Current issues in adeno-associated viral vector production

Beyond single targets: leveraging degeneracy in sodium channels for osteoarthritis analgesia

Commentary on: Shin SM, Itson-Zoske B, Xu H, Xiang H, Fan F, Hogan QH, Yu H. Sensory neuron-specific block of multifaceted sodium channels mitigates neuropathic pain behaviors of osteoarthritis. Pain Rep 2025. DOI: 10.1097/PR9.0000000000001288.

MR-Guidance of Gene Therapy for Brain Diseases: Moving From Palliative Treatment to Cures

Regulatory bodies in the U.S. and Europe recently approved a gene therapy for aromatic L-amino acid decarboxylase (AADC) deficiency, a rare neurologic disorder where a genetic mutation prevents dopamine production in the brain. Affected children fail to develop normal motor and cognitive functions. MRI-guided intraparenchymal delivery of AADC gene therapy to localized gray matter regions-specifically the substantia nigra and ventral tegmental area-has enabled the brain to produce dopamine, resulting in dramatic improvements in physical and cognitive outcomes. The need to target only a small brain region simplifies the surgical approach. However, gene therapy for broader neurodegenerative conditions has progressed more slowly than expected, despite significant global investment. Clinical efficacy depends heavily on the accurate delivery of gene therapeutics via direct brain infusion, cerebrospinal fluid (CSF) administration, or both. Inadequate image guidance during clinical trials makes it difficult to distinguish between true drug inefficacy and delivery failure. We highlight how increasing use of MRI for pre-surgical simulation and real-time therapy monitoring is accelerating gene therapy development for neurological diseases. This manuscript explores MRI's role in guiding intraparenchymal gene delivery, particularly using Convection Enhanced Delivery (CED). MRI contributes across the treatment timeline-from pre-surgical planning and infusion guidance to validating therapeutic coverage. We describe how MRI supports controlled therapeutic distribution for localized treatments and its potential to enable broader distributions needed for correcting widespread genetic anomalies. We also detail how structural and anatomical MRI sequences (T1, T2, Time of Flight, and Diffusion Tensor Imaging (DTI)) can help model likely infusion distributions. Finally, we provide an outlook on how advanced DTI-based algorithms and poroelastic theory could further improve modeling of infusion dynamics. Current MRI-based technologies can be integrated and enhanced to improve CED effectiveness, especially in very young pediatric patients. EVIDENCE LEVEL: 1. TECHNICAL EFFICACY: Stage 4.

Evaluation of Purification Methods for Minimizing Transgene Expression Background During Viral Manufacturing

Gene therapy has emerged as a promising therapeutic avenue, offering targeted treatments for various diseases. Purification of viral vectors presents a pivotal challenge, demanding the removal of impurities while preserving integrity and potency. During manufacturing, producer cells in transfection systems can be transiently transfected or retro-infected by the viral vectors they have just produced-a process referred to as "retro-transduction"-leading them to express the transgenes of interest. This can be a significant source of contamination in the viral solution pool, particularly when the transgenes encode extracellular, secreted proteins, resulting in cytotoxicity and reduced viral potency. Herein, we aimed to evaluate the efficiency of different viral purification systems commonly used in academic and industry settings in removing the transgene background from viral solutions. The efficiency of each system was assessed based on the levels of the secreted transgene Gaussia Luciferase (GLuc), which can be quickly detected in a solution and served as a readout for transgene background contamination in the viral pool during downstream processing. Through a systematic evaluation of purification methods, we identified the most effective approaches for producing pure viral batches with minimal transgene background, all while preserving viral potency and functionality. Our study revealed superior performance of batches that underwent purification via tangential flow filtration, which yielded over 90% reduction in GLuc background and the highest transduction efficiency rates. This work provides significant insights for advancing gene therapy applications that rely on the production of viral vectors encoding secreted transgenes.

Human umbilical cord mesenchymal stem cell-based gene therapy for hemophilia B using scAAV-DJ/8-LP1-hFIXco transduction

BACKGROUND

Hemophilia B is an X-linked bleeding disorder caused by a mutation in the gene responsible for encoding coagulation factor IX (FIX). Gene therapy offers promising potential for curing this disease. However, the current method of relatively high dosage of virus injection carries inherent risks. The purpose of this study was to introduce a novel scAAV-DJ/8-LP1-hFIXco vector transduced human umbilical cord blood derived mesenchymal stem cells (HUCMSCs) as an alternative cell-based gene therapy to conventional gene therapy for Hemophilia B.

METHODS

The LP1-hFIXco gene structure was designed by us through searching the literature from NCBI and the scAAV-DJ/8-LP1-hFIXco vector was constructed by a commercial company. The HUCMSCs were cultivated in routine approach and transduced with scAAV-DJ/8-LP1-hFIXco vector. The human FIX activation system was employed for detection of hFIXco activity. The RNA and protein expression levels of the hFIXco were evaluated using PCR and western blot techniques. In animal studies, both NSG and F9-KO mice were used for the experiment, in which clotting time was utilized as a parameter for bleeding assessment. The immunohistochemical analysis was used to assess the distribution of HUCMSCs in mouse tissue sections. The safety for tumorigenicity of this cell-based gene therapy was evaluated by pathological observation after hematoxylin-eosin staining.

RESULTS

The transduction of HUCMSCs with the scAAV-DJ/8-LP1-hFIXco vector results in consistent and sustainable secretion of human FIXco during 5 months period both in vitro and in mouse model. The secretion level (hFIXco activity: 97.1 ± 2.3% at day 7 to 48.8 ± 4.5% at 5 months) was comparable to that observed following intravenous injection with a high dose of the viral vector (hFIXco activity: 95.2 ± 2.2% to 40.8 ± 4.3%). After a 5-month observation period, no clonal expansions of the transduced cells in tissues were observed in any of the mice studied.

CONCLUSIONS

We have discovered a novel and safer HUCMSCs mediated approach potentially effective for gene therapy in hemophilia B.

