editing, AAVs represent a practical, rapid, and economical alternative to conditional knockout and transgenic mouse models. However, major obstacles remain for widespread AAV utilization, such as impractical purification strategies and low viral quantities. Here, we report an improved protocol to produce serotype-independent purified AAVs economically. Using a helper-free AAV system, we purified AAVs from HEK293T cell lysates and medium by polyethylene glycol precipitation with subsequent aqueous two-phase partitioning. Furthermore, we then implemented an iodixanol gradient purification, which resulted in preparations with purities adequate for in vivo use. Of note, we achieved titers of 10¹⁰-10¹¹ viral genome copies per µl with a typical production volume of up to 1 ml while requiring five times less than the usual number of HEK293T cells used in standard protocols. For proof of concept, we verified in vivo transduction via Western blot, qPCR, luminescence, and immunohistochemistry. AAVs coding for glutaredoxin-1 (Glrx) shRNA successfully inhibited Glrx expression by ~66% in the liver and skeletal muscle. Our study provides an improved protocol for a more economical and efficient purified AAV preparation.

Integration of Fluorescence Detection and Image-Based Automated Counting Increases Speed, Sensitivity, and Robustness of Plaque Assays

Plaque assays are used to measure the infectious titer of viral samples. These assays are multi-day and low-throughput and may be subject to analyst variability from biased or subjective manual plaque counting. Typically, on day 1, cells are adhered to plates overnight. On day 2, cells are infected with virus. After 3 additional days, plaques are fixed, stained with a horseradish peroxidase (HRP)-conjugated antibody and a HRP substrate, and counted by eye. Manual-based visual counting of plaques is time-consuming and laborious and may be subject to variability between analysts. Also, the assay must proceed for several days to allow the plaques to increase to sufficiently large sizes for manual identification. Here, we integrate fluorescent detection and automated plaque counting to increase the sensitivity and speed of the assay. First, we stain plaques with a fluorescent-labeled antibody. Second, we implement a plate-based cell imager to perform non-biased, non-subjective plaque counting. The integration of these two technologies decreases the assay length by 40%, from 5 days to 3 days, because plaque size, plaque signal to noise, and manual visualization are no longer limiting. This optimized plaque assay is sensitive, fast, and robust and expands the throughput and usage of this method for measuring plaque formation.

Evaluation of life cycle defective adenovirus mutants for production of adeno-associated virus vectors

BACKGROUND

Adeno-associated virus-based vectors are efficient and safe drug candidates for different in vivo gene therapy applications. With increasing numbers of clinical studies based on AAV2 vectors that include not only rare, but also common diseases as a therapeutic target, there is an increased demand for the development of improved production technologies.

METHODS

In the present study, we compared two life cycle defective adenovirus mutants as helper viruses for AAV2 vector production. They had deletions either in the gene coding for the preterminal protein (pTP) that is expressed early in the viral life cycle and is essential for genome replication or in the gene coding for the 100K protein, a protein with many functions, one of which is involved in virus assembly. AAV2 vector production efficiencies were evaluated by analyzing genome-containing particles using a real-time polymerase chain reaction and functional units were investigated by transduction assays.

RESULTS

Somewhat contrary to our expectations, the ∆100K mutant virus showed only a moderate efficiency as a helper virus for AAV2 vector production, whereas the replication-deficient ∆pTP mutant supported AAV2 production almost as efficiently as adenovirus wild-type. We also showed that a temperature shift to 32°C together with extended incubation times improved AAV2 vector productivity.

CONCLUSIONS

The present study indicates the advantages of using a ∆pTP mutant adenovirus rather than adenovirus wild-type as a helper virus for AAV2 production and also indicates that temperature shifts to lower temperatures may improve AAV2 vector production rates.

Systemic AAV vectors for widespread and targeted gene delivery in rodents

We recently developed adeno-associated virus (AAV) capsids to facilitate efficient and noninvasive gene transfer to the central and peripheral nervous systems. However, a detailed protocol for generating and systemically delivering novel AAV variants was not previously available. In this protocol, we describe how to produce and intravenously administer AAVs to adult mice to specifically label and/or genetically manipulate cells in the nervous system and organs, including the heart. The procedure comprises three separate stages: AAV production, intravenous delivery, and evaluation of transgene expression. The protocol spans 8 d, excluding the time required to assess gene expression, and can be readily adopted by researchers with basic molecular biology, cell culture, and animal work experience. We provide guidelines for experimental design and choice of the capsid, cargo, and viral dose appropriate for the experimental aims. The procedures outlined here are adaptable to diverse biomedical applications, from anatomical and functional mapping to gene expression, silencing, and editing.

