Rechallenge with FVIII after MZ B-cell repopulation results in primary immune response. (A) Mice with hemophilia A that previously underwent MZ B-cell depletion (MZ B cell depl) with FVIII challenge, received a “rechallenge” with 2 μg of FVIII at the indicated time points (black arrows), followed by plasma collection 1 week after the last injection (blue arrow). Plasma was evaluated for anti-FVIII IgG by ELISA (B) and inhibitor titer by Bethesda assay (C). Error bars indicate SD. Horizontal lines represent mean of each group. **P < .003, ***P < .0002, 1-way ANOVA, post hoc Tukey test.