Submitted to: American Society for Virology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2008
Publication Date: 7/12/2008
Citation: Suguitan, A.L., Marino, M.P., Desai, P.M., Chen, L., Matsuoka, Y., Donis, R.O., Jin, H., Swayne, D.E., Kemble, G., Subbarao, K. 2008. Elucidation of the molecular basis for the attenuation of a live, attenuated influenza A H5N1 cold-adapted vaccine virus [abstract]. American Society for Virology Meeting, July 12-16, 2008, Ithaca, New York. p. 93.
Technical Abstract: A recombinant, live influenza A H5N1 vaccine candidate with the hemagglutinin (HA) and neuraminidase (NA) genes derived from A/VietNam/1203/04 (H5N1) (H5N1 2004 wt) and the internal protein genes from A/Ann Arbor/6/60 (AA) (H2N2) cold-adapted (ca) virus has been previously shown to be attenuated in chickens, mice, and ferrets. The HA gene of the vaccine was modified by deleting the sequence encoding multiple basic amino acids at the HA1-HA2 cleavage site (MBS), a known virulence motif in poultry. Reassortant viruses were generated by reverse genetics to delineate the contributions of the modification of the HA gene, the phenotypes specified by the ca internal protein genes, and gene constellation effects to the observed attenuation of the vaccine virus. These included: (1) a recombinant H5N1 2004 wt virus with a deleted MBS in the HA ('MBS); (2) H5 HA and N1 NA from H5N1 2004 wt virus in an AA ca background; (3) H5 HA and N1 NA from H5N1 2004 wt virus in an AA wt background; and (4) H5 HA'MBS and N1 NA from H5N1 2004 wt virus in an AA wt background. The viruses were evaluated for dependence on trypsin for replication in vitro, temperature-sensitivity (ts) and ca phenotypes, and pathogenicity in chickens and mice. As expected, reassortant viruses possessing the AA ca virus genes exhibited ts and ca phenotypes. The presence of the MBS slightly increased the pathogenicity in mice; however, a greatly enhanced virulence in chickens and mice was observed when an intact H5 HA with MBS was present in the AA wt background. Replacing the H5N1 2004 wt internal protein gene segments with those of AA wt genes was associated with a decreased pathogenicity in chickens and mice. These results suggest that attenuation of H5N1 2004 ca vaccine is achieved through the combined effects of removal of the MBS in the H5 HA, the ts and ca phenotypes specified by the AA ca internal protein genes, and gene constellation effects.