Enhanced erythropoietin heterogeneity in a CHO culture is caused by proteolytic degradation and can be eliminated by a high glutamine level

Factors affecting the quality of therapeutic proteins in recombinant Chinese hamster ovary cell culture

Chinese hamster ovary (CHO) cells are the most widely used mammalian host cells for the commercial production of therapeutic proteins. Fed-batch culture is widely used to produce therapeutic proteins, including monoclonal antibodies, because of its operational simplicity and high product titer. Despite technical advances in the development of culture media and cell cultures, it is still challenging to maintain high productivity in fed-batch cultures while also ensuring good product quality. In this review, factors that affect the quality attributes of therapeutic proteins in recombinant CHO (rCHO) cell culture, such as glycosylation, charge variation, aggregation, and degradation, are summarized and categorized into three groups: culture environments, chemical additives, and host cell proteins accumulated in culture supernatants. Understanding the factors that influence the therapeutic protein quality in rCHO cell culture will facilitate the development of large-scale, high-yield fed-batch culture processes for the production of high-quality therapeutic proteins.

Cathepsin D: Removal strategy on protein A chromatography, near real time monitoring and characterisation during monoclonal antibody production

Monoclonal antibody (mAb) fragmentation is a well-known degradation pathway that results in product loss and can significantly impact product quality, efficacy, or even cause immunogenic reactions, thus potentially endangering patients' health. It is recognised that residual proteases present among host cell proteins (HCPs) such as those expressed by Chinese Hamster Ovary (CHO) can induce fragmentation, and failure of their complete removal during downstream processing could cause fragmentation during mAb production and in the final drug product. We identified, using a protease inhibitor screen, an aspartic protease that contributes to proteolytic fragmentation of partially purified mAbs in multiple projects. Subsequent LC-MS analysis indicated that cathepsin D, a typical aspartic protease, was responsible for the observed fragmentation of in-process samples. To address the issue, an alternative chromatography wash was implemented at the capture step and has been demonstrated to be an effective and scalable solution to mitigate the residual cathepsin D associated fragmentation risk. Furthermore, a near real time targeted mass spectrometry method has been developed to proactively monitor the presence of cathepsin D during upstream and downstream process. Our approach demonstrated an emerging HCP mitigation strategy through integrated upstream and downstream involvement and holds great promise for a range of future applications.

Process optimization for the rapid production of adenoviral vectors for clinical trials in a disposable bioreactor system

Recombinant adenoviral (Ad) vectors are highly efficient gene transfer vectors widely used in vaccine development and immunotherapy. To promote the industrial application of Ad vectors, studies focusing on reducing the cost of manufacturing, shortening the preclinical research period, and improving the quality of products are needed. Here, we describe a highly efficient and economical process for producing Ad vector in a novel, single-use bioreactor system suitable for clinical trials. A mini-bioreactor was used for parameter optimization and development of medium replacement protocols for Ad5-GFP production before scale-up. HEK293 cell culture and virus infection were monitored in a disposable AmProtein Current Perfusion Bioreactor and Bioflo310 bioreactor using optimized parameters and medium replacement protocols. The total cell number increased from 2.0 × 10⁹ to 3.2 × 10¹⁰ after 6 days of culture. The total number of viral particles obtained in a single batch was 1.2 × 10¹⁵. These results demonstrate the efficiency and suitability of this system for Ad vector production for research and GMP applications.

Glycoengineering in CHO Cells: Advances in Systems Biology

For several decades, glycoprotein biologics have been successfully produced from Chinese hamster ovary (CHO) cells. The therapeutic efficacy and potency of glycoprotein biologics are often dictated by their post-translational modifications, particularly glycosylation, which unlike protein synthesis, is a non-templated process. Consequently, both native and recombinant glycoprotein production generate heterogeneous mixtures containing variable amounts of different glycoforms. Stability, potency, plasma half-life, and immunogenicity of the glycoprotein biologic are directly influenced by the glycoforms. Recently, CHO cells have also been explored for production of therapeutic glycosaminoglycans (e.g., heparin), which presents similar challenges as producing glycoproteins biologics. Approaches to controlling heterogeneity in CHO cells and directing the biosynthetic process toward desired glycoforms are not well understood. A systems biology approach combining different technologies is needed for complete understanding of the molecular processes accounting for this variability and to open up new venues in cell line development. In this review, we describe several advances in genetic manipulation, modeling, and glycan and glycoprotein analysis that together will provide new strategies for glycoengineering of CHO cells with desired or enhanced glycosylation capabilities.

