In vitro characterization of recombinant factor VIII concentrates reveals significant differences in protein content, activity and thrombin activation profile.

Recombinant factor VIII (rFVIII) concentrates differ due to cell lines, culture conditions, presence of the B domain and authorized potency assays. This study characterizes three commercially available rFVIII concentrates: a second-generation full length (A), a third-generation full length (B) and a third-generation B domain-deleted (BDD) product (C). rFVIII concentrates were characterized for FVIII activity (FVIII:C) by one-stage clotting and chromogenic assays, FVIII antigen (FVIII:Ag), thrombin activation profile and FXa-generation assay. The rFVIII concentrates exhibited significant differences with regard to FVIII:C, FVIII:Ag and thrombin activation profile. Product A had significantly greater FVIII:C and FVIII:Ag relative to the measured values of products B and C. In addition, product A demonstrated faster and more complete activation by thrombin than the two others. BDD product C had the slowest measured thrombin activation rate. Product A exhibited a greater in vitro FXa generation than products B and C. We found no differences in FXa generation among all three products when FXa generation was normalized for FVIII:Ag. The greater FVIII:C and FVIII:Ag values for product A compared with that for products B and C are due to application of different authorized potency assays (one-stage assay for A vs. chromogenic assay for B and C). The variation in thrombin activation profiles may arise from differences in cell line-dependent posttranslational modifications of the various recombinant proteins.