Naive and activated OT-I cells are found within B16 melanoma tumors 24 h after transfer into mice. C57BL/6 mice bearing established s.c. (17–21-d-old), lung (17–21-d-old), or i.p. (10–15-d-old) B16-F1 (A) or B16-cOVA (B) tumors received Thy1-mismatched OT-I T cells. Axes on plots are displayed in Logicle scale. 24 h later, lymphocytes from tumors, LN, and spleen were harvested and stained for flow cytometry. Plots are gated on Thy1.1⁺ CD8⁺ lymphocytes, and numbers indicate the percentage of OT-I cells that are single positive for CD69 or CD25, or positive for both markers. Tumor location is noted to the right of dot plots. Results are representative of at least three independent experiments, with five or more mice each per tumor location.