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Effects of egg-adaptation on receptor-binding and antigenic properties of recent influenza A (H3N2) vaccine viruses.

ABSTRACT: Influenza A virus (subtype H3N2) causes seasonal human influenza and is included as a component of influenza vaccines. The majority of vaccine viruses are isolated and propagated in eggs, which commonly results in amino acid substitutions in the haemagglutinin (HA) glycoprotein. These substitutions can affect virus receptor-binding and alter virus antigenicity, thereby, obfuscating the choice of egg-propagated viruses for development into candidate vaccine viruses. To evaluate the effects of egg-adaptive substitutions seen in H3N2 vaccine viruses on sialic acid receptor-binding, we carried out quantitative measurement of virus receptor-binding using surface biolayer interferometry with haemagglutination inhibition (HI) assays to correlate changes in receptor avidity with antigenic properties. Included in these studies was a panel of H3N2 viruses generated by reverse genetics containing substitutions seen in recent egg-propagated vaccine viruses and corresponding cell culture-propagated wild-type viruses. These assays provide a quantitative approach to investigating the importance of individual amino acid substitutions in influenza receptor-binding. Results show that viruses with egg-adaptive HA substitutions R156Q, S219Y, and I226N, have increased binding avidity to ?2,3-linked receptor-analogues and decreased binding avidity to ?2,6-linked receptor-analogues. No measurable binding was detected for the viruses with amino acid substitution combination 156Q+219Y and receptor-binding increased in viruses where egg-adaptation mutations were introduced into cell culture-propagated virus. Substitutions at positions 156 and 190 appeared to be primarily responsible for low reactivity in HI assays with post-infection ferret antisera raised against 2012-2013 season H3N2 viruses. Egg-adaptive substitutions at position 186 caused substantial differences in binding avidity with an insignificant effect on antigenicity.

SUBMITTER: Parker L

PROVIDER: S-EPMC5394856 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Effects of egg-adaptation on receptor-binding and antigenic properties of recent influenza A (H3N2) vaccine viruses.

Parker Lauren L Wharton Stephen A SA Martin Stephen R SR Cross Karen K Lin Yipu Y Liu Yan Y Feizi Ten T Daniels Rodney S RS McCauley John W JW

The Journal of general virology 20160314 6

Influenza A virus (subtype H3N2) causes seasonal human influenza and is included as a component of influenza vaccines. The majority of vaccine viruses are isolated and propagated in eggs, which commonly results in amino acid substitutions in the haemagglutinin (HA) glycoprotein. These substitutions can affect virus receptor-binding and alter virus antigenicity, thereby, obfuscating the choice of egg-propagated viruses for development into candidate vaccine viruses. To evaluate the effects of egg ...[more]

PMID: 26974849

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Project description:BackgroundHuman influenza viruses are known to bind to sialic acid linked alpha2-6 to galactose, but the binding specificity beyond that linkage has not been systematically examined. H3N2 human influenza isolates lost binding to chicken red cells in the 1990s but viruses isolated since 2003 have re-acquired the ability to agglutinate chicken erythrocytes. We have investigated specificity of binding, changes in hemagglutinin sequence of the recent viruses and the role of sialic acid in productive infection.ResultsViruses that agglutinate, or do not agglutinate, chicken red cells show identical binding to a Glycan Array of 264 oligosaccharides, binding exclusively to a subset of alpha2-6-sialylsaccharides. We identified an amino acid change in hemagglutinin that seemed to correlate with chicken red cell binding but when tested by mutagenesis there was no effect. Recombinant hemagglutinins expressed on Sf-9 cells bound chicken red cells but the released recombinant baculoviruses agglutinated only human red cells. Similarly, an isolate that does not agglutinate chicken red cells show hemadsorption of chicken red cells to infected MDCK cells. We suggest that binding of chicken red cells to cell surface hemagglutinin but not to virions is due to a more favorable hemagglutinin density on the cell surface. We investigated whether a virus specific for alpha2-6 sialyloligosaccharides shows differential entry into cells that have varying proportions of alpha2-6 and alpha2-3 sialic acids, including human A549 and HeLa cells with high levels of alpha2-6 sialic acid, and CHO cells that have only alpha2-3 sialic acid. We found that the virus enters all cell types tested and synthesizes viral nucleoprotein, localized in the nucleus, and hemagglutinin, transported to the cell surface, but infectious progeny viruses were released only from MDCK cells.ConclusionAgglutination of chicken red cells does not correlate with altered binding to any oligosaccharide on the Glycan Array, and may result from increased avidity due to density of hemagglutinin and not increased affinity. Absence of alpha2-6 sialic acid does not protect a cell from influenza infection and the presence of high levels of alpha2-6-sialic acids on a cell surface does not guarantee productive replication of a virus with alpha2-6 receptor specificity.

