Comparison of transfection conditions for a lentivirus vector produced in large volumes

Effects of an indole derivative on cell proliferation, transfection, and alternative splicing in production of lentiviral vectors by transient co-transfection

Lentiviral vectors derived from human immunodeficiency virus type I are widely used to deliver functional gene copies to mammalian cells for research and gene therapies. Post-transcriptional splicing of lentiviral vector transgene in transduced host and transfected producer cells presents barriers to widespread application of lentiviral vector-based therapies. The present study examined effects of indole derivative compound IDC16 on splicing of lentiviral vector transcripts in producer cells and corresponding yield of infectious lentiviral vectors. Indole IDC16 was shown previously to modify alternative splicing in human immunodeficiency virus type I. Human embryonic kidney 293T cells were transiently transfected by 3rd generation backbone and packaging plasmids using polyethyleneimine. Reverse transcription-quantitative polymerase chain reaction of the fraction of unspliced genomes in human embryonic kidney 293T cells increased up to 31% upon the indole's treatment at 2.5 uM. Corresponding yield of infectious lentiviral vectors decreased up to 4.5-fold in a cell transduction assay. Adjusting timing and duration of IDC16 treatment indicated that the indole's disruption of early stages of transfection and cell cycle had a greater effect on exponential time course of lentiviral vector production than its reduction of post-transcriptional splicing. Decrease in transfected human embryonic kidney 293T proliferation by IDC16 became significant at 10 uM. These findings indicated contributions by early-stage transfection, cell proliferation, and post-transcriptional splicing in transient transfection of human embryonic kidney 293T cells for lentiviral vector production.

Optimizing and developing a scalable, chemically defined, animal component-free lentiviral vector production process in a fixed-bed bioreactor

Lentiviral vectors (LVVs) play a critical role in gene delivery for ex vivo gene-modified cell therapies. However, the lack of scalable LVV production methods and the high cost associated with them may limit their use. In this work, we demonstrate the optimization and development of a scalable, chemically defined, animal component-free LVV production process using adherent human embryonic kidney 293T cells in a fixed-bed bioreactor. The initial studies focused on the optimization of the culture process in 2D static cultures. Process changes such as decreasing cell seeding density on day 0 from 2.5 × 10⁴ to 5 × 10³ cells/cm², delaying the transient transfection from 24 to 120 h post-seeding, reducing plasmid DNA to 167 ng/cm², and adding 5 mM sodium butyrate 6 h post-transfection improved functional LVV titers by 26.9-fold. The optimized animal component-free production process was then transferred to the iCELLis Nano bioreactor, a fixed-bed bioreactor, where titers of 1.2 × 10⁶ TU/cm² were achieved when it was operated in perfusion. In this work, comparable functional LVV titers were obtained with FreeStyle 293 Expression medium and the conventional Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum both at small and large scale.

The ice age - A review on formulation of Adeno-associated virus therapeutics

Gene therapies offer promising therapeutic alternatives for many disorders that currently lack efficient treatment options. Due to their chemical nature and physico-chemical properties, delivery of polynucleic acids into target cells and subcellular compartments remains a significant challenge. Adeno-associated viruses (AAV) have gained a lot of interest for the efficient delivery of therapeutic single-stranded DNA (ssDNA) genomes over the past decades. More than a hundred products have been tested in clinical settings and three products have received market authorization by the US FDA in recent years. A lot of effort is being made to generate potent recombinant AAV (rAAV) vectors that show favorable safety and immunogenicity profiles for either local or systemic administration. Manufacturing processes are gradually being optimized to deliver a consistently high product quality and to serve potential market needs beyond rare indications. In contrast to protein therapeutics, most rAAV products are still supplied as frozen liquids within rather simple formulation buffers to enable sufficient product shelf life, significantly hampering global distribution and access. In this review, we aim to outline the hurdles of rAAV drug product development and discuss critical formulation and composition aspects of rAAV products under clinical evaluation. Further, we highlight recent development efforts in order to achieve stable liquid or lyophilized products. This review therefore provides a comprehensive overview on current state-of-the-art rAAV formulations and can further serve as a map for rational formulation development activities in the future.

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

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

Supplementary Information

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

Optimized protocol for high-titer lentivirus production and transduction of primary fibroblasts

The lentivirus-short hairpin RNA (shRNA) system is a widely used tool for RNA interference. Multiple factors may affect the RNA interference efficiency during lentivirus production and transduction procedures. Thus, an optimized protocol is required to achieve high-titer lentivirus and efficient gene delivery. In the present study, lentivirus was produced by transfecting lentiviral transfer and packaging plasmids into HEK 293T cells. The factors affecting lentiviral titer were assessed, including lentiviral plasmid ratio, lentiviral transfer plasmid type, serum type for cell culture, transfection reagent-plasmid mixture incubation time, and the inoculation density of 293T cells for transfection. The high-titer lentivirus was achieved when plasmids were transfected at a molar ratio of 1:1:1:2, and the transfection reagent-plasmid mixture was replaced 6-8 h after transfection. The pLVX-shRNA2 lentiviral transfer plasmid was associated with the highest lentiviral titer, while both pLVX-shRNA2 and psi-LVRU6GP plasmids were associated with efficient RNA interference in target cells. The serum type for 293T cell culture affected the lentiviral titer significantly, while the inoculation density of 293T cells showed no influence on transfection efficiency or lentiviral titer. Moreover, the human primary fibroblasts infected with lentivirus, using the centrifugation method, achieved higher transduction efficiency than those infected with the non-centrifugation method. In conclusion, this study helped optimize lentiviral production and transduction procedures for more efficient gene delivery.

