The enhancement of antibody concentration and achievement of high cell density CHO cell cultivation by adding nucleoside

Comparability strategy and demonstration for post-approval production cell line change of a bevacizumab biosimilar IBI305

High-producing cell line could improve the affordability and availability of biotherapeutic products. A post-approval production cell line change, low-titer CHO-K1S to high-titer CHO-K1SV GS-KO, was performed for a China marketed bevacizumab biosimilar IBI305. Currently, there is no regulatory guideline specifically addressing the requirements for comparability study of post-approval cell line change, which is generally regarded as the most complex process change for biological products. Following the quality by design principle and risk assessment, an extensive analytical characterization and three-way comparison was performed by using a panel of advanced analytical methods. Orthogonal and state-of-the-art techniques including nuclear magnetic resonance and high-resolution mass spectrometry were applied to mitigate the potential uncertainties of higher-order structures and to exclude any new sequence variants, scrambled disulfide bonds, glycan moiety and undesired process-related impurities such as host cell proteins. Nonclinical and clinical pharmacokinetics (PK) studies were conducted subsequently to further confirm the comparability. The results demonstrated that the post-change IBI305 was analytically comparable to the pre-change one and similar to the reference product in physicochemical and biological properties, as well as the degradation behaviors in accelerated stability and forced degradation studies. The comparability was further confirmed by comparable PK, pharmacodynamics, toxicological and immunogenicity profiles of nonclinical and clinical studies. The comparability strategy presented here might extend to cell line changes of other post-approval biological products, and particularly set a precedent in China for post-approval cell line change of commercialized biosimilars.

Rapid Identification of Chinese Hamster Ovary Cell Apoptosis and Its Potential Role in Process Robustness Assessment

Currently, the assessment of process robustness is often time-consuming, labor-intensive, and material-intensive using process characterization studies. Therefore, a simple and time-saving method is highly needed for the biopharmaceutical industry. Apoptosis is responsible for 80% of Chinese hamster ovary (CHO) cell deaths and affects the robustness of the cell culture process. This study’s results showed that a more robust process can support cells to tolerate apoptosis for a longer time, suggesting that the robustness of the process could be judged by the ability of cells to resist apoptosis. Therefore, it is necessary to establish a rapid method to detect the apoptosis of CHO cells. In trying to establish a new method for detecting apoptosis in large-scale cell cultures, glucose withdrawal was studied, and the results showed that CHO cells began to apoptose after glucose was consumed. Then, the concentration of extracellular potassium increased, and a prolongation of apoptosis time was observed. Further study results showed that the process with poor robustness was associated with a higher proportion of apoptosis and extracellular potassium concentration, so potassium could be used as a biochemical index of apoptosis. The strategy we present may be used to expedite the assessment of process robustness to obtain a robust cell culture process for other biologics.

Progress in fed-batch culture for recombinant protein production in CHO cells

Nearly 80% of the approved human therapeutic antibodies are produced by Chinese Hamster Ovary (CHO) cells. To achieve better cell growth and high-yield recombinant protein, fed-batch culture is typically used for recombinant protein production in CHO cells. According to the demand of nutrients consumption, feed medium containing multiple components in cell culture can affect the characteristics of cell growth and improve the yield and quality of recombinant protein. Fed-batch optimization should have a connection with comprehensive factors such as culture environmental parameters, feed composition, and feeding strategy. At present, process intensification (PI) is explored to maintain production flexible and meet forthcoming demands of biotherapeutics process. Here, CHO cell culture, feed composition in fed-batch culture, fed-batch culture environmental parameters, feeding strategies, metabolic byproducts in fed-batch culture, chemostat cultivation, and the intensified fed-batch are reviewed. KEY POINTS: • Fed-batch culture in CHO cells is reviewed. • Fed-batch has become a common technology for recombinant protein production. • Fed batch culture promotes recombinant protein production in CHO cells.

