Tumor-specific resistance to autochthonous, methylcholanthrene-induced tumors in inbred Lewis rats was demonstrated in vivo and in vitro. The effect of admixing tumor cells with immunocytes from the primary hosts was studied by three in vitro techniques: release of a 51Cr label as a quantitative assay, cinemicrography for dynamic morphology, and a Millipore chamber technique for detection of diffusible cytotoxic substance. Results were compared with the degree of resistance to tumor autotransplantation. In general, there was a direct relationship between in vivo transplantation resistance and in vitro cytotoxicity of autogenous immunocytes.

Peritoneal cells from primary hosts that had acquired resistance to their tumor were most effective in destroying tumor cells. Autogenous spleen cells were less effective, and lymph node cells produced no effect. The reactions were not influenced by addition of phytohemagglutinin or complement. The cell-mediated destruction of tumor cells required incubation for periods of 24 to 48 hr. Limited data suggest that the cytolytic effect was usually specific for individual tumors.

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This work was supported by Grants T404 and T229 from the American Cancer Society, and by Grants 5 ROI CA-07863 and CA-08748 from the NIH.

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