Murine bone marrow-derived mesenchymal stem cells as vehicles for interleukin-12 gene delivery into ewing sarcoma tumors

BACKGROUND: This study evaluated the therapeutic efficacy of interleukin 12 (IL-12) gene therapy in Ewing sarcoma and whether murine mesenchymal stem cells (MSCs) could serve as vehicles for IL-12 gene delivery. METHODS: MSCs were isolated from murine bone marrow cells. Cells were phenotyped using flow cytometry. Cultured MSCs differentiated into osteocytes and adipocytes using the appropriate media. Freshly isolated MSCs were transfected with adenoviral vectors containing either the β-galactosidase (Ad:β-gal) or the IL-12 (Ad:IL-12) gene. Expression of IL-12 was confirmed using reverse transcription polymerase chain reaction. Mice with TC71 Ewing sarcoma tumors were then treated intravenously with MSCs transfected with Ad:β-gal or Ad:IL-12. Tumors were measured and analyzed by immunohistochemical analysis for expression of IL-12 protein. RESULTS: Expression of both p35 and p40 IL-12 subunits was demonstrated in MSCs transfected in vitro with Ad:IL-12. IL-12 expression was seen in tumors from mice treated with MSCs transfected with Ad:IL-12. Tumor growth was also significantly inhibited compared with that in mice treated with MSCs transfected with Ad:β-gal. CONCLUSIONS: MSCs can be transfected with the IL-12 gene. These transfected cells localize to tumors after intravenous injection and induce local IL-12 protein production and the regression of established tumors.