Upscaling of lentiviral vector production by tangential flow filtration

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.

Time-tagged ticker tapes for intracellular recordings

Recording transcriptional histories of a cell would enable deeper understanding of cellular developmental trajectories and responses to external perturbations. Here we describe an engineered protein fiber that incorporates diverse fluorescent marks during its growth to store a ticker tape-like history. An embedded HaloTag reporter incorporates user-supplied dyes, leading to colored stripes that map the growth of each individual fiber to wall clock time. A co-expressed eGFP tag driven by a promoter of interest records a history of transcriptional activation. High-resolution multi-spectral imaging on fixed samples reads the cellular histories, and interpolation of eGFP marks relative to HaloTag timestamps provides accurate absolute timing. We demonstrate recordings of doxycycline-induced transcription in HEK cells and cFos promoter activation in cultured neurons, with a single-cell absolute accuracy of 30-40 minutes over a 12-hour recording. The protein-based ticker tape design we present here could be generalized to achieve massively parallel single-cell recordings of diverse physiological modalities.

Alternative biological sources for extracellular vesicles production and purification strategies for process scale-up

Extracellular vesicles (EVs) are phospholipidic bi-layer enclosed nanoparticles secreted naturally by all cell types. They are attracting increasing attention in the fields of nanomedicine, nutraceutics and cosmetics as biocompatible carriers for drug delivery, with intrinsic properties beneficial to human health. Scientific work now focuses on developing techniques for isolating EVs that can translate into industrial-scale production and meet rigorous clinical requirements. The science of EVs is ongoing, and many pitfalls must be addressed, such as the requirement for standard, reproducible, inexpensive, and Good Manufacturing Practices (GMP) adherent EV processing techniques. Researchers are exploring the use of alternative sources to EVs derived from mammalian cultures, such as plant EVs, as well as the use of bacteria, algae and milk. Regarding the downstream processing of EVs, many alternative techniques to the ultracentrifugation (UC) protocols most commonly used in the laboratory are emerging. In the context of process scale-up, membrane-based processes for isolation and purification of EVs are the most promising, either as stand-alone processes or in combination with chromatographic techniques. This review discusses current trends on EVs source selection and EVs downstream processing techniques, with a focus on plant-derived EVs and membrane-based techniques for EVs enrichment.

A survey to evaluate parameters governing the selection and application of extracellular vesicle isolation methods

Extracellular vesicles (EVs) continue to gain interest across the scientific community for diagnostic and therapeutic applications. As EV applications diversify, it is essential that researchers are aware of challenges, in particular the compatibility of EV isolation methods with downstream applications and their clinical translation. We report outcomes of the first cross-comparison study looking to determine parameters (EV source, starting volume, operator experience, application and implementation parameters such as cost and scalability) governing the selection of popular EV isolation methods across disciplines. Our findings highlighted an increased clinical focus, with 36% of respondents applying EVs in therapeutics and diagnostics. Data indicated preferential selection of ultracentrifugation for therapeutic applications, precipitation reagents in clinical settings and size exclusion chromatography for diagnostic applications utilising biofluids. Method selection was influenced by operator experience, with increased method diversity when EV research was not the respondents primary focus. Application and implementation criteria were indicated to be major influencers in method selection, with UC and SEC chosen for their abilities to process large and small volumes, respectively. Overall, we identified parameters influencing method selection across the breadth of EV science, providing a valuable overview of practical considerations for the effective translation of research outcomes.

A Phosphosite Mutant Approach on LRRK2 Links Phosphorylation and Dephosphorylation to Protective and Deleterious Markers, Respectively

The Leucine Rich Repeat Kinase 2 (LRRK2) gene is a major genetic determinant of Parkinson’s disease (PD), encoding a homonymous multi-domain protein with two catalytic activities, GTPase and Kinase, involved in intracellular signaling and trafficking. LRRK2 is phosphorylated at multiple sites, including a cluster of autophosphorylation sites in the GTPase domain and a cluster of heterologous phosphorylation sites at residues 860 to 976. Phosphorylation at these latter sites is found to be modified in brains of PD patients, as well as for some disease mutant forms of LRRK2. The main aim of this study is to investigate the functional consequences of LRRK2 phosphorylation or dephosphorylation at LRRK2’s heterologous phosphorylation sites. To this end, we generated LRRK2 phosphorylation site mutants and studied how these affected LRRK2 catalytic activity, neurite outgrowth and lysosomal physiology in cellular models. We show that phosphorylation of RAB8a and RAB10 substrates are reduced with phosphomimicking forms of LRRK2, while RAB29 induced activation of LRRK2 kinase activity is enhanced for phosphodead forms of LRRK2. Considering the hypothesis that PD pathology is associated to increased LRRK2 kinase activity, our results suggest that for its heterologous phosphorylation sites LRRK2 phosphorylation correlates to healthy phenotypes and LRRK2 dephosphorylation correlates to phenotypes associated to the PD pathological processes.

Luminescent Human iPSC-Derived Neurospheroids Enable Modeling of Neurotoxicity After Oxygen-glucose Deprivation

Despite the considerable impact of stroke on both the individual and on society, a neuroprotective therapy for stroke patients is missing. This is partially due to the current lack of a physiologically relevant human in vitro stroke model. To address this problem, we have developed a luminescent human iPSC-derived neurospheroid model that enables real-time read-out of neural viability after ischemia-like conditions. We subjected 1- and 4-week-old neurospheroids, generated from iPSC-derived neural stem cells, to 6 h of oxygen-glucose deprivation (OGD) and measured neurospheroid luminescence. For both, we detected a decrease in luminescent signal due to ensuing neurotoxicity, as confirmed by conventional LDH assay and flow cytometric viability analysis. Remarkably, 1-week-old, but not 4-week-old neurospheroids recovered from OGD-induced injury, as evidenced by their reduced but overall increasing luminescence over time. This underscores the need for more mature neurospheroids, more faithfully recapitulating the in vivo situation. Furthermore, treatment of oxygen- and glucose-deprived neurospheroids with the pan-caspase inhibitor Z-VAD-FMK did not increase overall neural survival, despite its successful attenuation of apoptosis, in a human-based 3D environment. Nevertheless, owing to its three-dimensional organization and real-time viability reporting potential, the luminescent neurospheroids may become readily adopted in high-throughput screens aimed at identification of new therapeutic agents to treat acute ischemic stroke patients.

