BACKGROUND: Fms-like tyrosine kinase 3 receptor (Flt3) is an important receptor expressed on the cell membrane of immature antigen-presenting cells. The binding of Flt3 to its ligand (FL) activates the proliferation of dendritic cells (DCs). This mechanism is currently being evaluated in the therapy of malignant tumors. The aim of the present study was to study the effect of FL gene transfer on the immune response and tumor growth in experimental pancreatic cancer. MATERIALS AND METHODS: The rat FL was sequenced and cloned from total mRNA extract of the spleen. Transfection efficiency of subcutaneously growing rat duct-like pancreatic cancer (DSL6A) with DOTAP-/cholesterol-based liposomes was tested using a pcDNA3.1-lacZ construct. Flt3 ligand production of in vitro transfected tumor cells and in vivo transfected tumors was measured by enzyme-linked immunosorbent assay. Tumor induction was achieved in Lewis rats by a subcutaneous inoculation of syngeneic pancreatic tumor cells (DSL6A). The animals were allocated into three groups: control, mock treatment, and treatment with FL plasmid. The plasmid was injected intratumorally three times per week for 2 weeks. The total observation time was 6 weeks. RESULTS: The tumor volume was significantly lower in the FL-transfected group during the first 3 weeks. The number of responders was significantly higher in the FL group compared with control and mock treatment. The number of CD80+ DCs in the spleen was significantly higher after FL gene transfer. The responders showed a significantly higher number of splenic natural killer (NK) cells. There were no differences of infiltrating lymphocytes, proliferation, and tumor blood vessels between the groups. CONCLUSION: Intratumoral gene transfer of FL in rats activated proliferation of DCs and NK cells, which causes a moderate reduction of tumor growth. This improvement of local tumor control during the first weeks could be explained by an improved antigen presentation.
BACKGROUND:Fms-like tyrosine kinase 3 receptor (Flt3) is an important receptor expressed on the cell membrane of immature antigen-presenting cells. The binding of Flt3 to its ligand (FL) activates the proliferation of dendritic cells (DCs). This mechanism is currently being evaluated in the therapy of malignant tumors. The aim of the present study was to study the effect of FL gene transfer on the immune response and tumor growth in experimental pancreatic cancer. MATERIALS AND METHODS: The rat FL was sequenced and cloned from total mRNA extract of the spleen. Transfection efficiency of subcutaneously growing rat duct-like pancreatic cancer (DSL6A) with DOTAP-/cholesterol-based liposomes was tested using a pcDNA3.1-lacZ construct. Flt3 ligand production of in vitro transfected tumor cells and in vivo transfected tumors was measured by enzyme-linked immunosorbent assay. Tumor induction was achieved in Lewis rats by a subcutaneous inoculation of syngeneic pancreatic tumor cells (DSL6A). The animals were allocated into three groups: control, mock treatment, and treatment with FL plasmid. The plasmid was injected intratumorally three times per week for 2 weeks. The total observation time was 6 weeks. RESULTS: The tumor volume was significantly lower in the FL-transfected group during the first 3 weeks. The number of responders was significantly higher in the FL group compared with control and mock treatment. The number of CD80+ DCs in the spleen was significantly higher after FL gene transfer. The responders showed a significantly higher number of splenic natural killer (NK) cells. There were no differences of infiltrating lymphocytes, proliferation, and tumor blood vessels between the groups. CONCLUSION: Intratumoral gene transfer of FL in rats activated proliferation of DCs and NK cells, which causes a moderate reduction of tumor growth. This improvement of local tumor control during the first weeks could be explained by an improved antigen presentation.
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