Proteomic Analysis of Host Cell Protein Dynamics in the Culture Supernatants of Antibody-Producing CHO Cells

Chinese hamster ovary (CHO) cells are the most common cell line used for the production of therapeutic proteins including monoclonal antibodies (mAbs). Host cell proteins (HCPs), secreted and released from lysed cells, accumulate extracellularly during the cultures of recombinant CHO (rCHO) cells, potentially impairing product quality. In an effort to maintain good mAb quality during the cultures, HCPs accumulated extracellularly in batch and fed-batch cultures of a mAb-producing rCHO cell line were identified and quantified by nanoflow liquid chromatography-tandem mass spectrometry, followed by their gene ontology and functional analysis. Due to higher cell concentration and longer culture duration, more HCPs were identified and quantitated in fed-batch culture (2145 proteins identified and 1673 proteins quantified) than in batch culture (1934 proteins identified and 1486 proteins quantified). Clustering analysis of HCPs showed that the concentration profiles of HCPs affecting mAb quality (Lgmn, Ctsd, Gbl1, and B4galt1) correlated with changes in mAb quality attributes such as aggregation, charge variants, and N-glycosylation during the cultures. Taken together, the dataset of HCPs obtained in this study provides insights into determining the appropriate target proteins to be removed during both the cultures and purification steps for ensuring good mAb quality.

Investigation of purification process stresses on erythropoietin peptide mapping profile

BACKGROUND

Full compliance of recombinant protein peptide mapping chromatogram with the standard reference material, is one of the most basic quality control tests of biopharmaceuticals. Changing a single amino acid substitution or side chain diversity for a given peptide changes protein hydrophobicity and causes peak shape or retention time alteration in a peptide mapping assay. In this work, the effect of different stresses during the recombinant erythropoietin (EPO) purification process, including pH 4, pH 5, and room temperature were checked on product peptide mapping results.

MATERIALS AND METHODS

Cell culture harvest was purified under stress by different chromatographic techniques consisting of gel filtration, anionic ion exchange, concentration by ultrafiltration, and high resolution size exclusion chromatography. To induce more pH stresses, the purified EPO was exposed to pH stress 4 and 5 by exchanging buffer by a 10 KDa dialysis sac overnight. The effects of temperature and partial deglycosylation (acid hydrolysis) on purified EPO were also studied by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and peptide mapping analysis. Removal of sialic acid by mild hydrolysis was performed by exposure to two molar acetic acid at 80°C for 3 h.

RESULTS

No significant effect was observed between intact and stressed erythropoietin peptide mapping profiles and SDS-PAGE results. To validate the sensibility of the technique, erythropoietin was partially acid hydrolyzed and significant changes in the chromatographic peptide map of the intact form and a reduction on its molecular weight were detected, which indicates some partial deglycosylation.

CONCLUSIONS

Purification process does not alter the peptide mapping profile and purification process stresses are not the cause of peptide mapping noncompliance.

More similar than different: Host cell protein production using three null CHO cell lines

