Naive T cells that infiltrate tumors proliferate in situ. (A and B) C57BL/6, ATA, or splenectomized C57BL/6 mice bearing established B16-cOVA, B16-AAD, or LLC-OVA tumors in the locations indicated received CFSE-labeled Thy1-mismatched OT-I or FH cells. FTY720 treatment was initiated at the time of T cell transfer and continued for the duration of the experiment. 4 d after T cell transfer, tumors and lymphoid organs were harvested, and lymphocytes were stained for flow cytometry. Only tumors are shown in B. Dot plots are gated on total lymphocytes. Numbers on dot plots indicate the percentage of tumor-specific T cells out of total lymphocytes. Axes on plots are displayed in Logicle scale. Histograms are gated on CD8⁺ OT-I or FH cells. Gates indicate all cells that have undergone at least one division. Results represent at least two independent experiments per tumor type, with at least three mice each. (C) Normal C57BL/6 mice or C56BL/6 mice lacking LN after in utero ablation were splenectomized. s.c. or lung tumors were established, and the mice received CFSE-labeled Thy 1.1⁺ OT-I cells. FTY720 treatment was initiated at the time of T cell transfer, and continued for the duration of the experiment. 4 d after T cell transfer, tumors were harvested and stained for flow cytometry. Plots are gated on total lymphocytes. Numbers on dot plots indicate the percentage of tumor-specific T cells out of total lymphocytes. Axes on plots are displayed in Logicle scale. Results represent n = 4 animals per tumor location in 2 independent experiments.