Why do we still use serum in the production of biopharmaceuticals?

Eukaryotic cells, in general, require serum for growth in vitro. Serum is a complex mixture of a large number of constituents, so the addition of serum introduces an ambiguous factor into cell cultivation. However, many commercially available sera are of a high uniform quality. Of these, foetal bovine serum is the most frequently used and is capable of supporting the growth of a wide variety of eukaryotic cells. However, with the identification of essential growth factors and nutrients required by different cells, several very effective serum-free media have been formulated. The use of these serum-free media is limited to a very narrow range of cells. Regulatory constraints generally make it impractical and uneconomic to alter existing biopharmaceutical production processes in which serum is used as a raw material.