Anifrolumab (anifrolumab) is an antagonist human monoclonal antibody that targets interferon α receptor 1 (IFNAR1). Anifrolumab has been developed to treat autoimmune diseases and is currently in clinical trials. To decipher the molecular basis of its mechanism of action, we engaged in multiple epitope mapping approaches to determine how it interacts with IFNAR1 and antagonizes the receptor. We identified the epitope of anifrolumab using enzymatic fragmentation, phage-peptide library panning and mutagenesis approaches. Our studies revealed that anifrolumab recognizes the SD3 subdomain of IFNAR1 with the critical residue R(279). Further, we solved the crystal structure of anifrolumab Fab to a resolution of 2.3 Å. Guided by our epitope mapping studies, we then used in silico protein docking of the anifrolumab Fab crystal structure to IFNAR1 and characterized the corresponding mode of binding. We find that anifrolumab sterically inhibits the binding of IFN ligands to IFNAR1, thus blocking the formation of the ternary IFN/IFNAR1/IFNAR2 signaling complex. This report provides the molecular basis for the mechanism of action of anifrolumab and may provide insights toward designing antibody therapies against IFNAR1.
Keywords: APBS, Adaptive Poisson-Boltzmann Solver; BSA, bovine serum albumin; CDR, complementarity-determining region; CHARMm, Chemistry at HARvard Macromolecular Mechanics; CHO, Chinese hamster ovary; EDTA, ethylene diamine tetra-acetic acid; ELISA, enzyme-linked immunosorbant assay; FBS, fetal bovine serum; Fab, fragment antigen-binding; Fc, fragment crystallizable; IFN, interferon; IFNAR1; IFNAR1, interferon alpha receptor 1; IFNAR2, interferon alpha receptor 2; IgG, immunoglobulin; KD, equilibrium dissociation constant; L-Cys, L-cysteine; MEDI546; MEMα, minimum essential alpha; MLE, murine lung epithelial; PBS, phosphate buffered saline; PBST, phosphate buffered saline tablets; PCR, polymerase chain reaction; PDB, protein data bank; PVDF, polyvinylidene difluoride; Ph.D., phage display; PyMOL, python-enhanced molecular graphics tool; RDOCK, rigid-body docking algorithm; RU, resonance units; SDS–PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; SPR, surface plasmon resonance; VH, variable heavy; VL, variable light; ZDOCK, rigid-body docking algorithm; anifrolumab; enzymatic fragmentation; epitope mapping; kDa, kilodaltons; mutagenesis; phage-peptide display; protein docking; systemic sclerosis; Å, ångström.