Recombinant proteins produced into yolk of genetically manipulated chickens are partly sialylated in N-glycan.

The transgenic chicken is a candidate for the production of biopharmaceutical proteins with several economic superiorities. In general, the addition of sialic acid at the terminal of N-glycan is important for the bioactivity of biopharmaceuticals including plasma half-life; however, sialic acid has not been detected in the N-glycan of proteins produced in the egg white of genetically manipulated chickens. In this study, the extracellular domain of the TNF receptor and single chain Fv fused to Fc (referred to as TNFR/Fc and scFv/Fc, respectively) were purified from the egg yolk of genetically manipulated chickens and their sialylation in N-glycan was examined. In contrast to the glycan in egg white, yolk-derived proteins were partly sialylated. Lectin blot showed the existence of α2,6-sialic acid on TNFR/Fc, which disappeared with the removal of N-glycan by PNGase. In scFv/Fc, up to 7 % of N-glycan contained sialic acid. Disialyl glycans, which were detected in serum-derived scFv/Fc in a previous study, were not found in the yolk sample. Ovarian follicular tissue, which surrounds growing yolk, expressed several neuraminidases, suggesting the partial truncation of glycan during the yolk transfer process from the blood.