Adaptation process of engineered cell line FCHO/IL-24 stably secreted rhIL-24 in serum-free suspension culture

Interleukin-24 (IL-24) displays tumor cell-specific proliferation inhibition in vitro and in vivo. Recombinant human IL-24 (rhIL-24) has significantly higher activity, yet significantly lower expression level in mammalian cells than in bacteria. To further realize therapeutic potential of IL-24, we enhanced rhIL-24 expression in mammalian cell systems by adapting engineered Flp-In^TMCHO/IL-24 (FCHO/IL-24) cells (adherent cultured in Ham's F12 medium with 10% serum) to serum-free suspension culture. First, MTT assay showed that among four different media (F12, DMEM/F12, 1640 and DMEM), DMEM/F12 medium was the most suitable media for lower-serum adherent culture. Then, cells were adherently cultured in DMEM/F12 with serum concentration reduced from 10% to 0.5% in a gradient manner. Compared to cells in 10% serum, cells in 0.5% serum displayed significantly lower relative cell viability by 40%, increased G0/G1 phase arrest (8.5 ± 2.4%, p < 0.05), decreased supernatant rhIL-24 concentration by 73%, and altered metabolite profiles, such as glucose, lactate and ammonia concentration. Next, the cells were directly adapted to 0.5% serum suspension culture in 125 mL shake flask at 119 rpm with the optimal cell seeding density of 5 × 10⁵ cells/mL (3.3 times higher than that of adherent culture), under which the concentration of rhIL-24 in culture medium was stable at 3.5 ng/mL. Finally, cells adapted to 0.5% serum proliferated better in serum-free medium Eden™-B300S with higher rhIL-24 expression level compared to CDM4CHO. The successful adaptation of engineered cells FCHO/IL-24 laid foundation for adapting cells from adherent culture to suspension serum-free culture to mass produce rhIL-24 protein for therapeutic purposes.

Expressing antigen binding fragments with high titers in a targeted integration CHO host by optimizing expression vector gene copy numbers and position: A case study

Antigen binding fragments (Fab) are a promising class of therapeutics as they maintain high potency while having significantly smaller size relative to full-length antibodies. Because Fab molecules are aglycosylated, many expression platforms, including prokaryotic, yeast, and mammalian cells, have been developed for their expression, with Escherichia coli being the most commonly used Fab expression system. In this study, we have examined production of a difficult to express Fab molecule in a targeted integration (TI) Chinese Hamster Ovary (CHO) host. Without a need for extensive host or process optimization, as is usually required for E. coli, by simply using different vector configurations, clones with very high Fab expression titers were obtained. In this case, by increasing heavy chain (HC) gene copy numbers, clones with titers of up to 7.4 g/L in the standard fed-batch production culture were obtained. Our findings suggest that having a predetermined transgene integration site, as well as the option to optimize gene copy number/dosage, makes CHO TI hosts an effective system for expression of Fab molecules, allowing Fab expression using platform process and without significant process development efforts.

[Research and Development of Manufacturing of Biologics-the Activities of Manufacturing Association of Biologics]

The industrial application of mammalian cells can be divided into two categories, where (1) the cells are mediators (i.e., the cell produces a desired product), or (2) the cells themselves are the product. The main application of cell-produced products is in biopharmaceuticals (biologics), and these include therapeutic enzymes, cytokines, antibodies, vaccines, and vectors for gene therapy. Among the 291 biopharmaceuticals launched in Europe and the United States by 2018, the number of products produced using mammalian cells exceeded 60%, with Chinese hamster ovary (CHO) cells being used for 131 products. The production of mammalian cells requires a comprehensive approach, including cell line development, cell culture, culture media, bioreactors, scale-up, separation and purification, process development, quality analysis and control, and research and development related to safety. In this manuscript, the activities of the "Manufacturing Technology Association of Biologics (MAB)" are introduced. MAB is a research organization composed of several companies, organizations, and academics that focuses on advanced manufacturing research for the production of biologics.

Recent advances in the production of recombinant factor IX: bioprocessing and cell engineering

Appropriate treatment of Hemophilia B is vital for patients' quality of life. Historically, the treatment used was the administration of coagulation Factor IX derived from human plasma. Advancements in recombinant technologies allowed Factor IX to be produced recombinantly. Successful recombinant production has triggered a gradual shift from the plasma derived origins of Factor IX, as it provides extended half-life and expanded production capacity. However, the complex post-translational modifications of Factor IX have made recombinant production at scale difficult. Considerable research has therefore been invested into understanding and optimizing the recombinant production of Factor IX. Here, we review the evolution of recombinant Factor IX production, focusing on recent developments in bioprocessing and cell engineering to control its post-translational modifications in its expression from Chinese Hamster Ovary (CHO) cells.

