Publications by authors named "Steven W de Taeye"

33 Publications

Enhancing glycan occupancy of soluble HIV-1 envelope trimers to mimic the native viral spike.

Cell Rep 2021 Apr;35(1):108933

Department of Medical Microbiology, Amsterdam Infection and Immunity Institute, Amsterdam UMC, University of Amsterdam, Amsterdam 1105 AZ, the Netherlands; Department of Microbiology and Immunology, Weill Cornell Medical College, Cornell University, New York, NY, USA. Electronic address:

Artificial glycan holes on recombinant Env-based vaccines occur when a potential N-linked glycosylation site (PNGS) is under-occupied, but not on their viral counterparts. Native-like SOSIP trimers, including clinical candidates, contain such holes in the glycan shield that induce strain-specific neutralizing antibodies (NAbs) or non-NAbs. To eliminate glycan holes and mimic the glycosylation of native BG505 Env, we replace all 12 NxS sequons on BG505 SOSIP with NxT. All PNGS, except N133 and N160, are nearly fully occupied. Occupancy of the N133 site is increased by changing N133 to NxS, whereas occupancy of the N160 site is restored by reverting the nearby N156 sequon to NxS. Hence, PNGS in close proximity, such as in the N133-N137 and N156-N160 pairs, affect each other's occupancy. We further apply this approach to improve the occupancy of several Env strains. Increasing glycan occupancy should reduce off-target immune responses to vaccine antigens.
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http://dx.doi.org/10.1016/j.celrep.2021.108933DOI Listing
April 2021

C-Reactive Protein Enhances IgG-Mediated Cellular Destruction Through IgG-Fc Receptors .

Front Immunol 2021 15;12:594773. Epub 2021 Mar 15.

Sanquin Research and Landsteiner Laboratory, Department of Experimental Immunohematology, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, Netherlands.

Antibody-mediated blood disorders ensue after auto- or alloimmunization against blood cell antigens, resulting in cytopenia. Although the mechanisms of cell destruction are the same as in immunotherapies targeting tumor cells, many factors are still unknown. Antibody titers, for example, often do not strictly correlate with clinical outcome. Previously, we found C-reactive protein (CRP) levels to be elevated in thrombocytopenic patients, correlating with thrombocyte counts, and bleeding severity. Functionally, CRP amplified antibody-mediated phagocytosis of thrombocytes by phagocytes. To investigate whether CRP is a general enhancer of IgG-mediated target cell destruction, we extensively studied the effect of CRP on IgG-Fc receptor (FcγR)-mediated cell destruction: through respiratory burst, phagocytosis, and cellular cytotoxicity by a variety of effector cells. We now demonstrate that CRP also enhances IgG-mediated effector functions toward opsonized erythrocytes, in particular by activated neutrophils. We performed a first-of-a-kind profiling of CRP binding to all human FcγRs and IgA-Fc receptor I (FcαRI) using a surface plasmon resonance array. CRP bound these receptors with relative affinities of FcγRIa = FcγRIIa/b = FcγRIIIa > FcγRIIIb = FcαRI. Furthermore, FcγR blocking (in particular FcγRIa) abrogated CRP's ability to amplify IgG-mediated neutrophil effector functions toward opsonized erythrocytes. Finally, we observed that CRP also amplified killing of breast-cancer tumor cell line SKBR3 by neutrophils through anti-Her2 (trastuzumab). Altogether, we provide for the first time evidence for the involvement of specific CRP-FcγR interactions in the exacerbation of IgG-mediated cellular destruction; a trait that should be further evaluated as potential therapeutic target e.g., for tumor eradication.
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http://dx.doi.org/10.3389/fimmu.2021.594773DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8006934PMC
March 2021

Afucosylated IgG characterizes enveloped viral responses and correlates with COVID-19 severity.

Science 2021 02 23;371(6532). Epub 2020 Dec 23.

Department of Rheumatology and Clinical Immunology, Amsterdam UMC, Amsterdam Rheumatology and Immunology Center, Amsterdam, Netherlands.

Immunoglobulin G (IgG) antibodies are crucial for protection against invading pathogens. A highly conserved N-linked glycan within the IgG-Fc tail, which is essential for IgG function, shows variable composition in humans. Afucosylated IgG variants are already used in anticancer therapeutic antibodies for their increased activity through Fc receptors (FcγRIIIa). Here, we report that afucosylated IgG (approximately 6% of total IgG in humans) are specifically formed against enveloped viruses but generally not against other antigens. This mediates stronger FcγRIIIa responses but also amplifies brewing cytokine storms and immune-mediated pathologies. Critically ill COVID-19 patients, but not those with mild symptoms, had high concentrations of afucosylated IgG antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), amplifying proinflammatory cytokine release and acute phase responses. Thus, antibody glycosylation plays a critical role in immune responses to enveloped viruses, including COVID-19.
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http://dx.doi.org/10.1126/science.abc8378DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7919849PMC
February 2021

IgG Subclasses Shape Cytokine Responses by Human Myeloid Immune Cells through Differential Metabolic Reprogramming.

J Immunol 2020 12 13;205(12):3400-3407. Epub 2020 Nov 13.

Amsterdam Rheumatology and Immunology Center, Department of Rheumatology and Clinical Immunology, Amsterdam University Medical Centers, University of Amsterdam, 1105 AZ Amsterdam, the Netherlands;

IgG Abs are crucial for various immune functions, including neutralization, phagocytosis, and Ab-dependent cellular cytotoxicity. In this study, we identified another function of IgG by showing that IgG immune complexes elicit distinct cytokine profiles by human myeloid immune cells, which are dependent on FcγR activation by the different IgG subclasses. Using monoclonal IgG subclasses with identical Ag specificity, our data demonstrate that the production of Th17-inducing cytokines, such as TNF, IL-1β, and IL-23, is particularly dependent on IgG2, whereas type I IFN responses are controlled by IgG3, and IgG1 is able to regulate both. In addition, we identified that subclass-specific cytokine production is orchestrated at the posttranscriptional level through distinct glycolytic reprogramming of human myeloid immune cells. Combined, these data identify that IgG subclasses provide pathogen- and cell type-specific immunity through differential metabolic reprogramming by FcγRs. These findings may be relevant for future design of Ab-related therapies in the context of infectious diseases, chronic inflammation, and cancer.
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http://dx.doi.org/10.4049/jimmunol.2000263DOI Listing
December 2020

Glycine 236 in the Lower Hinge Region of Human IgG1 Differentiates FcγR from Complement Effector Function.

