1
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Wei W, Zielewicz L, Zhang L. Duplication of a chromosome 2 segment in production CHO cell lines correlates with age-related growth improvement. Biotechnol J 2024; 19:e2300407. [PMID: 38403434 DOI: 10.1002/biot.202300407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Revised: 12/04/2023] [Accepted: 01/02/2024] [Indexed: 02/27/2024]
Abstract
Monitoring the stability of recombinant Chinese Hamster Ovary (CHO) cell lines is essential to ensure the selection of production cell lines suitable for biomanufacturing. It has been frequently observed that recombinant CHO cell lines develop phenotypic changes upon aging, such as accelerated cell growth in late generation cultures. However, the mechanism responsible for age-correlated changes is poorly understood. In this study, we investigated the molecular mechanisms underlying the age-correlated cell growth improvement in Pfizer's platform fed-batch production process, by examining multiple cell lines derived from different CHO expression systems, expressing a variety of monoclonal antibodies (mAbs). Comprehensive whole-genome resequencing analysis revealed duplication of a continuous 50.2 Mbp segment in chromosome 2 (Chr2) specific to clones that showed age-correlated growth change as compared to clones that did not exhibit age-correlated growth change. Moreover, such age- and growth-related Chr2 duplication was independent of the presence or type of recombinant monoclonal antibody expression. When we compared transcriptome profiles from low-growth and high-growth cell lines, we found that >95% of the genes overexpressed in high-growth cell lines were in the duplicated Chr2 segment. To the best of our knowledge, this is the first report of large genomic duplication, specific to Chr2, being associated with age-correlated growth change. Investigation of the cause-and-effect relationship between the genes identified in the duplicated regions and age-correlated growth change is underway. We are confident that this effort will lead to improved cell line screening and targeted rational cell line engineering efforts to develop cell lines with improved stability performance.
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Affiliation(s)
- Wei Wei
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc, Andover, Massachusetts, USA
| | - Laura Zielewicz
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc, Andover, Massachusetts, USA
| | - Lin Zhang
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc, Andover, Massachusetts, USA
- Bioprocess Research and Development, Merck & Co. Inc., Kenilworth, New Jersey, USA
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2
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Yamano-Adachi N, Hata H, Nakanishi Y, Omasa T. Effects of genome instability of parental CHO cell clones on chromosome number distribution and recombinant protein production in parent-derived subclones. J Biosci Bioeng 2024; 137:54-63. [PMID: 37981489 DOI: 10.1016/j.jbiosc.2023.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 10/11/2023] [Accepted: 10/16/2023] [Indexed: 11/21/2023]
Abstract
Chinese hamster ovary (CHO) cells are the de facto standard host cells for biopharmaceuticals, and there is great interest in developing methods for constructing stable production cell lines. In this study, clones with a wide chromosome number distribution were selected from isolated antibody-producing strains, and subclones obtained from these clones were evaluated. The transgene copy number varied between the subclones. Even among subclones with similar copy numbers of antibody genes and maintained insertion sites, clones with different productivity were generated. Although the chromosome number distribution differed between these subclones, there was no correlation between the variability in chromosome number after cloning (genome instability) and productivity. Most of the subclones obtained from a parental strain with a wide chromosome number had the same wide chromosome number distribution as the parental strain. Less frequently, cells with less variation (remaining in one distribution) in chromosome number were isolated from cells with a wide chromosome number distribution, from which subclones with less variation in chromosome number were obtained when subcloning was performed again. These results imply that the characteristics of clones with chromosomal instability are inherited by subclones, and thus provide a better understanding of cell line stability/instability.
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Affiliation(s)
- Noriko Yamano-Adachi
- Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan; Institute for Open and Transdisciplinary Research Initiatives, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
| | - Hirofumi Hata
- Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Yuto Nakanishi
- Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Takeshi Omasa
- Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan; Institute for Open and Transdisciplinary Research Initiatives, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
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3
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Barnard GC, Zhou M, Shen A, Yuk IH, Laird MW. Utilizing targeted integration CHO pools to potentially accelerate the GMP manufacturing of monoclonal and bispecific antibodies. Biotechnol Prog 2024; 40:e3399. [PMID: 37874920 DOI: 10.1002/btpr.3399] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 10/03/2023] [Accepted: 10/08/2023] [Indexed: 10/26/2023]
Abstract
Monoclonal antibodies (mAbs) are effective therapeutic agents against many acute infectious diseases including COVID-19, Ebola, RSV, Clostridium difficile, and Anthrax. mAbs can therefore help combat a future pandemic. Unfortunately, mAb development typically takes years, limiting its potential to save lives during a pandemic. Therefore "pandemic mAb" timelines need to be shortened. One acceleration tool is "deferred cloning" and leverages new Chinese hamster ovary (CHO) technology based on targeted gene integration (TI). CHO pools, instead of CHO clones, can be used for Phase I/II clinical material production. A final CHO clone (producing the mAb with a similar product quality profile and preferably with a higher titer) can then be used for Phase III trials and commercial manufacturing. This substitution reduces timelines by ~3 months. We evaluated our novel CHO TI platform to enable deferred cloning. We created four unique CHO pools expressing three unique mAbs (mAb1, mAb2, and mAb3), and a bispecific mAb (BsAb1). We then performed single-cell cloning for mAb1 and mAb2, identifying three high-expressing clones from each pool. CHO pools and clones were inoculated side-by-side in ambr15 bioreactors. CHO pools yielded mAb titers as high as 10.4 g/L (mAb3) and 7.1 g/L (BsAb1). Subcloning yielded CHO clones expressing higher titers relative to the CHO pools while yielding similar product quality profiles. Finally, we showed that CHO TI pools were stable by performing a 3-month cell aging study. In summary, our CHO TI platform can increase the speed to clinic for a future "pandemic mAb."
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Affiliation(s)
- Gavin C Barnard
- Cell Culture and Bioprocess Operations, Genentech, South San Francisco, California, USA
| | - Michelle Zhou
- Cell Culture and Bioprocess Operations, Genentech, South San Francisco, California, USA
| | - Amy Shen
- Cell Culture and Bioprocess Operations, Genentech, South San Francisco, California, USA
| | - Inn H Yuk
- Cell Culture and Bioprocess Operations, Genentech, South San Francisco, California, USA
| | - Michael W Laird
- Cell Culture and Bioprocess Operations, Genentech, South San Francisco, California, USA
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4
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Leitner K, Motheramgari K, Borth N, Marx N. Nanopore Cas9-targeted sequencing enables accurate and simultaneous identification of transgene integration sites, their structure and epigenetic status in recombinant Chinese hamster ovary cells. Biotechnol Bioeng 2023; 120:2403-2418. [PMID: 36938677 DOI: 10.1002/bit.28382] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 01/27/2023] [Accepted: 03/12/2023] [Indexed: 03/21/2023]
Abstract
The integration of a transgene expression construct into the host genome is the initial step for the generation of recombinant cell lines used for biopharmaceutical production. The stability and level of recombinant gene expression in Chinese hamster ovary (CHO) can be correlated to the copy number, its integration site as well as the epigenetic context of the transgene vector. Also, undesired integration events, such as concatemers, truncated, and inverted vector repeats, are impacting the stability of recombinant cell lines. Thus, to characterize cell clones and to isolate the most promising candidates, it is crucial to obtain information on the site of integration, the structure of integrated sequence and the epigenetic status. Current sequencing techniques allow to gather this information separately but do not offer a comprehensive and simultaneous resolution. In this study, we present a fast and robust nanopore Cas9-targeted sequencing (nCats) pipeline to identify integration sites, the composition of the integrated sequence as well as its DNA methylation status in CHO cells that can be obtained simultaneously from the same sequencing run. A Cas9-enrichment step during library preparation enables targeted and directional nanopore sequencing with up to 724× median on-target coverage and up to 153 kb long reads. The data generated by nCats provides sensitive, detailed, and correct information on the transgene integration sites and the expression vector structure, which could only be partly produced by traditional Targeted Locus Amplification-seq data. Moreover, with nCats the DNA methylation status can be analyzed from the same raw data without prior DNA amplification.
