E-selectin and very late activation antigen-4 mediate adhesion of hematopoietic progenitor cells to bone marrow endothelium

Adhesion of CD34(+) hematopoietic progenitor cells (HPCs) to sinusoidal endothelium probably plays a key role in homing of transplanted CD34(+) HPCs to the bone marrow (BM). We have investigated the role of various adhesion molecules in the interaction of purified CD34(+) HPCs derived from BM or peripheral blood (PB) and a human BM-derived endothelial cell line. Adhesion of CD34(+) HPCs to endothelial cells was measured with the use of a double-color flow microfluorimetric adhesion assay. In this assay, adhesion is measured under stirring conditions, simulating blood flow in sinusoidal marrow vessels. Adhesion of PB CD34+ cells to human BM endothelial cells (HBMECs) was observed only after interleukin (IL)-1 beta prestimulation of the endothelial cells. This adhesion was strongly increased after addition of phorbol-myristate acetate (PMA). Adhesion of PB CD34(+) cells to IL-1 beta-prestimulated HBMECs was inhibited by blocking monoclonal antibodies (mAbs) against E-selectin and by neuraminidase treatment of the PB CD34(+) cells, mAbs against very late activation antigen (VLA)-4 inhibited adhesion only when the E-selectin-mediated interaction was prevented. No clear inhibiting effect was found with blocking mAbs against beta(2)-integrins. Stimulation with the beta(1)-integrin-activating mAb, 8A2, induced adhesion of CD34(+) cells to endothelial cells. In conclusion, stimulation of both endothelial cells and CD34(+) HPCs is necessary for adhesion of CD34(+) HPCs to endothelial cells. We furthermore demonstrated that E-selectin and VLA-4 mediated this adhesion.