J Immunol 2020 12 13;205(12):3456-3467. Epub 2020 Nov 13.

Department of Experimental Immunohematology, Sanquin Research and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, 1066 CX, Amsterdam, the Netherlands;

Abs of the IgG isotype mediate effector functions like Ab-dependent cellular cytotoxicity and Ab-dependent cellular phagocytosis by Fc interactions with FcγRs and complement-dependent cytotoxicity upon IgG-Fc binding to C1q. In this study, we describe the crucial role of the highly conserved dual glycines at position 236-237 in the lower hinge region of human IgG, including the lack of one glycine as found in IgG2. We found several permutations in this region that either silence or largely abrogate FcγR binding and downstream FcγR effector functions, as demonstrated by surface plasmon resonance, Ab-dependent cellular phagocytosis, and Ab-dependent cellular cytotoxicity assays. Although the binding regions of FcγRs and C1q on the IgG-Fc largely overlap, IgG1 with a deletion of G236 only silences FcγR-mediated effector functions without affecting C1q-binding or activation. Several mutations resulted in only residual FcγRI binding with differing affinities that are either complement competent or silenced. Interestingly, we also found that IgG2, naturally only binding FcγRIIa, gains binding to FcγRI and FcγRIIIa after insertion of G236, highlighting the crucial importance of G236 in IgG for FcγR interaction. These mutants may become invaluable tools for FcγR-related research as well as for therapeutic purposes in which only complement-mediated functions are required without the involvement of FcγR.
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http://dx.doi.org/10.4049/jimmunol.2000961DOI Listing
December 2020

Neutralizing Antibody Responses Induced by HIV-1 Envelope Glycoprotein SOSIP Trimers Derived from Elite Neutralizers.

J Virol 2020 11 23;94(24). Epub 2020 Nov 23.

Department of Medical Microbiology, Amsterdam Infection & Immunity Institute (AI&II), Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands

The induction of broadly neutralizing antibodies (bNAbs) is a major goal in vaccine research. HIV-1-infected individuals that develop exceptionally strong bNAb responses, termed elite neutralizers, can inform vaccine design by providing blueprints for the induction of similar bNAb responses. We describe a new recombinant native-like envelope glycoprotein (Env) SOSIP trimer, termed AMC009, based on the viral founder sequences of an elite neutralizer. The subtype B AMC009 SOSIP protein formed stable native-like trimers that displayed multiple bNAb epitopes. Overall, its structure at 4.3-Å resolution was similar to that of BG505 SOSIP.664. The AMC009 trimer resembled one from a second elite neutralizer, AMC011, in having a dense and complete glycan shield. When tested as immunogens in rabbits, the AMC009 trimers did not induce autologous neutralizing antibody (NAb) responses efficiently while the AMC011 trimers did so very weakly, outcomes that may reflect the completeness of their glycan shields. The AMC011 trimer induced antibodies that occasionally cross-neutralized heterologous tier 2 viruses, sometimes at high titer. Cross-neutralizing antibodies were more frequently elicited by a trivalent combination of AMC008, AMC009, and AMC011 trimers, all derived from subtype B viruses. Each of these three individual trimers could deplete the NAb activity from the rabbit sera. Mapping the polyclonal sera by electron microscopy revealed that antibodies of multiple specificities could bind to sites on both autologous and heterologous trimers. These results advance our understanding of how to use Env trimers in multivalent vaccination regimens and the immunogenicity of trimers derived from elite neutralizers. Elite neutralizers, i.e., individuals who developed unusually broad and potent neutralizing antibody responses, might serve as blueprints for HIV-1 vaccine design. Here, we studied the immunogenicity of native-like recombinant envelope glycoprotein (Env) trimers based on viral sequences from elite neutralizers. While immunization with single trimers from elite neutralization did not recapitulate the breadth and potency of neutralization observed in these infected individuals, a combination of three subtype B Env trimers from elite neutralizers resulted in some neutralization breadth within subtype B viruses. These results should guide future efforts to design vaccines to induce broadly neutralizing antibodies.
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http://dx.doi.org/10.1128/JVI.01214-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7925178PMC
November 2020

MS-Based Allotype-Specific Analysis of Polyclonal IgG-Fc -Glycosylation.

Front Immunol 2020 21;11:2049. Epub 2020 Aug 21.

Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, Netherlands.

Current approaches to study glycosylation of polyclonal human immunoglobulins G (IgG) usually imply protein digestion or glycan release. While these approaches allow in-depth characterization, they also result in a loss of valuable information regarding certain subclasses, allotypes and co-occuring post-translational modifications (PTMs). Unfortunately, the high variability of polyclonal IgGs makes their intact mass spectrometry (MS) analysis extremely challenging. We propose here a middle-up strategy for the analysis of the intact fragment crystallizable (Fc) region of human plasma IgGs, with the aim of acquiring integrated information of the -glycosylation and other PTMs of subclasses and allotypes. Human plasma IgG was isolated using Fc-specific beads followed by an on-bead C 2 domain digestion with the enzyme IdeS. The obtained mixture of Fc subunits was analyzed by capillary electrophoresis (CE) and hydrophilic interaction liquid chromatography (HILIC) hyphenated with MS. CE-MS provided separation of different IgG-subclasses and allotypes, while HILIC-MS allowed resolution of the different glycoforms and their oxidized variants. The orthogonality of these techniques was key to reliably assign Fc allotypes. Five individual donors were analyzed using this approach. Heterozygosis was observed in all the analyzed donors resulting in a total of 12 allotypes identified. The assignments were further confirmed using recombinant monoclonal IgG allotypes as standards. While the glycosylation patterns were similar within allotypes of the same subclass, clear differences were observed between IgG subclasses and donors, highlighting the relevance of the proposed approach. In a single analysis, glycosylation levels specific for each allotype, relative abundances of subclasses and information on co-occurring modifications are obtained. This middle-up method represents an important step toward a comprehensive analysis of immunoglobulin G-Fc variants.
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http://dx.doi.org/10.3389/fimmu.2020.02049DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7472933PMC
April 2021

Cross-reactivity of mouse IgG subclasses to human Fc gamma receptors: Antibody deglycosylation only eliminates IgG2b binding.

Mol Immunol 2020 11 15;127:79-86. Epub 2020 Sep 15.

