Anti-CD3 prevents FVIII inhibitor formation in C57BL/6 hemophilia A mice. In 2 independent experiments, anti-CD3, at the dose optimized in the BALB/c model (10 μg/day for 5 days), was administered to C57BL/6 hemophilia A mice (n = 16). The C57BL/6 control mice (n = 11) received HBSS rather than anti-CD3 daily for 5 days. Three days later, they were immunized with FVIII as outlined for BALB/c hemophilia A mice.