Analysis of expression kinetics and activity of a new B-domain truncated and full-length FVIII protein in three different cell lines

Transient expression of full-length wild-type (wt) and a new B-domain trunc ated (Delta B) FVIII has been investigated in three eukaryotic cell lines ( HEK-293, COS, CHO). When expressed in CHO cells, both FVIII proteins reache d the same peak antigen levels, whereas in HEK-293 and COS cells those of F VIII/Delta B were up to sixfold those of FVIII/wt. Investigation of specifi c activity of the recombinant FVIII proteins using a chromogenic and a one- stage assay in addition to the FVIII-antigen ELISA revealed large variation s: In HEK-293 cells specific activity of FVIII/Delta B measured with both a ssays was higher than that of FVIII/wt. In COS cells specific activity of b oth FVIII proteins was higher measured in the one-stage assay than in the c hromogenic assay. In CHO cells both FVIII proteins had similar specific act ivity in each assay. In summary, expression kinetics and specific activity of conditioned medium vary depending on cell type used.