Organoids from human tooth showing epithelial stemness phenotype and differentiation potential

Insight into human tooth epithelial stem cells and their biology is sparse. Tissue-derived organoid models typically replicate the tissue’s epithelial stem cell compartment. Here, we developed a first-in-time epithelial organoid model starting from human tooth. Dental follicle (DF) tissue, isolated from unerupted wisdom teeth, efficiently generated epithelial organoids that were long-term expandable. The organoids displayed a tooth epithelial stemness phenotype similar to the DF’s epithelial cell rests of Malassez (ERM), a compartment containing dental epithelial stem cells. Single-cell transcriptomics reinforced this organoid-ERM congruence, and uncovered novel, mouse-mirroring stem cell features. Exposure of the organoids to epidermal growth factor induced transient proliferation and eventual epithelial-mesenchymal transition, highly mimicking events taking place in the ERM in vivo. Moreover, the ERM stemness organoids were able to unfold an ameloblast differentiation process, further enhanced by transforming growth factor-β (TGFβ) and abrogated by TGFβ receptor inhibition, thereby reproducing TGFβ's known key position in amelogenesis. Interestingly, by creating a mesenchymal-epithelial composite organoid (assembloid) model, we demonstrated that the presence of dental mesenchymal cells (i.e. pulp stem cells) triggered ameloblast differentiation in the epithelial stem cells, thus replicating the known importance of mesenchyme-epithelium interaction in tooth development and amelogenesis. Also here, differentiation was abrogated by TGFβ receptor inhibition. Together, we developed novel organoid models empowering the exploration of human tooth epithelial stem cell biology and function as well as their interplay with dental mesenchyme, all at present only poorly defined in humans. Moreover, the new models may pave the way to future tooth-regenerative perspectives.

Cytoplasmic Tail Truncation of SARS-CoV-2 Spike Protein Enhances Titer of Pseudotyped Vectors but Masks the Effect of the D614G Mutation

The high pathogenicity of SARS-CoV-2 requires it to be handled under biosafety level 3 conditions. Consequently, Spike protein-pseudotyped vectors are a useful tool to study viral entry and its inhibition, with retroviral, lentiviral (LV), and vesicular stomatitis virus (VSV) vectors the most commonly used systems. Methods to increase the titer of such vectors commonly include concentration by ultracentrifugation and truncation of the Spike protein cytoplasmic tail. However, limited studies have examined whether such a modification also impacts the protein's function. Here, we optimized concentration methods for SARS-CoV-2 Spike-pseudotyped VSV vectors, finding that tangential flow filtration produced vectors with more consistent titers than ultracentrifugation. We also examined the impact of Spike tail truncation on transduction of various cell types and sensitivity to convalescent serum neutralization. We found that tail truncation increased Spike incorporation into both LV and VSV vectors and resulted in enhanced titers but had no impact on sensitivity to convalescent serum. In addition, we analyzed the effect of the D614G mutation, which became a dominant SARS-CoV-2 variant early in the pandemic. Our studies revealed that, similar to the tail truncation, D614G independently increases Spike incorporation and vector titers, but this effect is masked by also including the cytoplasmic tail truncation. Therefore, the use of full-length Spike protein, combined with tangential flow filtration, is recommended as a method to generate high titer pseudotyped vectors that retain native Spike protein functions. IMPORTANCE Pseudotyped viral vectors are useful tools to study the properties of viral fusion proteins, especially those from highly pathogenic viruses. The Spike protein of SARS-CoV-2 has been investigated using pseudotyped lentiviral and VSV vector systems, where truncation of its cytoplasmic tail is commonly used to enhance Spike incorporation into vectors and to increase the titers of the resulting vectors. However, our studies have shown that such effects can also mask the phenotype of the D614G mutation in the ectodomain of the protein, which was a dominant variant arising early in the COVID-19 pandemic. To better ensure the authenticity of Spike protein phenotypes when using pseudotyped vectors, we recommend using full-length Spike proteins, combined with tangential flow filtration methods of concentration if higher-titer vectors are required.

Scaled preparation of extracellular vesicles from conditioned media

Extracellular vesicles (EVs) especially of mesenchymal stem/stomal cells (MSCs) are increasingly considered as biotherapeutic agents for a variety of different diseases. For translating them effectively into the clinics, scalable production processes fulfilling good manufacturing practice (GMP) are needed. Like for other biotherapeutic agents, the manufacturing of EV products can be subdivided in the upstream and downstream processing and the subsequent quality control, each of them containing several unit operations. During upstream processing (USP), cells are isolated, stored (cell banking) and expanded; furthermore, EV-containing conditioned media are produced. During downstream processing (DSP), conditioned media (CM) are processed to obtain concentrated and purified EV products. CM are either stored until DSP or are directly processed. As first unit operation in DSP, clarification removes remaining cells, debris and other larger impurities. The key operations of each EV DSP is volume-reduction combined with purification of the concentrated EVs. Most of the EV preparation methods used in conventional research labs including differential centrifugation procedures are limited in their scalability. Consequently, it is a major challenge in the therapeutic EV field to identify appropriate EV concentration and purification methods allowing scale up. As EVs share several features with enveloped viruses, that are used for more than two decades in the clinics now, several principles can be adopted to EV manufacturing. Here, we introduce and discuss volume reducing and purification methods frequently used for viruses and analyze their value for the manufacturing of EV-based therapeutics.

Critical Assessment of Purification and Analytical Technologies for Enveloped Viral Vector and Vaccine Processing and Their Current Limitations in Resolving Co-Expressed Extracellular Vesicles

Viral vectors and viral vaccines are invaluable tools in prevention and treatment of diseases. Many infectious diseases are controlled using vaccines designed from subunits or whole viral structures, whereas other genetic diseases and cancers are being treated by viruses used as vehicles for delivering genetic material in gene therapy or as therapeutic agents in virotherapy protocols. Viral vectors and vaccines are produced in different platforms, from traditional embryonated chicken eggs to more advanced cell cultures. All these expression systems, like most cells and cellular tissues, are known to spontaneously release extracellular vesicles (EVs). EVs share similar sizes, biophysical characteristics and even biogenesis pathways with enveloped viruses, which are currently used as key ingredients in a number of viral vectors and licensed vaccine products. Herein, we review distinctive features and similarities between EVs and enveloped viruses as we revisit the downstream processing steps and analytical technologies currently implemented to produce and document viral vector and vaccine products. Within a context of well-established viral vector and vaccine safety profiles, this review provides insights on the likely presence of EVs in the final formulation of enveloped virus products and discusses the potential to further resolve and document these components.

Lentiviral Vector Bioprocessing

Lentiviral vectors (LVs) are potent tools for the delivery of genes of interest into mammalian cells and are now commonly utilised within the growing field of cell and gene therapy for the treatment of monogenic diseases and adoptive therapies such as chimeric antigen T-cell (CAR-T) therapy. This is a comprehensive review of the individual bioprocess operations employed in LV production. We highlight the role of envelope proteins in vector design as well as their impact on the bioprocessing of lentiviral vectors. An overview of the current state of these operations provides opportunities for bioprocess discovery and improvement with emphasis on the considerations for optimal and scalable processing of LV during development and clinical production. Upstream culture for LV generation is described with comparisons on the different transfection methods and various bioreactors for suspension and adherent producer cell cultivation. The purification of LV is examined, evaluating different sequences of downstream process operations for both small- and large-scale production requirements. For scalable operations, a key focus is the development in chromatographic purification in addition to an in-depth examination of the application of tangential flow filtration. A summary of vector quantification and characterisation assays is also presented. Finally, the assessment of the whole bioprocess for LV production is discussed to benefit from the broader understanding of potential interactions of the different process options. This review is aimed to assist in the achievement of high quality, high concentration lentiviral vectors from robust and scalable processes.

