Serum-free transfection and selection in Chinese hamster ovary (CHO) cells

In this report a method for transfection and selection of mammalian cells in serum-free medium is described. Chinese hamster ovary (CHO) cells were grown in serum-free medium in plastic dishes coated with one of the following attachment factors: poly-D-lysine, Cell-Tak (polyphenolic proteins extracted from the marine mussel Mytilus edulis), fibronectin or laminin. Cells grown to 80% confluence were transfected with an expression vector encoding the hygromycin resistance gene as a selectable marker and beta-galactosidase as the reporter gene. Transfectants were selected using hygromycin at a concentration of 500 micrograms/ml. Both fibronectin and laminin supported colony formation following selection in serum-free medium. However, poly-D-lysine and Cell-Tak did not. This method can, thus, be used to select for clones producing a recombinant product in cells that are growing in serum-free medium from the onset to provide a better system from which to purify proteins.