Development of a serum-free culture medium for the large scale production of recombinant protein from a Chinese hamster ovary cell line

Development of a modified serum-free medium for Vero cell cultures: effects of protein hydrolysates, l-glutamine and SITE liquid media supplement on cell growth

Vero cells have been widely used in the viral vaccine production due to the recommendation of the World Health Organization regarding its safety and non-tumorigenicity. The aim of this study was to describe the development a modified serum-free medium for Vero cell cultures. Two protein hydrolysates (Bacto™ soytone and Bacto™ yeast extract), vitamin C, vitamin B12, SITE liquid media supplement, and recombinant human epidermal growth factor (rEGF) were investigated as serum substitutes. A sequential experiment of fractional factorial and central composite design was applied. A modified serum-free medium obtained (named as SFM01-M) was verified. Contrary to P0, the cell yields obtained at P1, P2, and P3 decreased continuously during the verification experiments indicating that Vero cells could not adapt to SFM01-M as expected according to the empirical mathematical model. To improve cell growth after P0, protein hydrolysates, l-glutamine, and SITE liquid media supplement were further investigated. The results showed that cell yields gradually decreased from P1 to P3 when a fixed concentration of Bacto™ yeast extract (7.0 g/L) combined with various concentrations of Bacto™ soytone (0.1-7.0 g/L) in SFM01-M were used. Similarly, cell yields also gradually decreased from P1 to P3 when a fixed concentration of Bacto™ soytone (7.0 g/L) combined with various concentrations of Bacto™ yeast extract (0.1-7.0 g/L) in SFM01-M were used. However, the combination of Bacto™ soytone at 0.1 g/L and Bacto™ yeast extract at 7.0 g/L or Bacto™ soytone at 7.0 g/L and Bacto™ yeast extract at 0.1 g/L in SFM01-M could give the maximum cell yield at P3 when compared with other combinations. In addition, the addition of SITE liquid media supplement (0.1-2.0% v/v) in SFM01-M in which the concentrations of Bacto™ soytone, Bacto™ yeast extract, and l-glutamine were fixed at 0.1 g/L, 0.1 g/L, and 4.0 mM, respectively, the results showed that the cell yields obtained at P3 were not significantly different. From this study, the optimum concentrations of SFM01-M components were as follows: Bacto™ soytone (0.1 g/L), Bacto™ yeast extract (0.1 g/L), vitamin C (9.719 mg/L), vitamin B12 (0.1725 mg/L), SITE liquid media supplement (0.1-2.0% v/v), rEGF (0.05756 mg/L), l-glutamine (4.0 mM), MEM non-essential amino acids (1.0% v/v), sodium pyruvate (1.0 mM), MEM (9.4 g/L), and sodium hydrogen carbonate (2.2 g/L). However, to evaluate SFM01-M in the long-term subculture of Vero cells, the efficiency of SFM01-M will be further investigated.

Impact of media components from different suppliers on enterokinase productivity in Pichia pastoris

Background

The aim of this study was to provide an information about the homogeneity on the level of enterokinase productivity in P. pastoris depending on different suppliers of the media components.

Results

In previous studies, we performed the optimisation process for the production of enterokinase by improving the fermentation process. Enterokinase is the ideal enzyme for removing fusion partners from target recombinant proteins. In this study, we focused our optimization efforts on the sources of cultivation media components. YPD media components were chosen as variables for these experiments. Several suppliers for particular components were combined and the optimisation procedure was performed in 24-well plates. Peptone had the highest impact on enterokinase production, where the difference between the best and worst results was threefold. The least effect on the production level was recorded for yeast extract with a 1.5 fold difference. The worst combination of media components had a activity of only 0.15 U/ml and the best combination had the activity of 0.88 U/ml, i.e., a 5.87 fold difference. A substantially higher impact on the production level of enterokinase was observed during fermentation in two selected media combinations, where the difference was almost 21-fold.

Conclusions

Results demonstrated in the present study show that the media components from different suppliers have high impact on enterokinase productivity and also provide the hypothesis that the optimization process should be multidimensional and for achieving best results it is important to perform massive process also in terms of the particular media component supplier .