Generation and Characterization of Stable Redox-Reporter Mammalian Cell Lines of Biotechnological Relevance

Cellular functions such as DNA replication and protein translation are influenced by changes in the intracellular redox milieu. Exogenous (i.e., nutrients, deterioration of media components, xenobiotics) and endogenous factors (i.e., metabolism, growth) may alter the redox homeostasis of cells. Thus, monitoring redox changes in real time and in situ is deemed essential for optimizing the production of recombinant proteins. Recently, different redox-sensitive variants of green fluorescent proteins (e.g., rxYFP, roGFP2, and rxmRuby2) have been engineered and proved suitable to detect, in a non-invasive manner, perturbations in the pool of reduced and oxidized glutathione, the major low molecular mass thiol in mammals. In this study, we validate the use of cytosolic rxYFP on two cell lines widely used in biomanufacturing processes, namely, CHO-K1 cells expressing the human granulocyte macrophage colony-stimulating factor (hGM-CSF) and HEK-293. Flow cytometry was selected as the read-out technique for rxYFP signal given its high-throughput and statistical robustness. Growth kinetics and cellular metabolism (glucose consumption, lactate and ammonia production) of the redox reporter cells were comparable to those of the parental cell lines. The hGM-CSF production was not affected by the expression of the biosensor. The redox reporter cell lines showed a sensitive and reversible response to different redox stimuli (reducing and oxidant reagents). Under batch culture conditions, a significant and progressive oxidation of the biosensor occurred when CHO-K1-hGM-CSF cells entered the late-log phase. Medium replenishment restored, albeit partially, the intracellular redox homeostasis. Our study highlights the utility of genetically encoded redox biosensors to guide metabolic engineering or intervention strategies aimed at optimizing cell viability, growth, and productivity.

Novel cell line development strategy for monoclonal antibody manufacturing using translational enhancing technology

Chinese hamster ovary (CHO) cells are widely used for constructing expression systems to produce therapeutic proteins. However, the establishment of high-producer clones remains a laborious and time-consuming process, despite various progresses having been made in cell line development. We previously developed a new strategy for screening high monoclonal antibody (mAb)-producing cells using flow cytometry (FCM). We also reported that p180 and SF3b4 play key roles in active translation on the endoplasmic reticulum, and that the productivity of secreted alkaline phosphatase was enhanced by the overexpression of p180 and SF3b4. Here, we attempted to apply the translational enhancing technology to high mAb-producing cells obtained after high-producer cell sorting. A high mAb-producing CHO clone, L003, which showed an mAb production level of >3 g/L in fed-batch culture, was established from a high mAb-producing cell pool fractionated by FCM. Clones generated by the overexpression of p180 and SF3b4 in L003 cells were evaluated by fed-batch culture. The specific productivity of clones overexpressing these two factors was ∼3.1-fold higher than that of parental L003 cells in the early phase of the culture period. Furthermore, the final mAb concentration was increased to 9.5 g/L during 17 days of fed-batch culture after optimizing the medium and culture process. These results indicate that the overexpression of p180 and SF3b4 would be promising for establishing high-producer cell lines applicable to industrial production.

A Metabolomics Approach to Increasing Chinese Hamster Ovary (CHO) Cell Productivity

