Nat. Biotechnol. 28, 1153–1156 (2010); published online 5 November 2010; addendum published after print 12 April 2011

Over the last 20 years, numerous investigations examining the glycosylation of proteins expressed in Chinese hamster ovary (CHO) cells have failed to document the ability of CHO cells to decorate proteins with galactose-α-1,3-galactose (α-Gal) epitopes1,2,3,4,5,6. However, the ability of CHO cells to produce the α-Gal epitope in recombinant proteins was reported before7. The mechanism of activation of the α-(1,3)-galactosyltransferase in CHO cells remains unclear. A possible factor may involve the transfection process, as similar activation has been documented with other glycosyltransferases8.