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Affiliation(s)
- Klaus Leitner
- Austrian Center of Industrial Biotechnology GmbH, Vienna, Austria
| | | | - Nicole Borth
- Austrian Center of Industrial Biotechnology GmbH, Vienna, Austria
- Department of Biotechnology, Institute of Animal Cell Technology and Systems Biology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Nicolas Marx
- Department of Biotechnology, Institute of Animal Cell Technology and Systems Biology, University of Natural Resources and Life Sciences, Vienna, Austria
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5
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Sacco SA, McAtee Pereira AG, Trenary I, Smith KD, Betenbaugh MJ, Young JD. Overexpression of peroxisome proliferator-activated receptor γ co-activator-1⍺ (PGC-1⍺) in Chinese hamster ovary cells increases oxidative metabolism and IgG productivity. Metab Eng 2023; 79:108-117. [PMID: 37473833 DOI: 10.1016/j.ymben.2023.07.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 04/17/2023] [Accepted: 07/17/2023] [Indexed: 07/22/2023]
Abstract
Chinese hamster ovary (CHO) cells are used extensively to produce protein therapeutics, such as monoclonal antibodies (mAbs), in the biopharmaceutical industry. MAbs are large proteins that are energetically demanding to synthesize and secrete; therefore, high-producing CHO cell lines that are engineered for maximum metabolic efficiency are needed to meet increasing demands for mAb production. Previous studies have identified that high-producing cell lines possess a distinct metabolic phenotype when compared to low-producing cell lines. In particular, it was found that high mAb production is correlated to lactate consumption and elevated TCA cycle flux. We hypothesized that enhancing flux through the mitochondrial TCA cycle and oxidative phosphorylation would lead to increased mAb productivities and final titers. To test this hypothesis, we overexpressed peroxisome proliferator-activated receptor γ co-activator-1⍺ (PGC-1⍺), a gene that promotes mitochondrial metabolism, in an IgG-producing parental CHO cell line. Stable cell pools overexpressing PGC-1⍺ exhibited increased oxygen consumption, indicating increased mitochondrial metabolism, as well as increased mAb specific productivity compared to the parental line. We also performed 13C metabolic flux analysis (MFA) to quantify how PGC-1⍺ overexpression alters intracellular metabolic fluxes, revealing not only increased TCA cycle flux, but global upregulation of cellular metabolic activity. This study demonstrates the potential of rationally engineering the metabolism of industrial cell lines to improve overall mAb productivity and to increase the abundance of high-producing clones in stable cell pools.
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Affiliation(s)
- Sarah A Sacco
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA
| | | | - Irina Trenary
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA
| | - Kevin D Smith
- Pharmaceutical Development and Manufacturing Sciences, Janssen Research and Development, Spring House, PA, USA
| | - Michael J Betenbaugh
- Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - Jamey D Young
- Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, USA.
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6
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Han HJ, Kim DH, Baik JY. A splinkerette PCR-based genome walking technique for the identification of transgene integration sites in CHO cells. J Biotechnol 2023:S0168-1656(23)00105-0. [PMID: 37257509 DOI: 10.1016/j.jbiotec.2023.05.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 05/02/2023] [Accepted: 05/28/2023] [Indexed: 06/02/2023]
Abstract
Identification of recombinant gene integrations sites in the Chinese hamster ovary (CHO) cell genome is increasingly important to assure monoclonality. While next-generation sequencing (NGS) is commonly used for the gene integration site analysis, it is a time-consuming and costly technique as it analyzes the entire genome. Hence, simple, easy, and inexpensive methods to analyze transgene insertion sites are necessary. To selectively capture the integration site of transgene in the CHO genome, we applied splinkerette-PCR (spPCR). SpPCR is an adaptor ligation-based method using splinkerette adaptors that have a stable hairpin loop. Restriction enzymes with high frequencies in the CHO genome were chosen using a Python script and used for the in vitro spPCR assay development. After testing on two CHO housekeeping genes with known loci, the spPCR-based genome walking technique was successfully applied to recombinant CHO cells to identify the transgene integration site. Finally, the comparison with NGS methods exhibited that the time and cost required for the analysis can be substantially reduced. Taken together, the established technique would aid the stable cell line development process by providing a rapid and cost-effective method for transgene integration site analysis.
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Affiliation(s)
- Hye-Jin Han
- Department of Biological Sciences and Bioengineering, Inha University, Incheon22212, Republic of Korea
| | - Dae Hoon Kim
- Department of Biological Sciences and Bioengineering, Inha University, Incheon22212, Republic of Korea
| | - Jong Youn Baik
- Department of Biological Sciences and Bioengineering, Inha University, Incheon22212, Republic of Korea.
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7
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Chitwood DG, Wang Q, Klaubert SR, Green K, Wu CH, Harcum SW, Saski CA. Microevolutionary dynamics of eccDNA in Chinese hamster ovary cells grown in fed-batch cultures under control and lactate-stressed conditions. Sci Rep 2023; 13:1200. [PMID: 36681715 PMCID: PMC9862248 DOI: 10.1038/s41598-023-27962-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 01/10/2023] [Indexed: 01/22/2023] Open
Abstract
Chinese hamster ovary (CHO) cell lines are widely used to manufacture biopharmaceuticals. However, CHO cells are not an optimal expression host due to the intrinsic plasticity of the CHO genome. Genome plasticity can lead to chromosomal rearrangements, transgene exclusion, and phenotypic drift. A poorly understood genomic element of CHO cell line instability is extrachromosomal circular DNA (eccDNA) in gene expression and regulation. EccDNA can facilitate ultra-high gene expression and are found within many eukaryotes including humans, yeast, and plants. EccDNA confers genetic heterogeneity, providing selective advantages to individual cells in response to dynamic environments. In CHO cell cultures, maintaining genetic homogeneity is critical to ensuring consistent productivity and product quality. Understanding eccDNA structure, function, and microevolutionary dynamics under various culture conditions could reveal potential engineering targets for cell line optimization. In this study, eccDNA sequences were investigated at the beginning and end of two-week fed-batch cultures in an ambr®250 bioreactor under control and lactate-stressed conditions. This work characterized structure and function of eccDNA in a CHO-K1 clone. Gene annotation identified 1551 unique eccDNA genes including cancer driver genes and genes involved in protein production. Furthermore, RNA-seq data is integrated to identify transcriptionally active eccDNA genes.
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Affiliation(s)
- Dylan G Chitwood
- Department of Bioengineering, Clemson University, Clemson, SC, USA
| | - Qinghua Wang
- Center for Bioinformatics and Computational Biology, University of Delaware, Newark, DE, USA
| | - Stephanie R Klaubert
- Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC, USA
| | - Kiana Green
- Department of Biological Sciences, University of South Carolina, Columbia, SC, USA
| | - Cathy H Wu
- Center for Bioinformatics and Computational Biology, University of Delaware, Newark, DE, USA
| | - Sarah W Harcum
- Department of Bioengineering, Clemson University, Clemson, SC, USA
- Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC, USA
| | - Christopher A Saski
- Department of Plant and Environmental Sciences, Clemson University, Clemson, SC, USA.
