FTY720 induces complete remission in NK-cell leukemic rats. (A) The Kaplan-Meier survival curves for normal rats after treatment with 4.5 mg/kg of FTY720 (n=16) or PBS (n=16) or leukemic rats after treatment with either 4.5 mg/kg (n=16) or PBS (n=16), were plotted. (B) Maintenance of normal white blood counts, hemoglobin values, and platelet counts in responding leukemic and normal rats treated with FTY720. Blood (200 μL) from leukemic rats treated with FTY720 (n=16) and PBS (n=16) and normal rats treated with FTY720 (n=16) and PBS (n=16) was collected every week from tail veins of the animals and placed in EDTA K2-coated tubes, then CBC (complete blood count) analysis was performed. Arrow indicates the cessation of the treatment. (C) Flow cytometry was used to identify rat leukemic NK cells, which are CD3⁻CD8a⁺. Comparison of CD3⁻CD8a⁺ NK cells isolated from multiple tissues among normal rats treated with PBS (n=16) or FTY720 (n=16), leukemic rats treated with PBS (n=16) or leukemic rats responsive to FTY720 treatment (n=5) or unresponsive to FTY720 (n=11). *P < .05, **P < .005, ***P < .005 indicates significance between leukemic rats responsive to FTY720 or unresponsive to FTY20 and leukemic rats treated with PBS (unpaired t test).