A region at the left end of the fowl adenovirus 9 genome that is non-essential in vitro has consequences in vivo

Abstract

The regions at the left and right ends of fowl adenovirus (FAdV) genomes are not wellcharacterized in comparison to those of human adenoviruses. Using a series of deletion mutants, we analysed a 2.4 kb region near the left end of the FAdV-9 genome (nt 400-2782) that contains packaging-signal motifs VI and VII and open reading frames (ORFs) 0, 1, 1A, 1B, 1C and 2. Viable viruses with specific deletions in this region had wild-type characteristics in vitro, as measured by cytopathic effect, plaque morphology, virus titres and growth kinetics. However, one mutant (FAdV-9D4), which lacked these ORFs and retained the packaging motifs, did not replicate at wild-type levels in vivo, as judged in infected eggs by virus titres in allantoic fluid and in infected chickens by antibody responses, virus titres in faeces and virus genome copy numbers in tissues. These findings indicate that some of the ORFs in this region, although dispensable in vitro, are important for in vivo replication of FAdV-9. INTRODUCTIONFowl adenoviruses (FAdVs) have a worldwide distribution, and some are important poultry pathogens that cause inclusion body hepatitis and hydropericardium syndrome in chickens (Adair & Fitzgerald, 2008). FAdV serotypes are grouped into five species (Fowl adenovirus A-E), all belonging to the genus Aviadenovirus, family Adenoviridae (Benkő et al., 2005). Complete nucleotide sequences are available for the genomes of FAdV-1 (CELO virus) and FAdV-9 (strain A-2A) (Chiocca et al., 1996;Ojkic & Nagy, 2000), and partial nucleotide sequences are also available for the left and right ends of the genomes of FAdV-2, -4, -8 and -10 (strain C-2B) (Corredor et al., 2006(Corredor et al., , 2008. None of the early genes at the left and right ends of the FAdV genomes are homologues of the E1, E3 and E4 genes of mastadenoviruses, which infect mammals Chiocca et al., 1996). In this study, the importance of ORFs at the left end of the FAdV-9 genome in virus replication in vitro and in vivo was investigated by analysing deletions, as a first step towards elucidating the roles of the early genes in this region. RESULTS Generation of deletionsThe ORF arrangement within the left-end genomic region of FAdV-9 and the features of all deletions are depicted in Fig. 1(a, b), respectively. Nine deletions were generated in the region within nt 250-4200 of the FAdV-9 genome as shown: FAdV-9D1 (D1194-2342), FAdV-9D2 (D854-2782), FAdV-9D3 (D854-2817), FAdV-9D4 (D491-2782), FAdV-9D5 (D491-2980), FAdV-9D6 (D491-4200), FAdV-9D7 (D400-2782), FAdV-9D8 (D330-2782) and FAdV-9D9 (D250-2782). Viable viruses were recovered following transfection of CH-SAH (chicken hepatoma) cells without complementation with only the FAdV-9D1, -9D2, -9D4 and -9D7 genomes at 5-7 days post-transfection (p.t.). The first viable deletion mutant, FAdV-9D1, was generated by Supplementary methods and a supplementary figure and table are available with the online version of this paper.

Oral Inoculation of Chickens with a Candidate Fowl Adenovirus 9 Vector

“…However, in that study (23), virus was given through water and feed, which means the amount of virus dose taken up by the chickens was unknown. In more recent studies (18,20), we evaluated the FAdV-9⌬4 vector virus administered intramuscularly (i.m. ), and in the present work, the chickens were inoculated orally.…”

“…and were stored at Ϫ80°C until processing. Sample preparation and virus titration were performed as described previously (18). A sample was regarded as negative if it tested negative at least twice and at two different times.…”

“…inoculation results of Corredor and Nagy (18). The fact that the mutant virus elicits a less-robust antibody response than the wildtype virus might be advantageous when the same vector virus is considered in a secondary treatment or vaccination.…”

“…We demonstrated that the tandem repeat region 2 (TR-2) at the right end of the genome is dispensable and is suitable for foreign gene insertion (17). More recently, a 2.4-kb region at the left end of the FAdV-9 genome, containing two putative motifs of the packaging signal domain and six open reading frames (ORFs), was shown to be nonessential for virus replication in vitro and in vivo; however, a deletion virus (FAdV-9⌬4) that lacks the six ORFs (0, 1, 1A, 1B, 1C, and 2) replicated less efficiently than the wild-type (unmodified) FAdV-9 (wtFAdV-9) in chickens inoculated intramuscularly, and the antibody (Ab) level was lower in the FAdV-9⌬4-inoculated birds (18). We have also demonstrated that the left end of the FAdV-9 genome is a suitable site for the insertion and replacement of foreign genes (19).…”

Circumventing Antivector Immunity: Potential Use of Nonhuman Adenoviral Vectors

“…After the identification of FAdV-9 (species FAdV D) regions that are nonessential for the virus Nagy, 2001, 2003;Corredor and Nagy, 2010a), FAdV-9 recombinants demonstrated wild-type growth kinetics, virus titers, cytopathic effect and plaque morphology (Corredor and Nagy, 2010a), expression in avian and mammalian cells, and lack of replication in mammalian cells, indicating their applicability as gene delivery vehicles for mammalian systems (Corredor and Nagy, 2010b). FAdV-8 (species FAdV E) vectors were also constructed and showed efficacious in vivo delivery of antibody fragments against pathogenic infectious bursal disease virus (Greenall et al, 2010).…”