Growth of endothelial and HeLa cells on a new multipurpose microcarrier that is positive,negative or collagen coated

A new cell culture microcarrier that can be covalently bonded by cell attachment proteins and can be thin-sectioned for electron microscopy was synthesized. It was easily made by sulfonating cross-linked polystyrene beads for a negative surface charge followed by covalent attachment of polyethylenimine for a positive charge. Cell attachment proteins, e.g. collagen, was covalently bonded directly to the microcarrier using a carbodiimide or after activating the microcarrier surface with glutaraldehyde. HeLa-S3 cells attached, spread and grew to confluence more efficiently on the positive microcarriers and those coated with collagen than on the negative ones. Endothelial cells grew best on those with a negative surface charge. The nature of the microcarrier surface was not the only aspect involved in cell adhesion but also the type of serum proteins adsorbed. Qualitatively different proteins coated the microcarriers depending upon whether the carrier was negative, positive or coated with collagen. Comparison of various types of available microcarriers indicated that the modified cross-linked polystyrene beads used here were best for transmission and scanning electron microscopy. Endothelial cells grown on the microcarriers had the same ultrastructure as cells grown in monolayers in culture dishes. Of a variety of microcarriers tested the modified cross-linked polystyrene beads were the only ones that could be used for both ultrastructural and biochemical techniques.     

Evaluation of production parameters with the vaccinia virus expression system using microcarrier attached HeLa cells

Parameters that affect production of the recombinant reporter protein, EGFP, in the T7 promoter based VOTE vaccinia virus-HeLa cell expression system were examined. Length of infection phase, inducer concentration, and timing of its addition relative to infection were evaluated in 6-well plate monolayer cultures. One hour infection with 1.0 mM IPTG added at the time of infection provided a robust process. For larger scale experiments, anchorage-dependent HeLa cells were grown on 5 g/L Cytodex 3 microcarriers. The change to this dynamic culture environment, with cell-covered microcarriers suspended in culture medium in spinner flasks, suggested a re-examination of the multiplicity of infection (MOI) for this culture type that indicated a need for an increase in the number of virus particles per cell to 5.0, higher than that needed for complete infection in monolayer tissue flask culture. Additionally, dissolved oxygen level and temperature during the protein production phase were evaluated for their effect on EGFP expression in microcarrier spinner flask culture. Both increased dissolved oxygen, based on surface area to volume (SA/V) adjustments, and decreased temperature from 37 to 31 degrees C showed increases in EGFP production over the course of the production phase. The level of production achieved with this system reached approximately 17 microg EGFP/10(6) infected cells.     

Transient gene expression in HEK293 and vero cells immobilised on microcarriers

The upscale of transient gene expression (TGE) gained popularity over the last decade as it drastically shortens timelines for the production of recombinant proteins. Bottlenecks of the method turned out to be media composition and media exchange, which is usually required as conditioned medium drastically reduces the transfection efficiency. Media exchanges are typically done by centrifugation, which limits upscale, is prone to contamination or is a high cost factor when continuous centrifuges are used. In this work HEK/EBNA cells were grown and transfected on microcarriers. Cell immobilisation allows easy media exchange after sedimentation. The transfection method was optimised regarding polyethylenimine (PEI) concentration, optimal DNA:PEI ratio, type of PEI, incubation time and polyplex formation time. In addition to HEK, Vero cells were also transfected using the same protocol. The method was established in spinner flasks and scaled up to a 1.5 litre stirred tank reactor. Transfection efficiencies of up to 33% with pCEP4 and 98% with pMAX were reached. Additionally immobilisation on microcarriers was used to retain the cells during cultivation, thus allowing media replacement and prolonging cultivation time from one to two weeks with continuous expression of the recombinant protein.     

