title: A subset of high-titer anti-factor VIII A2 domain antibodies is responsive to treatment with factor VIII.
abstract: The primary B-cell epitopes of factor VIII (fVIII) are in the A2 and C2 domains. Within the C2 domain, antibody epitope and kinetics are more important than inhibitor titer in predicting pathogenicity in a murine bleeding model. To investigate this within the A2 domain, the pathogenicity of a diverse panel of antihuman fVIII A2 domain monoclonal antibodies (MAbs) was tested in the murine model. MAbs were injected into hemophilia A mice, followed by injection of human B domain-deleted fVIII. Blood loss after a 4-mm tail snip was measured. The following anti-A2 MAbs were tested: high-titer type 1 inhibitors 4A4, 2-76, and 1D4; 2-54, a high-titer type 2 inhibitor; B94, a type 2 inhibitor; and noninhibitory MAbs GMA-012, 4C7, and B25. All high-titer type 1 MAbs produced blood loss that was significantly greater than control mice, whereas all non-inhibitory MAbs produced blood loss that was similar to control. The type 2 MAbs were not pathogenic despite 2-54 having an inhibitor titer of 34 000 BU/mg immunoglobulin G. In addition, a patient with a high-titer type 2 anti-A2 inhibitor who is responsive to fVIII is reported. The discrepancy between inhibitor titer and bleeding phenotype combined with similar findings in the C2 domain stress the importance of inhibitor properties not detected in the standard Bethesda assay in predicting response to fVIII therapy.
authors.affiliation: School of Medicine, Emory University, Atlanta, GA;
authors.forename: Joshua
authors.initials: J
authors.lastname: Eubanks
authors.affiliation: Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta/Emory University, Atlanta, GA; and.
authors.forename: W Hunter
authors.initials: WH
authors.lastname: Baldwin
authors.affiliation: School of Medicine, Emory University, Atlanta, GA;
authors.forename: Rebecca
authors.initials: R
authors.lastname: Markovitz
authors.affiliation: Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta/Emory University, Atlanta, GA; and.
authors.forename: Ernest T
authors.initials: ET
authors.lastname: Parker
authors.affiliation: Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta/Emory University, Atlanta, GA; and.
authors.forename: Courtney
authors.initials: C
authors.lastname: Cox
authors.affiliation: Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta/Emory University, Atlanta, GA; and Department of Hematology and Medical Oncology, Emory University School of Medicine, Atlanta, GA.
authors.forename: Christine L
authors.initials: CL
authors.lastname: Kempton
authors.affiliation: Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta/Emory University, Atlanta, GA; and.
authors.forename: Shannon L
authors.identifier: http://orcid.org/0000-0002-3683-8644
authors.initials: SL
authors.lastname: Meeks
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D002478:Cells, Cultured; D006224:Cricetinae; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D018985:Epitopes, B-Lymphocyte / Q000276:immunology*; D005169:Factor VIII / Q000737:chemistry / Q000276:immunology / Q000627:therapeutic use*; D005260:Female; D006467:Hemophilia A / Q000097:blood / Q000276:immunology / Q000628:therapy*; D006470:Hemorrhage / Q000097:blood / Q000188:drug therapy / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D017434:Protein Structure, Tertiary
chemical_list: D000911:Antibodies, Monoclonal; D018985:Epitopes, B-Lymphocyte; D007074:Immunoglobulin G; D005169:Factor VIII
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