AAV Vectors for Efficient Gene Delivery to Rodent Hearts

Currently, gene therapy is one of the most promising fields in biomedicine, with great therapeutic potential for an array of inherited and acquired diseases. Adeno-associated viral (AAV) vectors have emerged as promising tools to deliver selectively a therapeutic payload to target organs, including the heart. In this chapter, we describe the production and quality control of recombinant AAV (rAAV) vectors of the serotype 9, the most cardiotropic AAV serotype when delivered systemically in rodents. We also describe the systemic administration of rAAV vectors and the local delivery of rAAV vectors by direct intramyocardial injection. Taken together, the methods described in this chapter will allow the reader to deliver efficiently therapeutic genes to the rodent heart, both globally and regionally.

AAV-8 and AAV-9 Vectors Cooperate with Serum Proteins Differently Than AAV-1 and AAV-6

Under intravenous delivery, recombinant adeno-associated vectors (rAAVs) interact with blood-borne components in ways that can critically alter their therapeutic efficiencies. We have previously shown that interaction with human galectin 3 binding protein dramatically reduces rAAV-6 efficacy, whereas binding of mouse C-reactive protein improves rAAV-1 and rAAV-6 transduction effectiveness. Herein we have assessed, through qualitative and quantitative studies, the proteins from mouse and human sera that bind with rAAV-8 and rAAV-9, two vectors that are being considered for clinical trials for patients with neuromuscular disorders. We show that, in contrast to rAAV-1 and rAAV-6, there was a substantial similarity in protein binding patterns between mouse and human sera for these vector serotypes. To establish an in vivo role for the vector binding of these sera proteins, we chose to study platelet factor 4 (PF4), which interacts with both vectors in both mouse and human sera. Experiments using PF4-knockout mice showed that a complete lack of PF4 did not alter skeletal muscle transduction for these vectors, whereas heart transduction was moderately improved. Our results strongly support our position that the impact of serum proteins on the transduction properties of rAAV-8 and rAAV-9, already observed in mouse models, should be similar in human preclinical trials.

Retinal AAV8-RS1 Gene Therapy for X-Linked Retinoschisis: Initial Findings from a Phase I/IIa Trial by Intravitreal Delivery

This study evaluated the safety and tolerability of ocular RS1 adeno-associated virus (AAV8-RS1) gene augmentation therapy to the retina of participants with X-linked retinoschisis (XLRS). XLRS is a monogenic trait affecting only males, caused by mutations in the RS1 gene. Retinoschisin protein is secreted principally in the outer retina, and its absence results in retinal cavities, synaptic dysfunction, reduced visual acuity, and susceptibility to retinal detachment. This phase I/IIa single-center, prospective, open-label, three-dose-escalation clinical trial administered vector to nine participants with pathogenic RS1 mutations. The eye of each participant with worse acuity (≤63 letters; Snellen 20/63) received the AAV8-RS1 gene vector by intravitreal injection. Three participants were assigned to each of three dosage groups: 1e9 vector genomes (vg)/eye, 1e10 vg/eye, and 1e11 vg/eye. The investigational product was generally well tolerated in all but one individual. Ocular events included dose-related inflammation that resolved with topical and oral corticosteroids. Systemic antibodies against AAV8 increased in a dose-related fashion, but no antibodies against RS1 were observed. Retinal cavities closed transiently in one participant. Additional doses and immunosuppressive regimens are being explored to pursue evidence of safety and efficacy (ClinicalTrials.gov: NCT02317887).

Development and testing of AAV-delivered single-chain variable fragments for the treatment of methamphetamine abuse

Methamphetamine (METH) substance abuse disorders have major impact on society, yet no medications have proven successful at preventing METH relapse or cravings. Anti-METH monoclonal antibodies can reduce METH brain concentrations; however, this therapy has limitations, including the need for repeated dosing throughout the course of addiction recovery. An adeno-associated viral (AAV)-delivered DNA sequence for a single-chain variable fragment could offer long-term, continuous expression of anti-METH antibody fragments. For these studies, we injected mice via tail vein with 1 x 10¹² vector genomes of two AAV8 scFv constructs and measured long-term expression of the antibody fragments. Mice expressed each scFv for at least 212 days, achieving micromolar scFv concentrations in serum. In separate experiments 21 days and 50 days after injecting mice with AAV-scFvs mice were challenged with METH in vivo. The circulating scFvs were capable of decreasing brain METH concentrations by up to 60% and sequestering METH in serum for 2 to 3 hrs. These results suggest that AAV-delivered scFv could be a promising therapy to treat methamphetamine abuse.

