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Ghosh R, Arnheim A, van Zee M, Shang L, Soemardy C, Tang RC, Mellody M, Baghdasarian S, Sanchez Ochoa E, Ye S, Chen S, Williamson C, Karunaratne A, Di Carlo D. Lab on a Particle Technologies. Anal Chem 2024; 96:7817-7839. [PMID: 38650433 PMCID: PMC11112544 DOI: 10.1021/acs.analchem.4c01510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Revised: 04/14/2024] [Accepted: 04/16/2024] [Indexed: 04/25/2024]
Affiliation(s)
- Rajesh Ghosh
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Alyssa Arnheim
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Mark van Zee
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Lily Shang
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Citradewi Soemardy
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Rui-Chian Tang
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Michael Mellody
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Sevana Baghdasarian
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Edwin Sanchez Ochoa
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Shun Ye
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Siyu Chen
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Cayden Williamson
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Amrith Karunaratne
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
| | - Dino Di Carlo
- Department
of Bioengineering, University of California,
Los Angeles, Los Angeles, California 90095, United States
- Jonsson
Comprehensive Cancer Center, University
of California, Los Angeles, Los Angeles, California 90095, United States
- Department
of Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
- California
NanoSystems Institute, Los Angeles, California 90095, United States
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2
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Diep J, Le H, Le K, Zasadzinska E, Tat J, Yam P, Zastrow R, Gomez N, Stevens J. Microfluidic chip-based single-cell cloning to accelerate biologic production timelines. Biotechnol Prog 2021; 37:e3192. [PMID: 34323013 PMCID: PMC9285370 DOI: 10.1002/btpr.3192] [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: 03/15/2021] [Revised: 07/06/2021] [Accepted: 07/12/2021] [Indexed: 12/20/2022]
Abstract
Cell line development (CLD) represents a critical, yet time‐consuming, step in the biomanufacturing process as significant resources are devoted to the scale‐up and screening of several hundreds to thousands of single‐cell clones. Typically, transfected pools are fully recovered from selection and characterized for growth, productivity, and product quality to identify the best pools suitable for single‐cell cloning (SCC) using limiting dilution or fluorescence‐activated cell sorting (FACS). Here we report the application of the Berkeley Lights Beacon Instrument (BLI) in an early SCC process to accelerate the CLD timeline. Transfected pools were single‐cell cloned when viabilities reached greater than 85% or during selection when viabilities were less than 30%. Clones isolated from these accelerated processes exhibited comparable growth, productivity, and product quality to those derived from a standard CLD process and fit into an existing manufacturing platform. With these approaches, up to a 30% reduction in the overall CLD timeline was achieved. Furthermore, early process‐derived clones demonstrated equivalent long‐term stability compared with standard process‐derived clones over 50 population doubling levels (PDLs). Taken together, the data supported early SCC on the BLI as an attractive approach to reducing the standard CLD timeline while still identifying clones with acceptable manufacturability.
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Affiliation(s)
- Jonathan Diep
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Huong Le
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Kim Le
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Ewelina Zasadzinska
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Jasmine Tat
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Pheng Yam
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Ryan Zastrow
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Natalia Gomez
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
| | - Jennitte Stevens
- Drug Substance Technologies, Process Development, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California, USA
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3
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Ultra-high throughput screening for novel protease specificities. Methods Enzymol 2020. [PMID: 32943144 DOI: 10.1016/bs.mie.2020.06.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
The screening of large libraries of enzyme variants remains an essential tool in evolving biocatalysts toward improved properties for applications in medicine, chemistry, and a broad variety of other fields. Over the last decades, the technology for conducting systematic screens of arrayed members of a library of enzyme variants has made great strides in terms of increasing throughput and reducing assay volume. Here, we describe in detail an alternative to arrayed analysis, which is a screen based on density shifts in result of changed enzyme function, which allows highly parallelized screening. Specifically, we link changes in protease substrate specificity in vivo to the production of an alternative reporter protein, catalase. Depending on the catalase expression level, microcolonies of library bacteria with active protease variants contained in polymeric droplets generate an oxygen bubble, which causes a density shift in the droplet and enables it to float.
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4
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A novel selection strategy for antibody producing hybridoma cells based on a new transgenic fusion cell line. Sci Rep 2020; 10:1664. [PMID: 32015441 PMCID: PMC6997400 DOI: 10.1038/s41598-020-58571-w] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 01/14/2020] [Indexed: 12/28/2022] Open
Abstract
The use of monoclonal antibodies is ubiquitous in science and biomedicine but the generation and validation process of antibodies is nevertheless complicated and time-consuming. To address these issues we developed a novel selective technology based on an artificial cell surface construct by which secreted antibodies were connected to the corresponding hybridoma cell when they possess the desired antigen-specificity. Further the system enables the selection of desired isotypes and the screening for potential cross-reactivities in the same context. For the design of the construct we combined the transmembrane domain of the EGF-receptor with a hemagglutinin epitope and a biotin acceptor peptide and performed a transposon-mediated transfection of myeloma cell lines. The stably transfected myeloma cell line was used for the generation of hybridoma cells and an antigen- and isotype-specific screening method was established. The system has been validated for globular protein antigens as well as for haptens and enables a fast and early stage selection and validation of monoclonal antibodies in one step.