Unlike Its Paralog LEDGF/p75, HRP-2 Is Dispensable for MLL-R Leukemogenesis but Important for Leukemic Cell Survival

HDGF-related protein 2 (HRP-2) is a member of the Hepatoma-Derived Growth Factor-related protein family that harbors the structured PWWP and Integrase Binding Domain, known to associate with methylated histone tails or cellular and viral proteins, respectively. Interestingly, HRP-2 is a paralog of Lens Epithelium Derived Growth Factor p75 (LEDGF/p75), which is essential for MLL-rearranged (MLL-r) leukemia but dispensable for hematopoiesis. Sequel to these findings, we investigated the role of HRP-2 in hematopoiesis and MLL-r leukemia. Protein interactions were investigated by co-immunoprecipitation and validated using recombinant proteins in NMR. A systemic knockout mouse model was used to study normal hematopoiesis and MLL-ENL transformation upon the different HRP-2 genotypes. The role of HRP-2 in MLL-r and other leukemic, human cell lines was evaluated by lentiviral-mediated miRNA targeting HRP-2. We demonstrate that MLL and HRP-2 interact through a conserved interface, although this interaction proved less dependent on menin than the MLL-LEDGF/p75 interaction. The systemic HRP-2 knockout mice only revealed an increase in neutrophils in the peripheral blood, whereas the depletion of HRP-2 in leukemic cell lines and transformed primary murine cells resulted in reduced colony formation independently of MLL-rearrangements. In contrast, primary murine HRP-2 knockout cells were efficiently transformed by the MLL-ENL fusion, indicating that HRP-2, unlike LEDGF/p75, is dispensable for the transformation of MLL-ENL leukemogenesis but important for leukemic cell survival.

Advances in Lentivirus Purification

Lentiviral vectors (LVs) have been increasingly used as a tool for gene and cell therapies since they can stably integrate the genome in dividing and nondividing cells. LV production and purification processes have evolved substantially over the last decades. However, the increasing demands for higher quantities with more restrictive purity requirements are stimulating the development of novel materials and strategies to supply the market with LV in a cost-effective manner. A detailed review of each downstream process unit operation is performed, limitations, strengths, and potential outcomes being covered. Currently, the majority of large-scale LV manufacturing processes are still based on adherent cell culture, although it is known that the industry is migrating fast to suspension cultures. Regarding the purification strategy, it consists of batch chromatography and membrane technology. Nevertheless, new solutions are being created to improve the current production schemes and expand its clinical use.

A new simplified clarification approach for lentiviral vectors using diatomaceous earth improves throughput and safe handling

Lentiviral vectors have proven their great potential to serve as a DNA delivery tool for gene modified cell therapy and gene therapy applications. The downstream processing of these vectors is however still a great challenge, particularly because of the low stability of the virus. Harvesting and clarification are critical and until now insufficiently characterized steps for lentivirus processing. To address this bottleneck, we analyzed whether lentiviral vectors produced by transient transfection of HEK293 T/17 SF suspension cells can be efficiently clarified with a lab-scale method with the filter aid diatomaceous earth (DE) and bioburden reducing membrane filters achieving high lentivirus recoveries. Using a design of experiment approach we found that higher DE concentrations are advantageous for a higher turbidity reduction and shorter filtration times, but at the same time LV titer decreases with increasing DE concentration. A DE concentration of 9 g/L was identified with a DoE as a robust set-point. Clarification with DE was compared with for lab-scale traditionally employed centrifugation and subsequent bioburden reduction filtration of viral vectors. The use of DE allows to perform a harvest and clarification process, which does not only facilitate faster and safer virus handling, but enables a lower material consumption due to the extremely increased filter capacity, thus representing an efficient and robust lab-scale clarification process.

Large-Scale Production of Lentiviral Vectors: Current Perspectives and Challenges

Lentiviral vectors (LVs) have gained value over recent years as gene carriers in gene therapy. These viral vectors are safer than what was previously being used for gene transfer and are capable of infecting both dividing and nondividing cells with a long-term expression. This characteristic makes LVs ideal for clinical research, as has been demonstrated with the approval of lentivirus-based gene therapies from the Food and Drug Administration and the European Agency for Medicine. A large number of functional lentiviral particles are required for clinical trials, and large-scale production has been challenging. Therefore, efforts are focused on solving the drawbacks associated with the production and purification of LVsunder current good manufacturing practice. In recent years, we have witnessed the development and optimization of new protocols, packaging cell lines, and culture devices that are very close to reaching the target production level. Here, we review the most recent, efficient, and promising methods for the clinical-scale production ofLVs.

Production of high-titer transmission-defective RNA virus-based episomal vector using tangential flow filtration

In recent years, viral vector based in vivo gene delivery strategies have achieved a significant success in the treatment of genetic diseases. RNA virus-based episomal vector lacking viral glycoprotein gene (ΔG-REVec) is a nontransmissive gene delivery system that enables long-term gene expression in a variety of cell types in vitro, yet in vivo gene delivery has not been successful due to the difficulty in producing high titer vector. The present study showed that tangential flow filtration (TFF) can be effectively employed to increase the titer of ΔG-REVec. Concentration and diafiltration of ΔG-REVec using TFF significantly increased its titer without loss of infectious activity. Importantly, intracranial administration of high titer vector enabled persistent transgene expression in rodent brain.

Multiplexed Optical Sensors in Arrayed Islands of Cells for multimodal recordings of cellular physiology

Cells typically respond to chemical or physical perturbations via complex signaling cascades which can simultaneously affect multiple physiological parameters, such as membrane voltage, calcium, pH, and redox potential. Protein-based fluorescent sensors can report many of these parameters, but spectral overlap prevents more than ~4 modalities from being recorded in parallel. Here we introduce the technique, MOSAIC, Multiplexed Optical Sensors in Arrayed Islands of Cells, where patterning of fluorescent sensor-encoding lentiviral vectors with a microarray printer enables parallel recording of multiple modalities. We demonstrate simultaneous recordings from 20 sensors in parallel in human embryonic kidney (HEK293) cells and in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), and we describe responses to metabolic and pharmacological perturbations. Together, these results show that MOSAIC can provide rich multi-modal data on complex physiological responses in multiple cell types.

Preclinical Development of Autologous Hematopoietic Stem Cell-Based Gene Therapy for Immune Deficiencies: A Journey from Mouse Cage to Bed Side

Recent clinical trials using patient’s own corrected hematopoietic stem cells (HSCs), such as for primary immunodeficiencies (Adenosine deaminase (ADA) deficiency, X-linked Severe Combined Immunodeficiency (SCID), X-linked chronic granulomatous disease (CGD), Wiskott–Aldrich Syndrome (WAS)), have yielded promising results in the clinic; endorsing gene therapy to become standard therapy for a number of diseases. However, the journey to achieve such a successful therapy is not easy, and several challenges have to be overcome. In this review, we will address several different challenges in the development of gene therapy for immune deficiencies using our own experience with Recombinase-activating gene 1 (RAG1) SCID as an example. We will discuss product development (targeting of the therapeutic cells and choice of a suitable vector and delivery method), the proof-of-concept (in vitro and in vivo efficacy, toxicology, and safety), and the final release steps to the clinic (scaling up, good manufacturing practice (GMP) procedures/protocols and regulatory hurdles).