Rich production media as a platform for CHO cell line development

Recent cell culture media for mammalian cells can be abundantly formulated with nutrients supporting production, but such media can be limited to use in host cell culture, transfection, cell cloning, and cell growth under the low cell density conditions. In many cases, appropriate platform media are used for cell line development, and then replaced with rich media for production. In this study, we demonstrate rich chemically defined media for Chinese hamster ovary (CHO) cells that are suitable as basal media both for cell line development and for final production of culture process. Set up for transfection, semi-solid media optimization, mini-pool screening, and single cell cloning media development were performed, and final clones were obtained with higher productivity in fed-batch culture mode using rich formulated media comparing with lean formulated media. Developed methods may remove the requirements for cell adaptation to production media after cell line development, and relieve the clonality issues associated with changing the culture media. Furthermore, established methods have advantages over traditional approaches, including saving resources and decreasing the time and the effort required to optimize the production process.

Culture of Preimplantation Rabbit Embryos

It is surprising that so little attention is currently given to in vitro culture of preimplantation rabbit embryos, even though the rabbit is the only laboratory animal in which there is very considerable embryo growth before implantation, resulting in a 300-fold increase in protein content of embryonic cells during the preimplantation period and the formation of more than a 100,000 cells in the blastocyst. This growth pattern explains why blastocyst formation in vitro has an absolute requirement for amino acids, and vitamins, particularly inositol, are esssential for blastocyst growth. A semi-defined medium supplemented with 1.5% BSA (variously known as BSM II or modified F10) was developed at Cornell University at the end of the 1960s and allowed the systematic investigation of the requirements for development of 1-cell rabbit embryos to blastocysts. However, the requirements for in vitro blastocyst growth comparable to in vivo growth still remain an unsolved problem. Citrate, often found as a contaminant in serum albumin, may have an essential role in rabbit blastocyst growth, which would fit in with its role in the development of serum-free media for culture of various types of mammalian cells.A comprehensive account of the methodology is given to enable a researcher with experience culturing embryos of a different species to work on the rabbit embryo. This account covers medium preparation, hormonal stimulation of superovulation, natural breeding/artificial insemination, and collection of embryos of different stages from 1-cell to blastocyst either after euthanasia or under anesthesia. Peculiarities of the rabbit embryo such as the presence of the mucoprotein coat and its effects on behavior of cultured and transferred embryos are described. Suggestions are made for future avenues of research.

Comparative Assessment on the Expression Level of Recombinant Human Follicle-Stimulating Hormone (FSH) in Serum-Containing Versus Protein-Free Culture Media

Production of recombinant pharmaceutical proteins has made a great contribution to modern biotechnology. At present, quick advances in protein expression lead to the enhancement of product quantity and quality as well as reduction in timescale processing. In the current study, we assessed the expression level of recombinant human follicle-stimulating hormone (rhFSH) in adherent and suspension Chinese hamster ovary (CHO) cell lines by cultivation in serum-containing and chemically defined, protein-free media. The expression cassette entailing FSH subunits was transfected to CHO/dhfr- and CHO DG44 cell lines, and gene amplification was achieved using dihydrofolate reductase (DHFR)/methotrexate (MTX) system. Afterward, the expression level of rhFSH was studied using real-time PCR, Western blotting and ELISA. Our achievements revealed that stepwise increase in MTX [up to 2000 nano-molar (nM)] leads to boost the expression level of rhFSH mRNA in both cell lines, although DG44 have better results, as mRNA expression level reached 124.8- and 168.3-fold in alpha and beta subunits, respectively. DG44 cells have also the best protein production in 2000 nM MTX, which reached 1.7-fold in comparison with that of the mock group. According to the above results and many advantages of protein-free media, DG44 is preferable cell line for future steps.

Animal-cell culture media: History, characteristics, and current issues

Background

Cell culture technology has spread prolifically within a century, a variety of culture media has been designed. This review goes through the history, characteristics and current issues of animal‐cell culture media.

Methods

A literature search was performed on PubMed and Google Scholar between 1880 and May 2016 using appropriate keywords.

Results

At the dawn of cell culture technology, the major components of media were naturally derived products such as serum. The field then gradually shifted to the use of chemical‐based synthetic media because naturally derived ingredients have their disadvantages such as large batch‐to‐batch variation. Today, industrially important cells can be cultured in synthetic media. Nevertheless, the combinations and concentrations of the components in these media remain to be optimized. In addition, serum‐containing media are still in general use in the field of basic research. In the fields of assisted reproductive technologies and regenerative medicine, some of the medium components are naturally derived in nearly all instances.

Conclusions

Further improvements of culture media are desirable, which will certainly contribute to a reduction in the experimental variation, enhance productivity among biopharmaceuticals, improve treatment outcomes of assisted reproductive technologies, and facilitate implementation and popularization of regenerative medicine.