Gene therapy for Lafora disease in the Epm2a-/- mouse model

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy typically occurring early in adolescence. The disease results from mutations in the EPM2A gene, encoding laforin, or the EPM2B gene, encoding malin. Laforin and malin work together in a complex to control glycogen synthesis and prevent the toxicity produced by misfolded proteins via the ubiquitin-proteasome system. Disruptions in either protein cause alterations in this complex, leading to the formation of Lafora bodies containing abnormal, insoluble, and hyperphosphorylated forms of glycogen. We used the Epm2a-/- knockout mouse model of Lafora disease to apply gene therapy by administering intracerebroventricular injections of a recombinant adeno-associated virus carrying the human EPM2A gene. We evaluated the effects of this treatment through neuropathological studies, behavioral tests, video-electroencephalography, electrophysiological recordings, and proteomic/phosphoproteomic analysis. Gene therapy ameliorated neurological and histopathological alterations, reduced epileptic activity and neuronal hyperexcitability, and decreased the formation of Lafora bodies. Moreover, differential quantitative proteomics and phosphoproteomics revealed beneficial changes in various molecular pathways altered in Lafora disease. Our results represent proof of principle for gene therapy with the coding region of the human EPM2A gene as a treatment for EPM2A-related Lafora disease.

Enhancement of the viability of T cells electroporated with DNA via osmotic dampening of the DNA-sensing cGAS-STING pathway

Viral delivery of DNA for the targeted reprogramming of human T cells can lead to random genomic integration, and electroporation is inefficient and can be toxic. Here we show that electroporation-induced toxicity in primary human T cells is mediated by the cytosolic pathway cGAS-STING (cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) synthase-stimulator of interferon genes). We also show that an isotonic buffer, identified by screening electroporation conditions, that reduces cGAS-STING surveillance allowed for the production of chimaeric antigen receptor (CAR) T cells with up to 20-fold higher CAR T cell numbers than standard electroporation and with higher antitumour activity in vivo than lentivirally generated CAR T cells. The osmotic pressure of the electroporation buffer dampened cGAS-DNA interactions, affecting the production of the STING activator 2'3'-cGAMP. The buffer also led to superior efficiencies in the transfection of therapeutically relevant primary T cells and human haematopoietic stem cells. Our findings may facilitate the optimization of electroporation-mediated DNA delivery for the production of genome-engineered T cells.

Enhancing the production of recombinant adeno-associated virus in synthetic cell lines through systematic characterization

Recombinant adeno-associated virus (rAAV) is among the most commonly used in vivo gene delivery vehicles and has seen a number of successes in clinical application. Current manufacturing processes of rAAV employ multiple plasmid transfection or rely on virus infection and face challenges in scale-up. A synthetic biology approach was taken to generate stable cell lines with integrated genetic modules, which produced rAAV upon induction albeit at a low productivity. To identify potential factors that restrained the productivity, we systematically characterized virus production kinetics through targeted quantitative proteomics and various physical assays of viral components. We demonstrated that reducing the excessive expression of gene of interest by its conditional expression greatly increased the productivity of these synthetic cell lines. Further enhancement was gained by optimizing induction profiles and alleviating proteasomal degradation of viral capsid protein by the addition of proteasome inhibitors. Altogether, these enhancements brought the productivity close to traditional multiple plasmid transfection. The rAAV produced had comparable full particle contents as those produced by conventional transient plasmid transfection. The present work exemplified the versatility of our synthetic biology-based viral vector production platform and its potential for plasmid- and virus-free rAAV manufacturing.

Gene therapy for haemophilia A and B, from basic principles to clinical implementation: An illustrated review

INTRODUCTION

With recent approval of the first two gene therapies for haemophilia A and B, educational materials about AAV-based gene therapy are needed by the haemophilia community for a better understanding of this novel therapeutic approach and helping healthcare providers and patients making personalized choices amongst an increasing array of therapeutic options.

AIM

To provide a comprehensive summary of the whole process of AAV-based gene therapy from basic principles to clinical implementation through an illustrated review.

METHODS

The authors, with expertise in and knowledge about gene therapy for haemophilia A and B, reviewed relevant articles from PubMed database and translated them into illustrations.

RESULTS

The review is divided into eight illustrated sections providing an overview of gene therapy for haemophilia A and B from haemophilia basics and current treatment landscape, principles of the AAV-based liver-directed gene therapy, through exploring the efficacy and safety results of published phase III clinical trials, current and future challenges, to implementation in clinical practice, including the hub and spoke models and the patient journey.

CONCLUSION

This illustrated review educates healthcare professionals on AAV-based gene therapy for haemophilia A and B enabling them to further educate their peers and their patients.

Gene replacement therapy for Lafora disease in the Epm2a -/- mouse model

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy typically occurring early in adolescence. Common symptoms include seizures, dementia, and a progressive neurological decline leading to death within 5-15 years from onset. The disease results from mutations transmitted with autosomal recessive inheritance in the EPM2A gene, encoding laforin, a dual-specificity phosphatase, or the EPM2B gene, encoding malin, an E3-ubiquitin ligase. Laforin has glucan phosphatase activity, is an adapter of enzymes involved in glycogen metabolism, is involved in endoplasmic reticulum-stress and protein clearance, and acts as a tumor suppressor protein. Laforin and malin work together in a complex to control glycogen synthesis and prevent the toxicity produced by misfolded proteins via the ubiquitin-proteasome system. Disruptions in either protein can lead to alterations in this complex, leading to the formation of Lafora bodies that contain abnormal, insoluble, and hyperphosphorylated forms of glycogen called polyglucosans. We used the Epm2a -/- knock-out mouse model of Lafora disease to apply a gene replacement therapy by administering intracerebroventricular injections of a recombinant adeno-associated virus carrying the human EPM2A gene. We evaluated the effects of this treatment by means of neuropathological studies, behavioral tests, video-electroencephalography recording, and proteomic/phosphoproteomic analysis. Gene therapy with recombinant adeno-associated virus containing the EPM2A gene ameliorated neurological and histopathological alterations, reduced epileptic activity and neuronal hyperexcitability, and decreased the formation of Lafora bodies. Differential quantitative proteomics and phosphoproteomics revealed beneficial changes in various molecular pathways altered in Lafora disease. Improvements were observed for up to nine months following a single intracerebroventricular injection. In conclusion, gene replacement therapy with human EPM2A gene in the Epm2a -/- knock-out mice shows promise as a potential treatment for Lafora disease.