To understand the diversity in the cell culture harvest (i.e., feedstock) provided for downstream processing, we compared host cell protein (HCP) profiles using three Chinese Hamster Ovary (CHO) cell lines in null runs which did not generate any recombinant product. Despite differences in CHO lineage, upstream process, and culture performance, the cell lines yielded similar cell-specific productivities for immunogenic HCPs. To compare the dynamics of HCP production, we searched for correlations between the time-course profiles of HCP (as measured by multi-analyte ELISA) and those of two intracellular HCP species, phospholipase B-like 2 (PLBL2) and lactate dehydrogenase (LDH). Across the cell lines, proteins in the day 14 supernatants analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) showed different spot patterns. However, subsequent analysis by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) indicated otherwise: the total number of peptides and proteins identified were comparable, and 80% of the top 1,000 proteins identified were common to all three lines. Finally, to assess the impact of culture viability on extracellular HCP profiles, we analyzed supernatants from a cell line whose viability dropped after day 10. The amounts of HCP and PLBL2 (quantified by their respective ELISAs) as well as the numbers and major populations of HCPs (identified by LC-MS/MS) were similar across days 10, 14, and 17, during which viabilities declined from ∼80% to <20% and extracellular LDH levels increased several-fold. Our findings indicate that the CHO-derived HCPs in the feedstock for downstream processing may not be as diverse across cell lines and upstream processes, or change as dramatically upon viability decline as originally expected. In addition, our findings show that high density CHO cultures (>10(7) cells/mL)-operated in fed-batch mode and exhibiting high viabilities (>70%) throughout the culture duration-can accumulate a considerable amount of immunogenic HCP (∼1-2 g/L) in the extracellular environment at the time of harvest (day 14). This work also demonstrates the potential of using LC-MS/MS to overcome the limitations associated with ELISA and 2D-PAGE for HCP analysis.

Factors that determine stability of highly concentrated chemically defined production media

High cell density perfusion processes for the production of therapeutic antibodies require large volumes of media to meet cellular stoichiometric and energy demands. The use of media concentrates provides a way to reduce the cost of manufacturing. Reducing the number and size of liquid media batches reduces the media footprint in the manufacturing plant and cuts costs associated with single-use systems for preparation and storage of liquid media. Concentrates that can be stored at room temperature also reduce costs by eliminating the need for refrigerated storage. To meet these economic and operational objectives, we developed a complete concentrated medium system consisting of a 5X medium concentrate that can be used in conjunction with a concentrated supplement of cystine, tyrosine, and folic acid. The effects of pyruvate, bicarbonate, and glutamine on the stability of the 5X concentrates were studied. Pyruvate and bicarbonate were found to have profound impacts on media stability, including media coloration, precipitate formation and ability to support cell culture. Bicarbonate was found to have detrimental effects in 5X concentrated media, resulting in precipitation of pyruvate-free media and accelerated glutamine degradation. Pyruvate prevented precipitation in bicarbonate-containing concentrates. Moreover, the presence of pyruvate in bicarbonate-free, glutamine-free 5X concentrates resulted in the substantial preservation of the functional activity of the medium for 1 month at room temperature.

Production of influenza H1N1 vaccine from MDCK cells using a novel disposable packed-bed bioreactor

A process for human influenza H1N1 virus vaccine production from Madin-Darby canine kidney (MDCK) cells using a novel packed-bed bioreactor is described in this report. The mini-bioreactor was used to study the relationship between cell density and glucose consumption rate and to optimize the infection parameters of the influenza H1N1 virus (A/New Caledonia/20/99). The MDCK cell culture and virus infection were then monitored in a disposable perfusion bioreactor (AmProtein Current Perfusion Bioreactor) with proportional-integral-derivative control of pH, dissolved O(2) (DO), agitation, and temperature. During 6 days of culture, the total cell number increased from 2.0 × 10(9) to 3.2 × 10(10) cells. The maximum virus titers of 768 hemagglutinin units/100 μL and 7.8 × 10(7) 50 % tissue culture infectious doses/mL were obtained 3 days after infection. These results demonstrate that using a disposable perfusion bioreactor for large-scale cultivation of MDCK cells, which allows for the control of DO, pH, and other conditions, is a convenient and stable platform for industrial-scale production of influenza vaccines.

Impaired synthesis of erythropoietin, glutamine synthetase and metallothionein in the skin of NOD/SCID/gamma(c)(null) and Foxn1 nu/nu mice with misbalanced production of MHC class II complex

