Evolution of Cell-Mediated Immunity in Mice Bearing Tumors Produced by a Mam- mary Carcinoma Cell Line. Influence of Tumor Growth, Surgical Removal, and Treat- ment With Irradiated Tumor Cells 1,2

SUMMARY-The test of colony growth inhibition of target tumor cells by host lymphoid cells in vitro was applied to study specific cell immunity in mammary tumor virus-free C3HeB/Fe mice. These mice bore neoplasms pro-duced by inoculation of a cell line developed from a syngeneic spon-taneous mammary tumor. Peritoneal washings were used as the source of lymphoid cells so that the mice could be checked periodically to Follow the evolution of their specific immunological status during tumor growth and after surgical removal of the tumor, followed or not by other treatment. As pre-viously demonstrated in other host-tumor systems, peritoneal cells taken from animals at the beginning of tumor growth had a moderate, but significant, specific immunological activity which disappeared entirely when the tumors reached 7 mm or more in diameter. AFter surgical removal of the tumors, this activity reappeared but only after a delay of nearly 20 days. This delay could be significantly shortened if the animals were inoculated subcutane-ously, 4 days after surgery, with their own tumor cells that had been trypsin