IL-9 modulates leukemic cell invasiveness in vivo by shaping the stromal chemokine landscape and predicts poor prognosis in CLL. (A) Overall survival of 52 CLL patients grouped as “<0.16” (n = 26) and “≥0.16” (n = 26) (0.16 corresponds to the median 2^−dCt IL-9 mRNA expression). After a median follow-up of 60 months, the estimated median overall survival was 83 months for patients in the “≥0.16” group, and it was not reached for patients with low IL-9 mRNA levels (P = .0377, log-rank test). (B) qRT-PCR analysis of IL-9 and p66Shc mRNA in B cells purified from 5 CLL patients at the earliest asymptomatic disease stage (asymptomatic) and after progression to a stage requiring treatment (active). Spleen size and weight (C) and the absolute number (D) and percentage (E) of CD19⁺IgM⁺CD5^low cells in the indicated organs of Eμ-TCL1/p66Shc^−/− mice with overt disease injected intraperitoneally with 100 μg of anti–IL-9 antibody (IL-9 Ab; n = 4) or isotype-control antibody (ctr Ab; n = 4) twice a week (days 1 and 5) for 4 weeks, as well as for healthy age-matched C57BL6/J control mice (healthy ctr; n = 2). Flow cytometric analysis of surface expression (left panel) and RT-PCR analysis of mRNA expression (right panel) of CCL2 in splenocytes (F) and LN cells (G) from Eμ-TCL1/p66Shc^−/− or C57BL6/J control mice treated as above. The relative gene transcript abundance was determined on triplicate samples using the dCt method and normalized to GAPDH. Data are mean ± standard deviation. ***P ≤ .001, **P ≤ .01, *P ≤ .05, Mann-Whitney rank-sum test (B), 1-way ANOVA with Tukey’s post hoc test (blue text), multiple comparisons (black text) (C-G).