An anti-apoptotic HEK293 cell line provides a robust and high titer platform for transient protein expression in bioreactors

ABSTRACT

HEK293 transient expression systems are used to quickly generate proteins for research and pre-clinical studies. With the aim of engineering a high-producing host that grows and transfects robustly in bioreactors, we deleted the pro-apoptotic genes Bax and Bak in an HEK293 cell line. The HEK293 Bax Bak double knock-out (HEK293 DKO) cell line exhibited resistance to apoptosis and shear stress. HEK293 DKO cells sourced from 2 L seed train bioreactors were most productive when a pH setpoint of 7.0, a narrow pH deadband of ±0.03, and a DO setpoint of 30% were used. HEK293 DKO seed train cells cultivated for up to 60 days in a 35 L bioreactor showed similar productivities to cells cultivated in shake flasks. To optimize HEK293 DKO transfection cultures, we first evaluated different pH and agitation parameters in ambr15 microbioreactors before scaling up to 10 L wavebag bioreactors. In ambr15 microbioreactors with a pH setpoint of 7.0, a wide pH deadband of ±0.3, and an agitation of 630 rpm, HEK293 DKO transient cultures yielded antibody titers up to 650 mg/L in 7 days. The optimal ambr15 conditions prompted us to operate the 10 L wavebag transfection without direct pH control to mimic the wide pH deadband ranges. The HEK293 DKO transfection process produces high titers at all scales tested. Combined, our optimized HEK293 DKO 35 L bioreactor seed train and 10 L high titer transient processes support efficient, large-scale recombinant protein production for research studies.     

Transient gene expression: recombinant protein production with suspension-adapted HEK293-EBNA cells

Transient gene expression (TGE) in mammalian cells at the reactor scale is becoming increasingly important for the rapid production of recombinant proteins. We improved a process for transient calcium phosphate-based transfection of HEK293-EBNA cells in a 1-3 L bioreactor volume. Cells were adapted to suspension culture using a commercially available medium (BioWhittaker, Walkersville, MD). Process parameters were optimized using a plasmid reporter vector encoding the enhanced green fluorescent protein (EGFP/CLONTECH, Palo Alto, CA, USA). Using GFP as a marker-protein, we observed by microscopic examination transfection efficiencies between 70-100%. Three different recombinant proteins were synthesized within a timeframe of 7 days from time of transfection to harvest. The first, a human recombinant IgG(1)-type antibody, was secreted into the supernatant of the cell culture and achieved a final concentration of >20 mg/L. An E. coli-derived DNA-binding protein remained intracellular, as expected, but accumulated to such a concentration that the lysate of cells, taken up into the entire culture volume, gave a concentration of 18 mg/L. The third protein, a transmembrane receptor, was expressed at 3-6 x 10(6) molecules/cell.     

表面等离子体激元共振与生物分子相互作用分析

对表面等离子体激元共振（surface plasmon resonance, SPR）的原理和在生物学研究方面的应用进行了综述.这种技术可以直接原位、实时地跟踪生物学实验研究系统,而不需要附加参数如进行标记等手段,具有高敏感性,也可以连续监测吸附或解吸附过程,目前有关的应用涉及到生物学结合分析、动力学及亲和力测定、免疫识别研究、结构与活性研究和核酸研究等多个领域.     

利用表面等离子体共振仪检测黄瓜花叶病毒

目的：研究一种便捷、高效地检测黄瓜花叶病毒（CMV）的方法。方法：利用表面等离子体共振（SPR）技术检测CMV。首先用11-MUA修饰SPR金片,再用EDC／NHS活化,之后通过NHS酯基与CMV抗体结合,用BSA封闭未结合的NHS酯基。将SPR金片装入SPR仪,通入待检样品,通过折射率变化实时监测实验过程。结果：该方法检测CMV的灵敏度能够达到10ng／mL,具有良好的特异性,与同属的花生矮化病毒、番茄不孕病毒无交叉反应。结论：建立的SPR方法操作简单、灵敏度高、特异性好,是一种新的高效检测CMV的方法。     

Sensitive and Label-Free Detection of DNA by Surface Plasmon Resonance

While an array of technologies based on radioactive labels or luminescent tags are dominant in modern biomedical research on DNA, surface plasmon resonance (SPR) and SPR imaging measurements are sensitive, rapid, and label-free. This review summarizes recent advances in the development of SPR and coupled techniques and their applications in DNA research, including the gene analysis at trace levels and studies of DNA–protein and DNA–drug interactions.     

