Different Infectivity of HIV-1 Strains Is Linked to Number of Envelope Trimers Required for Entry

Brandenberg, Oliver F.; Magnus, Carsten; Rusert, Peter; Regoes, Roland R.; Trkola, Alexandra

doi:10.1371/journal.ppat.1004595

Cited by 82 publications

(108 citation statements)

References 82 publications

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“…It is tempting to speculate that HIV-1 will reach maximum infectivity near to its natural number of spikes of 7 to 14 spikes per virion and that a dense array of Env is unnecessary for maximum infectivity. A caveat, however, is that infectivity requirements can differ with the type of target cell, particularly with cells having low levels of CD4 (e.g., macrophages) (63), or in the case of Envs of low intrinsic infectivity (48,50,51). Additional studies to determine the infectivity of hVLPs in which target cells and envelopes are varied will therefore be informative.…”

Section: Discussionmentioning

confidence: 99%

Dense Array of Spikes on HIV-1 Virion Particles

Stano

Leaman

Kim

et al. 2017

J Virol

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HIV-1 is rare among viruses for having a low number of envelope glycoprotein (Env) spikes per virion, i.e., ϳ7 to 14. This exceptional feature has been associated with avoidance of humoral immunity, i.e., B cell activation and antibody neutralization. Virus-like particles (VLPs) with increased density of Env are being pursued for vaccine development; however, these typically require protein engineering that alters Env structure. Here, we used instead a strategy that targets the producer cell. We employed fluorescence-activated cell sorting (FACS) to sort for cells that are recognized by trimer cross-reactive broadly neutralizing antibody (bnAb) and not by nonneutralizing antibodies. Following multiple iterations of FACS, cells and progeny virions were shown to display higher levels of antigenically correct Env in a manner that correlated between cells and cognate virions (P ϭ 0.027). High-Env VLPs, or hVLPs, were shown to be monodisperse and to display more than a 10-fold increase in spikes per particle by electron microscopy (average, 127 spikes; range, 90 to 214 spikes). Sequencing revealed a partial truncation in the C-terminal tail of Env that had emerged in the sort; however, iterative rounds of "cell factory" selection were required for the high-Env phenotype. hVLPs showed greater infectivity than standard pseudovirions but largely similar neutralization sensitivity. Importantly, hVLPs also showed superior activation of Env-specific B cells. Hence, high-Env HIV-1 virions, obtained through selection of producer cells, represent an adaptable platform for vaccine design and should aid in the study of native Env.IMPORTANCE The paucity of spikes on HIV is a unique feature that has been associated with evasion of the immune system, while increasing spike density has been a goal of vaccine design. Increasing the density of Env by modifying it in various ways has met with limited success. Here, we focused instead on the producer cell. Cells that stably express HIV spikes were screened on the basis of high binding by bnAbs and low binding by nonneutralizing antibodies. Levels of spikes on cells correlated well with those on progeny virions. Importantly, high-Env virus-like particles (hVLPs) were produced with a manifest array of well-defined spikes, and these were shown to be superior in activating desirable B cells. Our study describes HIV particles that are densely coated with functional spikes, which should facilitate the study of HIV spikes and their development as immunogens.KEYWORDS antigenicity, broadly neutralizing antibodies, envelope glycoprotein, fluorescence-activated cell sorting, HIV-1, vaccine design, virus-like particles, cellPACK, electron microscopy, viral infectivity H uman immunodeficiency virus type 1 (HIV-1) displays around 7 to 14 envelope (Env) spikes per virion (1-3). This low number of spikes is unusual for enveloped viruses in comparison to numbers for influenza virus (ϳ400 to 500 spikes), vesicular

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Section: Discussionmentioning

confidence: 99%

Dense Array of Spikes on HIV-1 Virion Particles

Stano

Leaman

Kim

et al. 2017

J Virol

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“…HIV mediates target cell infection through binding of 2 to 3 spikes to cell surface CD4 (82). This constitutes the first step in the dynamic process in which structural elements of the envelope shift and rearrange to gain function, ultimately leading to gp41-mediated membrane fusion and the introduction of the viral nucleocapsid into the cytoplasm of target cells (83).…”

Section: Discussionmentioning

confidence: 99%

Range of CD4-Bound Conformations of HIV-1 gp120, as Defined Using Conditional CD4-Induced Antibodies

