title: High-affinity, noninhibitory pathogenic C1 domain antibodies are present in patients with hemophilia A and inhibitors.
abstract: Inhibitor formation in hemophilia A is the most feared treatment-related complication of factor VIII (fVIII) therapy. Most inhibitor patients with hemophilia A develop antibodies against the fVIII A2 and C2 domains. Recent evidence demonstrates that the C1 domain contributes to the inhibitor response. Inhibitory anti-C1 monoclonal antibodies (mAbs) have been identified that bind to putative phospholipid and von Willebrand factor (VWF) binding epitopes and block endocytosis of fVIII by antigen presenting cells. We now demonstrate by competitive enzyme-linked immunosorbent assay and hydrogen-deuterium exchange mass spectrometry that 7 of 9 anti-human C1 mAbs tested recognize an epitope distinct from the C1 phospholipid binding site. These mAbs, designated group A, display high binding affinities for fVIII, weakly inhibit fVIII procoagulant activity, poorly inhibit fVIII binding to phospholipid, and exhibit heterogeneity with respect to blocking fVIII binding to VWF. Another mAb, designated group B, inhibits fVIII procoagulant activity, fVIII binding to VWF and phospholipid, fVIIIa incorporation into the intrinsic Xase complex, thrombin generation in plasma, and fVIII uptake by dendritic cells. Group A and B epitopes are distinct from the epitope recognized by the canonical, human-derived inhibitory anti-C1 mAb, KM33, whose epitope overlaps both groups A and B. Antibodies recognizing group A and B epitopes are present in inhibitor plasmas from patients with hemophilia A. Additionally, group A and B mAbs increase fVIII clearance and are pathogenic in a hemophilia A mouse tail snip bleeding model. Group A anti-C1 mAbs represent the first identification of pathogenic, weakly inhibitory antibodies that increase fVIII clearance.
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.|Children's Healthcare of Atlanta, Atlanta, GA; and.
authors.forename: Glaivy
authors.initials: G
authors.lastname: Batsuli
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: Wei
authors.initials: W
authors.lastname: Deng
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: John F
authors.initials: JF
authors.lastname: Healey
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: Ernest T
authors.identifier: 0000-0002-4271-4621
authors.initials: ET
authors.lastname: Parker
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: W Hunter
authors.initials: WH
authors.lastname: Baldwin
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: Courtney
authors.initials: C
authors.lastname: Cox
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: Brenda
authors.initials: B
authors.lastname: Nguyen
authors.affiliation: Clinical and Molecular Haemostasis and Immunodeficiency, Department of Paediatrics, Goethe University Hospital, Frankfurt am Main, Germany.
authors.forename: Joerg
authors.initials: J
authors.lastname: Kahle
authors.affiliation: Clinical and Molecular Haemostasis and Immunodeficiency, Department of Paediatrics, Goethe University Hospital, Frankfurt am Main, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Königs
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: Renhao
authors.identifier: 0000-0002-5806-5080
authors.initials: R
authors.lastname: Li
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.
authors.forename: Pete
authors.identifier: 0000-0002-1206-8104
authors.initials: P
authors.lastname: Lollar
authors.affiliation: Aflac Cancer and Blood Disorders Center, Emory University, Atlanta, GA.|Children's Healthcare of Atlanta, Atlanta, GA; and.
authors.forename: Shannon L
authors.identifier: 0000-0002-3683-8644
authors.initials: SL
authors.lastname: Meeks
mesh_terms: D000818:Animals; D058846:Antibodies, Monoclonal, Murine-Derived / Q000276:immunology*; D000915:Antibody Affinity; D001666:Binding Sites, Antibody; D019774:Blood Coagulation Factor Inhibitors / Q000276:immunology*; D003713:Dendritic Cells / Q000276:immunology* / Q000473:pathology; D004195:Disease Models, Animal; D000939:Epitopes / Q000276:immunology*; D005169:Factor VIII / Q000037:antagonists & inhibitors / Q000276:immunology; D006467:Hemophilia A / Q000276:immunology* / Q000473:pathology; D006801:Humans; D051379:Mice; D000072417:Protein Domains; D014841:von Willebrand Factor / Q000276:immunology
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D019774:Blood Coagulation Factor Inhibitors; D000939:Epitopes; D014841:von Willebrand Factor; C078147:F8 protein, human; D005169:Factor VIII