Optimized Transgene Delivery Using Third-Generation Lentiviruses

The lentivirus system enables efficient genetic modification of both dividing and non-dividing cells and therefore is a useful tool for elucidating developmental processes and disease pathogenesis. The development of third-generation lentiviruses has resulted in improved biosafety, low immunogenicity, and substantial packaging capabilities. However, because third-generation lentiviruses require successful co-transfection with four plasmids, this typically means that lower titers are attained. This is problematic, as it is often desirable to produce purified lentiviruses with high titers (>1 × 108 TU/ml), especially for in vivo applications. The manufacturing process for lentiviruses involves several critical experimental factors that can influence titer, purity, and transduction efficiency. Here, we describe a straightforward, stepwise protocol for the reproducible manufacture of high-titer third-generation lentiviruses (1 × 108 to 1 × 109 TU/ml). This optimized protocol enhances transgene expression by use of Lipofectamine transfection and optimized serum replacement medium, a single ultracentrifugation step, use of a sucrose cushion, and addition of a histone deacetylation inhibitor. Furthermore, we provide alternate methods for titration analyses, including functional and genomic integration analyses, using common laboratory techniques such as FACS as well as genomic DNA extraction and qPCR. These optimized methods will be beneficial for investigating developmental processes and disease pathogenesis in vitro and in vivo. © 2020 The Authors. Basic Protocol 1: Lentivirus production Support Protocol: Lentivirus concentration Basic Protocol 2: Lentivirus titration Alternate Protocol 1: Determination of viral titration by FACS analysis Alternate Protocol 2: Determination of viral titration by genome integration analysis.

Laboratory-Scale Lentiviral Vector Production and Purification for Enhanced Ex Vivo and In Vivo Genetic Engineering

Lentiviral vectors (LVs) are increasingly employed in gene and cell therapy. Standard laboratory production of LVs is not easily scalable, and research-grade LVs often contain contaminants that can interfere with downstream applications. Moreover, purified LV production pipelines have been developed mainly for costly, large-scale, clinical-grade settings. Therefore, a standardized and cost-effective process is still needed to obtain efficient, reproducible, and properly executed experimental studies and preclinical development of ex vivo and in vivo gene therapies, as high infectivity and limited adverse reactions are important factors potentially influencing experimental outcomes also in preclinical settings. We describe here an optimized laboratory-scale workflow whereby an LV-containing supernatant is purified and concentrated by sequential chromatographic steps, obtaining biologically active LVs with an infectious titer and specific activity in the order of 10⁹ transducing unit (TU)/mL and 5 × 10⁴ TU/ng of HIV Gag p24, respectively. The purification workflow removes >99% of the starting plasmid, DNA, and protein impurities, resulting in higher gene transfer and editing efficiency in severe combined immunodeficiency (SCID)-repopulating hematopoietic stem and progenitor cells (HSPCs) ex vivo, as well as reduced activation of inflammatory responses ex vivo and in vivo as compared to TU-matched, laboratory-grade vectors. Our results highlight the value of accessible purified LV production for experimental studies and preclinical testing.

High-Titer Production of HIV-Based Lentiviral Vectors in Roller Bottles for Gene and Cell Therapy

Lentiviral vectors are becoming preferred vectors of choice for clinical gene therapy trials due to their safety, efficacy, and the long-term gene expression they provide. Although the efficacy of lentiviral vectors is mainly predetermined by the therapeutic genes they carry, they must be produced at high titers to exert therapeutic benefit for in vivo applications. Thus, there is need for practical, robust, and scalable viral vector production methods applicable to any laboratory setting. Here, we describe a practical lentiviral production technique in roller bottles yielding high-titer third-generation lentiviral vectors useful for in vivo gene transfer applications. CaPO₄-mediated transient transfection protocol involving the use of a transfer vector and three different packaging plasmids is employed to generate lentivectors in roller bottles. Following clearance of cellular debris via low-speed centrifugation and filtration, virus is concentrated by high-speed ultracentrifugation over sucrose cushion.

Optimization of lentiviral vector production for scale-up in fixed-bed bioreactor

Lentiviral vectors (LVs) are promising tools for gene therapy. However, scaling up the production methods of LVs in order to produce high-quality vectors for clinical purposes has proven to be difficult. In this article, we present a scalable and efficient method to produce LVs with transient transfection of adherent 293T cells in a fixed-bed bioreactor. The disposable iCELLis bioreactors are scalable with a large three-dimensional (3D) growth area range between 0.53 and 500 m², an integrated perfusion system, and a controllable environment for production. In this study, iCELLis Nano (2.67–4 m²) was used for optimizing production parameters for scale-up. Transfections were first done using traditional calcium phosphate method, but in later runs polyethylenimine was found to be more reliable and easier to use. For scalable LV production, perfusion rate control by measuring cell metabolite concentrations in the bioreactor leads to higher productivity and reduced costs. Optimization of cell seeding density for targeted cell concentration during transfection, use of low compaction fixed-bed and lowering the culture pH have a positive effect on LV productivity. These results show for the first time that iCELLis bioreactor is scalable from bench level to clinical scale LV production.

Assessment of selected media supplements to improve F/HN lentiviral vector production yields

The development of lentiviral-based therapeutics is challenged by the high cost of current Good Manufacturing Practices (cGMP) production. Lentiviruses are enveloped viruses that capture a portion of the host cell membrane during budding, which then constitutes part of the virus particle. This process might lead to lipid and protein depletion in the cell membrane and affect cell viability. Furthermore, growth in suspension also causes stresses that can affect virus production yields. To assess the impact of these issues, selected supplements (Cholesterol Lipid Concentrate, Chemically Defined Lipid Concentrate, Lipid Mixture 1, Gelatin Peptone N3, N-Acetyl-L-Cysteine and Pluronic F-68) were assayed in order to improve production yields in a transient transfection production of a Sendai virus F/HN-pseudotyped HIV-1-based third generation lentiviral vector in FreeStyle 293 (serum-free media) in suspension. None of the supplements tested had a significant positive impact on lentiviral vector yields, but small non-significant improvements could be combined to increase vector production in a cell line where other conditions have been optimised.

