CD44 deficiency of leukemic B cells leads to a homing defect to SPL and BM and reduces proliferation of leukemic cells in SPL in competitive adoptive transfer experiments. (A) Scheme of short-term, competitive, adoptive transfer approach. Splenocytes of Tcl1-tg and Cd44ΔB Tcl1-tg mice were analyzed for the content of leukemic CD5⁺/CD19⁺ B cells and stained with different cell dyes, CFSE or CTV, mixed and injected into tail veins of 3 to 4 C57BL/6J recipients per experiment. After 3 hours or 3 days, the number of CD5⁺/CD19⁺ cells that had homed to the SPL and BM of the recipients was determined by flow cytometry. (B) Homing of CD5⁺/CD19⁺ cells after 3 hours was determined as previously described,^11,13  in 4 independent experiments using splenocytes from 4 different Tcl1-tg and 4 Cd44ΔB Tcl1-tg mice. Briefly, homing rate is defined as the number of measured leukemic cells per 1 million measured lymphocytes per 1 million injected cells. (Ci) The number of completed division cycles of injected CD5⁺/CD19⁺ cells in SPL and BM of C57BL/6J wild-type recipients after 3 days was analyzed by cell trace dye dilution with FlowJo software and quantified in 3 independent experiments. (Cii) Representative histogram plots of CFSE and CTV fluorescence of in vivo proliferated CD5⁺/CD19⁺ cells in SPL and BM after 3 days in C57BL/6J wild-type mice are shown.