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

Herein, we described a scale-up strategy focused on the dissolved carbon dioxide concentration (dCO ) 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 was higher compared with the 200-L scale bioreactor. Therefore, we developed an alternative approach by evaluating the k a values of O (k a[O ]) and CO [k a(CO )] in the SS bioreactors as a scale-up factor for dCO reduction. The k a ratios [k a(CO )/k a(O )] were different between the 200-L and 2000-L bioreactors under the same P/V condition. When the agitation conditions were changed, the k 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 trends in fed-batch cultures performed in 2000-L scale bioreactors under the modified agitation conditions were similar to the control. This k a ratio method was used for process development in single-use bioreactors (SUBs) with shapes different from those of the SS bioreactor. The k a ratios for the SUBs were evaluated and conditions that provided k 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 a ratio is a powerful scale-up factor useful to control dCO during fed-batch cultures.