Isolation and culture of human bone marrow endothelial cells

Bone marrow endothelial cells are likely to play an important role in the homing of hematopoietic progenitor cells. In view of analyzing the interactions between endothelial cells and hematopoietic progenitor cells, we studied several methods of isolating endothelial cells from human bone marrow, including fluorescence activated cell sorting (FACS) and separation by immunomagnetic beads. FACS sorting gave the best results as contamination with other cells did not occur. After density-gradient centrifugation of bone marrow aspirates, the mononuclear cell (MNC) fraction was depleted for T cells, B cells, and myeloid cells by immunomagnetic separation. Further enrichment of endothelial cells was achieved by FACS sorting using BNH9 or S-Endo1 monoclonal antibodies (MAbs). These MAbs, in contrast to several other endothelial-cell reactive MAbs, were found to react highly specifically with sinus endothelial cells as tested by immunohistochemistry on bone marrow tissue sections and cell culture preparations and by double-colored FACS analysis on bone marrow MNCs (BMMNC). Sorted cells, which formed 0.05% of the MNC fraction, showed strong intracytoplasmic von Willebrand factor positivity. Ultrastructural analysis revealed cells with endothelial characteristics. Cells were cultured in fibronectin-coated, 24-well culture plates in endothelial-cell culture medium or long-term bone marrow culture medium. After 1 to 3 weeks of culture, a monolayer of spindle-shaped cells developed expressing endothelial cell antigens. Cells could be kept in culture for 4 to 6 weeks. In conclusion, the method described provides highly purified preparations of human bone marrow endothelium that may permit in vitro adhesion experiments with normal and leukemic hematopoietic progenitor cells.