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5
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Abali F, Broekmaat J, Tibbe A, Schasfoort RBM, Zeune L, Terstappen LWMM. A microwell array platform to print and measure biomolecules produced by single cells. LAB ON A CHIP 2019; 19:1850-1859. [PMID: 31041434 DOI: 10.1039/c9lc00100j] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Here we describe a combined method to monitor the secretion of molecules produced by single cells, followed by a method to isolate the individual cells that produced these molecules. The method is based on a self-sorting microwell chip that is connected to an activated membrane that collects the produced molecules. The produced molecules are printed by diffusion in small spots onto the membrane. The location of the printed spots can be correlated to the microwell number and the cell that produced these molecules. To demonstrate the method, we used the EpCAM antibody producing hybridoma cell line VU1D9 and a genetically engineered CHO cell-line producing Her2. VU1D9 cells produced 4.6 ± 5.6 pg (mean ± SD) of EpCAM antibody per 24 h and CHO cells 6.5 ± 8.2 pg per 24 h of Herceptin antibody.
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Affiliation(s)
- Fikri Abali
- Department of Medical Cell BioPhysics, University of Twente, Hallenweg 23, Enschede, 7522 NH, The Netherlands.
| | | | | | - Richard B M Schasfoort
- Department of Medical Cell BioPhysics, University of Twente, Hallenweg 23, Enschede, 7522 NH, The Netherlands.
| | - Leonie Zeune
- Department of Medical Cell BioPhysics, University of Twente, Hallenweg 23, Enschede, 7522 NH, The Netherlands.
| | - Leon W M M Terstappen
- Department of Medical Cell BioPhysics, University of Twente, Hallenweg 23, Enschede, 7522 NH, The Netherlands.
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6
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Puligedda RD, Sharma R, Al-Saleem FH, Kouiavskaia D, Velu AB, Kattala CD, Prendergast GC, Lynch DR, Chumakov K, Dessain SK. Capture and display of antibodies secreted by hybridoma cells enables fluorescent on-cell screening. MAbs 2019; 11:546-558. [PMID: 30794061 PMCID: PMC6512912 DOI: 10.1080/19420862.2019.1574520] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Hybridoma methods for monoclonal antibody (mAb) cloning are a mainstay of biomedical research, but they are hindered by the need to maintain hybridomas in oligoclonal pools during antibody screening. Here, we describe a system in which hybridomas specifically capture and display the mAbs they secrete: On-Cell mAb Screening (OCMS™). In OCMS™, mAbs displayed on the cell surface can be rapidly assayed for expression level and binding specificity using fluorescent antigens with high-content (image-based) methods or flow cytometry. OCMS™ demonstrated specific mAb binding to poliovirus and rabies virus by forming a cell surface IgG “cap”, as a universal assay for anti-viral mAbs. We produced and characterized OCMS™-enabled hybridomas secreting mAbs that neutralize poliovirus and used fluorescence microscopy to identify and clone a human mAb specific for the human N-methyl-D-aspartate receptor. Lastly, we used OCMS™ to assess expression and antigen binding of a recombinant mAb produced in 293T cells. As a novel method to physically associate mAbs with the hybridomas that secrete them, OCMS™ overcomes a central challenge to hybridoma mAb screening and offers new paradigms for mAb discovery and production.
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Affiliation(s)
| | - Rashmi Sharma
- a Lankenau Institute for Medical Research , Wynnewood , PA , USA
| | | | - Diana Kouiavskaia
- b Center for Biologics Evaluation and Research , Food and Drug Administration , Silver Spring , MD , USA
| | - Arul Balaji Velu
- a Lankenau Institute for Medical Research , Wynnewood , PA , USA
| | | | | | - David R Lynch
- c Division of Neurology , Children's Hospital of Pennsylvania , Philadelphia , PA , USA
| | - Konstantin Chumakov
- b Center for Biologics Evaluation and Research , Food and Drug Administration , Silver Spring , MD , USA
| | - Scott K Dessain
- a Lankenau Institute for Medical Research , Wynnewood , PA , USA
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7
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Trantidou T, Dekker L, Polizzi K, Ces O, Elani Y. Functionalizing cell-mimetic giant vesicles with encapsulated bacterial biosensors. Interface Focus 2018; 8:20180024. [PMID: 30443325 PMCID: PMC6227772 DOI: 10.1098/rsfs.2018.0024] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/27/2018] [Indexed: 12/15/2022] Open
Abstract
The design of vesicle microsystems as artificial cells (bottom-up synthetic biology) has traditionally relied on the incorporation of molecular components to impart functionality. These cell mimics have reduced capabilities compared with their engineered biological counterparts (top-down synthetic biology), as they lack the powerful metabolic and regulatory pathways associated with living systems. There is increasing scope for using whole intact cellular components as functional modules within artificial cells, as a route to increase the capabilities of artificial cells. In this feasibility study, we design and embed genetically engineered microbes (Escherichia coli) in a vesicle-based cell mimic and use them as biosensing modules for real-time monitoring of lactate in the external environment. Using this conceptual framework, the functionality of other microbial devices can be conferred into vesicle microsystems in the future, bridging the gap between bottom-up and top-down synthetic biology.
