Persistence of tolerance induced by B-cell blasts transduced with C2-IgG-MSCV and A2-IgG-MSCV in immunized E16 recipients. Protocol was as in Figure 3, except that mice received an additional booster with fVIII on day 102 and were euthanized on day 109. Recipient E16 mice were primed by 4 weekly injections of human fVIII. Total serum IgG anti-C2 (A) and anti-fVIII (B) antibody titers were determined by ELISA on days 28, 56, 102, and 109. Factor VIIII inhibitor titers are shown in panel C. The data represent the mean plus or minus SEM; ^*P < .05, ^**P < .01, P < .001 versus mock SAG-Ig control.