Large-scale production of Erythroid Differentiation Factor (EDF) by gene-engineered Chinese hamster ovary (CHO) cells in suspension culture

From Chinese hamster ovary (CHO) cells which were producing Erythroid Differentiation Factor (EDF) in a culture medium, anchorage-independent cells, named as CHO-SPN, were produced by repeated cultivating in a suspension system. The growth time and maximum cell density of the CHO-SPN cells were 48 h and 7.8×10⁵ viable cells/ml. CHO-SPN cells accumulated 8,000 units/ml (corresponding to 4 mg/ml) of EDF in 4d. After 20 cycles of culture, CHO-SPN cells still possessed the same EDF productivity and the same growth kinetics. Furthermore, in an appropriate dissolved oxygen concentration and pH controlled culture system, the growth time and cell density became 24 h and 1×10⁶ viable cells/ml. The critical level of dissolved oxygen for cell growth was 0.015 atm. The maximum oxygen demand was 3.3×10⁻⁹ mole of O₂/ml/min.

Fetal bovine serum (FBS) was indispensable for cell growth. However, a FBS-free medium (ASF201) was available for maintenance of the CHO-SPN cells, and EDF production occurred in the same medium.