An efficient and scalable process for helper-dependent adenoviral vector production using polyethylenimine-adenofection

Safety requirements for adenoviral gene therapy protocols have led to the development of the third generation of vectors commonly called helper-dependent adenoviral vectors (HDVs). HDVs have demonstrated a high therapeutic potential; however, the poor efficiency and reliability of the actual production process hampers further large-scale clinical evaluation of this new vector. The current HDV production methods involve a preliminary rescue step through transfection of adherent cell cultures by an HDV plasmid followed by a helper adenovirus (HV) infection. Amplification by serial co-infection of complementary cells allows an increase in the HDV titer. Using a HEK293 FLP/frt cell system in suspension culture, an alternative protocol to the current transfection/infection procedure was evaluated. In this work, the adenofection uses the HDV plasmid linked to the HV with the help of polyethylenimine (PEI) and has shown to outperform standard protocols by producing higher HDV yield. The influence of complex composition on the HDV production was examined by a statistical design. The optimized adenofection and amplification conditions were successively performed to generate HDV at the 3 L bioreactor scale. Following only two serial co-infection passages, up to 1.44 x 10(8) HDV infectious units/mL of culture were generated, which corresponded to 26% of the total particles produced. This production strategy, realized in cell suspension culture, reduced process duration and therefore the probability of vector recombination by introducing a cost-effective transfection protocol, ensuring production of high-quality vector stock.     

Identification of a novel miRNA that increases transient protein expression in combination with valproic acid

Transient gene expression in mammalian cells is an efficient process to produce recombinant proteins for various research applications and large molecule therapeutics development. For the first time, we report a screen to identify human microRNAs (miRNAs) that increase titers after polyethylenimine (PEI) mediated transient transfection of a HEK293 cell line. From a library of 875 miRNAs, we identified 2 miRNAs, miR‐26a‐5p and miR‐337‐5p, that increased human IgG1 (huIgG1) yields by 50 and 25%, respectively. The titer increase was achievable by expressing miR‐26a‐5p from oligonucleotides or a plasmid. Furthermore, combining miR‐26a‐5p with valproic acid (VPA) treatment doubled huIgG1 titers. Assessment of miR‐26a‐5p and VPA treatment across a panel of 32 human and murine antibodies demonstrates that the level of yield enhancement was molecule‐dependent, with most exhibiting a range of 50–100% titer increase. These findings exemplify that combining genetic and chemical manipulation can be an effective strategy to enhance transient transfection productivity. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1139–1145, 2017     

偏振干涉角度调制SPR传感技术研究及应用进展

针对一种新兴生物检测方法——表面等离子体波共振(SPR)技术,文中SPR传感系统采用偏振干涉和角度调制方案,使SPR传感灵敏度与光复反射系数的模和相位都相关,从而实现较大线形范围内的高灵敏测量。同时开展了该SPR传感系统在环保领域的应用研究,SPR共振信号可实时随甲烷含量线性改变,气体检测灵敏度达到1 070ppm,实验结果验证了这种SPR传感技术的检测性能并显示了其在环保监测领域的应用潜力。     

利用表面等离子共振传感器检测苏云金芽孢杆菌cry1F蛋白

目的：建立检测苏云金芽孢杆菌（Bt）crylF蛋白的表面等离子共振（SPR）传感器方法。方法：采用SPR检测技术,利用生物分子相互作用分析原理,在金表面修饰特异性单克隆抗体,对crylF蛋白的检测进行研究。结果：该方法可以较好地检测到crylF蛋白,最低检测限可达10ng／mL,并且具有很好的特异性。结论：SPR检测方法的重复性较好,灵敏度高,目前可用于crylF蛋白的定性检测,为crylF蛋白及其他Bt蛋白的检测提供了新方法,在检测转Bt基因植物方面具有广阔的应用前景。     

