L-selectin blockade decreases engraftment of BCR-ABL1⁺leukemia-initiating cells. (A) L-selectin–deficient leukemic progenitors have a defect in BM homing. Irradiated recipient mice (n = 3) were injected with a mixture of BM cells from mice with BCR-ABL1–induced CML-like disease induced from WT donor cells (expressing GFP) and Sell^−/− donor cells (expressing NGFR) and euthanized 2 hours later. (Upper left) Flow cytometric analysis of c-Kit⁺Lin^– normal BM stained with isotype-PE antibody. (Upper right) Input mixture of leukemic WT and Sell^−/− progenitors. (Lower) Corresponding c-Kit⁺Lin^– populations isolated from BM of the 3 recipients, stained with PE-conjugated antibody against human NGFR. The percentage of GFP⁺ and NGFR⁺ cells is shown adjacent to the respective regions. (B) No defect in engraftment of Sell^−/− HSC transduced with empty GFP virus. BM from WT and Sell^−/− donors was transduced with empty retrovirus expressing GFP alone and equivalent numbers of cells transplanted into lethally irradiated WT recipients. Ten weeks after transplant, recipient BM was harvested, and the number of engrafting proviral clones determined by Southern blotting of BglII-digested DNA with a GFP probe. Lanes 2 to 4 are recipients of WT BM, whereas lanes 5 to 7 are recipients of Sell^−/− BM. The probe also faintly detects a common sequence (*) in mouse genomic DNA. (C) Anti–L-selectin antibody treatment impairs engraftment of BCR-ABL1–transduced progenitors. Southern blot analysis with a GFP probe of genomic DNA of leukemic BM from recipients of BCR-ABL1–transduced WT BM that was untreated (lanes 2-4), isotype control antibody–treated (lanes 5-7), and anti–L-selectin antibody–treated (lanes 8-12). Con1 and Con2 are control DNAs containing 1 and 2 proviral clones, respectively.