Adhesion of hematopoiet 1c progenitor cells to endothelial cells: A comparison between human umbilical vein and human bone marrow derived endothelial cell lines

The interactions of bematopoiebc progenitor cells with the bone marrow endothetium is of great importance in the process of homing of these cells to the bone marrow. We investigated the role of various adhesion molecules in the binding of progenitor cells to an endothelial cell line established from human umbilical vein endomehal cells (HUVEC) in a tlow adhesion assay. With functional blocking monoclonal antibodies and enzyme treatment we demonstrated thai interactions of siafcc acid residues and VLA-4 expressed on progenitor cells, with, respectively Eselcctin and vascular ceD adhesion molecule-1 (VCAM-I ) present on the recombinant IL-l β prestimulated endothelial cells are involved in the adhesion process. To investigate whether there are differences between HUVEC and human bone marrow endothelial Us (HBMEC) in the interaction with hematopoietic progenitor cells. HBMEC have been immortafczod and several HBMEC-ceO Unes have been obtained. HBMEC were isolated from a bone marrow aspirate and immortalized using the replication defective rctrovirol construct LXSNI6 E6/E7. containing the human papilloma virus (HPV) E67E7 genes. Southern-blot analysis, using EcoRI-digested genomic DNA of the different clones and a probe specific for the E6/E7 genes, showed that 7 different unique clones were isolated. All clones stained positively tor von Willebrand factor, CD31, CD13, endoghn and 1C AM-I and showed no expression of E-selectin or VCAM-1. The expression of 1C AM-1, VCAM-1 andEselectin was upregulated both by stimulation with IL-l βor TNF-oc. No differences m uprcgulatioû were found between HUVEC and 4 tested HBMEC clones. To examine whether progenitor cells bind preferentially to HBMEC in comparison to HUVEC. we set up a triple-color tlow microfluorimetric adhesion assay, hi this adhesion assay progenitor cells, HUVEC and HBMEC were labelled with cither FTTC-labeUed-, PE-labeOed- or Cy-S-labeDed CD13 and mixed in an aggregomcter. At different time points the adhesion of the progenitor to the endothehal cells was quantitated by FACS-scao analysis Of the 3 HBMECckmes tested, the results of 2 clones did not differ from that of HUVEC. whereas 1 HBMEC clone showed a reduced binding of progenitor cells. When tested in a double color micToftuorimetric adhesion assay in which the progenitor cells were mixed with either HBMEC or HUVEC, the particular HBMEC-clone showed me same bindings-capacity of progenitor cells as HUVEC. These results suggest that no major differences exist between endothehal cell unes derived front human umbibca) vein or human bone marrow. We hypothesize that bone-marrow specific characteristics of'HBMEC are induced by their microenviranment. Therefore, we now study the changes in adhesion of progenitor cells to HBMEC upon exposure of HBMEC to stromal proteins or conditioned medium derived from long term cultures of bone-marrow stromal cells.