Live attenuated influenza vaccine (LAIV) represent reassortant viruses with hemagglutinin (HA) and neuraminidase (NA) gene segments inherited from circulating wild-type (WT) parental influenza viruses recommended for inclusion into seasonal vaccine formulation, and the 6 internal protein-encoding gene segments from cold-adapted attenuated master donor viruses (genome composition 6:2). In this study, we describe the obstacles in developing LAIV strains while taking into account the phenotypic peculiarities of WT viruses used for reassortment. Genomic composition analysis of 849 seasonal LAIV reassortants revealed that over 80% of reassortants based on inhibitor-resistant WT viruses inherited WT NA, compared to 26% of LAIV reassortants based on inhibitor-sensitive WT viruses. In addition, the highest percentage of LAIV genotype reassortants was achieved when WT parental viruses were resistant to non-specific serum inhibitors. We demonstrate that NA may play a role in influenza virus sensitivity to non-specific serum inhibitors. Replacing NA of inhibitor-sensitive WT virus with the NA of inhibitor-resistant master donor virus significantly decreased the sensitivity of the resulting reassortant virus to serum heat-stable inhibitors.

In this paper we describe the development and the outcomes of the preclinical studies of temperature-sensitive and cold-adapted candidates for live attenuated influenza vaccine (LAIV) based on highly pathogenic avian influenza viruses A/H5N1 with pandemic potential. The LAIV candidates were developed by methods of classical reassortment between H2N2 Master Donor Virus for Russian LAIV and H5N1 viruses generated by reverse genetics for inactivated vaccine. These reverse genetically generated viruses were chosen as a source of H5 hemagglutinin and contained a modified protease cleavage site believed to be associated with high virulence. The progeny of reassortment had 7:1 gene composition and were characterized by antigen specificity of the HA of the pandemic virus, a high growth rate in chicken embryos and their parameters of temperature sensitivity and cold adaptation confirmed preserved attenuation of the Master Donor Virus. In addition, one H5N1 LAIV 6:2 reassortant was generated by reverse genetics. When tested in appropriate animal models, all candidates for H5N2 LAIV vaccine were found to be safe, immunogenic and effective in protecting from severe disease, mortality and pathology caused by the homologues lethal challenge virus and they almost completely eliminated challenge virus replication in vaccinated animals. They did not appear to differ in tested properties from the reverse genetically generated H5N1 LAIV 6:2 reassortant which contained wild-type N1-neuraminidase in addition to H5-hemagglutinin. The most promising for further clinical trials has been considered a LAIV candidate to virus A/turkey/Turkey/1/2005 (H5N1, clade 2.2).

No abstract

No abstract

Avian influenza viruses remain a major pandemic threat. In response to this threat, a number of pandemic vaccines have been developed. The objective of this paper is to review and summarize data from preclinical and clinical evaluation of Russian live attenuated influenza vaccines (LAIVs) against pandemic influenza based on cold-adapted A/Leningrad/134/17/57 (H2N2) master donor virus (MDV). The described LAIVs consist of reassortant viruses of 6:2 and 7:1 genomic composition (6 MDV genes: 2 WT genes and 7 MDV genes: 1 WT gene, respectively). Despite the differences in their genomic composition (6:2 or 7:1), LAIV candidates of H5, H7 and H2 subtypes acquired temperature sensitivity, cold-adaptation, and attenuation for different animal models. In addition, they were safe and immunogenic for healthy adult volunteers. The collected data indicate that 7:1 reassortants carrying HA genes of potentially pandemic viruses and the remaining genes from the MDV might be preferable pandemic LAIV candidates.