Abstract
Cells from the malignant teratocarcinoma line PCC4.azal were treated with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine. Fifty-five clones were isolated from the surviving cells. Twelve clones are unable to form tumors in the syngeneic 129/Sv mice. However, these "tum-" clones form tumors as readily as the original cells when they are injected into irradiated mice. Moreover, they stimulate the production of immune memory cells, which protect the injected animals and confer resistance by adoptive transfer. The tum- clones are therefore unable to generate tumors in syngeneic mice because they elicit an immune rejection response.