Construction of attenuated influenza virus vaccines of 2006-2007

Six gene segments, PB1, PB2,PA, NP, M and NS, were fully synthesized which derived from the master donor virus(MDV), cold-adapted(ca),temperature sensitive(ts), live attenuated influenza virus strain A/Ann Arbor/6/60(MDV-A). Meanwhile, five amino acid substitutions (PB1-391E, 581G, 661T, PB2-265S, NP-34G) were artificially altered by human intervention. HA and NA fragments derived from the 2006～2007 circulating strain A/New Caledonia/20/99 (H1N1). Eight fragments were ligated with modified pAD3000 for rescue plasmid construction. Eight transcription/expression plasmids were named as pMDV-A-PB2, pMDV-A-PB1, pMDV-A-PA, pMDV-A-NP, pMDV-A-M, pMDV-A-NS, pMDV-A-HA, pMDV-A-NA, respectively. The COS-1 cells were co-transfected with eight plasmids representing 6 internal viral backbone of the strain A/AA/6/60 and two plasmids containing the cDNA of the HA and NA segments of the strain A/New Caledonia/20/99 (H1N1), the results showed that cold-adapted, attenuated reassortant influenza A virus was rescued successfully. Titers of a reassorted influenza A virus in embryonated chicken eggs ranged from 1∶29 to 1∶210. The rescue system of six internal genes used as backbone opens the way for further research on gene function and neotype vaccine candidate of cold-adapted, live attenuated human influenza virus.