Improvement of Recombinant CHO Cell Growth in Serum-Free Suspension Culture by Cell Engineering

Abstract

Recombinant Chinese hamster ovary (rCHO) cells are one of the most popular hosts for therapeutic protein production. For the purpose of higher protein production, numerous strategies have been tried by means of enhancing specific protein productivity (q) and increasing the time integral of viable cell density. Enhancing viable cell density considering time could be achieved by either/both enhanced culture longevity and/or improved specific growth rate ($\mu$). In this study, for this end, we investigate the effect of Bcl-xL, XIAP, and CA-Ras overexpression on cell growth and protein production in rCHO cells. Overexpression of Bcl-xL in rCHO cells has been known to suppress apoptotic cell death and thereby extend culture longevity during batch culture. However, its effect on q of rCHO cells is controversial. This study attempts to investigate the effect of Bcl-xL overexpression on q of rCHO cells producing erythropoietin (EPO). To regulate the Bcl-xL expression level, the Tet-off system was introduced in rCHO cells producing EPO (EPO-off-Bcl-xL). The Bcl-xL expression level was tightly controlled by doxycycline concentration. To evaluate the effect of Bcl-xL overexpression on specific EPO productivity ($q_{EPO}$) at different levels, EPO-off-Bcl-xL cells were cultivated at the two different culture temperatures, 33℃ and 37℃. The $q_{EPO}$ at 33℃ and 37℃ in the presence of 100 ng/mL doxycycline (without Bcl-xL overexpression) were 4.89±0.21 and 3.18±0.06 $\mu g$ / $10^6$ cells / day, respectively. In the absence of doxycycline, Bcl-xL overexpression did not affect $q_{EPO}$ significantly, regardless of the culture temperature, though it extended the culture longevity. Taken together, Bcl-xL overexpression showed no significant effect on the $q_{EPO}$ of rCHO cells grown at 33℃ and 37℃. Upon nutrient deprivation during culture, rCHO cells are subjected to two types of programmed cell death (PCD), apoptosis and autophagy. To investigate the effect of Bcl-xL ov...