Most skin pathologies are characterized by unbalanced synthesis of major histocompatability complex II (MHC-II) proteins. Healthy skin keratinocytes simultaneously produce large amounts of MHC-II and regeneration-supporting proteins, e.g. erythropoietin (EPO), EPO receptor (EPOR), glutamine synthetase (GS) and metallothionein (MT). To investigate the level of regeneration-supporting proteins in the skin during misbalanced production of MHC-II, skin sections from nonobese diabetic/severe combined immunodeficient (NOD/SCID)/gamma (c) (null) and or Foxn1 nu/nu mice which are a priory known to under- and over-express MHC II, respectively, were used. Double immunofluorescence analysis of NOD/SCID/gamma (c) (null) skin sections showed striking decrease in expression of MHC-II, EPO, GS and MT. In Foxn1 nu/nu mouse skin, GS was strongly expressed in epidermis and in hair follicles (HF), which lacked EPO. In nude mouse skin EPO and MHC-II were over-expressed in dermal fibroblasts and they were completely absent from cortex, channel, medulla and keratinocytes surrounding the HF, suggest a role for EPO in health and pathology of hair follicle. The level of expression of EPO and GS in both mutant mice was confirmed by results of Western blot analyses. Strong immunoresponsiveness of EPOR in the hair channels of NOD/SCID/gamma (c) (null) mouse skin suggests increased requirements of skin cells for EPO and possible benefits of exogenous EPO application during disorders of immune system accompanied by loss MHC-II in skin cells.

Temperature Reduction in Cultures of hGM-CSF-expressing CHO Cells: Effect on Productivity and Product Quality

We have demonstrated that temperature reduction from 37 to 33 degrees C in the culture of a CHO cell line producing recombinant human granulocyte macrophage colony stimulating factor (CHO-K1-hGM-CSF) leads to a reduced growth rate, increased cell viability, improved cellular productivity, and decreased cell metabolism. In the present study, CHO-K1-hGM-CSF cells were cultured in a biphasic mode: first, a 37 degrees C growth phase for achieving a high cell number, followed by a production phase where the culture temperature was shifted to 33 degrees C. The maximum cell density was not affected after temperature reduction while cell viability remained above 80% for a further 3.7 days in the culture kept at the lower temperature, when compared to the control culture maintained at 37 degrees C. Furthermore, the total rhGM-CSF production increased 6 times in the culture shifted to 33 degrees C. Because the quality and hence the in vivo efficacy of a recombinant protein might be affected by numerous factors, we have analyzed the N- and O-glycosylation of the protein produced under both cell culture conditions using high-pH anion-exchange chromatography and complementary mass spectrometry techniques. The product quality data obtained from the purified protein preparations indicated that decreasing temperature had no significant effect on the rhGM-CSF glycosylation profiles, including the degree of terminal sialylation. Moreover, both preparations exhibited the same specific in vitro biological activity. These results revealed that the employed strategy had a positive effect on the cell specific productivity of CHO-K1-hGM-CSF cells without affecting product quality, representing a novel procedure for the rhGM-CSF production process.

Differential display identifies genes in Chinese hamster ovary cells sensitive to elevated ammonium

Ammonium is a toxic waste product that has been reported to negatively inhibit cell growth and recombinant glycosylation in Chinese hamster ovary (CHO) cells; however, the effect of this toxicity on intracellular gene expression has received only limited investigation. We used a differential display method to identify genes in CHO cells that were affected by ammonium stress. Eight genes whose mRNA levels significantly changed in response to elevated ammonium were isolated and identified. Five of the genes were identified as having lower expression under the ammonium stress, whereas three genes were identified as having higher expression. Sequence homology with other mammalian organisms was used to attribute function to these newly identified genes. The identified ammonium-sensitive genes were grouped into three broad functional groups: cellular processes, energy metabolism, and genetic-information processing. The three cellular process-related genes had lower expression (anaphase-promoting complex subunit 5, eukaryotic initiation factor 5A II, KIAA1091 protein). The two energy-related genes had higher expression under ammonium stress (adenosine triphosphate synthase subunit C and mitofusin 1). Both of the genetic information-processing genes (endoplasmic reticulum [ER]-resident protein ERdj5 and structure-specific recognition protein 1) had lower expression under the ammonium stress, whereas the 26S proteasome subunit adenosine triphosphatase 3 gene had higher expression. These preliminary results indicate that ammonium stress lowers expression of genes controlling cell cycle, protein folding, and quality and raises genes that control energy metabolism and degradation. Our findings demonstrate the usefulness of mRNA differential-display techniques for the detection of CHO cell genes affected by ammonium stress.