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8
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Hertel O, Neuss A, Busche T, Brandt D, Kalinowski J, Bahnemann J, Noll T. Enhancing stability of recombinant CHO cells by CRISPR/Cas9-mediated site-specific integration into regions with distinct histone modifications. Front Bioeng Biotechnol 2022; 10:1010719. [PMID: 36312557 PMCID: PMC9606416 DOI: 10.3389/fbioe.2022.1010719] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 09/30/2022] [Indexed: 11/24/2022] Open
Abstract
Chinese hamster ovary (CHO) cells are the most important platform for producing biotherapeutics. Random integration of a transgene into epigenetically instable regions of the genome results in silencing of the gene of interest and loss of productivity during upstream processing. Therefore, cost- and time-intensive long-term stability studies must be performed. Site-specific integration into safe harbors is a strategy to overcome these limitations of conventional cell line design. Recent publications predict safe harbors in CHO cells based on omics data sets or by learning from random integrations, but those predictions remain theory. In this study, we established a CRISPR/Cas9-mediated site-specific integration strategy based on ChIP-seq data to improve stability of recombinant CHO cells. Therefore, a ChIP experiment from the exponential and stationary growth phase of a fed-batch cultivation of CHO-K1 cells yielded 709 potentially stable integration sites. The reporter gene eGFP was integrated into three regions harboring specific modifications by CRISPR/Cas9. Targeted Cas9 nanopore sequencing showed site-specific integration in all 3 cell pools with a specificity between 23 and 73%. Subsequently, the cells with the three different integration sites were compared with the randomly integrated donor vector in terms of transcript level, productivity, gene copy numbers and stability. All site-specific integrations showed an increase in productivity and transcript levels of up to 7.4-fold. In a long-term cultivation over 70 generations, two of the site-specific integrations showed a stable productivity (>70%) independent of selection pressure.
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Affiliation(s)
- Oliver Hertel
- Cell Culture Technology, Faculty of Technology, Bielefeld University, Bielefeld, Germany
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
- *Correspondence: Oliver Hertel,
| | - Anne Neuss
- Biochemical Engineering (AVT.BioVT), RWTH Aachen University, Aachen, Germany
| | - Tobias Busche
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
| | - David Brandt
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
| | - Jörn Kalinowski
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
| | | | - Thomas Noll
- Cell Culture Technology, Faculty of Technology, Bielefeld University, Bielefeld, Germany
- Center for Biotechnology (CeBiTec), Bielefeld University, Bielefeld, Germany
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9
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Spahn PN, Zhang X, Hu Q, Lu H, Hamaker NK, Hefzi H, Li S, Kuo CC, Huang Y, Lee JC, Davis AJ, Ly P, Lee KH, Lewis NE. Restoration of DNA repair mitigates genome instability and increases productivity of Chinese hamster ovary cells. Biotechnol Bioeng 2022; 119:963-982. [PMID: 34953085 PMCID: PMC8821244 DOI: 10.1002/bit.28016] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Accepted: 12/18/2021] [Indexed: 11/11/2022]
Abstract
Chinese hamster ovary (CHO) cells are the primary host for manufacturing of therapeutic proteins. However, productivity loss is a major problem and is associated with genome instability, as chromosomal aberrations reduce transgene copy number and decrease protein expression. We analyzed whole-genome sequencing data from 11 CHO cell lines and found deleterious single-nucleotide variants in DNA repair genes. Comparison with primary Chinese hamster cells confirmed DNA repair to be compromised in CHO. Correction of key DNA repair genes by single-nucleotide variant reversal or expression of intact complementary DNAs successfully improved DNA repair and mitigated karyotypic instability. Moreover, overexpression of intact copies of LIG4 and XRCC6 in a CHO cell line expressing secreted alkaline phosphatase mitigated transgene copy loss and improved protein titer retention. These results show that correction of DNA repair genes yields improvements in genome stability in CHO, and provide new opportunities for cell line development for sustainable protein expression.
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Affiliation(s)
- Philipp N. Spahn
- Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, The Novo Nordisk Foundation Center for Biosustainability at the University of California, San Diego School of Medicine, San Diego, La Jolla, CA 92093
| | - Xiaolin Zhang
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19711
| | - Qing Hu
- Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Huiming Lu
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Nathaniel K. Hamaker
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19711
| | - Hooman Hefzi
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093
| | - Shangzhong Li
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093
| | - Chih-Chung Kuo
- Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093
| | - Yingxiang Huang
- Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093
| | - Jamie C. Lee
- Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093
| | - Anthony J. Davis
- Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Peter Ly
- Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Kelvin H. Lee
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19711, These authors jointly supervised this work: Kelvin H. Lee, , 302-831-0344, Nathan E. Lewis, , 858-997-5844
| | - Nathan E. Lewis
- Department of Pediatrics, University of California, San Diego, La Jolla, CA 92093, The Novo Nordisk Foundation Center for Biosustainability at the University of California, San Diego School of Medicine, San Diego, La Jolla, CA 92093, Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093, These authors jointly supervised this work: Kelvin H. Lee, , 302-831-0344, Nathan E. Lewis, , 858-997-5844
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10
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Marx N, Eisenhut P, Weinguny M, Klanert G, Borth N. How to train your cell - Towards controlling phenotypes by harnessing the epigenome of Chinese hamster ovary production cell lines. Biotechnol Adv 2022; 56:107924. [PMID: 35149147 DOI: 10.1016/j.biotechadv.2022.107924] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2021] [Revised: 02/03/2022] [Accepted: 02/04/2022] [Indexed: 11/24/2022]
Abstract
Recent advances in omics technologies and the broad availability of big datasets have revolutionized our understanding of Chinese hamster ovary cells in their role as the most prevalent host for production of complex biopharmaceuticals. In consequence, our perception of this "workhorse of the biopharmaceutical industry" has successively shifted from that of a nicely working, but unknown recombinant protein producing black box to a biological system governed by multiple complex regulatory layers that might possibly be harnessed and manipulated at will. Despite the tremendous progress that has been made to characterize CHO cells on various omics levels, our understanding is still far from complete. The well-known inherent genetic plasticity of any immortalized and rapidly dividing cell line also characterizes CHO cells and can lead to problematic instability of recombinant protein production. While the high mutational frequency has been a focus of CHO cell research for decades, the impact of epigenetics and its role in differential gene expression has only recently been addressed. In this review we provide an overview about the current understanding of epigenetic regulation in CHO cells and discuss its significance for shaping the cell's phenotype. We also look into current state-of-the-art technology that can be applied to harness and manipulate the epigenetic network so as to nudge CHO cells towards a specific phenotype. Here, we revise current strategies on site-directed integration and random as well as targeted epigenome modifications. Finally, we address open questions that need to be investigated to exploit the full repertoire of fine-tuned control of multiplexed gene expression using epigenetic and systems biology tools.
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Affiliation(s)
- Nicolas Marx
- University of Natural Resources and Life Sciences, Vienna, Austria
| | - Peter Eisenhut
- Austrian Centre for Industrial Biotechnology GmbH, Vienna, Austria
| | - Marcus Weinguny
- University of Natural Resources and Life Sciences, Vienna, Austria; Austrian Centre for Industrial Biotechnology GmbH, Vienna, Austria
| | - Gerald Klanert
- Austrian Centre for Industrial Biotechnology GmbH, Vienna, Austria
| | - Nicole Borth
- University of Natural Resources and Life Sciences, Vienna, Austria; Austrian Centre for Industrial Biotechnology GmbH, Vienna, Austria.
