Lack of P-selectin changes the biologic properties of BCR/ABL-expressing myeloid progenitor cells in bone marrow. (A) Lack of P-selectin results in the early release of BCR/ABL-expressing myeloid progenitor cells from bone marrow. Bone marrow cells from wild-type and P-selectin^-/- mice that received transplants of BCR/ABL-transduced bone marrow cells were analyzed by FACS at days 8 and 12 after bone marrow transplantation. At both days 8 and 12, the percentage (mean values ± SD) of GFP⁺/Gr-1⁺ and GFP+/Mac-1+ cells was significantly higher in bone marrow cells of wild-type CML mice than in those of P-selectin^-/- CML mice (P = .007 and .023 for day 8 and P = .039 and .047 for day 12, respectively). (B) Mean spleen weight (mean values ± SD) of the diseased mice at days 8 and 12 after bone marrow transplantation. At both days, there was no significant difference in spleen weight between wild-type and P-selectin^-/-/ICAM1^-/-CML mice (P = .833 and 0.784 for days 8 and 12, respectively). (C) Pathological analysis (hematoxylin/eosin staining) of the lungs of CML mice (n = 5 for each transplant group) at day 12 after bone marrow transplantation. In the normal control group, nontransduced wild-type bone marrow cells were transplanted into lethally irradiated wild-type recipient mice. In contrast to normal control mice, BCR/ABL-transduced WT to WT, P-selectin^-/- to P-selectin-/-, and P-selectin^-/-/ICAM1^-/- to P-selectin^-/-/ICAM1^-/- transplant mice showed significant infiltration of the lungs by myeloid leukemic cells. Lung hemorrhages and leukemic cell masses were observed in P-selectin^-/- and P-selectin^-/-/ICAM1^-/-, but not WT CML mice. Scale bars, 100 μM (short bar at 25 ×) and 50 μM (long bar at 200 ×). (D) Lack of P-selectin does not alter the homing properties of the transplanted donor bone marrow cells to bone marrow of the recipient mice. Donor bone marrow cells from wild-type and P-selectin^-/- mice were transduced GFP retrovirus, followed by transplantation into wild-type and P-selectin^-/- recipient mice, respectively. Prior to the transplantation, the transduced marrow cells were analyzed by FACS for percentage (mean values ± SD) of GFP⁺ cells (20.0% and 18.1% for the transduced wild-type and P-selectin^-/- bone marrow cells, respectively) (top left panel).At 3 hours after the transplantation, cells were isolated from bone marrow, peripheral blood (PB), and spleens (Spl) of the recipient mice, and analyzed by FACS for GFP⁺ cells. Similar percentages of GFP⁺ wild-type and P-selectin-/- cells were detected in these locations (P = .86, .86, and .92 for BM, PB, and Spl, respectively). The transduced wild-type and P-selectin^-/- donor bone marrow cells were also labeled with a red fluorescent dye PKH26, followed by transplantation into wild-type and P-selectin^-/- recipient mice, respectively. Prior to the transplantation, the percentages (mean values ± SD) of PKH26⁺ cells were 99.4% and 98.7% for wild-type and P-selectin^-/- donor cells, respectively (top right panel).At 3 hours after the transplantation, cells were isolated from bone marrow and spleens of the recipient mice and analyzed by FACS for PKH26⁺ cells. Similar percentages of PKH26⁺ wild-type and P-selectin-/- cells were detected in these 2 locations (P = .50, .58 and .07 for BM, peripheral blood, and Spl, respectively). Cryosections of the lungs from the mice receiving the PKH26-labeled bone marrow cells were prepared in optimal cutting temperature (OCT) medium, and the labeled cells (arrow heads) on 10-μM sections were visualized under a fluorescent microscope (bottom panel).