ErbB2 regulates autophagic flux to modulate the proteostasis of APP-CTFs in Alzheimer's disease

Proteolytic processing of amyloid precursor protein (APP) C-terminal fragments (CTFs) by γ-secretase underlies the pathogenesis of Alzheimer's disease (AD). An RNA interference screen using APP-CTF [99-residue CTF (C99)]- and Notch-specific γ-secretase interaction assays identified a unique ErbB2-centered signaling network that was predicted to preferentially govern the proteostasis of APP-C99. Consistently, significantly elevated levels of ErbB2 were confirmed in the hippocampus of human AD brains. We then found that ErbB2 effectively suppressed autophagic flux by physically dissociating Beclin-1 from the Vps34-Vps15 complex independent of its kinase activity. Down-regulation of ErbB2 by CL-387,785 decreased the levels of C99 and secreted amyloid-β in cellular, zebrafish, and mouse models of AD, through the activation of autophagy. Oral administration of an ErbB2-targeted CL-387,785 for 3 wk significantly improves the cognitive functions of APP/presenilin-1 (PS1) transgenic mice. This work unveils a noncanonical function of ErbB2 in modulating autophagy and establishes ErbB2 as a therapeutic target for AD.

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.

Production of adeno-associated virus (AAV) serotypes by transient transfection of HEK293 cell suspension cultures for gene delivery

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Transient transfection of HEK293 suspension cells efficiently produce AAV vectors.

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Nine different AAV serotypes were produced with yields of 1E+13 Vg/L.

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AAV2 and AAV6 produced in 3-L bioreactors gave yields comparable to shake-flasks.

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The process is cGMP compatible using serum-free media and HEK293 master cell bank.

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Industrialization of the process is possible for manufacturing AAV serotypes.

Adeno-associated virus (AAV) is being used successfully in gene therapy. Different serotypes of AAV target specific organs and tissues with high efficiency. There exists an increasing demand to manufacture various AAV serotypes in large quantities for pre-clinical and clinical trials. A generic and scalable method has been described in this study to efficiently produce AAV serotypes (AAV1-9) by transfection of a fully characterized cGMP HEK293SF cell line grown in suspension and serum-free medium. First, the production parameters were evaluated using AAV2 as a model serotype. Second, all nine AAV serotypes were produced successfully with yields of 10¹³ Vg/L cell culture. Subsequently, AAV2 and AAV6 serotypes were produced in 3-L controlled bioreactors where productions yielded up to 10¹³ Vg/L similar to the yields obtained in shake-flasks. For example, for AAV2 10¹³ Vg/L cell culture (6.8 × 10¹¹ IVP/L) were measured between 48 and 64 h post transfection (hpt). During this period, the average cell specific AAV2 yields of 6800 Vg per cell and 460 IVP per cell were obtained with a Vg to IVP ratio of less than 20. Successful operations in bioreactors demonstrated the potential for scale-up and industrialization of this generic process for manufacturing AAV serotypes efficiently.

Ligand-dependent activation of EphA4 signaling regulates the proteolysis of amyloid precursor protein through a Lyn-mediated pathway

Alzheimer's disease is the most common dementia afflicting the elderly in modern society. This disease arises from the neurotoxicity elicited by abnormal aggregates of amyloid-β (Aβ) protein. Such aggregates form through the cleavage of amyloid precursor protein (APP) by β-secretase and the subsequent proteolysis of the APP C-terminal fragment (APP-βCTF or C99) by γ-secretase to yield Aβ and APP intracellular domain (AICD). Recent evidence suggests that C99 and AICD may exert harmful effects on cells, suggesting that the proteolytic products of APP, including Aβ, C99, and AICD, could play a pivotal role in neuronal viability. Here, we demonstrate that ligand-activated EphA4 signaling governs the proteostasis of C99, AICD, and Aβ, without significantly affecting γ-secretase activity. EphA4 induced accumulation of C99 and AICD through a Lyn-dependent pathway; activation of this pathway triggered phosphorylation of EphA4, resulting in positive feedback of C99 and AICD proteostasis. Inhibition of EphA4 by dasatinib, a receptor tyrosine kinase inhibitor, effectively suppressed C99 and AICD accumulation. Furthermore, EphA4 signaling controlled C99 and AICD proteolysis through the ubiquitin-proteasome system. In conclusion, we have identified an EphA4-Lyn pathway that is essential for the metabolism of APP and its proteolytic derivatives, thereby providing novel pharmacological targets for the development of anti-Aβ therapeutics for AD.

New developments in lentiviral vector design, production and purification

INTRODUCTION

Lentiviruses are a very potent class of viral vectors for which there is presently a rapidly growing interest for a number of gene therapy. However, their construction, production and purification need to be performed according to state-of-the-art techniques in order to obtain sufficient quantities of high purity material of any usefulness and safety.

AREAS COVERED

The recent advances in the field of recombinant lentivirus vector design, production and purification will be reviewed with an eye toward its utilization for gene therapy. Such a review should be helpful for the potential user of this technology.

EXPERT OPINION

The principal hurdles toward the use of recombinant lentivirus as a gene therapy vector are the low titer at which it is produced as well as the difficulty to purify it at an acceptable level without degrading it. The recent advances in the bioproduction of this vector suggest these issues are about to be resolved, making the retrovirus gene therapy a mature technology.

