Von Willebrand factor modulates factor VIII immunogenicity: comparative study of different factor VIII concentrates in a haemophilia A mouse model.

The development of an immune response towards factor VIII (FVIII) remains the major complication of haemophilia A replacement therapy. Product-related risk factors have recently been identified on the basis of epidemiological studies, but the mechanism is not understood. To this end, various commercially available FVIII concentrates were administered by the IV route to FVIII-knockout mice and the resulting immune response was characterised. Significantly higher inhibitor titres (Bethesda assay) were observed for one recombinant FVIII and one plasma-derived FVIII product depleted in von Willebrand factor (VWF). Inhibitor titres were reduced upon pre-incubation of FVIII with purified VWF. Epitope specificity of anti-FVIII IgG was characterised using FVIII-fragments produced in E. coli. Concentrates with no or reduced VWF-level elicited antibodies recognising predominantly the acidic a1 and a3 regions. Addition of VWF prior to injection also modified the epitope specificity. FVIII concentrates, therefore, show qualitative and quantitative variations in immunogenicity, which are at least partly modulated by VWF.