Tracking dipeptides at work-uptake and intracellular fate in CHO culture

Market demands for monoclonal antibodies (mAbs) are steadily increasing worldwide. As a result, production processes using Chinese hamster ovary cells (CHO) are in the focus of ongoing intensification studies for maximizing cell-specific and volumetric productivities. This includes the optimization of animal-derived component free (ADCF) cultivation media as part of good cell culture practice. Dipeptides are known to improve CHO culture performance. However, little or even conflicting assumptions exist about their putative import and functionality inside the cells. A set of well-known performance boosters and new dipeptide prospects was evaluated. The present study revealed that dipeptides are indeed imported in the cells, where they are decomposed to the amino acids building blocks. Subsequently, they are metabolized or, unexpectedly, secreted to the medium. Monoclonal antibody production boosting additives like l-alanine-l-glutamine (AQ) or glycyl-l-glutamine (GQ) can be assigned to fast or slow dipeptide uptake, respectively, thus pinpointing to the need to study dipeptide kinetics and to adjust their feeding individually for optimizing mAb production.

Cell growth stimulating effect of Ganoderma lucidum spores and their potential application for Chinese hamster ovary K1 cell cultivation

In this work, water-soluble extracts of Ganoderma lucidum spores (Gls), a Chinese medicinal herb that possesses cell growth stimulating function, were found to be an effective growth factor for Chinese hamster ovary (CHO) cell cultivation. The Gls extract was prepared and supplemented to CHO K1 cell culture media with various serum levels. Our results obtained from both the static culture and the spinner-flask suspension culture showed that use of small-amount Gls extract effectively promoted cell growth and suppressed cell apoptosis induced by serum deprivation with normal cell cycle maintained in a low-serum medium. The low-serum medium containing 1 % (v/v) fetal bovine serum (FBS) and 0.01 % (w/v) Gls extract showed a comparable performance on both cell growth and fusion protein productivity with the conventional CHO culture medium containing 10 % (v/v) FBS and a commercial serum-free medium. This is the first study of the potential of Gls extracts for use as an alternative cell growth factor and nutrient for CHO cells. The findings have presented a new approach to economic cultivation of CHO cells for therapeutic protein production.

Effects of Peptone Supplementation in Different Culture Media on Growth, Metabolic Pathway and Productivity of CHO DG44 Cells; a New Insight into Amino Acid Profiles

Background:

The optimization of bioprocess conditions towards improved growth profile and productivity yield is considered of great importance in biopharmaceutical manufacturing. Peptones as efficient sources of nutrients have been studied for their effect on media development; however, their role on metabolic pathway is not well understood.

Methods:

In the present study, the effect of different concentration of peptones on a recombinant Chinese hamster ovary (CHO) cell line grown in three serum-free suspension cultures was determined. Six peptones of different origins and available amino acid profiles were investigated regarding their impact on cell growth, productivity, and metabolic pathways changes.

Results:

In optimized feeding strategies, increases of 136% and 159% in volumetric productivity (for a low-nutrient culture media) and 55% (for a high-nutrient culture media) were achieved. Furthermore, particular sources of peptones with specific amino acid profile developed preferential results for each different culture medium. Two peptones, SoyA2SC and SoyE-110, were the only hydrolysates that showed production improvement in all three media. Casein Peptone plus Tryptone N1 and SoyA3SC showed different improved results based on their implemented concentration for each individual basal medium.

Conclusion:

The amino acid profile of peptones may provide clues to identify the most effective feeding strategies for recombinant CHO cells.

Knobs-into-holes antibody production in mammalian cell lines reveals that asymmetric afucosylation is sufficient for full antibody-dependent cellular cytotoxicity

Knobs-into-holes is a well-validated heterodimerization technology for the third constant domain of an antibody. This technology has been used to produce a monovalent IgG for clinical development (onartuzumab) and multiple bispecific antibodies.^1,2 The most advanced uses of this approach, however, have been limited to E. coli as an expression host to produce non-glycosylated antibodies. Here, we applied the technology to mammalian host expression systems to produce glycosylated, effector-function competent heterodimeric antibodies. In our mammalian host system, each arm is secreted as a heavy chain-light chain (H-L) fragment with either the knob or hole mutations to allow for preferential heterodimer formation in vitro with low levels of homodimer contaminants. Like full antibodies, the secreted H-L fragments undergo Fc glycosylation in the endoplasmic reticulum. Using a monospecific anti-CD20 antibody, we show that full antibody-dependent cell-mediated cytotoxicity (ADCC) activity can be retained in the context of a knobs-into-holes heterodimer. Because the knobs-into-holes mutations convert the Fc into an asymmetric heterodimer, this technology was further used to systematically explore asymmetric recognition of the Fc. Our results indicate that afucosylation of half the heterodimer is sufficient to produce ADCC-enhancement similar to that observed for a fully afucosylated antibody with wild-type Fc. However, the most dramatic effect on ADCC activity is observed when two carbohydrate chains are present rather than one, regardless of afucosylation state.

