Maintenance of immune tolerance to FVIII after a second challenge with FVIII plasmid. FVIII plasmid + anti-CD3–treated mice were given a second plasmid challenge at 23 weeks after the first plasmid injection. Three mice were chosen: 2 of these had persistent FVIII activity and the other one had lost FVIII activity. (A) FVIII activity and (B) anti-FVIII antibody titers were examined as described in Figure 1. Each line represents an individual mouse. Data shown are from one representative experiment (2 independent experiments, n = 3/group).