Much progress has been made in improving the viable cell density of bioreactor cultures in monoclonal antibody production from Chinese hamster ovary (CHO) cells; however, specific productivity (qP) has not been increased to the same degree. In this work, we analyzed a library of 24 antibody-expressing CHO cell clones to identify metabolites that positively associate with qP and could be used for clone selection or medium supplementation. An initial library of 12 clones, each producing one of two antibodies, was analyzed using untargeted LC-MS experiments. Metabolic model-based annotation followed by correlation analysis detected 73 metabolites that significantly correlated with growth, qP, or both. Of these, metabolites in the alanine, aspartate, and glutamate metabolism pathway, and the TCA cycle showed the strongest association with qP. To evaluate whether these metabolites could be used as indicators to identify clones with potential for high productivity, we performed targeted LC-MS experiments on a second library of 12 clones expressing a third antibody. These experiments found that aspartate and cystine were positively correlated with qP, confirming the results from untargeted analysis. To investigate whether qP correlated metabolites reflected endogenous metabolic activity beneficial for productivity, several of these metabolites were tested as medium additives during cell culture. Medium supplementation with citrate improved qP by up to 490% and more than doubled the titer. Together, these studies demonstrate the potential for using metabolomics to discover novel metabolite additives that yield higher volumetric productivity in biologics production processes.

A comparative analysis of recombinant Fab and full-length antibody production in Chinese hamster ovary cells

Monoclonal antibodies are the leading class of biopharmaceuticals in terms of numbers approved for therapeutic purposes. Antigen-binding fragments (Fab) are also used as biotherapeutics and used widely in research applications. The dominant expression systems for full-length antibodies are mammalian cell-based, whereas for Fab molecules the preference has been an expression in bacterial systems. However, advances in CHO and downstream technologies make mammalian systems an equally viable option for small- and large-scale Fab production. Using a panel of full-length IgG antibodies and their corresponding Fab pair with different antigen specificities, we investigated the impact of the IgG and Fab molecule format on production from Chinese hamster ovary (CHO) cells and assessed the cellular capability to process and produce these formats. The full-length antibody format resulted in the recovery of fewer mini-pools posttransfection when compared to the corresponding Fab fragment format that could be interpreted as indicative of a greater overall burden on cells. Antibody-producing cell pools that did recover were subsequently able to achieve higher volumetric protein yields (mg/L) and specific productivity than the corresponding Fab pools. Importantly, when the actual molecules produced per cell of a given format was considered (as opposed to mass), CHO cells produced a greater number of Fab molecules per cell than obtained with the corresponding IgG, suggesting that cells were more efficient at making the smaller Fab molecule. Analysis of cell pools showed that gene copy number was not correlated to the subsequent protein production. The amount of mRNA correlated with secreted Fab production but not IgG, whereby posttranscriptional processes act to limit antibody production. In summary, we provide the first comparative description of how full-length IgG and Fab antibody formats impact on the outcomes of a cell line construction process and identify potential limitations in their production that could be targeted for engineering increases in the efficiency in the manufacture of these recombinant antibody formats.

Identification of novel inhibitory metabolites and impact verification on growth and protein synthesis in mammalian cells

Mammalian cells consume large amount of nutrients during growth and production. However, endogenous metabolic inefficiencies often prevent cells to fully utilize nutrients to support growth and protein production. Instead, significant fraction of fed nutrients is diverted into extracellular accumulation of waste by-products and metabolites, further inhibiting proliferation and protein synthesis. In this study, an LC-MS/MS based metabolomics pipeline was used to screen Chinese hamster ovary (CHO) extracellular metabolites. Six out of eight identified inhibitory metabolites, caused by the inefficient cell metabolism, were not previously studied in CHO cells: aconitic acid, 2-hydroxyisocaproic acid, methylsuccinic acid, cytidine monophosphate, trigonelline, and n-acetyl putrescine. When supplemented back into a fed-batch culture, significant reduction in cellular growth was observed in the presence of each metabolite and all the identified metabolites were shown to impact the glycosylation of a model secreted antibody, with seven of these also reducing CHO cellular productivity (titer) and all eight inhibiting the formation of mono-galactosylated biantennary (G1F) and biantennary galactosylated (G2F) N-glycans. These inhibitory metabolites further impact the metabolism of cells, leading to a significant reduction in CHO cellular growth and specific productivity in fed-batch culture (maximum reductions of 27.2% and 40.6% respectively). In-depth pathway analysis revealed that these metabolites are produced when cells utilize major energy sources such as glucose and select amino acids (tryptophan, arginine, isoleucine, and leucine) for growth, maintenance, and protein production. Furthermore, these novel inhibitory metabolites were observed to accumulate in multiple CHO cell lines (CHO–K1 and CHO-GS) as well as HEK293 cell line. This study provides a robust and holistic methodology to incorporate global metabolomic analysis into cell culture studies for elucidation and structural verification of novel metabolites that participate in key metabolic pathways to growth, production, and post-translational modification in biopharmaceutical production.

