Background/Purpose: Increased type I interferon (IFN) activity is associated with the pathogenesis of SLE. Anifrolumab, a fully human immunoglobulin (Ig) G₁ κ monoclonal antibody in clinical development for the treatment of SLE and lupus nephritis, targets the interferon alpha receptor 1 (IFNAR1) and blocks IFNAR1-dependent signaling. Here we characterize the mechanistic and functional properties of anifrolumab.
Methods: Binding between anifrolumab and the IFNAR1 was measured by surface plasmon resonance. IFNAR1 internalization on monocytes was assessed by flow cytometry and confocal microscopy. The effect of three mutations in the fragment crystallizable region (Fc) of anifrolumab on Fcγ receptor–dependent cytotoxicity was assessed in antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays. IFNAR1-dependent signaling induced by recombinant human type I IFN (including IFN-α, -β, and -ω) and by plasmacytoid dendritic cell (pDC)–derived type I IFN was assessed in signal transducer and activator of transcription 1 (STAT1) phosphorylation and IFN-stimulated response element–luciferase reporter assays. Production of IFN-α, TNF, IL-6, and IL-8 by stimulated pDC was measured by enzyme-linked immunosorbent assay or Meso Scale Diagnostics, and expression of cluster of differentiation 80 and 86 was measured by flow cytometry. Expression of type I IFN–regulated genes was measured by quantitative PCR. B-cell differentiation in pDC-/B-cell cocultures was assessed by flow cytometry and Ig production.
Results: Anifrolumab blocked type I IFN–dependent IFNAR dimerization and STAT1 phosphorylation with high affinity and specificity. Anifrolumab elicited rapid IFNAR1 internalization and markedly reduced IFNAR1 cell surface levels. Fc mutations on anifrolumab reduced Fcγ receptor–dependent cytotoxicity. Anifrolumab potently inhibited recombinant human type I IFN (including 12 subtypes of α, β, and ω) and pDC-derived type I IFN activities. Anifrolumab suppressed IFN-α, proinflammatory cytokine induction, and upregulation of costimulatory molecules from stimulated pDCs and type I IFN–inducible genes in peripheral blood mononuclear cells. Blockade of IFNAR1 also suppressed plasma cell differentiation and Ig production.
Conclusion: Anifrolumab inhibits type I IFN–dependent signaling by sterically inhibiting and rapidly internalizing IFNAR1 on target cells. Anifrolumab has no detectable CDC or ADCC activity. Blockade of type I IFN signaling suppresses pDC functions and B-cell differentiation. Anifrolumab has the potential to be a promising therapeutic agent for treating SLE and other diseases that demonstrate chronic dysfunctional type I IFN signaling.