Background: There has been contradictory reports regarding the homing potential of hematopoietic cells briefly exposed to hematopoietic growth factors in vitro. To get a resolution to this controversy, we investigated the effects of
short-term growth factor treatment of hematopoietic cells on the expression of CXCR4 and adhesion molecules, and the chemotaxis in response to stromal cell-dervied factor-1 (SDF-1), which is widely accepted to play a critical role in bone marrow (BM) homing of hematopoietic stem cells.
Methods:
BM and cord blood(CB) CD34+ cells were incubated with various hematopoietic growth factors including IL-1β, IL-3, IL-6, G-CSF, GM-CSF, stem cell factor (SCF), flk-2 ligand, and thrombopoietin, alone or in combination for up to 48 hours. Before and after the incubation, the expression of CXCR4 and adhesion molecules of CD34+ cells was analyzed using flow cytometry. SDF-1-mediated transmembrane or transendothelial migration of CD34+ cells,
cobblestone area-forming cells CD34+ cells, cobblestone area-forming cells (CAFCs), and/or long-term culture-initiating cells (LTC-ICs) was measured using Transwell M system.
Results:
VLA-4 was moderately up-refulated by the incubation of
the cells with IL-3 and SCF, and ICAM-1 was slightly up-regulated by IL-1β and IL-3. The expression of L-selectin, PECAM-1 or LFA-1 was not altered by any growth factors. With the incubation of the cells in the absence of growth factors or SDF-1, CXCR4 expression of CD34+ cells was rapidly increased, reaching a plateau at 24 hours. The spontaneous up-regulation was abrogated with the addition of SDF-1. In agreement with the up-regulation of CXCR4, CD34+ cells incubated for 40 hours showed much enhanced chemotaxis in response to SDF-1 compared to non-incubated cells (24.7±3.5% vs. 7.0±1.6%, P=0.01). Any growth factors examined in this study did not alter the CXCR4 expression of CD34+ cells. Neither did growth factors affect the transendothelial migration of LTC-ICs toward bone marrow stromal cells as well as the SDF-1-induced transmembrane chemotaxis of CD34+ cells and CAFCs.
Conclusion:
Short-term treatment of hemotopoietic cells with hematopoietic growth factors does not alter the expression of CXCR4 or SDF-1-mdeiated transendothelial chemotaxis.

Keywords: Hematopoietic cells, CXCR4, SDF-1, Adhesion molecules, Bone marrow homing, Hematopoietic growth factors