Chinese hamster ovary (CHO) cells are a family of immortalized cell lines[1] derived from epithelial cells of the ovary of the Chinese hamster, often used in biological and medical research and commercially in the production of recombinant therapeutic proteins.[1][2] They have found wide use in studies of genetics, toxicity screening, nutrition and gene expression, and particularly since the 1980s to express recombinant proteins. CHO cells are the most commonly used mammalian hosts for industrial production of recombinant protein therapeutics.[2]