TGF‐β induces an inhibitory effect of normal cells directed against transformed cells

Co‐cultivation of normal and transformed fibroblasts in the presence of exogenously added transforming growth factor type beta 1 (TGF‐β1) leads to a drastic reduction of colony‐forming transformed cells. This inhibitory effect is dependent both on the dose of TGF‐β applied and the density of normal cells. It does not reflect a direct action of TGF‐β on transformed cells, but is rather induced by TGF‐β in normal cells. In the absence of exogenously added TGF‐β, normal cells exhibit a basal inhibitory activity, which can be abrogated by anti‐TGF‐β. TGF‐β‐mediated inhibition of transformed cells by normal cells may be considered as a novel potent controlling step in carcinogenesis.