An on-line method for the reduction of fouling of spin-filters for animal cell perfusion cultures

The main limitation in the use of spin-filters during perfusion cultures of animal cells was revealed to be filter fouling. This phenomenon involves cell-sieve interactions as well as cell attachment to, and growth on, the filter surface. The cell attachment effect has been analysed in the present study during long-term perfusion simulations with CHO animal cells. It was demonstrated that at low filter acceleration, below 6.2 m/s2, a high perfusion rate of 25 cm/h induced rapid filter pore clogging within 3 days, whereas increasing the filter acceleration to 25 m/s2 increased filter longevity from 3 to 25 days, for filters with a pore size of 8.5 microm. Increasing the filter pore size to 14.5 microm improved filter longevity by 84% with less viable and dead cell deposits on the filter surface. However, it was demonstrated that filter longevity was not necessarily dependent on the amount of cell deposit on the filter surface. In the second part of this study, ultrasonic technology was used to reduce filter fouling. Filter vibration, induced by a piezo actuator, improved filter longevity by 113% during CHO cells perfusion cultures.

Related effects of cell adaptation to serum-free conditions on murine EPO production and glycosylation by CHO cells

The necessity to perform serum-free cultures to produce recombinant glycoproteins generally requires an adaptation procedure of the cell line to new environmental conditions, which may therefore induce quantitative and qualitative effects on the product, particularly on its glycosylation. In previous studies, desialylation of EPO produced by CHO cells was shown to be dependent on the presence of serum in the medium. In this paper, to discriminate between the effects of the adaptation procedure to serum-free medium and the effects of the absence of serum on EPO production and glycosylation, adapted and non-adapted CHO cells were grown in serum-free and serum-containing media. The main kinetics of CHO cells were determined over batch processes as well as the glycosylation patterns of produced EPO by HPCE-LIF. A reversible decrease in EPO production was observed when cells were adapted to SFX-CHO(TM) medium, as the same cells partially recovered their production capacity when cultivated in serum-containing medium or in the enriched SFM(TM) serum-free medium. More interestingly, EPO desialylation that was not observed in both serum-free media was restored if the serum-independent cells were recultured in presence of serum. In the same way, while the serum-independent cells did not release a sialidase activity in both serum-free media, a significant activity was recovered when serum was added. In fact, the cell adaptation process to serum-free conditions did not specifically affect the sialidase release and the cellular mechanism of protein desialylation, which appeared to be mainly related to the presence of serum for both adapted and non-adapted cells.

Effect of low culture temperature on specific productivity, transcription level, and heterogeneity of erythropoietin in Chinese hamster ovary cells

To determine the effect of low culture temperature on erythropoietin (EPO) production in recombinant Chinese hamster ovary (rCHO) cells, rCHO cells producing EPO (LGE10-9-27) were cultivated at 30, 33, and 37 degrees C. At a culture temperature lower than 37 degrees C cell growth was suppressed, but cell viability remained high for a longer culture period. When the culture temperature was lowered from 37 degrees C to 33 degrees C, more than a 2.5-fold increase in the maximum EPO concentration was achieved. This enhanced EPO production at 33 degrees C was not just because of the extended culture longevity with the decreased release of proteolytic enzymes from dead cells, but mainly because of enhanced q(EPO). The q(EPO) at 33 degrees C was 0.35 +/- 0.08 microg/10(6) cells/h, which was approximately 4-fold higher than that at 37 degrees C. Although the highest q(EPO) of 0.49 +/- 0.14 micro/10(6) cells/h was obtained at 30 degrees C, the maximum EPO concentration was lowest because the detrimental effect of lowering culture temperature on cell growth outweighed its beneficial effect on q(EPO). Like q(EPO), the relative EPO mRNA content increased by lowering culture temperature, indicating that the increased transcription level of EPO was responsible in part for the enhanced q(EPO) at low culture temperature. The quality of EPO produced at 33 degrees C in regard to isoform pattern, sialic acid content, and in vivo biological activity was comparable to or even better than that produced at 37 degrees C. Taken together, the results obtained demonstrate the potential of the application of low culture temperature to the commercial EPO production in rCHO cells.