MZ B-cell depletion prevents FVIII inhibitor development. (A) Mice with hemophilia A (Hem A) received MZ B-cell–depleting antibodies (MZ B cell depl), isotype control antibody, or saline at the indicated time points (red arrows), followed by FVIII at the specified dose (black arrows). After 4 weekly doses of 2 μg of FVIII, day 28 plasma was evaluated for anti-FVIII IgG by ELISA (B) and inhibitor titer by Bethesda assay (C). After an additional “boost” dose of 4 μg of FVIII on day 35, day 42 plasma was evaluated for anti-FVIII IgG by ELISA (D) and inhibitor titer by Bethesda assay (E). Error bars indicate SD. Horizontal lines represent mean of each group. ***P < .0002, ****P < .0001, 1-way ANOVA, post hoc Tukey test.