Development of a novel purification method for AAV vectors using tangential flow filtration

Adeno-associated virus (AAV) vector can efficiently transduce therapeutic genes in various tissue types with less side effects; however, owing to complex multistep processes during manufacture, there have been surges in the pricing of recently approved AAV vector-based gene therapy products. This study aimed to develop a simple and efficient method for high-quality purification of AAV vector via tangential flow filtration (TFF), which is commonly used for concentration and diafiltration of solutions during AAV vector purification. We established a novel purification method using TFF and surfactants. Treatment with two classes of surfactants (anionic and zwitterionic) successfully inhibited the aggregation of residual proteins separated from the AAV vector in the crude product by TFF, obtaining a clearance of 99.5% residual proteins. Infectivity of the AAV vector purified using the new method was confirmed both in vitro and in vivo, and no remarkable inflammation or tissue damage was observed in mouse skeletal muscle after local administration. Overall, our proposed method could be used to establish a platform for the purification of AAV vector.

Peptide ligands for the affinity purification of adeno-associated viruses from HEK 293 cell lysates

Adeno-associated viruses (AAVs) are the vector of choice for delivering gene therapies that can cure inherited and acquired diseases. Clinical research on various AAV serotypes significantly increased in recent years alongside regulatory approvals of AAV-based therapies. The current AAV purification platform hinges on the capture step, for which several affinity resins are commercially available. These adsorbents rely on protein ligands-typically camelid antibodies-that provide high binding capacity and selectivity, but suffer from low biochemical stability and high cost, and impose harsh elution conditions (pH < 3) that can harm the transduction activity of recovered AAVs. Addressing these challenges, this study introduces peptide ligands that selectively capture AAVs and release them under mild conditions (pH = 6.0). The peptide sequences were identified by screening a focused library and modeled in silico against AAV serotypes 2 and 9 (AAV2 and AAV9) to select candidate ligands that target homologous sites at the interface of the VP1-VP2 and VP2-VP3 virion proteins with mild binding strength (KD  ~ 10-5 -10- 6  M). Selected peptides were conjugated to Toyopearl resin and evaluated via binding studies against AAV2 and AAV9, demonstrating the ability to target both serotypes with values of dynamic binding capacity (DBC10%  > 1013 vp/mL of resin) and product yields (~50%-80%) on par with commercial adsorbents. The peptide-based adsorbents were finally utilized to purify AAV2 from a HEK 293 cell lysate, affording high recovery (50%-80%), 80- to 400-fold reduction of host cell proteins (HCPs), and high transduction activity (up to 80%) of the purified viruses.

A novel dual-plasmid platform provides scalable transfection yielding improved productivity and packaging across multiple AAV serotypes and genomes

Transient transfection of mammalian cells using plasmid DNA is a standard method to produce adeno-associated virus (AAV) vectors allowing for flexible and scalable manufacture. Typically, three plasmids are used to encode the necessary components to facilitate vector production; however, a dual-plasmid system, termed pDG, was introduced over 2 decades ago demonstrating two components could be combined resulting in comparable productivity to triple transfection. We have developed a novel dual-plasmid system, pOXB, with an alternative arrangement of sequences that results in significantly increased AAV vector productivity and percentage of full capsids packaged in comparison to the pDG dual design and triple transfection. Here, we demonstrate the reproducibility of these findings across seven recombinant AAV genomes and multiple capsid serotypes as well as the scalability of the pOXB dual-plasmid transfection at 50-L bioreactor scale. Purified drug substance showed a consistent product quality profile in line with triple-transfected vectors, except for a substantial improvement in intact genomes packaged using the pOXB dual- transfection system. Furthermore, pOXB dual- and triple-transfection-based vectors performed consistently in vivo. The pOXB dual plasmid represents an innovation in AAV manufacturing resulting in significant process gains while maintaining the flexibility of a transient transfection platform.

Various AAV Serotypes and Their Applications in Gene Therapy: An Overview

Despite scientific discoveries in the field of gene and cell therapy, some diseases still have no effective treatment. Advances in genetic engineering methods have enabled the development of effective gene therapy methods for various diseases based on adeno-associated viruses (AAVs). Today, many AAV-based gene therapy medications are being investigated in preclinical and clinical trials, and new ones are appearing on the market. In this article, we present a review of AAV discovery, properties, different serotypes, and tropism, and a following detailed explanation of their uses in gene therapy for disease of different organs and systems.

Emerging Perspectives on Gene Therapy Delivery for Neurodegenerative and Neuromuscular Disorders

Neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD) and Parkinson's Disease (PD), are a group of heterogeneous diseases that mainly affect central nervous system (CNS) functions. A subset of NDDs exhibit CNS dysfunction and muscle degeneration, as observed in Gangliosidosis 1 (GM1) and late stages of PD. Neuromuscular disorders (NMDs) are a group of diseases in which patients show primary progressive muscle weaknesses, including Duchenne Muscular Dystrophy (DMD), Pompe disease, and Spinal Muscular Atrophy (SMA). NDDs and NMDs typically have a genetic component, which affects the physiological functioning of critical cellular processes, leading to pathogenesis. Currently, there is no cure or efficient treatment for most of these diseases. More than 200 clinical trials have been completed or are currently underway in order to establish safety, tolerability, and efficacy of promising gene therapy approaches. Thus, gene therapy-based therapeutics, including viral or non-viral delivery, are very appealing for the treatment of NDDs and NMDs. In particular, adeno-associated viral vectors (AAV) are an attractive option for gene therapy for NDDs and NMDs. However, limitations have been identified after systemic delivery, including the suboptimal capacity of these therapies to traverse the blood-brain barrier (BBB), degradation of the particles during the delivery, high reactivity of the patient's immune system during the treatment, and the potential need for redosing. To circumvent these limitations, several preclinical and clinical studies have suggested intrathecal (IT) delivery to target the CNS and peripheral organs via cerebrospinal fluid (CSF). CSF administration can vastly improve the delivery of small molecules and drugs to the brain and spinal cord as compared to systemic delivery. Here, we review AAV biology and vector design elements, different therapeutic routes of administration, and highlight CSF delivery as an attractive route of administration. We discuss the different aspects of neuromuscular and neurodegenerative diseases, such as pathogenesis, the landscape of mutations, and the biological processes associated with the disease. We also describe the hallmarks of NDDs and NMDs as well as discuss current therapeutic approaches and clinical progress in viral and non-viral gene therapy and enzyme replacement strategies for those diseases.