Rab38 modulates proteinuria in model of hypertension-associated renal disease

We previously reported that the fawn-hooded hypertensive (FHH) rat is a natural Rab38 knockout, supported by a congenic animal (FHH.BN-Rab38) having less proteinuria than FHH animals. Because these congenic animals contain Brown Norway (BN) alleles for five other named genes; however, a causal role for Rab38 in the FHH phenotype remains uncertain. Here, we used transgenic and knockout models to validate Rab38 and to exclude other genes within the 1.5 Mb congenic region from involvement in causing the FHH phenotype. Transgenic rats homozygous for the wild-type Rab38 BN allele on the FHH background exhibited phenotypic rescue, having 43% lower proteinuria and 75% lower albuminuria than nontransgenic FHH littermates. Conversely, knockout of the Rab38 gene on the FHH.BN-Rab38 congenic line recapitulated a proteinuric phenotype indistinguishable from the FHH strain. In addition, in cultured proximal tubule LLC-PK1 cells, knockdown of Rab38 mRNA significantly decreased endocytosis of colloidal gold-coupled albumin, supporting the hypothesis that Rab38 modulates proteinuria through effects on tubular re-uptake and not by altering glomerular permeability. Taken together, these findings validate Rab38 as a gene having a causal role in determining the phenotype of the FHH rat, which models hypertension-associated renal disease. Furthermore, our data suggest that Rab38 affects urinary protein excretion via effects in the proximal tubule.

Expression and function of heme oxygenase-1 in human gastric cancer

Heme oxygenase-1 (HO-1) potently influences tumor growth and metastasis. To date, no study has been performed on HO-1 expression pattern and its clinicopathological significance in human gastric cancer (GC) cases. In this study, the expression of HO-1 in human GC tissues (n = 74) and matched non-tumoral adjacent parenchyma (n = 46) was investigated by immunohistochemistry. The correlation of HO-1 with the clinicopathological characteristics was analyzed. Results showed that HO-1 was expressed in 62 GC tissues from 74 cases (83.8%), which is significantly higher than non-tumoral adjacent parenchyma (20/46, 43.8%, P < 0.05). A high HO-1 expression rate showed a close association with well/moderate histological differentiation and negative lymph node metastasis (P < 0.05). The expression of matrix metallopeptidase 9 (MMP9) and vascular endothelial growth factor A (VEGF-A) as well as chemosensitivity to cisplatin of MKN-45 cell lines with genetically altered HO-1 status were then determined by realtime polymerase chain reaction and 3-(4,5 dimethyl thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), respectively. Whether the induction or inhibition of HO-1 by cobalt-protoporphyrin-IX (CoPP) or zinc-protoporphyrin-IX (ZnPP) could affect the sensitivity of MKN-45 cells to cisplatin was also studied. Results showed that the expression of MMP9 and VEGF-A were up-regulated in MKN-45 cells overexpressing HO-1, and down-regulated in HO-1 interfered cells. HO-1 overexpression could lead to an increased resistance to cisplatin, whereas down-regulation of HO-1 expression by siRNA or chemical inhibition of HO-1 could lead to increased chemosensitivity to cisplatin in MKN-45 cells. HO-1 may have multiple effects on protection against carcinogenesis and progression in GC.

Efficient large volume lentiviral vector production using flow electroporation

Lentiviral vectors are beginning to emerge as a viable choice for human gene therapy. Here, we describe a method that combines the convenience of a suspension cell line with a scalable, nonchemically based, and GMP-compliant transfection technique known as flow electroporation (EP). Flow EP parameters for serum-free adapted HEK293FT cells were optimized to limit toxicity and maximize titers. Using a third generation, HIV-based, lentiviral vector system pseudotyped with the vesicular stomatitis glycoprotein envelope, both small- and large-volume transfections produced titers over 1×10(8) infectious units/mL. Therefore, an excellent option for implementing large-scale, clinical lentiviral productions is flow EP of suspension cell lines.

Scale-up and manufacturing of clinical-grade self-inactivating γ-retroviral vectors by transient transfection

The need for γ-retroviral (gRV) vectors with a self-inactivating (SIN) design for clinical application has prompted a shift in methodology of vector manufacturing from the traditional use of stable producer lines to transient transfection-based techniques. Herein, we set out to define and optimize a scalable manufacturing process for the production of gRV vectors using transfection in a closed-system bioreactor in compliance with current good manufacturing practices (cGMP). The process was based on transient transfection of 293T cells on Fibra-Cel disks in the Wave Bioreactor. Cells were harvested from tissue culture flasks and transferred to the bioreactor containing Fibra-Cel in the presence of vector plasmid, packaging plasmids and calcium-phosphate in Dulbecco's modified Eagle's medium and 10% fetal bovine serum. Virus supernatant was harvested at 10-14 h intervals. Using optimized procedures, a total of five ecotropic cGMP-grade gRV vectors were produced (9 liters each) with titers up to 3.6 × 10(7) infectious units per milliliter on 3T3 cells. One GMP preparation of vector-like particles was also produced. These results describe an optimized process for the generation of SIN viral vectors by transfection using a disposable platform that allows for the generation of clinical-grade viral vectors without the need for cleaning validation in a cost-effective manner.

Production of influenza pseudotyped lentiviral particles and their use in influenza research and diagnosis: an update

Pseudotyped viral particles are being used as safe surrogates to mimic the structure and surface of many viruses, including highly pathogenic viruses such as avian influenza H5N1, to investigate biological functions mediated by the envelope proteins derived from these viruses. The first part of this article evaluates and discusses the differences in the production and characterization of influenza pseudoparticles. The second part focuses on the applications that such a flexible tool can provide in modern influenza research, in particular in the fields of drug discovery, molecular biology and diagnosis.

