Temperature sensitive mutants of influenza virus: IX. Genetic and biological characterization of ts-1[E] lesions when transferred to a 1972 (H3N2) influenza A virus

Abstract

The temperature-sensitive ( ts) mutant recombinant influenza A/Hong Kong/1968- ts-1[E] (H3N2) previously was shown to possess properties desirable for a live attenuated vaccine. We investigated the regularity of transfer of these desirable properties by recombination to a newly emerged wild-type influenza A (H3N2) variant, A/Udorn/307/1972. Examination of Udorn/72- ts-1[E] recombinant clones confirmed that the ts-1[E] donor contained two independently segregating ts lesions, each of which segregated independently of the hemagglutinin and neuraminidase genes. Transfer of both of these ts lesions to a new recombinant was associated with a specific shutoff temperature in vitro of 38°, a moderate restriction of growth in the respiratory tract of hamsters, and infrequent reversion to ts+ phenotype in vivo. The absence of one of the two ts lesions in a Udorn/72- ts-1[E] recombinant clone resulted in a higher in vitro shutoff temperature (39°), less growth restriction in hamsters, and less genetic stability with regard to reversion to the ts+ phenotype. These results supported the hypothesis that well-defined ts lesions can be utilized as specific markers of attenuation which can be transferred to new, potentially epidemic, antigenic variants of influenza A virus.