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

The state of technological advancement to address challenges in the manufacture of rAAV gene therapies

Current processes for the production of recombinant adeno-associated virus (rAAV) are inadequate to meet the surging demand for rAAV-based gene therapies. This article reviews recent advances that hold the potential to address current limitations in rAAV manufacturing. A multidisciplinary perspective on technological progress in rAAV production is presented, underscoring the necessity to move beyond incremental refinements and adopt a holistic strategy to address existing challenges. Since several recent reviews have thoroughly covered advancements in upstream technology, this article provides only a concise overview of these developments before moving to pivotal areas of rAAV manufacturing not well covered in other reviews, including analytical technologies for rapid and high-throughput measurement of rAAV quality attributes, mathematical modeling for platform and process optimization, and downstream approaches to maximize efficiency and rAAV yield. Novel technologies that have the potential to address the current gaps in rAAV manufacturing are highlighted. Implementation challenges and future research directions are critically discussed.

Therapeutic Application and Structural Features of Adeno-Associated Virus Vector

Adeno-associated virus (AAV) is characterized by non-pathogenicity, long-term infection, and broad tropism and is actively developed as a vector virus for gene therapy products. AAV is classified into more than 100 serotypes based on differences in the amino acid sequence of the capsid protein. Endocytosis involves the uptake of viral particles by AAV and accessory receptors during AAV infection. After entry into the cell, they are transported to the nucleus through the nuclear pore complex. AAVs mainly use proteoglycans as receptors to enter cells, but the types of sugar chains in proteoglycans that have binding ability are different. Therefore, it is necessary to properly evaluate the primary structure of receptor proteins, such as amino acid sequences and post-translational modifications, including glycosylation, and the higher-order structure of proteins, such as the folding of the entire capsid structure and the three-dimensional (3D) structure of functional domains, to ensure the efficacy and safety of biopharmaceuticals. To further enhance safety, it is necessary to further improve the efficiency of gene transfer into target cells, reduce the amount of vector administered, and prevent infection of non-target cells.

Rational downstream development for adeno-associated virus full/empty capsid separation - A streamlined methodology based on high-throughput screening and mechanistic modeling

Recombinant adeno-associated virus (AAV) has emerged as one of the most promising systems for therapeutic gene delivery and has demonstrated clinical success in a wide range of genetic disorders. However, manufacturing of high-quality AAV in large amounts still remains a challenge. A significant difficulty for downstream processing is the need to remove empty capsids that are generated in all currently utilized expression systems and that represent product-related impurities that adversely affect safety and efficacy of AAV vectors. Empty and full capsids exhibit only subtle differences in surface charge and size, making chromatography-based separations highly challenging. Here, we present a rapid methodology for the systematic process development of the crucial AAV full/empty capsid separation on ion-exchange media based on high-throughput screening and mechanistic modeling. Two of the most commonly employed serotypes, AAV8 and AAV9, are used as case studies. First, high-throughput studies in filter-plate format are performed that allow the rapid and comprehensive study of binding and elution behavior of AAV on different resins, using different buffer systems, pH, salt conditions, and solution additives. Small amounts of separated empty and full AAV capsids are generated by iodixanol gradient centrifugation that allow studying the binding and elution behavior of the two vector species separately in miniaturized format. Process conditions that result in maximum differences in elution behavior between empty and full capsids are then transferred to benchtop chromatography systems that are used to generate calibration data for the estimation of steric mass-action isotherm and mass transport parameters for process simulation. The resulting column models are employed for in-silico process development that serves to enhance understanding of separation constraints and to identify optimized conditions for the removal of empty particles. Finally, optimized separation conditions are verified experimentally. The methodology presented in this work provides a systematic framework that affords mechanistic understanding of the crucial empty/full capsid separation and accelerates the development of a scalable AAV downstream process.

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.