Cell attachment to microcarriers affects growth, metabolic activity, and culture productivity in bioreactor culture

It is not well understood how changes from suspension to microcarrier cultures affect cell growth, metabolism, and yield of recombinant proteins. To investigate the effects of culture conditions on cell characteristics, fed-batch bioreactor cultures were performed under different culture conditions (suspension cultures, cultures attached to Cytodex 3 and Cytopore 1 microcarriers) using two different Chinese hamster ovary cell lines producing either secreted human placental alkaline phosphatase (TR2-255) or tissue plasminogen activator (CHO 1-15-500). In controlled, agitated bioreactors, suspension cultures reached cell densities and product titers higher than those in microcarrier cultures, in contrast to the results in static flask cultures. Growth and metabolic activities showed similar trends in suspension and microcarrier culture regardless of cell line. However, the responses of the specific productivities to the different culture conditions differed significantly between the cell lines.     

Hybridoma cell growth and anti-neuroblastoma monoclonal antibody production in spinner flasks using a protein-free medium with microcarriers

The main disadvantages of foetal calf serum as the world-wide common serum supplement for cell growth are its content of various proteins of variable concentrations between batches as well as its high cost. The use of serum-free and protein-free media is gradually becoming one of the goals of cell culture especially for standardizing culture conditions or for simple purification of cell products like monoclonal antibodies. The mouse hybridoma cells 14/2/1 were cultivated either in protein-free UltraDOMA medium or in serum-containing RPMI medium with and without microcarriers to generate high quantities of monoclonal antibodies against neuroblastoma tumour cells. Cell growth rate, IgG production, viability, glucose and lactate concentrations, attachment rate and doubling time have been used as investigation criteria. Modifications of culture procedures (static or stirred), inoculum density, and microcarrier concentration caused an improvement of monoclonal antibody production. The kinetics of antibody synthesis was best in spinner culture with 2 ml of microcarriers in protein-free medium. These results of short-term microcarrier culture in stirred spinner flasks indicate that IgG yields in protein-free medium 2.5-fold higher to those in serum-supplemented medium can be achieved.     

Growth of three established cell lines on glass microcarriers

Three established cell lines were examined for growth on a newly developed microcarrier which consists of glass beads. The cells were simultaneously exmined for growth on commercially available microcarriers made from DEAE-dextran and from plastic. Cell yields on the glass microcarriers were comparble to the cell yields on the commercially available products. Cells grown on the glass microcarriers were easily separated from the substratum by trypsinization (as were the cells grown on the plastic substratum) while the cells grown on the DEAE-dextran particles were much more trypsin resistant. After removal of cells from the glass microcarriers, the cells reattached and spread out in plastic flasks as readily as cells harvested from monolayer. Scanning electron microscopy revealed dramatic differences in the appearence of the cell grown on the glass microcarriers and cells grown on the DEAE-dextran microcarriers. On the glass microcarriers, cells attached to the substratum through lond, slender filopodia while on the DEAE-dextran microcarriers, the entire edge of the cell appeared to be in contact with the substratum. This dissimilarity in attachment could underly the difference in sensitivity to trypsin-mediated detachment. Finally, the glass microcarriers were washed after being used once and retested for their ability to support cell growth a second time. Nearly identical results were obtained with the reprocessed beads as with previously unused ones.     

Effect of glucocorticoid hormones on growth of human fibroblast cells and interferon production in a microcarrier culture system

Glucocorticoid hormones promoted the growth of fibroblast cells derived from human neonatal foreskins and prolonged their life span in a microcarrier culture system that used Eagle's minimum essential medium (MEM) supplemented with fetal calf serum (FCS). But, these hormones suppressed cell growth in conventional monolayer cultures. Precolostrum newborn calf serum (PNCS) was the only species that supported the serial propagation of fibroblast cells on microcarriers, possibly because of its high content of hydrocortisone (HC). Fibroblast cells grown on microcarriers in the presence of glucocorticoid hormones maintained their ability to produce interferon (IFN)-beta in a superinduction method with poly I: poly C and antimetabolites. These cells had more than 93% diploidy and no chromosomal aberration or translocation. Use of PNCS for the cultivation of human fibroblast cells has high potential for providing a microcarrier culture system for the mass production of human IFN-beta.     