The base excision repair pathway is required for efficient lentivirus integration

An siRNA screen has identified several proteins throughout the base excision repair (BER) pathway of oxidative DNA damage as important for efficient HIV infection. The proteins identified included early repair factors such as the base damage recognition glycosylases OGG1 and MYH and the late repair factor POLß, implicating the entire BER pathway. Murine cells with deletions of the genes Ogg1, Myh, Neil1 and Polß recapitulate the defect of HIV infection in the absence of BER. Defective infection in the absence of BER proteins was also seen with the lentivirus FIV, but not the gammaretrovirus MMLV. BER proteins do not affect HIV infection through its accessory genes nor the central polypurine tract. HIV reverse transcription and nuclear entry appear unaffected by the absence of BER proteins. However, HIV integration to the host chromosome is reduced in the absence of BER proteins. Pre-integration complexes from BER deficient cell lines show reduced integration activity in vitro. Integration activity is restored by addition of recombinant BER protein POLß. Lentiviral infection and integration efficiency appears to depend on the presence of BER proteins.

Effect of increased HoxB4 on human megakaryocytic development

In order to produce clinically useful quantities of platelets ex vivo we may need to firstly enhance early self-renewal of hematopoietic stem cells (HSCs) and/or megakaryocyte (Mk) progenitors. The homeodomain transcription factor HoxB4 has been shown to be an important regulator of stem cell renewal and hematopoiesis; however, its effect on megakaryopoiesis is unclear. In this study, we investigated the effect of HoxB4 overexpression or RNA silencing on megakaryocytic development in the human TF1 progenitor cell line; we then used recombinant tPTD-HoxB4 fusion protein to study the effect of exogenous HoxB4 on megakaryocytic development of human CD34 positively-selected cord blood cells. We found that ectopic HoxB4 in TF1 cells increased the antigen expression of CD61and CD41a, increased the gene expression of thrombopoietin receptor (TpoR), Scl-1, Cyclin D1, Fog-1 and Fli-1 while it decreased c-Myb expression. HoxB4 RNA silencing in TF1 cells decreased the expression of CD61 and CD41a and decreased Fli-1 expression while it increased the expression of c-Myb. Recombinant tPTD-HoxB4 fusion protein increased the percentages and absolute numbers of CD41a and CD61 positive cells during megakaryocytic differentiation of CD34 positively-selected cord blood cells and increased the numbers of colony-forming unit-megakaryocyte (CFU-Mk). Adding tPTD-HoxB4 fusion protein increased the gene expression of TpoR, Cyclin D1, Fog-1 and Fli-1 while it inhibited c-Myb expression. Our data suggest that increased HoxB4 enhanced early megakaryocytic development in human TF1 cells and CD34 positively-selected cord blood cells primarily by upregulating TpoR and Fli-1 expression and downregulating c-Myb expression. Increasing HoxB4 expression or adding recombinant HoxB4 protein might be a way to expand Mks for the production of platelets for use in transfusion medicine.

Development of a scalable process for high-yield lentiviral vector production by transient transfection of HEK293 suspension cultures

BACKGROUND

Lentiviral vectors (LV) offer several advantages over other gene delivery vectors. Their potential for the integration and long-term expression of therapeutic genes renders them an interesting tool for gene and cell therapy interventions. However, large-scale LV production remains an important challenge for the translation of LV-based therapeutic strategies to the clinic. The development of robust processes for mass production of LV is needed.

METHODS

A suspension-grown HEK293 cell line was exploited for the production of green fluorescent protein-expressing LV by transient polyethylenimine (PEI)-based transfection with LV-encoding plasmid constructs. Using third-generation packaging plasmids (Gag/Pol, Rev), a vesicular stomatitis virus G envelope and a self-inactivating transfer vector, we employed strategies to increase volumetric and specific productivity. Functional LV titers were determined using a flow cytometry-based gene transfer assay.

RESULTS

A combination of the most promising conditions (increase in cell density, medium selection, reduction of PEI-DNA complexes per cell, addition of sodium butyrate) resulted in significantly increased LV titers of more than 150-fold compared to non-optimized small-scale conditions, reaching infectious titers of approximately 10(8) transducing units/ml. These conditions are readily scalable and were validated in 3-liter scale perfusion cultures.

CONCLUSIONS

Our process produces LV in suspension cultures and is consequently easily scalable, industrially viable and generated more than 10(11) total functional LV particles in a single bioreactor run. This process will allow the production of LV by transient transfection in sufficiently large quantities for phase I clinical trials at the 10-20-liter bioreactor scale.

The function of the intermediate compartment in pre-Golgi trafficking involves its stable connection with the centrosome

Because the functional borders of the intermediate compartment (IC) are not well defined, the spatial map of the transport machineries operating between the endoplasmic reticulum (ER) and the Golgi apparatus remains incomplete. Our previous studies showed that the IC consists of interconnected vacuolar and tubular parts with specific roles in pre-Golgi trafficking. Here, using live cell imaging, we demonstrate that the tubules containing the GTPase Rab1A create a long-lived membrane compartment around the centrosome. Separation of this pericentrosomal domain of the IC from the Golgi ribbon, due to centrosome motility, revealed that it contains a distinct pool of COPI coats and acts as a temperature-sensitive way station in post-ER trafficking. However, unlike the Golgi, the pericentrosomal IC resists the disassembly of COPI coats by brefeldin A, maintaining its juxtaposition with the endocytic recycling compartment, and operation as the focal point of a dynamic tubular network that extends to the cell periphery. These results provide novel insight into the compartmental organization of the secretory pathway and Golgi biogenesis. Moreover, they reveal a direct functional connection between the IC and the endosomal system, which evidently contributes to unconventional transport of the cystic fibrosis transmembrane conductance regulator to the cell surface.

