Identification and characterization of a leukemic stem cell–like population that expresses both endothelial and hematopoietic progenitor cell surface markers. (A) Confocal laser scanning microphotographs (LSMs) of Ph⁺ ALL Sup-B15 cells stained with anti–VE-cadherin in the presence of 10 mM EGTA and 5 mM CaCl₂. Cell nuclei were counterstained with propidium iodide (PI) and 1024 × 1024 12-bit confocal images were collected using 40×/0.75 Plan -Neofluar objective. (B) Cell lysates prepared from Ph⁻ acute leukemia cell lines JM1, RS4;11, REH, Jurkat, HL60, and Ph⁺ acute leukemia cell lines K562, Sup-B15, OP-1, Nalm20, Nalm27, and Nalm29 were Western blotted with anti–VE-cadherin. The same membranes were stripped and reprobed with anti–β-tubulin as a loading control. (C) Immunophenotyping of Ph⁺/VE-cadherin⁺ Sup-B15 cells by flow cytometry. Cells were surface stained to evaluate hematopoietic stem/progenitor cell and classic endothelial markers.