Escape mutant harboring three substitutions completely escapes 53C10 recognition. (A) Alignment of the HA sequences of CA/04 and the survived antibody escape mutant. Three substitutions (G172E, S207R, and E212A) identified from the in vitro antibody selection assay are highlighted using boxes. (B) The structural locations of these three substitutions in the context of CA/04 HA (PDB accession number 3LZG) are shown. G172E, S207R, and E212A are in the antigenic site Sa, receptor-binding site (RBS), and antigenic site Sb, respectively. The influenza virus HA binding sialic acid is shown as sticks. This figure was generated using PyMOL.