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Journal of Virology, November 2002, p. 10627-10636, Vol. 76, No. 21
0022-538X/02/$04.00+0 DOI: 10.1128/JVI.76.21.10627-10636.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Egbert Flory,1 Stefanie Steidl,1 Jeanette Neumann,1 Cheick Coulibaly,1 Edgar Holznagel,1 Silke Holzammer,2 Stephen Norley,2 and Klaus Cichutek1*
Department of Medical Biotechnology, Paul-Ehrlich-Institut, 63225 Langen,1 Robert-Koch-Institut, 13353 Berlin, Germany2
Received 2 April 2002/ Accepted 24 July 2002
During human immunodeficiency virus type 1 (HIV-1) infection, disease progression correlates with the occurrence of variants using the coreceptor CXCR4 for cell entry. In contrast, apathogenic simian immunodeficiency virus (SIV) from African green monkeys (SIVagm), specifically the molecular virus clone SIVagm3mc, uses CCR5, Bob, and Bonzo as coreceptors throughout the course of infection. The influence of an altered coreceptor usage on SIVagm3mc replication was studied in vitro and in vivo. The putative coreceptor binding domain, the V3 region of the surface envelope (SU) glycoprotein, was replaced by the V3 loop of a CD4- and CXCR4-tropic HIV-1 strain. The resulting virus, termed SIVagm3-X4mc, exclusively used CD4 and CXCR4 for cell entry. Consequently, its in vitro replication was inhibited by SDF-1, the natural ligand of CXCR4. Surprisingly, SIVagm3-X4mc was able to replicate in vitro not only in interleukin-2- and phytohemagglutinin-stimulated but also in nonstimulated peripheral blood mononuclear cells (PBMCs) from nonhuman primates. After experimental infection of two pig-tailed macaques with either SIVagm3-X4mc or SIVagm3mc, the coreceptor usage was maintained during in vivo replication. Cell-associated and plasma viral loads, as well as viral DNA copy numbers, were found to be comparable between SIVagm3mc and SIVagm 3-X4mc infections, and no pathological changes were observed up to 14 months postinfection. Interestingly, the V3 loop exchange rendered SIVagm3-X4mc susceptible to neutralizing antibodies present in the sera of SIVagm3-X4mc- and SIVagm3mc-infected pig-tailed macaques. Our study describes for the first time a successful exchange of a V3 loop in nonpathogenic SIVagm resulting in CD4 and CXCR4 usage and modulation of virus replication in nonstimulated PBMCs as well as sensitivity toward neutralization.
Present address: Infectious Disease Laboratory, The Salk Institute, La Jolla, CA 92037.
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