Impact of aeration strategy on CHO cell performance during antibody production

Exploring metabolic responses and pathway changes in CHO-K1 cells under varied aeration conditions and copper supplementations using 1 H NMR-based metabolomics

The optimization of bioprocess for CHO cell culture involves careful consideration of factors such as nutrient consumption, metabolic byproduct accumulation, cell growth, and monoclonal antibody (mAb) production. Valuable insights can be obtained by understanding cellular physiology to ensure robust and efficient bioprocess. This study aims to improve our understanding of the CHO-K1 cell metabolism using 1 H NMR-based metabolomics. Initially, the variations in culture performance and metabolic profiles under varied aeration conditions and copper supplementations were thoroughly examined. Furthermore, a comprehensive metabolic pathway analysis was performed to assess the impact of these conditions on the implicated pathways. The results revealed substantial alterations in the pyruvate metabolism, histidine metabolism, as well as phenylalanine, tyrosine and tryptophan biosynthesis, which were especially evident in cultures subjected to copper deficiency conditions. Conclusively, significant metabolites governing cell growth and mAb titer were identified through orthogonal partial least square-discriminant analysis (OPLS-DA). Metabolites, including glycerol, alanine, formate, glutamate, phenylalanine, and valine, exhibited strong associations with distinct cell growth phases. Additionally, glycerol, acetate, lactate, formate, glycine, histidine, and aspartate emerged as metabolites influencing cell productivity. This study demonstrates the potential of employing 1 H NMR-based metabolomics technology in bioprocess research. It provides valuable guidance for feed medium development, feeding strategy design, bioprocess parameter adjustments, and ultimately the enhancement of cell proliferation and mAb yield.

Experimental and computational characterization of mass transfer in high turndown bioreactors

Single-use bioreactors (SUBs, or disposable bioreactors) are extensively used for the clinical and commercial production of biologics. Despite widespread application, minimal results have been reported utilizing the turndown ratio; an operation mode where the working range of the bioreactor can be expanded to include low fluid volumes. In this work, a systematic investigation into free surface mass transfer and cell growth in high turndown single-use bioreactors is presented. This approach, which combines experimental mass transfer measurements with numerical simulation, deconvolutes the combined effects of headspace mixing and the free surface convective mass transfer on cell growth. Under optimized conditions, mass transfer across the interface alone may be sufficient to satisfy oxygen demands of the cell culture. Within the context of high turndown bioreactors, this finding provides a counterpoint to traditional sparge-based bioreactor operational philosophy. Multiple monoclonal antibody-producing cell lines grown using this high turndown approach showed similar viable cell densities to those cells expanded using a traditional cell bag rocker. Furthermore, cells taken directly from the turndown expansion and placed into production showed identical growth characteristics to traditionally expanded cultures. Taken together, these results suggest that the Xcellerex SUB can be run at a 5:1 working volume as a seed to itself, with no need for system modifications, potentially simplifying preculture operations.

Membrane bioreactors for the production of value-added products: Recent developments, challenges and perspectives

The potential of membrane bioreactors to produce value-added products such as biofuels, biopolymers, proteins, organic acids and lipids at high productivities is emerging. Despite the promising results at laboratory scale, industrial deployment of this technology is hindered due to challenges associated with scale-up. This review aims to address these challenges and create a framework to encourage further research directed towards industrial application of membrane bioreactors to produce value-added products. This review describes the current state-of-the art in such bioreactor systems by exploiting membranes to increase the mass transfer rate of the limiting substrates, reach high cell concentrations and separate the inhibitory substances that may inhibit the bioconversion reaction. It also covers the current trends in commercialization, challenges linked with membrane usage, such as high costs and membrane fouling, and proposes possible future directions for the wider application of membrane bioreactors.

Equal mixing time enables scale-down and optimization of a CHO cell culture process using a shaken microbioreactor system

The advancement of microbioreactor technology in recent years has transformed early- and mid-stage process development. The monitoring and control capabilities of microbioreactors not only promote the quick accumulation of process knowledge but has also led to an increased scalability when compared to traditionally used systems such as shake flasks and microtitre plates. This study seeks to establish a framework for the micro-Matrix microbioreactor (Applikon-Biotechnology BV) as process development tool. Using the Dual Indicator System for Mixing Time, the system was initially characterized for mixing properties at varying operating conditions, which was found to yield mixing times between 0.9 and 41.8 s. A matched mixing time was proposed as scale-down criterion for an IgG4 producing GS-CHO fed-batch process between a 5 L stirred tank reactor (STR) and the micro-Matrix microbioreactor. Growth trends, maximum viable cell concentrations, final titre, and glycoprofiles were nearly identical at both scales. The scale-down model was then employed to optimize a bolus feeding regime using response surface methodology, which led to a 25.4% increase of the space-time yield and a 25% increase of the final titre. The optimized feeding strategy was validated at the small-scale and successfully scaled up to the 5 L STR. This work for the first time provides a framework of how the micro-Matrix microbioreactor can be implemented in a bioprocess development workflow and demonstrates scalability of growth and production kinetics as well as IgG4 glycosylation between the micro-Matrix and a benchtop-scale STR system.

