LARGE-SCALE TRANSIENT EXPRESSION WITH COS CELLS

We demonstrate here that transient expression with COS cells can be pe rformed at the one litre scale for a period of more than 10 days. Cell s grown in T225 flasks were transfected by electroporation, transferre d into spinners, and then grown either in suspension or on microcarrie rs. A daily medium change significantly extented culture life and prod uction time, compared with standard protocols. Concentrations of the p roduct, the secreted fusion protein CD40-Fc, were comparable in microc arrier and suspension culture. Cultures were started in fetal calf ser um containing medium and the subsequent production process was perform ed in a low protein serum free medium which allowed easy downstream pr ocessing. 10 litres of supernatant, collected from one transfected bat ch of cells, yielded 30 mg of purified and biologically active protein . In addition to developing a simplified protocol for generation of ce lls we also reduced the material (DNA, cuvettes) required for electrop oration. Our results show that scale up of transient expression to the litre scale can be successfully acieved. This provides a new tool to generate milligram quantities of protein within weeks of gene cloning.