Protective efficacy of an H5N1 DNA vaccine against challenge with a lethal H5N1 virus in quail.

Some H5N1 avian influenza viruses (AIVs) are lethal to quail; however, the use of inactivated vaccines in these birds is largely restricted because of side effects caused by oil adjuvants. Here we evaluated the protective efficacy of a DNA vaccine against lethal challenge with H5N1 highly pathogenic avian influenza virus (HPAIV) in quail. Groups of ten 3-wk-old quail were intramuscularly inoculated three times at 3-wk intervals with 10, 15, 30, or 60 microg, respectively, of plasmid pCAGGoptiHA, which expresses a codon-optimized hemagglutinin gene of the H5N1 virus A/goose/Guangdong/1/96 (GS/GD/96). The control group was inoculated with phosphate-buffered saline. Hemagglutination-inhibition (HI) antibodies were monitored every week after the primary vaccination. The quail were challenged intranasally with 10(5) EID50 of heterologous HPAIV A/duck/Fujian/31/2007 (DK/ FJ/31) (H5N1) 2 wk after the third inoculation. Oropharyngeal and cloacal swab specimens were collected 3, 5, and 7 days after inoculation, and quail were observed daily for disease signs and death for 2 wk. The quail showed no side effects after the plasmid inoculation, and HI antibodies were detectable 1 wk after the second vaccination in all groups and increased sharply after the third inoculation. All quail in the PBS-inoculated group and 20% of the birds in the 10 microg plasmid-inoculated group died after the lethal H5N1 virus challenge; however, birds in the 15, 30, and 60 jg plasmid-inoculated groups were completely protected. These results indicate that this DNA vaccine holds promise for use in quail to protect against H5N1 AIV.