Department of Experimental Immunohematology, Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, The Netherlands. Electronic address:

Immunoglobulin G (IgG) antibodies are important for protection against pathogens and exert effector functions through binding to IgG-Fc receptors (FcγRs) on myeloid and natural killer cells, resulting in destruction of opsonized target cells. Despite interspecies differences, IgG subclasses and FcγRs show substantial similarities and functional conservation between mammals. Accordingly, binding of human IgG (hIgG) to mouse FcγRs (mFcγRs) has been utilized to study effector functions of hIgG in mice. In other applications, such as immunostaining with mouse IgG monoclonal antibodies (mAbs), these cross-reactivities are undesired and prone to misinterpretation. Despite this drawback, the binding of mouse IgG (mIgG) subclasses to human FcγR (hFcγR) classes has never been fully documented. Here, we report detailed and quantifiable characterization of binding affinities for all mIgG subclasses to hFcγRs, including functional polymorphic variants. mIgG subclasses show the strongest binding to hFcγRIa, with relative affinities mIgG2a = mIgG2c > mIgG3 > mIgG2b, and no binding by mIgG1. hFcγRIIa/b showed general low reactivities to all mIgG (mIgG1> mIgG2a/c > mIgG2b), with no reactivity to mIgG3. A particularly high affinity was observed for mIgG1 to the hFcγRIIa-R131 polymorphic variant. hFcγRIIIa showed lower binding (mIgG2a/c > mIgG3), slightly favouring binding to the hFcγRIIIa-V158 over the F158 polymorphic variant. No binding was observed of mIgG to hFcγRIIIb. Deglycosylation of mIgG1 did not abrogate binding to hFcγRIIa-R131, nor did deglycosylation of mIgG2a/c and mIgG3 prevent hFcγRIa binding. Importantly, deglycosylation of the least cross-reactive mIgG subclass, mIgG2b, abrogated reactivity to all hFcγRs. Together, these data document for the first time the full spectrum of cross-reactivities of mouse IgG to human FcγRs.
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http://dx.doi.org/10.1016/j.molimm.2020.08.015DOI Listing
November 2020

FcγR Binding and ADCC Activity of Human IgG Allotypes.

Front Immunol 2020 6;11:740. Epub 2020 May 6.

Sanquin Research and Landsteiner Laboratory, Department of Experimental Immunohematology, Amsterdam UMC, University of Amsterdam, Amsterdam, Netherlands.

Antibody dependent cellular cytotoxicity (ADCC) is an Fc-dependent effector function of IgG important for anti-viral immunity and anti-tumor therapies. NK-cell mediated ADCC is mainly triggered by IgG-subclasses IgG1 and IgG3 through the IgG-Fc-receptor (FcγR) IIIa. Polymorphisms in the immunoglobulin gamma heavy chain gene likely form a layer of variation in the strength of the ADCC-response, but this has never been studied in detail. We produced all 27 known IgG allotypes and assessed FcγRIIIa binding and ADCC activity. While all IgG1, IgG2, and IgG4 allotypes behaved similarly within subclass, large allotype-specific variation was found for IgG3. ADCC capacity was affected by residues 291, 292, and 296 in the CH2 domain through altered affinity or avidity for FcγRIIIa. Furthermore, allotypic variation in hinge length affected ADCC, likely through altered proximity at the immunological synapse. Thus, these functional differences between IgG allotypes have important implications for therapeutic applications and susceptibility to infectious-, allo- or auto-immune diseases.
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http://dx.doi.org/10.3389/fimmu.2020.00740DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7218058PMC
March 2021

Functional Attributes of Antibodies, Effector Cells, and Target Cells Affecting NK Cell-Mediated Antibody-Dependent Cellular Cytotoxicity.

J Immunol 2019 12 20;203(12):3126-3135. Epub 2019 Nov 20.

Department of Experimental Immunohematology, Sanquin Research and Landsteiner Laboratory, Amsterdam University Medical Center, University of Amsterdam, 1066 CX Amsterdam, the Netherlands;

Ab-dependent cellular cytotoxicity (ADCC) is one of the most important effector mechanisms of tumor-targeting Abs in current immunotherapies. In ADCC and other Ab-dependent activation of myeloid effector cells, close cell-cell contact (between effector and target cell) and formation of immunological synapses are required. However, we still lack basic knowledge on the principal factors influencing ADCC potential by therapeutic Abs. In this study we investigated the combined roles of five factors affecting human NK cell-mediated ADCC, namely: 1) Ag density, 2) target cell membrane composition, 3) IgG FcγR polymorphism, 4) FcγR-blocking cytophilic Abs, and 5) Ab fucosylation. We demonstrate that the magnitude of NK cell-mediated ADCC responses is predominantly influenced by Ag density and Ab fucosylation. Afucosylation consistently induced efficient ADCC, even at very low Ag density, where fucosylated target Abs did not elicit ADCC. On the side of the effector cell, the FcγRIIIa-Val/Phe158 polymorphism influenced ADCC potency, with NK cells expressing the Val158 variant showing more potent ADCC. In addition, we identified the sialic acid content of the target cell membrane as an important inhibitory factor for ADCC. Furthermore, we found that the presence and glycosylation status of aspecific endogenous Abs bound to NK cell FcγRIIIa (cytophilic Abs) determine the blocking effect on ADCC. These five parameters affect the potency of Abs in vitro and should be further tested as predictors of in vivo capacity.
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http://dx.doi.org/10.4049/jimmunol.1900985DOI Listing
December 2019

The Ligands for Human IgG and Their Effector Functions.

Antibodies (Basel) 2019 Apr 25;8(2). Epub 2019 Apr 25.

Sanquin Research, Dept Experimental Immunohematology and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, 1066 CX Amsterdam, The Netherlands.

Activation of the humoral immune system is initiated when antibodies recognize an antigen and trigger effector functions through the interaction with Fc engaging molecules. The most abundant immunoglobulin isotype in serum is Immunoglobulin G (IgG), which is involved in many humoral immune responses, strongly interacting with effector molecules. The IgG subclass, allotype, and glycosylation pattern, among other factors, determine the interaction strength of the IgG-Fc domain with these Fc engaging molecules, and thereby the potential strength of their effector potential. The molecules responsible for the effector phase include the classical IgG-Fc receptors (FcγR), the neonatal Fc-receptor (FcRn), the Tripartite motif-containing protein 21 (TRIM21), the first component of the classical complement cascade (C1), and possibly, the Fc-receptor-like receptors (FcRL4/5). Here we provide an overview of the interactions of IgG with effector molecules and discuss how natural variation on the antibody and effector molecule side shapes the biological activities of antibodies. The increasing knowledge on the Fc-mediated effector functions of antibodies drives the development of better therapeutic antibodies for cancer immunotherapy or treatment of autoimmune diseases.
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http://dx.doi.org/10.3390/antib8020030DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640714PMC
April 2019

Reduced FcRn-mediated transcytosis of IgG2 due to a missing Glycine in its lower hinge.

