RAG2^−/−x γc^−/− regressors are edited when transplanted into RAG2^−/− mice, but are not specifically recognized by NK cells. Two independent MCA-induced sarcoma cell lines generated from RAG2^−/−x γc^−/− mice were transplanted into syngeneic RAG2^−/−x γc^−/− or RAG2^−/− mice, and tumor masses were harvested at day 25 and converted into “passaged” daughter cell lines, which were transplanted into syngeneic WT mice (number of cell lines and mice are shown in the figure), and (A) the percentage of WT mice that remained tumor-free is shown for each group of cell lines. Tumor-free mice were defined to have a nonenlarging mass <9 mm in average diameter by day 40. (B) MCA sarcoma cell lines were cultured with IL-2–activated NK cells in a 5-h chromium release cytotoxicity assay and specific lysis normalized to YAC-1–specific lysis is plotted for each cell line based on immune background and phenotype. (C) Regressor and progressor cell lines were transplanted into RAG-deficient mice and analyzed for infiltrating NK cells by FACS.