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Affiliation(s)
- Tatiana Trantidou
- Department of Chemistry, Imperial College London, London SW7 2AZ, UK
| | - Linda Dekker
- Department of Life Sciences and Centre for Synthetic Biology and Innovation, Imperial College London, London SW7 2AZ, UK
| | - Karen Polizzi
- Department of Life Sciences and Centre for Synthetic Biology and Innovation, Imperial College London, London SW7 2AZ, UK
| | - Oscar Ces
- Department of Chemistry, Imperial College London, London SW7 2AZ, UK
- Institute of Chemical Biology, Imperial College London, London SW7 2AZ, UK
- fabriCELL, Imperial College London, London SW7 2AZ, UK
| | - Yuval Elani
- Department of Chemistry, Imperial College London, London SW7 2AZ, UK
- Institute of Chemical Biology, Imperial College London, London SW7 2AZ, UK
- fabriCELL, Imperial College London, London SW7 2AZ, UK
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8
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Fang Y, Chu TH, Ackerman ME, Griswold KE. Going native: Direct high throughput screening of secreted full-length IgG antibodies against cell membrane proteins. MAbs 2017; 9:1253-1261. [PMID: 28933630 PMCID: PMC5680790 DOI: 10.1080/19420862.2017.1381812] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Gel microdroplet – fluorescence activated cell sorting (GMD-FACS) is an innovative high throughput screening platform for recombinant protein libraries, and we show here that GMD-FACS can overcome many of the limitations associated with conventional screening methods for antibody libraries. For example, phage and cell surface display benefit from exceptionally high throughput, but generally require high quality, soluble antigen target and necessitate the use of anchored antibody fragments. In contrast, the GMD-FACS assay can screen for soluble, secreted, full-length IgGs at rates of several thousand clones per second, and the technique enables direct screening against membrane protein targets in their native cellular context. In proof-of-concept experiments, rare anti-EGFR antibody clones were efficiently enriched from a 10,000-fold excess of anti-CCR5 clones in just three days. Looking forward, GMD-FACS has the potential to contribute to antibody discovery and engineering for difficult targets, such as ion channels and G protein-coupled receptors.
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Affiliation(s)
- Yongliang Fang
- a Thayer School of Engineering, Dartmouth , Hanover , NH , USA
| | - Thach H Chu
- a Thayer School of Engineering, Dartmouth , Hanover , NH , USA
| | - Margaret E Ackerman
- a Thayer School of Engineering, Dartmouth , Hanover , NH , USA.,b Department of Microbiology and Immunology , Dartmouth , Hanover , NH , USA
| | - Karl E Griswold
- a Thayer School of Engineering, Dartmouth , Hanover , NH , USA.,c Immunology & Cancer Immunotherapy Program, Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center , Lebanon , NH , USA.,d Department of Biological Sciences , Dartmouth , Hanover , NH.,e Department of Chemistry , Dartmouth , Hanover , NH , USA
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9
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Holzlöhner P, Hanack K. Generation of Murine Monoclonal Antibodies by Hybridoma Technology. J Vis Exp 2017. [PMID: 28117810 DOI: 10.3791/54832] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Monoclonal antibodies are universal binding molecules and are widely used in biomedicine and research. Nevertheless, the generation of these binding molecules is time-consuming and laborious due to the complicated handling and lack of alternatives. The aim of this protocol is to provide one standard method for the generation of monoclonal antibodies using hybridoma technology. This technology combines two steps. Step 1 is an appropriate immunization of the animal and step 2 is the fusion of B lymphocytes with immortal myeloma cells in order to generate hybrids possessing both parental functions, such as the production of antibody molecules and immortality. The generated hybridoma cells were then recloned and diluted to obtain stable monoclonal cell cultures secreting the desired monoclonal antibody in the culture supernatant. The supernatants were tested in enzyme-linked immunosorbent assays (ELISA) for antigen specificity. After the selection of appropriate cell clones, the cells were transferred to mass cultivation in order to produce the desired antibody molecule in large amounts. The purification of the antibodies is routinely performed by affinity chromatography. After purification, the antibody molecule can be characterized and validated for the final test application. The whole process takes 8 to 12 months of development, and there is a high risk that the antibody will not work in the desired test system.