Sci Rep 2019 05 14;9(1):7363. Epub 2019 May 14.

Sanquin Research, Department of Experimental Immunohematology, Amsterdam, The Netherlands, and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands, Plesmanlaan 125, Amsterdam, 1066 CX, The Netherlands.

Neonatal Fc-receptor (FcRn), the major histocompatibility complex (MHC) class I-like Fc-receptor, transports immunoglobuline G (IgG) across cell layers, extending IgG half-life in circulation and providing newborns with humoral immunity. IgG1 and IgG2 have similar half-lives, yet IgG2 displays lower foetal than maternal concentration at term, despite all known FcRn binding residues being preserved between IgG1 and IgG2. We investigated FcRn mediated transcytosis of V-matched IgG1 and IgG2 and mutated variants thereof lacking Fc-gamma receptor (FcγR) binding in human cells expressing FcRn. We observed that FcγR binding was not required for transport and that FcRn transported less IgG2 than IgG1. Transport of IgG1 with a shortened lower hinge (ΔGly236, absent in germline IgG2), was reduced to levels equivalent to IgG2. Conversely, transport of IgG2 + Gly236 was increased to IgG1 levels. Gly236 is not a contact residue between IgG and FcRn, suggesting that its absence leads to an altered conformation of IgG, possibly due to a less flexible Fab, positioned closer to the Fc portion. This may sterically hinder FcRn binding and transport. We conclude that the lack of Gly236 is sufficient to explain the reduced FcRn-mediated IgG2 transcytosis and accounts for the low maternal/fetal IgG2 ratio at term.
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http://dx.doi.org/10.1038/s41598-019-40731-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6517591PMC
May 2019

Stabilization of the V2 loop improves the presentation of V2 loop-associated broadly neutralizing antibody epitopes on HIV-1 envelope trimers.

J Biol Chem 2019 04 6;294(14):5616-5631. Epub 2019 Feb 6.

From the Department of Medical Microbiology, Amsterdam UMC, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands,

A successful HIV-1 vaccine will likely need to elicit broadly neutralizing antibodies (bNAbs) that target the envelope glycoprotein (Env) spike on the virus. Native-like recombinant Env trimers of the SOSIP design now serve as a platform for achieving this challenging goal. However, SOSIP trimers usually do not bind efficiently to the inferred germline precursors of bNAbs (gl-bNAbs). We hypothesized that the inherent flexibilities of the V1 and V2 variable loops in the Env trimer contribute to the poor recognition of gl-bNAb epitopes at the trimer apex that extensively involve V2 residues. To reduce local V2 flexibility and improve the binding of V2-dependent bNAbs and gl-bNAbs, we designed BG505 SOSIP.664 trimer variants containing newly created disulfide bonds intended to stabilize the V2 loop in an optimally antigenic configuration. The first variant, I184C/E190C, contained a new disulfide bond within the V2 loop, whereas the second variant, E153C/R178C, had a new disulfide bond that cross-linked V2 and V1. The resulting engineered native-like trimer variants were both more reactive with and were neutralized by V2 bNAbs and gl-bNAbs, a finding that may be valuable in the design of germline targeting and boosting trimer immunogens to create an antigenic conformation optimal for HIV vaccine development.
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http://dx.doi.org/10.1074/jbc.RA118.005396DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6462529PMC
April 2019

HIV-1 anchor inhibitors and membrane fusion inhibitors target distinct but overlapping steps in virus entry.

J Biol Chem 2019 04 29;294(15):5736-5746. Epub 2019 Jan 29.

From the Laboratory of Experimental Virology, Department of Medical Microbiology, Amsterdam University Medical Centers (Amsterdam UMC), Location AMC, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands; the Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, New York 10065. Electronic address:

HIV-1 entry into cells is mediated by the envelope glycoprotein (Env) and represents an attractive target for therapeutic intervention. Two drugs that inhibit HIV entry are approved for clinical use: the membrane fusion-inhibitor T20 (Fuzeon, enfuvirtide) and the C-C chemokine receptor type 5 (CCR5) blocker maraviroc (Selzentry). Another class of entry inhibitors supposedly target the fusion peptide (FP) and are termed anchor inhibitors. These include the VIRIP peptide and VIRIP derivatives such as VIR165, VIR353, and VIR576. Here, we investigated the mechanism of inhibition by VIR165. We show that substitutions within the FP modulate sensitivity to VIR165, consistent with the FP being the drug target. Our results also revealed that VIR165 acts during an intermediate post-CD4-binding entry step that is overlapping but not identical to the step inhibited by fusion inhibitors such as T20. We found that some but not all resistance mutations to heptad repeat 2 (HR2)-targeting fusion inhibitors can provide cross-resistance to VIR165. In contrast, resistance mutations in the HR1-binding site for the fusion inhibitors did not cause cross-resistance to VIR165. However, Env with mutations located outside this binding site and thought to affect fusion kinetics, exhibited decreased sensitivity to VIR165. Although we found a strong correlation between Env stability and resistance to HR2-based fusion inhibitors, such correlation was not observed for Env stability and VIR165 resistance. We conclude that VIRIP analogs target the FP during an intermediate, post-CD4-binding entry step that overlaps with but is distinct from the step(s) inhibited by HR2-based fusion inhibitors.
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http://dx.doi.org/10.1074/jbc.RA119.007360DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6463712PMC
April 2019

Variable Domain -Linked Glycans Acquired During Antigen-Specific Immune Responses Can Contribute to Immunoglobulin G Antibody Stability.

Front Immunol 2018 12;9:740. Epub 2018 Apr 12.

Sanquin Research, Department of Immunopathology, Amsterdam, Netherlands.

