Patent ID: 7504256

Claim:
A process for producing a polypeptide which comprises: (a) selecting a rat cell line capable of adapting in a serum-free medium (b) culturing the rat cell line selected in step (a) in a serum-free medium while an insulin concentration in the culture is maintained at 10 mg/l or above, followed by culturing while an insulin concentration in the culture is maintained at 20 mg/l or below, and (c) recovering the desired polypeptide from the culture, wherein the step (a) is carried out by inoculating a rat cell line into a serum-free medium at the cell density of 1×10 5 to 10×10 5 cells/ml of serum free medium and selecting a rat cell line that reaches a cell density of 10×10 5 to 40×10 5 cells/ml of serum-free medium.