To prepare candidate influenza pandemic vaccines, we are developing an approach based on reassortment of antigenically appropriate nonpathogenic avian viruses of different subtypes (H5, H9, H7) with the cold-adapted master strain (MS) A/Leningrad/134/17/57 (Len/17) that is currently used in Russia for preparing licensed live attenuated vaccines for adults and children. In the present study, reassortants between A/Duck/Potsdam/1402-6/86(H5N2) (H5N2-wt) and Len/17 were obtained. One of the clones, A/17/Duck/Potsdam/86-92(H5N2) (Len17/H5), was chosen for further detailed genetic and antigenic analysis. Len17/1-15 inherited the HA gene from the H5N2-wt and all other genes from Len/17 (7:1 genome composition). The HA gene sequence of Len17/H5 was identical to that of the parent H5N2-wt virus. The antigenic profile of the reassortant virus was similar to that of the H5N2-wt parent strain in the hemagglutination-inhibition (HI) test with a panel of antisera to different avian and human H5 viruses. The reassortant demonstrated high growth ability (9.3+0.3 lg EID50/ml) in embryonated hens' eggs (CE) at optimal (34 degreesC) temperature, comparable with that of the parent Len/17 MS. Also, Len17/H5 demonstrated cold-adapted (ca) and temperature-sensitive (ts) phenotypes similar to those of Len/17 and was attenuated for mice. (C) 2004 Elsevier B.V. All rights reserved.