CHO DUKX cell lineages preadapted to growth in serum-free suspension culture enable rapid development of cell culture processes for the manufacture of recombinant proteins

Optimization of recombinant antibody production based on the vector design and the level of metabolites for generation of Ig- producing stable cell lines

BACKGROUND

The biopharmaceutical industry is significantly growing worldwide, and the Chinese hamster ovary (CHO) cells are used as a main expression host for the production of recombinant monoclonal antibodies. Various metabolic engineering approaches have been investigated to generate cell lines with improved metabolic characteristics for increasing longevity and mAb production. A novel cell culture method based on the 2-stage selection makes it possible to develop a stable cell line with high-quality mAb production.

RESULTS

We have constructed several design options of mammalian expression vectors for the high production of recombinant human IgG antibodies. Versions for bipromoter and bicistronic expression plasmids different in promoter orientation and cistron arrangements were generated. The aim of the work presented here was to assess a high-throughput mAb production system that integrates the advantages of high-efficiency cloning and stable cell clones to stage strategy selection reducing the time and effort required to express therapeutic monoclonal mAbs. Development of a stable cell line using bicistronic construct with EMCV IRES-long link gave an advantage in high mAb expression and long-term stability. Two-stage selection strategies allowed the elimination of low-producer clones by using metabolic level intensity to estimate the IgG production in the early steps of selection. The practical application of the new method allows to reduce time and costs during stable cell line development.

Biopharmaceutical Manufacturing: Historical Perspectives and Future Directions

This review describes key milestones related to the production of biopharmaceuticals-therapies manufactured using recombinant DNA technology. The market for biopharmaceuticals has grown significantly since the first biopharmaceutical approval in 1982, and the scientific maturity of the technologies used in their manufacturing processes has grown concomitantly. Early processes relied on established unit operations, with research focused on process scale-up and improved culture productivity. In the early 2000s, changes in regulatory frameworks and the introduction of Quality by Design emphasized the importance of developing manufacturing processes to deliver a desired product quality profile. As a result, companies adopted platform processes and focused on understanding the dynamic interplay between product quality and processing conditions. The consistent and reproducible manufacturing processes of today's biopharmaceutical industry have set high standards for product efficacy, quality, and safety, and as the industry continues to evolve in the coming decade, intensified processing capabilities for an expanded range of therapeutic modalities will likely become routine. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Tetrahydrofolate increases suspension growth of dihydrofolate reductase-deficient chinese hamster ovary DG44 cells in chemically defined media

Adaptation of dihydrofolate reductase (DHFR)-deficient Chinese hamster ovary (CHO) DG44 cells to chemically defined suspension culture conditions is a time-consuming and labor-intensive process because nonadapted DHFR-deficient CHO DG44 cells normally show poor growth in chemically defined medium (CDM). We examined the effects of folate derivatives, ribonucleotides, and nucleobases on the growth of suspension-adapted DHFR-deficient CHO DG44 cells in CDM. Among the tested additives, tetrahydrofolate (THF) was identified as an effective component for increasing cell growth. THF supplementation in the range of 0.2-359 μM enhanced cell growth in in-house CDM. Addition of 3.6 μM THF to in-house CDM resulted in a more than 2.5-fold increase in maximum viable cell density. Moreover, supplementation of six different commercial CDMs with 3.6 μM THF yielded up to 2.9-fold enhancement of maximum viable cell density. An anchorage- and serum-dependent DHFR-deficient CHO DG44 cell line was adapted within two consecutive passages to suspension growth in in-house CDM supplemented with 3.6 μM THF. These data indicate that supplementation of chemically defined cell culture media with greater than 0.2 μM THF can help achieve a high density of suspension-adapted DHFR-deficient CHO DG44 cells and may facilitate rapid adaptation of nonadapted DHFR-deficient CHO DG44 cells to suspension culture. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1539-1546, 2016.

