Protection of chickens from lethal avian influenza A virus infection by live-virus vaccination with infectious laryngotracheitis virus recombinants expressing the hemagglutinin (H5) gene

The H5 hemagglutinin (HA) gene of a highly pathogenic avian influenza virus (AIV) isolate (A/chicken/Italy/8/98) was cloned and sequenced, and inserte d at the non-essential UL50 (dUTPase) gene locus of a virulent strain of in fectious laryngotracheitis virus (ILTV). Northern and Western blot analyses of the obtained ILTV recombinants demonstrated stable expression of the HA gene under control of the human cytomegalovirus immediate-early gene promo ter. In vitro replication of the HA-expressing ILTV mutants was not affecte d, and infection of chickens revealed a reduced but still considerable viru lence, similar to that of a UL50 gene deletion mutant without foreign gene insertion. The immunized animals produced specific antibodies against ILTV and AIV HA, and were protected against challenge infections with either vir ulent ILTV, or two different highly pathogenic AIV strains (A/chicken/Italy /8/98, A/chicken/Scotland/59). After challenge, no ILTV could be reisolated from protected animals, and shedding of AIV was considerably reduced. Thus , although attenuation remains to be improved, genetically engineered ILTV live-virus vaccines might be used as vectors to protect chickens also again st other pathogens. (C) 2001 Elsevier Science Ltd. All rights reserved.