Glycan remodeled erythrocytes facilitate antigenic characterization of recent A/H3N2 influenza viruses

During circulation in humans and natural selection to escape antibody recognition for decades, A/H3N2 influenza viruses emerged with altered receptor specificities. These viruses lost the ability to agglutinate erythrocytes critical for antigenic characterization and give low yields and acquire adaptive mutations when cultured in eggs and cells, contributing to recent vaccine challenges. We examined receptor specificities of A/H3N2 viruses, revealing that recent viruses compensated for decreased binding of the prototypic human receptor by recognizing 2,6-sialosides on extended LacNAc moieties. Erythrocyte glycomics showed an absence of extended glycans, providing a rationale for lack of agglutination by recent A/H3N2 viruses. A glycan remodeling approach installed functional receptors on erythrocytes, allowing antigenic characterization of recent A/H3N2 viruses and confirming the cocirculation of several antigenically different viruses in humans. Computational studies of HAs in complex with a sialoside having an extended LacNAc moiety revealed that mutations distal to the RBD reoriented the Y159 side chain, resulting in an extended receptor binding site.