BACKGROUND: Gene therapy is an effective expression of genes within target cells after transferring exogenous target genes. Both vector selection and transfection method are important factors for gene transfection. An ideal gene vector is required for a high transfusion of target gene and an exact introduction of target gene into specific target cells so as to express gene products. OBJECTIVE: To study the expression of mRNA and protein after transfecting rat bone marrow mesenchymal stem cells (BMSCs) with brain-derived neurotrophic factor (BDNF) genes based on cationic polymer vector. DESIGN, TIME AND SETTING: A randomized, controlled in vitro study using gene engineering, performed at the Neurobiology Laboratory, Xuzhou Medical College between October 2007 and April 2008. MATERIALS: PcDNA3.1 BDNF was obtained from Youbiai Biotechnological Company, Beijing and cationic polymer vector used was the SofastTM gene transfection reagent that was made by Taiyangma Biotechnological Co., Ltd., Xiamen. METHODS: BMSCs extracted from six Sprague Dawley (SD) rats aged 1 month were isolated and cultured in vitro. Third passage BMSCs were inoculated on a 6-well culture plate at the density of 1×106 cells/L. At about 80% confluence, BMSCs were transfected with PcDNA3.1-BDNF (2 μg) combined with SofastTM gene transfection reagent (6 μg) (BDNF group) or with PcDNA3.1 (2 μg) combined with SofastTM gene transfection reagent (6 μg) (blank vector group). Cells that were not transfected with any reagents but still cultured under primary culture conditions were used as a non-transfection group.MAIN OUTCOME MEASURES: Enzyme linked immunosorbent assay was used to measure time efficiency of BMSC-secreted BDNF protein. Twenty-four hours after gene transfection, RT-PCR was used to detect expression of BDNF mRNA in the BMSCs. Immunohistochemistry was used to determine expression of BDNF protein in the BMSCs.RESULTS: BDNF protein expression was detected at day 1 after gene transfection, rapidly increased after 5-9 days and gradually increased after 11-15 days in the BDNF group; moreover, BDNF protein expression was higher than that in the non-transfection group and the blank vector group at different time points (P < 0.01). Additionally, BDNF mRNA expression in the BDNF group was higher than that in the blank vector group and the non-transfection group (P < 0.01).CONCLUSION: A cationic polymer vector can effectively mediate the BDNF gene to transfect BMSCs; genetically modified BMSCs can express BDNF protein effectively for a long term.