Human hepatoma cell lines HepG2 and HBV-positive HepG2.2.15 cells conserved in our laboratory were cultured in DMEM (GIBCO/BRL, Grand Island, N.Y. USA) containing 10% fetal bovine serum in a humidified incubator with 5% CO2 at 37°C. The empty expression vector pSecTagB was obtained from Invitrogen (CA, USA). The recombinant vector (pSecTagB-IFN-α) which contains IFN-α1 cDNA was constructed in our laboratory.