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Mammalian metabolic inefficiencies lead to accumulation of waste by-products.

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Untargeted and targeted metabolomics for identification of novel metabolites.

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Identified six CHO metabolic inhibitors negatively impact growth and titer production.

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Inhibitors were shown to accumulate across different mammalian cell lines.

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A holistic methodology incorporating metabolomics analysis into cell culture studies.

Quantifying the impact of cell culture media on CHO cell growth and protein production

In recombinant protein production, cell culture media development and optimization is typically seen as a useful strategy to increase titer and cell density, reduce by-products, as well as improve product quality (with cell density and titer often serving as the primary reported outcome of media studies). However, despite the large number of media optimization studies, there have been few attempts to comprehensively assess the overall effectiveness of media additives. The aim of this review is therefore both to document published media optimization studies over the last twenty years (in the context of Chinese hamster ovary cell recombinant production) and quantitatively estimate the impact of this media optimization on cell culture performance. In considering 78 studies, we have identified 238 unique media components that have been supplemented over the last 20 years. Among these additives, trace elements stood out as having a positive impact on cell density while nucleotides show potential for increasing titer, with commercial supplements benefiting both. However, we also identified that the impact of specific additives is far more variable than often perceived. With relatively few media studies considering multiple cell lines or multiple basal media, teasing out consistent and general trends becomes a considerable challenge. By extracting cell density and titer values from all of the reviewed studies, we were able to build a mixed-effect model capable of estimating the relative impact of additives, cell line, product type, basal medium, cultivation method (flask or reactor), and feeding strategy (batch or fed-batch). Overall, additives only accounted for 3% of the variation in cell density and 1% of the variation in titer. Similarly, the impact of basal media was also relatively modest, at 10% for cell density and 0% for titer. Cell line, product type, and feeding strategy were all found to have more impact. These results emphasize the need for media studies to consider more factors to ensure that reported observations can be generalized and further developed.

Developments and opportunities in continuous biopharmaceutical manufacturing

Today’s biologics manufacturing practices incur high costs to the drug makers, which can contribute to high prices for patients. Timely investment in the development and implementation of continuous biomanufacturing can increase the production of consistent-quality drugs at a lower cost and a faster pace, to meet growing demand. Efficient use of equipment, manufacturing footprint, and labor also offer the potential to improve drug accessibility. Although technological efforts enabling continuous biomanufacturing have commenced, challenges remain in the integration, monitoring, and control of traditionally segmented unit operations. Here, we discuss recent developments supporting the implementation of continuous biomanufacturing, along with their benefits.

Biomanufacturing evolution from conventional to intensified processes for productivity improvement: a case study

Process intensification has shown great potential to increase productivity and reduce costs in biomanufacturing. This case study describes the evolution of a manufacturing process from a conventional processing scheme at 1000-L scale (Process A, n = 5) to intensified processing schemes at both 1000-L (Process B, n = 8) and 2000-L scales (Process C, n = 3) for the production of a monoclonal antibody by a Chinese hamster ovary cell line. For the upstream part of the process, we implemented an intensified seed culture scheme to enhance cell densities at the seed culture step (N-1) prior to the production bioreactor (N) by using either enriched N-1 seed culture medium for Process B or by operating the N-1 step in perfusion mode for Process C. The increased final cell densities at the N-1 step allowed for much higher inoculation densities in the production bioreactor operated in fed-batch mode and substantially increased titers by 4-fold from Process A to B and 8-fold from Process A to C, while maintaining comparable final product quality. Multiple changes were made to intensify the downstream process to accommodate the increased titers. New high-capacity resins were implemented for the Protein A and anion exchange chromatography (AEX) steps, and the cation exchange chromatography (CEX) step was changed from bind-elute to flow-through mode for the streamlined Process B. Multi-column chromatography was developed for Protein A capture, and an integrated AEX-CEX pool-less polishing steps allowed semi-continuous Process C with increased productivity as well as reductions in resin requirements, buffer consumption, and processing times. A cost-of-goods analysis on consumables showed 6.7–10.1 fold cost reduction from the conventional Process A to the intensified Process C. The hybrid-intensified process described here is easy to implement in manufacturing and lays a good foundation to develop a fully continuous manufacturing with even higher productivity in the future.

