Development of a serum-free culture medium for the large scale production of recombinant protein from a Chinese hamster ovary cell line

A serum-free medium, WCM5, has been developed for the large scale propagation of CHO (Chinese hamster ovary) cells which express recombinant protein using dihydrofolate reductase as a selectable marker. WCM5 was prepared by supplementing Iscoves medium without lecithin, albumin or transferrin with a number of components which were shown to benefit growth. WCM5 medium contained 5 mg l−1 human recombinant insulin (Nucellin) but was otherwise protein-free. CHO 3D11* cells which had been engineered to express a humanised antibody, CAMPATH*-1H, were routinely grown using serum-containing medium. From a seeding density of 105 cells ml−1, cells grown in static culture with serum reached a maximal cell density of 6.5×105 cells ml−1 after 6 days in culture and produced a maximal antibody concentration of 69 mg l−1 after 11 days in culture. CHO 3D11* cells grown with serum were washed in serum-free medium then cultured in WCM5 medium. Following a period of adaptation the cell growth and product yield was superior to that achieved with serum-containing medium. CHO cells producing CAMPATH-1H grown in an 8000 l stirred bioreactor seeded with 2×105 cells ml−1 reached a maximal viable cell density of 2.16×106 cells ml−1 after 108 h in culture and a maximal antibody concentration of 131.1 mg l−1 after 122 h in culture.