Method development for the clearance study of the Pluronic F-68 nonionic surfactant used in the upstream process of monoclonal antibody production

Pluronic F-68 is a nonionic surfactant, which is often used in the upstream process of biopharmaceutical production. However, the number of analytical methods developed for determination of Pluronic F-68 in the in-process and drug substance samples of biological drug production process is quite low. The lack of chromophore groups on the molecule and the interference caused by the high protein content of the samples hamper analysis. In this paper the development and qualification of a mixed-mode (MM) HPLC method with charged aerosol detection is reported. The method enables the analysis of samples with up to 85 g/L protein concentration. The range of the method was set to 250-500 μg/mL, where it was found to be accurate (89-111 % recovery) and precise (0.8-3.2 % relative standard deviation). The high sensitivity of the method indicates that even lower concentration range can be feasible. The novel method successfully demonstrates Pluronic F-68 clearance during the downstream process of the monoclonal antibody production.

Single-Use Bioreactors for Human Pluripotent and Adult Stem Cells: Towards Regenerative Medicine Applications

Research on human stem cells, such as pluripotent stem cells and mesenchymal stromal cells, has shown much promise in their use for regenerative medicine approaches. However, their use in patients requires large-scale expansion systems while maintaining the quality of the cells. Due to their characteristics, bioreactors have been regarded as ideal platforms to harbour stem cell biomanufacturing at a large scale. Specifically, single-use bioreactors have been recommended by regulatory agencies due to reducing the risk of product contamination, and many different systems have already been developed. This review describes single-use bioreactor platforms which have been used for human stem cell expansion and differentiation, along with their comparison with reusable systems in the development of a stem cell bioprocess for clinical applications.

Apoptosis: A mammalian cell bioprocessing perspective

Apoptosis is a form of programmed and controlled cell death that accounts for the majority of cellular death in bioprocesses. Cell death affects culture longevity and product quality; it is instigated by several stresses experienced by the cells within a bioreactor. Understanding the factors that cause apoptosis as well as developing strategies that can protect cells is crucial for robust bioprocess development. This review aims to a) address apoptosis from a bioprocess perspective; b) describe the significant apoptotic mechanisms linking them to the most relevant stresses encountered in bioreactors; c) discuss the design of operating conditions in order to avoid cell death; d) focus on industrially relevant cell lines; and e) present anti-apoptosis strategies including cell engineering and model-based optimization of bioprocesses. In addition, the importance of apoptosis in quality-by-design bioprocess development from clone screening to production scale are highlighted.

A synthetic biology standard for Chinese Hamster Ovary cell genome monitoring and contaminant detection by polymerase chain reaction

Background

Chinese Hamster Ovary (CHO) cells are the current industry standard for production of therapeutic monoclonal antibodies at commercial scales. Production optimisation in CHO cells hinges on analytical technologies such as the use of the polymerase chain reaction (PCR) to quantify genetic factors within the CHO genome and to detect the presence of contaminant organisms. PCR-based assays, whilst sensitive and accurate, are limited by (i) requiring lengthy sample preparation and (ii) a lack of standardisation.

Results

In this study we directly assess for the first time the effect of CHO cellular material on quantitative PCR (qPCR) and end-point PCR (e-pPCR) when used to measure and detect copies of a CHO genomic locus and a mycoplasma sequence. We also perform the first head-to-head comparison of the performance of a conventional qPCR method to that of the novel linear regression of efficiency (LRE) method when used to perform absolute qPCR on CHO-derived material. LRE qPCR features the putatively universal ‘CAL1’ standard.

Conclusions

We find that sample preparation is required for accurate quantitation of a genomic target locus, but mycoplasma DNA sequences can be detected in the presence of high concentrations of CHO cellular material. The LRE qPCR method matches performance of a conventional qPCR approach and as such we invite the synthetic biology community to adopt CAL1 as a synthetic biology calibration standard for qPCR.

Automated High-Throughput Permethylation for Glycosylation Analysis of Biologics Using MALDI-TOF-MS

Monitoring glycoprotein therapeutics for changes in glycosylation throughout the drug's life cycle is vital, as glycans significantly modulate the stability, biological activity, serum half-life, safety, and immunogenicity. Biopharma companies are increasingly adopting Quality by Design (QbD) frameworks for measuring, optimizing, and controlling drug glycosylation. Permethylation of glycans prior to analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is a valuable tool for glycan characterization and for screening of large numbers of samples in QbD drug realization. However, the existing protocols for manual permethylation and liquid-liquid extraction (LLE) steps are labor intensive and are thus not practical for high-throughput (HT) studies. Here we present a glycan permethylation protocol, based on 96-well microplates, that has been developed into a kit suitable for HT work. The workflow is largely automated using a liquid handling robot and includes N-glycan release, enrichment of N-glycans, permethylation, and LLE. The kit has been validated according to industry analytical performance guidelines and applied to characterize biopharmaceutical samples, including IgG4 monoclonal antibodies (mAbs) and recombinant human erythropoietin (rhEPO). The HT permethylation enabled glycan characterization and relative quantitation with minimal side reactions: the MALDI-TOF-MS profiles obtained were in good agreement with hydrophilic liquid interaction chromatography (HILIC) and ultrahigh performance liquid chromatography (UHPLC) data. Automated permethylation and extraction of 96 glycan samples was achieved in less than 5 h and automated data acquisition on MALDI-TOF-MS took on average less than 1 min per sample. This automated and HT glycan preparation and permethylation showed to be convenient, fast, and reliable and can be applied for drug glycan profiling and clinical glycan biomarker studies.