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Affiliation(s)
| | - Katja Hanack
- Department of Biochemistry and Biology, University of Potsdam;
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10
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Hanack K, Messerschmidt K, Listek M. Antibodies and Selection of Monoclonal Antibodies. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 917:11-22. [DOI: 10.1007/978-3-319-32805-8_2] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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11
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Chen W, Zhao X, Zhang M, Yuan Y, Ge L, Tang B, Xu X, Cao L, Guo H. High-efficiency secretory expression of human neutrophil gelatinase-associated lipocalin from mammalian cell lines with human serum albumin signal peptide. Protein Expr Purif 2015; 118:105-12. [PMID: 26518367 DOI: 10.1016/j.pep.2015.10.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 10/19/2015] [Accepted: 10/21/2015] [Indexed: 12/18/2022]
Abstract
Human neutrophil gelatinase associated lipocalin (NGAL) is a secretory glycoprotein initially isolated from neutrophils. It is thought to be involved in the incidence and development of immunological diseases and cancers. Urinary and serum levels of NGAL have been investigated as a new biomarker of acute kidney injury (AKI), for an earlier and more accurate detection method than with creatinine level. However, expressing high-quality recombinant NGAL is difficult both in Escherichia coli and mammalian cells for the low yield. Here, we cloned and fused NGAL to the C-terminus of signal peptides of human NGAL, human interleukin-2 (IL2), gaussia luciferase (Gluc), human serum albumin preproprotein (HSA) or an hidden Markov model-generated signal sequence (HMM38) respectively for transient expression in Expi293F suspension cells to screen for their ability to improve the secretory expression of recombinant NGAL. The best results were obtained with signal peptide derived from HSA. The secretory recombinant protein could react specifically with NGAL antibody. For scaled production, we used HSA signal peptide to establish stable Chinese hamster ovary cell lines. Then we developed a convenient colony-selection system to select high-expression, stable cell lines. Moreover, we purified the NGAL with Ni-Sepharose column. The recombinant human NGAL displayed full biological activity. We provide a method to enhance the secretory expression of recombinant human NGAL by using the HSA signal peptide and produce the glycoprotein in mammalian cells.
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Affiliation(s)
- Wei Chen
- Department of Urology, Drum Tower Hospital, Medical School of Nanjing University, Institute of Urology, Nanjing University, Nanjing 210008, Jiangsu, PR China
| | - Xiaozhi Zhao
- Department of Urology, Drum Tower Hospital, Medical School of Nanjing University, Institute of Urology, Nanjing University, Nanjing 210008, Jiangsu, PR China
| | - Mingxin Zhang
- Department of Urology, Drum Tower Hospital, Medical School of Nanjing University, Institute of Urology, Nanjing University, Nanjing 210008, Jiangsu, PR China
| | - Yimin Yuan
- Department of Urology, Drum Tower Hospital, Medical School of Nanjing University, Institute of Urology, Nanjing University, Nanjing 210008, Jiangsu, PR China
| | - Liyuan Ge
- Department of Urology, Drum Tower Hospital, Medical School of Nanjing University, Institute of Urology, Nanjing University, Nanjing 210008, Jiangsu, PR China
| | - Bo Tang
- Vazyme Biotech Co., Ltd, Nanjing 210000, Jiangsu, PR China
| | - Xiaoyu Xu
- Vazyme Biotech Co., Ltd, Nanjing 210000, Jiangsu, PR China
| | - Lin Cao
- College of Food Science and Technology, Nanjing Agricultural University, Nanjing 210095, Jiangsu, PR China; Vazyme Biotech Co., Ltd, Nanjing 210000, Jiangsu, PR China.
| | - Hongqian Guo
- Department of Urology, Drum Tower Hospital, Medical School of Nanjing University, Institute of Urology, Nanjing University, Nanjing 210008, Jiangsu, PR China.
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12
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Vidigal J, Dias MM, Fernandes F, Patrone M, Bispo C, Andrade C, Gardner R, Carrondo MJ, Alves PM, Teixeira AP. A cell sorting protocol for selecting high-producing sub-populations of Sf9 and High Five™ cells. J Biotechnol 2013; 168:436-9. [DOI: 10.1016/j.jbiotec.2013.10.020] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 10/10/2013] [Accepted: 10/15/2013] [Indexed: 10/26/2022]
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13
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Helman D, Toister-Achituv M, Bar-Shimon M, Cohen B, Otmi I, Berger N, Kalimi D, Kimalov B, Medina T, Sapir A, Rotemberg O, Zabavnik N, Zauberman A, Smolarsky M. Novel membrane-bound reporter molecule for sorting high producer cells by flow cytometry. Cytometry A 2013; 85:162-8. [PMID: 23765751 DOI: 10.1002/cyto.a.22308] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2012] [Revised: 02/27/2013] [Accepted: 05/11/2013] [Indexed: 12/28/2022]
Abstract
We developed a membrane bound reporter and selection molecule for sorting by fluorescence activated cell sorting (FACS) of cells producing a protein of interest. This molecule is composed of a transmembrane (TM) domain, fused on its extracellular end to a biotin mimetic peptide (BMP) and on its intracellular side to puromycin N-acetyl transferase (PAC). In this format BMP is displayed on the cell membrane surface and PAC faces the cell cytoplasm. BMP was detected and quantified on the cell surface by fluorescently labelled streptavidin, allowing cell sorting by FACS, according to the reporter expression level. The reporter and a gene of interest (GOI) were connected on the same transcript via an internal ribosomal entry site (IRES). The reporter expression level was found to correlate with that of the GOI, enabling sorting of high producer cells by FACS. Thus, the highest fluorescent cells sorted had also the highest protein of interest (POI) productivity level.