The downstream bioprocess toolbox for therapeutic viral vectors

Viral vectors are poised to acquire a prominent position in modern medicine and biotechnology owing to their role as delivery agents for gene therapies, oncolytic agents, vaccine platforms, and a gateway to engineer cell therapies as well as plants and animals for sustainable agriculture. The success of viral vectors will critically depend on the availability of flexible and affordable biomanufacturing strategies that can meet the growing demand by clinics and biotech companies worldwide. In this context, a key role will be played by downstream process technology: while initially adapted from protein purification media, the purification toolbox for viral vectors is currently undergoing a rapid expansion to fit the unique biomolecular characteristics of these products. Innovation efforts are articulated on two fronts, namely (i) the discovery of affinity ligands that target adeno-associated virus, lentivirus, adenovirus, etc.; (ii) the development of adsorbents with innovative morphologies, such as membranes and 3D printed monoliths, that fit the size of viral vectors. Complementing these efforts are the design of novel process layouts that capitalize on novel ligands and adsorbents to ensure high yield and purity of the product while safeguarding its therapeutic efficacy and safety; and a growing panel of analytical methods that monitor the complex array of critical quality attributes of viral vectors and correlate them to the purification strategies. To help explore this complex and evolving environment, this study presents a comprehensive overview of the downstream bioprocess toolbox for viral vectors established in the last decade, and discusses present efforts and future directions contributing to the success of this promising class of biological medicines.

Critical challenges and advances in recombinant adeno-associated virus (rAAV) biomanufacturing

Gene therapy is a promising therapeutic approach for genetic and acquired diseases nowadays. Among DNA delivery vectors, recombinant adeno-associated virus (rAAV) is one of the most effective and safest vectors used in commercial drugs and clinical trials. However, the current yield of rAAV biomanufacturing lags behind the necessary dosages for clinical and commercial use, which embodies a concentrated reflection of low productivity of rAAV from host cells, difficult scalability of the rAAV-producing bioprocess, and high levels of impurities materialized during production. Those issues directly impact the price of gene therapy medicine in the market, limiting most patients' access to gene therapy. In this context, the current practices and several critical challenges associated with rAAV gene therapy bioprocesses are reviewed, followed by a discussion of recent advances in rAAV-mediated gene therapy and other therapeutic biological fields that could improve biomanufacturing if these advances are integrated effectively into the current systems. This review aims to provide the current state-of-the-art technology and perspectives to enhance the productivity of rAAV while reducing impurities during production of rAAV.

Size-selective downstream processing of virus particles and non-enveloped virus-like particles

Non-enveloped virus-like particles (VLPs) are versatile protein nanoparticles with great potential for biopharmaceutical applications. However, conventional protein downstream processing (DSP) and platform processes are often not easily applicable due to the large size of VLPs and virus particles (VPs) in general. The application of size-selective separation techniques offers to exploit the size difference between VPs and common host-cell impurities. Moreover, size-selective separation techniques offer the potential for wide applicability across different VPs. In this work, basic principles and applications of size-selective separation techniques are reviewed to highlight their potential in DSP of VPs. Finally, specific DSP steps for non-enveloped VLPs and their subunits are reviewed as well as the potential applications and benefits of size-selective separation techniques are shown.

Novel anion exchange membrane chromatography method for the separation of empty and full adeno-associated virus

A challenge in the production of recombinant Adeno-Associated Virus (AAV) for gene therapies is the presence of capsids that lack the required gene of interest. The impact of these empty vectors in therapies is not fully understood, however the ability to control the ratio of empty to full particles, which contain the genetic payload, is a necessary step in the purification of these viruses. In this study, a novel anion exchange chromatography elution method for enrichment of full AAV particles is demonstrated. A step gradient with small conductivity increases of around 1 mS cm^-1 provides more efficient separation of empty and full AAV serotype 5 across membrane media as compared to conventional linear gradient method. The use of this approach in optimizing a simpler method for manufacturing processes and scalability to a larger chromatographic volume is explored. With this approach, the authors achieved greater than 4-fold enrichment of full capsids, to give a total of ≈50%-60% full capsids, using a 25 mM Bis-Tris Propane pH 9.0 buffer system with NaCl as the eluting salt. Results suggest that this elution method can be implemented into a scalable process and can provide insight into development of elution methods for other AAV serotypes.

