TEMPERATURE-SENSITIVE MUTANTS OF INFLUENZA-VIRUS .15. GENETIC AND BIOLOGICAL CHARACTERIZATION OF A RECOMBINANT INFLUENZA-VIRUS CONTAINING 2-TS LESIONS PRODUCED BY MATING 2 COMPLEMENTING, SINGLE LESION TS MUTANTS

The influenza A/Hong Kong/68-ts-1[E] virus and its recombinants (38° shutoff temperature for plaque formation) were satisfactorily attenuated for individuals with neuraminidase immunity who lacked serum antibody for hemagglutinin antigen but not for persons who lacked immunity to both viral surface antigens, i.e., doubly seronegative individuals. It was necessary to produce a virus more defective than the Hong Kong/68-ts-1[E] virus to meet the need for an attenuated virus suitable for use in doubly seronegative persons. We produced a new recombinant which contained a ts mutation(s) on the genes believed to code for the Pl and P3 viral proteins, both of which are involved in cRNA synthesis. This recombinant was produced by mating two complementing ts mutants, one with a mutation affecting the Pl protein and the other with a mutation affecting the P3 protein. The new double ts recombinant, the Udorn/72-ts-1A2 virus, was 700-fold more restricted in plaque formation at 37° than either of its ts parents. In addition, it was defective in complementation-recombination when tested against prototypes of seven complementation groups. The Udorn/72-ts-1A2 recombinant failed to replicate in the hamster's lungs (37°) and was 100-fold restricted in its growth in the nasal turbinates (32°). Each of the isolates from Udorn/72-ts-1A2 infected hamsters was ts. Despite restricted replication in vivo, infection of hamsters with this virus induced significant resistance to wild-type virus challenge. Thus, the Udorn/72-ts-1A2 recombinant was (1) more restricted in replication in vitro at 37° and in vivo in the hamster and (2) more stable genetically in vivo than the HK/68-ts-1[E] virus. © 1978.