The culture of rat myeloma and rat hybridoma cells in a protein-free medium

Y0 is a rat x rat hybridoma cell line, which does not secrete immunoglobulin, produced using a fusion partner derived from the Y3 (Y3,Ag.1.2.3) rat myoloma cell line. Y0 and Y3 have both been widely used as fusion partners in the production of rat x rat hybridomas. Y0 has also been used in recombinant gene technology. Y0 cells grown in shake flask culture, using RPMI 1640 medium with 4mM l-glutamine and 5% foetal bovine serum, reached a maximal cell density of 1.5×10(6) cells ml(-1) with 86% viability. Y0 cells which has been adapted to grow in ABC protein-free medium reached a maximal density, in shake flask culture, of 8.75×10(5) cells ml(-1) with 79% viability. An improved protein-free medium, designated W38 medium, was developed. In shake flask culture, W38 medium supported Y0 cell growth to a density of 2.02×10(6) cells ml(-1) with 96% viability. Two Y3 hybridomas, YID 13.9.4 cells and SAM 618 cells were adapted to growth in W38 medium. For both hybridomas, cell growth and product yield in shake flask culture using W38 medium was superior to that obtained with serum-containing RPMI 1640 medium.

The use of serum-free medium for the production of functionally active humanised monoclonal antibody from NS0 mouse myeloma cells engineered using glutamine synthetase as a selectable marker

A protein-free growth medium (W38 medium) had previously been developed for the NS0 mouse myeloma cell line which is cholesterol-auxotrophic. This paper describes the development of a protein-free growth medium for NS0 cells expressing humanised monoclonal antibody using GS (glutamine synthetase) as a selectable marker. Several GS-engineered NS0 cell lines expressing humanised monoclonal antibody grew in a modification of W38 medium which maintained GS-selection, supplemented with cholesterol, phosphatidylcholine and β-cyclodextrin. Further studies showed that additional glutamic acid, asparagine, ribonucleosides and choline chloride improved cell growth. Amino acid analysis identified a number of amino acids that were being depleted from the culture medium. NS0 cell lines 9D4 and 2H5 expressing CAMPATH-1H(*) were adapted to enable them to grow serum-free in the absence of cholesterol and β-cyclodextrin. Cholesterol-independent 9D4 (9D4.CF) cells grown in shake flask culture using an enriched protein-free medium (WNSD medium), supplemented with human recombinant insulin (Nucellin), reached a maximum cell density to 1.86×10(6) cells ml(-1) producing 76.6 mg l(-1) of antibody. CAMPATH-1H antibody produced using serum-free medium was found to be functionally activein vitro in the Antibody Dependant Cellular Cytotoxicity (ADCC) assay.

Promoting effect of rapeseed proteins and peptides on Sf9 insect cell growth

The Baculovirus Expression Vector System has become widely used for the production of recombinant proteins for research and diagnostics. Serum-free culture media able to support high cell densities have been developed for the large scale culture of insect cells. While serum elimination aims at avoiding the risks associated with the introduction of an ill defined component of bovine origin, additives such as protein hydrolysates from animal sources are still used. An alternative could be the supplementation of culture media with protein hydrolysates derived from plants. In this study, we describe the replacement of lactalbumin hydrolysate with a laboratory produced hydrolysate of rapeseed proteins. Its effect on Sf9 cell growth kinetics, substrate consumption and by-product formation in low-serum or serum-free medium was evaluated. Cells were unable to grow in the presence of a rapeseed protein hydrolysate generated by PTN 3.0 Special((R)) enzyme and containing only 24% of peptides under 1 kDa in size. On the other hand, serum-free medium supplementation with a rapeseed protein hydrolysate obtained with Orientase 90N((R)) enzyme had a strong growth promoting effect, leading to a 60% increase in maximal cell density without affecting cell metabolism. This significant positive effect could be explained by the higher degree of hydrolysis of this digest, with 74% of peptides under 1 kDa in size.