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.

Development of a scale-up strategy for Chinese hamster ovary cell culture processes using the kL a ratio as a direct indicator of gas stripping conditions

Herein, we described a scale-up strategy focused on the dissolved carbon dioxide concentration (dCO₂ ) during fed-batch cultivation of Chinese hamster ovary cells. A fed-batch culture process for a 2000-L scale stainless steel (SS) bioreactor was scaled-up from similarly shaped 200-L scale bioreactors based on power input per unit volume (P/V). However, during the 2000-L fed-batch culture, the dCO₂ was higher compared with the 200-L scale bioreactor. Therefore, we developed an alternative approach by evaluating the k_L a values of O₂ (k_L a[O₂ ]) and CO₂ [k_L a(CO₂ )] in the SS bioreactors as a scale-up factor for dCO₂ reduction. The k_L a ratios [k_L a(CO₂ )/k_L a(O₂ )] were different between the 200-L and 2000-L bioreactors under the same P/V condition. When the agitation conditions were changed, the k_L a ratio of the 2000-L scale bioreactor became similar and the P/V value become smaller compared with those of the 200-L SS bioreactor. The dCO₂ trends in fed-batch cultures performed in 2000-L scale bioreactors under the modified agitation conditions were similar to the control. This k_L a ratio method was used for process development in single-use bioreactors (SUBs) with shapes different from those of the SS bioreactor. The k_L a ratios for the SUBs were evaluated and conditions that provided k_L a ratios similar to the 200-L scale SS bioreactors were determined. The cell culture performance and product quality at the end of the cultivation process were comparable for all tested SUBs. Therefore, we concluded that the k_L a ratio is a powerful scale-up factor useful to control dCO₂ during fed-batch cultures.

Development of an intensified fed-batch production platform with doubled titers using N-1 perfusion seed for cell culture manufacturing

The goal of cell culture process intensification is to increase volumetric productivity, generally by increasing viable cell density (VCD), cell specific productivity or production bioreactor utilization in manufacturing. In our previous study, process intensification in fed-batch production with higher titer or shorter duration was demonstrated by increasing the inoculation seeding density (SD) from ~ 0.6 (Process A) to 3–6 × 106 cells/mL (Process B) in combination with media enrichment. In this study, we further increased SD to 10–20 × 106 cells/mL (Process C) using perfusion N-1 seed cultures, which increased titers already at industrially relevant levels by 100% in 10–14 day bioreactor durations for four different mAb-expressing CHO cell lines. Redesigned basal and feed media were critical for maintaining higher VCD and cell specific productivity during the entire production duration, while medium enrichment, feeding strategies and temperature shift optimization to accommodate high VCDs were also important. The intensified Process C was successfully scaled up in 500-L bioreactors for 3 of the 4 mAbs, and quality attributes were similar to the corresponding Process A or Process B at 1000-L scale. The fed-batch process intensification strategies developed in this study could be applied for manufacturing of other mAbs using CHO and other host cells.

Improvement of growth rates through nucleoside media supplementation of CHO clones

Chinese Hamster Ovary (CHO) cells are used for the production of therapeutic proteins. This work examines improving passaging growth rate of two CHO clones. Growth rates were significantly improved for both clones with supplementation of the nucleosides cytidine, hypoxanthine, uridine, and thymidine to the culturing media at the optimal concentration of 100 µM of each nucleoside. We investigated supplementing the same combination of nucleosides to seed bioreactors and production fed batch bioreactors. In the seed bioreactors, growth rate and harvest density were improved. However, in the production fed batch bioreactors, no improvements in growth rate or peak viable cell density were observed. Cell cycle analysis of the passaging cells provides evidence that nucleosides can affect the cell cycle. It is not clear from our work how the nucleosides impact the cell cycle regulatory pathways. Overall, nucleoside supplementation in cell culture media is an effective approach for improving growth rate in passaging and seed bioreactors of certain CHO cells.

