Development of a scale‐up strategy for Chinese hamster ovary cell culture processes using the k L a ratio as a direct indicator of gas stripping conditions

Abstract Herein, we described a scale‐up strategy focused on the dissolved carbon dioxide concentration (dCO 2 ) during fed‐batch cultivation of Chinese hamster ovary cells. A fed‐batch culture process for a 2000‐L scale stainless steel (SS) bioreactor was scaled‐up from similarly shaped 200‐L scale bioreactors based on power input per unit volume ( P / V ). However, during the 2000‐L fed‐batch culture, the dCO 2 was higher compared with the 200‐L scale bioreactor. Therefore, we developed an alternative approach by evaluating the k L a values of O 2 ( k L a[O 2 ]) and CO 2 [ k L a(CO 2 )] in the SS bioreactors as a scale‐up factor for dCO 2 reduction. The k L a ratios [ k L a(CO 2 )/ k L a(O 2 )] were different between the 200‐L and 2000‐L bioreactors under the same P / V condition. When the agitation conditions were changed, the k L a ratio of the 2000‐L scale bioreactor became similar and the P / V value become smaller compared with those of the 200‐L SS bioreactor. The dCO 2 trends in fed‐batch cultures performed in 2000‐L scale bioreactors under the modified agitation conditions were similar to the control. This k L a ratio method was used for process development in single‐use bioreactors (SUBs) with shapes different from those of the SS bioreactor. The k L a ratios for the SUBs were evaluated and conditions that provided k L a ratios similar to the 200‐L scale SS bioreactors were determined. The cell culture performance and product quality at the end of the cultivation process were comparable for all tested SUBs. Therefore, we concluded that the k L a ratio is a powerful scale‐up factor useful to control dCO 2 during fed‐batch cultures.