CHO cells adapted to hypothermic growth produce high yields of recombinant beta-interferon

Mild hypothermic conditions (30-33 degrees C) have previously been shown to increase cell-specific productivity (Q(p)) of recombinant proteins from mammalian cells. However, this is often associated with a lower growth rate which off-sets any potential advantage of higher product titers. We report the isolation of a population of Chinese Hamster Ovary (CHO) cells that have been adapted to low-temperature growth by continuous subculture at low temperature for up to 300 days. This adapted cell population achieved a growth rate twofold greater than nonadapted cells under low-temperature conditions (32 degrees C) while maintaining an elevated level of cell-specific expression of recombinant beta-interferon. The volumetric titer of beta-interferon was enhanced by 70% in stationary cultures and by more than twofold by application of a temperature-shift strategy involving a growth to production phase. However, the low-temperature-adapted cells were fragile and demonstrated an increased sensitivity to hydrodynamic stress in agitated cultures. This problem was resolved by the use of macroporous microcarriers which protected the cells and allowed growth of high-density cultures under hypothermic conditions. This eventually resulted in a threefold enhancement of volumetric titer of monomeric beta-interferon compared to the original control culture at 37 degrees C.