Platelet-derived growth factor enhances expansion of umbilical cord blood CD34+ cells in contact with hematopoietic stroma.

Stem cell expansion remains an elusive but highly desirable goal. Here we show that platelet-derived growth factor (PDGF), along with cultured endothelial or stromal cells, significantly enhances expansion of human CD34+ cells in vitro. In media supplemented with thrombopoietin, stem cell factor, flt-3 ligand, and granulocyte-colony stimulating factor, CD34+ cells, as well as CFU-GM, BFU-CFU-E, CFU-GEMM, and CFU-MK, increased by 34.3-, 138-, 59.7-, 38.4-, and 86.0-fold, respectively. Co-culturing of CD34+ cells with cultured stromal cells or human umbilical cord vein endothelial cells (HUVECs) greatly enhanced expansion efficiency. The presence of PDGF (50 ng/ml) further augmented expansion, such that increases of 77.0-, 262-, 90.0-, 93.0-, and 200-fold, respectively, were achieved. Six weeks after infusion of expanded cells into NOD/SCID mice, human CD45+ cells were detected in recipients' bone marrow, spleen, and peripheral blood. Our results provide a rationale for development of a stem cell expansion protocol for clinical applications.