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

Baculovirus containing the mammalianCMV promoter, in place of the insect polyhedronpromoter (BacMam), has been used to transientlytransfect COS, CHO and CHOE1a (CHO cells expressing theE1a transcriptional activator). Using this system forthe expression of a cellular adhesion factor (SAF-3) Fcfusion protein in CHOE1a, we found that levels ofexpression were highest with a MOI of 100, 20mM sodiumbutyrate, at 34 degrees C. Production increased furtherif the cells were resuspended in fresh medium, about3 x 10(6) cells ml(-1), prior to addition of the virus. These conditions were used to express 3 secretedproteins, SAF-3-Fc, CD40-hexa his and Asp 2-Fc, and, at2 to 6 days post infection, protein levels ranged from4 ug ml(-1) to 25 ug ml(-1). Based on these results, theBacMam system represents a viable technique forproducing protein at ug ml(-1) levels in a relatively shortperiod of time.