Functional evaluation of prevascularization in one-stage versus two-stage tissue engineering approach of human bio-artificial muscle

A common shortcoming of current tissue engineered constructs is the lack of a functional vasculature, limiting their size and functionality. Prevascularization is a possible strategy to introduce vascular networks in these constructs. It includes among others co-culturing target cells with endothelial (precursor) cells that are able to form endothelial networks through vasculogenesis. In this paper, we compared two different prevascularization approaches of bio-artificial skeletal muscle tissue (BAM) in vitro and in vivo. In a one-stage approach, human muscle cells were directly co-cultured with endothelial cells in 3D. In a two-stage approach, a one week old BAM containing differentiated myotubes was coated with a fibrin hydrogel containing endothelial cells. The obtained endothelial networks were longer and better interconnected with the two-stage approach. We evaluated whether prevascularization had a beneficial effect on in vivo perfusion of the BAM and improved myotube survival by implantation on the fascia of the latissimus dorsi muscle of NOD/SCID mice for 5 or 14 d. Also in vivo, the two-stage approach displayed the highest vascular density. At day 14, anastomosis of implanted endothelial networks with the host vasculature was apparent. BAMs without endothelial networks contained longer and thicker myotubes in vitro, but their morphology degraded in vivo. In contrast, maintenance of myotube morphology was well supported in the two-stage prevascularized BAMs. To conclude, a two-stage prevascularization approach for muscle engineering improved the vascular density in the construct and supported myotube maintenance in vivo.

Optimized Pre-Clinical Grade Production of Two Novel Lentiviral Vector Pseudotypes for Lung Gene Delivery

Lung gene therapy requires efficient transduction of slow-replicating epithelia and stable expression of delivered transgenes in the respiratory tract. Lentiviral (LV) vectors have the ideal coding, expression, and transducing capacity required for gene therapy. A modified envelope glycoprotein from the Jaagsiekte Sheep Retrovirus, termed Jenv, is well suited for LV-mediated lung gene therapy due to its inherent lung tropism. Here, two novel Jenv-pseudotyped LVs that effectively transduce lung tissue and yield titers similar to the gold standard, vesicular stomatitis virus glycoprotein (VSVg)-pseudotyped LVs, were generated. As the concentration efficiency of LVs was found to depend on envelope pseudotype, a large-scale production method tailored for Jenv-pseudotyped LVs was developed and the most appropriate method of concentration was determined. In contrast to VSVg and Ebola virus glycoprotein-pseudotyped LVs, ultracentrifugation through a sucrose cushion drastically reduced the yield of Jenv LVs, whereas polyethylene glycol precipitation and tangential flow filtration (TFF) proved to be more suitable methods for concentrating Jenv LVs. Importantly, pressure during TFF was found to be crucial for increasing LV recovery. Finally, a unique mouse model was developed to test the suitability of these novel Jenv-pseudotyped LVs for use in lung gene therapy applications.

Development of Large-Scale Downstream Processing for Lentiviral Vectors

The interest in lentiviral vectors (LVs) has increased prominently for gene therapy applications, but few have reached the later stages of clinical trials. The main challenge has remained in scaling up the manufacturing process for the fragile vector to obtain high titers for in vivo usage. We have previously scaled up the LV production to iCELLis 500, being able to produce up to 180 L of harvest material in one run with perfusion. The following challenge considers the purification and concentration of the product to meet titer and purity requirements for clinical use. We have developed a downstream process, beginning with clarification, buffer exchange, and concentration, by tangential flow filtration. This is followed by a purification step using single membrane-based anion exchange chromatography and final formulation with tangential flow filtration. Different materials and conditions were compared to optimize the process, especially for the chromatography step that has been the bottleneck in lentiviral vector purification scale-up. The final infectious titer of the lentiviral vector product manufactured using the optimized scale-up process was determined to be 1.97 × 10⁹ transducing units (TU)/mL, which can be considered as a high titer for lentiviral vectors.

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.

Lentiviral Vector Purification Using Nanofiber Ion-Exchange Chromatography

Lentiviral vectors (LVs) are used in cell and gene therapies due to their ability to transduce both dividing and non-dividing cells while carrying a relatively large genetic payload and providing long-term gene expression via gene integration. Current cultivation methods produce titers of 10⁵–10⁷ transduction unit (TU)/mL; thus, it is necessary to concentrate LVs as well as remove process- and product-related impurities. In this work, we used a packaging cell line WinPac-RD-HV for LV production to simplify upstream processing. A direct capture method based on ion-exchange chromatography and cellulose nanofibers for LV concentration and purification was developed. This novel scalable stationary phase provides a high surface area that is accessible to LV and, therefore, has potential for high-capacity operation compared to traditional bead-based supports. We were able to concentrate LVs 100-fold while achieving a two-log removal of host cell protein and maintaining up to a 90% yield of functional vector.

High-Grade Purification of Third-Generation HIV-Based Lentiviral Vectors by Anion Exchange Chromatography for Experimental Gene and Stem Cell Therapy Applications

Lentiviral vectors (LVs) have been increasingly used in clinical gene therapy applications particularly due to their efficient gene transfer ability, lack of interference from preexisting viral immunity, and long-term gene expression they provide. Purity of LVs is essential in in vivo applications, for a high therapeutic benefit with minimum toxicity. Accordingly, laboratory scale production of LVs frequently involves transient cotransfection of 293T cells with packaging and transfer plasmids in the presence of CaPO₄. After clearance of the cellular debris by low-speed centrifugation and filtration, lentivectors are usually concentrated by high-speed ultracentrifugation in sucrose cushion. Concentrated viral samples are then purified by anion exchange chromatography (AEX) after benzonase treatment to remove the residual cellular DNA. Here, we describe an improved practical method for LV purification using AEX, useful for experimental studies concerning gene and stem cell therapy.

High-Efficiency Lentiviral Gene Modification of Primary Murine Bone-Marrow Mesenchymal Stem Cells

Lentiviral vectors are the method of choice for stable gene modification of a variety of cell types. However, the efficiency with which they transduce target cells varies significantly, in particular their typically poor capacity to transduce primary stem cells. Here we describe the isolation and enrichment of murine bone-marrow mesenchymal stem cells (MSCs) via fluorescence-activated cell sorting (FACS); the cloning, production, and concentration of high-titer second generation lentiviral vectors via combined tangential flow filtration (TFF) and ultracentrifugation; and the subsequent high-efficiency gene modification of MSCs into insulin-producing cells via overexpression of the furin-cleavable human insulin (INS-FUR) gene.

