FreeStyle™ CHO Expression Medium

With FreeStyle 293 Expression Medium, we would recommend harvesting the cells a little earlier to reduce any nonspecific binding by host cell proteins and then filtering the culture supernatant through a 0.2 or 0.1 µM membrane before loading onto the column. On the other hand, FreeStyle CHO Expression Medium contains EDTA that will strip the nickel column. The medium can be subjected to dialysis or buffer exchange prior to loading on the column, or the EDTA can be chelated by adding 1-3 mg/L NiSO4 or NiCl to the supernatant. Iron or cobalt salts can also be used.

When cells meant to be grown in suspension are grown in static culture, they may form clumps. These clumps will severely limit transfection efficiency and protein expression. It is suggested that FreeStyle 293 cells in FreeStyle media and CHO-S cells in CD-CHO or CHO-SFM are grown in agitated suspension to reduce the appearance of clumps. However, if clumps do form, you can try the following protocol to select for cells that don't form clumps:

- Transfer cells into an appropriate size centrifuge tube that will hold the entire cell suspension.
- Allow cells to sit undisturbed for about 5 minutes. The time can vary depending on the specific cell line. Larger cell clumps will settle to the bottom of the tube.
- Collect cells from the upper portion of the tube to passage into a new flask.

Find additional tips, troubleshooting help, and resources within our Cell Culture Support Center.