Pilot production of high-titer interferon and virus with a microcarrier suspension culture system.

We have successfully cultured four cell lines--L929, BHK-13, BHK-21 and CHO-K1 using an MC-1 type microcarrier made in our academy. With the microcarrier in a concentration of 5 mg/ml, the cell density was about 30 x 10(4) cells/ml; after 3 days in suspension culture, the cells could proliferate to 1 x 10(6) cells/ml. At this time, when L929 cells were primed with 25 IU/ml MuIFN for 14-24 h and then superinduced with NDV, cycloheximide (20 micrograms/ml) and actinomycin D (2 micrograms/ml), the titer of IFN reached approximately 10(5) IU/ml (10(5) IU/mg of protein, expressed in specific activity). When VSV was inoculated into the other three cell line cultures, the viral titer reached 6 Log TCID50/ml or much higher. The yield with the CHO-K1 cell line was the highest, reaching titers of 7-8 Log TCID50/ml. These titers were similar to those seen in stationary culture. With trypsin-citrate solution and a more rapid stirring speed, the cells could be satisfactorily released from the microcarriers and reattached on fresh ones. These experiments show that the microcarrier suspension culture system is suitable for producing large scale, high-titer, low-cost vaccines and IFNs, both natural and recombinant, using genetically-engineered CHO cell lines.