Recombinant protein production by CHO cells cultured in a chemically defined medium.

Serum-free culture of chinese hamster ovary (CHO) cells has become increasingly common as a way of obtaining high levels of expression of recombinant proteins while simplifying recovery and downstream processing of the product. However, serum-free media may still contain one or more of a variety of animal-derived components including albumin, fetuin, various hormones and other proteins. We have demonstrated that it is possible to eliminate animal-derived proteins from a CHO medium formulation. Plasma protein fractions like albumin and fetuin may be replaced by plant-derived hydrolysates, resulting in medium that is protein-free but still undefined (CHO III PFM). CD CHO Medium is a chemically defined formulation which contains no protein or hydrolysates of either plant or animal origin. Peak cell densities and recombinant protein expression in CD CHO cultures compared favorably to expression in other media, although the maximal cell density and the highest levels of expression were observed at later time points. We were able to successfully supplement the culture with sodium butyrate to increase expression levels at the expense of peak cell density, so for recombinant cell lines showing an inverse relationship between growth and expression of recombinant product, strategies which limit the peak cell density may be useful for increasing expression.