Characterization of the epitope for anti-human respiratory syncytial virus F protein monoclonal antibody 101F using synthetic peptides and genetic approaches

Chimeric 101F (ch101F) is a mouse-human chimeric anti-human respiratory syncytial virus (HRSV) neutralizing antibody that recognizes residues within antigenic site IV, V, VI of the fusion (F) glycoprotein. The binding of ch101F to a series of peptides overlapping aa 422-438 spanning antigenic site IV, V, VI was analysed. Residues 423-436 comprise the minimal peptide sequence for ch101IF binding. Substitution analysis revealed that R429 and K433 are critical for ch101F binding, whilst K427 makes a minor contribution. Binding of ch101IF to a series of single mutations at positions 427, 429 and 433 in the IF protein expressed recombinantly on the cell surface confirmed the peptide results. Sequence analysis of viruses selected for resistance to neutralization by ch101IF indicated that a single change (K433T) in the F protein allowed ch101IF escape. The results confirm that ch101IF and palivizumab have different epitope specificity and define key residues for ch101F recognition.