Linda S. Richardson

Isolation and characterization of further defective clones of a temperature sensitive mutant (ts-1) of respiratory syncytial virus

SummaryAfter exposure of the temperature sensitivets-1 mutant of respiratory syncytial virus to the chemical mutagen, nitrosoguanidine (NG), 2 clones of virus were recovered which were more temperature sensitive and stable genetically than thets-1 mutant. The initial criterion used for selection of the 2 clones was decreased ability to produce plaques at 36° C. Subsequently it was shown that the 2 clones grew less well at the restrictive temperatures of 37° and 38° C than did thets-1 parent. Peak titers of the NG derived clones were decreased 10–30 told at 37° C and over 100-fold at 38° C compared tots-1. Complementation analysis indicated that the NG mutants retained the same complementation pattern as thets-1 parent.

Growth and genetic stability of 4 temperature sensitive (ts) mutants of respiratory syncytial (RS) virus in newborn ferrets.

SummaryFour temperature sensitive(ts) mutants of respiratory syncytial (RS) virus were evaluated for growth and genetic stability in newborn ferrets.ts-1, the mutant previously tested in children as a possible live virus vaccine and found to be insufficiently attenuated for the upper respiratory tract, grew in the lungs of newborn ferrets to the same peak titer as wild type RS virus. In addition some genetic alteration of thets-1 mutant occurred. Two more defective subclones ofts-1,ts-1 NG-1 andts-1 NG-16, were greatly restricted in growth in the ferrets lungs.ts-1 NG-16 was also restricted in the nasal turbinates, butts-1 NG-1 grew to high titer in the nasal turbinates. Growth ofts-1 NG-1, however, was delayed 2 weeks compared to the growth of wild type virus. Genetic alteration occurred during growth of either subclone; the virus isolated was intermediate between wild type and input virus in plaque forming ability at restrictive temperatures. In no instance was wild type virus isolated from the ferrets infected with either subclone.ts-2, a plaque morphology mutant that does not fuse cells to form syncytia even at the permissive temperature of 32° C, was restricted in growth in both the lungs and nasal turbinates, and genetically altered virus was not recovered from these animals. Of the mutants tested,ts-2 was the most restricted mutant in the newborn ferret and should be evaluated further as a candidate vaccine virus.

CURRENT APPROACHES TO VIRAL IMMUNOPROPHYLAXIS

Publisher Summary This chapter discusses the current approaches to viral immunoprophylaxis. Virulence is the result of the efficient functioning of a number of different steps in the replicative cycle. Interference with any of these can lead to reduction in virulence. Thus, attenuated strains produced by genetic recombination presumably contain one or more genes derived from the attenuated parent and this gene or these genes limit replication of the recombinant virus in man. There is considerable experimental evidence that supports the polygenic nature of virulence of influenza virus. Accordingly, attenuation of influenza virus by recombination is thought to result from a redistribution of avirulent and virulent genes from the two parental viruses. The biological basis for attenuation of serum inhibitor–resistant influenza A viruses is yet to be understood. Presumably, inhibitor–resistant viruses undergo a mutation in the gene which codes for the surface glycoprotein that is responsible for hemagglutination.