Simplified production and concentration of HIV-1-based lentiviral vectors using HYPERFlask vessels and anion exchange membrane chromatography

Background

During the past twelve years, lentiviral (LV) vectors have emerged as valuable tools for transgene delivery because of their ability to transduce nondividing cells and their capacity to sustain long-term transgene expression in target cells in vitro and in vivo. However, despite significant progress, the production and concentration of high-titer, high-quality LV vector stocks is still cumbersome and costly.

Methods

Here we present a simplified protocol for LV vector production on a laboratory scale using HYPERFlask vessels. HYPERFlask vessels are high-yield, high-performance flasks that utilize a multilayered gas permeable growth surface for efficient gas exchange, allowing convenient production of high-titer LV vectors. For subsequent concentration of LV vector stocks produced in this way, we describe a facile protocol involving Mustang Q anion exchange membrane chromatography.

Results

Our results show that unconcentrated LV vector stocks with titers in excess of 10⁸ transduction units (TU) per ml were obtained using HYPERFlasks and that these titers were higher than those produced in parallel using regular 150-cm² tissue culture dishes. We also show that up to 500 ml of an unconcentrated LV vector stock prepared using a HYPERFlask vessel could be concentrated using a single Mustang Q Acrodisc with a membrane volume of 0.18 ml. Up to 5.3 × 10¹⁰ TU were recovered from a single HYPERFlask vessel.

Conclusion

The protocol described here is easy to implement and should facilitate high-titer LV vector production for preclinical studies in animal models without the need for multiple tissue culture dishes and ultracentrifugation-based concentration protocols.

An optimized lentivirus-mediated RNAi screen reveals kinase modulators of kinesin-5 inhibitor sensitivity

Abstract: Induction of RNA interference (RNAi) in human cells has enabled comprehensive functional annotation of the human genome via reverse genetic screens. Here we describe an optimized semiautomated method to produce, titrate, and screen large collections of short hairpin RNA (shRNA)-containing lentiviral vectors. We also present results from a pilot lentiviral RNAi screen for kinases whose silencing modulates sensitivity to a mitotic spindle protein kinesin-5 inhibitor (kinesin-5i). Our screen identified three distinct serine/threonine kinase 6 shRNA vectors within our library as enhancers of kinesin-5i-mediated HT29 cell growth inhibition. In contrast, three distinct shRNAs targeting cell division cycle 2/cyclin-dependent kinase 1 resulted in kinesin-5i resistance. These results demonstrate the feasibility of screening with large collections of lentiviral vectors to identify drug enhancers and suppressors.

Gene delivery by lentivirus vectors

The capacity to efficiently transduce nondividing cells, shuttle large genetic payloads, and maintain stable long-term transgene expression are attributes that have brought lentiviral vectors to the forefront of gene delivery vehicles for research and therapeutic applications in a clinical setting. Our discussion initiates with advances in lentiviral vector development and how these sophisticated lentiviral vectors reflect improvements in safety, regarding the prevention of replication competent lentiviruses (RCLs), vector mobilization, and insertional mutagenesis. Additionally, we describe conventional molecular regulatory systems to manage gene expression levels in a spatial and temporal fashion in the context of a lentiviral vector. State of the art technology for lentiviral vector production by transient transfection and packaging cell lines are explicitly presented with current practices used for concentration, purification, titering, and determining the safety of a vector stock. We summarize lentiviral vector applications that have received a great deal of attention in recent years including the generation of transgenic animals and the stable delivery of RNA interference molecules. Concluding remarks address some of the successes in preclinical animals, and the recent transition of lentiviral vectors to human clinical trials as therapy for a variety of infectious and genetic diseases.

Ex Vivo Gene Therapy for Hemophilia A That Enhances Safe Delivery and Sustained In Vivo Factor VIII Expression from Lentivirally Engineered Endothelial Progenitors

Novel therapeutic strategies for hemophilia must be at least as effective as current treatments and demonstrate long-term safety. To date, several small clinical trials of hemophilia gene transfer have failed to show the promise of preclinical evaluations. Therefore, we wanted to develop and evaluate the feasibility of a novel ex vivo gene transfer strategy whereby cells derived from progenitor cells are engineered to express factor VIII (FVIII) and then implanted subcutaneously to act as a depot for FVIII expression. Circulating blood outgrowth endothelial cells (BOECs) were isolated from canine and murine blood and transduced with a lentiviral vector encoding the canine FVIII transgene. To enhance safety, these cells were implanted subcutaneously in a Matrigel scaffold, and the efficacy of this strategy was compared with i.v. delivery of engineered BOECs in nonhemophilic nonobese diabetic/severe combined immunodeficiency mice. Therapeutic levels of FVIII persisted for 15 weeks, and these levels of stable expression were extended to 20 weeks when the cytomegalovirus promoter was replaced with the thrombomodulin regulatory element. Subsequent studies in immunocompetent hemophilic mice, pretreated with tolerizing doses of FVIII or with transient immunosuppression, showed therapeutic FVIII expression for 27 weeks before the eventual return to baseline levels. This loss of transgene expression appears to be due to the disappearance of the implanted cells. The animals treated with either of the two tolerizing regimens did not develop anti-FVIII antibodies. Biodistribution analysis demonstrated that BOECs were retained inside the subcutaneous implants. These results indicate, for the first time, that genetically modified endothelial progenitor cells implanted in a subcutaneous scaffold can provide sustained therapeutic levels of FVIII and are a promising and safe treatment modality for hemophilia A. Disclosure of potential conflicts of interest is found at the end of this article.