Real-time and Label-free Bio-sensing of Molecular Interactions by Surface Plasmon Resonance: A Laboratory Medicine Perspective

Radioactive, chromogenic, fluorescent and other labels have long provided the basis of detection systems for biomolecular interactions including immunoassays and receptor binding studies. However there has been unprecedented growth in a number of powerful label free biosensor technologies over the last decade. While largely at the proof-of-concept stage in terms of clinical applications, the development of more accessible platforms may see surface plasmon resonance (SPR) emerge as one of the most powerful optical detection platforms for the real-time monitoring of biomolecular interactions in a label-free environment.In this review, we provide an overview of SPR principles and current and future capabilities in a diagnostic context, including its application for monitoring a wide range of molecular markers of disease. The advantages and pitfalls of using SPR to study biomolecular interactions are discussed, with particular emphasis on its potential to differentiate subspecies of analytes and the inherent ability for quantitation through calibration-free concentration analysis (CFCA). In addition, recent advances in multiplex applications, high throughput arrays, miniaturisation, and enhancements using noble metal nanoparticles that promise unprecedented sensitivity to the level of single molecule detection, are discussed.In summary, while SPR is not a new technique, technological advances may see SPR quickly emerge as a highly powerful technology, enabling rapid and routine analysis of molecular interactions for a diverse range of targets, including those with clinical applicability. As the technology produces data quickly, in real-time and in a label-free environment, it may well have a significant presence in future developments in lab-on-a-chip technologies including point-of-care devices and personalised medicine.     

基于表面等离子体共振和电化学联用的DNA传感器研究进展

表面等离子共振(surface plasmon resonance,SPR)技术旨在检测物体表面附近折射率的变化,其特点是无标记、实时、灵敏和快速,该技术多用于研究分子的相互作用,包括动力学、效率常数和大分子构象变化等。电化学(electrochemical,EC)技术是一项用于定性定量研究电子转移、物质氧化还原、界面吸附等过程的成熟技术,具有简单、低成本和设备小型化的优点。现有的DNA杂交技术,例如光学、电化学或压电转导技术,主要关注于提高DNA杂交检测系统的选择性和灵敏度。传统的SPR在DNA分析方面,由于无法测量折射率的极小变化而在超灵敏检测中的应用受到限制。因此,随着纳米材料的研发和联用技术的飞速发展,SPR与EC联用的生物传感器研究越来越成为人们关注的热点。近年来,关于SPR和EC联用在DNA检测方面的综述鲜有报道。对SPR和EC检测DNA的技术原理、联用方法、应用进展等方面作出了简要的介绍,以期为表面等离子共振和电化学联用的DNA传感器相关研究提供参考。     

Continuous production and recovery of recombinant Ca2+ binding receptor from HEK 293 cells using perfusion through a packed bed bioreactor

The extracellular domain of human parathyroid Ca²⁺ receptor was needed in order to study itsstructure and clinical application. The Ca²⁺receptor is a unique member of the G protein-coupledreceptor super-family, expressed in parathyroid andkidney cells where it has been shown to play acritical role in extracellular calcium homeostasis.The desired protein was produced by immobilizing thetransformed HEK 293 cells in a packed-bedconfiguration using a 1.6 l (working volume)bioreactor equipped with a vertical mixing impellerassembly and an internal basket. The process includeda propagation phase followed by a production phase. Inthe propagation phase, lasting approximately 160 h, the bed was perfused with a serum-containingmedium, allowing the cells to grow at a constantgrowth rate to approximately 3 × 10¹⁰. At this point the production phase was begun, replacing themedium with serum-free medium and continuing theperfusion process for additional 350 h. Duringthis phase, the medium was pumped through the packedbed at a rate of 4–6 l per day, keeping theresidual glucose concentration around 1 g l^-1 andcollecting and processing approximately 80 l ofspent medium. This continuous perfusion method of thepacked-bed bioreactor was compared to a repeated batchmethod in which existing medium was replenished whenthe glucose concentration was down to 1 g l^-1. Using this method, serum-free medium was replaced withserum containing medium a few times when a decline inthe glucose consumption was observed. Though mediumconsumption and protein yield are similar in bothmethods (roughly 10 mg l^-1), there aredifferences related to the ease of operation andprocessing of the produced protein. The continuousperfusion operation was found to be preferable and waschosen as the production strategy.     