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11
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Altamura R, Doshi J, Benenson Y. Rational design and construction of multi-copy biomanufacturing islands in mammalian cells. Nucleic Acids Res 2022; 50:561-578. [PMID: 34893882 PMCID: PMC8754653 DOI: 10.1093/nar/gkab1214] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 11/21/2021] [Accepted: 11/26/2021] [Indexed: 11/14/2022] Open
Abstract
Cell line development is a critical step in the establishment of a biopharmaceutical manufacturing process. Current protocols rely on random transgene integration and amplification. Due to considerable variability in transgene integration profiles, this workflow results in laborious screening campaigns before stable producers can be identified. Alternative approaches for transgene dosage increase and integration are therefore highly desirable. In this study, we present a novel strategy for the rapid design, construction, and genomic integration of engineered multiple-copy gene constructs consisting of up to 10 gene expression cassettes. Key to this strategy is the diversification, at the sequence level, of the individual gene cassettes without altering their protein products. We show a computational workflow for coding and regulatory sequence diversification and optimization followed by experimental assembly of up to nine gene copies and a sentinel reporter on a contiguous scaffold. Transient transfections in CHO cells indicates that protein expression increases with the gene copy number on the scaffold. Further, we stably integrate these cassettes into a pre-validated genomic locus. Altogether, our findings point to the feasibility of engineering a fully mapped multi-copy recombinant protein 'production island' in a mammalian cell line with greatly reduced screening effort, improved stability, and predictable product titers.
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Affiliation(s)
- Raffaele Altamura
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, Basel, 4058, Switzerland
| | - Jiten Doshi
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, Basel, 4058, Switzerland
| | - Yaakov Benenson
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, Basel, 4058, Switzerland
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12
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Stadermann A, Gamer M, Fieder J, Lindner B, Fehrmann S, Schmidt M, Schulz P, Gorr IH. Structural analysis of random transgene integration in CHO manufacturing cell lines by targeted sequencing. Biotechnol Bioeng 2021; 119:868-880. [PMID: 34935125 PMCID: PMC10138747 DOI: 10.1002/bit.28012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 11/29/2021] [Accepted: 11/30/2021] [Indexed: 11/08/2022]
Abstract
Genetically modified CHO cell lines are traditionally used for the production of biopharmaceuticals. However, an in-depth molecular understanding of the mechanism and exact position of transgene integration into the genome of pharmaceutical manufacturing cell lines is still scarce. Next Generation Sequencing (NGS) holds great promise for strongly facilitating the understanding of CHO cell factories, as it has matured to a powerful and affordable technology for cellular genotype analysis. Targeted Locus Amplification (TLA) combined with NGS allows for robust detection of genomic positions of transgene integration and structural genomic changes occurring upon stable integration of expression vectors. TLA was applied to generate comparative genomic fingerprints of several CHO production cell lines expressing different monoclonal antibodies. Moreover, high producers resulting from an additional round of transfection of an existing cell line (supertransfection) were analyzed to investigate the integrity and the number of integration sites. Our analyses enabled detailed genetic characterization of the integration regions with respect to the number of integrates and structural changes of the host cell's genome. Single integration sites per clone with concatenated transgene copies could be detected and were in some cases found to be associated with genomic rearrangements, deletions or translocations. Supertransfection resulted in an increase in titer associated with an additional integration site per clone. Based on the TLA fingerprints, CHO cell lines originating from the same mother clone could clearly be distinguished. Interestingly, two CHO cell lines originating from the same mother clone were shown to differ genetically and phenotypically despite of their identical TLA fingerprints. Taken together, TLA provides an accurate genetic characterization with respect to transgene integration sites compared to conventional methods and represents a valuable tool for a comprehensive evaluation of CHO production clones early in cell line development. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Anna Stadermann
- Bioprocess Development Biologicals, Cell Line Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Martin Gamer
- R&D Project Management NBEs, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Jürgen Fieder
- Bioprocess Development Biologicals, Cell Line Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Benjamin Lindner
- Bioprocess Development Biologicals, Cell Line Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Steffen Fehrmann
- Genedata AG, Selector BU, Margarethenstrasse 38, 4053, Basel, Switzerland
| | - Moritz Schmidt
- Bioprocess Development Biologicals, Cell Line Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Patrick Schulz
- Bioprocess Development Biologicals, Cell Line Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Ingo H Gorr
- Analytical Development Biologicals, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
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13
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Nmagu D, Singh SK, Lee KH. Creation of monoclonal antibody expressing CHO cell lines grown with sodium butyrate and characterization of resulting antibody glycosylation. Methods Enzymol 2021; 660:267-295. [PMID: 34742393 DOI: 10.1016/bs.mie.2021.06.039] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Chinese hamster ovary (CHO) cells are the primary mammalian cell lines utilized to produce monoclonal antibodies (mAbs). The upsurge in biosimilar development and the proven health benefits of mAb treatments reinforces the need for innovative methods to generate robust CHO clones and enhance production, while maintaining desired product quality attributes. Among various product titer-enhancing approaches, the use of histone deacetylase inhibitors (HDACis) such as sodium butyrate (NaBu) has yielded promising results. The titer-enhancing effect of HDACi treatment has generally been observed in lower producer cell lines but those studies are typically done on individual clones. Here, we describe a cell line development (CLD) platform approach for creating clones with varying productivities. We then describe a method for selecting an optimal NaBu concentration to evaluate potential titer-enhancing capabilities in a fed-batch study. Finally, a method for purifying the mAb using protein A chromatography, followed by glycosylation analysis using mass spectrometry, is described. The proposed workflow can be applied for a robust CLD process optimization to generate robust clones, enhance product expression, and improve product quality attributes.
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Affiliation(s)
- Douglas Nmagu
- Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, United States
| | - Sumit K Singh
- Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, United States
| | - Kelvin H Lee
- Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, United States.
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14
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Langsdorf E, Yu L, Kanevskaia L, Felkner R, Sturner S, McVey D, Khetan A. Retrospective assessment of clonal origin of cell lines. Biotechnol Prog 2021; 37:e3157. [PMID: 33896120 DOI: 10.1002/btpr.3157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2020] [Revised: 04/11/2021] [Accepted: 04/19/2021] [Indexed: 11/08/2022]
Abstract
Cell lines used for the manufacture of recombinant proteins are expected to arise from a single cell as a control strategy to limit variability and ensure consistent protein production. Health authorities require a minimum of two rounds of limiting dilution cloning or its equivalent to meet the requirement of single cell origin. However, many legacy cell lines may not have been generated with process meeting this criteria potentially impeding the path to commercialization. A general monoclonality assessment strategy was developed based on using the site of plasmid integration for a cell's identity. By comparing the identities of subclones from a master cell bank (MCB) to each other and that of the MCB, a probability of monoclonality was established. Two technologies were used for cell identity, Southern blot and a PCR assay based on plasmid-genome junction sequences identified by splinkerette PCR. Southern blot analysis revealed that subclones may have banding patterns that differ from each other and yet indicate monoclonal origin. Splinkerette PCR identifies cellular sequence flanking the point(s) of plasmid integration. The two assays together provide complimentary data for cell identity that enables proper monoclonality assessment and establishes that the three legacy cell lines investigated are all of clonal origin.
