title: Simian immunodeficiency virus promoter exchange results in a highly attenuated strain that protects against uncloned challenge virus.
abstract: Among the many simian immunodeficiency virus (SIV) immunogens, only live attenuated viral vaccines have afforded strong protection to a natural pathogenic isolate. Since the promoter is crucial to the tempo of viral replication in general, it was reasoned that promoter exchange might confer a novel means of attenuating SIV. The core enhancer and promoter sequences of the SIV macaque 239nefstop strain (NF-kappaB/Sp1 region from -114 bp to mRNA start) have been exchanged for those of the human cytomegalovirus immediate-early promoter (CMV-IE; from -525 bp to mRNA start). During culture of the resulting virus, referred to as SIVmegalo, on CEMx174 or rhesus macaque peripheral blood mononuclear cells, deletions arose in distal regions of the CMV-IE sequences that stabilized after 1 or 2 months of culture. However, when the undeleted form of SIVmegalo was inoculated into rhesus macaques, animals showed highly controlled viremia during primary and persistent infection. Compared to parental virus infection in macaques, primary viremia was reduced by >1,000-fold to undetectable levels, with little sign of an increase of cycling cells in lymph nodes, CD4(+) depletion, or altered T-cell activation markers in peripheral blood. Moreover, in contrast to wild-type infection in most infected animals, the nef stop mutation did not revert to the wild-type codon, indicating yet again that replication was dramatically curtailed. Despite such drastic attenuation, antibody titers and enzyme-linked immunospot reactivity to SIV peptides, although slower to appear, were comparable to those seen in a parental virus infection. When animals were challenged intravenously at 4 or 6 months with the uncloned pathogenic SIVmac251 strain, viremia was curtailed by approximately 1,000-fold at peak height without any sign of hyperactivation in CD4(+)- or CD8(+)-T-cell compartment or increase in lymph node cell cycling. To date, there has been a general inverse correlation between attenuation and protection; however, these findings show that promoter exchange constitutes a novel means to highly attenuate SIV while retaining the capacity to protect against challenge virus.
authors.affiliation: Unité de Rétrovirologie Moléculaire. Unité de Physiopathologie des Infections Lentivirales, Institut Pasteur, 75724 Paris Cedex 15, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Blancou
authors.forename: Nicole
authors.initials: N
authors.lastname: Chenciner
authors.forename: Raphaël
authors.initials: R
authors.lastname: Ho Tsong Fang
authors.forename: Valérie
authors.initials: V
authors.lastname: Monceaux
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Cumont
authors.forename: Denise
authors.initials: D
authors.lastname: Guétard
authors.forename: Bruno
authors.initials: B
authors.lastname: Hurtrel
authors.forename: Simon
authors.initials: S
authors.lastname: Wain-Hobson
mesh_terms: D016915:AIDS Vaccines / Q000008:administration & dosage / Q000276:immunology; D000818:Animals; D001483:Base Sequence; D003587:Cytomegalovirus / Q000235:genetics; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D008253:Macaca mulatta; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D018449:SAIDS Vaccines / Q000008:administration & dosage / Q000276:immunology; D016097:Simian Acquired Immunodeficiency Syndrome / Q000276:immunology / Q000517:prevention & control*; D015302:Simian Immunodeficiency Virus / Q000235:genetics / Q000276:immunology / Q000472:pathogenicity*; D020079:Terminal Repeat Sequences / Q000235:genetics; D014613:Vaccines, Attenuated / Q000008:administration & dosage* / Q000276:immunology; D014766:Viremia / Q000276:immunology / Q000517:prevention & control; D014779:Virus Replication
chemical_list: D016915:AIDS Vaccines; D017874:Immediate-Early Proteins; D011993:Recombinant Fusion Proteins; D018449:SAIDS Vaccines; D014613:Vaccines, Attenuated