Mammalian cells are grown in serum- or protein-free media to densities higher than 2×107 viable cells per ml. At this level the cells can be continuously cultured for more than three months, yielding the desired productivity without the use of serum supplements or other undefined ingredients.

For bacteria a pH-controlled fed batch process optimized for recombinant E. coli allows optical densities beyond 100 and yields up to 1 kg of cells from a 10 liter fermentation broth.

To avoid any possible endotoxin cross contamination, bacteria and mammalian cells are cultured in separate fermentation units.