Mutagen treatment as a means for selecting immunogenic variants from otherwise poorly immunogenic malignant murine tumors.

The selection of nontumorigenic (turn'), highly immunogenic variants from four different tumorigenic but poorly immuno genic murine tumors by mutagen treatment and cloning is described. Several factors were found to determine the suc cessful nature of this selection procedure including: the nature of the tumor used; the nature of the mutagen; the number of mutagen treatments; and the time at which cloning is performed after treatment. In some cases, e.g., the TA3 adenocarcinoma or the BALB/ e SS1 spontaneous mammary adenoacanthoma, a single treat ment with ethyl methanesulfonate or A/-methyl-A/'-nitro-/v-nitrosoguanidine led to a very high frequency of turn" clones, whereas in others, e.g., the MDAY-D2 tumor line, no stable turn" clones were obtained. The immunogenic clones selected were always immunologically cross-reactive with the parent tumor from which they were derived and were found to protect the murine host against challenge with the parent tumor in vivo. Thus, the cloned immunogenic variants share an antigen with the parent tumor. Additional evidence, however, suggested that each clone also expresses a new private or unique antigen. The frequency of immunogenic variant selection ranged from a low of 6% to a high of 95%. In some cases in which the frequencies were very high, cloning was not required to reveal the turn" phenotype. Finally, we also noted that selection for drug resistance, e.g., resistance to 6-thioguanine, after mutagenesis could have an enhancing effect on the generation of highly immunogenic turn" clones. The results show that the immunogenicity of poorly immunogenic tumors, including those of spontaneous origin, can be dramatically enhanced by ap propriate mutagen treatments but that there is considerable variation in the ease with which highly immunogenic variants can be obtained.