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Affiliation(s)
- Erik Langsdorf
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
| | - Le Yu
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
| | - Lioudmila Kanevskaia
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
| | - Roland Felkner
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
| | - Stephen Sturner
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
| | - Duncan McVey
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
| | - Anurag Khetan
- Biologics Development, Global Product Development and Supply, Bristol-Myers Squibb, New Brunswick, New Jersey, USA
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15
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Tevelev B, Patel H, Shields K, Wei W, Cooley C, Zhang S, Bitzas G, Duan W, Khetemenee L, Jackobek R, D'Antona A, Sievers A, King A, Tam A, Zhang Y, Sousa E, Cohen J, Wroblewska L, Marshall J, Jackson M, Scarcelli JJ. Genetic rearrangement during site specific integration event facilitates cell line development of a bispecific molecule. Biotechnol Prog 2021; 37:e3158. [PMID: 33891804 PMCID: PMC8459265 DOI: 10.1002/btpr.3158] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 04/16/2021] [Accepted: 04/19/2021] [Indexed: 11/13/2022]
Abstract
Site specific integration (SSI) expression systems offer robust means of generating highly productive and stable cell lines for traditional monoclonal antibodies. As complex modalities such as antibody‐like molecules comprised of greater than two peptides become more prevalent, greater emphasis needs to be placed on the ability to produce appreciable quantities of the correct product of interest (POI). The ability to screen several transcript stoichiometries could play a large role in ensuring high amounts of the correct POI. Here we illustrate implementation of an SSI expression system with a single site of integration for development and production of a multi‐chain, bi‐specific molecule. A SSI vector with a single copy of all of the genes of interest was initially selected for stable Chinese hamster ovary transfection. While the resulting transfection pools generated low levels of the desired heterodimer, utilizing an intensive clone screen strategy, we were able to identify clones having significantly higher levels of POI. In‐depth genotypic characterization of clones having the desirable phenotype revealed that a duplication of the light chain within the landing pad was responsible for producing the intended molecule. Retrospective transfection pool analysis using a vector configuration mimicking the transgene configuration found in the clones, as well as other vector configurations, yielded more favorable results with respect to % POI. Overall, the study demonstrated that despite the theoretical static nature of the SSI expression system, enough heterogeneity existed to yield clones having significantly different transgene phenotypes/genotypes and support production of a complex multi‐chain molecule.
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Affiliation(s)
- Barbara Tevelev
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - Himakshi Patel
- Analytical Research and Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - Kathleen Shields
- Analytical Research and Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - Wei Wei
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - Cecilia Cooley
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - Sam Zhang
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | | | - Weili Duan
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Lam Khetemenee
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Ryan Jackobek
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Aaron D'Antona
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Annette Sievers
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Amy King
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Amy Tam
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Yan Zhang
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Eric Sousa
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Justin Cohen
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Lila Wroblewska
- BioMedicine Design, Pfizer Inc., Andover, Massachusetts, USA
| | - Jeffrey Marshall
- Analytical Research and Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - Martha Jackson
- Analytical Research and Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
| | - John J Scarcelli
- Cell Line Development, Biotherapeutics Pharmaceutical Sciences, Pfizer Inc., Andover, Massachusetts, USA
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16
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Baik JY, Han HJ, Lee KH. DNA Double-Strand Breaks Affect Chromosomal Rearrangements during Methotrexate-Mediated Gene Amplification in Chinese Hamster Ovary Cells. Pharmaceutics 2021; 13:pharmaceutics13030376. [PMID: 33809068 PMCID: PMC8000239 DOI: 10.3390/pharmaceutics13030376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 02/28/2021] [Accepted: 03/05/2021] [Indexed: 11/16/2022] Open
Abstract
Methotrexate (MTX)-mediated gene amplification has been widely used in Chinese hamster ovary (CHO) cells for the biomanufacturing of therapeutic proteins. Although many studies have reported chromosomal instability and extensive chromosomal rearrangements in MTX-mediated gene-amplified cells, which may be associated with cell line instability issues, the mechanisms of chromosomal rearrangement formation remain poorly understood. We tested the impact of DNA double-strand breaks (DSBs) on chromosomal rearrangements using bleomycin, a DSB-inducing reagent. Bleomycin-treated CHO-DUK cells, which are one of the host cell lines deficient in dihydrofolate reductase (Dhfr) activity, exhibited a substantial number of cells containing radial formations or non-radial formations with chromosomal rearrangements, suggesting that DSBs may be associated with chromosomal rearrangements. To confirm the causes of DSBs during gene amplification, we tested the effects of MTX treatment and the removal of nucleotide base precursors on DSB formation in Dhfr-deficient (i.e., CHO-DUK) and Dhfr-expressing (i.e., CHO-K1) cells. Immunocytochemistry demonstrated that MTX treatment did not induce DSBs per se, but a nucleotide shortage caused by the MTX-mediated inhibition of Dhfr activity resulted in DSBs. Our data suggest that a nucleotide shortage caused by MTX-mediated Dhfr inhibition in production cell lines is the primary cause of a marked increase in DSBs, resulting in extensive chromosomal rearrangements after gene amplification processes.
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Affiliation(s)
- Jong Youn Baik
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA
- Delaware Biotechnology Institute, University of Delaware, Newark, DE 19711, USA
- Department of Biological Engineering, Inha University, Incheon 22212, Korea;
- Correspondence: (J.Y.B.); (K.H.L.); Tel.: +82-32-860-7513 (J.Y.B.); +1-302-831-0344 (K.H.L.)
| | - Hye-Jin Han
- Department of Biological Engineering, Inha University, Incheon 22212, Korea;
| | - Kelvin H. Lee
- Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716, USA
- Delaware Biotechnology Institute, University of Delaware, Newark, DE 19711, USA
- Correspondence: (J.Y.B.); (K.H.L.); Tel.: +82-32-860-7513 (J.Y.B.); +1-302-831-0344 (K.H.L.)
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17
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Lee Z, Raabe M, Hu WS. Epigenomic features revealed by ATAC-seq impact transgene expression in CHO cells. Biotechnol Bioeng 2021; 118:1851-1861. [PMID: 33521928 DOI: 10.1002/bit.27701] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Revised: 01/14/2021] [Accepted: 01/25/2021] [Indexed: 12/15/2022]
Abstract
Different regions of a mammalian genome have different accessibilities to transcriptional machinery. The integration site of a transgene affects how actively it is transcribed. Highly accessible genomic regions called super-enhancers have been recently described as strong regulatory elements that shape cell identity. Super-enhancers have been identified in Chinese hamster ovary (CHO) cells using the Assay for Transposase-Accessible Chromatin Sequencing (ATAC-seq). Genes near super-enhancer regions had high transcript levels and were enriched for oncogenic signaling and proliferation functions, consistent with an immortalized phenotype. Inaccessible regions in the genome with low ATAC signal also had low transcriptional activity. Genes in inaccessible regions were enriched for remote tissue functions such as taste, smell, and neuronal activation. A lentiviral reporter integration assay showed integration into super-enhancer regions conferred higher reporter expression than insertion into inaccessible regions. Targeted integration of an IgG vector into the Plec super-enhancer region yielded clones that expressed the immunoglobulin light chain gene mostly in the top 20% of all transcripts with the majority in the top 5%. The results suggest the epigenomic landscape of CHO cells can guide the selection of integration sites in the development of cell lines for therapeutic protein production.
