Reversion of Somatic Mutations of the Respiratory Syncytial Virus-Specific Human Monoclonal Antibody Fab19 Reveal a Direct Relationship between Association Rate and Neutralizing Potency

Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37232
The Journal of Immunology (Impact Factor: 4.92). 03/2013; 190(7). DOI: 10.4049/jimmunol.1202964
Source: PubMed


The role of affinity in determining neutralizing potency of mAbs directed against viruses is not well understood. We investigated the kinetic, structural, and functional advantage conferred by individual naturally occurring somatic mutations in the Ab H chain V region of Fab19, a well-described neutralizing human mAb directed to respiratory syncytial virus. Comparison of the affinity-matured Ab Fab19 with recombinant Fab19 Abs that were variants containing reverted amino acids from the inferred unmutated ancestor sequence revealed the molecular basis for affinity maturation of this Ab. Enhanced binding was achieved through mutations in the third H chain CDR (HCDR3) that conferred a markedly faster on-rate and a desirable increase in antiviral neutralizing activity. In contrast, most somatic mutations in the HCDR1 and HCDR2 regions did not significantly enhance Ag binding or antiviral activity. We observed a direct relationship between the measured association rate (Kon) for F protein and antiviral activity. Modeling studies of the structure of the Ag-Ab complex suggested the HCDR3 loop interacts with the antigenic site A surface loop of the respiratory syncytial virus F protein, previously shown to contain the epitope for this Ab by experimentation. These studies define a direct relationship of affinity and neutralizing activity for a viral glycoprotein-specific human mAb.

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    • "Other studies to optimize palivizumab binding of RSV are consistent with the association rate being the dominant factor in the ability of mAbs to neutralize RSV by interacting with the RSV F protein antigenic site A (Wu et al., 2005). We also have shown previously that a direct relationship exists between association rate and RSV-neutralizing activity of the human mAb Fab19 using germline reversion variations of that antibody to remove individual somatic mutations in the antibody that contribute to enhanced affinity and potency (Bates et al., 2013). Association rate is not necessarily the driving factor for all antibody mediated viral neutralization, however, as studies with other viral pathogens also have shown that virus inhibitory activity can be determined predominantly by the dissociation rate (Kallewaard et al., 2008; VanCott et al., 1994). "
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