A PCR-amplified transgene fragment flanked by a single copy of a truncated inverted terminal repeat for recombinant adeno-associated virus production prevents unnecessary plasmid DNA packaging

The application of recombinant adeno-associated viruses (rAAVs) for gene therapy faces certain challenges, including genome packaging of non-vector sequences. Inverted terminal repeats (ITRs) flanking the rAAV genome, comprising three inverted repeat regions (A, B, and C) and a non-inverted repeat region (D), contribute to non-vector genome packaging. We aimed to circumvent this issue by comparing the properties of rAAV containing DNA plasmids and PCR-amplified transgenes, including a single copy of the AD sequence (rAAV-pAD/L-AD, respectively), which is a truncated form of ITR, with those of wild-type ITR genome (single-stranded and self-complementary AAV; ssAAV and scAAV). The packaging efficiency of rAAV-pAD/L-AD was found to be comparable to that of scAAV, whereas the transduction efficiency of rAAV-pAD/L-AD was lower than that of ss/scAAV. Remarkably, rAAV-L-AD reduced the plasmid backbone packaging contamination compared to ss/scAAV. Furthermore, to confirm the functionality of this system, we generated a rAAV-L-AD harboring a short hairpin RNA targeting ATP5B (rAAV-L-AD-shATP5B) and found that it caused a significant decrease in ATP5B mRNA levels when transduced into HEK293EB cells, suggesting that it was functional. Thus, our system successfully packaged L-AD into capsids with minimal contamination of plasmid DNA, offering a novel functional packaging platform without causing plasmid backbone encapsidation.

TDP-43 transports ribosomal protein mRNA to regulate axonal local translation in neuronal axons

Mislocalization and abnormal deposition of TDP-43 into the cytoplasm (TDP-43 proteinopathy) is a hallmark in neurons of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). However, the pathogenic mechanism of the diseases linked to TDP-43 is largely unknown. We hypothesized that the failure of mRNA transport to neuronal axons by TDP-43 may contribute to neurodegeneration in ALS and FTLD, and sought to examine the function of TDP-43 by identifying its target mRNA for axonal transport. We found that mRNAs related to translational function including ribosomal proteins (RPs) were decreased by shRNA-based TDP-43 knock-down in neurites of cortical neurons. TDP-43 binds to and transports the RP mRNAs through their 5' untranslated region, which contains a common 5' terminal oligopyrimidine tract motif and a downstream GC-rich region. We showed by employing in vitro and in vivo models that the RP mRNAs were translated and incorporated into native ribosomes locally in axons to maintain functionality of axonal ribosomes, which is required for local protein synthesis in response to stimulation and stress to axons. We also found that RP mRNAs were reduced in the pyramidal tract of sporadic ALS cases harboring TDP-43 pathology. Our results elucidated a novel function of TDP-43 to control transport of RP mRNAs and local translation by ribosomes to maintain morphological integrity of neuronal axons, and proved the influence of this function of TDP-43 on neurodegeneration in ALS and FTLD associated with TDP-43 proteinopathy.

Purification Methods and the Presence of RNA in Virus Particles and Extracellular Vesicles

The fields of extracellular vesicles (EV) and virus infections are marred in a debate on whether a particular mRNA or non-coding RNA (i.e., miRNA) is packaged into a virus particle or copurifying EV and similarly, whether a particular mRNA or non-coding RNA is contained in meaningful numbers within an EV. Key in settling this debate, is whether the purification methods are adequate to separate virus particles, EV and contaminant soluble RNA and RNA:protein complexes. Differential centrifugation/ultracentrifugation and precipitating agents like polyethylene glycol are widely utilized for both EV and virus purifications. EV are known to co-sediment with virions and other particulates, such as defective interfering particles and protein aggregates. Here, we discuss how encased RNAs from a heterogeneous mixture of particles can be distinguished by different purification methods. This is particularly important for subsequent interpretation of whether the RNA associated phenotype is contributed solely by virus or EV particles or a mixture of both. We also discuss the discrepancy of miRNA abundance in EV from different input material.

A Versatile Adeno-Associated Viral Vector Cross-Linking Platform Capable of Tuning Cellular Tropisms and Simultaneously Inducing Solid-Phase Gene Delivery

