Administration of plasma-derived human FVIII (a product that contains VWF) to hemophilia A mice induces a lower inhibitor response than recombinant FVIII. Interestingly, the inhibitor titers cannot be reduced by administration of a mixture of recombinant FVIII with VWF, suggesting that antigenic properties of FVIII complexed to VWF in plasma are not identical to those obtained from in vitro mixing of these molecules. See the complete figure in the article beginning on page 871.