Rapid expression of recombinant proteins in modified CHO cells using the baculovirus system

Baculovirus containing the mammalian CMV promoter, in place of the insect polyhedron promoter (BacMam), has been used to transiently transfect COS, CHO and CHOE1a (CHO cells expressing the E1a transcriptional activator). Using this system for the expression of a cellular adhesion factor (SAF-3) Fc fusion protein in CHOE1a, we found that levels of expression were highest with a MOI of 100, 20mM sodium butyrate, at 34degreesC. Production increased further if the cells were resuspended in fresh medium, about 3 x 10(6) cells ml(-1), prior to addition of the virus. These conditions were used to express 3 secreted proteins, SAF-3-Fc, CD40-hexa his and Asp 2-Fc, and, at 2 to 6 days post infection, protein levels ranged from 4 ug ml(-1) to 25 ug ml(-1). Based on these results, the BacMam system represents a viable technique for producing protein at ug ml(-1) levels in a relatively short period of time.