Tumor surveillance of NK cell–controlled tumors is missing in Stat5^f/fNcr1-iCreTg mice. (A-D) B16F10 cells were injected intravenously into (A) WT, WT depleted of CD8⁺ cells, and WT depleted of NK1.1⁺ cells and (C) Stat5^f/f and Stat5^f/fNcr1-iCreTg mice. Numbers of metastatic infiltrates per lung were counted under the binocular microscope after (A) 21 days and (C) 12 days. (B,D) One representative example of an infiltrated lung of the indicated genotype is shown. Top panel: photographs, digital camera, Canon EOS 300D. Bottom panel: H&E-stained histological lung sections; magnification, 100× Zeiss Axiolmager 21, 10× objective, NA 0.25, air; camera: Pixelink Color, 1600 × 1200; software: PixelNK Capture 3.0. (E-F) MC38 cells were injected subcutaneously into (E) WT, WT depleted of CD8⁺cells, and WT depleted of NK1.1⁺ cells and (F) Stat5^f/f and Ncr1-iCreTg Stat5^f/f mice, and after 17 days, tumor weights were analyzed. (G) Histograms showing CD44 (top panel) and CD25 (bottom panel) expression on in vitro–activated T cells from the indicated genotypes. CD8⁺ T cells were cultured under IL2 and stimulated with plate-bound anti–CD3 + anti–CD28 antibodies. Cells were gated on CD3⁺CD8⁺ populations. Open histograms indicate the percentage of CD44⁺ or CD25⁺ T cells. Gray histograms indicate unstimulated T cells. (A, C, E, F) n ≥ 5 per genotype. (G) Five mice per genotype were pooled. Data are representative of 3 independent experiments.