Infusion of pdFVIII concentrate results in reduced anti-FVIII titers and the formation of anti-human VWF antibodies. Comparison of (A) FVIII inhibitors, (B) anti-FVIII IgG subclasses, and (C) anti-human VWF IgG subclasses in Balb/c mice after 4 infusions of either VWF alone, pdFVIII, rFVIII, or in vitro mixed rFVIII and highly purified pdVWF. Naive hemophilic Balb/c mice were treated with 4 weekly infusions of 2 IU VWF, 2 IU pdFVIII, 2 IU rFVIII, or 2 IU rFVIII mixed in vitro with a 50-molar excess of pdVWF. Mice were sampled 1 week after the fourth treatment. The horizontal lines and error bars represent the mean and SEM for 8 to 10 mice.