Recombinant NDV expressing cytokines or fliC confers a quick immune response against NDV challenge and resistance to maternal antibody

Currently, there are two major bottleneck problems which seriously affect prevention of the Newcastle disease (ND): interference of maternal antibody on NDV vaccination and slow production of neutralization antibody. To overcome these problems, in present study, four rNDV vaccine strains expressing bio-adjuvants chIL2, chIL15, chGM-CSF or fliC gene were constructed and rescued using reverse genetics approach. The HI antibody titers of SPF birds immunized with rNDV reached to 5.5log2, 4.7log2, 6.5log2 and 5.8log2, respectively at the 8th day post immunization, while the antibody titers of the parental virus and control were 3.3log2 and 1log2, respectively. The immunized chickens were challenged by 10 ELD dose of the virulent NDV BJ strains at the 7th day post immunization. The protection rate of the four rNDVs bio-adjuvant groups was 100%, while the protection rate of the parental group was 80%. We also examined the anti-maternal antibody activity of these adjuvant vaccines by detection HI titer after vaccination of chickens with high (8.4log2) or low (5log2) maternal antibody levels. In chicken flock with higher maternal antibody, parental strain could not resist the influence of the maternal antibody and induce any notable change of HI antibody kinetics. However, both rClon30-chGM-CSF and rClon30-flic were able to resist the influence of the maternal antibody and maintained the HI antibody above the protection level during the 14day's experiment. In chicken flock with lower maternal antibody, the parental rclone30 strain could not induce HI titer to the protection level until the 14th day, but both rClon30-GM-CSF and clone30-fliC raised the HI antibody to above the protection level at the 7th day post vaccination.