Assessment of UCOE on Recombinant EPO Production and Expression Stability in Amplified Chinese Hamster Ovary Cells.

CHO cells are the most frequently used host for commercial production of therapeutic proteins, and DHFR-mediated gene amplification is extensively applied to generate cell lines with increased protein production. However, decreased protein productivity is observed unpredictably during the time required for scale-up with consequences for yield, time, finance and regulatory approval. In this study, we have examined the interaction between Ubiquitous Chromatin Opening Elements (UCOE) and DHFR-linked amplification in relation to cell expression stability. In summary, the inclusion of UCOE elements generated cells that (1) achieved higher cell densities and exhibited increased production of recombinant mRNA per cell and protein yield, (2) allowed isolation of greater numbers of high-producing clones, (3) resulted in greater mRNA recovery per recombinant gene copy, (4) retained stable mRNA and protein expression after amplification provided Methotrexate (MTX) was present (but not in the absence of MTX when instability was observed) and (5) conferred copy number-dependent expression to linked transgene, suggesting that they are resistant to positional gene-silencing effects. It was concluded that the inclusion of UCOEs within expression constructs offers significant advantages for certainty of cell line generation (and the number of recovered clones for more detailed characterisation/optimisation) and that UCOEs are compatible with DHFR amplification protocols. The data suggested that enhanced cell line recovery by transcriptional enhancement of selection markers, such as DHFR, could be achieved.