Effect of copper sulfate on performance of a serum-free CHO cell culture process and the level of free thiol in the recombinant antibody expressed.

A recombinant Chinese hamster ovary (CHO) cell line was used to express a humanized antibody. Product quality analysis of this humanized antibody showed the presence of free thiol, due to unpaired cysteine residues in the Fab region. Decreased potency of this thiol Fab made it critical to minimize the levels of free thiol.