B-cell–specific CD44 deletion leads to a delayed leukemic onset and reduced tumor infiltration in vivo. (A) A CLL mouse model with a B-cell–specific Cd44 knockout, henceforth the Cd44ΔB Tcl1-tg mouse, was established. The amount of PB CD5⁺/CD19⁺ cells per microliter in wild-type, Tcl1-tg, and Cd44ΔB Tcl1-tg mice was measured by flow cytometry during early disease development (3 and 5 months) and progressive disease (7 and 9 months). (B) Organ infiltration of Tcl1-tg and Cd44ΔB Tcl1-tg mice at end stage of disease or age-matched C57BL/6 (wild-type) mice was determined by histology of 3 different mice per genotype. Hematoxylin and eosin staining of LIV, lung (LUG), SPL, and BM of 3 different mice of each genotype was analyzed. Images from representative regions are shown. (Ci) Representative spleens of Tcl1-tg, Cd44ΔB Tcl1-tg, and wild-type mice are shown. (Cii) Spleen size and weight were measured at end stage of disease from Tcl1-tg and Cd44ΔB Tcl1-tg mice. (D) The absolute number of CD5⁺/CD19⁺ cells in the whole spleen (i) and in both femora (ii) of end-stage diseased Tcl1-tg (n = 12) and Cd44ΔB Tcl1-tg (n = 14) mice was determined by flow cytometry. Mio, million.