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14
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Current state and recent advances in biopharmaceutical production in Escherichia coli, yeasts and mammalian cells. J Ind Microbiol Biotechnol 2013; 40:257-74. [PMID: 23385853 DOI: 10.1007/s10295-013-1235-0] [Citation(s) in RCA: 139] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Accepted: 01/22/2013] [Indexed: 12/28/2022]
Abstract
Almost all of the 200 or so approved biopharmaceuticals have been produced in one of three host systems: the bacterium Escherichia coli, yeasts (Saccharomyces cerevisiae, Pichia pastoris) and mammalian cells. We describe the most widely used methods for the expression of recombinant proteins in the cytoplasm or periplasm of E. coli, as well as strategies for secreting the product to the growth medium. Recombinant expression in E. coli influences the cell physiology and triggers a stress response, which has to be considered in process development. Increased expression of a functional protein can be achieved by optimizing the gene, plasmid, host cell, and fermentation process. Relevant properties of two yeast expression systems, S. cerevisiae and P. pastoris, are summarized. Optimization of expression in S. cerevisiae has focused mainly on increasing the secretion, which is otherwise limiting. P. pastoris was recently approved as a host for biopharmaceutical production for the first time. It enables high-level protein production and secretion. Additionally, genetic engineering has resulted in its ability to produce recombinant proteins with humanized glycosylation patterns. Several mammalian cell lines of either rodent or human origin are also used in biopharmaceutical production. Optimization of their expression has focused on clonal selection, interference with epigenetic factors and genetic engineering. Systemic optimization approaches are applied to all cell expression systems. They feature parallel high-throughput techniques, such as DNA microarray, next-generation sequencing and proteomics, and enable simultaneous monitoring of multiple parameters. Systemic approaches, together with technological advances such as disposable bioreactors and microbioreactors, are expected to lead to increased quality and quantity of biopharmaceuticals, as well as to reduced product development times.
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15
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Kim YG, Park B, Ahn JO, Jung JK, Lee HW, Lee EG. New cell line development for antibody-producing Chinese hamster ovary cells using split green fluorescent protein. BMC Biotechnol 2012; 12:24. [PMID: 22587529 PMCID: PMC3428690 DOI: 10.1186/1472-6750-12-24] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 04/30/2012] [Indexed: 11/21/2022] Open
Abstract
Background The establishment of high producer is an important issue in Chinese hamster ovary (CHO) cell culture considering increased heterogeneity by the random integration of a transfected foreign gene and the altered position of the integrated gene. Fluorescence-activated cell sorting (FACS)-based cell line development is an efficient strategy for the selection of CHO cells in high therapeutic protein production. Results An internal ribosome entry site (IRES) was introduced for using two green fluorescence protein (GFP) fragments as a reporter to both antibody chains, the heavy chain and the light chain. The cells co-transfected with two GFP fragments showed the emission of green fluorescence by the reconstitution of split GFP. The FACS-sorted pool with GFP expression had a higher specific antibody productivity (qAb) than that of the unsorted pool. The qAb was highly correlated with the fluorescence intensity with a high correlation coefficient, evidenced from the analysis of median GFP and qAb in individual selected clones. Conclusions This study proved that the fragment complementation for split GFP could be an efficient indication for antibody production on the basis of high correlation of qAb with reconstitution of GFP. Taken together, we developed an efficient FACS-based screening method for high antibody-producing CHO cells with the benefits of the split GFP system.
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Affiliation(s)
- Yeon-Gu Kim
- Process Engineering Center, KRIBB, Daejeon 305-806, Korea
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16
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Park S, Han J, Kim W, Lee GM, Kim HS. Rapid selection of single cells with high antibody production rates by microwell array. J Biotechnol 2011; 156:197-202. [DOI: 10.1016/j.jbiotec.2011.08.031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2011] [Revised: 08/10/2011] [Accepted: 08/30/2011] [Indexed: 10/17/2022]
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17
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Hammill L, Welles J, Carson GR. The gel microdrop secretion assay: Identification of a low productivity subpopulation arising during the production of human antibody in CHO cells. Cytotechnology 2011; 34:27-37. [PMID: 19003378 DOI: 10.1023/a:1008186113245] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The long-term stability of high-level expression is the mostimportant factor to consider when choosing cell lines for the expression of recombinant proteins. Declining volumetricyields in large-scale fermentation can be caused by changes affecting the cell population as a whole such as loss in viability, depletion of nutrients or accumulation of metabolites affecting cell growth. Alternatively, geneticinstability may lead to the outgrowth of a less productive,metabolically favored sub-population. Currently a variety ofparameters are measured to monitor the condition of cells infermenters including glucose uptake, lactate accumulation andoxygen consumption; in addition, periodic viable cell countsallow the determination of the growth rate and viability of the population. All of these methods measure the condition ofthe cell population as a whole and changes must involve a significantly large proportion of the total culture in orderto be detectable. Here we report on a method that allows theevaluation of the productivity of individual cells. Using the gel microdrop secretion assay, we detected the appearance ofa sub-population of cells with lower productivity. Subsequentanalysis of the culture confirmed the existence of lower productivity cells with a lower vector copy number. Therefore,the single cell secretion assay proved to be a rapid method todetect and isolate a low productivity variant of the producer cell line.