Adeno-Associated Virus (AAV) as a Vector for Gene Therapy

There has been a resurgence in gene therapy efforts that is partly fueled by the identification and understanding of new gene delivery vectors. Adeno-associated virus (AAV) is a non-enveloped virus that can be engineered to deliver DNA to target cells, and has attracted a significant amount of attention in the field, especially in clinical-stage experimental therapeutic strategies. The ability to generate recombinant AAV particles lacking any viral genes and containing DNA sequences of interest for various therapeutic applications has thus far proven to be one of the safest strategies for gene therapies. This review will provide an overview of some important factors to consider in the use of AAV as a vector for gene therapy.

Large-Scale Transient Transfection of Suspension Mammalian Cells for VLP Production

Large-scale transient transfection of mammalian cell suspension cultures enables the production of biological products in sufficient quantity and under stringent quality attributes to perform accelerated in vitro evaluations and has the potential to support preclinical or even clinical studies. Here we describe the methodology to produce VLPs in a 3L bioreactor, using suspension HEK 293 cells and PEIPro as a transfection reagent. Cells are grown in the bioreactor to 1 × 10⁶ cells/mL and transfected with a plasmid DNA-PEI complex at a ratio of 1:2. Dissolved oxygen and pH are controlled and are online monitored during the production phase and cell growth and viability can be measured off line taking samples from the bioreactor. If the product is labeled with a fluorescent marker, transfection efficiency can be also assessed using flow cytometry analysis. Typically, the production phase lasts between 48 and 96 h until the product is harvested.

Hemophilia gene therapy comes of age

Concurrent with the development of recombinant factor replacement products, the characterization of the F9 and F8 genes over 3 decades ago allowed for the development of recombinant factor products and made the hemophilias a target disease for gene transfer. The progress of hemophilia gene therapy has been announced in 3 American Society of Hematology scientific plenary sessions, including the first "cure" in a large animal model of hemophilia B in 1998, first in human sustained vector-derived factor IX activity in 2011, and our clinical trial results reporting sustained vector-derived factor IX activity well into the mild or normal range in 2016. This progression to clinically meaningful success combined with numerous ongoing recombinant adeno-associated virus (rAAV)-mediated hemophilia gene transfer clinical trials suggest that the goal of gene therapy to alter the paradigm of hemophilia care may soon be realized. Although several novel therapeutics have recently emerged for hemophilia, gene therapy is unique in its potential for a one-time disease-altering, or even curative, treatment. This review will focus on the prior progress and current clinical trial investigation of rAAV-mediated gene transfer for hemophilia A and B.

Hemophilia gene therapy comes of age

Concurrent with the development of recombinant factor replacement products, the characterization of the F9 and F8 genes over 3 decades ago allowed for the development of recombinant factor products and made the hemophilias a target disease for gene transfer. The progress of hemophilia gene therapy has been announced in 3 American Society of Hematology scientific plenary sessions, including the first "cure" in a large animal model of hemophilia B in 1998, first in human sustained vector-derived factor IX activity in 2011, and our clinical trial results reporting sustained vector-derived factor IX activity well into the mild or normal range in 2016. This progression to clinically meaningful success combined with numerous ongoing recombinant adeno-associated virus (rAAV)-mediated hemophilia gene transfer clinical trials suggest that the goal of gene therapy to alter the paradigm of hemophilia care may soon be realized. Although several novel therapeutics have recently emerged for hemophilia, gene therapy is unique in its potential for a one-time disease-altering, or even curative, treatment. This review will focus on the prior progress and current clinical trial investigation of rAAV-mediated gene transfer for hemophilia A and B.

