Construction and immunogenicity of recombinant fowlpox vaccines coexpressing HA of AIV H5N1 and chicken IL18

cDNAs of the HA genes of subtype H5N1 AIV were fused to form a single open reading frame, designated H5HA-H7HA. The H5HA-H7HA cDNA and chicken Interleukin-18 (IL18) were inserted into the fowlpox virus (FPV) expression vector pUTA-16-LacZ to produce pUTAL-H5-H7-IL18. cDNA of H5N1 AIV HA was inserted into the FPV expression vector pUTA2 to create the recombinant expression plasmid pUTA2-H5. Plasmids were then co-transected into CEF cells. The two recombinant fowlpox viruses (rFPV) were produced by three cycles with the BrdU and verified by RT-PCR, IFA and Western blotting. One-day-old specific pathogen free (SPF) chickens and 7-day-old commercial Leghorn egg-laying chickens were inoculated with 106 PFU recombinant or parental fowlpox vaccine viruses by wing-web puncture. Hemagglutination inhibition (HI) antibody titer and nonspecific cellular immunity level were assessed after 1–3 weeks post-immunization. We found that all rFPV-vaccinated groups produced HI-specific antibodies, and the level of cellular immunity induced by the rFPV-H5-H7-IL18 strain was significantly higher than that induced by rFPV-H5HA. At 3 weeks post-inoculation, immunized SPF and Leghorn chickens were challenged with H5N1 HP AIV. The rFPV-H5-H7-IL18 vaccine strains were able to induce complete (10/10) protection, while the rFPV-H5HA vaccine strain induced (9/10) protection. Cloacal swabbing samples were collected from immunized leghorn chickens during the first week post-challenge; no shedding was found in the rFPV-H5-H7-IL18 vaccinated group. The rFPV-H5-H7-IL18 vaccinated group displayed significantly increased weight gain relative to the rFPV-H5HA group. This study reports a significant step in the further development of new AIV vaccines.