Scalable Production of a Multifunctional Protein (TSG-6) That Aggregates with Itself and the CHO Cells That Synthesize It

TNF-α stimulated gene/protein 6 (TNFAIP6/TSG-6) is a multifunctional protein that has a number of potential therapeutic applications. Experiments and clinical trials with TSG-6, however, have been limited by the technical difficulties of producing the recombinant protein. We prepared stable clones of CHO cells that expressed recombinant human TSG-6 (rhTSG-6) as a secreted glycoprotein. Paradoxically, both cell number and protein production decreased dramatically when the clones were expanded. The decreases occurred because the protein aggregated the synthesizing CHO cells by binding to the brush border of hyaluronan that is found around many cultured cells. In addition, the rhTSG-6 readily self-aggregated. To address these problems, we added to the medium an inhibitor of hyaluronan synthesis and heparin to compete with the binding of TSG-6 to hyaluronan. Also, we optimized the composition of the culture medium, and transferred the CHO cells from a spinner culture system to a bioreactor that controlled pH and thereby decreased pH-dependent binding properties of the protein. With these and other improvements in the culture conditions, we obtained 57.0 mg ± 9.16 S.D. of rhTSG-6 in 5 or 6 liter of medium. The rhTSG-6 accounted for 18.0% ± 3.76 S.D. of the total protein in the medium. We then purified the protein with a Ni-chelate column that bound the His tag engineered into the C-terminus of the protein followed by an anion exchange column. The yield of the purified monomeric rhTSG-6 was 4.1 mg to 5.6 mg per liter of culture medium. After intravenous injection into mice, the protein had a longer plasma half-life than commercially available rhTSG-6 isolated from a mammalian cell lysate, apparently because it was recovered as a secreted glycoprotein. The bioactivity of the rhTSG-6 in suppressing inflammation was demonstrated in a murine model.

Representative mammalian cell culture test materials for assessment of primary recovery technologies: a rapid method with industrial applicability

Mammalian cell culture material is often difficult to produce accurately and reproducibly for downstream studies. This article presents a methodology for the creation of a set of cell culture test materials where key variables including cell density, cell viability, product, and the host cell protein (HCP) load can be manipulated individually. The methodology was developed using a glutamine synthetase Chinese hamster ovary cell line cultured at 5-L and 70-L scales. Cell concentration post-cell growth was manipulated using tangential flow filtration to generate a range of target cell densities of up to 100 × 10⁶ cells/mL. A method to prepare an apoptotic cell stock to achieve target viabilities of 40–90% is also described. In addition, a range of IgG₁ and HCP concentrations was achieved. The results illustrate that the proposed methodology is able to mimic different cell culture profiles by decoupling the control of the key variables. The cell culture test materials were shown to be representative of typical cell culture feed material in terms of particle size distribution and HCP population. This provides a rapid method to create the required feeds for assessing the feasibility of primary recovery technologies designed to cope with higher cell density cultures.

Differential response in downstream processing of CHO cells grown under mild hypothermic conditions

The manufacture of complex therapeutic proteins using mammalian cells is well established, with several strategies developed to improve productivity. The application of sustained mild hypothermic conditions during culture has been associated with increases in product titer and improved product quality. However, despite associated cell physiological effects, very few studies have investigated the impact on downstream processing (DSP). Characterization of cells grown under mild hypothermic conditions demonstrated that the stationary phase was prolonged by delaying the onset of apoptosis. This enabled cells to maintain viability for extended periods and increase volumetric productivity from 0.74 to 1.02 g L⁻¹. However, host cell proteins, measured by ELISA, increased by ∼50%, attributed to the extended time course and higher peak and harvest cell densities. The individual components making up this impurity, as determined by SELDI-TOF MS and 2D-PAGE, were shown to be largely comparable. Under mild hypothermic conditions, cells were less shear sensitive than those maintained at 37°C, enhancing the preliminary primary recovery step. Adaptive changes in membrane fluidity were further investigated by adopting a pronounced temperature shift immediately prior to primary recovery and the improvement observed suggests that such a strategy may be implementable when shear sensitivity is of concern. Early and late apoptotic cells were particularly susceptible to shear, at either temperature, even under the lowest shear rate investigated. These findings demonstrate the importance of considering the impact of cell culture strategies and cell physiology on DSP, by implementing a range of experimental methods for process characterization. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:688–696, 2013