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 Different Liquid Chromatography-Based Purification Strategies for Adeno-Associated Virus Vectors

Recombinant adeno-associated virus (rAAV) vectors have evolved as one of the most promising technologies for gene therapy due to their good safety profile, high transduction efficacy, and long-term gene expression in nondividing cells. rAAV-based gene therapy holds great promise for treating genetic disorders like inherited blindness, muscular atrophy, or bleeding disorders. There is a high demand for efficient and scalable production and purification methods for rAAVs. This is particularly true for the downstream purification methods. The current standard methods are based on multiple steps of gradient ultracentrifugation, which allow for the purification and enrichment of full rAAV particles, but the scale up of this method is challenging. Here, we explored fast, scalable, and universal liquid chromatography-based strategies for the purification of rAAVs. In contrast to the hydrophobic interaction chromatography (HIC), where a substantial amount of AAV was lost, the cation exchange chromatography (CEX) was performed robustly for multiple tested serotypes and resulted in a mixture of full and empty rAAVs with a good purity profile. For the used affinity chromatography (AC), a serotype dependence was observed. Anion exchange chromatography (AEX) worked well for the AAV8 serotype and achieved high levels of purification and a baseline separation of full and empty rAAVs. Depending on the AAV serotype, a combination of CEX and AEX or AC and AEX is recommended and holds promise for future translational projects that require highly pure and full particle-enriched rAAVs.

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.

Robust Approaches for the Production of Active Ingredient and Drug Product for Human Phage Therapy

To be successful, academic and commercial efforts to reintroduce phage therapy must ensure that only safe and efficacious products are used to treat patients. This raises a number of manufacturing, formulation, and delivery challenges. Since phages are biologics, robust manufacturing processes will be crucial to avoid unwanted variability in each step of the process. The quality standards themselves need to be developed, as patients are currently being treated with phages produced under quality standards ranging from cGMP for clinical trials in EMA and FDA regulated environments to no standards at all in some last resort treatments. In this short review, we will systematically review the literature covering technical issues and approaches to increase robustness at every step of the production process: the identity of the phage and bacterial production strains, the fermentation process and purification, the formulation of the drug product, the quality controls and the documentation standards themselves. We conclude that it is possible to control cost at the same time, which is critical to re-introduce phage therapy to western medicine.

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.

Scalable Production of AAV Vectors in Orbitally Shaken HEK293 Cells

Adeno-associated virus (AAV) vectors are currently among the most commonly applied for in vivo gene therapy approaches. The evaluation of vectors during clinical development requires the production of considerable amounts of highly pure and potent vectors. Here, we set up a scalable process for AAV production, using orbitally shaken bioreactors and a fully characterized suspension-adapted cell line, HEKExpress. We conducted a proof-of-concept production of AAV2/8 and AAV2/9 vectors using HEKExpress cells. Furthermore, we compared the production of AAV2/9 vectors using this suspension cell line to classical protocols based on adherent HEK293 cells to demonstrate bioequivalence in vitro and in vivo. Following upstream processing, we purified vectors via gradient centrifugation and immunoaffinity chromatography. The in vitro characterization revealed differences due to the purification method, as well as the transfection protocol and the corresponding HEK293 cell line. The purification method and cell line used also affected in vivo transduction efficiency after bilateral injection of AAV2/9 vectors expressing a GFP reporter fused with a nuclear localization signal (AAV2/9-CBA-nlsGFP) into the striatum of adult mice. These results show that AAV vectors deriving from suspension HEKExpress cells are bioequivalent and may exhibit higher potency than vectors produced with adherent HEK293 cells.

Highly Efficient Ultracentrifugation-free Chromatographic Purification of Recombinant AAV Serotype 9

Recombinant adeno-associated virus serotype 9 (rAAV9) can specifically transduce muscle and neuronal tissues; thus, rAAV9 can potentially be used in gene therapy. However, rAAV9 is the most challenging rAAV serotype to purify. Traditionally, rAAV9 has been purified by ultracentrifugation, which is not scalable. We recently described a chromatographic purification protocol for rAAV1; this protocol can achieve scalable purifications. In this study, we attempted to optimize this protocol for purifying rAAV9 preparations, and we developed a novel, effective method for high-yield purification of rAAV9 using quaternary ammonium anion exchangers and size-exclusion chromatography. The final purified rAAV9 contained mainly three capsid proteins, as observed by SDS-PAGE. Furthermore, negative-stain electron microscopy demonstrated that 96.1% ± 1.1% of rAAV9 particles carried the viral genome containing the EGFP transgene, indicating that impurities and empty capsids can be eliminated with our purification protocol. The final rAAV9 titer obtained by our protocol totaled 2.5 ± 0.4 × 10¹⁵ viral genomes produced from ∼3.2 × 10⁹ HEK293EB cells. We confirmed that our protocol can also be applied to purify other varied AAV genome constructs. Our protocol can scale up production of pure rAAV9, in compliance with current good manufacturing practice, for clinical applications in human gene therapy.