Cell line development for biomanufacturing processes: recent advances and an outlook

At the core of a biomanufacturing process for recombinant proteins is the production cell line. It influences the productivity and product quality. Its characteristics also dictate process development, as the process is optimized to complement the producing cell to achieve the target productivity and quality. Advances in the past decade, from vector design to cell line screening, have greatly expanded our capability to attain producing cell lines with certain desired traits. Increasing availability of genomic and transcriptomic resources for industrially important cell lines coupled with advances in genome editing technology have opened new avenues for cell line development. These developments are poised to help biosimilar manufacturing, which requires targeting pre-defined product quality attributes, e.g., glycoform, to match the innovator's range. This review summarizes recent advances and discusses future possibilities in this area.

The relationship between mTOR signalling pathway and recombinant antibody productivity in CHO cell lines

Background

High recombinant protein productivity in mammalian cell lines is often associated with phenotypic changes in protein content, energy metabolism, and cell growth, but the key determinants that regulate productivity are still not clearly understood. The mammalian target of rapamycin (mTOR) signalling pathway has emerged as a central regulator for many cellular processes including cell growth, apoptosis, metabolism, and protein synthesis. This role of this pathway changes in response to diverse environmental cues and allows the upstream proteins that respond directly to extracellular signals (such as nutrient availability, energy status, and physical stresses) to communicate with downstream effectors which, in turn, regulate various essential cellular processes.

Results

In this study, we have performed a transcriptomic analysis using a pathway-focused polymerase chain reaction (PCR) array to compare the expression of 84 target genes related to the mTOR signalling in two recombinant CHO cell lines with a 17.4-fold difference in specific monoclonal antibody productivity (q_p). Eight differentially expressed genes that exhibited more than a 1.5-fold change were identified. Pik3cd (encoding the Class 1A catalytic subunit of phosphatidylinositol 3-kinase [PI3K]) was the most differentially expressed gene having a 71.3-fold higher level of expression in the high producer cell line than in the low producer. The difference in the gene’s transcription levels was confirmed at the protein level by examining expression of p110δ.

Conclusion

Expression of p110δ correlated with specific productivity (q_p) across six different CHO cell lines, with a range of expression levels from 3 to 51 pg/cell/day, suggesting that p110δ may be a key factor in regulating productivity in recombinant cell lines.

Laboratory production of human prolactin from CHO cells adapted to serum-free suspension culture

Human prolactin (hPRL) is a polypeptide with 199 amino acids and a molecular mass of 23 kDa. Previously, a eukaryotic hPRL expression vector was used to transfect Chinese hamster ovary (CHO) cells: this work describes a fast and practical laboratory adaptation of these transfected cells, in ~40 days, to grow in suspension in serum-free medium. High cell densities of up to 4.0 × 10(6) cell/ml were obtained from spinner flask cultures and a stable and continuous production process was developed for at least 30 days. Two harvesting strategies were set up, 50 or 100 % of the total conditioned medium being collected daily and replaced by fresh culture medium. The volumetric productivity was 5-7 μg hPRL/ml, as determined directly in the collected medium via reversed-phase HPLC (RP-HPLC). A two-step process based on a cationic exchanger followed by size exclusion chromatography was applied to obtain purified hPRL from conditioned medium. Two hPRL isoforms, non-glycosylated and glycosylated, could also be separated by high-performance size-exclusion chromatography (HPSEC) and, when analyzed by RP-HPLC, HPSEC, Western blotting, and bioassay, were found to be comparable to the World Health Organization International Reference Reagent of hPRL. These results are useful for the practical scale-up to the pilot and industrial scale of a bioprocess based on CHO cell culture.

