Gleevec alone or combined with FL induced NK cell activation in vivo. (A) Long-term exposure to Gleevec in C57BL/6 mice induced reduction of the splenic T lymphocyte counts but selectively maintained the NK cell subset. After red blood cell removal and an adherence step, splenocytes were enumerated after 15-–21 days of oral feeding with Gleevec (150 mg/kg bid) or H₂O (200 μl) and analyzed by flow cytometry using anti-CD3 and anti-NK1.1 mAb’s. The absolute numbers of CD3⁺/NK1.1^– T cells and CD3^–/NK1.1⁺ NK cells were deduced from the percentages obtained in 2 independent experiments and are indicated in the boxes (B). T lymphocytes were not activated during Gleevec oral feeding. In the CD3⁺/NK1.1^– T cell gate, the CD69 expression is shown. (C) NK lymphocytes were activated during therapy with Gleevec. In the CD3^–/NK1.1⁺ NK cell gate, the CD69 expression is shown. Swiss^nu/nu mice (D) and C57BL/6 littermates (E) were injected intraperitonealy with 10 μg of FL or 100 μl of PBS each day for 10 days. From day 7 to day 10, mice received either Gleevec (150 mg/kg bid) or H₂O (200 μl). At day 11, all mice were sacrificed to analyze the expression of the NK activation marker CD69 on NK1.1⁺ or DX5⁺/CD3^– splenocytes. Positive controls included mice treated with rhuIL-2 (1 × 10⁵ IU intraperitoneally, bid for 4 days). Groups were compared by analysis of variance (ANOVA) using the nonparametric Kruskall-Wallis test. *P < 0.05 as compared to PBS. ^#P < 0.05 as compared to Gleevec. P < 0.05 as compared to FL.