Rapid production of a H 9 N 2 influenza vaccine from MDCK cells for protecting chicken against influenza virus infection

H 9 N 2 subtype avian influenza viruses are widespread in domestic poultry, and vaccination remains the most effective way to protect the chicken population from avian influenza pandemics. Currently, egg-based H 9 N 2 influenza vaccine production has several disadvantages and mammalian MDCK cells are being investigated as candidates for influenza vaccine production. However, little research has been conducted on low pathogenic avian influenza viruses (LPAIV) such as H 9 N 2 replicating in mammalian cells using microcarrier beads in a bioreactor. In this study, we present a systematic analysis of a safe H 9 N 2 influenza vaccine derived from MDCK cells for protecting chickens against influenza virus infection. In 2008, we isolated two novel H 9 N 2 influenza viruses from chickens raised in southern China, and these H 9 N 2 viruses were adapted to MDCK cells. The H 9 N 2 virus was produced in MDCK cells in a scalable bioreactor, purified, inactivated, and investigated for use as a vaccine. The MDCK-derived H 9 N 2 vaccine was able to induce high titers of neutralizing antibodies in chickens of different ages. Histopathological examination, direct immunofluorescence, HI assay, CD4 + /CD8 + ratio test, and cytokine evaluation indicated that the MDCK-derived H 9 N 2 vaccine evoked a rapid and effective immune response to protect chickens from influenza infection. High titers of H 9 N 2 -specific antibodies were maintained in chickens for 5 months, and the MDCK-derived H 9 N 2 vaccine had no effects on chicken growth. The use of MDCK cells in bioreactors for LPAIV vaccine production is an attractive option to prevent outbreaks of LPAIV in poultry.