Functional Demonstration of Connexin—Protein Binding Using Surface Plasmon Resonance

Surface plasmon resonance (SPR) allows examination of protein-protein interactions in real time, from which both binding affinities and kinetics can be directly determined. We have used the SPR technique to search for proteins in heart tissue that would be candidate binding partners for the cardiac gap junction protein, connexin43 (Cx43). Heart lysate showed a strong, pH-dependent binding to the carboxyl terminus (CT) of Cx43 (amino acids 254-382) covalently linked to an SPR cuvette. Binding was inhibited by the presence of v-src transfected 3T3 cell lysate, suggesting that binding partners in these two lysates may compete for overlapping epitopes on Cx43CT. The combined application of proteomic and functional studies is expected to identify which proteins within heart tissue interact with Cx43 and what roles they may play in gap junction function.     

At-line quantification of bioactive antibody in bioreactor by surface plasmon resonance using epitope detection

We report an innovative at-line method to monitor concentration of bioactive antibody (i.e., antibody with conserved antigen-binding activity) secreted during bioreactor culture by the use of surface plasmon resonance (SPR)-based biosensor technology. In a first series of experiments, conditions for SPR-based measurements were validated off-line by monitoring bioactive antibody concentration in conditioned medium from 500-ml baffled flask hybridoma cell cultures. A fully automated experimental setup in which the SPR-based biosensor was harnessed to a bioreactor was then used at-line to monitor the concentration of bioactive antibody produced in a 3.5-L bioreactor. Quantitative SPR measurements performed both at-line and off-line were in excellent agreement with quantitative Western blotting followed by densitometry analyses. Thus, our experimental study confirms that SPR biosensors can be applied to at-line quantification of correctly folded proteins that are secreted by cells cultured in a bioreactor. Our experimental approach represents a novel and robust analytical strategy to be applied to the control and optimization of the production of bioactive secreted proteins.     

表面等离子体共振技术在分子生物学中的应用

表面等离子体共振(SPR)技术可以实时、原位地测定生物分子间的相互作用而无需任何标记,可以连续监测吸附和解离过程,并可以进行多组分复合物的相互作用的研究。SPR技术在DNA的复制和转录、DNA的修复、核酸与药物的作用以及肽库和抗体库的筛选等分子生物学领域的应用研究取得了令人瞩目的进展,显示了常规技术无法比拟的优越性。     

High throughput screening identifies novel,cell cycle‐arresting small molecule enhancers of transient protein expression

Transient gene expression in mammalian cells is an efficient process for producing recombinant proteins for various research applications to support large molecule therapeutics development. For the first time, we report a high throughput small molecule (SM) screen to identify novel compounds that increase antibody titers after polyethylenimine (PEI) transient transfection of a HEK293 cell line. After screening 31,413 SMs in a 50 μL scaled‐down process, we validated 164 SMs to improve yields by up to twofold. The titer increase mediated by the SMs varied for different antibodies. SM dose optimizations resulted in almost threefold higher titers. The top 2, structurally distinct SM hits, increased antibody titers more than twofold in a 1 mL production process. Averaged across three antibodies of different expression levels, the compounds enhanced transient productivity by ～80%. Intriguingly, both compounds arrested cells in the G2/M cell cycle phase leading to a decrease in growth and nutrient consumption, while elevating titer, nuclear plasmid DNA (pDNA) copy numbers, and mRNA levels. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 3:1579–1588, 2017