Reactivity profile of anti‐factor VIII antibodies with designed synthetic peptides mimicking epitopes of the C2 and a1 domains

Summary Antibodies (Abs) that block factor VIII (FVIII) activity occur in hemophilia A patients treated with FVIII replacement therapy and severely impair treatment. In this work, we designed and synthesized ten peptides whose sequences are found in putative epitopes at the surface of a1 and C2 domains of the FVIII molecule. These peptides were screened for their ability to inhibit the binding of anti‐FVIII Abs from plasmas of hemophilia A patients to FVIII. All peptides were efficient in inhibiting anti‐FVIII Abs in plasma from patients with inhibitors, with however different efficiencies. It was found that each tested patient’s plasma had a different profile of reactivity with peptides, consistent with an individual anti‐FVIII Ab specificity. The profile of recognized peptides was also changing during the treatment of the patients. Three peptides were used in an affinity chromatography assay to attempt to remove anti‐FVIII Abs from patients’ plasma. Anti‐FVIII IgGs were significantly captured by the peptide‐Sepharose affinity matrixes as assessed by enzyme‐linked immunosorbent assay. However, due to the low level of Abs in the plasma samples, other methods (Chromogenic and Bethesda assays) were not sensitive enough to properly detect the reduction of inhibitors.