Structural Insights Into the Neutralization Properties of the Fully Human, Anti-Interferon Monoclonal Antibody Sifalimumab [Immunology]

April 29th, 2015 by Oganesyan, V., Peng, L., Woods, R. M., Wu, H., Dall'Acqua, W. F.

We report the three-dimensional structure of human interferon α-2A (IFN-α2A) bound to the Fab fragment of a therapeutic monoclonal antibody (sifalimumab; IgG1/k). The structure of the corresponding complex was solved at a resolution of 3.0 Å using molecular replacement and constitutes the first reported structure of a human type I IFN bound to a therapeutic antibody. This study revealed the major contribution made by the first complementarity determining region (CDR) in each of sifalimumab light and heavy chains. These data also provided the molecular basis for sifalimumab mechanism of action. We propose that its interferon-neutralizing properties are the results of direct competition for IFN-α2A binding to the IFN receptor subunit 1 (IFNAR1) and do not involve inhibiting IFN-α2A binding to the IFN receptor subunit 2 (IFNAR2).