Engineered mRNA-expressed antibodies prevent respiratory syncytial virus infection

The lung is a critical prophylaxis target for clinically important infectious agents, including human respiratory syncytial virus (RSV) and influenza. Here, we develop a modular, synthetic mRNA-based approach to express neutralizing antibodies directly in the lung via aerosol, to prevent RSV infections. First, we express palivizumab, which reduces RSV F copies by 90.8%. Second, we express engineered, membrane-anchored palivizumab, which prevents detectable infection in transfected cells, reducing in vitro titer and in vivo RSV F copies by 99.7% and 89.6%, respectively. Finally, we express an anchored or secreted high-affinity, anti-RSV F, camelid antibody (RSV aVHH and sVHH). We demonstrate that RSV aVHH, but not RSV sVHH, significantly inhibits RSV 7 days post transfection, and we show that RSV aVHH is present in the lung for at least 28 days. Overall, our data suggests that expressing membrane-anchored broadly neutralizing antibodies in the lungs could potentially be a promising pulmonary prophylaxis approach.

Engineered neutralizing antibodies are potential therapeutics for numerous viruses, such as respiratory syncytial virus (RSV). Here, the authors develop an mRNA-based approach to express membrane-anchored neutralizing antibodies in the lung and demonstrate that it inhibits RSV infections in mice.

Extension of the crRNA enhances Cpf1 gene editing in vitro and in vivo

Engineering of the Cpf1 crRNA has the potential to enhance its gene editing efficiency and non-viral delivery to cells. Here, we demonstrate that extending the length of its crRNA at the 5' end can enhance the gene editing efficiency of Cpf1 both in cells and in vivo. Extending the 5' end of the crRNA enhances the gene editing efficiency of the Cpf1 RNP to induce non-homologous end-joining and homology-directed repair using electroporation in cells. Additionally, chemical modifications on the extended 5' end of the crRNA result in enhanced serum stability. Also, extending the 5' end of the crRNA by 59 nucleotides increases the delivery efficiency of Cpf1 RNP in cells and in vivo cationic delivery vehicles including polymer nanoparticle. Thus, 5' extension and chemical modification of the Cpf1 crRNA is an effective method for enhancing the gene editing efficiency of Cpf1 and its delivery in vivo.

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.

Bone mesenchymal stem cells co-expressing VEGF and BMP-6 genes to combat avascular necrosis of the femoral head

The aim of the present study was to investigate the potential of bone mesenchymal stem cells (BMSCs) treated with a combination of vascular endothelial growth factor (VEGF) and bone morphogenetic protein-6 (BMP-6) genes for the treatment of avascular necrosis of the femoral head (ANFH). Rat BMSCs were isolated and purified using a density gradient centrifugation method. The purity and characteristics of the BMSCs were detected by cell surface antigens identification using flow cytometry. The experimental groups were administered with one of the following adeno-associated virus (AAV) vector constructs: AAV-green fluorescent protein (AAV-GFP), AAV-BMP-6, AAV-VEGF or AAV-VEGF-BMP-6. The expression of VEGF and BMP-6 was detected by reverse transcription-quantitative polymerase chain reaction, western blotting and ELISA assays. The effects of VEGF and BMP-6 on BMSCs were evaluated by angiogenic and osteogenic assays. The transfected BMSCs were combined with a biomimetic synthetic scaffold poly lactide-co-glycolide (PLAGA) and they were then subcutaneously implanted into nude mice. After four weeks, the implants were analyzed with histology and subsequent immunostaining to evaluate the effects of BMSCs on blood vessel and bone formation in vivo. In the AAV-VEGF-BMP-6 group, the expression levels of VEGF and BMP-6 were significantly increased and human umbilical vein endothelial cells tube formation was significantly enhanced compared with other groups. Capillaries and bone formation in the AAV-VEGF-BMP-6 group was significantly higher compared with the other groups. The results of the present study suggest that BMSCs expressing both VEGF and BMP-6 induce an increase in blood vessels and bone formation, which provides theoretical support for ANFH gene therapy.

Preparation and implementation of optofluidic neural probes for in vivo wireless pharmacology and optogenetics

This Protocol Extension describes the fabrication and technical procedures for implementing ultrathin, flexible optofluidic neural probe systems that provide targeted, wireless delivery of fluids and light into the brains of awake, freely behaving animals. As a Protocol Extension article, this article describes an adaptation of an existing Protocol that offers additional applications. This protocol serves as an extension of an existing Nature Protocol describing optoelectronic devices for studying intact neural systems. Here, we describe additional features of fabricating self-contained platforms that involve flexible microfluidic probes, pumping systems, microscale inorganic LEDs, wireless-control electronics, and power supplies. These small, flexible probes minimize tissue damage and inflammation, making long-term implantation possible. The capabilities include wireless pharmacological and optical intervention for dissecting neural circuitry during behavior. The fabrication can be completed in 1-2 weeks, and the devices can be used for 1-2 weeks of in vivo rodent experiments. To successfully carry out the protocol, researchers should have basic skill sets in photolithography and soft lithography, as well as experience with stereotaxic surgery and behavioral neuroscience practices. These fabrication processes and implementation protocols will increase access to wireless optofluidic neural probes for advanced in vivo pharmacology and optogenetics in freely moving rodents.This protocol is an extension to: Nat. Protoc. 8, 2413-2428 (2013); doi:10.1038/nprot.2013.158; published online 07 November 2013.

Manufacturing of recombinant adeno-associated viral vectors for clinical trials

The ability to elicit robust and long-term transgene expression in vivo together with minimal immunogenicity and little to no toxicity are only a few features that make recombinant adeno-associated virus (rAAV) vectors ideally suited for many gene therapy applications. Successful preclinical studies have encouraged the use of rAAV for therapeutic gene transfer to patients in the clinical setting. Nevertheless, the use of rAAV in clinical trials has underscored the need for production and purification systems capable of generating large amounts of highly pure rAAV particles. To date, generating vector quantities sufficient to meet the expanding clinical demand is still a hurdle when using current production systems. In this chapter, we will provide a description of the current methods to produce clinical grade of rAAV under current good manufacturing practice (cGMP) settings.

