Animals carrying a chemically or virally induced malignant tumor can develop an immune response to that tumor and cause its regression. In the course of neoplastic transformation, new antigens, called tumor-associated antigens (TAAs), develop at the cell surface, and the host recognizes such cells as “nonself.” An immune response then causes the tumor to regress.
In chemically induced tumors in experimental animals, TAAs are highly specific (i.e., cells of one tumor will have different TAAs from those on cells of another tumor even when they arise within the same animal). In contrast, virally induced tumors possess TAAs that cross-react with one another if induced by the same virus. TAAs on tumor cells induced by different viruses do not cross-react.
MECHANISM OF TUMOR IMMUNITY
Cell-mediated reactions attack these nonself tumor cells and limit their proliferation. Such immune responses probably act as a surveillance system to detect and eliminate newly arising clones of neoplastic cells. In general, the immune response against tumor cells is weak and can be overcome experimentally by a large dose of tumor cells. Some tumor cells can escape surveillance by “modulation” (i.e., internalizing the surface antigen so that it no longer presents a target for immune attack).