Immunomodulatory effects of tumor-associated fibroblasts in colorectal-tumor development

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Abstract
In order to elucidate the role of myofibroblasts in tumor development, we compared fibroblastic reactions and their implications in the immune response in progressive and regressive rat colorectal‐tumor models. Immunohistochemical analyses revealed that T lymphocytes and monocytes/macrophages were found outside progressive tumors that were surrounded by a large sheath of myofibroblasts. In vitro experiments using fibroblast‐ vs. myofibroblast‐containing collagen gels showed that the mechanical properties of these tumor‐activated myofibroblasts prevent penetration of T lymphocytes and macrophages within tumor nodules. These results indicate that tumor‐activated myofibroblasts may prevent physical contact between cancer‐cells and immune cells, an essential phenomenon for effective destruction of cancer cells. Successful immunotherapy against cancer should therefore include complementary treatments against these tumor‐associated fibroblasts. Int. J. Cancer 81:629–636, 1999.