Assorted Mutations in the Envelope Gene of Simian Immunodeficiency Virus Lead to Loss of Neutralization Resistance against Antibodies Representing a Broad Spectrum of Specificities

Abstract

Simian immunodeficiency virus (SIV) of macaques isolate SIVmac239 is highly resistant to neutralization by polyclonal antisera or monoclonal antibodies, a property that it shares with most primary isolates of human immunodeficiency virus type 1 (HIV-1). This resistance is important for the ability of the virus to persist at high levels in vivo. To explore the physical features of the viral envelope complex that contribute to the neutralization-resistant phenotype, we examined a panel of SIVmac239 derivatives for sensitivity to neutralization by a large collection of monoclonal antibodies (MAbs). These MAbs recognize both linear and conformational epitopes throughout the viral envelope proteins. The variant viruses included three derivatives of SIVmac239 with substitutions in specific N-linked glycosylation sites of gp120 and a fourth variant that lacked the100 amino acids that encompass the V1 and V2 loops. Also included in this study was SIVmac316, a variant of SIVmac239 with distributed mutations in env that confer significantly increased replicative capacity in tissue macrophages. These viruses were chosen to represent a broad range of neutralization sensitivities based on susceptibility to pooled, SIV-positive plasma. All three of these very different kinds of mutations (amino acid substitutions, elimination of N-glycan attachment sites, and a 100-amino-acid deletion spanning variable loops V1 and V2) dramatically increased sensitivity to neutralization by MAbs from multiple competition groups. Thus, the mutations did not simply expose localized epitopes but rather conferred global increases in neutralization sensitivity. The removal of specific N-glycan attachment sites from V1 and V2 led to increased sensitivity to neutralization by antibodies recognizing epitopes from both within and outside of the V1-V2 sequence. Surprisingly, while most of the mutations that gave rise to increased sensitivity were located in the N-terminal half of gp120 (surface subunit [SU]), the greatest increases in sensitivity were to MAbs recognizing the C-terminal half of gp120 or the ectodomain of gp41 (transmembrane subunit [TM]). This reagent set and information should now be useful for defining the physical, structural, thermodynamic, and kinetic factors that influence relative sensitivity to antibody-mediated neutralization.

Kinetic Rates of Antibody Binding Correlate with Neutralization Sensitivity of Variant Simian Immunodeficiency Virus Strains

“…This suggests that more antibody remains bound to the SIV/17E-CL virion, occupying more envelope trimers, than the same MAb does on the SIVmac239 virion over time. Taken together, the results presented in this study and others support the hypothesis that neutralization involves a combination of epitope specificity and binding properties (i.e., rates and affinity) (9,24,56).…”

“…It has been proposed that neutralizing antibody epitopes on CD4-independent envelope proteins may be more accessible, since the envelope is suggested to be in a more "open" or "triggered" conformation (3,17,22,42). In addition, increases in sensitivity to MAbmediated neutralization have also been reported for viruses containing limited amino acid changes with respect to SIVmac239 or containing deletions of glycosylation sites and/or variable regions that have previously been shown to limit antibody recognition (24). Despite differences in amino acid sequence between SIV/17E-CL and SIVmac239, to our surprise, we observed faster MAb association with SIVmac239 than with SIV/17E-CL rgp140.…”

Canine Distemper Viruses Expressing a Hemagglutinin without N-Glycans Lose Virulence but Retain Immunosuppression

“…Our comparative neutralization assays demonstrated that not only are fully glycosylated and deglycosylated wild-type viruses neutralized with equal efficiency by all sera, including those raised against the vaccine H protein, but the vaccine H protein is more immunogenic than circulating wild-type H proteins. These results, together with the remarkable conservation of the wild-type N-glycosylation pattern despite high vaccine coverage, thus argues against a glycan shield escape mechanism in morbilliviruses, as has been proposed for HIV (20,34,53).…”

Significance of the oligosaccharides of the porcine reproductive and respiratory syndrome virus glycoproteins GP2a and GP5 for infectious virus production

“…Another level at which the GP 2a -linked sugars might act is the immune system. Several studies have shown that the oligosaccharides can shield critical epitopes from immune recognition (see for example Back et al, 1994;Huso et al, 1988;Johnson et al, 2003). Results of such studies might also be relevant for an understanding of the protective features of the Primepac vaccine strain.…”