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      A Next-Generation Cleaved, Soluble HIV-1 Env Trimer, BG505 SOSIP.664 gp140, Expresses Multiple Epitopes for Broadly Neutralizing but Not Non-Neutralizing Antibodies

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          Abstract

          A desirable but as yet unachieved property of a human immunodeficiency virus type 1 (HIV-1) vaccine candidate is the ability to induce broadly neutralizing antibodies (bNAbs). One approach to the problem is to create trimeric mimics of the native envelope glycoprotein (Env) spike that expose as many bNAb epitopes as possible, while occluding those for non-neutralizing antibodies (non-NAbs). Here, we describe the design and properties of soluble, cleaved SOSIP.664 gp140 trimers based on the subtype A transmitted/founder strain, BG505. These trimers are highly stable, more so even than the corresponding gp120 monomer, as judged by differential scanning calorimetry. They are also homogenous and closely resemble native virus spikes when visualized by negative stain electron microscopy (EM). We used several techniques, including ELISA and surface plasmon resonance (SPR), to determine the relationship between the ability of monoclonal antibodies (MAbs) to bind the soluble trimers and neutralize the corresponding virus. In general, the concordance was excellent, in that virtually all bNAbs against multiple neutralizing epitopes on HIV-1 Env were highly reactive with the BG505 SOSIP.664 gp140 trimers, including quaternary epitopes (CH01, PG9, PG16 and PGT145). Conversely, non-NAbs to the CD4-binding site, CD4-induced epitopes or gp41 ECTO did not react with the trimers, even when their epitopes were present on simpler forms of Env (e.g. gp120 monomers or dissociated gp41 subunits). Three non-neutralizing MAbs to V3 epitopes did, however, react strongly with the trimers but only by ELISA, and not at all by SPR and to only a limited extent by EM. These new soluble trimers are useful for structural studies and are being assessed for their performance as immunogens.

          Author Summary

          A protective HIV-1 vaccine is badly needed, but no candidate has yet provided an adequate level of protection against infection. Most existing vaccines provide immune protection by inducing neutralizing antibodies, also a goal of many HIV-1 immunogen design projects. The trimeric envelope protein complex on the HIV-1 surface is the only relevant target for neutralizing antibodies, and is the basis for most strategies aimed at their induction. However, making a soluble, recombinant envelope protein complex that adequately mimics the structure present on the virus has been challenging. Here, we describe a newly designed and engineered Env protein that has the appropriate properties. This protein, termed BG505 SOSIP.664 gp140, binds most of the known neutralizing antibodies but generally does not bind antibodies that lack neutralization activity. Its appearance in negative stain electron micrographs also resembles native envelope complexes.

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          Most cited references67

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          Molecular architecture of native HIV-1 gp120 trimers.

          The envelope glycoproteins (Env) of human and simian immunodeficiency viruses (HIV and SIV, respectively) mediate virus binding to the cell surface receptor CD4 on target cells to initiate infection. Env is a heterodimer of a transmembrane glycoprotein (gp41) and a surface glycoprotein (gp120), and forms trimers on the surface of the viral membrane. Using cryo-electron tomography combined with three-dimensional image classification and averaging, we report the three-dimensional structures of trimeric Env displayed on native HIV-1 in the unliganded state, in complex with the broadly neutralizing antibody b12 and in a ternary complex with CD4 and the 17b antibody. By fitting the known crystal structures of the monomeric gp120 core in the b12- and CD4/17b-bound conformations into the density maps derived by electron tomography, we derive molecular models for the native HIV-1 gp120 trimer in unliganded and CD4-bound states. We demonstrate that CD4 binding results in a major reorganization of the Env trimer, causing an outward rotation and displacement of each gp120 monomer. This appears to be coupled with a rearrangement of the gp41 region along the central axis of the trimer, leading to closer contact between the viral and target cell membranes. Our findings elucidate the structure and conformational changes of trimeric HIV-1 gp120 relevant to antibody neutralization and attachment to target cells.
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            Sensitivity of human immunodeficiency virus type 1 to the fusion inhibitor T-20 is modulated by coreceptor specificity defined by the V3 loop of gp120.

