LOSS OF THE SIVSMMPBJ14 PHENOTYPE AND NEF GENOTYPE DURING LONG-TERM SURVIVAL OF MACAQUES INFECTED BY MUCOSAL ROUTES

The ability of the simian immunodeficiency virus SIVsmmPBj14 (SIV-PBj1 4) to activate and induce proliferation of quiescent peripheral blood lymphocytes from macaques is an in vitro correlate of its acutely leth al in vivo phenotype. SIV-PBj14 differs from other SIV strains by enco ding tyrosine at amino acid 17 (Y17) in Nef, which generates an activa tion motif important for signal transduction. Although intravenous ino culation of pig-tailed macaques with SIV-PBj14 uniformly leads to deat h within 2 weeks, inoculation by mucosal routes results in persistent infections that progress to AIDS. In the present study, we determined whether viruses in long-term survivors retained not only the Nef Y17 r esidue but also the biologic properties associated with rapid disease and death. Viruses reisolated at early and late times after mucosal in fection of macaques with SIV-PBj14 were tested in vivo for acute letha lity and in vitro for the ability to replicate In and induce activatio n and proliferation of quiescent macaque lymphocytes. In addition, the coding sequence for the first 55 amino acids in Nef was amplified fro m proviral DNA or plasma virion RNA by PCR or RT-PCR, respectively, an d nucleotide sequences were obtained. The results showed that the majo rity of the quasispecies that: persisted as disease progressed not onl y lost biological properties unique to SIV-PBj14, but also lost throug h mutation either Y17 or Y28 in Nef, which together were part of the a ctivation motif. In the case of Y17, these mutations were stepwise to histidine then arginine, the amino acid encoded in this position in ot her SIV strains. We conclude, therefore, that replicative properties o f the acutely lethal virus provide no selective advantage during long- term infections with SIV-PBj14 and that disruption of the activation m otif in Nef is associated with loss of the acutely lethal phenotype. ( C) 1997 Academic Press.