Dissolvable Gelatin-Based Microcarriers Generated through Droplet Microfluidics for Expansion and Culture of Mesenchymal Stromal Cells

Microcarriers are synthetic particles used in bioreactor-based cell manufacturing of anchorage-dependent cells to promote proliferation at efficient physical volumes, mainly by increasing the surface area-to-volume ratio. Mesenchymal stromal cells (MSCs) are adherent cells that are used for numerous clinical trials of autologous and allogeneic cell therapy, thus requiring avenues for large-scale cell production at efficiently low volumes and cost. Here, a dissolvable gelatin-based microcarrier is developed for MSC expansion. This novel microcarrier shows comparable cell attachment efficiency and proliferation rate when compared to several commercial microcarriers, but with higher harvesting yield due to the direct dissolution of microcarrier particles and thus reduced cell loss at the cell harvesting step. Furthermore, gene expression and in vitro differentiation suggest that MSCs cultured on gelatin microcarriers maintain trilineage differentiation with similar adipogenic differentiation efficiency and higher chondrogenic and osteogenic differentiation efficiency when compared to MSCs cultured on 2D planar polystyrene tissue culture flask; on the contrary, MSCs cultured on conventional microcarriers appear to be bipotent along osteochondral lineages whereby adipogenic differentiation potential is impeded. These results suggest that these gelatin microcarriers are suitable for MSC culture and expansion, and can also potentially be extended for other types of anchorage-dependent cells.     

Attachment and growth kinetics of anchorage-dependent BHK cells on microcarriers

Anchorage-dependent Baby Hamster Kidney (BHK) cells were cultivated on polyhydroxyethylmethacrylate (PHEMA), polystyrene (PS), and Cytodex microcarriers. Analysis of the experimental data indicated that there were a finite number of sites on the microcarrier surfaces, available for anchorage. The number of these sites was determined by the chemical and physical structure of the surface. A small fraction of these sites were suitable for attachment of the cells before proliferation. A larger fraction of these sites did not support attachment but the cells could proliferate on them by the help of previously attached mother cells. The attachment and proliferation of the BHK cells on these microcarriers were satisfactorily modeled by surface saturation type of mathematical expressions.     

Systematic microcarrier screening and agitated culture conditions improves human mesenchymal stem cell yield in bioreactors

Production of human mesenchymal stem cells for allogeneic cell therapies requires scalable, cost‐effective manufacturing processes. Microcarriers enable the culture of anchorage‐dependent cells in stirred‐tank bioreactors. However, no robust, transferable methodology for microcarrier selection exists, with studies providing little or no reason explaining why a microcarrier was employed. We systematically evaluated 13 microcarriers for human bone marrow‐derived MSC (hBM‐MSCs) expansion from three donors to establish a reproducible and transferable methodology for microcarrier selection. Monolayer studies demonstrated input cell line variability with respect to growth kinetics and metabolite flux. HBM‐MSC1 underwent more cumulative population doublings over three passages in comparison to hBM‐MSC2 and hBM‐MSC3. In 100 mL spinner flasks, agitated conditions were significantly better than static conditions, irrespective of donor, and relative microcarrier performance was identical where the same microcarriers outperformed others with respect to growth kinetics and metabolite flux. Relative growth kinetics between donor cells on the microcarriers were the same as the monolayer study. Plastic microcarriers were selected as the optimal microcarrier for hBM‐MSC expansion. HBM‐MSCs were successfully harvested and characterised, demonstrating hBM‐MSC immunophenotype and differentiation capacity. This approach provides a systematic method for microcarrier selection, and the findings identify potentially significant bioprocessing implications for microcarrier‐based allogeneic cell therapy manufacture.     

Production and glycosylation of recombinant beta-interferon in suspension and cytopore microcarrier cultures of CHO cells

