Effect of antisense TGF-beta transgene expression on the immunogenicity of EMT6 murine mammary carcinoma cells

Abstract

Transforming growth factor-beta (TGF-β) is a multi-functional cytokine produced by many tumor cells that is known to potently inhibit immune cell functions. Secretion of TGF-β by malignant cells may therefore be a mechanism by which tumor cells escape destruction by tumor-specific T lymphocytes. If this is the case, prevention of TGF-β production by tumor cells could be expected to eliminate tumor-derived immunosuppression and enable the development of effective anti-tumor immune responses. To evaluate the role of tumor-derived TGF-β on tumor progression, production of this cytokine was interrupted by introducing a gene encoding antisense TGF-β1 into the EMT6 murine mammary tumor cell line using a retroviral vector (LasTGF-β1SN). EMT6 cells transduced with this vector (EMT6asTGF-β1) stably expressed the antisense gene and secreted 48% less TGF-β than did tumor cells transduced with the backbone vector alone (EMT6-Neo). Supernatant fluid recovered from tumor calls expressing the antisense TGF-β1 gene also exhibited a decreased capacity to suppress alloantigen-specific cytotoxic T cell responses in vitro. Furthermore, tumor growth in mice injected with EMT6asTGF-β1 tumor cells was inhibited compared to mice injected with control EMT6-Neo tumor cells. Immune cell involvement in the growth inhibition of the antisense TGF-β transduced tumors was suggested by the ability of EMT6asTGF-β tumors to grow unchecked in immunodeficient scid mice and by the finding that immunocompetent mice that rejected antisense TGF-β1-expressing tumors developed long term tumor immunity. These results demonstrate that expression of antisense TGF-β1 by transduced EMT6 cells decreases their tumorigenicity and that this approach of eliminating immune suppression is a potentially useful strategy to enhance antitumor responses.