Strategies for adaptation of mAb-producing CHO cells to serum-free medium

Abstract

Large-scale production of biopharmaceuticals commonly requires the use of serum-free medium, for safety and cost reasons. However, serum is essential to most mammalian cells growth, and its removal implies a very time-consuming process for cell adaptation. Thus, the aim of the study was to evaluate different strategies for cell adaptation to serum-free medium. Three cell types were used to assess the impact of transfection on adaptation: one common CHO-K1 cell line and two CHO-K1 cells transfected with different technologies for antibody production. Cultures were started with a known cell concentration in Dulbecco’s Modified Eagle Medium supplemented with 10% serum. The effect of five combinations of supplements, that could support cells during adaptation, was tested. These supplements included insulin and trace elements (copper sulfate, zinc sulfate, sodium selenite, ammonium iron citrate, ferrous ammonium sulfate, ammonium metavanadate, nickel chloride and stannous chloride). A methodology of gradual adaptation was followed, consisting on sequential steps of serum reduction, after assuring good cell adaptation from the previous step. After reaching 0.625% serum, medium was gradually switched to the chemically defined serum-free EX-CELL CHO DHFR- medium. It was observed that supplements influence cell adaptation to serum-free medium. Indeed, the combinations containing the trace element ammonium iron citrate gave the worst results, with cell death at 2.5% serum. In contrast, the combination of ammonium metavanadate, nickel chloride and stannous chloride proved to be the most favorable to the three cell lines. Comparing the cells, it seems that the ability to produce antibody and the transfection methodology used does not have a great impact on adaptation. During the study, some procedure details were identified as particularly important and should be carefully considered in the process of cell adaptation to serum-free medium. These include the use of a higher initial cell concentration that will allow the survival of an increased number of cells during the process; avoiding harsh procedures to the cells such as centrifugation and the use of enzymes (i.e. trypsin), due to a higher cell sensibility during adaptation; and to give enough time for a full cell adaptation at each step.