Encouraging results, obtained by administrating anti-IL-9 antibodies in Eμ-TCL1 mice, the mouse model of CLL (122), demonstrate that this approach counteracts leukemia progression by on the one hand decreasing PD-1 expression in CD8+ T cells (44) and on the other hand lowering the expression of homing chemokines by stromal cells of lymphoid organs (74). The gene discussed is IL9; the disease is B-cell chronic lymphocytic leukemia.