Isolation, characterization and recombinant protein expression in Veggie-CHO: A serum-free CHO host cell line

The dihydrofolate reductase-deficient Chinese hamster ovary cell line, DXB11-CHO, commonly used as a host cell for the production of recombinant proteins requires 7.5% serum-supplementation for optimal growth. Regulatory issues surrounding the use of serum in clinical production processes and the direct and indirect costs of using serum in large-scale production and recovery processes have triggered efforts to derive serum-independent host cell lines. We have successfully isolated a serum-free host that we named Veggie- CHO. Veggie-CHO was generated by adapting DXB11-CHO cells to growth in serum-free media in the absence of exogenous growth factors such as Transferrin and Insulin-like growth factor, which we have previously shown to be essential for growth and viability of DXB11- CHO cells. Veggie-CHO cells have been shown to maintain an average doubling time of 22 hr in continuous growth cultures over a period of three months and have retained the dihydrofolate reductase -deficient phenotype of their parental DXB11-CHO cells. These properties and the stability of its serum-free phenotype have allowed the use of Veggie- CHO as host cells for transfection and amplified expression of recombinant proteins. We describe the derivation a serum-free recombinant cell line with an average doubling time of 20 hr and specific productivity of 2.5 Units recombinant Flt-3L protein per 10e6 cells per day.

A new mammalian host cell with enhanced survival enables completely serum-free development of high-level protein production cell lines

With over 25 monoclonal antibodies (mAbs) currently approved and many more in development, there is considerable interest in gaining improved productivity by increasing cell density and enhancing cell survival of production cell lines. In addition, high costs and growing safety concerns with use of animal products have made the availability of serum-free cell lines more appealing. We elected to transfect the myeloma cell line Sp2/0-Ag14 with Bcl2-EEE, the constitutively active phosphomimetic mutant of Bcl2, for extended cell survival. After adaptation of the initial transfectants to serum-independent growth, a clone with superior growth properties, referred to as SpESF, was isolated and further subjected to iterative rounds of stressful growth over a period of 4 months. The effort resulted in the selection of a promising clone, designated SpESFX-10, which was shown to exhibit robust growth and resist apoptosis induced by sodium butyrate or glutamine deprivation. The advantage of SpESFX-10 as a host for generating mAb-production cell lines was demonstrated by its increased transfection efficiency, culture longevity, and mAb productivity, as well as by the feasibility of accomplishing the entire cell line development process, including transfection, subcloning, and cryopreservation, in the complete absence of serum.

Heparin promotes suspension adaptation process of CHO-TS28 cells by eliminating cell aggregation

While heparin has been shown to eliminate cell aggregation in suspension adaptations of insect and HEK293 cells for virus-based cell cultures, the role of heparin in long period serum-free suspension adaptation of the anchorage-dependent Chinese hamster ovary (CHO) cell lines remains inconclusive. In this paper, we explore the potential application of heparin in suspension adaptation of CHO cell line which produces an anti-human chimeric antibody cHAb18. Heparin showed a concentration-dependent inhibition of CHO-TS28 cell-to-cell adhesion, with a significant inhibitory effect occurring when the concentration exceeded 250 μg/ml (P < 0.001). Heparin also exhibited a cell aggregation elimination role at all concentrations (P < 0.001). Furthermore, heparin promoted cell growth and antibody secretion, with the highest cell density ((99.83 ± 12.21) × 10(4) cells/ml, P = 0.034) and maximum antibody yield ((9.46 ± 0.94) mg/l, P < 0.001) both occurring at 250 μg/ml heparin. When agitated, cell aggregates were effectively dispersed by 250 μg/ml heparin and a single-cell suspension culture process was promoted. In suspension adapted CHO-TS28 cells, cell growth rates and specific antibody productivity were maintained; while antigen-binding activity improved slightly. Together, our results show that heparin may promote suspension adaptation of anchorage-depended CHO cells by resisting cell aggregation without reducing cell growth, antibody secretion, and antigen-binding activity.