The use of peptones as medium additives for the production of a recombinant therapeutic protein in high density perfusion cultures of mammalian cells

Protein hydrolysates as substitutes for serum havebeen employed by many in cell culture mediumformulation, especially with the shift to low proteinor protein-free media. More recently, vegetablehydrolysates have also been added as nutritionalsupplements to fortify the amino acid content in smallpeptide form for batch and fed-batch fermentations. Several of these new hydrolysates (peptones of soy,rice, wheat gluten etc.) were tested as protein-freemedium supplements for the production of a recombinanttherapeutic protein. Multiple peptone-supplemented,continuous perfusion bioreactor experiments wereconducted, varying dilution rates and basal mediumcomposition over the various runs. Cell specificrates and product quality studies were obtained forthe various peptones and compared with peptone-freemedium. The potential for peptones to decreaseintrinsic and proteolytic degradation of the productwas also investigated.It was found that peptones confer a nutritionalbenefit, especially at low dilution rates, for therecombinant BHK cell line used in this investigation.The specific productivity increased 20-30% comparedto the peptone-free controls. However, this benefitwas also fully delivered by using fortified medium inplace of the peptone-enriched media. Therefore, whilepeptones may be considered as useful medium additiveswhen development time is limited, their addition maybe avoided by systematic medium development ifpermitted by the time line of the project.

Plant protein hydrolysates support CHO-320 cells proliferation and recombinant IFN-gamma production in suspension and inside microcarriers in protein-free media

We have recently developed a protein-free medium (PFS) able to support the growth of Chinese hamster ovary (CHO) cells in suspension. Upon further supplementation with some plant protein hydrolysates, medium performances reached what could be observed in serum-containing media [Burteau et al. In Vitro Cell. Dev. Biol.-Anim. 39 (2003) 291]. Now, we describe the use of rice and wheat protein hydrolysates, as non-nutritional additives to the culture medium to support productivity and cell growth in suspension or in microcarriers. When CHO-320 cells secreting recombinant interferon-gamma (IFN-gamma) were cultivated in suspension in a bioreactor with our PFS supplemented with wheat hydrolysates, the maximum cell density increased by 25% and the IFN-gamma secretion by 60% compared to the control PFS. A small-scale perfusion system consisting of CHO-320 cells growing on and inside fibrous microcarriers under discontinuous operation was first developed. Under these conditions, rice protein hydrolysates stimulated recombinant IFN-gamma secretion by 30% compared to the control PFS. At the bioreactorscale, similar results were obtained but when compared to shake-flasks studies, nutrients, oxygen or toxic by-products gradients inside the microcarriers seemed to be the main limitation of the system. An increase of the perfusion rate to maintain glucose concentration over 5.5 mM and dissolved oxygen (DO) at 60% was able to stimulate the production of IFN-gamma to a level of 6.6 mug h(-1) g(-1) of microcarriers after 160 h when a cellular density of about 4 x 10(8) cell g(-1) of carriers was reached.

CHO-K1 host cells adapted to growth in glutamine-free medium by FACS-assisted evolution

During the process of recombinant cell line optimisation for production of biopharmaceuticals, multiple cellular properties like robustness against stress, the attainment of high cell concentrations and maintenance of high viability must be considered to maximize protein yield. To improve growth and viability, glutamine is supplemented as an alternative energy source for rapidly dividing cells that oxidize glucose inefficiently. However, the resulting by-product ammonia is toxic at high concentrations and has a negative impact on protein glycosylation, a major quality-determining parameter of biopharmaceuticals. In this work, the CHO-K1 cell line was adapted to a chemically defined medium and suspension growth within 3 weeks. Subsequently, the glutamine concentration was stepwise reduced from 8 to 4 and 2 mM. After each reduction, both the final cell concentration in the batch and the viability decreased. To force a rapid evolution of cells to achieve high final cell concentrations, cells were seeded at high densities (10(7) cells/mL) and surviving cells were sorted by FACS or MACS when viability declined to 10% (typically after 24 h). Sorted cells were grown in batch until viability declined to 10% and viable cells recovered again. The final sorted population was able to reach comparable or even better viable cell concentrations and showed a significantly improved viability compared to their ancestors. The 2 mM glutamine-adapted cell line was directly transferred into glutamine-free medium and was able to grow at comparable rates without requiring further adaptation. Cells compensated the lack of glutamine by increasing their consumption of glutamate and aspartate.