Immunoglobulin G (IgG) can contain -linked glycans in the variable domains, the so-called Fab glycans, in addition to the Fc glycans in the C2 domains. These Fab glycans are acquired following introduction of -glycosylation sites during somatic hypermutation and contribute to antibody diversification. We investigated whether Fab glycans may-in addition to affecting antigen binding-contribute to antibody stability. By analyzing thermal unfolding profiles of antibodies with or without Fab glycans, we demonstrate that introduction of Fab glycans can improve antibody stability. Strikingly, removal of Fab glycans naturally acquired during antigen-specific immune responses can deteriorate antibody stability, suggesting selection of stable, glycosylated antibodies. Collectively, our data show that variable domain -linked glycans acquired during somatic hypermutation can contribute to IgG antibody stability. These findings indicate that introducing Fab glycans may represent a mechanism to improve therapeutic/diagnostic antibody stability.
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http://dx.doi.org/10.3389/fimmu.2018.00740DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5906590PMC
June 2019

Immunogenicity in Rabbits of HIV-1 SOSIP Trimers from Clades A, B, and C, Given Individually, Sequentially, or in Combination.

J Virol 2018 04 28;92(8). Epub 2018 Mar 28.

Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands

Recombinant soluble HIV-1 envelope glycoprotein (Env) SOSIP trimers are a design platform for inducing broadly neutralizing antibodies (bNAbs) by vaccination. To date, these and alternative designs of native-like trimers, given singly or in pairs, have not induced bNAbs in test animals such as rabbits or macaques. Here, we have evaluated whether trivalent and tetravalent combinations of SOSIP trimers from clades A, B, and C, delivered simultaneously or sequentially, induce better neutralizing antibody responses in rabbits than when given alone. None of the tested formulations led to the induction of bNAbs. We found that BG505 clade A trimers dominated the autologous NAb responses induced by combinations, which probably relates to the presence of immunodominant glycan holes on the BG505 trimer. Furthermore, autologous NAb responses to all individual trimers were reduced when they were delivered in combinations compared with when delivered alone, suggesting that immunogen interference had occurred. Finally, in a sequential regimen, a heterologous clade C trimer cross-boosted NAb responses that were primed by earlier immunizations with clade A and B trimers. Taken together, these findings should allow us to improve the design of immunization regimens based on native-like HIV-1 Env trimers. A successful HIV-1 vaccine most probably requires a trimeric envelope glycoprotein (Env) component, as Env is the only viral protein on the surface of the virus and therefore the only target for neutralizing antibodies. Native-like Env trimers can induce strain-specific neutralizing antibodies but not yet broadly neutralizing antibodies. To try to broaden the antibody response, we immunized rabbits with soluble native-like Env trimers from three different clades using monovalent, multivalent, and sequential regimens. We found that the neutralizing antibody response against each immunogen was reduced when the immunogens were delivered in combination or sequentially compared to the monovalent regimen. In contrast, when the Env trimers from different clades were delivered sequentially, the neutralizing antibody response could be cross-boosted. Although the combination of native-like Env trimers from different clades did not induce broadly neutralizing antibodies, the results provide clues on how to use native-like trimers in vaccination experiments.
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http://dx.doi.org/10.1128/JVI.01957-17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5874403PMC
April 2018

Stabilization of the gp120 V3 loop through hydrophobic interactions reduces the immunodominant V3-directed non-neutralizing response to HIV-1 envelope trimers.

J Biol Chem 2018 02 8;293(5):1688-1701. Epub 2017 Dec 8.

From the Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam, 1105 AZ, The Netherlands,

To provide protective immunity against circulating primary HIV-1 strains, a vaccine most likely has to induce broadly neutralizing antibodies to the HIV-1 envelope glycoprotein (Env) spike. Recombinant Env trimers such as the prototype BG505 SOSIP.664 that closely mimic the native Env spike can induce autologous neutralizing antibodies (NAbs) against relatively resistant (tier 2) primary viruses. Ideally, Env immunogens should present broadly neutralizing antibody epitopes but limit the presentation of immunodominant non-NAb epitopes that might induce off-target and potentially interfering responses. The V3 loop in gp120 is such a non-NAb epitope that can effectively elicit non-NAbs when animals are immunized with SOSIP.664 trimers. V3 immunogenicity can be diminished, but not abolished, by reducing the conformational flexibility of trimers via targeted sequence changes, including an A316W substitution in V3, that create the SOSIP.v4.1 and SOSIP.v5.2 variants. Here, we further modified these trimer designs by introducing leucine residues at V3 positions 306 and 308 to create hydrophobic interactions with the tryptophan residue at position 316 and with other topologically proximal sites in the V1V2 domain. Together, these modifications further stabilized the resulting SOSIP.v5.2 S306L/R308L trimers in the prefusion state in which V3 is sequestered. When we tested these trimers as immunogens in rabbits, the induction of V3 non-NAbs was significantly reduced compared with the SOSIP.v5.2 trimers and even more so compared with the SOSIP.664 prototype, without affecting the autologous NAb response. Hence, these additional trimer sequence modifications may be beneficial for immunization strategies that seek to minimize off-target non-NAb responses.
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http://dx.doi.org/10.1074/jbc.RA117.000709DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5798299PMC
February 2018

Design and crystal structure of a native-like HIV-1 envelope trimer that engages multiple broadly neutralizing antibody precursors in vivo.

J Exp Med 2017 Sep 28;214(9):2573-2590. Epub 2017 Aug 28.

Department of Immunology and Microbiology, Scripps CHAVI-ID, The Scripps Research Institute, La Jolla, CA.

Induction of broadly neutralizing antibodies (bNAbs) by HIV-1 envelope glycoprotein immunogens would be a major advance toward an effective vaccine. A critical step in this process is the activation of naive B cells expressing germline (gl) antibody precursors that have the potential to evolve into bNAbs. Here, we reengineered the BG505 SOSIP.664 glycoprotein to engage gl precursors of bNAbs that target either the trimer apex or the CD4-binding site. The resulting BG505 SOSIP.v4.1-GT1 trimer binds multiple bNAb gl precursors in vitro. Immunization experiments in knock-in mice expressing gl-VRC01 or gl-PGT121 show that this trimer activates B cells in vivo, resulting in the secretion of specific antibodies into the sera. A crystal structure of the gl-targeting trimer at 3.2-Å resolution in complex with neutralizing antibodies 35O22 and 9H+109L reveals a native-like conformation and the successful incorporation of design features associated with binding of multiple gl-bNAb precursors.
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http://dx.doi.org/10.1084/jem.20161160DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5584115PMC
September 2017

Improving the Immunogenicity of Native-like HIV-1 Envelope Trimers by Hyperstabilization.