Optimized production and concentration of lentiviral vectors containing large inserts

Generation of high titer lentiviral stocks and efficient virus concentration are central to maximize the utility of lentiviral technology. Here we evaluate published protocols for lentivirus production on a range of transfer vectors differing in size (7.5-13.2 kb). We present a modified virus production protocol robustly yielding useful titers (up to 10(7)/ml) for a range of different transfer vectors containing packaging inserts up to 7.5 kb. Moreover, we find that virus recovery after concentration by ultracentrifugation depends on the size of the packaged inserts, heavily decreasing for large packaged inserts. We describe a fast (4 h) centrifugation protocol at reduced speed allowing high virus recovery even for large and fragile lentivirus vectors. The protocols outlined in the current report should be useful for many labs interested in producing and concentrating high titer lentiviral stocks.

Transgenes delivered by lentiviral vector are suppressed in human embryonic stem cells in a promoter-dependent manner

Lentiviruses have been increasingly used for genetic modification of human cells including embryonic stem (ES) cells. Using four ubiquitous promoters--cytomegalovirus (CMV), cytomegalovirus immediate-early enhancer/chicken beta-actin hybrid (CAG), phosphoglycerate kinase (PGK), and human elongation factor-1alpha (EF1alpha)--in a lentiviral vector to drive the expression of the enhanced green fluorescent protein (EGFP) gene in human ES cells and mouse ES cells, we determined the extent of EGFP suppression by assessing the percentage of cells that were transduced with the EGFP gene but did not fluoresce green. A much higher level of transgene suppression was observed in human ES cells as compared to mouse ES cells. The suppression was also highly promoter dependent, leading to inactivation of more than 95% of the EGFP genes under the CMV or CAG promoter while only 55% under the PGK promoter. No promoter-dependent suppression was observed in transient transfection of human ES cells. Thus, the common phenomenon of poor transgene expression in human ES cells may be caused mainly by suppression of the transgene right after transduction and integration. Cautions should be taken to choose the optimal promoter when lentiviruses are used for genetic modification of human ES cells.

Transgenes delivered by lentiviral vector are suppressed in human embryonic stem cells in a promoter-dependent manner

Lentiviruses have been increasingly used for genetic modification of human cells including embryonic stem (ES) cells. Using four ubiquitous promoters--cytomegalovirus (CMV), cytomegalovirus immediate-early enhancer/chicken beta-actin hybrid (CAG), phosphoglycerate kinase (PGK), and human elongation factor-1alpha (EF1alpha)--in a lentiviral vector to drive the expression of the enhanced green fluorescent protein (EGFP) gene in human ES cells and mouse ES cells, we determined the extent of EGFP suppression by assessing the percentage of cells that were transduced with the EGFP gene but did not fluoresce green. A much higher level of transgene suppression was observed in human ES cells as compared to mouse ES cells. The suppression was also highly promoter dependent, leading to inactivation of more than 95% of the EGFP genes under the CMV or CAG promoter while only 55% under the PGK promoter. No promoter-dependent suppression was observed in transient transfection of human ES cells. Thus, the common phenomenon of poor transgene expression in human ES cells may be caused mainly by suppression of the transgene right after transduction and integration. Cautions should be taken to choose the optimal promoter when lentiviruses are used for genetic modification of human ES cells.

Cytosolic catechols inhibit alpha-synuclein aggregation and facilitate the formation of intracellular soluble oligomeric intermediates

Aberrant aggregation of alpha-synuclein (alpha-syn) to form fibrils and insoluble aggregates has been implicated in the pathogenic processes of many neurodegenerative diseases. Despite the dramatic effects of dopamine in inhibiting the formation of alpha-syn fibrils by stabilization of oligomeric intermediates in cell-free systems, no studies have examined the effects of intracellular dopamine on alpha-syn aggregation. To study this process and its association with neurodegeneration, intracellular catechol levels were increased to various levels by expressing different forms of tyrosine hydroxylase, in cells induced to form alpha-syn aggregates. The increase in the steady-state dopamine levels inhibited the formation of alpha-syn aggregates and induced the formation of innocuous oligomeric intermediates. Analysis of transgenic mice expressing the disease-associated A53T mutant alpha-syn revealed the presence of oligomeric alpha-syn in nondegenerating dopaminergic neurons that do contain insoluble alpha-syn. These data indicate that intraneuronal dopamine levels can be a major modulator of alpha-syn aggregation and inclusion formation, with important implications on the selective degeneration of these neurons in Parkinson's disease.

Silencing of human α-synuclein in vitro and in rat brain using lentiviral-mediated RNAi

Human alpha-synuclein overexpression and its toxic accumulation in neurons or glia are known to play key roles in the pathogenesis of Parkinson's disease and other related neurodegenerative synucleinopathies. Several single point mutations in the alpha-synuclein gene, as well as gene duplication and triplication, have been linked to familial Parkinson's disease. Moreover, genetic variability of the alpha-synuclein gene promoter is associated with idiopathic Parkinson's disease. Silencing of the human alpha-synuclein gene by vector-based RNA interference (RNAi) is a promising therapeutic approach for synucleinopathies. Here, we report identification of a 21-nucleotide sequence in the coding region of human alpha-synuclein that constitutes an effective target for robust silencing by RNAi and demonstrate allele-specific silencing of the A53T mutant of human alpha-synuclein. Furthermore, we have developed a plasmid vector-based RNAi for silencing of human alpha-synuclein in vitro. Lastly, using a dual cassette lentivirus that co-expresses an alpha-synuclein-targeting small hairpin RNA (shRNA) and enhanced green fluorescent protein (EGFP) as a marker gene, we demonstrate effective silencing of endogenous human alpha-synuclein in vitro in the human dopaminergic cell line SH-SY5Y and also of experimentally expressed human alpha-synuclein in vivo in rat brain. Our results demonstrate potent silencing of human alpha-synuclein expression in vitro and in vivo by viral vector-based RNAi and provide the tools for developing effective gene silencing therapeutics for synucleinopathies, including Parkinson's disease.

