Differential gene expression in CHO cells cultivated in shake flasks and bioreactors

Chinese Hamster Ovary cell lines are currently the primary host for production of therapeutic glycoproteins. Fast process development resulting in robust and scalable processes is a critical success factor in the highly competitive market for biosimilars. In process development screening of hundreds of clones and selection of process conditions are routinely performed in uncontrolled cultivation systems like shake flasks. A handful of potential candidate clones is nominated to be evaluated more intensively in well controlled small-scale bioreactors. Cell performance in the uncontrolled systems and to a lesser extent in the small-scale bioreactors may, however, be different from that in the final production reactor, which may result in failures during scale-up and thus extra development time. In this work, the focus is on better understanding the differences in cell performance between controlled and uncontrolled systems, which can be used to make process development faster and more robust in terms of scale-up. For this, we evaluated differences in gene expression profiles between shake flask and bioreactor cultures at three different time points during the exponential and stationary phase of a batch culture using commercially available Affymetrix GeneChip CHO Gene 2.1 ST arrays and multivariate data analysis on the outcomes. The outcomes were correlated with differences in glycosylation patterns and other culture parameters. Results showed large differences in gene expression over time and much smaller differences between the two cultivation systems. Furthermore, our study identified differentially expressed genes and corresponding metabolic and mechanistic pathways between the two systems, which were directly related to the degree of the control of the systems. CHO cells, that originated from the same pre-culture, were grown in uncontrolled shake flasks and controlled bioreactors, and gene expression profiles were determined after 2, 4 and 5 days of culture.