Project description:BackgroundInfluenza vaccine effectiveness (VE) is generally interpreted in the context of vaccine match/mismatch to circulating strains with evolutionary drift in the latter invoked to explain reduced protection. During the 2012-13 season, however, detailed genotypic and phenotypic characterization shows that low VE was instead related to mutations in the egg-adapted H3N2 vaccine strain rather than antigenic drift in circulating viruses.Methods/findingsComponent-specific VE against medically-attended, PCR-confirmed influenza was estimated in Canada by test-negative case-control design. Influenza A viruses were characterized genotypically by amino acid (AA) sequencing of established haemagglutinin (HA) antigenic sites and phenotypically through haemagglutination inhibition (HI) assay. H3N2 viruses were characterized in relation to the WHO-recommended, cell-passaged vaccine prototype (A/Victoria/361/2011) as well as the egg-adapted strain as per actually used in vaccine production. Among the total of 1501 participants, influenza virus was detected in 652 (43%). Nearly two-thirds of viruses typed/subtyped were A(H3N2) (394/626; 63%); the remainder were A(H1N1)pdm09 (79/626; 13%), B/Yamagata (98/626; 16%) or B/Victoria (54/626; 9%). Suboptimal VE of 50% (95%CI: 33-63%) overall was driven by predominant H3N2 activity for which VE was 41% (95%CI: 17-59%). All H3N2 field isolates were HI-characterized as well-matched to the WHO-recommended A/Victoria/361/2011 prototype whereas all but one were antigenically distinct from the egg-adapted strain as per actually used in vaccine production. The egg-adapted strain was itself antigenically distinct from the WHO-recommended prototype, and bore three AA mutations at antigenic sites B [H156Q, G186V] and D [S219Y]. Conversely, circulating viruses were identical to the WHO-recommended prototype at these positions with other genetic variation that did not affect antigenicity. VE was 59% (95%CI:16-80%) against A(H1N1)pdm09, 67% (95%CI: 30-85%) against B/Yamagata (vaccine-lineage) and 75% (95%CI: 29-91%) against B/Victoria (non-vaccine-lineage) viruses.ConclusionsThese findings underscore the need to monitor vaccine viruses as well as circulating strains to explain vaccine performance. Evolutionary drift in circulating viruses cannot be regulated, but influential mutations introduced as part of egg-based vaccine production may be amenable to improvements.

Project description:Influenza A H3N2 variant [A(H3N2)v] viruses, which have caused human infections in the United States in recent years, originated from human seasonal H3N2 viruses that were introduced into North American swine in the mid-1990s, but they are antigenically distinct from both the ancestral and current circulating H3N2 strains. A reference A(H3N2)v virus, A/Minnesota/11/2010 (MN/10), and a seasonal H3N2 strain, A/Beijing/32/1992 (BJ/92), were chosen to determine the molecular basis for the antigenic difference between A(H3N2)v and the ancestral viruses. Viruses containing wild-type and mutant MN/10 or BJ/92 hemagglutinins (HAs) were constructed and probed for reactivity with ferret antisera against MN/10 and BJ/92 in hemagglutination inhibition assays. Among the amino acids that differ between the MN/10 and BJ/92 HAs, those in antigenic site A had little impact on the antigenic phenotype. Within antigenic site B, mutations at residues 156, 158, 189, and 193 of MN/10 HA to those in BJ/92 switched the MN/10 antigenic phenotype to that of BJ/92. Mutations at residues 156, 157, 158, 189, and 193 of BJ/92 HA to amino acids present in MN/10 were necessary for BJ/92 to become antigenically similar to MN/10. The HA amino acid substitutions responsible for switching the antigenic phenotype also impacted HA binding to sialyl receptors that are usually present in the human respiratory tract. Our study demonstrates that antigenic site B residues play a critical role in determining both the unique antigenic phenotype and receptor specificity of A(H3N2)v viruses, a finding that may facilitate future surveillance and risk assessment of novel influenza viruses. IMPORTANCE:Influenza A H3N2 variant [A(H3N2)v] viruses have caused hundreds of human infections in multiple states in the United States since 2009. Most cases have been children who had contact with swine in agricultural fairs. These viruses originated from human seasonal H3N2 viruses that were introduced into the U.S. swine population in the mid-1990s, but they are different from both these ancestral viruses and current circulating human seasonal H3N2 strains in terms of their antigenic characteristics as measured by hemagglutination inhibition (HI) assay. In this study, we identified amino acids in antigenic site B of the surface glycoprotein hemagglutinin (HA) that explain the antigenic difference between A(H3N2)v and the ancestral H3N2 strains. These amino acid mutations also alter binding to minor human-type glycans, suggesting that host adaptation may contribute to the selection of antigenically distinct H3N2 variants which pose a threat to public health.

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Effects of egg-adaptation on receptor-binding and antigenic properties of recent influenza A (H3N2) vaccine viruses.

Publications

Effects of egg-adaptation on receptor-binding and antigenic properties of recent influenza A (H3N2) vaccine viruses.

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