title: Simian immunodeficiency virus engrafted with human immunodeficiency virus type 1 (HIV-1)-specific epitopes: replication, neutralization, and survey of HIV-1-positive plasma.
abstract: To date, only a small number of anti-human immunodeficiency virus type 1 (HIV-1) monoclonal antibodies (MAbs) with relatively broad neutralizing activity have been isolated from infected individuals. Adequate techniques for defining how frequently antibodies of these specificities arise in HIV-infected people have been lacking, although it is generally assumed that such antibodies are rare. In order to create an epitope-specific neutralization assay, we introduced well-characterized HIV-1 epitopes into the heterologous context of simian immunodeficiency virus (SIV). Specifically, epitope recognition sequences for the 2F5, 4E10, and 447-52D anti-HIV-1 neutralizing monoclonal antibodies were introduced into the corresponding regions of SIVmac239 by site-directed mutagenesis. Variants with 2F5 or 4E10 recognition sequences in gp41 retained replication competence and were used for neutralization assays. The parental SIVmac239 and the neutralization-sensitive SIVmac316 were not neutralized by the 2F5 and 4E10 MAbs, nor were they neutralized significantly by any of the 96 HIV-1-positive human plasma samples that were tested. The SIV239-2F5 and SIV239-4E10 variants were specifically neutralized by the 2F5 and 4E10 MAbs, respectively, at concentrations within the range of what has been reported previously for HIV-1 primary isolates (J. M. Binley et al., J. Virol. 78:13232-13252, 2004). The SIV239-2F5 and SIV239-4E10 epitope-engrafted variants were used as biological screens for the presence of neutralizing activity of these specificities. None of the 92 HIV-1-positive human plasma samples that were tested exhibited significant neutralization of SIV239-2F5. One plasma sample exhibited >90% neutralization of SIV239-4E10, but this activity was not competed by a 4E10 target peptide and was not present in concentrated immunoglobulin G (IgG) or IgA fractions. We thus confirm by direct analysis that neutralizing activities of the 2F5 and 4E10 specificities are either rare among HIV-1-positive individuals or, if present, represent only a very small fraction of the total neutralizing activity in any given plasma sample. We further conclude that the structures of gp41 from SIVmac239 and HIV-1 are sufficiently similar such that epitopes engrafted into SIVmac239 can be readily recognized by the cognate anti-HIV-1 monoclonal antibodies.
authors.affiliation: New England Primate Research Center, Department of Microbiology and Molecular Genetics, Harvard Medical Scool, One Pine Hill Drive, Box 9102, Southborough, Massachusetts 01772-9102, USA.
authors.forename: Eloisa
authors.initials: E
authors.lastname: Yuste
authors.forename: Hannah B
authors.initials: HB
authors.lastname: Sanford
authors.forename: Jill
authors.initials: J
authors.lastname: Carmody
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Bixby
authors.forename: Susan
authors.initials: S
authors.lastname: Little
authors.forename: Michael B
authors.initials: MB
authors.lastname: Zwick
authors.forename: Tom
authors.initials: T
authors.lastname: Greenough
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Burton
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Richman
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Desrosiers
authors.forename: Welkin E
authors.initials: WE
authors.lastname: Johnson
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D002460:Cell Line; D000939:Epitopes / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D015483:HIV Antibodies / Q000097:blood*; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D015658:HIV Infections / Q000276:immunology / Q000821:virology; D015497:HIV-1 / Q000737:chemistry / Q000276:immunology; D006801:Humans; D009500:Neutralization Tests; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology*; D015302:Simian Immunodeficiency Virus / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D014779:Virus Replication
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; C059762:HIV envelope protein gp120 (305-321); D010446:Peptide Fragments