In vivo antileukemic effects of FTY720 and lack of toxicity in long-term treated animals. (A) Jak2^V617F leukemic burden at 6 weeks after Ba/F3-Jak2^V617F cell injection measured by SNapShot assay in untreated (gray square) and FTY720 -treated (red square) (5 weeks; 10 mg/kg/d) mice. Age-matched mice (white square) were used as a control. Levels of WT and V617F Jak2 alleles are shown by the blue and red curves, respectively. (B) Average spleen weights of untreated or FTY720-treated age-matched and leukemic mice. (C) H&E-stained sections of spleen, BM, liver, heart, and kidney of untreated (white square) and FTY720-treated (green square) age-matched control mice and, untreated (gray square) and FTY720-treated (red square) leukemic mice. (D) Kaplan-Meier curve shows survival of untreated leukemic (gray line), FTY720-treated leukemic (red line), and age-matched control (green line) mice. (E) Electrocardiographic and cardiomyocyte contractile performance in untreated or FTY720-treated (10 weeks) control mice. *P ≤ .05.