Molecular design for recombinant adeno-associated virus (rAAV) vector production

Recombinant adeno-associated virus (rAAV) vectors are increasingly popular tools for gene therapy applications. Their non-pathogenic status, low inflammatory potential, availability of viral serotypes with different tissue tropisms, and prospective long-lasting gene expression are important attributes that make rAAVs safe and efficient therapeutic options. Over the last three decades, several groups have engineered recombinant AAV-producing platforms, yielding high titers of transducing vector particles. Current specific productivity yields from different platforms range from 10³ to 10⁵ vector genomes (vg) per cell, and there is an ongoing effort to improve vector yields in order to satisfy high product demands required for clinical trials and future commercialization.

Crucial aspects of vector production include the molecular design of the rAAV-producing host cell line along with the design of AAV genes, promoters, and regulatory elements. Appropriately, configuring and balancing the expression of these elements not only contributes toward high productivity, it also improves process robustness and product quality. In this mini-review, the rational design of rAAV-producing expression systems is discussed, with special attention to molecular strategies that contribute to high-yielding, biomanufacturing-amenable rAAV production processes. Details on molecular optimization from four rAAV expression systems are covered: adenovirus, herpesvirus, and baculovirus complementation systems, as well as a recently explored yeast expression system.

Advancements in the design and scalable production of viral gene transfer vectors

The last 10 years have seen a rapid expansion in the use of viral gene transfer vectors, with approved therapies and late stage clinical trials underway for the treatment of genetic disorders, and multiple forms of cancer, as well as prevention of infectious diseases through vaccination. With this increased interest and widespread adoption of viral vectors by clinicians and biopharmaceutical industries, there is an imperative to engineer safer and more efficacious vectors, and develop robust, scalable and cost-effective production platforms for industrialization. This review will focus on major innovations in viral vector design and production systems for three of the most widely used viral vectors: Adenovirus, Adeno-Associated Virus, and Lentivirus.

Efficacy and safety of voretigene neparvovec (AAV2-hRPE65v2) in patients with RPE65-mediated inherited retinal dystrophy: a randomised, controlled, open-label, phase 3 trial

BACKGROUND

Phase 1 studies have shown potential benefit of gene replacement in RPE65-mediated inherited retinal dystrophy. This phase 3 study assessed the efficacy and safety of voretigene neparvovec in participants whose inherited retinal dystrophy would otherwise progress to complete blindness.

METHODS

In this open-label, randomised, controlled phase 3 trial done at two sites in the USA, individuals aged 3 years or older with, in each eye, best corrected visual acuity of 20/60 or worse, or visual field less than 20 degrees in any meridian, or both, with confirmed genetic diagnosis of biallelic RPE65 mutations, sufficient viable retina, and ability to perform standardised multi-luminance mobility testing (MLMT) within the luminance range evaluated, were eligible. Participants were randomly assigned (2:1) to intervention or control using a permuted block design, stratified by age (<10 years and ≥10 years) and baseline mobility testing passing level (pass at ≥125 lux vs <125 lux). Graders assessing primary outcome were masked to treatment group. Intervention was bilateral, subretinal injection of 1·5 × 10¹¹ vector genomes of voretigene neparvovec in 0·3 mL total volume. The primary efficacy endpoint was 1-year change in MLMT performance, measuring functional vision at specified light levels. The intention-to-treat (ITT) and modified ITT populations were included in primary and safety analyses. This trial is registered with ClinicalTrials.gov, number NCT00999609, and enrolment is complete.

FINDINGS

Between Nov 15, 2012, and Nov 21, 2013, 31 individuals were enrolled and randomly assigned to intervention (n=21) or control (n=10). One participant from each group withdrew after consent, before intervention, leaving an mITT population of 20 intervention and nine control participants. At 1 year, mean bilateral MLMT change score was 1·8 (SD 1·1) light levels in the intervention group versus 0·2 (1·0) in the control group (difference of 1·6, 95% CI 0·72-2·41, p=0·0013). 13 (65%) of 20 intervention participants, but no control participants, passed MLMT at the lowest luminance level tested (1 lux), demonstrating maximum possible improvement. No product-related serious adverse events or deleterious immune responses occurred. Two intervention participants, one with a pre-existing complex seizure disorder and another who experienced oral surgery complications, had serious adverse events unrelated to study participation. Most ocular events were mild in severity.

INTERPRETATION

Voretigene neparvovec gene replacement improved functional vision in RPE65-mediated inherited retinal dystrophy previously medically untreatable.

FUNDING

Spark Therapeutics.