Microcarriers are suitable for high-density cultures of cells requiring surface attachment and also offer the advantage of easy media removal for product recovery. We have used the macroporous microcarriers Cytopore 1 and 2 for the growth of CHO cells producing recombinant human beta-interferon (beta-IFN) in stirred batch cultures. Although these cells may grow in suspension, in the presence of Cytopore microcarriers they become entrapped in the inner bead matrix where they can be maintained at high densities. Cell growth rates were reduced in microcarrier cultures compared to suspension cultures. However, the beta-IFN yield was up to 3-fold greater as a result of an almost 5-fold higher specific productivity. Maximum productivity was found in cultures containing 1.0 mg/mL of Cytopore 1 or 0.5 mg/mL of Cytopore 2 with a cell/bead ratio of 1029 and 822, respectively. Beta-IFN molecules aggregated in the later stages of all cultures, causing a decrease in response by ELISA. However, the degree of aggregation was significantly less in the microcarrier cultures. The N-linked glycans from beta-IFN were isolated and analyzed by normal phase HPLC. There was no apparent difference in the profile of glycans obtained from each of the suspension and Cytopore culture systems. This suggests that Cytopore microcarriers may be useful in bioprocess development for enhanced recombinant glycoprotein production without affecting the glycosylation profile of the protein.     

Attachment characteristics of normal human cells and virus-infected cells on microcarriers

The attachment kinetics of normal and virus-infected LuMA cells were studied to improve the production of live attenuated varicella viruses in human embryonic lung (LuMA) cells. Normal LuMA cells and LuMA cells infected by varicella virus at various cytopathic effects (CPE) were grown on microcarriers. Ninety-three percent of suspended LuMA cells attached to the solid surface microcarriers within fifteen minutes and cell viability was greater than 95% when the cell suspension was stirred. Low serum levels did not affect the attachment rate of virus-infected cells in the microcarrier culture system. Kinetic studies showed that varicella infected cells had a lower attachment rate than normal LuMA cells. Virus inoculum (= infected cells) at low CPE showed a relatively better attachment rate on cell-laden microcarriers than virus inoculum at a higher CPE. Maximum titers were obtained at 2 days post-infection. Based on cell densities, the use of viral inoculum showing a 40% CPE led to an approximately 2- and 1.2-fold increase in the cell associated and in cell free viruses, respectively, than a virus inoculum with a CPE of 10%.However, the ratio of cell-free to cell-associated virus in a microcarrier culture was very low, approximately0.04–0.06. These studies demonstrate that the virus inoculum resulting in a high CPE yielded a high production of cell-associated and cell-free virus in microcarrier cultures because of the high cellular affinity of the varicella virus. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effects of microcarrier culture on recombinant CHO cells under biphasic hypothermic culture conditions

A Chinese hamster ovary (CHO) cell line, producing recombinant secreted human placental alkaline phosphatase (SEAP) was investigated under three different culture conditions (suspension cells, cells attached to Cytodex 3 and Cytopore 1 microcarriers) in a biphasic culture mode using a temperature shift to mild hypothermic conditions (33 °C) in a fed-batch bioreactor. The cell viability in both the suspension and the Cytodex 3 cultures was maintained for significantly longer periods under hypothermic conditions than in the single-temperature cultures, leading to higher integrated viable cell densities. For all culture conditions, the specific productivity of SEAP increased after the temperature reduction; the specific productivities of the microcarrier cultures increased approximately threefold while the specific productivity of the suspension culture increased nearly eightfold. The glucose and glutamine consumption rates and lactate and ammonia production rates were significantly lowered after the temperature reduction, as were the yields of lactate from glucose. However, the yield of ammonia from glutamine increased in response to the temperature shift.     

Large scale transient expression with COS cells

We demonstrate here that transient expression with COS cells can be performed at the one litre scale for a period of more than 10 days. Cells grown in T225 flasks were transfected by electroporation, transferred into spinners, and then grown either in suspension or on microcarriers. A daily medium change significantly extented culture life and production time, compared with standard protocols.Concentrations of the product, the secreted fusion protein CD40-Fc, were comparable in microcarrier and suspension culture. Cultures were started in fetal calf serum containing medium and the subsequent production process was performed in a low protein serum free medium which allowed easy downstream processing. 10 litres of supernatant, collected from one transfected batch of cells, yielded 30 mg of purified and biologically active protein.In addition to developing a simplified protocol for generation of cells we also reduced the material (DNA, cuvettes) required for electroporation. Our results show that scale up of transient expression to the litre scale can be successfully acieved. This provides a new tool to generate milligram quantities of protein within weeks of gene cloning.     