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Affiliation(s)
- Zion Lee
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, USA
| | - Marina Raabe
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, USA
| | - Wei-Shou Hu
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, USA
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18
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Turilova VI, Goryachaya TS, Yakovleva TK. Chinese hamster ovary cell line DXB-11: chromosomal instability and karyotype heterogeneity. Mol Cytogenet 2021; 14:11. [PMID: 33596973 PMCID: PMC7888135 DOI: 10.1186/s13039-021-00528-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Accepted: 01/07/2021] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Chinese hamster ovary cell lines, also known as CHO cells, represent a large family of related, yet quite different, cell lines which are metabolic mutants derived from the original cell line, CHO-ori. Dihydrofolate reductase-deficient DXB-11 cell line, one of the first CHO derivatives, serves as the host cell line for the production of therapeutic proteins. It is generally assumed that DXB-11 is identical to DUKX or CHO-DUK cell lines, but, to our knowledge, DXB-11 karyotype has not been described yet. RESULTS Using differential staining approaches (G-, C-banding and Ag-staining), we presented DXB-11 karyotype and revealed that karyotypes of DXB-11 and CHO-DUK cells have a number of differences. Although the number of chromosomes is equal-20 in each cell line-DXB-11 has normal chromosomes of the 1st and 5th pairs as well as an intact chromosome 8. Besides, in DXB-11 line, chromosome der(Z9) includes the material of chromosomes X and 6, whereas in CHO-DUK it results from the translocation of chromosomes 1 and 6. Ag-positive nucleolar organizer regions were revealed in the long arms of chromosome del(4)(q11q12) and both chromosome 5 homologues, as well as in the short arms of chromosomes 8 and add(8)(q11). Only 19 from 112 (16.96%) DXB-11 cells display identical chromosome complement accepted as the main structural variant of karyotype. The karyotype heterogeneity of all the rest of cells (93, 83.04%) occurs due to clonal and nonclonal additional structural rearrangements of chromosomes. Estimation of the frequency of chromosome involvement in these rearrangements allowed us to reveal that chromosomes 9, der(X)t(X;3;4), del(2)(p21p23), del(2)(q11q22) /Z2, der(4) /Z7, add(6)(p11) /Z8 are the most stable, whereas mar2, probably der(10), is the most unstable chromosome. A comparative analysis of our own and literary data on CHO karyotypes allowed to designate conservative chromosomes, both normal and rearranged, that remain unchanged in different CHO cell lines, as well as variable chromosomes that determine the individuality of karyotypes of CHO derivatives. CONCLUSION DXB-11and CHO-DUK cell lines differ in karyotypes. The revealed differential instability of DXB-11 chromosomes is likely not incidental and results in karyotype heterogeneity of cell population.
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Affiliation(s)
- Victoria I Turilova
- Laboratory of Cell Morphology, Institute of Cytology, Russian Academy of Sciences, Tikhoretsky ave., 4, St Petersburg, Russia, 194064.
| | - Tatyana S Goryachaya
- Centre of Cell Technologies, Institute of Cytology, Russian Academy of Sciences, Tikhoretsky ave., 4, St Petersburg, Russia, 194064
| | - Tatiana K Yakovleva
- Laboratory of Cell Morphology, Institute of Cytology, Russian Academy of Sciences, Tikhoretsky ave., 4, St Petersburg, Russia, 194064
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19
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Weinguny M, Klanert G, Eisenhut P, Lee I, Timp W, Borth N. Subcloning induces changes in the DNA-methylation pattern of outgrowing Chinese hamster ovary cell colonies. Biotechnol J 2021; 16:e2000350. [PMID: 33484505 DOI: 10.1002/biot.202000350] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2020] [Revised: 01/17/2021] [Accepted: 01/21/2021] [Indexed: 12/12/2022]
Abstract
Chinese hamster ovary (CHO) cells are the most extensively used mammalian production system for biologics intended for use in humans. A critical step in the establishment of production cell lines is single cell cloning, with the objective of achieving high productivity and product quality. Despite general use, knowledge of the effects of this process is limited. Importantly, single cell cloned cells display a wide array of observed phenotypes, which so far was attributed to the instability and variability of the CHO genome. In this study we present data indicating that the emergence of diverse phenotypes during single cell cloning is associated with changes in DNA methylation patterns and transcriptomes that occur during the subcloning process. The DNA methylation pattern of each analyzed subclone, randomly picked from all outgrowing clones of the experiment, had unique changes preferentially found in regulatory regions of the genome such as enhancers, and de-enriched in actively transcribed sequences (not including the respective promoters), indicating that these changes resulted in adaptations of the relative gene expression pattern. The transcriptome of each subclone also had a significant number of individual changes. These results indicate that epigenetic regulation is a hidden, but important player in cell line development with a major role in the establishment of high performing clones with improved characteristics for bioprocessing.
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Affiliation(s)
- Marcus Weinguny
- ACIB Gmbh, Austrian Centre of Industrial Biotechnology, Vienna, Austria.,Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Vienna, Austria
| | - Gerald Klanert
- ACIB Gmbh, Austrian Centre of Industrial Biotechnology, Vienna, Austria
| | - Peter Eisenhut
- ACIB Gmbh, Austrian Centre of Industrial Biotechnology, Vienna, Austria.,Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Vienna, Austria
| | - Isac Lee
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, USA
| | - Winston Timp
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, USA
| | - Nicole Borth
- ACIB Gmbh, Austrian Centre of Industrial Biotechnology, Vienna, Austria.,Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Vienna, Austria
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20
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Chitwood DG, Wang Q, Elliott K, Bullock A, Jordana D, Li Z, Wu C, Harcum SW, Saski CA. Characterization of metabolic responses, genetic variations, and microsatellite instability in ammonia-stressed CHO cells grown in fed-batch cultures. BMC Biotechnol 2021; 21:4. [PMID: 33419422 PMCID: PMC7791692 DOI: 10.1186/s12896-020-00667-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 12/11/2020] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND As bioprocess intensification has increased over the last 30 years, yields from mammalian cell processes have increased from 10's of milligrams to over 10's of grams per liter. Most of these gains in productivity can be attributed to increasing cell densities within bioreactors. As such, strategies have been developed to minimize accumulation of metabolic wastes, such as lactate and ammonia. Unfortunately, neither cell growth nor biopharmaceutical production can occur without some waste metabolite accumulation. Inevitably, metabolic waste accumulation leads to decline and termination of the culture. While it is understood that the accumulation of these unwanted compounds imparts a suboptimal culture environment, little is known about the genotoxic properties of these compounds that may lead to global genome instability. In this study, we examined the effects of high and moderate extracellular ammonia on the physiology and genomic integrity of Chinese hamster ovary (CHO) cells. RESULTS Through whole genome sequencing, we discovered 2394 variant sites within functional genes comprised of both single nucleotide polymorphisms and insertion/deletion mutations as a result of ammonia stress with high or moderate impact on functional genes. Furthermore, several of these de novo mutations were found in genes whose functions are to maintain genome stability, such as Tp53, Tnfsf11, Brca1, as well as Nfkb1. Furthermore, we characterized microsatellite content of the cultures using the CriGri-PICR Chinese hamster genome assembly and discovered an abundance of microsatellite loci that are not replicated faithfully in the ammonia-stressed cultures. Unfaithful replication of these loci is a signature of microsatellite instability. With rigorous filtering, we found 124 candidate microsatellite loci that may be suitable for further investigation to determine whether these loci may be reliable biomarkers to predict genome instability in CHO cultures. CONCLUSION This study advances our knowledge with regards to the effects of ammonia accumulation on CHO cell culture performance by identifying ammonia-sensitive genes linked to genome stability and lays the foundation for the development of a new diagnostic tool for assessing genome stability.
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Affiliation(s)
- Dylan G Chitwood
- Department of Bioengineering, College of Engineering, Computing and Applied Sciences, Clemson University, Clemson, SC, 29634, USA
| | - Qinghua Wang
- Center for Bioinformatics & Computational Biology, University of Delaware, Newark, DE, 19716, USA
| | - Kathryn Elliott
- Department of Bioengineering, College of Engineering, Computing and Applied Sciences, Clemson University, Clemson, SC, 29634, USA
| | - Aiyana Bullock
- Department of Biological Sciences, College of Agriculture, Science & Technology, Delaware State University, Dover, DE, 19901, USA
| | - Dwon Jordana
- Department of Biological Sciences, Grambling State University, Grambling, LA, 71245, USA
| | - Zhigang Li
- Department of Plant and Environmental Sciences, College of Agriculture, Forestry and Life Sciences, Clemson University, Clemson, SC, 29634, USA
| | - Cathy Wu
- Center for Bioinformatics & Computational Biology, University of Delaware, Newark, DE, 19716, USA
| | - Sarah W Harcum
- Department of Bioengineering, College of Engineering, Computing and Applied Sciences, Clemson University, Clemson, SC, 29634, USA
| | - Christopher A Saski
- Department of Plant and Environmental Sciences, College of Agriculture, Forestry and Life Sciences, Clemson University, Clemson, SC, 29634, USA.
