Published data and authors' original material on the use of temperaturesensitive influenza virus mutants (ts) as donors in attenuation process aimed at obtaining the recombinant live influenza vaccines (LIV) are reviewed. The so called cold adapted ts donors are shown to be superior for this aim. The data are presented in the review on the association of the mutations in the genome of cold adapted donors with attenuation, on the reactivity, immunogenicity and genetical stability of the recombinant LIVs constructed on the basis of the cold adapted donors.
The reactogenicity and immunizing activity of vaccine influenza virus A (H1N1) and B strains used as mono- and bi-preparations in children of 3 to 14 years was studied. No increased reactogenicity after the use of bivaccine was observed in the children. Febrile reactions as well as 9 other clinical symptoms which could indicate the reactogenicity of the vaccines were identical for mono- and bivaccine and corresponded to the requirements of the technical documents for the vaccine. The optimal conditions for the evaluation of the immunogenicity of the B component by HI test were developed, and the necessity of using additionally the enzyme immunoassay for this purpose is substantiated. The above method demonstrated that the immunogenicity of the live influenza type A and B vaccine was high in children. No significant inhibition of immunological parameters was observed when the two viruses were combined in the bivaccine.
The informativity of RCT40, RCT37.5, and RCT25 markers for differentiation of wild type strains from ca-recombinants obtained on the basis of ca donors of attenuation was studied. The RCT25 marker and express RCT37.5 marker (determined within 24 hours) were found to be universal characteristics differentiating ca-recombinants from virulent viruses.
Using mutants of fowl plague virus (FRV) which have single temperature-sensitive (ts) mutations in some genes, an analysis was carried out on reisolates from children of 3-6 years, vaccinated with a monovaccine from recombinant strains of influenza type A virus. The recombinants were obtained by crossing of current epidemic strains of subtypes A (HINI) and a (H3N2) with the cold-adapted (XA) ts-donor of attenuation A/Leningrad/134/47/57 (H2N2) from which they, as a rule, inherited 5 ts-mutations in genes 1 (PB2), 2 (PB1), 5 (NP), 7 (M), and 8 (NS). All the reisolates were shown to retain the ts-phenotype. However, in the recombination test some reisolates (most frequently those isolated at late periods of vaccination infection) no ts-mutations could be found in 1-3 genes coding for proteins of the polymerase complex, less frequently for NP and NS proteins but not for M proteins.
The influenza A/Leningrad/134/47/57 (H2N2) (A/Len/47) cold-adapted virus expresses the ability to reproduce at 25 degrees C (the ca phenotype) and inability to reproduce at 40 degrees C (the ts phenotype). It was attenuated for mice. Reassortants of this donor virus with the genes coding for the surface glycoproteins from the epidemic viruses, i.e. hemagglutinin (HA) and neuraminidase (NA), have been shown to be attenuated, immunogenic and genetically stable. We made attempts to reveal the influence of individual genes from the A/Len/47 ca virus on the expression of some phenotypic properties. Different "single-gene" reassortants were created and investigated using the influenza A/PR/8/34 (H1N1) virus as another parent with the opposite phenotypic properties, i.e. lack of ca+ and ts+ phenotypes and high virulence for mice. We managed to obtain "single-gene" reassortants with PB1, NA and NS genes at this stage of the work. None of them (probably including the M gene as well) could determine the ca or ts phenotypes, nor could the presence of the NA and NS genes from the strain A/Len/47 influence these properties. However, our findings show that the combined influence (synergism) of the PB1 and NS genes from the ca donors results in the ts phenotype of the reassortants. Significant role of the NS gene for attenuation of influenza viruses in mice has been revealed.
