The impact of VWF on FVIII memory immune responses in vivo. Splenocytes were isolated from rhF8-immunized FVIII^null mice, and CD138⁺ plasma cells were depleted. The remaining cells (CD138⁻) were used as memory B-cell pools. CD138⁻ memory B-cell pools were infused into age- and sex-matched paired immunocompromised NSGF8KO littermates followed by rhF8 immunization with or without rhVWF. One week after immunization, plasma was collected for Bethesda (to determine inhibitor titers) and ELISA assays (to determine anti-FVIII total IgG titers). (A-B) Inhibitor titers. (C-D) Anti-FVIII total IgG titers. Data are normalized by defining the titer in the group immunized with rhF8 only as 100%. The paired Student t test was used to compare the actual titer data sets, and the Mann-Whitney U test was used to compare the normalized data sets. These data demonstrate that VWF can mitigate anti-FVIII memory immune responses in vivo.