Effect of surfactant pluronic F-68 on CHO cell growth, metabolism, production, and glycosylation of human recombinant IFN-γ in mild operating conditions

The control of glycosylation to satisfy regulatory requirements and quality consistency of recombinant proteins produced by different processes has become an important issue. With two N-glycosylation sites, γ-interferon (IFN-γ) can be seen as a prototype of a recombinant therapeutic glycoprotein for this purpose. The effect of the nonionic surfactant Pluronic F-68 (PF-68) on cell growth and death was investigated, as well as production and glycosylation of recombinant IFN-γ produced by a CHO cell line that was maintained in a rich protein-free medium in the absence or presence of low agitation. Under these conditions, a dose-dependent effect of PF-68 (0-0.1%) was shown not only to significantly enhance growth but also to reduce cell lysis. Interestingly, supplementing the culture medium with PF-68 led to increased IFN-γ production as a result of both higher cell densities and a higher specific production rate of IFN-γ. If cells were grown with agitation, lack of PF-68 in the culture medium decreased the fraction of the fully glycosylated IFN-γ glycoform (2N) from 80% to 65-70% during the initial period. This effect appeared to be due to a lag phase in cell growth observed during this period. Finally, a global kinetic study of CHO cell metabolism indicated higher efficiency in the utilization of the two major carbon substrates when cultures were supplemented with PF-68. Therefore, these results highlight the importance of understanding how media surfactant can affect cell growth as well as cell death and the product quality of a recombinant glycoprotein expressed in CHO cell cultures.

Effect of alpha-ketoglutarate on monoclonal antibody production of hybridoma cell lines in serum-free and serum-containing medium

Process development and optimization for increase population growth and protein productivity in mammalian cell culture have been studied for many years. In this study, the behavior of hybridoma cells was investigated using six-well micro-titer plate systems with a working volume of 4 ml. Mouse hybridoma cell lines D2 and 2C83G2 were seeded in serum-free and serum-containing media and cultured for 8 days. alpha-Ketoglutarate is an integral component of the tricarboxylic acid (TCA) cycle and is produced from glutamine via glutamate. To study its effect on cell growth, metabolism, and monoclonal antibody (mAb) production, 2 mM alpha-ketoglutarate (pH 7.2) was added in both media at the beginning of the cultivation and in another set after 72 h. High cell density was observed in D2 cell culturing in serum-free medium, while 2C83G2 cell line showed high cell density in serum-containing medium. However, both cell lines cultured in serum-free medium gave viability above 70% when grown for 8 days. The supplement of 2 mM alpha-ketoglutarate supported cell growth and mAb production of both hybridoma cell lines in serum-free and serum-containing medium. The addition of alpha-ketoglutarate at the beginning of the batch cultivation gave better result in cell growth and mAb production as compared to alpha-ketoglutarate supplementation after 72 h. However, addition after 72 h was better than no addition at all. This indicates that alpha-ketoglutarate have a positive effect on production and release of antibody.

Pluronic enhances the robustness and reduces the cell attachment of mammalian cells

The addition of the non-ionic surfactant, Pluronic F-68, to serum-free CHO cultures causes multi-functional effects that enhance cell yield in agitated cultures and reduce cell adhesion in stationary cultures. Three independent CHO cell lines were subjected to high liquid shear in assay systems that either included or excluded a liquid-gas interface. In the absence of Pluronic, there was a loss in cell viability in either assay system, although there was an intrinsic variability in sensitivity of the cell lines to shear damage. Supplementation with Pluronic prevented loss of cell viability, indicating protection in either a gas sparged or bubble-free environment. However, we found no evidence of long-term protection of cells once Pluronic was removed. Pluronic was capable of repairing trypsin-damaged cells as evidenced by enhanced growth, reduced membrane porosity, and improved robustness under liquid shear. The proportion of adherent cells was reduced to a minimal level by the presence of Pluronic although its effect was rapidly reversible with a high proportion (70%) of adherent cells observed within a few culture passages of its removal. The observed effects of Pluronic on these cultures are compatible with a mechanism in which the polymer forms a protective layer on the cell membrane, which has a significantly lower hydrophobicity.

