Effect of mAbs ESH4 and BO2C11 on activities of factor VIII and mutants. ESH4 and BO2C11 inhibited activity of wild-type factor VIII and mutants on vesicles with 15% PS. Factor VIII (0.15 U/mL) in the absence (■) or presence of excess ESH4 (○) or BO2C11 (●) was added to various concentrations of phospholipid vesicles. Factor VIII was preincubated with ESH4 or BO2C11 for 30 minutes at room temperature. Data are mean ± SEM for 3 separate experiments, each performed in duplicate.