The immune response to a chemically induced fibrosarcoma

Summary A clone of C3H10T 1/2 fibroblasts transformed in vitro with the carcinogen 3-methylcholanthrene readily produced tumors when as few as 10³ cells were injected into immunocompetent adult syngeneic mice. A non-transformed clone of the same parentage did not produce tumors. Because the cell-mediated immune response has an important role in inhibiting the growth of tumors, we have compared the ability of both these transformed and non-transformed fibroblasts to stimulate and to act as targets in cell-mediated cytotoxicity (CMC) assays. This model is unique in that studies of the immune response to tumors rarely have or utilize appropriate normal controls. When both types of irradiated fibroblasts were used as stimulators in vitro, neither syngeneic nor allogeneic effector spleen cells capable of efficiently lysing the tumor fibroblasts were generated. In contrast, the normal fibroblasts could both stimulate and be lysed by allogeneic cytolytic T cells (CTL). However, the tumor fibroblasts could be lysed by allogeneic effector spleen cells that had been sensitized to C3H/He spleen cells. These results suggest that the expression of alloantigenic determinants necessary for stimulating a CMC response may vary substantially among normal cell types. They further indicate that the tumor cells are not resistant to lysis by appropriately stimulated effector cells. Thus, they must express antigenic determinants necessary for immune lysis and they do not inhibit the functional expression of cytolytic cells once generated. Consequently, tumor growth in vivo may be dependent, in part, upon a failure of the syngeneic host's immunocompetent cells to respond appropriately to the tumor cells. Additional data are provided which suggest that this failure is attributable in large part to immunosuppressive properties of the tumor cells.