Human diploid fibroblast growth on polystyrene microcarriers in aggregates

Polystyrene microcarriers were prepared in four size ranges (53–63 m, 90–125 m, 150–180 m and 300–355 m) and examined for ability to support attachment and growth of human diploid fibroblasts. Cells attached rapidly to the microcarriers and there was a direct relationship between cell attachment and microcarrier aggregation. Phasecontrast and scanning electron microscopic studies revealed that while aggregation was extensive, most of the aggregate consisted of void volume. Cell growth studies demonstrated that human diploid fibroblasts proliferated well in microcarrier aggregates, reaching densities of 2.5–3×10⁶ cells per 2 ml dish after 6 days from an inoculum of 0.5×10⁶ cells per dish. When cells were added to the microcarriers at higher density (up to 5×10⁶ cells per 2-ml culture), there was little net growth but the cells remained viable over a 7-day period. In contrast, cells died when plated under the same conditions in monolayer culture. When the microcarriers were used in suspension culture, rapid cell attachment and rapid microcarrier aggregation also occurred. In 100-ml suspension culture, a cell density of 0.7×10⁶ cells per ml was reached after 7 days from an inoculum of 0.1×10⁶ cells. Based on these data, we conclude that microcarrier aggregation is not detrimental to fibroblast growth. These data also indicate that small microcarriers (53–63 m) (previously thought to be too small to support the growth of diploid fibroblasts) can support fibroblast growth and this occurs primarily because microcarriers in this size range efficiently form aggregates with the cells.     

Chitosan/gelatin composite microcarrier for hepatocyte culture

Solid and porous chitosan/gelatin (CG) composite microcarriers were prepared by a water-in-oil emulsion process with additional freezing and lyophilization. Adult rat hepatocytes (10(6) cells ml(-1)) attached on CG microcarriers maintained at least 15 d of viability and differentiated functions. Over 15 d, unimmobilized hepatocytes released 1.34-fold less lactate dehydrogenase (LDH), and retained 1.63-, 1.51- and 1.28-fold higher albumin secretion, urea synthesis and 7-ethoxycoumarin deethylation activities, respectively, than those on collagen-coated microcarriers. The CG matrix is therefore a promising microcarrier for hepatocyte culture.     

Cell-microcarrier adhesion to gas-liquid interfaces and foam

The interaction of microcarriers, both with and without cells attached, with gas bubbles was studied. These studies consisted of qualitative microscopic observations of microcarriers with bubbles, quantitative measurements of microcarrier entrapment in foam, and quantitative measurements of the effect of bubble rupture at gas-medium interfaces. Ten different "protective additives" were evaluated for their ability to change the dynamic surface tension of the culture media and to prevent microcarrier adhesion to air bubbles during gas sparging and to prevent entrapment in the foam layer. These studies indicate that microcarriers, with and without cells, readily attach to gas-medium interfaces; yet unlike suspended cells, cells attached to microcarriers are not damaged by bubble ruptures at gas-medium interfaces. Only one surfactant was found to substantially prevent microcarrier entrapment in the foam layer; however, this surfactant was toxic to cells. No correlation was observed between surface tension and the prevention of microcarrier adhesion to gas-liquid interfaces. It is suggested that cell damage as a result of sparging in microcarrier cultures is the result of cells, attached to microcarriers, attaching to rising bubbles and then detaching from the microcarrier as this combination rises through the medium. It is further suggested that the hydrodynamic drag force of the rising microcarrier is sufficiently high to remove the bubble-attached cell from the microcarrier.     

