Project Number: 6612-32000-052-00
Project Type: Appropriated

Start Date: Feb 01, 2007
End Date: Jan 31, 2012

Objective:
1. Identify genetic predictors of MDV virulence. (SEPRL) (ADOL) 2. Identify host-viral genetic determinants that control avian tumor virus pathogenicity and shedding. (ADOL) (SEPRL) 5. Discover safe and highly effective vaccine platforms that convey protection against emerging Marek¿s disease viral strains. (SERPL) (ADOL)

Approach:
1. Identify genetic predictors of MDV virulence. The nucleotide sequences of the long repeat region in the genomes of both attenuated and mildly virulent strains of MDV will be determined using conventional sequencing technologies. Viral DNA will be isolated, subjected to the polymerase chain reaction and sequenced. Whole genome sequences of serial passaged viruses will be determined using 454 Life Sciences technologies. To determine the collection of mutations responsible for attenuation and the multigenic nature of attenuation, virus samples at defined passage intervals will be collected and processed for pathotyping in a bioassay and 454-based sequencing. 2. Identify host-viral genetic determinants that control avian tumor virus pathogenicity and shedding. The expression level of viral genes and their effects on the expression of cellular genes will be examined using Chicken genome microarrays. Two chicken lines (72 and 63) infected with various MDV pathotypes will be used in these studies. Various tissue samples will be collected 5 days post challenge and RNA will be isolated using commercially available reagents. cDNA will then be made for isolated RNA, labeled with fluorophores and hybridized to the microarrays. 5. Discover safe and highly effective vaccine platforms that convey protection against emerging Marek¿s disease viral strains. The genomes of currently circulating very virulent plus (vv+) pathotypes will be modified by deletion of virulence genes and incorporation of genes encoding immune modulators (i.e. cytokines, soluble cytokine receptors and microrna constructs) in order to modulate the TH1/TH2 immune response. To achieve this, vv+ genomes will be cloned as a bacterial artificial chromosome and modified using recE/T mutagenesis of E.coli. Recombinants will be tested for loss of pathogenicity in birds. Efficacy of vaccine candidates will then be determined in protection trials.