Ex Vivo Expansion of Stem Cells from Umbilical Cord Blood: Expression of Cell Adhesion Molecules

Expansion of stem cells from cord blood has been demonstrated to increase the numbers of CD34+ cells, CD34+ subsets, long‐term culture‐initiating cells, and severe combined immunodeficient mouse, repopulating cells. However, reports suggest that the ex vivo expanded population behaves differently than freshly isolated cells and shows a delayed or diminished engraftment. In this study, we investigated the effects of the cytokines flt3 ligand, stem cell factor, and thrombopoietin on expansion of CD34+ and CD34+/CD38− cells. In addition, we studied the expression of adhesion molecules, very late activation antigen‐4 (VLA‐4) and leukocyte function antigen‐1 (LFA‐1), on CD34+ cells from cord blood by flow cytometry. We also looked at the expression of an adhesion receptor, namely, vascular cell adhesion molecule‐1 (VCAM‐1) on bone marrow stromal cells by Western blot analysis after exposure to low dose γ irradiation. After culturing for 7 days, increases in the absolute numbers of CD34+, CD34+/CD38−, CD34+/VLA‐4+, and CD34+/LFA‐1+ cells were 5.67 ± 2.91 (mean ± standard deviation) fold, 7.21 ± 4.38 fold, 99.56 ± 101.5 fold, and 101.39 ± 83.25 fold, respectively. There was a transient upregulation in the expression levels of VCAM‐1 on stromal cells, which peaked at 4 hours. Though there was an increase in the absolute numbers of CD34+ cells expressing the adhesion molecules, the expression levels (antigen density) of the adhesion molecules on the CD34+ cells remained unaffected.