The specific activity for WT and mutant FVIII. CM of WT and mutant FVIII were harvested at 60 hours posttransfection for FVIII assay. The activity and antigen in the CM were measured by COAMATIC chromogenic assay and ELISA using an anti-FVIII light chain antibody, respectively. Specific activity is expressed as percent of WT. Bars are expressed as a mean ± standard deviation (SD) of three independent transfection experiments.