Virus rescue.To generate virus from the plasmids, HEp-2 cells grown in a six-well plate were infected with MVA-T7 at a multiplicity of infection (MOI) of 1 and then transfected with 1 μg of pLa and either pLa-H5w or pLa-H5m together with the following expression plasmids: pT7-NP at 0.4 μg, pT7-P at 0.2 μg, and pT7-L at 0.2 μg. After 16 h of incubation at 37°C, the medium was replaced with 2 ml of fresh Opti-MEM (Invitrogen Corp., Carlsbad, CA) containing 0.5 μg of the protease inhibitor N-tosyl-phenylalanine chloromethylketone (TPCK) trypsin, and the cells were incubated for another three days at 37°C. The supernatant was then inoculated into the allantoic cavities of 10-day-old embryonated SPF eggs. After 72 h of incubation at 39°C, the allantoic fluid was harvested and the virus was identified by hemagglutination assay using 0.5% chicken red blood cells. Viral RNAs were isolated from the rescued viruses, and the presence of the inserted foreign genes was confirmed by RT-PCR and sequence analysis. The rescued viruses were designated as rLa, rLa-H5w, and rLa-H5m.