Developing gene carriers with improved affinities for target cells and the simultaneous diversification of their delivery modes will be pivotal for upgrading gene therapy technologies. In this study, a simple and versatile adeno-associated virus (AAV) conjugation platform using the cross-linker 3,3'-dithiobis(sulfosuccinimidyl propionate) (DTSSP) is proposed. Depending on the quantity of the DTSSP molecules, the AAV-DTSSP complexes could either be linked with the relevant biomolecules for altering cellular tropisms or further form a self-assembled AAV-DTSSP pellet capable of mimicking a polymeric gene delivery system. At lower quantities of DTSSP, the AAV-DTSSP complexes were conjugated with aminated l-fucose molecules, whose levels are typically upregulated in pancreatic cancer cells, resulting in enhanced gene delivery efficiencies in pancreatic cancer cells. At higher concentrations of DTSSP, visible solid forms of the AAV-DTSSP pellets were formed, and the AAV pellets demonstrated the capability to induce a localized, sustained gene expression pattern comparable to that of conventional biomaterial-based approaches. Thus, a multipurpose AAV cross-linking platform, which can enable AAV vector systems that are capable of altering cellular tropisms and simultaneously inducing solid-phase delivery, will provide crucial insights into vector design for further upgrading of gene delivery technologies.

Polysaccharide-based chromatographic adsorbents for virus purification and viral clearance

Viruses still pose a significant threat to human and animal health worldwide. In the fight against viral infections, high-purity viral stocks are needed for manufacture of safer vaccines. It is also a priority to ensure the viral safety of biopharmaceuticals such as blood products. Chromatography techniques are widely implemented at both academic and industrial levels in the purification of viral particles, whole viruses and virus-like particles to remove viral contaminants from biopharmaceutical products. This paper focuses on polysaccharide adsorbents, particulate resins and membrane adsorbers, used in virus purification/removal chromatography processes. Different chromatographic modes are surveyed, with particular attention to ion exchange and affinity/pseudo-affinity adsorbents among which commercially available agarose-based resins (Sepharose®) and cellulose-based membrane adsorbers (Sartobind®) occupy a dominant position. Mainly built on the development of new ligands coupled to conventional agarose/cellulose matrices, the development perspectives of polysaccharide-based chromatography media in this antiviral area are stressed in the conclusive part.

Tyrosine triple mutated AAV2-BDNF gene therapy in an inner retinal injury model induced by intravitreal injection of N-methyl-D-aspartate (NMDA)

Purpose

Glaucoma is a group of chronic optic neuropathies characterized by the degeneration of retinal ganglion cells (RGCs) and their axons, and they ultimately cause blindness. Because neuroprotection using neurotrophic factors against RGC loss has been proven a beneficial strategy, extensive attempts have been made to perform gene transfer of neurotrophic proteins. This study used the inner retinal injury mouse model to evaluate the neuroprotective effect of tyrosine triple mutated and self-complementary adeno-associated virus (AAV) encoding brain-derived neurotrophic factor (BDNF; tm-scAAV2-BDNF).

Methods

C57BL/6J mice were intravitreally injected with 1 μl of tm-scAAV2-BDNF and its control AAV at a titer of 6.6 E+13 genome copies/ml. Three weeks later, 1 μl of 2 mM N-methyl-D-aspartate (NMDA) was administered in the same way as the viral injection. Six days after the NMDA injection, we assessed the dark-adapted electroretinography (ERG). Mice were sacrificed at one week after the NMDA injection, followed by RNA quantification, protein detection, and histopathological analysis.

Results

The RNA expression of BDNF in retinas treated with tm-scAAV2-BDNF was about 300-fold higher than that of its control AAV. Meanwhile, the expression of recombinant BDNF protein increased in retinas treated with tm-scAAV2-BDNF. In addition, histological analysis revealed that tm-scAAV2-BDNF prevented thinning of the inner retina. Furthermore, b-wave amplitudes of the tm-scAAV2-BDNF group were significantly higher than those of the control vector group. Histopathological and electrophysiological evaluations showed that tm-scAAV2-BDNF treatment offered significant protection against NMDA toxicity.

Conclusions

Results showed that tm-scAAV2-BDNF-treated retinas were resistant to NMDA injury, while retinas treated with the control AAV exhibited histopathological and functional changes after the administration of NMDA. These results suggest that tm-scAAV2-BDNF is potentially effective against inner retinal injury, including normal tension glaucoma.