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Affiliation(s)
- L Hammill
- Department of Molecular Biology, BASF Bioresearch Corporation, 100 Research Drive, Worcester, MA, 01605, U.S.A
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Park S, Kim W, Kim Y, Son YD, Lee SC, Kim E, Kim SH, Kim JH, Kim HS. Array-Based Analysis of Secreted Glycoproteins for Rapid Selection of a Single Cell Producing a Glycoprotein with Desired Glycosylation. Anal Chem 2010; 82:5830-7. [DOI: 10.1021/ac100992n] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sunyoung Park
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Wanjung Kim
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Yongtae Kim
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Young Dok Son
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Sang-Chul Lee
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Eunkyung Kim
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Sung Ho Kim
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Jung Hoe Kim
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
| | - Hak-Sung Kim
- Departments of Biological Sciences and Mathematical Sciences and Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701, Korea
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Karoubi G, Ormiston ML, Stewart DJ, Courtman DW. Single-cell hydrogel encapsulation for enhanced survival of human marrow stromal cells. Biomaterials 2009; 30:5445-55. [PMID: 19595454 DOI: 10.1016/j.biomaterials.2009.06.035] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2009] [Accepted: 06/21/2009] [Indexed: 02/08/2023]
Abstract
Inadequate extracellular matrix cues and subsequent apoptotic cell death are among crucial factors currently limiting cell viability and organ retention in cell-based therapeutic strategies for vascular regeneration. Here we describe the use of a single-cell hydrogel capsule to provide enhanced cell survival of adherent cells in transient suspension culture. Human marrow stromal cells (hMSCs) were singularly encapsulated in agarose capsules containing the immobilized matrix molecules, fibronectin and fibrinogen to ameliorate cell-matrix survival signals. MSCs in the enriched capsules demonstrated increased viability, greater metabolic activity and enhanced cell-cytoskeletal patterning. Increased cell viability resulted from the re-induction of cell-matrix interactions likely via integrin clustering and subsequent activation of the extracellular signal regulated MAPK (ERK)/mitogen activated protein kinase (MAPK) signaling cascade. Proof of principle in-vivo studies, investigating autologous MSC delivery into Fisher 344 rat hindlimb, depicted a significant increase in the number of engrafted cells using the single-cell encapsulation system. Incorporation of immobilized adhesion molecules compensates, at least in part, for the missing cell-matrix cues, thereby attenuating the initial anoikis stimuli and providing protection from subsequent apoptosis. Thus, this single-cell encapsulation strategy may markedly enhance therapeutic cell survival in targeted tissues.
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Affiliation(s)
- Golnaz Karoubi
- University of Toronto and St. Michael's Hospital, Toronto, ON, Canada
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20
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Caron AW, Nicolas C, Gaillet B, Ba I, Pinard M, Garnier A, Massie B, Gilbert R. Fluorescent labeling in semi-solid medium for selection of mammalian cells secreting high-levels of recombinant proteins. BMC Biotechnol 2009; 9:42. [PMID: 19432976 PMCID: PMC2689207 DOI: 10.1186/1472-6750-9-42] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Accepted: 05/11/2009] [Indexed: 11/10/2022] Open
Abstract
Background Despite the powerful impact in recent years of gene expression markers like the green fluorescent protein (GFP) to link the expression of recombinant protein for selection of high producers, there is a strong incentive to develop rapid and efficient methods for isolating mammalian cell clones secreting high levels of marker-free recombinant proteins. Recently, a method combining cell colony growth in methylcellulose-based medium with detection by a fluorescently labeled secondary antibody or antigen has shown promise for the selection of Chinese Hamster Ovary (CHO) cell lines secreting recombinant antibodies. Here we report an extension of this method referred to as fluorescent labeling in semi-solid medium (FLSSM) to detect recombinant proteins significantly smaller than antibodies, such as IGF-E5, a 25 kDa insulin-like growth factor derivative. Results CHO cell clones, expressing 300 μg/ml IGF-E5 in batch culture, were isolated more easily and quickly compared to the classic limiting dilution method. The intensity of the detected fluorescent signal was found to be proportional to the amount of IGF-E5 secreted, thus allowing the highest producers in the population to be identified and picked. CHO clones producing up to 9.5 μg/ml of Tissue-Plasminogen Activator (tPA, 67 kDa) were also generated using FLSSM. In addition, IGF-E5 high-producers were isolated from 293SF transfectants, showing that cell selection in semi-solid medium is not limited to CHO and lymphoid cells. The best positive clones were collected with a micromanipulator as well as with an automated colony picker, thus demonstrating the method's high throughput potential. Conclusion FLSSM allows rapid visualization of the high secretors from transfected pools prior to picking, thus eliminating the tedious task of screening a high number of cell isolates. Because of its rapidity and its simplicity, FLSSM is a versatile method for the screening of high producers for research and industry.
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Affiliation(s)
- Antoine W Caron
- Institut de Recherche en Biotechnologie, Conseil National de Recherches du Canada, Montréal, QC, Canada.