Stable expression of recombinant human coagulation factor XIII in protein-free suspension culture of Chinese hamster ovary cells

The recombinant a and bsubunits for human coagulation factor XIII were transfected into Chinese hamster ovary (CHO) cells. CHO cells were amplified and selected with methotrexate in adherent cultures containing serum, and CHO 1-62 cells were later selected in protein-free medium. To develop a recombinant factor XIII production process in a suspension culture, we have investigated the growth characteristics of CHO cells and the maintenance of factor XIII expression in the culture medium. Suspension adaptation of CHO cells was performed in protein-free medium, GC-CHO-PI, by two methods, such as serum weaning and direct switching from serum containing media to protein-free media. Although the growth of CHO cells in suspension culture was affected initially by serum depletion, cell specific productivity of factor XIII showed only minor changes by the direct switching to protein-free medium during a suspension culture. As for the long-term stability of factor XIII, CHO 1-62 cells showed a stable expression of factor XIII in protein-free condition for 1000 h. These results indicate that the CHO 1-62cells can be adapted to express recombinant human factor XIII in a stable maimer in suspension culture using a protein-free medium. Our results demonstrate that enhanced cell growth in a continuous manner is achievable for factor XIII production in a protein-free medium when a perfusion bioreactor culture system with a spin filter is employed.

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.

The effects of culture conditions on the glycosylation of secreted human placental alkaline phosphatase produced in Chinese hamster ovary cells

The effects of different culture conditions, suspension and microcarrier culture and temperature reduction on the structures of N-linked glycans attached to secreted human placental alkaline phosphatase (SEAP) were investigated for CHO cells grown in a controlled bioreactor. Both mass spectrometry and anion-exchange chromatography were used to probe the N-linked glycan structures and distribution. Complex-type glycans were the dominant structures with small amounts of high mannose glycans observed in suspension and reduced temperature cultures. Biantennary glycans were the most common structures detected by mass spectrometry, but triantennary and tetraantennary forms were also detected. The amount of sialic acid present was relatively low, approximately 0.4 mol sialic acid/mol SEAP for suspension cultures. Microcarrier cultures exhibited a decrease in productivity compared with suspension culture due to a decrease in both maximum viable cell density (15-20%) and specific productivity (30-50%). In contrast, a biphasic suspension culture in which the temperature was reduced at the beginning of the stationary phase from 37 to 33 degrees C, showed a 7% increase in maximum viable cell density, a 62% increase in integrated viable cell density, and a 133% increase in specific productivity, leading to greater than threefold increase in total productivity. Both microcarrier and reduced temperature cultures showed increased sialylation and decreased fucosylation when compared to suspension culture. Our results highlight the importance of glycoform analysis after process modification as even subtle changes (e.g., changing from one microcarrier to another) may affect glycan distributions.

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.

Proteomic profiling of recombinant cells from large-scale mammalian cell culture processes

Global expression profiling of mammalian cells used for the production of biopharmaceuticals will allow greater insights into the molecular mechanisms that result in a high producing cellular phenotype. These studies may give insights for genetic intervention to possibly create better host cell lines or even to provide clues to more rational strategies for cell line and process development. In this review I will focus on the contribution of proteomic technologies to a greater understanding of the biology of Chinese hamster ovary cells and other producing cell lines such as NS0 mouse cells.

Antibody production

The clinical and commercial success of monoclonal antibodies has led to the need for very large-scale production in mammalian cell culture. This has resulted in rapid expansion of global manufacturing capacity [1], an increase in size of reactors (up to 20,000 L) and a greatly increased effort to improve process efficiency with concomitant manufacturing cost reduction. This has been particularly successful in the upstream part of the process where productivity of cell cultures has improved 100 fold in the last 15 years. This success has resulted from improvements in expression technology and from process optimisation, especially the development of fed-batch cultures. In addition to improving process/cost efficiencies, a second key area has been reducing the time taken to develop processes and produce the first material required for clinical testing and proof-of-principle. Cell line creation is often the slowest step in this stage of process development. This article will review the technologies currently used to make monoclonal antibodies with particular emphasis on mammalian cell culture. Likely future trends are also discussed.

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.

Understanding and modulating apoptosis in industrial cell culture

Currently, the production of therapeutic recombinant proteins relies heavily on the large-scale culture of eukaryotic cells that secrete the protein of interest into the media. It has been recognized that programmed cell death, or apoptosis, may pose a significant hurdle to maximum productivity in such systems. With a greater understanding of the molecular events causing apoptosis, alterations can be made to the cells and culture conditions to prevent apoptosis and enhance volumetric productivity.

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.

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.