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Production of Trimeric SARS-CoV-2 Spike Protein by CHO Cells for Serological COVID-19 Testing
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  • Yusuf Johari,
  • Stephen Jaffe,
  • Joseph Scarrott,
  • Abayomi Johnson,
  • Théo Mozzanino,
  • Thilo Pohle,
  • Sheetal Maisuria,
  • Amina Bhayat-Cammack,
  • Adam Brown,
  • Kang Lan Tee,
  • Philip Jackson,
  • Tuck Seng Wong,
  • Mark Dickman,
  • Ravishankar Sargur,
  • David James
Yusuf Johari
University of Sheffield
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Stephen Jaffe
University of Sheffied
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Joseph Scarrott
University of Sheffield
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Abayomi Johnson
University of Sheffield
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Théo Mozzanino
University of Sheffield
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Thilo Pohle
University of Sheffield
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Sheetal Maisuria
Sheffield Teaching Hospitals NHS Foundation Trust
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Amina Bhayat-Cammack
Sheffield Teaching Hospitals NHS Foundation Trust
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Adam Brown
University of Sheffield
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Kang Lan Tee
University of Sheffield
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Philip Jackson
University of Sheffield
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Tuck Seng Wong
University of Sheffield
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Mark Dickman
University of Sheffield
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Ravishankar Sargur
Sheffield Teaching Hospitals NHS Foundation Trust
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David James
University of Sheffield
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Abstract

We describe scalable and cost-efficient production of full length, His-tagged SARS-CoV-2 spike glycoprotein trimer by CHO cells that can be used to detect SARS-CoV-2 antibodies in patient sera at high specificity and sensitivity. Transient production of spike in both HEK and CHO cells mediated by PEI was increased significantly (up to 10.9-fold) by a reduction in culture temperature to 32ºC to permit extended duration cultures. Based on these data GS-CHO pools stably producing spike trimer under the control of a strong synthetic promoter were cultured in hypothermic conditions with combinations of bioactive small molecules to increase yield of purified spike product 4.9-fold to 53 mg/L. Purification of recombinant spike by Ni-chelate affinity chromatography initially yielded a variety of co-eluting protein impurities identified as host cell derived by mass spectrometry, which were separated from spike trimer using a modified imidazole gradient elution. Purified CHO spike trimer antigen was used in ELISA format to detect IgG antibodies against SARS-CoV-2 in sera from patient cohorts previously tested for viral infection by PCR, including those who had displayed COVID-19 symptoms. The antibody assay, validated to ISO 15189 Medical Laboratories standards, exhibited a specificity of 100% and sensitivity of 92.3%. Our data show that CHO cells are a suitable host for the production of larger quantities of recombinant SARS-CoV-2 trimer which can be used as antigen for mass serological testing.

Peer review status:UNDER REVIEW

05 Aug 2020Submitted to Biotechnology and Bioengineering
05 Aug 2020Assigned to Editor
05 Aug 2020Submission Checks Completed
03 Sep 2020Reviewer(s) Assigned