Current challenges in biotherapeutic particles manufacturing

Introduction: The development of novel complex biotherapeutics led to new challenges in biopharmaceutical industry. The potential of these particles has been demonstrated by the approval of several products, in the different fields of gene therapy, oncolytic therapy, and tumor vaccines. However, their manufacturing still presents challenges related to the high dosages and purity required.Areas covered: The main challenges that biopharmaceutical industry faces today and the most recent developments in the manufacturing of different biotherapeutic particles are reported here. Several unit operations and downstream trains to purify virus, virus-like particles and extracellular vesicles are described. Innovations on the different purification steps are also highlighted with an eye on the implementation of continuous and integrated processes.Expert opinion: Manufacturing platforms that consist of a low number of unit operations, with higher-yielding processes and reduced costs will be highly appreciated by the industry. The pipeline of complex therapeutic particles is expanding and there is a clear need for advanced tools and manufacturing capacity. The use of single-use technologies, as well as continuous integrated operations, are gaining ground in the biopharmaceutical industry and should be supported by more accurate and faster analytical methods.

Gene suppressing therapy for Pelizaeus-Merzbacher disease using artificial microRNA

Copy number increase or decrease of certain dosage-sensitive genes may cause genetic diseases with distinct phenotypes, conceptually termed genomic disorders. The most common cause of Pelizaeus-Merzbacher disease (PMD), an X-linked hypomyelinating leukodystrophy, is genomic duplication encompassing the entire proteolipid protein 1 (PLP1) gene. Although the exact molecular and cellular mechanisms underlying PLP1 duplication, which causes severe hypomyelination in the central nervous system, remain largely elusive, PLP1 overexpression is likely the fundamental cause of this devastating disease. Here, we investigated if adeno-associated virus-mediated (AAV-mediated) gene-specific suppression may serve as a potential cure for PMD by correcting quantitative aberrations in gene products. We developed an oligodendrocyte-specific Plp1 gene suppression therapy using artificial microRNA under the control of human CNP promoter in a self-complementary AAV (scAAV) platform. A single direct brain injection achieved widespread oligodendrocyte-specific Plp1 suppression in the white matter of WT mice. AAV treatment in Plp1-transgenic mice, a PLP1 duplication model, ameliorated cytoplasmic accumulation of Plp1, preserved mature oligodendrocytes from degradation, restored myelin structure and gene expression, and improved survival and neurological phenotypes. Together, our results provide evidence that AAV-mediated gene suppression therapy can serve as a potential cure for PMD resulting from PLP1 duplication and possibly for other genomic disorders.

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.

Impact of Dental Pulp Stem Cells Overexpressing Hepatocyte Growth Factor after Cerebral Ischemia/Reperfusion in Rats

Hepatocyte growth factor (HGF) has neuroprotective effects against ischemia-induced injuries. Dental pulp stem cell (DPSC) transplantation attenuates tissue injury in the brain of rats with post-transient middle cerebral artery occlusion. We sought to determine whether DPSCs that overexpress HGF can enhance their therapeutic effects on brain damage post-ischemia/reperfusion injury. Treatment with DPSCs overexpressing HGF reduced infarct volumes compared to unmodified DPSC treatment at 3 and 7 days post-transient middle cerebral artery occlusion. The use of unmodified DPSCs and DPSCs overexpressing HGF was associated with improved motor function compared to that with administration of vehicle at 7 days post-transient middle cerebral artery occlusion. DPSCs overexpressing HGF significantly inhibited microglial activation and pro-inflammatory cytokine production along with suppression of neuronal degeneration. Post-reperfusion, DPSCs overexpressing HGF attenuated the decreases in tight junction proteins, maintained blood-brain barrier integrity, and increased microvessel density in peri-infarct areas. The administration of DPSCs overexpressing HGF during the acute phase of stroke increased their neuroprotective effects by modulating inflammation and blood-brain barrier permeability, thereby promoting improvements in post-ischemia/reperfusion brain injury.

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.

DOK7 gene therapy enhances motor activity and life span in ALS model mice

Amyotrophic lateral sclerosis (ALS) is a progressive, multifactorial motor neurodegenerative disease with severe muscle atrophy. The glutamate release inhibitor riluzole is the only medication approved by the FDA, and prolongs patient life span by a few months, testifying to a strong need for new treatment strategies. In ALS, motor neuron degeneration first becomes evident at the motor nerve terminals in neuromuscular junctions (NMJs), the cholinergic synapse between motor neuron and skeletal muscle; degeneration then progresses proximally, implicating the NMJ as a therapeutic target. We previously demonstrated that activation of muscle‐specific kinase MuSK by the cytoplasmic protein Dok‐7 is essential for NMJ formation, and forced expression of Dok‐7 in muscle activates MuSK and enlarges NMJs. Here, we show that therapeutic administration of an adeno‐associated virus vector encoding the human DOK7 gene suppressed motor nerve terminal degeneration at NMJs together with muscle atrophy in the SOD1‐G93A ALS mouse model. Ultimately, we show that DOK7 gene therapy enhanced motor activity and life span in ALS model mice.

