Isolation, characterization and recombinant protein expression in Veggie-CHO: A serum-free CHO host cell line

The dihydrofolate reductase-deficient Chinese hamster ovary cell line, DXB1 1-CHO, commonly used as a host cell for the production of recombinant prote ins requires 7.5% serum-supplementation for optimal growth. Regulatory issu es surrounding the use of serum in clinical production processes and the di rect and indirect costs of using serum in large-scale production and recove ry processes have triggered efforts to derive serum-independent host cell l ines. We have successfully isolated a serum-free host that we named Veggie- CHO. Veggie-CHO was generated by adapting DXB11-CHO cells to growth in seru m-free media in the absence of exogenous growth factors such as Transferrin and Insulin-like growth factor, which we have previously shown to be essen tial for growth and viability of DXB11-CHO cells. Veggie-CHO cells have bee n shown to maintain an average doubling time of 22 hr in continuous growth cultures over a period of three months and have retained the dihydrofolate reductase -deficient phenotype of their parental DXB11-CHO cells. These pro perties and the stability of its serum-free phenotype have allowed the use of Veggie-CHO as host cells for transfection and amplified expression of re combinant proteins. We describe the derivation a serum-free recombinant cel l line with an average doubling time of 20 hr and specific productivity of 2.5 Units recombinant Flt-3L protein per 10e6 cells per day.