Developement of serum-free media in CHO-DG44 cells using a central composite statistical design

A serum free medium was developed for the production of recombinant antibody against Botulinum A (BoNTA) using dihydrofolate reductase deficient Chinese Hamster Ovary Cells (CHO-DG44) in suspension culture. An initial control basal medium was prepared, which was similar in composition to HAM's F12: IMDM (1:1) supplemented with insulin, transeferrin, selenium and a lipid mixture. The vitamin concentration of the basal medium was twice that of HAM's F12: IMDM (1:1). CHO-DG44 cells expressing S25 antibody grew from 2 x 10(5) cells to maximum cell density of 1.04 x 10(6) cells/ml after 5 days in this control medium. A central composite design was used to identify optimal levels and interaction among five groups of medium components. These five groups were glutamine, Essential Amino Acids (EAA), Non Essential Amino Acids (NEAA), Insulin, Transferrin, Selenium (ITS), and lipids. Fifty experiments were carried out in four batches, with two controls in each batch. There was little effect of ITS and Lipid concentrations over the range studied, and glutamine concentration showed a strong interaction with EAA. The optimal concentrations of the variables studied were 2.5 mM Glutamine, 7.4 mM (2x) EAA, 1.4 mM (0.5x) NEAA, 1x ITS supplement, 0.7x Lipids supplement. The maximum viable cell density attained in the optimized medium was 1.4 x 10(6) cells/ml, a 35% improvement over the control culture, while the final antibody titer attained was 22 +/- 3.4 mug/mL, a 50% improvement.

Large-scale gene expression analysis of cholesterol dependence in NS0 cells

NS0, a nonsecreting mouse myeloma cell, is a major host line used for recombinant antibody production. These cells have a cholesterol-dependent phenotype and rely on an exogenous supply of cholesterol for their survival and growth. To better understand the physiology underlying cholesterol dependence, we compared NS0 cells, cultivated under standard cholesterol-dependent growth conditions (NS0), to cells adapted to cholesterol-independent conditions (NS0 revertant, NS0_r). Large-scale transcriptional analyses were done using the Affymetrix GeneChip array, MG-U74Av2. The transcripts expressed differentially across the two cell lines were identified. Additionally, proteomic tools were employed to analyze cell lysates from these two cell lines. Cellular proteins from both NS0 and NS0_r were subjected to 2D gel electrophoresis. MALDI-TOF mass spectrometry was performed to determine the identity of the differentially expressed spots. We examined the expression level of mouse genes directly involved in cholesterol biosynthesis, lipid metabolism, and central energy metabolism. Most of these genes were downregulated in the revertant cell type, NS0_r, compared to NS0. Overall, a large number of genes are expressed differentially, indicating that the reversal of cholesterol dependency has a profound effect on cell physiology. It is probable that a single gene mutation, activation, or inactivation is responsible for cholesterol auxotrophy. However, the wide-ranging changes in gene expression point to the distinct possibility of a regulatory event affecting the reversibility of auxotrophy, either directly or indirectly.

Serum- and protein-free media formulations for the Chinese hamster ovary cell line DUKXB11

The production of therapeutic proteins in mammalian cell lines is of outstanding importance. The maintenance of most mammalian cell lines in culture requires the addition of serum to the culture medium. The elimination of serum from mammalian cell culture is desirable since serum is expensive and a source of contaminants, e.g. viruses, mycoplasma or prions. Here we describe the composition of serum- and protein-free media for the Chinese hamster ovary (CHO) cell line DUKXB11. The serum-free formulation supports excellent growth of CHO DUKXB11 cells at low (23cells/cm2) and high (2 x 10(4) cells/cm2) seeding densities characterized by a generation time of 10-12h, and, after addition of 0.2% pluronic F-68, the growth of a recombinant suspension cell line derived from DUKXB11. In addition, this formulation also allowed us to adapt recombinant cell lines expressing various amounts of human antithrombin ATIII (ATIII) to serum-free conditions. Secretion of ATIII was readily observed in the serum-free medium. Minor changes to the serum-free formulation resulted in a protein free formulation that supported growth of CHO DUKXB11 cells, growth of recombinant CHO cells expressing ATIII, and production of ATIII.

Higher expression of fab antibody fragments in a CHO cell line at reduced temperature

A chimeric Fab was expressed in Chinese hamster ovary cells under the control of the CMV promoter in a two-stage production process. Cells were first grown to 90% confluence at 37 degrees C in a proliferation phase, followed by a production phase at either 37 degrees C or 28 degrees C. Medium supplemented with serum and medium free from serum was tested in the production phase at both temperatures. Comparison of Fab expression revealed that reducing the temperature to 28 degrees C resulted in a 14-fold increase in product yield when cells were cultivated in serum-containing medium, and in a 38-fold increase in product yield when serum-free medium was applied.

