Antigen improves binding of IgGs to FcγRs in SPR analysis

FcγR binding characterization is one of the critical attributes during the development of therapeutic antibodies. Here, we report a novel assay format to characterize IgG-FcγR interaction in the presence of antigen using Surface plasmon resonance (SPR). The new assay format was developed by creating stable antigen/antibody immunocomplexes on a sensor chip surface before injection of FcγRs. In this assay format, binding activity of both huIgG1 (including IgG1 Fc fusion Protein) and huIgG2 increased significantly to most activating human FcγRs, especially to FcγRI, FcγRIIa-131H and FcγRIIIa-158F. To our knowledge, this study provides the first set of evidence using a biophysical method to demonstrate antigen binding facilitating IgG-FcγR interaction, especially for huIgG2 where previous studies did not indicate its binding to human FcγRI or FcγRIIIa-158F. Although further studies are needed to investigate the correlation of the binding data with effector function data in vivo, our results suggest that it may be useful to evaluate the IgG-FcγR interaction in the presence of antigen to help design safer and more effective biotherapeutics.