L-selectin contributes to engraftment of BCR-ABL1⁺leukemic stem cells. (A) Kaplan-Meier–style curves for (A) mortality due to CML-like leukemia and (B) overall survival of WT B6129 F2 recipients of BCR-ABL1–transduced BM from WT (solid line, n = 33) and L-selectin KO (Sele^−/−; dotted line, n = 16) donors transduced with BCR-ABL1 retrovirus and of L-selectin KO BM transduced with retrovirus coexpressing BCR-ABL1 and chimeric E/L-selectin (dashed line, n = 7). The difference in survival between recipients of WT and L-selectin KO BM was significant (P = .05, Mantel-Cox test), whereas there was no significant difference between WT and L-selectin KO + E/L-selectin (P = .45). Interestingly, the majority of mice in the E/L-selectin rescue cohort had evidence of malignant ascites and/or pleural effusions in addition to organomegaly, which might reflect an increased tendency of leukocytes expressing the stabilized selectin to traffic to serosal surfaces.⁵⁰  (C) Serial flow cytometric analysis of a representative B6129 F2 WT recipient of BCR-ABL1–transduced L-selectin KO BM on days 14, 19, 27, 34, 41, and 54 after transplantation, with the PB leukocyte count indicated. (D) Flow cytometric analysis of a representative B6129 F2 WT recipient of L-selectin KO BM transduced with retrovirus coexpressing BCR-ABL1 and human E/L-selectin chimera, where human E-selectin expression is detected with monoclonal antibody CL-37 (y-axis). (Upper) Serial analysis of PB, showing rapid accumulation of circulating myeloid cells expressing human E-selectin. PB from an untransplanted WT mouse is shown in the last panel. (Lower) Analysis of leukocytes from spleen, pleural effusion, and ascites at necropsy. (E) Restoration of polyclonal engraftment by coexpression of E/L-selectin. Genomic DNA from the indicated tissues (asc, ascites; PE, pleural effusion) was analyzed by Southern blot using a probe from the human E-selectin gene. Brackets indicate different tissues from the same mouse. The BM donor was WT in lanes 4 to 8 and L-selectin KO in lanes 9 to 18. The BCR-ABL1 retrovirus used for transduction coexpressed GFP in lanes 3 to 5 and human E/L-selectin in lanes 6 to 18. Note the increased clonality in most recipients in lanes 9 to 18. Proviral copy number is indicated below. *Bands from the endogenous murine E-selectin gene.