Analysis of the immunoglobulin G (IgG) secretion efficiency in recombinant Chinese hamster ovary (CHO) cells by using Citrine-fusion IgG

Biopharmaceuticals represented by immunoglobulin G (IgG) are produced by the cultivation of recombinant animal cells, especially Chinese hamster ovary (CHO) cells. It is thought that the intracellular secretion process of IgG is a bottleneck in the production of biopharmaceuticals. Many studies on the regulation of endogenous secretory protein expression levels have shown improved productivity. However, these strategies have not universally improved the productivity of various proteins. A more rational and efficient establishment of high producer cells is required based on an understanding of the secretory processes in IgG producing CHO cells. In this study, a CHO cell line producing humanized IgG1, which was genetically fused with fluorescent proteins, was established to directly analyze intracellular secretion. The relationship between the amount of intracellular and secreted IgG was analyzed at the single cell level by an automated single-cell analysis and isolation system equipped with dual color fluorescent filters. The amounts of intracellular and secreted IgG showed a weak positive correlation. The amount of secreted IgG analyzed by the system showed a weak negative linear correlation with the specific growth of isolated clones. An immunofluorescent microscopy study showed that the established clones could be used to analyze the intracellular secretion bottleneck. This is the first study to report the use of fluorescent protein fusion IgG as a tool to analyze the secretion of recombinant CHO cells.

Secretion analysis of intracellular "difficult-to-express" immunoglobulin G (IgG) in Chinese hamster ovary (CHO) cells

The Chinese hamster ovary (CHO) cell line is the most widely used host cell for therapeutic antibody production. Although its productivity has been improved by various strategies to satisfy the growing global demand, some difficult-to-express (DTE) antibodies remain at low secretion levels. To improve the production of various therapeutic antibodies, it is necessary to determine possible rate-limiting steps in DTE antibody secretion in comparison with other high IgG producers. Here, we analyzed the protein secretion process in CHO cells producing the DTE immunoglobulin G (IgG) infliximab. The results from chase assays using a translation inhibitor revealed that infliximab secretion could be nearly completed within 2 h, at which time the cells still retained about 40% of heavy chains and 65% of light chains. Using fluorescent microscopy, we observed that these IgG chains remained in the endoplasmic reticulum and Golgi apparatus. The cells inefficiently form fully assembled heterodimer IgG by making LC aggregates, which may be the most serious bottleneck in the production of DTE infliximab compared with other IgG high producers. Our study could contribute to establish the common strategy for constructing DTE high-producer cells on the basis of rate-limiting step analysis.

Improving titer while maintaining quality of final formulated drug substance via optimization of CHO cell culture conditions in low-iron chemically defined media

During biopharmaceutical process development, it is important to improve titer to reduce drug manufacturing costs and to deliver comparable quality attributes of therapeutic proteins, which helps to ensure patient safety and efficacy. We previously reported that relative high-iron concentrations in media increased titer, but caused unacceptable coloration of a fusion protein during early-phase process development. Ultimately, the fusion protein with acceptable color was manufactured using low-iron media, but the titer decreased significantly in the low-iron process. Here, long-term passaging in low-iron media is shown to significantly improve titer while maintaining acceptable coloration during late-phase process development. However, the long-term passaging also caused a change in the protein charge variant profile by significantly increasing basic variants. Thus, we systematically studied the effect of media components, seed culture conditions, and downstream processing on productivity and quality attributes. We found that removing β-glycerol phosphate (BGP) from basal media reduced basic variants without affecting titer. Our goals for late-phase process development, improving titer and matching quality attributes to the early-phase process, were thus achieved by prolonging seed culture age and removing BGP. This process was also successfully scaled up in 500-L bioreactors. In addition, we demonstrated that higher concentrations of reactive oxygen species were present in the high-iron Chinese hamster ovary cell cultures compared to that in the low-iron cultures, suggesting a possible mechanism for the drug substance coloration caused by high-iron media. Finally, hypotheses for the mechanisms of titer improvement by both high-iron and long-term culture are discussed.