Escape mutants of pandemic influenza A/H1N1 2009 virus: variations in antigenic specificity and receptor affinity of the hemagglutinin.

A panel of 6 neutralizing monoclonal antibodies (MAbs) raised against A/Moscow/IIV01/2009 (H1N1) virus isolated during the 2009 pandemic was used for the selection of 26 escape mutants. The mutants were characterized in immune cross-reactions with the panel of MAbs. The sequencing of the mutant HA genes revealed 5 amino acid positions recognized by monoclonal antibodies: 129, 156, 158, 159, and 190 (H3 numbering). The amino acid positions were distributed in two epitopes belonging to antigenic sites Sa and Sb. The mutant HAs exhibited variations in the affinity to synthetic high molecular mass sialic acid-containing receptor analogues. Results are discussed in connection with the antigenic drift potential of the "swine-like" pandemic 2009 influenza virus.