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Browne SM, Al-Rubeai M. Selection Methods for High-Producing Mammalian Cell Lines. CELL ENGINEERING 2009. [DOI: 10.1007/978-90-481-2245-5_7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Walser M, Leibundgut RM, Pellaux R, Panke S, Held M. Isolation of monoclonal microcarriers colonized by fluorescent E. coli. Cytometry A 2008; 73:788-98. [PMID: 18561199 DOI: 10.1002/cyto.a.20597] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Microencapsulation gains increasing importance for processing of bacterial libraries and especially in high-throughput (HT) environments where >10(6) samples per day are studied. As a rule, a one-to-one relationship between an individual cell and analytical results is of key importance. Ideally, each microcarrier would therefore contain exactly one cell or colony. However, synthesis of larger numbers of capsules containing exactly one cell is not feasible as cells are randomly distributed during carrier-production. The dilemma is that high dilution conditions will yield a satisfactory degree of monoclonality, but also a very large fraction of empty compartments, whereas distribution under low dilution generates unacceptable numbers of polyclonal compartments for whose removal no satisfactory technologies exist. Hydrogel carriers with a volume of 35 nL were used as growth compartments for individual microbial colonies. E. coli cells expressing green fluorescent protein (GFP) were encapsulated at low dilution thereby intentionally producing a considerable amount of polyclonal microcarrieres. Empty and polyclonal microcarriers were then removed from the desired monoclonal fraction by a COPAS Plus particle analyzer. The results were compared with model predictions in order to investigate possible limitations in the analysis and sorting of monoclonal microcarriers by COPAS. Fluorescent E. coli cells (GFP) distributed randomly throughout the microcarrier population. Cells were successfully propagated to colonies in the microcarriers and enriched to 95% monoclonality by a COAPS sorter. Enrichment-efficiency was found to mainly depend on the colony diameter. With increasing colony size two contrary effects were observed: First, improved sorting efficiency due to increased fluorescence intensity and therefore higher detection efficiency, and second, deterioration of sorting efficiency due to occlusion occurring in polyclonal carriers. The combination of microencapsulation under low dilution conditions followed by HT sorting procedures is an efficient way for isolating larger amount of monoclonal carriers from bacterial libraries while concomitantly keeping the amounts of empty carriers at a moderate level.
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Affiliation(s)
- Marcel Walser
- ETH Zurich, Institute of Process Engineering, BioProcess Laboratory, Universitätsstr. 6/CAB H88, CH-8092 Zurich, Switzerland
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Browne SM, Al-Rubeai M. Selection methods for high-producing mammalian cell lines. Trends Biotechnol 2007; 25:425-32. [PMID: 17659798 DOI: 10.1016/j.tibtech.2007.07.002] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2007] [Revised: 04/30/2007] [Accepted: 07/18/2007] [Indexed: 10/23/2022]
Abstract
The selection of high-producing mammalian cell lines represents a bottleneck in process development for the production of biopharmaceuticals. Traditional methods are time consuming (development times often exceed six months) and significantly limited by the number of clones that can be feasibly screened. The market for therapeutic proteins is set to double by 2010, so there is an increasing need to develop methods for the selection of mammalian cell lines stably expressing recombinant products at high levels in an efficient, cost-effective and high-throughput manner. Alternatives include higher throughput methods based on flow-cytometric screening and recently developed automated systems for the selection of high-producing cell lines.
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Affiliation(s)
- Susan M Browne
- School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland
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Akselband Y, Moen PT, McGrath P. Isolation of Rare Isotype Switch Variants in Hybridoma Cell Lines Using an Agarose Gel Microdrop-Based Protein Secretion Assay. Assay Drug Dev Technol 2003; 1:619-26. [PMID: 15090234 DOI: 10.1089/154065803770380977] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Using gel microdrop (GMD) encapsulation technology and fluorescence-activated cell storing (FACS), we have developed a rapid, sensitive, and reliable method for discriminating and recovering rare isotypic switch variants in hybridoma cell lines. Using the GMD-based IgSwitch assay, a novel approach for isolating subpopulations of IgG-secreting hybridoma cells present at a frequency of approximately 1-10 in 10(6), we successfully isolated spontaneous and in vitro-induced isotypic switch variants in less than half the time required for conventional sublining. The effectiveness and specificity of the assay are demonstrated.
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Abstract
Cytokines represent a multi-diverse family of polypeptide regulators; they are of relatively low molecular weight, pharmacologically active proteins that are secreted by one cell for the purpose of altering either its own functions (autocrine effect) or those of adjacent cells (paracrine effect). Cytokines are small, non-enzymatic glycoproteins whose actions are both diverse and overlapping (specificity/redundancy) and may affect diverse and overlapping target cell populations. In many instances, individual cytokines have multiple biological activities. Different cytokines can also have the same activity, which provides for functional redundancy within the inflammatory and immune systems. As biological cofactors that are released by specific cells, cytokines have specific effects on cell-cell interaction, communication, and behavior of other cells. As a result, it is infrequent that loss or neutralization of one cytokine will markedly interfere with either of these systems. The biological effect of one cytokine is often modified or augmented by another. Because an inter-digitating, redundant network of cytokines is involved in the production of most biological effects, both under physiologic and pathologic conditions, it usually requires more than a single defect in the network to alter drastically the outcome of the process. This fact therefore may have crucial significance in the development of therapeutic strategies for bio-pharmacologic intervention in cytokine-mediated inflammatory processes and infections.
