Suppression of tumor metastasis by blockade of transforming growth factor β signaling in bone marrow cells through a retroviral-mediated gene therapy in mice

Transforming growth factor B (TGF-β) is a potent immunosuppressive cytokine that is frequently associated with mechanisms of tumor escape from immunosurveillance. We report that transplantation of murine bone marrow (BM) expressing a dominant-negative TGF-β type II receptor (TβRIIDN) leads to the generation of mature leukocytes capable of a potent antitumor response in vivo. Hematopoietic precursors in murine BM from donor mice were rendered insensitive to TGF-β via retroviral expression of the TβRIIDN construct and were transplanted in C57BL/6 mice before tumor challenge. After i.v. administration of 5 × 10⁵ B16-F10 murine melanoma cells into TβRIIDN-BM transplanted recipients, survival of challenged mice at 45 days was 70% (7 of 10) versus 0% (0 of 10) for vector-control treated mice, and surviving TβRIIDN-BM mice showed a virtual absence of metastatic lesions in the lung. We also investigated the utility of the TGF-β-targeted approach in a mouse metastatic model of prostate cancer, TRAMP-C2. Treatment of male C57BL/6 mice with TβRIIDN-BM resulted in the survival of 80% (4 of 5) of recipients versus 0% (0 of 5) in green fluorescent protein-BM recipients or wild-type controls. Cytolytic T-cell assays indicate that a specific T-cell response against B16-F10 cells was generated in the TβRIIDN-BM-treated mice, suggesting that a gene therapy approach to inducing TGF-β insensitivity in transplanted BM cells may be a potent anticancer therapy.