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

Transforming growth factor B (TGF-beta) 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-beta type II receptor (TbetaRIIDN) 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-beta via retroviral expression of the TbetaRIIDN construct and were transplanted in C57BL/6 mice before tumor challenge. After i.v. administration of 5 x 10(5) B16-F10 murine melanoma cells into TbetaRIIDN-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 TbetaRIIDN-BM mice showed a virtual absence of metastatic lesions in the lung. We also investigated the utility of the TGF-beta-targeted approach in a mouse metastatic model of prostate cancer, TRAMP-C2. Treatment of male C57BL/6 mice with TbetaRIIDN-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 TbetaRIIDN-BM-treated mice, suggesting that a gene therapy approach to inducing TGF-beta insensitivity in transplanted BM cells may be a potent anticancer therapy.

Tumor evasion of the immune system by converting CD4+CD25- T cells into CD4+CD25+ T regulatory cells: role of tumor-derived TGF-beta.

CD4+CD25+ T regulatory (T(reg)) cells were initially described for their ability to suppress autoimmune diseases in animal models. An emerging interest is the potential role of T(reg) cells in cancer development and progression because they have been shown to suppress antitumor immunity. In this study, CD4+CD25- T cells cultured in conditioned medium (CM) derived from tumor cells, RENCA or TRAMP-C2, possess similar characteristics as those of naturally occurring T(reg) cells, including expression of Foxp3, a crucial transcription factor of T(reg) cells, production of low levels of IL-2, high levels of IL-10 and TGF-beta, and the ability to suppress CD4+CD25- T cell proliferation. Further investigation revealed a critical role of tumor-derived TGF-beta in converting CD4+CD25- T cells into T(reg) cells because a neutralizing Ab against TGF-beta, 1D11, completely abrogated the induction of T(reg) cells. CM from a nontumorigenic cell line, NRP-152, or irradiated tumor cells did not convert CD4+CD25- T cells to T(reg) cells because they produce low levels of TGF-beta in CM. Finally, we observed a reduced tumor burden in animals receiving 1D11. The reduction in tumor burden correlated with a decrease in tumor-derived TGF-beta. Treatment of 1D11 also reduced the conversion of CD4+ T cells into T(reg) cells and subsequent T(reg) cell-mediated suppression of antitumor immunity. In summary, we have demonstrated that tumor cells directly convert CD4+CD25- T cells to T(reg) cells through production of high levels of TGF-beta, suggesting a possible mechanism through which tumor cells evade the immune system.

Reconstitution of lethally irradiated adult mice with dominant negative TGF-beta type II receptor-transduced bone marrow leads to myeloid expansion and inflammatory disease.

TGF-beta regulation of immune homeostasis has been investigated in the context of cytokine knockout (TGF-beta null) mice, in which particular TGF-beta isoforms are disrupted throughout the entire organism, as well as in B and T cell-specific transgenic models, but to date the immunoregulatory effects of TGF-beta have not been addressed in the context of an in vivo mouse model in which multi-isoform TGF-beta signaling is abrogated in multiple leukocyte lineages while leaving nonhemopoietic tissue unaffected. Here we report the development of a murine model of TGF-beta insensitivity limited to the hemopoietic tissue of adult wild-type C57BL/6 mice based on retroviral-mediated gene transfer of a dominant negative TGF-beta type II receptor targeting murine bone marrow. Unlike the lymphoproliferative syndrome observed in TGF-beta1-deficient mice, the disruption of TGF-beta signaling in bone marrow-derived cells leads to dramatic expansion of myeloid cells, primarily monocytes/macrophages, and is associated with cachexia and mortality in lethally irradiated mice reconstituted with dominant negative receptor-transduced bone marrow. Surprisingly, there was a notable absence of T cell expansion in affected animals despite the observed differentiation of most cells in the T cell compartment to a memory phenotype. These results indicate not only that TGF-beta acts as a negative regulator of immune function, but that lack of functional TGF-beta signaling in the myeloid compartment of adult mice may trigger suppression of lymphocytes, which would otherwise proliferate when rendered insensitive to TGF-beta.