The adaptation of Chinese hamster ovary cells to hypothermic temperatures increases yields of monomeric recombinant interferon-beta

Mild hypothermic conditions (30°C to 33°C) have previously been shown to increase cell specific productivity (QP) 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 titres. This thesis describes the isolation of a novel population of Chinese Hamster Ovary (CHO) cells that have been adapted to low temperature growth by continuous subculture at low temperature for a duration of 400 days.;This adapted cell population achieved a growth rate 2-fold greater than non-adapted cells under low temperature conditions (32°C) while maintaining an elevated level of cell-specific expression of recombinant beta-interferon. The volumetric titre of beta-interferon was enhanced by 70% in stationary cultures and by more than 2-fold 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, caused by a weakened vimentin intermediate filament network, was resolved by the use of macroporous microcarriers which were demonstrated to entrap and protect the cold-adapted cells. Cold-adapted microcarrier cultures were able to achieve high cell densities (greater than 5x106 nuclei/mL) cultures under hypothermic conditions. This resulted in a 3-fold enhancement of volumetric titre of monomeric beta-interferon compared to the original control culture at 37°C.