Inhibition of LRRK2 or Casein Kinase 1 Results in LRRK2 Protein Destabilization

Mutations and variations in the leucine-rich repeat kinase 2 (LRRK2) gene are strongly associated with an increased risk to develop Parkinson's disease (PD). Most pathogenic LRRK2 mutations display increased kinase activity, which is believed to underlie LRRK2-mediated toxicity. Therefore, major efforts have been invested in the development of potent and selective LRRK2 kinase inhibitors. Several of these compounds have proven beneficial in cells and in vivo, even in a LRRK2 wild-type background. Therefore, LRRK2 kinase inhibition holds great promise as disease-modifying PD therapy, and is currently tested in preclinical and early clinical studies. One of the safety concerns is the development of lung pathology in mice and non-human primates, which is most likely related to the strongly reduced LRRK2 protein levels after LRRK2 kinase inhibition. In this study, we aimed to better understand the molecular consequences of chronic LRRK2 kinase inhibition, which may be pivotal in the further development of a LRRK2 kinase inhibitor-based PD therapy. We found that LRRK2 protein levels are not restored during long-term LRRK2 kinase inhibition, but are recovered upon inhibitor withdrawal. Interestingly, LRRK2 kinase inhibitor-induced destabilization does not occur in all pathogenic LRRK2 variants and the N-terminal part of LRRK2 appears to play a crucial role in this process. In addition, we identified CK1, an upstream kinase of LRRK2, as a regulator of LRRK2 protein stability in cell culture and in vivo. We propose that pharmacological LRRK2 kinase inhibition triggers a cascade that results in reduced CK1-mediated phosphorylation of yet unidentified LRRK2 phosphorylation sites. This process involves the N-terminus of LRRK2 and ultimately leads to LRRK2 protein degradation.

All-optical synaptic electrophysiology probes mechanism of ketamine-induced disinhibition

Optical assays of synaptic strength could facilitate studies of neuronal transmission and its dysregulation in disease. Here we introduce a genetic toolbox for all-optical interrogation of synaptic electrophysiology (synOptopatch) via mutually exclusive expression of a channelrhodopsin actuator and an archaerhodopsin-derived voltage indicator. Optically induced activity in the channelrhodopsin-expressing neurons generated excitatory and inhibitory postsynaptic potentials that we optically resolved in reporter-expressing neurons. We further developed a yellow spine-targeted Ca2+ indicator to localize optogenetically triggered synaptic inputs. We demonstrated synOptopatch recordings in cultured rodent neurons and in acute rodent brain slice. In synOptopatch measurements of primary rodent cultures, acute ketamine administration suppressed disynaptic inhibitory feedbacks, mimicking the effect of this drug on network function in both rodents and humans. We localized this action of ketamine to excitatory synapses onto interneurons. These results establish an in vitro all-optical model of disynaptic disinhibition, a synaptic defect hypothesized in schizophrenia-associated psychosis.

Y-box-binding protein 1 supports the early and late steps of HIV replication

The human immunodeficiency virus (HIV) depends on cellular proteins, so-called cofactors, to complete its replication cycle. In search for new therapeutic targets we identified the DNA and RNA binding protein Y-box-binding Protein 1 (YB-1) as a cofactor supporting early and late steps of HIV replication. YB-1 depletion resulted in a 10-fold decrease in HIV-1 replication in different cell lines. Dissection of the replication defects revealed that knockdown of YB-1 is associated with a 2- to 5-fold decrease in virion production due to interference with the viral RNA metabolism. Using single-round virus infection experiments we demonstrated that early HIV-1 replication also depends on the cellular YB-1 levels. More precisely, using quantitative PCR and an in vivo nuclear import assay with fluorescently labeled viral particles, we showed that YB-1 knockdown leads to a block between reverse transcription and nuclear import of HIV-1. Interaction studies revealed that YB-1 associates with integrase, although a direct interaction with HIV integrase could not be unambiguously proven. In conclusion, our results indicate that YB-1 affects multiple stages of HIV replication. Future research on the interaction between YB-1 and the virus will reveal whether this protein qualifies as a new antiviral target.

Manufacture of Third-Generation Lentivirus for Preclinical Use, with Process Development Considerations for Translation to Good Manufacturing Practice

Lentiviral vectors are used in laboratories around the world for in vivo and ex vivo delivery of gene therapies, and increasingly clinical investigation as well as preclinical applications. The third-generation lentiviral vector system has many advantages, including high packaging capacity, stable gene expression in both dividing and post-mitotic cells, and low immunogenicity in the recipient organism. Yet, the manufacture of these vectors is challenging, especially at high titers required for direct use in vivo, and further challenges are presented by the process of translating preclinical gene therapies toward manufacture of products for clinical investigation. The goals of this paper are to report the protocol for manufacturing high-titer third-generation lentivirus for preclinical testing and to provide detailed information on considerations for translating preclinical viral vector manufacture toward scaled-up platforms and processes in order to make gene therapies under Good Manufacturing Practice that are suitable for clinical trials.

Ultrawidefield microscope for high-speed fluorescence imaging and targeted optogenetic stimulation

The rapid increase in the number and quality of fluorescent reporters and optogenetic actuators has yielded a powerful set of tools for recording and controlling cellular state and function. To achieve the full benefit of these tools requires improved optical systems with high light collection efficiency, high spatial and temporal resolution, and patterned optical stimulation, in a wide field of view (FOV). Here we describe our 'Firefly' microscope, which achieves these goals in a Ø6 mm FOV. The Firefly optical system is optimized for simultaneous photostimulation and fluorescence imaging in cultured cells. All but one of the optical elements are commercially available, yet the microscope achieves 10-fold higher light collection efficiency at its design magnification than the comparable commercially available microscope using the same objective. The Firefly microscope enables all-optical electrophysiology ('Optopatch') in cultured neurons with a throughput and information content unmatched by other neuronal phenotyping systems. This capability opens possibilities in disease modeling and phenotypic drug screening. We also demonstrate applications of the system to voltage and calcium recordings in human induced pluripotent stem cell derived cardiomyocytes.

Geometry-dependent functional changes in iPSC-derived cardiomyocytes probed by functional imaging and RNA sequencing

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are a promising platform for cardiac studies in vitro, and possibly for tissue repair in humans. However, hiPSC-CM cells tend to retain morphology, metabolism, patterns of gene expression, and electrophysiology similar to that of embryonic cardiomyocytes. We grew hiPSC-CM in patterned islands of different sizes and shapes, and measured the effect of island geometry on action potential waveform and calcium dynamics using optical recordings of voltage and calcium from 970 islands of different sizes. hiPSC-CM in larger islands showed electrical and calcium dynamics indicative of greater functional maturity. We then compared transcriptional signatures of the small and large islands against a developmental time course of cardiac differentiation. Although island size had little effect on expression of most genes whose levels differed between hiPSC-CM and adult primary CM, we identified a subset of genes for which island size drove the majority (58%) of the changes associated with functional maturation. Finally, we patterned hiPSC-CM on islands with a variety of shapes to probe the relative contributions of soluble factors, electrical coupling, and direct cell-cell contacts to the functional maturation. Collectively, our data show that optical electrophysiology is a powerful tool for assaying hiPSC-CM maturation, and that island size powerfully drives activation of a subset of genes involved in cardiac maturation.