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Affiliation(s)
- John J Haddad
- Severinghaus-Radiometer Research Labs, Molecular Neuroscience Research Division, School of Medicine, University of California-San Francisco, Medical Sciences Building S-261, 513 Parnassus Avenue, San Francisco, CA 94143-0542, USA.
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Haddad JJ. Pharmaco-redox regulation of cytokine-related pathways: from receptor signaling to pharmacogenomics. Free Radic Biol Med 2002; 33:907-26. [PMID: 12361802 DOI: 10.1016/s0891-5849(02)00985-1] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cytokines represent a multi-diverse family of polypeptide regulators; they are relatively low molecular weight (< 30 kDa), pharmacologically active proteins that are secreted by one cell for the purpose of altering either its own functions (autocrine effect) or those of adjacent cells (paracrine effect). Cytokines are small, nonenzymatic glycoproteins whose actions are both diverse and overlapping (specificity/redundancy) and may affect diverse and overlapping target cell populations. In many instances, individual cytokines have multiple biological activities. Different cytokines can also have the same activity, which provides for functional redundancy (network) within the inflammatory and immune systems. As biological cofactors that are released by specific cells, cytokines have specific effects on cell-cell interaction, communication, and behavior of other cells. As a result, it is infrequent that loss or neutralization of one cytokine will markedly interfere with either of these systems. The biological effect of one cytokine is often modified or augmented by another. Because an interdigitating, redundant network of cytokines is involved in the production of most biological effects, both under physiologic and pathologic conditions, it usually requires more than a single defect in the network to alter drastically the outcome of the process. This fact, therefore, may have crucial significance in the development of therapeutic strategies for biopharmacologic intervention in cytokine-mediated inflammatory processes and infections.
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Affiliation(s)
- John J Haddad
- Severinghaus-Radiometer Research Labs, Molecular Neuroscience Research Division, Dept of Anesthesia and Perioperative Care, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143-0542, USA.
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Bogen KT, Enns L, Hall LC, Keating GA, Weinfeld M, Murphy G, Wu RW, Panteleakos FN. Gel microdrop flow cytometry assay for low-dose studies of chemical and radiation cytotoxicity. Toxicology 2001; 160:5-10. [PMID: 11246118 DOI: 10.1016/s0300-483x(00)00432-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Low-level cytotoxicity may affect low-dose dose-response relations for cancer and other endpoints. Conventional colony-forming assays are rarely sensitive enough to examine small changes in cell survival and growth. Automated image-analysis techniques are limited to ca. 10(4) cells/plate. An alternative method involves encapsulation of single proliferating cells into ca. 35-75-microm-diameter agarose gel microdrops (GMDs) that are randomly grouped, differential exposure of these groups, culture at 37 degrees C for 3-5 days, and finally GMD analysis by flow cytometry (FC) to determine the ratio of GMDs containing multiple versus single cells as a measure of clonogenic survival. This GMD/FC assay was used to examine low-dose cell killing induced by a cooked-meat mutagen/rodent-carcinogen (MeIQx) in DNA-repair-deficient/metabolically-sensitive CHO cells. Results of conventional colony-forming assays using up to 30 replicate plates indicate a shouldered, threshold-like dose-response; in contrast, those obtained using the GMD/FC assay suggest "hypersensitivity"-like nonlinearity in dose-response. The GMD/FC assay was also applied to human A549 lung cells after GMD-encapsulation and gamma radiation followed by culture for a total of 4 days, to examine survival after exposure to > or =100 cGy delivered at a relatively low dose rate (0.18 cGy/min). Dose-response for clonogenic growth was again observed to be reduced with apparent nonlinear suggesting hypersensitivity between 0 and 50 cGy, insofar as doses of 5 and 10 cGy appear to be ca. fivefold more effective per unit dose than the 50- or 100-cGy doses used. The GMD/FC assay may thus reveal low-dose dose-response relations for chemical and radiation effects on cell proliferation/killing with implications for low-dose risk assessment.
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Affiliation(s)
- K T Bogen
- Health and Ecological Assessment Division (L.396), Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550-9900, USA.
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Turcanu V, Williams NA. Cell identification and isolation on the basis of cytokine secretion: a novel tool for investigating immune responses. Nat Med 2001; 7:373-6. [PMID: 11231640 DOI: 10.1038/85533] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- V Turcanu
- University of Bristol, Department of Pathology and Microbiology, School of Medical Sciences, University Walk, Bristol, UK
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Gift EA, Weaver JC. Simultaneous quantitative determination of electroporative molecular uptake and subsequent cell survival using gel microdrops and flow cytometry. ACTA ACUST UNITED AC 2000. [DOI: 10.1002/(sici)1097-0320(20000401)39:4<243::aid-cyto1>3.0.co;2-v] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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