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J. Virol., Jan 1998, 405-414, Vol 72, No. 1
P Edmonson, M Murphey-Corb, LN Martin, C Delahunty, J Heeney, H Kornfeld, PR Donahue, GH Learn, L Hood and JI Mullins
Analysis of disease induction by simian immunodeficiency viruses (SIV) in
macaques was initially hampered by a lack of molecularly defined pathogenic
strains. The first molecularly cloned SIV strains inoculated into macaques,
SIVmacBK28 and SIVmacBK44 (hereafter designated BK28 and BK44,
respectively), were cases in point, since they failed to induce disease
within 1 year postinoculation in any inoculated animal. Here we report the
natural history of infection with BK28 and BK44 in inoculated rhesus
macaques and efforts to increase the pathogenicity of BK28 through genetic
manipulation and in vivo passage. BK44 infection resulted in no disease in
four animals infected for more than 7 years, whereas BK28 induced disease
in less than half of animals monitored for up to 7 years. Elongation of the
BK28 transmembrane protein (TM) coding sequence truncated by prior passage
in human cells marginally increased pathogenicity, with two of four animals
dying in the third year and one dying in the seventh year of infection.
Modification of the BK28 long terminal repeat to include four consensus
nuclear factor SP1 and two consensus NF-kappaB binding sites enhanced early
virus replication without augmenting pathogenicity. In contrast, in vivo
passage of BK28 from the first animal to die from immunodeficiency disease
(1.5 years after infection) resulted in a consistently pathogenic strain
and a 50% survival time of about 1.3 years, thus corresponding to one of
the most pathogenic SIV strains identified to date. To determine whether
the diverse viral quasispecies that evolved during in vivo passage was
required for pathogenicity or whether a more virulent virus variant had
evolved, we generated a molecular clone composed of the 3' half of the
viral genome derived from the in vivo-passaged virus (H824) fused with the
5' half of the BK28 genome. Kinetics of disease induction with this cloned
virus (BK28/H824) were similar to those with the in vivo- passaged virus,
with four of five animals surviving less than 1.7 years. Thus, evolution of
variants with enhanced pathogenicity can account for the increased
pathogenicity of this SIV strain. The genetic changes responsible for this
virulent transformation included at most 59 point mutations and 3
length-change mutations. The critical mutations were likely to have been
multiple and dispersed, including elongation of the TM and Nef coding
sequences; changes in RNA splice donor and acceptor sites, TATA box sites,
and Sp1 sites; multiple changes in the V2 region of SU, including a
consensus neutralization epitope; and five new N-linked glycosylation sites
in SU.
Copyright © 1998, American Society for Microbiology
Evolution of a simian immunodeficiency virus pathogen
Department of Pathology, University of Washington, Seattle 98195-7740, USA.
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