F VIII subunits: purification and antigenic properties

Factor VIII-Light Chain (FVIII-LC) and FVIII-Heavy Chain (FVIII-HC) were purified from human plasma by the use of immunosorbents containing monoclonal antibodies or human inhibitor antibodies. FVIII-LC was subsequently isolated in essentially pure state by cation exchange chromatography. The preparations obtained contained 50 ng of protein for each unit of FVIII-LC antigen (FVIII-LC:Ag). Affinity purified FVIII-LC and FVIII-HC preparations containing less than 0.3% of the opposite subunit were added in FVIII:C inhibition assay of hemophilia A inhibitor antibodies. FVIII-LC was able to fully block the inhibitor activity in 6 out of 7 hemophilia A plasmas and partially block the inhibitor activity of one plasma. FVIII-HC only blocked FVIII:C inhibiting antibodies form the plasma that was not fully blocked by FVIII-LC. It is suggested that FVIII-LC can be used for immunotherapy of the patients whose FVIII:C inhibiting antibodies are directed towards FVIII-LC. When FVIII-LC was coupled to Sepharose at a concentration of 4800 units of FVIII-LC:Ag per ml Sepharose, 0.2 ml of the immunosorbent was able to bind 900 Bethesda units from 100 ml hemophilia A inhibitor plasma. This opens the possibility to remove FVIII inhibitor antibodies from circulation by extracorporeal immunotherapy with FVIII-LC coupled to Sepharose.