Cell Rep 2017 Aug;20(8):1805-1817

Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam 1105 AZ, the Netherlands; Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, NY 10021, USA. Electronic address:

The production of native-like recombinant versions of the HIV-1 envelope glycoprotein (Env) trimer requires overcoming the natural flexibility and instability of the complex. The engineered BG505 SOSIP.664 trimer mimics the structure and antigenicity of native Env. Here, we describe how the introduction of new disulfide bonds between the glycoprotein (gp)120 and gp41 subunits of SOSIP trimers of the BG505 and other genotypes improves their stability and antigenicity, reduces their conformational flexibility, and helps maintain them in the unliganded conformation. The resulting next-generation SOSIP.v5 trimers induce strong autologous tier-2 neutralizing antibody (NAb) responses in rabbits. In addition, the BG505 SOSIP.v6 trimers induced weak heterologous NAb responses against a subset of tier-2 viruses that were not elicited by the prototype BG505 SOSIP.664. These stabilization methods can be applied to trimers from multiple genotypes as components of multivalent vaccines aimed at inducing broadly NAbs (bNAbs).
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http://dx.doi.org/10.1016/j.celrep.2017.07.077DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5590011PMC
August 2017

Elicitation of Robust Tier 2 Neutralizing Antibody Responses in Nonhuman Primates by HIV Envelope Trimer Immunization Using Optimized Approaches.

Immunity 2017 06;46(6):1073-1088.e6

Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037, USA; Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology, and Harvard University, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA; Departments of Biological Engineering and Materials Science & Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

The development of stabilized recombinant HIV envelope trimers that mimic the virion surface molecule has increased enthusiasm for a neutralizing antibody (nAb)-based HIV vaccine. However, there is limited experience with recombinant trimers as immunogens in nonhuman primates, which are typically used as a model for humans. Here, we tested multiple immunogens and immunization strategies head-to-head to determine their impact on the quantity, quality, and kinetics of autologous tier 2 nAb development. A bilateral, adjuvanted, subcutaneous immunization protocol induced reproducible tier 2 nAb responses after only two immunizations 8 weeks apart, and these were further enhanced by a third immunization with BG505 SOSIP trimer. We identified immunogens that minimized non-neutralizing V3 responses and demonstrated that continuous immunogen delivery could enhance nAb responses. nAb responses were strongly associated with germinal center reactions, as assessed by lymph node fine needle aspiration. This study provides a framework for preclinical and clinical vaccine studies targeting nAb elicitation.
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http://dx.doi.org/10.1016/j.immuni.2017.05.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5483234PMC
June 2017

Direct Probing of Germinal Center Responses Reveals Immunological Features and Bottlenecks for Neutralizing Antibody Responses to HIV Env Trimer.

Cell Rep 2016 11;17(9):2195-2209

Division of Vaccine Discovery, La Jolla Institute for Allergy and Immunology, La Jolla, CA 92037, USA; Scripps Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, La Jolla, CA 92037, USA; Department of Medicine, Division of Infectious Diseases, University of California, San Diego, La Jolla, CA 92037, USA. Electronic address:

Generating tier 2 HIV-neutralizing antibody (nAb) responses by immunization remains a challenging problem, and the immunological barriers to induction of such responses with Env immunogens remain unclear. Here, some rhesus monkeys developed autologous tier 2 nAbs upon HIV Env trimer immunization (SOSIP.v5.2) whereas others did not. This was not because HIV Env trimers were immunologically silent because all monkeys made similar ELISA-binding antibody responses; the key difference was nAb versus non-nAb responses. We explored the immunological barriers to HIV nAb responses by combining a suite of techniques, including longitudinal lymph node fine needle aspirates. Unexpectedly, nAb development best correlated with booster immunization GC B cell magnitude and Tfh characteristics of the Env-specific CD4 T cells. Notably, these factors distinguished between successful and unsuccessful antibody responses because GC B cell frequencies and stoichiometry to GC Tfh cells correlated with nAb development, but did not correlate with total Env Ab binding titers.
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http://dx.doi.org/10.1016/j.celrep.2016.10.085DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5142765PMC
November 2016

An HIV-1 antibody from an elite neutralizer implicates the fusion peptide as a site of vulnerability.

Nat Microbiol 2016 Nov 14;2:16199. Epub 2016 Nov 14.

Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, 1105 AZ, Amsterdam, The Netherlands.

The induction by vaccination of broadly neutralizing antibodies (bNAbs) capable of neutralizing various HIV-1 viral strains is challenging, but understanding how a subset of HIV-infected individuals develops bNAbs may guide immunization strategies. Here, we describe the isolation and characterization of the bNAb ACS202 from an elite neutralizer that recognizes a new, trimer-specific and cleavage-dependent epitope at the gp120-gp41 interface of the envelope glycoprotein (Env), involving the glycan N88 and the gp41 fusion peptide. In addition, an Env trimer, AMC011 SOSIP.v4.2, based on early virus isolates from the same elite neutralizer, was constructed, and its structure by cryo-electron microscopy at 6.2 Å resolution reveals a closed, pre-fusion conformation similar to that of the BG505 SOSIP.664 trimer. The availability of a native-like Env trimer and a bNAb from the same elite neutralizer provides the opportunity to design vaccination strategies aimed at generating similar bNAbs against a key functional site on HIV-1.
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http://dx.doi.org/10.1038/nmicrobiol.2016.199DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5372380PMC
November 2016

HIV-1 Escape from a Peptidic Anchor Inhibitor through Stabilization of the Envelope Glycoprotein Spike.

J Virol 2016 Dec 14;90(23):10587-10599. Epub 2016 Nov 14.