Optimization of hepatocyte attachment to microcarriers: Importance of oxygen

Many potential applications of primary hepatocytes cultured on microcarriers, such as an artificial liver or hepatocyte transplantation, would benefit from having a large number of hepatocytes attached to each microcarrier. In addition, the supply of primary hepatocytes is usually limited, so the efficient utilization of hepatocytes during attachment to microcarriers is necessary. Several physical parameters involved in the attachment process have been investigated, and the number of cells attached per microcarrier and the fraction of hepatocytes which attach have been quantitatively monitored. Variation of the partial pressure of gas phase oxygen in the incubation flask produced significant effects on the attachment of hepatocytes to microcarriers, with higher partial pressures of oxygen found to be necessary for attachment. In addition, variation of fluid depth and cell number, both of which influence the partial pressure of oxygen at the cell surface, affected hepatocyte attachment. The partial pressure of oxygen at the cell surface as a function of the physical parameters was analyzed using a simple one-dimensional theoretical model. Variations in the cell-to-microcarrier ratio used for incubation indicate that a compromise must be made in terms of maximizing the number of cells per microcarrier and the fraction of total hepatocytes which attach. The maximum number of hepatocytes per microcarrier obtained in this work was approximately 100. The best attachment fraction, defined as the ratio of the number of hepatocytes attached to the total number added to the incubation, was approximately 90%. (c) 1993 John Wiley & Sons, Inc.     

WAVETM反应器和搅拌瓶中微载体球转球放大培养的比较

目的:哺乳动物细胞目前已广泛用于生物工程药物如单抗和疫苗的生产.而用于贴壁细胞规模化培养的微载体,也应时应需得以开发并应用于生物制药.贴壁细胞微载体培养在搅拌罐和WAVETM反应器中都能进行.而如要进行进一步的放大培养,球转球工艺不可或缺.为了发展球转球这一新的放大技术,以及考量WAVETM反应器这种新型大规模培养设备的应用性,大量的细胞培养和球转球实验在WAVETM反应器和搅拌瓶中进行.收集到的数据得以分析比较.方法:将Vero细胞分别接入WAVETM反应器和搅拌瓶中用微载体Cytodex 1进行培养.适当补充营养并控制温度、pH等培养条件使细胞增殖.长满微载体的细胞用清洗、消化等球转球工艺的一系列步骤而分离,并放大接种到新的培养体系.球转球工艺的有效性通过记录并统计分析细胞消化分离的回收率,以及细胞重新接种生长的存活力来评估.结果:统计学分析比较WAVETM反应器和搅拌瓶中得到的细胞分离回收率分别是67.56％和39.39％,数理统计P值小于0.0003;细胞重新接种存活率分别是95.17％和78.45％,P值等于0.0107.结论:在WAVETM反应器中进行的球转球放大工艺,其总体表现和有效性远高于在搅拌瓶中得到的结果.在WAVETM反应器中培养的Vero细胞有很好的细胞状态,作为种子链和生产用罐相比搅拌型反应罐均有很大的优越性.     

Optimization of physical parameters for cell attachment and growth on macroporous microcarriers

The rates of cell attachment of the anchorage-dependent mammalian cell line Vero to the gelatin-based macroporous microcarrier Cultispher-G were determined under various conditions. An optimal rate of attachment (0.98 x 10(-2) min(-1)) occurred by an intermittent stirring regimen of 3 min stirring at 40 rpm per 33 min. This stirring regimen appeared to maximize cell-to-bead attachment and minimized cell aggregation which occurred at a broadly comparable rate.A further increase in the rate of cell-to-bead attachment occurred by preincubation of the microcarriers in serum-supplemented medium prior to cell inoculation in a serum-free medium. However, serum supplementation (>5%) was required for maximal cell growth. The pH of the medium had little effect on cell attachment over a broad range (pH 7.1-8.0). An initial cell/bead inoculum of 30 ensured an even distribution of cells on the available microcarriers with a low proportion of unoccupied beads.The rate of cell attachment to Cultispher-G was an order of magnitude lower than the determined value for the charged dextran microcarrier Cytodex-1, which was measured as 9.05 x 10(-2) min(-1). The optimal conditions for cell attachment were significantly different for the two bead types. Cell attachment to the electrostatic surface of the Cytodex-1 microcarriers was highly dependent on pH and serum supplementation. Cell aggregation during attachment to the Cytodex-1 microcarriers was minimal because of the higher rate of cell-microcarrier attachment.The porous nature of the Cultispher-G microcarriers allowed a maximum cell/bead loading of >1400, which was at least 3 times higher than equivalent loading of the cells on Cytodex-1. The Cultispher-G matrix also allowed the use of higher agitation rates (up to 100 rpm) in spinner flasks without affecting the cell growth rate or maximum cell density. (c) 1996 John Wiley & Sons, Inc.