Regulation of astrocytic glutamate transporter expression by Akt: evidence for a selective transcriptional effect on the GLT-1/EAAT2 subtype

In the nervous system, astrocytes express different ratios of the two glial glutamate transporters, glutamate transporter subtype 1 (GLT-1) and glutamate/aspartate transporter (GLAST), but little is known about the signaling pathways that independently regulate their expression. Treatment with dibutyryl-cAMP, epidermal growth factor (EGF) or other growth factors both induces expression of GLT-1 and increases expression of GLAST in astrocyte cultures. The induction of GLT-1 is correlated with morphological and biochemical changes that are consistent with astrocyte maturation. Pharmacological studies suggest that phosphatidylinositol 3-kinase (PI-3K) and the nuclear transcription factor-kappaB (NF-kappaB) may be involved in the induction of GLT-1 expression. In several signaling systems Akt, also known as protein kinase B (PKB), functions downstream of PI-3K. In these present studies we used lentiviral vectors engineered to express dominant-negative (DN), constitutively active (CA), or null variants of Akt to study the possible involvement of Akt in the regulation of GLT-1. Expression of DN-Akt attenuated the EGF-dependent induction of GLT-1. Expression of CA-Akt caused a dose- and time-dependent increase in GLT-1 protein, increased GLT-1 mRNA levels, increased dihydrokainate-sensitive (presumably GLT-1 mediated) transport activity, and caused a change in astrocyte morphology to a more stellate shape, but had no effect on GLAST protein levels. Finally, the expression of CA-Akt increased the expression of a reporter construct containing a putative promoter fragment from the human homolog of GLT-1, called EAAT2. From these studies, we conclude that Akt induces the expression of GLT-1 through increased transcription and that Akt can regulate GLT-1 expression without increasing GLAST expression in astrocytes.

Upscaling of lentiviral vector production by tangential flow filtration

BACKGROUND

HIV-1-derived vectors are promising tools for gene transfer into the brain. Application of these vectors for gene therapy or for the creation of animal models for neurodegenerative diseases requires standardization and upscaling of lentiviral vector production methods.

METHODS

In this study, serum-free HIV-1 vector production was efficiently upscaled by use of cell factories and the introduction of tangential flow filtration (TFF) prior to centrifugation.

RESULTS

Vector titers (TU/ml) and p24 values (pg p24/ml) for a serum-free HIV-1 vector produced in cell factories and using TFF prior to centrifugation were comparable to those of small-scale productions. TFF allowed a 66-fold concentration of the vectors with complete vector recovery. Further concentration of the vector (30-fold) was achieved either by low-speed centrifugation or by ultracentrifugation. Combination of TFF and ultracentrifugation resulted in a vector recovery of 90-100% and titers that increased 1800-fold and 900-fold for transducing units and p24 concentration, respectively.

CONCLUSIONS

With this new standardized method for lentiviral vector production and concentration, 1 ml of concentrated vector is routinely produced with titers of 10(9)-10(10) TU/ml starting from 2 l of cell-culture medium. Moreover, stereotactic injection of this vector in mouse striatum resulted in a large transduced brain volume in the absence of any immune response.

Optimisation of a multipartite human immunodeficiency virus based vector system; control of virus infectivity and large-scale production

BACKGROUND

We have previously described a five-plasmid HIV-1 vector system that utilises a codon-optimised gagpol gene. While this system was shown to be safer than systems using proviral type helpers, the titre of virus produced was relatively low. Therefore, a process of optimising all aspects of virus production was initiated.

METHODS

A systematic approach was taken to the optimisation of virus production by transient expression using a five-plasmid packaging system. Codon-manipulation was used to reduce homology between helper and vector constructs. Ultrafiltration and ultracentrifugation were used for large-scale virus production.

RESULTS

We describe codon-optimised reading frames for Tat and Rev and the optimisation of virus production. The optimisation process resulted in an increase in virus titre of 7- to 8-fold. Several other approaches to increasing viral titre described by others proved ineffective in our system after it had been optimised. In addition, we show that by varying the ratio of the GagPol helper construct to vector, the infectivity of the virus could be controlled. The use of a novel codon-optimised HIV-1 GagPol expression construct with reduced homology to vector sequences significantly reduced transfer of gagpol sequences to transduced cells. Virus could be collected in serum-free medium without a significant loss of titre, which facilitated subsequent processing. Processing using a combination of ultrafiltration and ultracentrifugation allowed efficient and rapid processing of litre volumes of virus supernatant.

CONCLUSIONS

By taking a systematic approach to optimising all aspects of our five-plasmid lentiviral vector system we improved titre, safety, large-scale production, and demonstrated that infectivity could be specifically controlled.

Gene therapy progress and prospects: development of improved lentiviral and retroviral vectors--design, biosafety, and production

Replication defective vectors derived from simple retroviruses or the more complex genomes of lentiviruses continue to offer the advantages of long-term expression, cell and tissue specific tropism, and large packaging capacity for the delivery of therapeutic genes. The occurrence of adverse events caused by insertional mutagenesis in three patients in a gene therapy trial for X-linked SCID emphasizes the potential for problems in translating this approach to the clinic. Several genome-wide studies of retroviral integration are now providing novel insights into the integration site preferences of different vector classes. We review recent developments in vector design, integration, biosafety, and production.