| Abstract: | Introduction: Current egg-based influenza vaccine production technology is labor-intensive and lack of flexibility. Moreover, its capacity would not be able to meet the demand during influenza pandemics. This was illustrated in the 2009 H1N1 pandemic where only 22% of expected doses were supplied within the first 6 months after the pandemic was declared. Therefore, cell-based tchnology is becoming attractive for production of pandemic influenza vaccines. Objectives: Two cell lines, MDCK and Vero cells are currently used for manufacturing human influenza vaccines. MDCK cells can only be used formanufacturing influenza vaccines. In contrast, Vero cells have been widely used for the production of human vaccines. This study was conducted to develop Vero cell-based influenza H5N1 vaccines. Methods: The current WHO-recommended influenza H5N1 clade-1 vaccine strain (NIBRG-14), a reassortant virus between A/Vietnam/1194/2004 (H5N1) virus and egg-adapted high-growth A/PR/8/1934 virus, could growefficiently in eggs andMDCK cells but not Vero cells. Therefore, we first adapted the egg-derived NIBRG-14 in Vero cells to become a Vero cell-adapted high-growth H5N1 vaccine virus (Vero-15). Then, we analyzed the gene sequences, antigenicity and growth efficiency of the Vero-15virus. In addition,we also established reverse genetics plaform to generate high-growth reassortant H5N1 clade-2 viruses using the Vero-15 virus as a master donor virus. Results: After serial passages and plaque purifications of the NIBRG-14 vaccine virus in Vero cells, high-growth influenza H5N1 virus strains were generated in NHRI in 2006–07. In 2009, we further proved the suitability of mass production in microcarrier-based culture system using the Vero-adapted vaccine virus. We further tested immunogenicity of the Vero cell-derived H5N1 vaccine in mice. Mice immunized with 2ug of HA antigen adjuvanted with alum developed strong antibody response, which is better than mice immunized with 2ug of HA antigen without adjuvant (HI antibody geometric mean titer 320 vs. 28). In addition, we also proved highgrowth (>108 TCID50/ml) of the Vero cell-derived H5N1 vaccine virus in a disposable bioreactor cell culture system (BelloCell, CESCO Biotechnology, Taiwan). Moreover, we also successfully generated high-growth reassortant vaccine viruses for influenza calde-2 viruses using the Vero-15 virus as a master donor virus by reverse genetics. Conclusion: A Vero cell-adapted high growth influenzaH5N1 vaccine virus has been developed and could reach high virus titer (>108 TCID50/ml) in Vero cells in multiple culture systems including T flasks, mirocarriers and TideCell cultures. Therefore, the Vero-15 H5N1 vaccine virus has the commercial potential to become a seed virus formanufacturing H5N1 vaccines. In addition, the Vero-15H5N1 vaccine virus could become a mater donor virus to generate seed viruses for other influenza A subtypes. |