Fluorescent Quail: A Transgenic Model System for the Dynamic Study of Avian Development

Real-time four-dimensional (4D, xyzt) imaging of cultured avian embryos is an ideal method for investigating the complex movements of cells and tissues during early morphogenesis. While methods that transiently label cells, such as electroporation, are highly useful for dynamic imaging, they can also be limiting due to the number and type of cells that can be effectively targeted. In contrast, the heritable, stable, and long-term expression of a fluorescent protein driven by the exogenous promoter of a transgene overcomes these challenges. We have used lentiviral vectors to produce several novel transgenic quail lines that express fluorescent proteins either ubiquitously or in a cell-specific manner. These lines have proven to be useful models for dynamic imaging and analysis. Here, we provide detailed protocols for generating transgenic quail with the emphasis on producing high titer lentivirus , effectively introducing it into the early embryo and efficiently screening for G1 founder birds .

Intracerebral transplantation of interleukin 13-producing mesenchymal stem cells limits microgliosis, oligodendrocyte loss and demyelination in the cuprizone mouse model

Background

Promoting the neuroprotective and repair-inducing effector functions of microglia and macrophages, by means of M2 polarisation or alternative activation, is expected to become a new therapeutic approach for central nervous system (CNS) disorders in which detrimental pro-inflammatory microglia and/or macrophages display a major contribution to the neuropathology. In this study, we present a novel in vivo approach using intracerebral grafting of mesenchymal stem cells (MSC) genetically engineered to secrete interleukin 13 (IL13-MSC).

Methods

In the first experimental setup, control MSC and IL13-MSC were grafted in the CNS of eGFP⁺ bone marrow chimaeric C57BL/6 mice to histologically evaluate IL13-mediated expression of several markers associated with alternative activation, including arginase1 and Ym1, on MSC graft-recognising microglia and MSC graft-infiltrating macrophages. In the second experimental setup, IL13-MSC were grafted on the right side (or on both the right and left sides) of the splenium of the corpus callosum in wild-type C57BL/6 mice and in C57BL/6 CX₃CR1^eGFP/+CCR2^RFP/+ transgenic mice. Next, CNS inflammation and demyelination was induced by means of a cuprizone-supplemented diet. The influence of IL13-MSC grafting on neuropathological alterations was monitored by non-invasive T₂-weighted magnetic resonance imaging (MRI) and quantitative histological analyses, as compared to cuprizone-treated mice with control MSC grafts and/or cuprizone-treated mice without MSC injection.

Results

In the first part of this study, we demonstrate that MSC graft-associated microglia and MSC graft-infiltrating macrophages are forced into alternative activation upon grafting of IL13-MSC, but not upon grafting of control MSC. In the second part of this study, we demonstrate that grafting of IL13-MSC, in addition to the recruitment of M2 polarised macrophages, limits cuprizone-induced microgliosis, oligodendrocyte death and demyelination. Furthermore, we here demonstrate that injection of IL13-MSC at both sides of the splenium leads to a superior protective effect as compared to a single injection at one side of the splenium.

Conclusions

Controlled and localised production of IL13 by means of intracerebral MSC grafting has the potential to modulate cell graft- and pathology-associated microglial/macrophage responses, and to interfere with oligodendrocyte death and demyelinating events in the cuprizone mouse model.

The feasibility of incorporating Vpx into lentiviral gene therapy vectors

While current antiretroviral therapy has significantly improved, challenges still remain in life-long targeting of HIV-1 reservoirs. Lentiviral gene therapy has the potential to deliver protective genes into the HIV-1 reservoir. However, inefficient reverse transcription (RT) occurs in HIV-1 reservoirs during lentiviral gene delivery. The viral protein Vpx is capable of increasing lentiviral RT by antagonizing the restriction factor SAMHD1. Incorporating Vpx into lentiviral vectors could substantially increase gene delivery into the HIV-1 reservoir. The feasibility of this Vpx approach was tested in resting cell models utilizing macrophages and dendritic cells. Our results showed Vpx exposure led to increased permissiveness of cells over a period that exceeded 2 weeks. Consequently, significant lower potency of HIV-1 antiretrovirals inhibiting RT and integration was observed. When Vpx was incorporated with anti-HIV-1 genes inhibiting either pre-RT or post-RT stages of the viral life-cycle, transduction levels significantly increased. However, a stronger antiviral effect was only observed with constructs that inhibit pre-RT stages of the viral life cycle. In conclusion this study demonstrates a way to overcome the major delivery obstacle of gene delivery into HIV-1 reservoir cell types. Importantly, incorporating Vpx with pre-RT anti-HIV-1 genes, demonstrated the greatest protection against HIV-1 infection.

Challenges of up-scaling lentivirus production and processing

Lentiviruses are becoming an increasingly popular choice of gene transfer vehicle for use in the treatment of a variety of genetic and acquired human diseases. As research progresses from basic studies into pre-clinical and clinical phases, there is a growing demand for large volumes of high purity, concentrated vector, and accordingly, the means to produce such quantities. Unlike other viral vectors, lentiviruses are difficult to produce using stable cell lines, therefore transient transfection of adherent cell lines is conventionally used, and this method has proven challenging to up-scale. Furthermore, with the required increases in the volume of vector needed for larger animal and human use, comes the need for more efficient and sophisticated supernatant purification and concentration techniques. This review presents the challenges of up-scaling lentivirus production and processing approaches, novel systems for overcoming these issues, and the quality assessments recommended for producing a clinical grade lentiviral gene therapy product.

Lentivirus Production and Purification

Lentiviral (LV) vectors offer unique advantages over other gene delivery systems, namely the ability to integrate transgenes into the genome of both dividing and nondividing cells. Detailed herein is a simple protocol for the production LV vectors, describing the triple transfection of an LV transfer vector and LV helper plasmids into HEK-293 cells, and the subsequent purification of virions from the cellular media. The current protocol is versatile, and can be easily modified to fit the specific needs of the researcher in order to produce relatively high-titer LV vectors which can be used to transduce a wide variety of cells both in vitro and in vivo.

Interleukin-13 immune gene therapy prevents CNS inflammation and demyelination via alternative activation of microglia and macrophages

Detrimental inflammatory responses in the central nervous system are a hallmark of various brain injuries and diseases. With this study we provide evidence that lentiviral vector-mediated expression of the immune-modulating cytokine interleukin 13 (IL-13) induces an alternative activation program in both microglia and macrophages conferring protection against severe oligodendrocyte loss and demyelination in the cuprizone mouse model for multiple sclerosis (MS). First, IL-13 mediated modulation of cuprizone induced lesions was monitored using T₂ -weighted magnetic resonance imaging and magnetization transfer imaging, and further correlated with quantitative histological analyses for inflammatory cell influx, oligodendrocyte death, and demyelination. Second, following IL-13 immune gene therapy in cuprizone-treated eGFP⁺ bone marrow chimeric mice, we provide evidence that IL-13 directs the polarization of both brain-resident microglia and infiltrating macrophages towards an alternatively activated phenotype, thereby promoting the conversion of a pro-inflammatory environment toward an anti-inflammatory environment, as further evidenced by gene expression analyses. Finally, we show that IL-13 immune gene therapy is also able to limit lesion severity in a pre-existing inflammatory environment. In conclusion, these results highlight the potential of IL-13 to modulate microglia/macrophage responses and to improve disease outcome in a mouse model for MS. GLIA 2016;64:2181-2200.