Kaplan

Roitburd-Berman

Lewis

et al. 2016

J Virol

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The HIV envelope binds cellular CD4 and undergoes a range of conformational changes that lead to membrane fusion and delivery of the viral nucleocapsid into the cellular cytoplasm. This binding to CD4 reveals cryptic and highly conserved epitopes, the molecular nature of which is still not fully understood. The atomic structures of CD4 complexed with gp120 core molecules (a form of gp120 in which the V1, V2, and V3 loops and N and C termini have been truncated) have indicated that a hallmark feature of the CD4-bound conformation is the bridging sheet minidomain. Variations in the orientation of the bridging sheet hairpins have been revealed when CD4-liganded gp120 was compared to CD4-unliganded trimeric envelope structures. Hence, there appears to be a number of conformational transitions possible in HIV-1 monomeric gp120 that are affected by CD4 binding. The spectrum of CD4-bound conformations has been interrogated in this study by using a well-characterized panel of conditional, CD4-induced (CD4i) monoclonal antibodies (MAbs) that bind HIV-1 gp120 and its mutations under various conditions. Two distinct CD4i epitopes of the outer domain were studied: the first comprises the bridging sheet, while the second contains elements of the V2 loop. Furthermore, we show that the unliganded extended monomeric core of gp120 (core e ) assumes an intermediate CD4i conformation in solution that further undergoes detectable rearrangements upon association with CD4. These discoveries impact both accepted paradigms concerning gp120 structure and the field of HIV immunogen design. IMPORTANCE Elucidation of the conformational transitions that the HIV-1 envelope protein undergoes during the course of entry into CD4؉ cells is fundamental to our understanding of HIV biology. The binding of CD4 triggers a range of gp120 structural rearrangements that could present targets for future drug design and development of preventive vaccines. Here we have systematically interrogated and scrutinized these conformational transitions using a panel of antibody probes that share a specific preference for the CD4i conformations. These have been employed to study a collection of gp120 mutations and truncations. Through these analyses, we propose 4 distinct sequential steps in CD4i transitions of gp120 conformations, each defined by antibody specificities and structural requirements of the HIV envelope monomer. As a result, we not only provide new insights into this dynamic process but also define probes to further investigate HIV infection. V iral tropism is mediated by the specific binding of the viral spike protein to its corresponding cell surface receptor. Evolution has driven human immunodeficiency virus (HIV) to elaborate on this canonical paradigm, introducing a series of orchestrated sequential events involving two receptors: CD4 as a primary receptor (1-3) and a chemokine receptor (CXCR4 or CCR5) as a subsequent coreceptor (4-10). However, many critical details of the molecular mechanisms by which CD4 triggers a number of conformati...

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“…2B and C) (86)(87)(88). Env incorporation into virions is regulated by interactions with other viral proteins and host factors (reviewed in references 89 and 90).…”

Section: Human Immunodeficiency Virus Typementioning

confidence: 99%

“…Next, rearrangements in HR1 and HR2 facilitate the refolding of gp41 into a six-helix bundle that brings together the cellular and viral membranes, creating a pore that allows the viral core to enter cells (117). The number of functional Env trimers needed to interact with target cell receptors and mediate virus entry has not been precisely determined and may vary by strain but has been estimated to be between one and eight (88,(118)(119)(120)(121).…”

Section: Human Immunodeficiency Virus Typementioning

confidence: 99%

“…The low density of Env on HIV-1 virions has been suggested to limit the neutralizing activity of some HIV-1-reactive MAbs (reviewed in reference 214). Biochemical and structural studies have estimated that the average HIV-1 virion has a small number of Env spikes on its surface (ϳ14) (86)(87)(88). Comparisons of the neutralization potencies of IgG and Fab fragments of anti-HIV-1 antibodies revealed similar potencies, suggesting that bivalent recognition is uncommon (214).…”

Section: Low Density Of Surface Glycoproteinsmentioning

confidence: 99%

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Deconstructing the Antiviral Neutralizing-Antibody Response: Implications for Vaccine Development and Immunity

VanBlargan

Goo

Pierson

2016

Microbiol Mol Biol Rev

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SUMMARY The antibody response plays a key role in protection against viral infections. While antiviral antibodies may reduce the viral burden via several mechanisms, the ability to directly inhibit (neutralize) infection of cells has been extensively studied. Eliciting a neutralizing-antibody response is a goal of many vaccine development programs and commonly correlates with protection from disease. Considerable insights into the mechanisms of neutralization have been gained from studies of monoclonal antibodies, yet the individual contributions and dynamics of the repertoire of circulating antibody specificities elicited by infection and vaccination are poorly understood on the functional and molecular levels. Neutralizing antibodies with the most protective functionalities may be a rare component of a polyclonal, pathogen-specific antibody response, further complicating efforts to identify the elements of a protective immune response. This review discusses advances in deconstructing polyclonal antibody responses to flavivirus infection or vaccination. Our discussions draw comparisons to HIV-1, a virus with a distinct structure and replication cycle for which the antibody response has been extensively investigated. Progress toward deconstructing and understanding the components of polyclonal antibody responses identifies new targets and challenges for vaccination strategies.

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Different Infectivity of HIV-1 Strains Is Linked to Number of Envelope Trimers Required for Entry

Cited by 82 publications

References 82 publications

Dense Array of Spikes on HIV-1 Virion Particles

Dense Array of Spikes on HIV-1 Virion Particles

Range of CD4-Bound Conformations of HIV-1 gp120, as Defined Using Conditional CD4-Induced Antibodies

Deconstructing the Antiviral Neutralizing-Antibody Response: Implications for Vaccine Development and Immunity

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