Structure of a factor VIII C2 domain–immunoglobulin G4κ Fab complex: identification of an inhibitory antibody epitope on the surface of factor VIII

• Published in: Blood 2001-07, Vol.98 (1), p.13-19
• Main Authors: Spiegel, Paul Clint, Jacquemin, Marc, Saint-Remy, Jean-Marie R., Stoddard, Barry L., Pratt, Kathleen P.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Hematologic and hematopoietic diseases; Medical sciences; Platelet diseases and coagulopathies
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V98.1.13

The development of an immune response to infused factor VIII is a complication affecting many patients with hemophilia A. Inhibitor antibodies bind to antigenic determinants on the factor VIII molecule and block its procoagulant activity. A patient-derived inhibitory immunoglobulin G4κ antibody (BO2C11) produced by an immortalized memory B-lymphocyte cell line interferes with the binding of factor VIII to phospholipid surfaces and to von Willebrand factor. The structure of a Fab fragment derived from this antibody complexed with the factor VIII C2 domain was determined at 2.0 Å resolution. The Fab interacts with solvent-exposed basic and hydrophobic side chains that form a membrane-association surface of factor VIII. This atomic resolution structure suggests a variety of amino acid substitutions in the C2 domain of factor VIII that might prevent the binding of anti-C2 inhibitor antibodies without significantly compromising the procoagulant functions of factor VIII.