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Increasing Type 1 Poliovirus Capsid Stability by Thermal Selection.

ABSTRACT: Poliomyelitis is a highly infectious disease caused by poliovirus (PV). It can result in paralysis and may be fatal. Integrated global immunization programs using live-attenuated oral (OPV) and/or inactivated (IPV) PV vaccines have systematically reduced its spread and paved the way for eradication. Immunization will continue posteradication to ensure against reintroduction of the disease, but there are biosafety concerns for both OPV and IPV. They could be addressed by the production and use of virus-free virus-like particle (VLP) vaccines that mimic the "empty" capsids (ECs) normally produced in viral infection. Although ECs are antigenically indistinguishable from mature virus particles, they are less stable and readily convert into an alternative conformation unsuitable for vaccine purposes. Stabilized ECs, expressed recombinantly as VLPs, could be ideal candidate vaccines for a polio-free world. However, although genome-free PV ECs have been expressed as VLPs in a variety of systems, their inherent antigenic instability has proved a barrier to further development. In this study, we selected thermally stable ECs of type 1 PV (PV-1). The ECs are antigenically stable at temperatures above the conversion temperature of wild-type (wt) virions. We have identified mutations on the capsid surface and in internal networks that are responsible for EC stability. With reference to the capsid structure, we speculate on the roles of these residues in capsid stability and postulate that such stabilized VLPs could be used as novel vaccines. IMPORTANCE:Poliomyelitis is a highly infectious disease caused by PV and is on the verge of eradication. There are biosafety concerns about reintroduction of the disease from current vaccines that require live virus for production. Recombinantly expressed virus-like particles (VLPs) could address these inherent problems. However, the genome-free capsids (ECs) of wt PV are unstable and readily change antigenicity to a form not suitable as a vaccine. Here, we demonstrate that the ECs of type 1 PV can be stabilized by selecting heat-resistant viruses. Our data show that some capsid mutations stabilize the ECs and could be applied as candidates to synthesize stable VLPs as future genome-free poliovirus vaccines.

SUBMITTER: Adeyemi OO

PROVIDER: S-EPMC5286869 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Increasing Type 1 Poliovirus Capsid Stability by Thermal Selection.

Adeyemi Oluwapelumi O OO Nicol Clare C Stonehouse Nicola J NJ Rowlands David J DJ

Journal of virology 20170131 4

Poliomyelitis is a highly infectious disease caused by poliovirus (PV). It can result in paralysis and may be fatal. Integrated global immunization programs using live-attenuated oral (OPV) and/or inactivated (IPV) PV vaccines have systematically reduced its spread and paved the way for eradication. Immunization will continue posteradication to ensure against reintroduction of the disease, but there are biosafety concerns for both OPV and IPV. They could be addressed by the production and use of ...[more]

PMID: 27928008

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Project description:Virus capsid proteins must perform a number of roles. These include self-assembly and maintaining stability under challenging environmental conditions, while retaining the conformational flexibility necessary to uncoat and deliver the viral genome into a host cell. Fulfilling these roles could place conflicting constraints on the innate abilities encoded within the protein sequences. In a previous study, we identified a number of mutations within the capsid-coding sequence of poliovirus (PV) that were established in the population during selection for greater thermostability by sequential treatment at progressively higher temperatures. Two mutations in the VP1 protein acquired at an early stage were maintained throughout this selection procedure. One of these mutations prevented virion assembly when introduced into a wild-type (wt) infectious clone. Here we show, by sequencing beyond the capsid-coding region of the heat-selected virions, that two mutations had arisen within the coding region of the 2A protease. Both mutations were maintained throughout the selection process. Introduction of these mutations into a wt infectious clone by site-directed mutagenesis considerably reduced replication. However, they permitted a low level of assembly of infectious virions containing the otherwise lethal mutation in VP1. The 2Apro mutations were further shown to slow the kinetics of viral polyprotein processing, and we suggest that this delay improves the correct folding of the mutant capsid precursor protein to permit virion assembly.IMPORTANCE RNA viruses, including poliovirus, evolve rapidly due to the error-prone nature of the polymerase enzymes involved in genome replication. Fixation of advantageous mutations may require the acquisition of complementary mutations which can act in concert to achieve a favorable phenotype. This study highlights a compensatory role of a nonstructural regulatory protein, 2Apro, for an otherwise lethal mutation of the structural VP1 protein to facilitate increased thermal resistance. Studying how viruses respond to selection pressures is important for understanding mechanisms which underpin emergence of resistance and could be applied to the future development of antiviral agents and vaccines.

Project description:BackgroundSabin strains used in oral poliovirus vaccines (OPV) can revert to virulence and, in rare instances, cause disease or generate vaccine-derived strains leading to outbreaks in areas of low immunisation coverage. A novel OPV2 (nOPV2) was designed to stabilise the viral genome against reversion and reduce recombination events that might lead to virulent strains. In this study, we evaluated the genetic and phenotypic stability of shed poliovirus following administration of one dose of monovalent OPV2 (mOPV2) or nOPV2 to infants aged 18-22 weeks.MethodsIn two similarly designed clinical trials (NCT02521974 and NCT03554798) conducted in Panama, infants aged 18-22-weeks, after immunisation with three doses of bivalent OPV (types 1 and 3) and one dose of inactivated poliovirus vaccine, were administered one or two doses of mOPV2 or nOPV2. In this analysis of two clinical trials, faecally shed polioviruses following one dose of mOPV2 or nOPV2 were isolated from stools meeting predetermined criteria related to sample timing and viral presence and quantity and assessed for nucleotide polymorphisms using next-generation sequencing. A transgenic mouse neurovirulence test was adapted to assess the effect of the possible phenotypic reversion of shed mOPV2 and nOPV2 with a logistic regression model.FindingsOf the 91 eligible samples, 86 were able to be sequenced, with 72 evaluated in the transgenic mouse assay. Sabin-2 poliovirus reverts rapidly at nucleotide 481, the primary attenuation site in domain V of the 5' untranslated region of the genome. There was no evidence of neurovirulence-increasing polymorphisms in domain V of shed nOPV2. Reversion of shed Sabin-2 virus corresponded with unadjusted paralysis rates of 47·6% at the 4 log10 50% cell culture infectious dose (CCID50) and 76·7% at the 5 log10 CCID50 inoculum levels, with rates of 2·8% for 4 log10 CCID50 and 11·8% for 5 log10 CCID50 observed for shed nOPV2 samples. The estimated adjusted odds ratio at 4·5 log10 of 0·007 (95% CI 0·002-0·023; p<0·0001) indicates significantly reduced odds of mouse paralysis from virus obtained from nOPV2 recipients compared with mOPV2 recipients.InterpretationThe data indicate increased genetic stability of domain V of nOPV2 relative to mOPV2, with significantly lower neurovirulence of shed nOPV2 virus compared with shed mOPV2. While this vaccine is currently being deployed under an emergency use listing, the data on the genetic stability of nOPV2 will support further regulatory and policy decision-making regarding use of nOPV2 in outbreak responses.FundingBill & Melinda Gates Foundation.

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Dataset Information

Increasing Type 1 Poliovirus Capsid Stability by Thermal Selection.

Publications

Increasing Type 1 Poliovirus Capsid Stability by Thermal Selection.

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