Strain-dependent neutralization reveals antigenic variation of human parechovirus 3

Abstract

Human parechovirus 3 (HPeV3), a member of the Picornavirus family, is frequently detected worldwide. However, the observed seropositivity rates for HPeV3 neutralizing antibodies (nAbs) vary from high in Japan to low in the Netherlands and Finland. To study if this can be explained by technical differences or antigenic diversity among HPeV3 strains included in the serological studies, we determined the neutralizing activity of Japanese and Dutch intravenous immunoglobulin batches (IVIG), a rabbit HPeV3 hyperimmune polyclonal serum, and a human HPeV3-specific monoclonal antibody (mAb) AT12-015, against the HPeV3 A308/99 prototype strain and clinical isolates from Japan, the Netherlands and Australia, collected between 1989 and 2015. The rabbit antiserum neutralized all HPeV3 isolates whereas the neutralization capacity of the IVIG batches varied, and the mAb exclusively neutralized the A308/99 strain. Mapping of the amino acid variation among a subset of the HPeV3 strains on an HPeV3 capsid structure revealed that the majority of the surface-exposed amino acid variation was located in the VP1. Furthermore, amino acid mutations in a mAb AT12-015-resistant HPeV3 A308/99 variant indicated the location for potential antigenic determinants. Virus aggregation and the observed antigenic diversity in HPeV3 can explain the varying levels of nAb seropositivity reported in previous studies.

2.8 Å resolution cryo-EM structure of human parechovirus 3 in complex with Fab from a neutralizing antibody

“…Of particular interest is His 206 of VP3 as it was recently shown that an HPeV3 A308/99 variant mutated at this residue position to Tyr escapes neutralization by AT12-015. Our results provide important context to this observation by showing that the nitrogen atom of VP3 His 206 forms a salt bridge with the carbonyl oxygen of Glu 105 in the Fab heavy chain at the center of the antibody footprint (27). Thus we can confirm a key role for VP3 His 206 in driving complex formation.…”

“…One salt bridge between heavy chain amino acid Glu 105 and VP3 residue His 206 was inferred by the fact that centroids of the oppositely charged functional groups of the residues were within a 4 Å cutoff; and the Glu carbonyl oxygen atom was within 4 Å distance from the nitrogen atom of the His side chain (Figure 3B). This His 206 is centrally located in the footprint for the antibody and it was recently reported to be critical for binding and neutralization based on experimental selection of an antibody AT12-015 resistant HPeV3 variant (VP3 His 206 to Tyr) (27).…”

“…Neutralization occurs thus presumably by either directly or indirectly preventing receptor engagement. Such specific targeting rather than generalized clumping is supported by the fact that of all HPeV3 strains bound by AT12-015, only isolate A308/99 is neutralized (27). To date, little is known about HPeV3 receptor and co-receptor dependencies as it lacks the RGD motif and hence probably utilizes an uptake mechanism that differs from other parechovirus types.…”

A 2.8-Angstrom-Resolution Cryo-Electron Microscopy Structure of Human Parechovirus 3 in Complex with Fab from a Neutralizing Antibody

“…Here we report a 2.8-Å-resolution cryo-EM structure of an AT12-015 Fab-decorated HPeV3 virion (isolate A308/99). We have shown in a recent study that this particular virus isolate is neutralized by monoclonal antibody AT12-015 (28). In the highresolution structure, the antigen-antibody interface was well defined, and modeling of viral coat proteins and Fab molecules into densities revealed an extended conformational epitope across the interface of adjacent asymmetric units, involving residues from different parts of neighboring VP0, VP1, and VP3 chains spatially juxtaposed by the structure of the capsid.…”

“…3B). This His 206 is centrally located in the footprint for the antibody, and it was recently reported to be critical for binding and neutralization based on experimental selection of an antibody AT12-015-resistant HPeV3 variant (VP3 His 206 to Tyr) (28). Human monoclonal antibody AT12-015 prevents HPeV3 entry into cells.…”