Reassortment of high-yield influenza viruses in vero cells and safety assessment as candidate vaccine strains

Abstract

Vaccination is the practiced and accessible measure for preventing influenza infection. Because chicken embryos used for vaccine production have various insufficiencies, more efficient methods are needed. African green monkey kidney (Vero) cells are recommended by the World Health Organization (WHO) as a safe substitute for influenza vaccine production for humans. However, the influenza virus usually had low-yield in Vero cells, which limits the usage of Vero cellular vaccines. This study used 2 high-yield influenza viruses in Vero cells: A/Yunnan/1/2005Va (H3N2) and B/Yunnan/2/2005Va (B) as donor viruses. It used 3 wild strain viruses to reassort new adaptation viruses, including: A/Tianjin/15/2009(H1N1), A/Fujian/196/2009(H3N2), and B/Chongqing/1384/2010(B). These three new viruses could maintain the characteristic of high-yield in Vero cells. Furthermore, they could keep the immunogenic characteristics of the original wild influenza viruses. Importantly, these viruses were shown as safe in chicken embryo and guinea pigs assessment systems. These results provide an alternative method to produce influenza vaccine based on Vero cells.

Keywords: Vero cells; influenza virus; reassortant; safety assessment.

Figure 1.

Growth profiles of 2 master donor YN/05A, YN/05B, and reassortant viruses FJ/09Va, TJ/09Va, and CQ/10Va and 3 wild type parental viruses. Wild type and reassortant viruses grown in Vero cell incubated at 33°C for 3 d. Viral titers were determined by HA assay. Error bars indicate the SD of each cohort. “Passage 1” represented the original wild viruses and new reassortant viruses at the first generation. Earlier, it constructed a bank of donor viruses with adaption of the Vero cell, which called stock viruses. It used the 57th (A/Yunnan/1/2005Va (H3N2)) and 64th (B/Yunnan/2/2005Va (B)) passage for depth study of reassortment. But when used for the first time in this study, it was marked as passage 1.

Figure 2.

Immunogenicity of reassortant viruses FJ/09Va, TJ/09Va, and CQ/10Va and 3 wild type parental viruses. (A) Group of mice were immunized with one dose of 0.2 mL, 5 ug HA formalin-inactivated reassortant viruses and wild type parental viruses by subcutaneous injection, weight changes of the mice were monitored daily. (B, C) The level of antibodies was estimated by HI assay using each wild-type virus as a binding antigen. The titers of HI antibody (middle) and NT antibody (right) against FJ/09 TJ/09 CQ/10 are shown. Dashed lines indicate the detection limit of NT assay. Error bars indicate the SD of each cohort.