VACCINATION OF CHICKENS WITH A RECOMBINANT FOWLPOX VIRUS CONTAINING THE HEMAGGLUTININ-NEURAMINIDASE GENE OF NEWCASTLE-DISEASE VIRUS UNDER THE CONTROL OF THE FOWLPOX VIRUS THYMIDINE KINASE PROMOTER

When chickens were vaccinated with a recombinant fowlpox virus (FPV) c ontaining the Newcastle disease virus (NDV) hemagglutininneuraminidase (HN) cDNA under the control of the thymidine kinase (TK) promoter and inserted into the FPV TK gene, the FPV antibody response to the recom binant virus was similar to the response to vaccination with standard FPV, and the recombinant virus protected chickens against challenge wi th virulent FPV. While the presence of the NDV HN cDNA was demonstrate d in the recombinant virus, which was stable on serial passage, expres sion of HN was not detected by hemagglutination, Western blot analysis or immunoprecipitation of infected cell lysate. Chickens vaccinated w ith the recombinant virus failed to mount an NDV hemagglutination-inhi bition antibody response, and they did not resist challenge with velog enic NDV. It was concluded that the TK promoter was too weak to drive the HN gene, but that the insertion into the FPV TK gene did not reduc e the immunogenicity of the virus.