Rev-RRE Functional Activity Differs Substantially Among Primary HIV-1 Isolates

The HIV-1 replication cycle requires the nucleocytoplasmic export of intron-containing viral RNAs, a process that is ordinarily restricted. HIV overcomes this by means of the viral Rev protein, which binds to an RNA secondary structure called the Rev response element (RRE) present in all unspliced or incompletely spliced viral RNA transcripts. The resulting mRNP complex is exported through interaction with cellular factors. The Rev-RRE binding interaction is increasingly understood to display remarkable structural plasticity, but little is known about how Rev-RRE sequence differences affect functional activity. To study this issue, we utilized a lentiviral vector assay in which vector titer is dependent on the activity of selected Rev-RRE pairs. We found that Rev-RRE functional activity varies significantly (up to 24-fold) between naturally occurring viral isolates. The activity differences of the Rev-RRE cognate pairs track closely with Rev, but not with RRE activity. This variation in Rev activity is not correlated with differences in Rev steady state protein levels. These data suggest that Rev sequence differences drive substantial variation in Rev-RRE functional activity between patients. Such variation may play a role in viral adaptation to different immune milieus within and between patients and may be significant in the establishment of latency. The identification of differences in Rev-RRE functional activity in naturally occurring isolates may also permit more efficient production of lentiviral vectors.

rAAV-CFTRΔR Rescues the Cystic Fibrosis Phenotype in Human Intestinal Organoids and Cystic Fibrosis Mice

RATIONALE

Gene therapy holds promise for a curative mutation-independent treatment applicable to all patients with cystic fibrosis (CF). The various viral vector-based clinical trials conducted in the past have demonstrated safety and tolerance of different vectors, but none have led to a clear and persistent clinical benefit. Recent clinical breakthroughs in recombinant adeno-associated viral vector (rAAV)-based gene therapy encouraged us to reexplore an rAAV approach for CF.

OBJECTIVES

We evaluated the preclinical potential of rAAV gene therapy for CF to restore chloride and fluid secretion in two complementary models: intestinal organoids derived from subjects with CF and a CF mouse model, an important milestone toward the development of a clinical rAAV candidate for CF gene therapy.

METHODS

We engineered an rAAV vector containing a truncated CF transmembrane conductance regulator (CFTRΔR) combined with a short promoter (CMV173) to ensure optimal gene expression. A rescue in chloride and fluid secretion after rAAV-CFTRΔR treatment was assessed by forskolin-induced swelling in CF transmembrane conductance regulator (CFTR)-deficient organoids and by nasal potential differences in ΔF508 mice.

MEASUREMENTS AND MAIN RESULTS

rAAV-CFTRΔR transduction of human CFTR-deficient organoids resulted in forskolin-induced swelling, indicating a restoration of CFTR function. Nasal potential differences demonstrated a clear response to low chloride and forskolin perfusion in most rAAV-CFTRΔR-treated CF mice.

CONCLUSIONS

Our study provides robust evidence that rAAV-mediated gene transfer of a truncated CFTR functionally rescues the CF phenotype across the nasal mucosa of CF mice and in patient-derived organoids. These results underscore the clinical potential of rAAV-CFTRΔR in offering a cure for all patients with CF in the future.

Progress and challenges in viral vector manufacturing

Promising results in several clinical studies have emphasized the potential of gene therapy to address important medical needs and initiated a surge of investments in drug development and commercialization. This enthusiasm is driven by positive data in clinical trials including gene replacement for Hemophilia B, X-linked Severe Combined Immunodeficiency, Leber's Congenital Amaurosis Type 2 and in cancer immunotherapy trials for hematological malignancies using chimeric antigen receptor T cells. These results build on the recent licensure of the European gene therapy product Glybera for the treatment of lipoprotein lipase deficiency. The progress from clinical development towards product licensure of several programs presents challenges to gene therapy product manufacturing. These include challenges in viral vector-manufacturing capacity, where an estimated 1-2 orders of magnitude increase will likely be needed to support eventual commercial supply requirements for many of the promising disease indications. In addition, the expanding potential commercial product pipeline and the continuously advancing development of recombinant viral vectors for gene therapy require that products are well characterized and consistently manufactured to rigorous tolerances of purity, potency and safety. Finally, there is an increase in regulatory scrutiny that affects manufacturers of investigational drugs for early-phase clinical trials engaged in industry partnerships. Along with the recent increase in biopharmaceutical funding in gene therapy, industry partners are requiring their academic counterparts to meet higher levels of GMP compliance at earlier stages of clinical development. This chapter provides a brief overview of current progress in the field and discusses challenges in vector manufacturing.

Production of lentiviral vectors

Lentiviral vectors (LV) have seen considerably increase in use as gene therapy vectors for the treatment of acquired and inherited diseases. This review presents the state of the art of the production of these vectors with particular emphasis on their large-scale production for clinical purposes. In contrast to oncoretroviral vectors, which are produced using stable producer cell lines, clinical-grade LV are in most of the cases produced by transient transfection of 293 or 293T cells grown in cell factories. However, more recent developments, also, tend to use hollow fiber reactor, suspension culture processes, and the implementation of stable producer cell lines. As is customary for the biotech industry, rather sophisticated downstream processing protocols have been established to remove any undesirable process-derived contaminant, such as plasmid or host cell DNA or host cell proteins. This review compares published large-scale production and purification processes of LV and presents their process performances. Furthermore, developments in the domain of stable cell lines and their way to the use of production vehicles of clinical material will be presented.

In Vivo Interleukin-13-Primed Macrophages Contribute to Reduced Alloantigen-Specific T Cell Activation and Prolong Immunological Survival of Allogeneic Mesenchymal Stem Cell Implants

Transplantation of mesenchymal stem cells (MSCs) into injured or diseased tissue-for the in situ delivery of a wide variety of MSC-secreted therapeutic proteins-is an emerging approach for the modulation of the clinical course of several diseases and traumata. From an emergency point-of-view, allogeneic MSCs have numerous advantages over patient-specific autologous MSCs since "off-the-shelf" cell preparations could be readily available for instant therapeutic intervention following acute injury. Although we confirmed the in vitro immunomodulatory capacity of allogeneic MSCs on antigen-presenting cells with standard coculture experiments, allogeneic MSC grafts were irrevocably rejected by the host's immune system upon either intramuscular or intracerebral transplantation. In an attempt to modulate MSC allograft rejection in vivo, we transduced MSCs with an interleukin-13 (IL13)-expressing lentiviral vector. Our data clearly indicate that prolonged survival of IL13-expressing allogeneic MSC grafts in muscle tissue coincided with the induction of an alternatively activated macrophage phenotype in vivo and a reduced number of alloantigen-reactive IFNγ- and/or IL2-producing CD8(+) T cells compared to nonmodified allografts. Similarly, intracerebral IL13-expressing MSC allografts also exhibited prolonged survival and induction of an alternatively activated macrophage phenotype, although a peripheral T cell component was absent. In summary, this study demonstrates that both innate and adaptive immune responses are effectively modulated in vivo by locally secreted IL13, ultimately resulting in prolonged MSC allograft survival in both muscle and brain tissue. Stem Cells 2016;34:1971-1984.

