Delivery of avian cytokines by adenovirus vectors

A fowl adenovirus serotype 8 (FAV-8) recombinant was constructed by inserting an expression cassette consisting of the FAV major late promoter/splice leader sequences (MLP/SL), the chicken interferon-gamma (ChIFN-gamma) gene and SV40 polyA into sites in the right hand end of the FAV-8 genome. One recombinant (A3-13) was constructed by an insertion of ChIFN-gamma into a 1.3 kilobase pair (kbp) deletion which removed a putative open reading frame (ORF) with identity to the CELO (FAV serotype 1) 36 kDa homologue. A second recombinant (S4) removed a further 0.9 kbp and a third recombinant (AA1) was constructed in a small 50 base pair (bp) SpeI deletion. The recombinants displayed differing growth characteristics in CK monolayers. A3-13 grew slowly and only attained a titre of 10(5) pfu/ml, S4 had intermediate growth and AA1 showed wild type growth kinetics. These differing growth properties indicated that removal of the 36 kDa homologue had an effect on growth in vitro. Supernatants from CK monolayers infected with the recombinant virus were assayed for the production of ChIFN-gamma. Detectable levels of ChIFN-gamma were observed in supernatants as early as 24 h post infection (p.i.), peaked at 48 h p.i. and this level was maintained for at least 10 days. The level of production of ChIFN-gamma correlated with each recombinant's growth characteristics in vitro. Chickens treated with rFAV-ChIFN-gamma showed increased weight gains compared to controls and suffered reduced weight loss when challenged with the coccidial parasite Eimeria acervulina.