Asymmetric antiviral effects of ebolavirus antibodies targeting glycoprotein stem and glycan cap.

Philipp A Ilinykh,Rodrigo I Santos,Bronwyn M Gunn,Pavlo Gilchuk,James E Crowe,Galit Alter,Xiaoli Shen,Patrick Younan,Natalia A Kuzmina,Kai Huang,Alexander Bukreyev,Andrew I Flyak,Jens H Kuhn

doi:10.1371/journal.ppat.1007204

Abstract

Recent studies suggest that some monoclonal antibodies (mAbs) specific for ebolavirus glycoprotein (GP) can protect experimental animals against infections. Most mAbs isolated from ebolavirus survivors appeared to target the glycan cap or the stalk region of the viral GP, which is the envelope protein and the only antigen inducing virus-neutralizing antibody response. Some of the mAbs were demonstrated to be protective in vivo. Here, a panel of mAbs from four individual survivors of ebolavirus infection that target the glycan cap or stem region were selected for investigation of the mechanisms of their antiviral effect. Comparative characterization of the inhibiting effects on multiple steps of viral replication was performed, including attachment, post-attachment, entry, binding at low pH, post-cleavage neutralization of virions, viral trafficking to endosomes, cell-to-cell transmission, viral egress, and inhibition when added early at various time points post-infection. In addition, Fc-domain related properties were characterized, including activation and degranulation of NK cells, antibody-dependent cellular phagocytosis and glycan content. The two groups of mAbs (glycan cap versus stem) demonstrated very different profiles of activities suggesting usage of mAbs with different epitope specificity could coordinate inhibition of multiple steps of filovirus infection through Fab- and Fc-mediated mechanisms, and provide a reliable therapeutic approach.

Highlights

Filoviruses are enveloped, filamentous-like viruses with non-segmented RNA genome of negative polarity
Recent progress in isolation of monoclonal antibodies (mAbs) from survivors of filovirus infections suggests that the human adaptive immune system is capable of producing strong antibody responses
We evaluated a panel of mAbs obtained from survivors of natural filovirus infections, specific for the glycan cap or stem region of GP, for their effects on the attachment of viral particles to the cell surface, intracellular traffic of viral particles, proteolytic processing of GP, its interaction with the NPC1 receptor, cell-to-cell virus transmission, virus egress from infected cells, activation of natural killer cells and antibody-dependent cellular phagocytosis through Fc-mediated mechanisms

Summary

Introduction

Filoviruses are enveloped, filamentous-like viruses with non-segmented RNA genome of negative polarity. The Ebolavirus genus of the Filoviridae family includes five species: Ebola (EBOV), Sudan (SUDV), Bundibugyo (BDBV), Taï Forest (TAFV) and Reston (RESTV) viruses. Most of these viruses are responsible for highly lethal disease outbreaks, for example the occurrence of 11,323 human fatalities during the 2013–2016 EBOV epidemic in West Africa [1, 2]. The GP2 subunit forms a GP stalk containing the hydrophobic internal fusion loop (IFL), two heptad repeats (HR1 and HR2), the membrane-proximal external region (MPER), the transmembrane anchor and the short cytoplasmic domain This subunit is responsible for fusion of the viral and host cell membranes during the entry

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Conclusion