To study the possibility of somatic gene therapy for hemophilia B via gene transfer to primary factor Ⅸ-deficient skin fibroblasts, we constructed four retroviral vectors containing factor Ⅸ cDNA driven by retroviral LTR promoter, SV40 early promoter and mouse MT-I promoter, respectively. These retroviral vectors were transfected into an amphotropic packaging cell line, PA317 cells, by electroporation, and a human iibrosarcoma cell line, HT1080 cells, was used to assay the factor Ⅸ-virus titers of these four virus-producing PA317 cells, which ranged from 2×10~4 to 5×10~5 cfu/ml. The factor Ⅸ proteins produced by bulk population of four virus-producing PA317 cells were determined by ELISA. Results showed that LTR promoter directed the highest production of factor Ⅸ at the rate of 584 rig/10~6 cells/24h, while SV40 early promoter and MT promoter directed about 10 and 20 times less production of factor Ⅸ than LTR promoter. The highest expressed retroviral vector XL-Ⅸ was used to infect a line of f To study the possibility of somatic gene therapy for hemophilia B via gene transfer to primary factor IX-deficient skin fibroblasts, we constructed four retroviral vectors containing factor IX cDNA driven by retroviral LTR promoter, SV40 early promoter and mouse MT-I promoter, respectively. These retroviral vectors were transfected into an amphotropic packaging cell line, PA317 cells, by electroporation, and a human iibrosarcoma cell line, HT1080 cells, was used to assay the factor IX-virus titers of these four virus-producing PA317 cells, which ranged from 2 × 10 ~ 4 to 5 × 10 ~ 5 cfu / ml. The factor Ⅸ proteins produced by bulk population of four virus-producing PA317 cells were determined by ELISA. Results showed that LTR promoter directed the highest production of factor Ⅸ at the rate of 584 rig / 10 ~ 6 cells / 24h, while SV40 early promoter and MT promoter directed about 10 and 20 times less production of factor IX than LTR promoter. The highest expressed retroviral vector XL-IX was u sed to in a line of f