MicroRNA cluster miR-17-92 regulates multiple functionally related voltage-gated potassium channels in chronic neuropathic pain

miR-17-92 is a microRNA cluster with six distinct members. Here, we show that the miR-17-92 cluster and its individual members modulate chronic neuropathic pain. All cluster members are persistently upregulated in primary sensory neurons after nerve injury. Overexpression of miR-18a, miR-19a, miR-19b and miR-92a cluster members elicits mechanical allodynia in rats, while their blockade alleviates mechanical allodynia in a rat model of neuropathic pain. Plausible targets for the miR-17-92 cluster include genes encoding numerous voltage-gated potassium channels and their modulatory subunits. Single-cell analysis reveals extensive co-expression of miR-17-92 cluster and its predicted targets in primary sensory neurons. miR-17-92 downregulates the expression of potassium channels, and reduced outward potassium currents, in particular A-type currents. Combined application of potassium channel modulators synergistically alleviates mechanical allodynia induced by nerve injury or miR-17-92 overexpression. miR-17-92 cluster appears to cooperatively regulate the function of multiple voltage-gated potassium channel subunits, perpetuating mechanical allodynia.

Dysregulation of voltage gated potassium channels is a feature of neuropathic pain. Here in a rat model the authors identify the microRNA cluster miR-17-92 as a regulator of voltage gated potassium channels in the dorsal root ganglion neurons.

Mesenchymal Stem Cells Overexpressing Interleukin-10 Promote Neuroprotection in Experimental Acute Ischemic Stroke

Interleukin (IL)-10 is a contributing factor to neuroprotection of mesenchymal stem cell (MSC) transplantation after ischemic stroke. Our aim was to increase therapeutic effects by combining MSCs and ex vivo IL-10 gene transfer with an adeno-associated virus (AAV) vector using a rat transient middle cerebral artery occlusion (MCAO) model. Sprague-Dawley rats underwent 90 min MCAO followed by intravenous administration of MSCs alone or IL-10 gene-transferred MSCs (MSC/IL-10) at 0 or 3 hr after ischemia reperfusion. Infarct lesions, neurological deficits, and immunological analyses were performed within 7 days after MCAO. 0-hr transplantation of MSCs alone and MSC/IL-10 significantly reduced infarct volumes and improved motor function. Conversely, 3-hr transplantation of MSC/IL-10, but not MSCs alone, significantly reduced infarct volumes (p < 0.01) and improved motor function (p < 0.01) compared with vehicle groups at 72 hr and 7 days after MCAO. Immunological analysis showed that MSC/IL-10 transplantation significantly inhibits microglial activation and pro-inflammatory cytokine expression compared with MSCs alone. Moreover, overexpressing IL-10 suppressed neuronal degeneration and improved survival of engrafted MSCs in the ischemic hemisphere. These results suggest that overexpressing IL-10 enhances the neuroprotective effects of MSC transplantation by anti-inflammatory modulation and thereby supports neuronal survival during the acute ischemic phase.

Improving the Quality of Adeno-Associated Viral Vector Preparations: The Challenge of Product-Related Impurities

Adeno-associated viral (AAV) vectors have emerged as one of the most popular gene transfer systems in both research and clinical gene therapy. As AAV vectors are derived from a stealth, nonpathogenic virus and lack active integrase activity, these vectors are frequently applied for in vivo gene therapy of liver, muscle, and other postmitotic tissues. Although long-term transgene expression from AAV vector episomes is reported from these tissues, the episomal nature of AAV-once regarded as disadvantage-has become an attractive feature for gene-editing approaches targeting proliferating cells. In response to the high demand, AAV vector production is receiving special attention. Besides particle yields and biological activity, the most important concern is improving vector purity. The most difficult task in this regard is removal of defective particles, that is, capsids that are either empty or contain DNA other than the full-length vector genomes. Herein, we characterize and discuss these so-called product-related impurities, methods for their detection, as well as strategies to avoid or reduce their formation.