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21
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O’Brien SA, Hu WS. Cell culture bioprocessing - the road taken and the path forward. Curr Opin Chem Eng 2020; 30:100663. [PMID: 33391982 PMCID: PMC7773285 DOI: 10.1016/j.coche.2020.100663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Cell culture processes are used to produce the vast majority of protein therapeutics, valued at over US$180 billion per annum worldwide. For more than a decade now, these processes have become highly productive. To further enhance capital efficiency, there has been an increase in the adoption of disposable apparatus and continuous processing, as well as a greater exploration of in-line sensing, various -omic tools, and cell engineering to enhance process controllability and product quality consistency. These feats in cell culture processing for protein biologics will help accelerate the bioprocess advancements for virus and cell therapy applications.
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Affiliation(s)
- Sofie A. O’Brien
- Department of Biomedical Engineering and Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455-0132 USA
| | - Wei-Shou Hu
- Department of Biomedical Engineering and Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455-0132 USA
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22
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Violacein improves recombinant IgG production by controlling the cell cycle of Chinese hamster ovary cells. Cytotechnology 2020; 73:319-332. [PMID: 34149168 DOI: 10.1007/s10616-020-00434-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2020] [Accepted: 10/28/2020] [Indexed: 10/22/2022] Open
Abstract
Chinese hamster ovary (CHO) cells are used as host cells for industrial monoclonal antibody (mAb) production. Cell cycle control is an effective approach to increase mAb production in the cell culture. Violacein, a purple-colored pigment produced by microorganisms, has diverse bioactive properties and has been proposed for various industrial applications. In this study, we evaluated the potency of violacein for cell cycle control and improvement of recombinant immunoglobulin G (IgG) production in CHO cells. Compared with the control, 0.9 μM violacein in a 14-day fed-batch culture increased the maximum IgG concentration by 37.6% via increasing the specific production rate and cell longevity. Cell cycle analysis showed that violacein induced G1 and G2/M phase arrest. However, the G1 arrest was observed only on day 1, while G2/M arrest lasted more than 3 days, suggesting that G2/M arrest mediated the violacein-induced enhanced IgG production. Moreover, in line with the increased protein expression, the expression levels of IgG mRNA and nutrient metabolic rates were also increased. N-Linked glycosylation and charge variant profiles were barely affected by violacein treatment. Our results indicate that violacein affects the cell cycle of CHO cells and increases IgG production without changing product quality, showing promise as a mAb production enhancer in CHO cells. The study provides insight into violacein utilization in industrial mAb manufacturing and can help develop advanced, effective mAb production technologies using CHO cell cultures.
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23
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Dhiman H, Campbell M, Melcher M, Smith KD, Borth N. Predicting favorable landing pads for targeted integrations in Chinese hamster ovary cell lines by learning stability characteristics from random transgene integrations. Comput Struct Biotechnol J 2020; 18:3632-3648. [PMID: 33304461 PMCID: PMC7710658 DOI: 10.1016/j.csbj.2020.11.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 11/04/2020] [Accepted: 11/04/2020] [Indexed: 01/06/2023] Open
Abstract
Chinese Hamster Ovary (CHO) cell lines are considered to be the preferred platform for the production of biotherapeutics, but issues related to expression instability remain unresolved. In this study, we investigated potential causes for an unstable phenotype by comparing cell lines that express stably to such that undergo loss in titer across 10 passages. Factors related to transgene integrity and copy number as well as the genomic profile around the integration sites were analyzed. Horizon Discovery CHO-K1 (HD-BIOP3) derived production cell lines selected for phenotypes with low, medium or high copy number, each with stable and unstable transgene expression, were sequenced to capture changes at genomic and transcriptomic levels. The exact sites of the random integration events in each cell line were also identified, followed by profiling of the genomic, transcriptomic and epigenetic patterns around them. Based on the information deduced from these random integration events, genomic loci that potentially favor reliable and stable transgene expression were reported for use as targeted transgene integration sites. By comparing stable vs unstable phenotypes across these parameters, we could establish that expression stability may be controlled at three levels: 1) Good choice of integration site, 2) Ensuring integrity of transgene and observing concatemerization pattern after integration, and 3) Checking for potential stress related cellular processes. Genome wide favorable and unfavorable genomic loci for targeted transgene integration can be browsed at https://www.borthlabchoresources.boku.ac.at/
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Affiliation(s)
- Heena Dhiman
- University of Natural Resources and Life Sciences, Vienna, Austria.,Austrian Centre of Industrial Biotechnology, Vienna, Austria
| | | | - Michael Melcher
- University of Natural Resources and Life Sciences, Vienna, Austria
| | | | - Nicole Borth
- University of Natural Resources and Life Sciences, Vienna, Austria.,Austrian Centre of Industrial Biotechnology, Vienna, Austria
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24
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Muralidharan-Chari V, Wurz Z, Doyle F, Henry M, Diendorfer A, Tenenbaum SA, Borth N, Eveleth E, Sharfstein ST. PTSelect™: A post-transcriptional technology that enables rapid establishment of stable CHO cell lines and surveillance of clonal variation. J Biotechnol 2020; 325:360-371. [PMID: 33115662 DOI: 10.1016/j.jbiotec.2020.09.025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 09/07/2020] [Accepted: 09/27/2020] [Indexed: 10/23/2022]
Abstract
Currently, stable Chinese hamster ovary cell lines producing therapeutic, recombinant proteins are established either by antibiotic and/or metabolic selection. Here, we report a novel technology, PTSelect™ that utilizes an siRNA cloned upstream of the gene of interest (GOI) that is processed to produce functional PTSelect™-siRNAs, which enable cell enrichment. Cells with stably integrated GOI are selected and separated from cells without GOI by transfecting CD4/siRNA mRNA regulated by PTSelect™-siRNAs and exploiting the variable expression of CD4 on the cell surface. This study describes the PTSelect™ principle and compares the productivity, doubling time and stability of clones developed by PTSelect™ with conventionally developed clones. PTSelect™ rapidly established a pool population with comparable stability and productivity to pools generated by traditional methods and can further be used to easily monitor productivity changes due to clonal drift, identifying individual cells with reduced productivity.
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Affiliation(s)
| | - Zachary Wurz
- HocusLocus, LLC, 253 Fuller Road, Albany NY 12203, USA
| | - Francis Doyle
- College of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, NY, New York 12203, USA
| | - Matthew Henry
- Australian Institute for Bioengineering and Nanotechnology (AIBN), The University of Queensland, St. Lucia, QLD, 4072, Australia
| | - Andreas Diendorfer
- Austrian Centre of Industrial Biotechnology, Graz, Austria, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Scott A Tenenbaum
- College of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, NY, New York 12203, USA
| | - Nicole Borth
- Austrian Centre of Industrial Biotechnology, Graz, Austria, University of Natural Resources and Life Sciences, Vienna, Austria
| | | | - Susan T Sharfstein
- College of Nanoscale Science and Engineering, SUNY Polytechnic Institute, Albany, NY, New York 12203, USA.
