Properties of ras-amplified recombinant BHK-21 cells in protein-free culture

We compared serum and protein-free cultures of a ras-amplified recombinant BHK-21 cell line (ras-rBHK-IgG), which hyperproduces a lung cancer specific recombinant human monoclonal antibody. Ras-rBHK-IgG cells were shown to grow well, even in protein-free medium and to be morphologically similar to cells cultured in serum containing medium. However, the growth rate of ras-rBHK-IgG cells was considerably slower in protein-free medium, which results in a longer maintenance period compared with cells cultured in serum containing medium. In addition, it was found that antibody production in protein-free culture had a ten times higher maximum than cells cultured in serum containing medium. On the other hand, in high density culture, using the hollow fiber bioreactor system, ras-rBHK-IgG cells could be maintained for a month in protein-free culture in contrast with serum culture, which only lasted for half a month. However, the marked increase of antibody production was not observed. A total amount of about 15 mg of the recombinant antibody, obtained in protein-free culture, was about two times of that obtained in serum culture, and was shown to be reactive to lung cancer cells in tissue. From these properties in protein-free medium, it is concluded that protein-free culture of ras-rBHK-IgG cells is suitable for middle scale production of recombinant human monoclonal antibody.