Ultracentrifugation-free chromatography-mediated large-scale purification of recombinant adeno-associated virus serotype 1 (rAAV1)

Recombinant adeno-associated virus (rAAV) is an attractive tool for gene transfer and shows potential for use in human gene therapies. The current methods for the production and purification of rAAV from the transfected cell lysate are mainly based on cesium chloride and iodixanol density ultracentrifugation, although those are not scalable. Meanwhile, chromatography-based systems are more scalable. Therefore, in this study, we developed a novel method for the production and purification of rAAV serotype 1 (rAAV1) from serum-free culture supernatant based on ion-exchange and gel-filtration chromatography to obtain highly purified products with an ultracentrifugation-free technique towards Good Manufacturing Practice (GMP) production. The purified rAAV1 displayed three clear and sharp bands (VP1, VP2, and VP3) following sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and more than 90% of rAAV1 particles contained fully packaged viral genomes according to negative-stain electron micrographic analysis. Consequently, the resultant genomic titer of the purified rAAV1 was 3.63 × 10(13) v.g./ml (the total titer was 4.17 × 10(13) v.g.) from the 4 × 10(9) HEK293 cells. This novel chromatography-based method will facilitate scale-up of manufacturing for clinical applications in gene therapy.

Repair effect of coexpression of the hVEGF and hBMP genes via an adeno-associated virus vector in a rabbit model of early steroid-induced avascular necrosis of the femoral head

We investigated the repair effect of coexpression of the human vascular endothelial growth factor (hVEGF) and human bone morphogenetic protein (hBMP) genes via an adeno-associated virus (AAV) vector in a rabbit model of early steroid-induced avascular necrosis of the femoral head (SANFH). The following AAV vectors were constructed: AAV-green fluorescent protein, AAV-VEGF, AAV-BMP, and AAV-VEGF/BMP. The rabbit model was induced using lipopolysaccharide and methylprednisolone. Virus vector was injected into the core decompression region at a dose of 25 μL per side after core decompression operation in each group. hVEGF165 and BMP-7 expressions were determined by Western blotting and immunohistochemical staining, and the femoral head was examined by magnetic resonance image scan, histopathologic staining, ink vessel staining, microcomputed tomography scan, and biomechanical assessment to determine the repair effect. The vector AAV-VEGF/BMP successfully expressed hVEGF165 and BMP-7 at the gene and protein levels at 12 weeks after virus injection. The expression of hVEGF165 promoted metabolism of the necrotic region by inducing vessel formation. The expression of BMP-7 promoted osteogenesis by increasing the mineral density and biomechanical strength of the femoral head. The repair effect of the AAV-VEGF/BMP group was better than those of the AAV-VEGF and AAV-BMP groups in the rabbit early SANFH model. The AAV-VEGF/BMP vector improved the bone repair capacity of the necrotic femoral head by inducing angiogenesis and improving bone quality in the femoral head.

Adeno-associated virus vectors for human gene therapy

Adeno-associated virus (AAV) is a small, non-enveloped virus that contains a single-stranded DNA genome. It was the first gene therapy drug approved in the Western world in November 2012 to treat patients with lipoprotein lipase deficiency. AAV made history and put human gene therapy in the forefront again. More than four decades of research on AAV vector biology and human gene therapy has generated a huge amount of valuable information. Over 100 AAV serotypes and variants have been isolated and at least partially characterized. A number of them have been used for preclinical studies in a variety of animal models. Several AAV vector production platforms, especially the baculovirus-based system have been established for commercial-scale AAV vector production. AAV purification technologies such as density gradient centrifugation, column chromatography, or a combination, have been well developed. More than 117 clinical trials have been conducted with AAV vectors. Although there are still challenges down the road, such as cross-species variation in vector tissue tropism and gene transfer efficiency, pre-existing humoral immunity to AAV capsids and vector dose-dependent toxicity in patients, the gene therapy community is forging ahead with cautious optimism. In this review I will focus on the properties and applications of commonly used AAV serotypes and variants, and the technologies for AAV vector production and purification. I will also discuss the advancement of several promising gene therapy clinical trials.

Production of first generation adenoviral vectors for preclinical protocols: amplification, purification and functional titration

Gene therapy represents a promising approach in the treatment of several diseases. Currently, the ideal vector has yet to be designed; though, adenoviral vectors (Ad-v) have provided the most utilized tool for gene transfer due principally to their simple production, among other specific characteristics. Ad-v viability represents a critical variable that may be affected by storage or shipping conditions and therefore it is advisable to be assessed previously to protocol performance. The present work is unique in this matter, as the complete detailed process to obtain Ad-v of preclinical grade is explained. Amplification in permissive HEK-293 cells, purification in CsCl gradients in a period of 10 h, spectrophotometric titration of viral particles (VP) and titration of infectious units (IU), yielding batches of AdβGal, AdGFP, AdHuPA and AdMMP8, of approximately 10¹³-10¹⁴ VP and 10¹²-10¹³ IU were carried out. In vivo functionality of therapeutic AdHuPA and AdMMP8 was evidenced in rats presenting CCl₄-induced fibrosis, as more than 60% of fibrosis was eliminated in livers after systemic delivery through iliac vein in comparison with irrelevant AdβGal. Time required to accomplish the whole Ad-v production steps, including IU titration was 20 to 30 days. We conclude that production of Ad-v following standard operating procedures assuring vector functionality and the possibility to effectively evaluate experimental gene therapy results, leaving aside the use of high-cost commercial kits or sophisticated instrumentation, can be performed in a conventional laboratory of cell culture.

