ST3GAL6 Knockout Cell Line (HEK293)

N-glycosylated proteins produced in human embryonic kidney 293 (HEK 293) cells often carry terminal N-acetylgalactosamine (GalNAc) and only low levels of sialylation. On therapeutic proteins, such N-glycans often trigger rapid clearance from the patient's bloodstream via efficient binding to asialoglycoprotein receptor (ASGP-R) and mannose receptor (MR). This currently limits the use of HEK 293 cells for therapeutic protein production. To eliminate terminal GalNAc, we knocked-out GalNAc transferases B4GALNT3 and B4GALNT4 by CRISPR/Cas9 in FreeStyle 293-F cells. The resulting cell line produced a coagulation factor VII-albumin fusion protein without GalNAc but with increased sialylation. This glyco-engineered protein bound less efficiently to both the ASGP-R and MR in vitro and it showed improved recovery, terminal half-life and area under the curve in pharmacokinetic rat experiments. By overexpressing sialyltransferases ST6GAL1 and ST3GAL6 in B4GALNT3 and B4GALNT4 knock-out cells, we further increased factor VII-albumin sialylation; for ST6GAL1 even to the level of human plasma-derived factor VII. Simultaneous knock-out of B4GALNT3 and B4GALNT4 and overexpression of ST6GAL1 further lowered factor VII-albumin binding to ASGP-R and MR. This novel glyco-engineered cell line is well-suited for the production of factor VII-albumin and presumably other therapeutic proteins with fully human N-glycosylation and superior pharmacokinetic properties.