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The use of glutamine synthetase as a selection marker: recent advances in Chinese hamster ovary cell line generation processes

Lianchun Fan* Christopher C Frye & Andrew J Racher

Central to the needs of the biopharmaceutical industry to support the development of innovative biologics and biosimilars are more effective and efficient manufacturing processes which require highly productive cell lines with desired quality attributes. New designs of molecules such as antibody humanization have greatly reduced immunogenicity concerns, and advances in cell culture technology including media optimization and process control have driven monoclonal antibody productivities in excess of 10 g/l with peak cell densities in bioreactors climbing to over 35 million per ml. However, over this same timeframe, the fundamental processes utilized for cell line generation have not changed significantly, especially in the selection step for top-producing clonal cell lines. Cell line generation continues to be time consuming and labor intensive and has become the timeline limiting step for the majority of the industry. In order to meet the ‘Fast-to- Proof-of-Principle’ strategy, multiple efforts including host cell and expression plasmid engineering have been pursued in order to improve the effectiveness and efficiency of cell line generation processes. This review will summarize the recent advancements in cell line generation processes in Chinese hamster ovary cells, with a focus on the glutamine synthetase selection system.