The CHO cell line is originally derived from the Chinese hamster ovary, and has become a staple source of cells due to their robust growth as adherent cells or in suspension. They are amenable to genetic modifications and methods for cell transfection, recombinant protein expression, and clone selection are well characterized. CHO cells can also undergo human-compatible post-translational modifications, making them ideal for therapeutic and pharmaceutical applications like protein manufacturing. CHO cells lack proline synthesis abilities and do not express EGFR. Various variant cell lines have emerged from CHO, such as CHO-K1 which lack dihydrofolate reductase (DHFR) activity.