High-content analysis of α-synuclein aggregation and cell death in a cellular model of Parkinson's disease

BACKGROUND

Alpha-synuclein (α-SYN) aggregates represent a key feature of Parkinson's disease, but the exact relationship between α-SYN aggregation and neurodegeneration remains incompletely understood. Therefore, the availability of a cellular assay that allows medium-throughput analysis of α-SYN-linked pathology will be of great value for studying the aggregation process and for advancing α-SYN-based therapies.

NEW METHOD

Here we describe a high-content neuronal cell assay that simultaneously measures oxidative stress-induced α-SYN aggregation and apoptosis.

RESULTS

We optimized an automated and reproducible assay to quantify both α-SYN aggregation and cell death in human SH-SY5Y neuroblastoma cells.

COMPARISON WITH EXISTING METHODS

Quantification of α-SYN aggregates in cells has typically relied on manual imaging and counting or cell-free assays, which are time consuming and do not allow a concurrent analysis of cell viability. Our high-content analysis method for quantification of α-SYN aggregation allows simultaneous measurements of multiple cell parameters at a single-cell level in a fast, objective and automated manner.

CONCLUSIONS

The presented analysis approach offers a rapid, objective and multiparametric approach for the screening of compounds and genes that might alter α-SYN aggregation and/or toxicity.

Chloride-hydrogen antiporters ClC-3 and ClC-5 drive osteoblast mineralization and regulate fine-structure bone patterning in vitro

Osteoblasts form an epithelium-like layer with tight junctions separating bone matrix from extracellular fluid. During mineral deposition, calcium and phosphate precipitation in hydroxyapatite liberates 0.8 mole of H⁺ per mole Ca⁺². Thus, acid export is needed for mineral formation. We examined ion transport supporting osteoblast vectorial mineral deposition. Previously we established that Na/H exchangers 1 and 6 are highly expressed at secretory osteoblast basolateral surfaces and neutralize massive acid loads. The Na/H exchanger regulatory factor-1 (NHERF1), a pdz-organizing protein, occurs at mineralizing osteoblast basolateral surfaces. We hypothesized that high-capacity proton transport from matrix into osteoblast cytosol must exist to support acid transcytosis for mineral deposition. Gene screening in mineralizing osteoblasts showed dramatic expression of chloride–proton antiporters ClC-3 and ClC-5. Antibody localization showed that ClC-3 and ClC-5 occur at the apical secretory surface facing the bone matrix and in membranes of buried osteocytes. Surprisingly, the Clcn3^−/− mouse has only mildly disordered mineralization. However, Clcn3^−/− osteoblasts have large compensatory increases in ClC-5 expression. Clcn3^−/− osteoblasts mineralize in vitro in a striking and novel trabecular pattern; wild-type osteoblasts form bone nodules. In mesenchymal stem cells from Clcn3^−/− mice, lentiviral ClC-5 shRNA created Clcn3^−/−, ClC-5 knockdown cells, validated by western blot and PCR. Osteoblasts from these cells produced no mineral under conditions where wild-type or Clcn3^−/− cells mineralize well. We conclude that regulated acid export, mediated by chloride–proton exchange, is essential to drive normal bone mineralization, and that CLC transporters also regulate fine patterning of bone.

Long-Term Fate Mapping Using Conditional Lentiviral Vectors Reveals a Continuous Contribution of Radial Glia-Like Cells to Adult Hippocampal Neurogenesis in Mice

Newborn neurons are generated throughout life in two neurogenic regions, the subventricular zone and the hippocampal dentate gyrus. Stimulation of adult neurogenesis is considered as an attractive endogenous repair mechanism to treat different neurological disorders. Although tremendous progress has been made in our understanding of adult hippocampal neurogenesis, important questions remain unanswered, regarding the identity and the behavior of neural stem cells in the dentate gyrus. We previously showed that conditional Cre-Flex lentiviral vectors can be used to label neural stem cells in the subventricular zone and to track the migration of their progeny with non-invasive bioluminescence imaging. Here, we applied these Cre-Flex lentiviral vectors to study neurogenesis in the dentate gyrus with bioluminescence imaging and histological techniques. Stereotactic injection of the Cre-Flex vectors into the dentate gyrus of transgenic Nestin-Cre mice resulted in specific labeling of the nestin-positive neural stem cells. The labeled cell population could be detected with bioluminescence imaging until 9 months post injection, but no significant increase in the number of labeled cells over time was observed with this imaging technique. Nevertheless, the specific labeling of the nestin-positive neural stem cells, combined with histological analysis at different time points, allowed detailed analysis of their neurogenic potential. This long-term fate mapping revealed that a stable pool of labeled nestin-positive neural stem cells continuously contributes to the generation of newborn neurons in the mouse brain until 9 months post injection. In conclusion, the Cre-Flex technology is a valuable tool to address remaining questions regarding neural stem cell identity and behavior in the dentate gyrus.

Chemical genetic approach identifies microtubule affinity-regulating kinase 1 as a leucine-rich repeat kinase 2 substrate

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of autosomal-dominant forms of Parkinson's disease. LRRK2 is a modular, multidomain protein containing 2 enzymatic domains, including a kinase domain, as well as several protein-protein interaction domains, pointing to a role in cellular signaling. Although enormous efforts have been made, the exact pathophysiologic mechanisms of LRRK2 are still not completely known. In this study, we used a chemical genetics approach to identify LRRK2 substrates from mouse brain. This approach allows the identification of substrates of 1 particular kinase in a complex cellular environment. Several of the identified peptides are involved in the regulation of microtubule (MT) dynamics, including microtubule-associating protein (MAP)/microtubule affinity-regulating kinase 1 (MARK1). MARK1 is a serine/threonine kinase known to phosphorylate MT-binding proteins such as Tau, MAP2, and MAP4 at KXGS motifs leading to MT destabilization. In vitro kinase assays and metabolic-labeling experiments in living cells confirmed MARK1 as an LRRK2 substrate. Moreover, we also showed that LRRK2 and MARK1 are interacting in eukaryotic cells. Our findings contribute to the identification of physiologic LRRK2 substrates and point to a potential mechanism explaining the reported effects of LRRK2 on neurite morphology.