Production and purification of recombinant adeno-associated vectors

The use of recombinant adeno-associated virus (rAAV) vectors in gene therapy for preclinical studies in animal models and human clinical trials is increasing, as these vectors have been shown to be safe and to mediate persistent transgene expression in vivo. Constant improvement in rAAV manufacturing processes (upstream production and downstream purification) has paralleled this evolution to meet the needs for larger vector batches, higher vector titer, and improved vector quality and safety. This chapter provides an overview of existing production and purification systems used for adeno-associated virus (AAV) vectors, and the advantages and disadvantages of each system are outlined. Regulatory guidelines that apply to the use of these systems for clinical trials are also presented. The methods described are examples of protocols that have been utilized for establishing rAAV packaging cell lines, production of rAAV vectors using recombinant HSV infection, and for chromatographic purification of various AAV vector serotypes. A protocol for the production of clinical-grade rAAV type 2 vectors using transient transfection and centrifugation-based purification is also described.

Adeno-associated virus vectorology, manufacturing, and clinical applications

Adeno-associated virus (AAV) has emerged as an attractive vector for gene therapy. The benefits of using AAV for gene therapy include long-term gene expression, the inability to autonomously replicate without a helper virus, transduction of dividing and nondividing cells, and the lack of pathogenicity from wild-type infections. A number of Phase I and Phase II clinical trials utilizing AAV have been carried out worldwide (Aucoin et al., 2008; Mueller and Flotte, 2008). A number of challenges have been identified based upon data generated from these clinical trials. These challenges include (1) large scale manufacturing technologies in accordance with current Good Manufacturing Practices (cGMP), (2) tissue specific tropism of AAV vectors, (3) high-quality/high potency recombinant AAV vectors (rAAV), and (4) immune response to AAV capsids and transgene. In this chapter, we will provide an overview of AAV biology, AAV vectorology, rAAV manufacturing, and the current status on the latest rAAV clinical trials.

Latest developments in the large-scale production of adeno-associated virus vectors in insect cells toward the treatment of neuromuscular diseases

Adeno-associated viral (AAV) vectors are gene vectors of choice for the development of gene therapy treatments for many rare diseases affecting various tissues including retina, central nervous system, liver, and muscle. The AAV based gene therapy approach became conceivable only after the development of easily scalable production systems including the Sf9 cell/baculovirus expression system. Since the establishment of the production of AAV in the Sf9/baculovirus system by the group of Rob Kotin, this new production system has largely been developed for optimizing the large scale production of different serotypes of AAV for preclinical and clinical purposes. Today this manufacturing system allows for the production of purified vector genome (vg) quantities of up to 2 × 10(15) for AAV1 using a 50L reactor and the scale up to larger reactor volumes is paralleled by a corresponding increase in the vector yield. This review presents the principles and achievements of the Sf9/baculovirus system for the production of AAV in comparison to other expression systems based on mammalian cells. In addition, new developments and improvements, which have not yet been implemented at a large scale, and perspectives for further optimization of this production system will be discussed. All of these achievements as well as further process intensifications are urgently needed for the production of clinical doses for the treatment of neuromuscular diseases for which estimated doses of up to 10(14)vg/kg body mass are required.

Effects of recombinant adeno-associated viral vectors on angiopoiesis and osteogenesis in cultured rabbit bone marrow stem cells via co-expressing hVEGF and hBMP genes: a preliminary study in vitro

OBJECTIVE

VEGF and BMP play important roles in angiogenesis and osteogenesis. Combining these two factors may be a promising therapeutic strategy for avascular necrosis of the femoral head (ANFH).

METHODS

Rabbit bone marrow-derived mesenchymal stem cells (BMSCs) were isolated and purified by density gradient centrifugation combined with attachment culture methods. The purity and characteristics of the BMSCs were detected by cell surface antigen identification. The best MOI of BMSCs transfected with rAAV was detected by fluorescent cell counting, and cell viability was determined by MTT assay. Expression of the genes of interest was detected by GFP gene expression, RT-PCR assay, and ELISA assay. The biological activities of VEGF and BMP were detected by angiogenic and osteogenic assays.

RESULTS

The best MOI of BMSCs transfected with rAAV was 5 x 10(4)v.g./cell. Cell growth curves showed vigorous cell viability. Expressions of the GFP, VEGF165, and BMP(7) genes were detected 1 day post-transfection and peaked 14 days post-transfection. Expression of the genes of interest was sustained over 1 month. VEGF and BMP proteins secreted from BMSCs transfected with rAAV-hVEGF(165)-IRES-hBMP(7) enhanced angiogenesis and osteogenesis in vitro.

CONCLUSION

Recombinant adeno-associated viral vectors co-expressing the hVEGF(165) and hBMP(7) genes showed efficient gene expression ability. The VEGF(165) and BMP(7) proteins expressed from the vector have efficient biological activity in vitro.

Host cells and cell banking

Gene therapy based on the use of viral vectors is entirely dependent on the use of animal cell lines, mainly of mammalian origin, but also of insect origin. As for any biotechnology product for clinical use, viral -vectors have to be produced with cells derived from an extensively characterized cell bank to maintain the appropriate standard for assuring the lowest risk for the patients to be treated. Although many different cell types and lines have been used for the production of viral vectors, HEK293 cells or their derivatives have been extensively used for production of different vector types: adenovirus, oncorectrovirus, lentivirus, and AAV vectors, because of their easy handling and the possibility to grow them adherently in serum-containing medium as well as in suspension in serum-free culture medium. Despite this, these cells are not necessarily the best for the production of a given viral vector, and there are many other cell lines with significant advantages including superior growth and/or production characteristics, which have been tested and also used for the production of clinical vector batches. This chapter presents basic -considerations concerning the characterization of cell banks, in the first part, and, in the second part, practically all cell lines (at least when public information was available) established and developed for the production of the most important viral vectors (adenoviral, oncoretroviral, lentiviral, AAV, baculovirus).

Adeno-associated viruses

Adeno-associated virus (AAV) vectors have evolved over the past decade as a particularly useful gene -vector for in vivo applications. In contrast to oncoretro- and lentiviral vectors, this vector stays essentially episomal after gene transfer, making it safer because of the absence of insertional mutagenesis. AAV's non-pathogenicity is a further advantage. For decades, this vector could only be produced at a small scale for research purposes and, eventually, used at very small doses for clinical studies, because only transfection methods were available, which have limited scalability. However, since the development of scalable production methods, this bottleneck is resolved and, from a technical point of view, large quantities of AAV vectors can be produced, opening the possibility of using AAV vectors for whole body treatments in gene therapy trials. This chapter presents the basic principles of small- and large-scale production procedures as well as detailed procedure of small-scale production, purification, and analytical protocols for AAV vectors. In Chapter 10, the reader will find a large-scale production method based on the use of the insect cell/baculovirus system.