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25
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Abstract
Following the success of and the high demand for recombinant protein-based therapeutics during the last 25 years, the pharmaceutical industry has invested significantly in the development of novel treatments based on biologics. Mammalian cells are the major production systems for these complex biopharmaceuticals, with Chinese hamster ovary (CHO) cell lines as the most important players. Over the years, various engineering strategies and modeling approaches have been used to improve microbial production platforms, such as bacteria and yeasts, as well as to create pre-optimized chassis host strains. However, the complexity of mammalian cells curtailed the optimization of these host cells by metabolic engineering. Most of the improvements of titer and productivity were achieved by media optimization and large-scale screening of producer clones. The advances made in recent years now open the door to again consider the potential application of systems biology approaches and metabolic engineering also to CHO. The availability of a reference genome sequence, genome-scale metabolic models and the growing number of various “omics” datasets can help overcome the complexity of CHO cells and support design strategies to boost their production performance. Modular design approaches applied to engineer industrially relevant cell lines have evolved to reduce the time and effort needed for the generation of new producer cells and to allow the achievement of desired product titers and quality. Nevertheless, important steps to enable the design of a chassis platform similar to those in use in the microbial world are still missing. In this review, we highlight the importance of mammalian cellular platforms for the production of biopharmaceuticals and compare them to microbial platforms, with an emphasis on describing novel approaches and discussing still open questions that need to be resolved to reach the objective of designing enhanced modular chassis CHO cell lines.
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26
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Kido M, Idogaki H, Nishikawa K, Motoishi K, Omasa T. Screening of new cell cycle suppressive compounds from marine-derived microorganisms in Chinese hamster ovary cells. J Biosci Bioeng 2020; 130:106-113. [PMID: 32253091 DOI: 10.1016/j.jbiosc.2020.03.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2019] [Revised: 03/01/2020] [Accepted: 03/03/2020] [Indexed: 02/06/2023]
Abstract
Monoclonal antibodies (mAbs) are active pharmaceutical ingredients in antibody drugs, produced mainly using recombinant Chinese hamster ovary (CHO) cells. The regulation of recombinant CHO cell proliferation can improve the productivity of heterologous proteins. Chemical compound approaches for cell cycle regulation have the advantages of simplicity and ease of use in industrial processes. However, CHO cells have genetic and phenotypic diversity, and the effects of such compounds might depend on cell line and culture conditions. Increasing the variety of cell cycle inhibitors is a promising strategy to overcome the dependency. Marine microorganisms are a vast and largely undeveloped source of secondary metabolites with physiological activity. In this study, we focused on secondary metabolites of marine microorganisms and evaluated their effectiveness as cell cycle inhibitory compounds. Of 720 extracts from microorganisms (400 actinomycetes and 320 filamentous fungi) collected from the Okinawan Sea, we identified nine extracts that decreased the specific growth rate and increased the specific production rate without reducing cell viability. After fractionating the extracts, the components of active fractions were estimated using time-of-flight mass spectrometry analysis. Then, four compounds, including staurosporine and undecylprodigiosin were deduced to be active compounds. These compounds have been reported to exert a cell cycle inhibitory effect on mammalian cells. These compounds might serve as additives to improve mAb production in CHO cells. This study indicates that secondary metabolites of marine microorganisms are a useful source for new cell cycle inhibitory compounds that can increase mAb production in CHO cells.
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Affiliation(s)
- Masahide Kido
- Research and Development Division of OSAKA SODA Co., Ltd., Amagasaki, Hyogo 660-0842, Japan; Graduate School of Engineering. Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
| | - Hideaki Idogaki
- Research and Development Division of OSAKA SODA Co., Ltd., Amagasaki, Hyogo 660-0842, Japan
| | - Kouji Nishikawa
- Research and Development Division of OSAKA SODA Co., Ltd., Amagasaki, Hyogo 660-0842, Japan
| | - Kana Motoishi
- Research and Development Division of OSAKA SODA Co., Ltd., Amagasaki, Hyogo 660-0842, Japan
| | - Takeshi Omasa
- Graduate School of Engineering. Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
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27
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O'Brien SA, Ojha J, Wu P, Hu WS. Multiplexed clonality verification of cell lines for protein biologic production. Biotechnol Prog 2020; 36:e2978. [PMID: 32034880 PMCID: PMC7803388 DOI: 10.1002/btpr.2978] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 12/11/2019] [Accepted: 02/05/2020] [Indexed: 12/11/2022]
Abstract
During the development of cell lines for therapeutic protein production, a vector harboring a product transgene is integrated into the genome. To ensure production stability and consistent product quality, single-cell cloning is then performed. Since cells derived from the same parental clone have the same transgene integration locus, the identity of the integration site can also be used to verify the clonality of a production cell line. In this study, we present a high-throughput pipeline for clonality verification through integration site analysis. Sequence capture of genomic fragments that contain both vector and host cell genome sequences was used followed by next-generation sequencing to sequence the relevant vector-genome junctions. A Python algorithm was then developed for integration site identification and validated using a cell line with known integration sites. Using this system, we identified the integration sites of the host vector for 31 clonal cell lines from five independent vector integration events while using one set of probes against common features of the host vector for transgene integration. Cell lines from the same lineage had common integration sites, and they were distinct from unrelated cell lines. The integration sites obtained for each clone as part of the analysis may also be used for clone selection, as the sites can have a profound effect on the transgene’s transcript level and the stability of the resulting cell line. This method thus provides a rapid system for integration site identification and clonality verification.
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Affiliation(s)
- Sofie A O'Brien
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota
| | - Juhi Ojha
- Pharmaceuticals Division, Biologics Development Department, Bayer HealthCare, Berkeley, California
| | - Paul Wu
- Pharmaceuticals Division, Biologics Development Department, Bayer HealthCare, Berkeley, California
| | - Wei-Shou Hu
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota
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28
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Lieske PL, Wei W, Crowe KB, Figueroa B, Zhang L. HIF-1 Signaling Pathway Implicated in Phenotypic Instability in a Chinese Hamster Ovary Production Cell Line. Biotechnol J 2020; 15:e1900306. [PMID: 31872551 DOI: 10.1002/biot.201900306] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2019] [Revised: 11/14/2019] [Indexed: 12/13/2022]
Abstract
Monitoring genotypic and phenotypic stability is crucial during the development of recombinant Chinese hamster ovary (CHO) cell lines. Although genotypic instability is well-studied, there are few reports on phenotypic instability. Here, a case study of two clonal cell lines derived from Pfizer's site-specific integration expression platform that expresses the same monoclonal antibody is described. It is shown that both cell lines (herein referred to as "Cell Line A" and "Cell Line B") are genotypically stable up to 130 generations. However, when both cell lines are run side-by-side in a fed-batch production assay, productivity from Cell Line A later generation cells is much lower when compared to earlier generation cells. Phenotypically, later generation Cell Line A cells display increased lactate production, decreased productivity, and decreased cell viability. Metabolic analysis reveals that Cell Line A exhibits increased glycolysis activity and capacity at higher generational age. Whole transcriptomic sequencing shows significant upregulation of the hypoxia-inducible factor 1-alpha (HIF-1α) signaling pathway and associated downstream targets. Furthermore, Western blot analysis confirms elevated HIF-1α protein in Cell Line A cells at later generation. These results suggest a novel role for HIF-1α in the age-associated metabolic changes that result in the phenotypic instability of a recombinant CHO cell line.
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Affiliation(s)
| | - Wei Wei
- Cell Line Development, Pfizer Inc., Andover, MA, 01810, USA
| | | | - Bruno Figueroa
- Cell Culture Development, Sanofi R&D Biologics Development, Framingham, MA, 01701, USA
| | - Lin Zhang
- Cell Line Development, Pfizer Inc., Andover, MA, 01810, USA
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