Laboratory of Experimental Virology, Department of Medical Microbiology, Center for Infection and Immunity Amsterdam (CINIMA), Academic Medical Center of the University of Amsterdam, Amsterdam, the Netherlands

The trimeric HIV-1 envelope glycoprotein spike (Env) mediates viral entry into cells by using a spring-loaded mechanism that allows for the controlled insertion of the Env fusion peptide into the target membrane, followed by membrane fusion. Env is the focus of vaccine research aimed at inducing protective immunity by antibodies as well as efforts to develop drugs that inhibit the viral entry process. The molecular factors contributing to Env stability and decay need to be understood better in order to optimally design vaccines and therapeutics. We generated viruses with resistance to VIR165, a peptidic inhibitor that binds the fusion peptide of the gp41 subunit and prevents its insertion into the target membrane. Interestingly, a number of escape viruses acquired substitutions in the C1 domain of the gp120 subunit (A60E, E64K, and H66R) that rendered these viruses dependent on the inhibitor. These viruses could infect target cells only when VIR165 was present after CD4 binding. Furthermore, the VIR165-dependent viruses were resistant to soluble CD4-induced Env destabilization and decay. These data suggest that VIR165-dependent Env proteins are kinetically trapped in the unliganded state and require the drug to negotiate CD4-induced conformational changes. These studies provide mechanistic insight into the action of the gp41 fusion peptide and its inhibitors and provide new ways to stabilize Env trimer vaccines.

Importance: Because of the rapid development of HIV-1 drug resistance, new drug targets need to be explored continuously. The fusion peptide of the envelope glycoprotein can be targeted by anchor inhibitors. Here we describe virus escape from the anchor inhibitor VIR165. Interestingly, some escape viruses became dependent on the inhibitor for cell entry. We show that the identified escape mutations stabilize the ground state of the envelope glycoprotein and should thus be useful in the design of stabilized envelope-based HIV vaccines.
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http://dx.doi.org/10.1128/JVI.01616-16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110188PMC
December 2016

HIV-1 escapes from N332-directed antibody neutralization in an elite neutralizer by envelope glycoprotein elongation and introduction of unusual disulfide bonds.

Retrovirology 2016 Jul 7;13(1):48. Epub 2016 Jul 7.

Department of Microbiology and Immunology, Weill Medical College, Cornell University, New York, NY, 10065, USA.

Background: Current HIV-1 immunogens are unable to induce antibodies that can neutralize a broad range of HIV-1 (broadly neutralizing antibodies; bNAbs). However, such antibodies are elicited in 10-30 % of HIV-1 infected individuals, and the co-evolution of the virus and the humoral immune responses in these individuals has attracted attention, because they can provide clues for vaccine design.

Results: Here we characterized the NAb responses and envelope glycoprotein evolution in an HIV-1 infected "elite neutralizer" of the Amsterdam Cohort Studies on HIV-1 infection and AIDS who developed an unusually potent bNAb response rapidly after infection. The NAb response was dependent on the N332-glycan and viral resistance against the N332-glycan dependent bNAb PGT135 developed over time but viral escape did not occur at or near this glycan. In contrast, the virus likely escaped by increasing V1 length, with up to 21 amino acids, accompanied by the introduction of 1-3 additional glycans, as well as 2-4 additional cysteine residues within V1.

Conclusions: In the individual studied here, HIV-1 escaped from N332-glycan directed NAb responses without changing the epitope itself, but by elongating a variable loop that shields this epitope.
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http://dx.doi.org/10.1186/s12977-016-0279-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4936165PMC
July 2016

HIV-1 Envelope Trimer Design and Immunization Strategies To Induce Broadly Neutralizing Antibodies.

Trends Immunol 2016 Mar 9;37(3):221-232. Epub 2016 Feb 9.

Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands; Department of Microbiology and Immunology, Weill Medical College of Cornell University, New York, NY 10021, USA. Electronic address:

The identification of multiple broadly neutralizing antibodies (bNAbs) against the HIV-1 envelope glycoprotein (Env) trimer has facilitated its structural characterization and guided Env immunogen design. Several recent studies constitute progress in utilizing this knowledge for the development of an HIV-1 vaccine that induces bNAbs. Native-like Env trimers can induce autologous NAb responses against resistant (Tier-2) viruses in several animal models. Here we review recent studies aimed at addressing the challenge of driving the strong but narrowly focused NAb responses to Env trimers towards ones with much greater breadth. Among strategies that merit pursuing are using multiple trimers as sequential or simultaneous immunogens, targeting the germline precursors of bNAbs, delivering sequential lineages of trimers derived from infected individuals who developed bNAbs, and presenting trimers as particulate antigens.
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http://dx.doi.org/10.1016/j.it.2016.01.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5454186PMC
March 2016

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

Cell 2015 Dec;163(7):1702-15

Department of Integrative Structural and Computational Biology, Scripps CHAVI-ID, IAVI Neutralizing Antibody Center and Collaboration for AIDS Vaccine Discovery (CAVD), The Scripps Research Institute, La Jolla, CA 92037, USA.

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.
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http://dx.doi.org/10.1016/j.cell.2015.11.056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4732737PMC
December 2015

Chemical Cross-Linking Stabilizes Native-Like HIV-1 Envelope Glycoprotein Trimer Antigens.

J Virol 2016 01 28;90(2):813-28. Epub 2015 Oct 28.

The Sir William Dunn School of Pathology, The University of Oxford, Oxford, United Kingdom

Unlabelled: Major neutralizing antibody immune evasion strategies of the HIV-1 envelope glycoprotein (Env) trimer include conformational and structural instability. Stabilized soluble trimers such as BG505 SOSIP.664 mimic the structure of virion-associated Env but nevertheless sample different conformational states. Here we demonstrate that treating BG505 SOSIP.664 trimers with glutaraldehyde or a heterobifunctional cross-linker introduces additional stability with relatively modest effects on antigenicity. Thus, most broadly neutralizing antibody (bNAb) epitopes were preserved after cross-linking, whereas the binding of most weakly or nonneutralizing antibodies (non-NAb) was reduced. Cross-linking stabilized all Env conformers present within a mixed population, and individual conformers could be isolated by bNAb affinity chromatography. Both positive selection of cross-linked conformers using the quaternary epitope-specific bNAbs PGT145, PGT151, and 3BC315 and negative selection with non-NAbs against the V3 region enriched for trimer populations with improved antigenicity for bNAbs. Similar results were obtained using the clade B B41 SOSIP.664 trimer. The cross-linking method may, therefore, be useful for countering the natural conformational heterogeneity of some HIV-1 Env proteins and, by extrapolation, also vaccine immunogens from other pathogens.

