Adhesion of hematopoietic progenitor cells to human bone marrow or umbilical vein derived endothelial cell lines: A comparison

Homing of hematopoietic progenitor cells (HPC) to the bone marrow may be me diated by adhesion molecules specifically expressed on human bone marrow en dothelial cells (HBMEC). This hypothesis suggests that HPC would preferenti ally bind to HBMEC compared to endothelial cells from other origins. In thi s study, HPC were allowed to adhere either to HBMEC cell lines or to human umbilical vein endothelial cells (HUVEC) in two different experimental set- ups. First, adherence was measured using a flow cytometric assay with three different colors identifying each cell population (HPC, HBMEC, HUVEC). HPC could adhere (in a competitive way) to the two endothelial cell lines unde r stirring conditions, which simulated adhesion under shear stress, as pres ent in blood vessels. Because this assay requires relatively firm adhesion and the endothelial cells don't form a monolayer, we studied the same inter actions under less stringent conditions. HPC were allowed to adhere to endo thelial monolayers under gently rocking conditions. Differential adhesion o f HPC to a set of endothelial cell lines did not correlate with the origin of the endothelial cells. Adhesion of HPC to both types of endothelial cell s was inhibited in the presence of various combinations of monoclonal antib odies against the adhesion molecules VLA-4, CD18, and/or E-selectin. No ind ications ere obtained for qualitative differences in the role of these mole cules in adhesion of HPC to either HBR;IEC or HUVEC cell lines. In conclusi on, no preferential adhesion of HPC to HBMEC compared to HUVEC cells was ob served. This may be due to a lack of origin-specific differences between en dothelial cells, implying that the specificity of homing is not regulated a t the entrance of the bone marrow. Otherwise, the origin-specific differenc es between endothelial cells of different origins may be micro environment- induced, rather then intrinsic, implying that care should be exercised with the use of endothelial cell lines in studies investigating the specificity of homing of HPC. (C) 1999 International Society for Experimental Hematolo gy. Published by Elsevier Science Inc.