            T-20 is a synthetic peptide that potently inhibits replication of human immunodeficiency virus type 1 by interfering with the transition of the transmembrane protein, gp41, to a fusion active state following interactions of the surface glycoprotein, gp120, with CD4 and coreceptor molecules displayed on the target cell surface. Although T-20 is postulated to interact with an N-terminal heptad repeat within gp41 in a trans-dominant manner, we show here that sensitivity to T-20 is strongly influenced by coreceptor specificity. When 14 T-20-naive primary isolates were analyzed for sensitivity to T-20, the mean 50% inhibitory concentration (IC(50)) for isolates that utilize CCR5 for entry (R5 viruses) was 0.8 log(10) higher than the mean IC(50) for CXCR4 (X4) isolates (P = 0. 0055). Using NL4.3-based envelope chimeras that contain combinations of envelope sequences derived from R5 and X4 viruses, we found that determinants of coreceptor specificity contained within the gp120 V3 loop modulate this sensitivity to T-20. The IC(50) for all chimeric envelope viruses containing R5 V3 sequences was 0.6 to 0.8 log(10) higher than that for viruses containing X4 V3 sequences. In addition, we confirmed that the N-terminal heptad repeat of gp41 determines the baseline sensitivity to T-20 and that the IC(50) for viruses containing GIV at amino acid residues 36 to 38 was 1.0 log(10) lower than the IC(50) for viruses containing a G-to-D substitution. The results of this study show that gp120-coreceptor interactions and the gp41 N-terminal heptad repeat independently contribute to sensitivity to T-20. These results have important implications for the therapeutic uses of T-20 as well as for unraveling the complex mechanisms of virus fusion and entry.
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              HIV vaccine design and the neutralizing antibody problem.

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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS Pathog
                PLoS Pathog
                plos
                plospath
                PLoS Pathogens
                Public Library of Science (San Francisco, USA )
                1553-7366
                1553-7374
                September 2013
                September 2013
                19 September 2013
                : 9
                : 9
                : e1003618
                Affiliations
                [1 ]Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York, United States of America
                [2 ]Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
                [3 ]Department of Integrative Structural and Computational Biology, IAVI Neutralizing Antibody Center and CHAVI-ID, The Scripps Research Institute, La Jolla, California, United States of America
                [4 ]International AIDS Vaccine Initiative, New York, New York, United States of America
                [5 ]The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California, United States of America
                University of Zurich, Switzerland
                Author notes

                I have read the journal's policy and have the following conflicts: A patent application on BG505 SOSIP.664 gp140. This does not alter our adherence to all PLoS Pathogens policies on sharing data and materials.

                Conceived and designed the experiments: RWS RD JPJ CRK IAW ABW PJK JPM. Performed the experiments: RD AC JPJ AY NdV HJK CB ATdlP JK MG KdlR TJK. Analyzed the data: RWS RD JPJ AC JPJ MJvG ABW PJK. Wrote the paper: RWS RD JPJ IAW ABW PJK JPM.

                Article
                PPATHOGENS-D-13-01512
                10.1371/journal.ppat.1003618
                3777863
                24068931
                e3a2acff-3098-4a79-ba8a-605cf1e66475
                Copyright @ 2013

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 7 June 2013
                : 30 July 2013
                Page count
                Pages: 20
                Funding
                This work was supported by National Institutes of Health Grants P01 AI82362 and R37 AI36082, by the International AIDS Vaccine Initiative (IAVI), and by the Aids fonds Netherlands, grants #2011032 and 2012041. JPJ is a recipient of a Canadian Institutes of Health Research (CIHR) Fellowship. RWS is a recipient of a Vidi grant from the Netherlands Organization for Scientific Research (NWO) and a Starting Investigator Grant from the European Research Council (ERC-StG-2011-280829-SHEV). The electron microscopy data were collected at the National Resource for Automated Molecular Microscopy (NRAMM), which is supported by the National Institutes of Health through the National Center for Research Resources' P41 Program Grant RR017573. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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