Kinetics of FIXa, FXa, and FIIa formation in the OS assay. Plasma samples containing transgene-produced FVIII-SQ (gene therapy plasma), collected from 2 different participants treated with BMN 270, and plasma samples containing native FVIII (normal plasma, diluted) with the same CS activity were compared in stop kinetics experiments in the OS assay. FIXa generation (A-B), FXa generation (C-D), and FIIa (thrombin) generation (E-F) were monitored for 60 seconds after addition of CaCl₂. Error bars represent standard deviations between replicate assessments.