CLL proliferation in NSG mice. (A) Retro-orbital sinus bleeding was done at 2-week intervals. CLL cells only proliferate in presence of human hematopoietic elements. Representative example of 9 CLL samples, with a minimum of 29 mice per group (supplemental Table 2). Histograms only show CFSE⁺ cells. (B) hMSCs are not necessary for CLL proliferation because virtually identical CFSE dilution patterns are seen in the presence or absence of transferred hMSCs. Representative example of 4 CLL samples with a minimum of 10 mice per group (supplemental Table 2) is shown. (C) Early after CLL transfer, most B cells in PB are CFSE⁻, deriving from transplanted hCD34⁺ cells (supplemental Figure 2). (D) Late after CLL transfer, a relatively selective loss of CFSE⁻ B cells occurs; remaining B cells are mostly CFSE⁺ and of leukemic origin (supplemental Figure 2).