the 10 highest expressing clones were expanded into 125 mL Erlenmeyer flasks containing 40 mL of culture media. Single clone cell banks were made when cell viability reached >90%.
Material generated from the stable pool and the single clone cultures were used in this study, as it was observed that the antibody quality from each differed after capture via Protein A chromatography. The pooled material that had been banked during the selection process was later found to have a higher aggregate content than the single cell clone produced downstream, giving two populations of the same antibody; one highly aggregated and one less aggregated. Downstream processing was the same for both cultures, and the increased aggregation was not due to be process dependent.
Cell culture and cell harvest
Cell cultures were performed in a 20 L WAVE bioreactor (GE Healthcare Life Sciences) with a 10 L working volume. Following expansion in culture flasks, the CHO seed culture of 2 L was transferred into 8 L of preheated media to a final volume of 10 L. At this point, the cell viability was 100% and had a viable cell density (VCD) of 1.0 3 106 cells/mL. Culture conditions were maintained as follows; 2.5 LMH air, 3% CO2, rocker speed of 10 rocks per minute, and a 7 rocker angle and an initial temperature of 37 C. When the cells reached a VCD of 3.0 3 106 cells/mL, the temperature was shifted to 30 C. This point marked day zero of a 21-day culture. Samples were taken daily to determine VCD and viability (NOVA Bioflex). After 21 days of culture cells were harvested by filtration (1.2 mm 0.464 m2 filter, part number 5555303P0-SS followed by 0.45/0.20 mm 0.186 m2 part number 544307H9-FF [Sartorius]) and concentrated to a 1 L working volume by 30 kD ultrafiltration (SiusTM-LS TFF Cassette, 0.1 m2, part number PP030L01L, TangenX).