Overexpression of alpha-2,6-sialyltransferase stimulates propagation of human influenza viruses in Vero cells

Human influenza viruses are major concern as the leading cause of global pandemics. In infecting cells, they preferentially bind to sialyloligosaccharides containing terminal N-acetyl sialic acid linked to galactose by an alpha-2,6-linkage (NeuAc alpha 2,6Gal). The amount of NeuAc alpha 2,6Gal in Vero cells, which are predominantly used for production of influenza vaccines over the past 30 years, may not be as high as that in epithelial cells of human respiratory tract, what leads to the suboptimal virus growth in Vero cells. In this study, we stably transfected Vero cells with cDNA of human alpha-2,6-sialyltransferase (SIAT1), an enzyme catalyzing alpha-2,6-sialylation of galactose on glycoproteins. Overexpression of SIAT1 in the transfected Vero cells (Vero-SIAT1 cells) was confirmed by Western blot analysis and immunofluorescence microscopy. Vero-SIAT1 cells expressed 7 times higher amounts of NeuAc alpha 2,6Gal, but 3 times lower amounts of NeuAc alpha 2,3Gal as compared to parental Vero cells. Furthermore, the influenza viruses A (H1N1 and H3N2) and B grew in Vero-SIAT1 cells to the higher titers than in Vero cells. Taken together, these results imply that Vero-SIATI1 cells are useful not only for the propagation of human influenza viruses, but also for the preparation of influenza vaccines.