Manufacturing of adeno-associated viruses, for example: AAV2

Adeno-associated virus (AAV) is one of the most promising vectors for gene therapy. There are several ways of producing AAV vectors but large-scale production of this vector remains a major challenge. Virovek developed a novel method of expressing the AAV Rep and Cap genes in insect cells mediated by intron-splicing mechanism and producing AAV vectors with these Rep and Cap sequences containing the artificial intron. The recombinant baculoviruses harboring these artificial intron-containing Rep and Cap sequences are very stable and the AAV vectors produced in insect cells with these recombinant baculoviruses are very infectious.

Methods for Gene Delivery

The success of any gene transfer procedure, either through in vivo inoculation of the genetic material or after gene transfer into the patient’s cells ex vivo, strictly depends upon the efficiency of nucleic acid internalization by the target cells. As a matter of fact, making gene transfer more efficient continues to represent the most relevant challenge to the clinical success of gene therapy.

Angiopoiesis and bone regeneration via co-expression of the hVEGF and hBMP genes from an adeno-associated viral vector in vitro and in vivo

AIM

To investigate the therapeutic potential of adeno-associated virus (AAV)-mediated expression of vascular endothelial growth factor (VEGF) and bone morphogenetic protein (BMP).

METHODS

Four experimental groups were administered the following AAV vector constructs: rAAV-hVEGF(165)-internal ribosome entry site (IRES)-hBMP-7 (AAV-VEGF/BMP), rAAV-hVEGF(165)-GFP (AAV-VEGF), rAAV-hBMP-7-GFP (AAV-BMP), and rAAV-IRES-GFP (AAV-GFP). VEGF(165) and BMP-7 gene expression was detected using RT-PCR. The VEGF(165) and BMP-7 protein expression was determined by Western blotting and ELISA. The rabbit ischemic hind limb model was adopted and rAAV was administered intramuscularly into the ischemic limb.

RESULTS

Rabbit bone marrow-derived mesenchymal stem cells (BMSCs) were cultured and infected with the four viral vectors. The expression of GFP increased from the 7th day of infection and could be detected on the 28th day post-infection. In the AAV-VEGF/BMP group, the levels of VEGF165 and BMP-7 increased with prolonged infection time. The VEGF(165) and BMP-7 secreted from BMSCs in the AAV-VEGF/BMP group enhanced HUVEC tube formation and resulted in a stronger osteogenic ability, respectively. In rabbit ischemic hind limb model, GFP expression increased from the 4th week and could be detected at 8 weeks post-injection. The rAAV vector had superior gene expressing activity. Eight weeks after gene transfer, the mean blood flow was significantly higher in the AAV-VEGF/BMP group. Orthotopic ossification was radiographically evident, and capillary growth and calcium deposits were obvious in this group.

CONCLUSION

AAV-mediated VEGF and BMP gene transfer stimulates angiogenesis and bone regeneration and may be a new therapeutic technique for the treatment of avascular necrosis of the femoral head (ANFH).

Modeling electrostatic interactions of baculovirus vectors for ion-exchange process development

Product-related impurities constitute a major burden in the production of recombinant viral vectors for gene therapy and vaccination; it impairs not only the biological efficacy of the preparation but the process yield/productivity. Recombinant baculovirus was used as an enveloped virus model to address this issue. Given that ion-exchange chromatography is a process of choice for purification of viral vectors, the analysis of the electrostatic behavior can be instrumental for the improvement of impurity removal. The main species, product (infective virus particle) and product-derived impurities (dsDNA-, glycoprotein-, and envelope-deprived baculovirus particles), were isolated and correspondent zeta potentials were analyzed through dynamic light scattering. A model of the virus based on the viral components critical for biological function is proposed. The contribution of these viral components to the overall particle electrostatic interaction energy profile (calculated between the particle and a putative ion-exchange surface) was assessed as a function of ionic strength and pH. This resulted in a deterministic tool capable of distinguishing the electrostatic properties of the infective virus particle from the major virus-related impurities. Within an ion-exchange bind-elute process, this knowledge helps narrow the optimization space in early stage process development for viral vectors by predicting the best selectivity conditions.

Scalable purification of adeno-associated virus serotype 1 (AAV1) and AAV8 vectors, using dual ion-exchange adsorptive membranes

In vivo gene transduction with adeno-associated virus (AAV)-based vectors depends on laborious procedures for the production of high-titer vector stocks. Purification steps for efficient clearance of impurities such as host cell proteins and empty vector particles are required to meet end-product specifications. Therefore, the development of alternative, realistic methods to facilitate a scalable virus recovery procedure is critical to promote in vivo investigations. However, the conventional purification procedure with resin-based packed-bed chromatography suffers from a number of limitations, including variations in pressure, slow pore diffusion, and large bed volumes. Here we have employed disposable high-performance anion- and cation-exchange membrane adsorbers to effectively purify recombinant viruses. As a result of isoelectric focusing analysis, the isoelectric point of empty particles was found to be significantly higher than that of packaged virions. Therefore, AAV vector purification with the membrane adsorbers was successful and allowed higher levels of gene transfer in vivo without remarkable signs of toxicity or inflammation. Electron microscopy of the AAV vector stocks obtained revealed highly purified virions with as few as 0.8% empty particles. Furthermore, the membrane adsorbers enabled recovery of AAV vectors in the transduced culture supernatant. Also, the ion-exchange enrichment of retroviral vectors bearing the amphotropic envelope was successful. This rapid and scalable viral purification protocol using disposable membrane adsorbers is particularly promising for in vivo experimentation and clinical investigations.