Antibody Binding in Proximity to the Receptor/Glycoprotein Complex Leads to a Basal Level of Virus Neutralization

155

187

Severe acute respiratory syndrome coronavirus (SARS-CoV) emerged in 2002, and detailed phylogenetic and epidemiological analyses have suggested that it originated from animals. The spike (S) glycoprotein has been identified as a major component of protective immunity, and 23 different amino acid changes were noted during the expanding epidemic. Using a panel of SARS-CoV recombinants bearing the S glycoproteins from isolates representing the zoonotic and human early, middle, and late phases of the epidemic, we identified 23 monoclonal antibodies (MAbs) with neutralizing activity against one or multiple SARS-CoV spike variants and determined the presence of at least six distinct neutralizing profiles in the SARS-CoV S glycoprotein. Four of these MAbs showed cross-neutralizing activity against all human and zoonotic S variants in vitro, and at least three of these were mapped in distinct epitopes using escape mutants, structure analyses, and competition assays. These three MAbs (S109.8, S227.14, and S230.15) were tested for use in passive vaccination studies using lethal SARS-CoV challenge models for young and senescent mice with four different homologous and heterologous SARS-CoV S variants. Both S227.14 and S230.15 completely protected young and old mice from weight loss and virus replication in the lungs for all viruses tested, while S109.8 completely protected mice from weight loss and clinical signs in the presence of viral titers. We conclude that a single human MAb can confer broad protection against lethal challenge with multiple zoonotic and human SARS-CoV isolates, and we identify a robust cocktail formulation that targets distinct epitopes and minimizes the likely generation of escape mutants.

Section: Discussionmentioning

confidence: 92%

Structural Basis for Potent Cross-Neutralizing Human Monoclonal Antibody Protection against Lethal Human and Zoonotic Severe Acute Respiratory Syndrome Coronavirus Challenge

Rockx¹,

Corti²,

Donaldson

et al. 2008

155

187

“…Previous studies have shown that steric hindrance is sufficient for neutralization of viral entry by targeting molecules to the vicinity of the virus and its receptor (33,34). In the human cornea, transmembrane mucins localize to apical membranes of apical epithelial cells, where they closely associate with galectin-3 (13,35).…”

Section: Hsv-1 Binds To Human Galectin-3mentioning

confidence: 99%

Binding of Transmembrane Mucins to Galectin-3 Limits Herpesvirus 1 Infection of Human Corneal Keratinocytes

Woodward

Mauris

Argüeso

2013

Epithelial cells lining mucosal surfaces impose multiple barriers to viral infection. At the ocular surface, the carbohydrate-binding protein galectin-3 maintains barrier function by cross-linking transmembrane mucins on the apical glycocalyx. Despite these defense mechanisms, many viruses have evolved to exploit fundamental cellular processes on host cells. Here, we use affinity assays to show that herpes simplex virus type 1 (HSV-1), but not HSV-2, binds human galectin-3. Knockdown of galectin-3 in human corneal keratinocytes by small interfering RNA significantly impaired HSV-1 infection, but not expression of nectin-1, indicating that galectin-3 is a herpesvirus entry mediator. Interestingly, exposure of epithelial cell cultures to transmembrane mucin isolates decreased viral infectivity. Moreover, HSV-1 failed to elute the biological counterreceptor MUC16 from galectin-3 affinity columns, suggesting that association of transmembrane mucins to galectin-3 provides protection against viral infection. Together, these results indicate that HSV-1 exploits galectin-3 to enhance virus attachment to host cells and support a protective role for transmembrane mucins under physiological conditions by masking viral entry mediators on the epithelial glycocalyx.

“…The feasibility of HIV epitope tagging has been demonstrated recently in elegant studies using HIV and simian immunodeficiency virus (SIV) engrafted with a FLAG epitope tag (DYKDDDDK). These studies showed that antibody binding to envelope spikes is necessary and sufficient for virus neutralization in vitro (36,60,77,78). However, given that only a single anti-epitope tag MAb was utilized in all of these studies, they provided relatively limited information on accessibility of the target epitope to different antibodies.…”

mentioning

confidence: 99%

The Human Immunodeficiency Virus Type 1 Envelope Spike of Primary Viruses Can Suppress Antibody Access to Variable Regions

Pantophlet¹,

Wang²,

Aguilar-Sino³

et al. 2009

The human immunodeficiency virus type 1 (HIV-1) envelope spike is a heavily glycosylated trimeric structure in which protein surfaces conserved between different HIV-1 isolates are particularly well hidden from antibody recognition. However, even variable regions on the spike tend to be less antigenic and immunogenic than one might have anticipated for external structures. Here we show that the envelope spike of primary viruses has an ability to restrict antibody recognition of variable regions. We show that access to an artificial epitope, introduced at multiple positions across the spike, is frequently limited, even though the epitope has been inserted at surface-exposed regions on the spike. Based on the data, we posit that restricted antibody access may be the result, at least in part, of a rigidification of the epitope sequence in the context of the spike and/or a highly effective flexible arrangement of the glycan shield on primary viruses. Evolution of the HIV envelope structure to incorporate extra polypeptide sequences into nominally accessible regions with limited antibody recognition may contribute to reducing the magnitude of antibody responses during infection and allow the virus to replicate unhindered by antibody pressure for longer periods.