Importance: The development of a vaccine to induce protective antibodies against HIV-1 is of primary public health importance. Recent advances in immunogen design have provided soluble recombinant envelope glycoprotein trimers with near-native morphology and antigenicity. However, these trimers are conformationally flexible, potentially reducing B-cell recognition of neutralizing antibody epitopes. Here we show that chemical cross-linking increases trimer stability, reducing binding of nonneutralizing antibodies while largely maintaining neutralizing antibody binding. Cross-linking followed by positive or negative antibody affinity selection of individual stable conformational variants further improved the antigenic and morphological characteristics of the trimers. This approach may be generally applicable to HIV-1 Env and also to other conformationally flexible pathogen antigens.
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http://dx.doi.org/10.1128/JVI.01942-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4702668PMC
January 2016

Antibodies to a conformational epitope on gp41 neutralize HIV-1 by destabilizing the Env spike.

Nat Commun 2015 Sep 25;6:8167. Epub 2015 Sep 25.

Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California 92037, USA.

The recent identification of three broadly neutralizing antibodies (bnAbs) against gp120-gp41 interface epitopes has expanded the targetable surface on the HIV-1 envelope glycoprotein (Env) trimer. By using biochemical, biophysical and computational methods, we map the previously unknown trimer epitopes of two related antibodies, 3BC315 and 3BC176. A cryo-EM reconstruction of a soluble Env trimer bound to 3BC315 Fab at 9.3 Å resolution reveals that the antibody binds between two gp41 protomers, and neutralizes the virus by accelerating trimer decay. In contrast, bnAb 35O22 binding to a partially overlapping quaternary epitope at the gp120-gp41 interface does not induce decay. A conserved gp41-proximal glycan at N88 was also shown to play a role in the binding kinetics of 3BC176 and 3BC315. Finally, our data suggest that the dynamic structure of the Env trimer influences exposure of bnAb epitopes.
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http://dx.doi.org/10.1038/ncomms9167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586043PMC
September 2015

Design and structure of two HIV-1 clade C SOSIP.664 trimers that increase the arsenal of native-like Env immunogens.

Proc Natl Acad Sci U S A 2015 Sep 8;112(38):11947-52. Epub 2015 Sep 8.

Department of Integrative Structural and Computational Biology, International AIDS Vaccine Initiative ( IAVI) Neutralizing Antibody Center, Collaboration for AIDS Vaccine Discovery, Center for HIV/AIDS Vaccine Immunology and Immunogen Discovery, The Scripps Research Institute, La Jolla, CA 92037; The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA 92037

A key challenge in the quest toward an HIV-1 vaccine is design of immunogens that can generate a broadly neutralizing antibody (bnAb) response against the enormous sequence diversity of the HIV-1 envelope glycoprotein (Env). We previously demonstrated that a recombinant, soluble, fully cleaved SOSIP.664 trimer based on the clade A BG505 sequence is a faithful antigenic and structural mimic of the native trimer in its prefusion conformation. Here, we sought clade C native-like trimers with comparable properties. We identified DU422 and ZM197M SOSIP.664 trimers as being appropriately thermostable (Tm of 63.4 °C and 62.7 °C, respectively) and predominantly native-like, as determined by negative-stain electron microscopy (EM). Size exclusion chromatography, ELISA, and surface plasmon resonance further showed that these trimers properly display epitopes for all of the major bnAb classes, including quaternary-dependent, trimer-apex (e.g., PGT145) and gp120/gp41 interface (e.g., PGT151) epitopes. A cryo-EM reconstruction of the ZM197M SOSIP.664 trimer complexed with VRC01 Fab against the CD4 binding site at subnanometer resolution revealed a striking overall similarity to its BG505 counterpart with expected local conformational differences in the gp120 V1, V2, and V4 loops. These stable clade C trimers contribute additional diversity to the pool of native-like Env immunogens as key components of strategies to induce bnAbs to HIV-1.
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http://dx.doi.org/10.1073/pnas.1507793112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4586835PMC
September 2015

Murine Antibody Responses to Cleaved Soluble HIV-1 Envelope Trimers Are Highly Restricted in Specificity.

J Virol 2015 Oct 5;89(20):10383-98. Epub 2015 Aug 5.

Division of Vaccine Discovery, La Jolla Institute for Allergy and Immunology, La Jolla, California, USA Center for HIV-1/AIDS Vaccine Immunology and Immunogen Discovery (CHAVI-ID), La Jolla, California, USA

Unlabelled: Generating neutralizing antibodies (nAbs) is a major goal of many current HIV-1 vaccine efforts. To be of practical value, these nAbs must be both potent and cross-reactive in order to be capable of preventing the transmission of the highly diverse and generally neutralization resistant (Tier-2) HIV-1 strains that are in circulation. The HIV-1 envelope glycoprotein (Env) spike is the only target for nAbs. To explore whether Tier-2 nAbs can be induced by Env proteins, we immunized conventional mice with soluble BG505 SOSIP.664 trimers that mimic the native Env spike. Here, we report that it is extremely difficult for murine B cells to recognize the Env epitopes necessary for inducing Tier-2 nAbs. Thus, while trimer-immunized mice raised Env-binding IgG Abs and had high-quality T follicular helper (Tfh) cell and germinal center (GC) responses, they did not make BG505.T332N nAbs. Epitope mapping studies showed that Ab responses in mice were specific to areas near the base of the soluble trimer. These areas are not well shielded by glycans and likely are occluded on virions, which is consistent with the lack of BG505.T332N nAbs. These data inform immunogen design and suggest that it is useful to obscure nonneutralizing epitopes presented on the base of soluble Env trimers and that the glycan shield of well-formed HIV Env trimers is virtually impenetrable for murine B cell receptors (BCRs).

Importance: Human HIV vaccine efficacy trials have not generated meaningful neutralizing antibodies to circulating HIV strains. One possible hindrance has been the lack of immunogens that properly mimic the native conformation of the HIV envelope trimer protein. Here, we tested the first generation of soluble, native-like envelope trimer immunogens in a conventional mouse model. We attempted to generate neutralizing antibodies to neutralization-resistant circulating HIV strains. Various vaccine strategies failed to induce neutralizing antibodies to a neutralization-resistant HIV strain. Further analysis revealed that mouse antibodies targeted areas near the bottom of the soluble envelope trimers. These areas are not easily accessible on the HIV virion due to occlusion by the viral membrane and may have resulted from an absence of glycan shielding. Our results suggest that obscuring the bottom of soluble envelope trimers is a useful strategy to reduce antibody responses to epitopes that are not useful for virus neutralization.
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http://dx.doi.org/10.1128/JVI.01653-15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4580201PMC
October 2015