BACKGROUND: The particular bystander effect of suicide gene can remarkably kill tumor cells. Meanwhile, it can be used together with radiotherapy as well as immune gene therapy, and overcome the defect of low gene transduction efficiency.Cytosine deaminase (CD) can generate a powerful bystander effect.OBJECTIVE: To observe the effect of a eukaryotic expression plasmid plRES2-AcGFP1-CD mediated by liposome transfected into bone marrow mesenchymal stem cells (BMSCs) and its gene expression.DESIGN, TIME AND SETTING: A cytologic experiment at genetic level was performed at Research and Development Center of Stem Cell and Tissue Engineering, Dalian University of Technology from May to December 2007.MATERIALS: A total of 6 C57BL mice of SPF degree and weighing 18-20 g were used for separation and culture of BMSCs.Escherichia coli DH5a was provided by Research and Development Center of Stem Cell and Tissue Engineering, Dalian University of Technology. Lipofectamine~(TM) 2000 was provided by Invitrogen, China.METHODS: The DNA plasmids were extracted from transformed Escherichia coli DH5a. plRES2-AcGFP1-CD plasmid was identified by BamHI/Xhol double digestion. The BMSCs derived from mouse femur and tibia were cultured and purified by adhesion method in vitro. Signal cell suspension prepared by BMSCs of the third generation was cultured by adding fluorescence-labeled CD44, CD45, CD90 and CD105 antibodies. BMSCs of the third generation were transfected by LipofectamineTM 2000 mediation.MAIN OUTCOME MEASURES: Identification of recombinant plasmids; the expressions of surface markers on BMSCs were detected by flow cytometry; the expressions of cytosine deaminase gene were observed at 36 and 48 hours after transfection under fluorescent inverted microscope.RESULTS: After agarose gel electrophoresis, a band appeared at 1.0-1.5 kb of the digested products of plRES2-AcGFP1-CD plasmids, and the band was accorded with the length of cytosine deaminase gene in the length. Flow cytometry demonstrated that the cells were negative for CD45 but positive for CD44, CD90 and CD105. Fluorescent inverted phase contrast microscope suggested that at 36 hours after plRES2-AcGFP1-CD gene transfection an expression of green fluorescent protein was found in the BMSCs; additionally, at 48 hours after transfection, the expression of green fluorescent protein remained and the intensity was remarkably increased.CONCLUSION: The liposome-mediated plRES2-AcGFP1-CD gene successfully expressed in BMSCs, and the expression peaked at 48 hours after transfection.