STAT5B^N642H induces NK-cell leukemia in mice. Cre neg, GFP^NK/NK, STAT5B^NK/NK, and N642H^NK/NK mice were aged and monitored for signs of disease development. (A) Survival analysis of Cre neg, GFP^NK/NK, STAT5B^NK/NK, and N642H^NK/NK mice (n ≥ 12 per genotype). (B) Flow cytometric analysis of GFP⁺ cells in different tissues of Cre neg, GFP^NK/NK, STAT5B^NK/NK, nondiseased N642H^NK/NK, and diseased N642H^NK/NK mice (n ≥ 8 per group; mean ± standard deviation [SD]). (C) Body weight quantification of Cre neg, GFP^NK/NK, STAT5B^NK/NK, nondiseased N642H^NK/NK, and diseased N642H^NK/NK mice (n ≥ 8 per group; mean ± SD). (D) Quantification of the leukemia type developed by N642H^NK/NK mice. (E) Relative quantification of CD3⁺NK1.1^– T cells, CD3⁺NK1.1⁺ NKT cells, CD3^–NK1.1⁺ NK cells and CD3^–NK1.1^– “undifferentiated” cells among GFP⁺ cells in the spleen of diseased N642H^NK/NK mice (n = 8). (F) Flow cytometric analysis of GFP⁺ cells in the liver of Cre neg, GFP^NK/NK, STAT5B^NK/NK, nondiseased N642H^NK/NK, and diseased N642H^NK/NK mice (n ≥ 8 per group; mean ± SD). Heat map depicts percentage of GFP⁺ cells out of living cells, percentages of double-negative (DN; CD27^–CD11b^–), CD27⁺, double-positive (DP; CD27⁺CD11b⁺), CD11b⁺, CD49a⁺, CD49b⁺, and KLRG1⁺ cells out of GFP⁺ NK cells (CD3^–NK1.1⁺) and median fluorescence intensity (MFI) of NKp46, KLRG1, and NKG2D on GFP⁺ NK cells. (G) Percentages of KLRG1⁺ (left) and MFI (right) of KLRG1 on GFP⁺ NK cells in the spleen and liver of Cre neg, GFP^NK/NK, STAT5B^NK/NK, nondiseased N642H^NK/NK, and diseased N642H^NK/NK mice (n ≥ 8 per group; mean ± SD). Levels of significance were calculated using the Mantel-Cox test (A) and the 1-way analysis of variance (B-C and G). ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001.