Dataset Information

Immunogenicity of Stabilized HIV-1 Envelope Trimers with Reduced Exposure of Non-neutralizing Epitopes.

ABSTRACT: The envelope glycoprotein trimer mediates HIV-1 entry into cells. The trimer is flexible, fluctuating between closed and more open conformations and sometimes sampling the fully open, CD4-bound form. We hypothesized that conformational flexibility and transient exposure of non-neutralizing, immunodominant epitopes could hinder the induction of broadly neutralizing antibodies (bNAbs). We therefore modified soluble Env trimers to stabilize their closed, ground states. The trimer variants were indeed stabilized in the closed conformation, with a reduced ability to undergo receptor-induced conformational changes and a decreased exposure of non-neutralizing V3-directed antibody epitopes. In rabbits, the stabilized trimers induced similar autologous Tier-1B or Tier-2 NAb titers to those elicited by the corresponding wild-type trimers but lower levels of V3-directed Tier-1A NAbs. Stabilized, closed trimers might therefore be useful components of vaccines aimed at inducing bNAbs.

SUBMITTER: de Taeye SW

PROVIDER: S-EPMC4732737 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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Publications

Immunogenicity of Stabilized HIV-1 Envelope Trimers with Reduced Exposure of Non-neutralizing Epitopes.

de Taeye Steven W SW Ozorowski Gabriel G Torrents de la Peña Alba A Guttman Miklos M Julien Jean-Philippe JP van den Kerkhof Tom L G M TL Burger Judith A JA Pritchard Laura K LK Pugach Pavel P Yasmeen Anila A Crampton Jordan J Hu Joyce J Bontjer Ilja I Torres Jonathan L JL Arendt Heather H DeStefano Joanne J Koff Wayne C WC Schuitemaker Hanneke H Eggink Dirk D Berkhout Ben B Dean Hansi H LaBranche Celia C Crotty Shane S Crispin Max M Montefiori David C DC Klasse P J PJ Lee Kelly K KK Moore John P JP Wilson Ian A IA Ward Andrew B AB Sanders Rogier W RW

Cell 20151201 7

The envelope glycoprotein trimer mediates HIV-1 entry into cells. The trimer is flexible, fluctuating between closed and more open conformations and sometimes sampling the fully open, CD4-bound form. We hypothesized that conformational flexibility and transient exposure of non-neutralizing, immunodominant epitopes could hinder the induction of broadly neutralizing antibodies (bNAbs). We therefore modified soluble Env trimers to stabilize their closed, ground states. The trimer variants were inde ...[more]

PMID: 26687358

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Project description:The trimeric envelope spikes on the HIV-1 virus surface initiate infection and comprise key targets for antiviral humoral responses. Circulating virions variably present intact envelope spikes, which react with neutralizing antibodies; and altered envelope structures, which bind non-neutralizing antibodies. Once bound, either type of antibody can enable humoral effector mechanisms with the potential to control HIV-1 infection in vivo. However, it is not clear how the presentation of neutralizing vs. non-neutralizing epitopes defines distinct virus populations and/or envelope structures on single particles. Here we used single-virion fluorescence correlation spectroscopy (FCS), fluorescence resonance energy transfer (FRET), and two-color coincidence FCS approaches to examine whether neutralizing and non-neutralizing antibodies are presented by the same envelope structure. Given the spatial requirements for donor-acceptor energy transfer (≤10 nm), FRET signals generated by paired neutralizing and non-neutralizing fluorescent Fabs should occur via proximal binding to the same target antigen. Fluorescent-labeled Fabs of the neutralizing anti-gp120 antibodies 2G12 and b12 were combined with Fabs of the non-neutralizing anti-gp41 antibody F240, previously thought to mainly bind gp41 "stumps." We find that both 2G12-F240 and/or b12-F240 Fab combinations generate FRET signals on multiple types of virions in solution. FRET efficiencies position the neutralizing and non-neutralizing epitopes between 7.1 and 7.8 nm apart; potentially fitting within the spatial dimensions of a single trimer-derived structure. Further, the frequency of FRET detection suggests that at least one of such structures occurs on the majority of particles in a virus population. Thus, there is frequent, overlapping presentation of non-neutralizing and neutralizing epitope on freely circulating HIV-1 surfaces. Such information provides a broader perspective of how anti-HIV humoral immunity interfaces with circulating virions.

Project description:The immunogenicity of gp41-stabilized HIV-1 BG505 envelope (Env) trimers and nanoparticles (NPs) was recently assessed in mice and rabbits. Here, we combined Env-specific B-cell sorting and repertoire sequencing to identify neutralizing antibodies (NAbs) from immunized animals. A panel of mouse NAbs was isolated from mice immunized with a 60-meric I3-01 NP presenting 20 stabilized trimers. Three mouse NAbs potently neutralized BG505.T332N by recognizing a glycan epitope centered in the C3/V4 region on BG505 Env, as revealed by electron microscopy (EM), X-ray crystallography, and epitope mapping. A set of rabbit NAbs was isolated from rabbits immunized with a soluble trimer and a 24-meric ferritin NP presenting 8 trimers. Neutralization assays against BG505.T332N variants confirmed that potent rabbit NAbs targeted previously described glycan holes on BG505 Env and accounted for a significant portion of the autologous NAb response in both the trimer and ferritin NP groups. Last, we examined NAb responses that were induced by non-BG505 Env immunogens. We determined a 3.4-Å-resolution crystal structure for the clade C transmitted/founder (T/F) Du172.17 Env with a redesigned heptad repeat 1 (HR1) bend in gp41. This clade C Env, in a soluble trimer form and in a multivalent form with 8 trimers attached to ferritin NP, and the gp41-stabilized clade A Q482-d12 Env trimer elicited distinct NAb responses in rabbits, with notable differences in neutralization breadth. Although eliciting a broad NAb response remains a major challenge, our study provides valuable information on an HIV-1 vaccine design strategy that combines gp41 stabilization and NP display. IMPORTANCE Self-assembling protein nanoparticles (NPs) presenting BG505 envelope (Env) trimers can elicit tier 2 HIV-1-neutralizing antibody (NAb) responses more effectively than soluble trimers. In the present study, monoclonal NAbs were isolated from previously immunized mice and rabbits for structural and functional analyses, which revealed that potent mouse NAbs recognize the C3/V4 region and small NP-elicited rabbit NAbs primarily target known glycan holes on BG505 Env. This study validates the gp41 stabilization strategy for HIV-1 Env vaccine design and highlights the challenge in eliciting a broad NAb response.

Dataset Information

Immunogenicity of Stabilized HIV-1 Envelope Trimers with Reduced Exposure of Non-neutralizing Epitopes.

Publications

Immunogenicity of Stabilized HIV-1 Envelope Trimers with Reduced Exposure of Non-neutralizing Epitopes.

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