Genetic silencing of S100A9 in murine B-CLL cells delays disease progression. (A-B) Splenocytes from 10- to 12-month-old Eμ-TCL1 or C57BL6 mice were used to evaluate S100-A9, EMMPRIN, RAGE, and TLR4 expression in CD19⁺CD5⁺ leukemic lymphocytes and CD19⁺CD5^– normal murine B cells. (C) We created a novel Eμ-TCL1/S100A9^–/– mouse model, and leukemic infiltration of CD19⁺CD5⁺ cells in the spleen of 10-month-old mice was compared between Eμ-TCL1 and the Eμ-TCL1/S100A9^–/– mice. (D) Aged Eμ-TCL1/S100A9^–/– mice show longer survival than the aged Eμ-TCL1 mouse model. (E-K) CD19⁺/CD5⁺ B cells isolated from Eμ-TCL1 or Eμ-TCL1/S100A9^–/– mice were transferred via TVI into NSG mice. (E-F) The tumor burden in PB was assessed weekly; the percentage of CD19⁺CD5⁺ cells and the absolute count of B-CLL cells were measured by FC. (G) Spleen size from both groups after 5 weeks of adoptive transfer. (H) Malignant B-cell infiltration in the spleen and bone marrow at week 5 after adoptive transfer. (I) Longer survival was observed in the Eμ-TCL1/S100A9^–/– group (n = 4) compared to the Eμ-TCL1 recipient mice (n = 5). (J) B cells were isolated from NSG mice after 5 weeks of adoptive transfer (AT), and then the mRNA was used for NanoString analysis. Volcano plot showing upregulated (red) and downregulated (blue) genes in S100A9^–/– B cells vs B cells from NSG adoptive transfer Eμ-TCL1 mice. (K) Downregulated genes in S100A9^–/– B cells relative to B cells from NSG adoptive transfer Eμ-TCL1 mice, belonging to the TNF-α signaling via NF-κB from the MSigDB Hallmark genes. ∗∗∗∗P < .0001; ∗∗∗P < .001; ∗∗P < .005; ∗P < .05. MSigDB, Molecular Signatures Database; ns, not significant; TNF-α, tumor necrosis factor α.