Development of a serum-free medium for the production of erythropoietin by suspension culture of recombinant Chinese hamster ovary cells using a statistical design

In order to develop a serum-free (SF) medium for the production of erythropoietin (EPO) by suspension culture of recombinant Chinese hamster ovary (rCHO) cells, a statistical optimization approach based on a Plackett-Burman design was adopted. A basal medium was prepared by supplementing Iscove's modified Dulbecco's medium (IMDM) with Fe(NO3)3.9H2O, CuCl2 and ZnSO4.7H2O which are generally contained in SF medium formulations. Insulin, transferrin and ethanolamine were also supplemented to the basal medium to determine their optimal concentrations. From this statistical analysis, glutamate, serine, methionine, phosphatidylcholine, hydrocortisone and pluronic F68 were identified as positive determinants for cell growth. The SF medium was formulated by supplementing the basal medium with components showing positive effects on cell growth in suspension culture. An EPO titer in this optimized SF medium was 79% of that in IMDM supplemented with 5% dialyzed fetal bovine serum (dFBS). Furthermore, the in vitro and in vivo biological activities of EPO produced in the SF medium were comparable to those produced in the serum-supplemented medium. Taken together, the results obtained here show that a Plackett-Burman design facilitates the development of SF media for the production of EPO by suspension culture of rCHO cells.

Development of a serum-free medium for dihydrofolate reductase-deficient Chinese hamster ovary cells (DG44) using a statistical design: beneficial effect of weaning of cells

To develop serum-free (SF) medium for dihydrofolate reductase-deficient Chinese hamster ovary cells (DG44), a statistical optimization approach based on a Plackett-Burman design was adopted. DG44 cells which were normally maintained in 10 serum medium were gradually weaned to 0.5% serum medium to increase the probability of successful growth in SF medium. A basal medium was prepared by supplementing Dulbecco's modified Eagle's medium and Ham's nutrient mixture F12 with hypoxanthine (10 mg/l) and thymidine (10 mg/l). Twenty-eight different supplements were selected as variables on the basis of their growth-promoting abilities. From statistical analysis, leucine, tryptophan, lysine, proline, histidine, hydrocortisone, ethanolamine, and phosphatidylcholine were identified as important components showing positive effects on cell growth. A new SF medium (SF-DG44) was formulated by supplementing the basal medium with these components. When the weaned cells were inoculated at 1.0 x 10(5) cells/ml, a maximum viable cell concentration of 6.4 x 10(3)) cells/ ml was achieved in SF-DG44 medium. In contrast, when the unweaned cells were used, a concentration of only 4.1 x 10(5) cells/ml was reached under the same culture conditions, indicating that weaning of cells improves cell growth in SF medium. In summary, we found that development of a novel SF medium for DG44 cells was facilitated using a Plackett-Burman design technique and weaning of cells.

Development of a serum-free medium for the production of humanized antibody from Chinese hamster ovary cells using a statistical design

To develop serum-free (SF) media for the production of humanized antibody from recombinant Chinese hamster ovary (rCHO) cells, a statistical optimization approach based on a Plackett-Burman design was adopted. A basal medium was prepared by supplementing alpha-minimal essential medium (alpha-MEM) with Fe(NO3)3.9H2O, CuCl2, ZnSO4.7H2O, and Na2SeO3 which are generally contained in SF medium formulations. Insulin, transferrin, and ethanolamine were also supplemented to the basal medium to determine their optimal concentrations. From this statistical analysis, serine, phenylalanine, and tyrosine were identified as important determinants for cell growth. Also, putrescine, linoleic acid, and hydrocortisone were shown to be important for both cell growth and antibody production. The SF medium was formulated by supplementing the basal medium with components showing positive effects on cell growth and/or antibody production. Cell growth and antibody production in this SF medium were comparable to those in alpha-MEM supplemented with 5% dialyzed fetal bovine serum. Taken together, the results obtained here show that a Plackett-Burman design facilitates the development of SF media for rCHO cells aimed at producing a humanized antibody.

Large-scale mammalian cell culture

Mammalian cell culture continues to draw major research efforts. A great deal of progress has recently been made in cellular physiology, especially in factors adversely affecting cell growth or viability. Through molecular genetic manipulation, cells are more readily cultivated in a medium free of animal proteins. Achieving a high cell concentration and high viability continue to be common themes in engineering research. The need to implement a control policy for fed-batch and perfusion cultures has prompted increased efforts in process monitoring and control. Integrating these advances will be beneficial for ensuring product quality and process consistency.