Identification and characterization of bone marrow plasma cells producing IFN-γ-neutralizing autoantibodies in adult-onset immunodeficiency.

Adult-onset immunodeficiency (AOID) can be associated with anti-interferon (IFN)-γ autoantibodies (AIGAs). Rituximab (RTX) reduces circulating B cells but often fails to eliminate AIGAs, suggesting the presence of long-lived antibody-secreting cells (ASCs) in immune-privileged sites. Here, we identified 23 distinct IFN-γ-specific monoclonal antibodies (mAbs) from bone marrow (BM) ASCs of AOID patients using microwell array chip technology and single-cell RNA sequencing. Competitive assays demonstrated that neutralizing mAbs disrupt IFN-γ engagement with IFN-γR1 or IFN-γR2, impairing JAK-STAT1 signaling. Structural analysis of neutralizing mAb A01BM-03 revealed its binding to a quaternary epitope on dimeric IFN-γ, disrupting IFN-γR2 interaction. Notably, clonally expanded IFN-γ-specific ASCs were localized within a CD11c+ZEB2+ age-associated B cell (ABC)-like plasma cell cluster in one AOID patient, implicating its role in AOID pathogenesis. These findings provide direct evidence for IFN-γ-specific ASCs in the BM despite RTX treatment, supporting targeted ASC therapy to restore immune homeostasis in AOID.