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.The presumed rarity of broadly reactive, human immunodeficiency virus type 1 (HIV-1)-specific neutralizing antibodies in the plasma of HIV-positive individuals arises from the observation that very few monoclonal antibodies (MAbs) with such activity have been isolated since HIV-1 was first characterized 20 years ago. Among the small number of well-characterized, broadly neutralizing anti-HIV-1 MAbs, three recognize distinct elements of the gp120 subunit of envelope, including the CD4 binding site (b12), specific glycans on the surface of gp120 (2G12), and the V3 loop (447-52D) (32,47). In contrast, three other MAbs (2F5, 4E10, and Z13) recognize determinants clustered within a single 30-amino-acid str...

Antigenic and Immunogenic Study of Membrane-Proximal External Region-Grafted gp120 Antigens by a DNA Prime-Protein Boost Immunization Strategy

“…5 and 8B). Yuste et al screened 92 HIV-positive plasma samples from 47 different patients in neutralizing 4E10 epitopeengrafted SIV and found that only 4 samples possessed anti-4E10 epitope activity (73). This study highlights the fact that the 4E10 epitope is poorly immunogenic in natural infections.…”

Human Immunodeficiency Virus Type 2 (HIV-2)/HIV-1 Envelope Chimeras Detect High Titers of Broadly Reactive HIV-1 V3-Specific Antibodies in Human Plasma

“…Previously, we along with others have demonstrated that HIV-2 Env could be used as a scaffold to present HIV-1 MPER and CD4i epitopes in the context of a functional glycoprotein and that such viruses could serve as sensitive and specific probes for HIV-1-elicited epitope-specific NAbs (18,19,34,61,102 In the present study, we focused on HIV-1 V3, which continues to attract substantial attention as a target of NAbs (2,54,72,74,76,99,107). Mamounas and colleagues first demonstrated that a chimeric virus containing an HIV-2 backbone and an HIV-1 MN V3 loop was capable of infecting human T cells and showed susceptibility to HIV-1 V3-specific antiserum (64).…”

Generation of a neutralization-resistant CCR5 tropic simian/human immunodeficiency virus (SHIV-MK38) molecular clone, a derivative of SHIV-89.6

“…Although SIV is an excellent model of HIV-1, homology of the env gene between SIV and HIV-1 is low (Yuste et al, 2006), and consequently reciprocal neutralizing antibodies do not show cross-reactivity (Javaherian et al, 1992). Thus, an important limitation of the SIV/macaque model is that the protective effects of neutralizing antibodies against HIV-1 cannot be examined.…”