Structure of pathogenic anti-PF4 autoantibodies reveals the mechanism of immune response formation in vaccine-induced thrombotic thrombocytopenia (VITT).

Abstract Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a severe, but rare, side effect of adenoviral-vectored COVID-19 vaccines. It attributed to formation autoantibodies recognizing Platelet Factor 4 (PF4) and capable triggering platelet activation, which leads thrombosis. We used mass spectrometry (MS) determine the structure VITT patient-derived anti-PF4 antibodies (VITT IgG) identified their unique properties underlying pathogenicity. The IgGs studied in this work were extracted from plasma ChAdOx1 vaccine recipient, who developed VITT. Intact-mass MS analysis these revealed one major clone, its complete structural characterization was carried out using MS-based de novo sequencing. This allowed us establish subclass (IgG2), amino acid sequence, identify an N-glycan variable region. information build 3D model IgG, presence large polyanionic patch within paratope involving four CDR regions. Molecular dynamics simulations highlight role electrostatics as driver IgG binding PF4. equatorial belt positive charge circumscribing PF4 tetramer serves distributed epitope, allowing it cross-link up three molecules, giving rise complexes FcyRIIa-mediated activation. molecular mechanism pathogenesis emerging explains how form absence heparin, essential for activation similar disease, heparin-induced thrombocytopenia, sheds light on etiology devastating condition. Supported by grant NIH R01 GM112666