(458g) Serum-Free Medium Adaptation of Chinese Hamster Ovary (CHO) Cell Lines: A Transcriptome Analysis Using RNA-Seq

By 2018, recombinant protein therapeutics are estimated to generate revenue of over $165 billion. Chinese hamster ovary (CHO) cell lines are a well-established mammalian cell line used for over 25 years, in the biopharmaceutical industry for the production of recombinant protein therapeutics. CHO cell lines are the preferred host for protein expression due to their ability to perform human-like post-translational modification of the product protein, ease of culturing in large-scale bioreactors and protein expression stability.  Like most mammalian cells, parental CHO cell lines are grown as adherent cells in serum supplemented media. Due to regulatory issues about the use of serum, CHO cells are grown as suspension cells in serum-free media in large industrial bioreactors. Hence, CHO cell lines have to be adapted to serum-free media by gradual reduction of serum in media. Adaptation of CHO cells to serum-free media is a tedious, sensitive process and can take anywhere between 2-6 months for the cells to be fully adapted. Current literature on the serum-free adaptation process is limited and not completely understood. The objectives of this study are to elucidate the transcriptional changes during the process of serum-free adaptation of CHO cells to gain a better understanding of the adaptation process and to identify potential targets for adaptation optimization. Two CHO cell lines were gradually adapted to serum-free medium: CHO DP-12 – an IgG producing cell line and CHO DHFR^- – the parental cell line. Although CHO DP-12 completely adapted to serum-free medium, the CHO DHFR^- cells could not successfully proceed beyond medium containing less than 5% serum. For transcriptome analysis, RNA was extracted from the two cell lines at different stages of serum-free adaptation and sequenced by Illumina HiSeq 2500. Various genes involved in cellular transport, cellular metabolism and maintenance were observed to be differentially regulated. For example, lactate dehydrogenase gene was observed to be down-regulated as serum level decreased in agreement with the lactate profiles.