Disulfide stabilization of human norovirus GI.1 virus-like particles focuses immune response toward blockade epitopes

Raffaello Verardi,Caitlin E Edwards,Li Ou,Arne Schön,Paul D Brewer-Jensen,Jason Gorman,Lisa C Lindesmith,Ralph S Baric,Ena S Tully,Wei Shi,Gwo-Yu Chuang,Peter D Kwong,George Georgiou,Yaroslav Tsybovsky,Michael L Mallory

doi:10.1038/s41541-020-00260-w

Raffaello Verardi, Caitlin E Edwards + Show 13 more

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https://doi.org/10.1038/s41541-020-00260-w

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Human noroviruses are non-enveloped, single-strand RNA viruses that cause pandemic outbreaks of acute gastroenteritis. A bivalent vaccine containing GI.1 and GII.4 virus-like particles (VLPs) has been shown to be safe and highly immunogenic, but its efficacy and durability have been limited. Here, we show that norovirus GI.1 VLPs are unstable and contain a substantial fraction of dissociated VLP components. Broadly reactive, non-neutralizing antibodies isolated from vaccinated donors bound to the dissociated components, but not to the intact VLPs. Engineering of interprotomer disulfide bonds within the shell domain prevented disassembly of the VLPs, while preserving antibody accessibility to blockade epitopes. Without adjuvant, mice immunized with stabilized GI.1 VLPs developed faster blockade antibody titers compared to immunization with wild-type GI.1 VLPs. In addition, immunization with stabilized particles focused immune responses toward surface-exposed epitopes and away from occluded epitopes. Overall, disulfide-stabilized norovirus GI.1 VLPs elicited improved responses over the non-disulfide-stabilized version, suggesting their promise as candidate vaccines.

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Noroviruses are single-stranded RNA viruses that cause pandemic outbreaks of acute gastroenteritis[1]
In this study, we found that purification of GI.[1] wild-type virus-like particles (VLPs) consistently resulted in a mixture of intact particles and partially dissociated VLP components
negative staining electron microscopy (NS-EM) analysis of these smaller components revealed that the primary species were VP1 dimers

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Introduction

Noroviruses are single-stranded RNA viruses that cause pandemic outbreaks of acute gastroenteritis[1]. They are the primary viral agents of food borne diseases worldwide, and they are responsible for >200,000 deaths per year (mostly among infants and elderly in developing countries)[2]. In the absence of a widely available tissue culture system that can sustain replication of human noroviruses, virus-like particles (VLPs) have been used as a surrogate to study the capsid’s structural features and as immunogens to elicit protective humoral responses[6,7,8]. VLPs have emerged as valuable immunogens for the elicitation of durable protective serological memory[9,10]

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