FOREIGN PROTEIN EXPRESSION FROM S-PHASE SPECIFIC PROMOTERS IN CONTINUOUS CULTURES OF RECOMBINANT CHO CELLS

Foreign protein expression from the commonly used SV40 promoter has be en found to be primarily during the S-phase of the cell cycle. Simple mathematical models with this cell cycle phase dependent expression of foreign protein suggest that the specific production rate will be pro portional to the cell growth rate, which is particularly disadvantageo us in high cell density fed-batch or perfusion bioreactors. In this st udy we investigate this predicted relationship between the production rate and growth rate by culturing recombinant CHO cells in a continuou s suspension bioreactor. One CHO cell line, GS-26, has been stably tra nsfected with the plasmid pSVgal, which contains the E. coli lac Z gen e under the control of the SV40 promoter. This GS-26 cell line was gro wn in suspension cultures over a range of specific growth rates in bat ch and continuous modes. The intracellular beta-galactosidase activity was assayed using a standard spectrophotometric method after breaking the cells open and releasing the enzyme. A strong growth associated r elationship is found between the intracellular beta-galactosidase cont ent and the specific growth rate in batch and continuous cultures, as predicted.