Platelet-derived growth factor promotes ex vivo expansion of CD34+ cells from human cord blood and enhances long-term culture-initiating cells,non-obese diabetic/severe combined immunodeficient repopulating cells and formation of adherent cells

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells. In this study, we investigated the effects and mechanism of PDGF on the ex vivo expansion of cord blood CD34+ cells. Our data demonstrated that among various cytokine combinations of thrombopoietin (TPO), interleukin 1 beta (IL-1beta), IL-3, IL-6 and Flt-3 ligand (Flt-3L), TPO + IL-6 + Flt-3L was most efficient in promoting the expansion of CD34+ cells, CD34+CD38- cells, mixed-lineage colony-forming units (CFU-GEMM) and long-term culture-initiating cells (LTC-IC) by 21.7 +/- 5.00-, 103 +/- 27.9-, 10.7 +/- 7.94- and 6.52 +/- 1.51-fold, respectively, after 12-14 d of culture. The addition of PDGF increased the yield of these early progenitors by 45.0%, 66.5%, 45.1% and 79.8% respectively. More significantly, PDGF enhanced the engraftment of human CD45+ cells and their myeloid subsets (CD33+, CD14+ cells) in non-obese diabetic (NOD)/severe-combined immunodeficient (SCID) mice. The expression of PDGF receptor (PDGFR)-beta was not detectable in fresh CD34+ cells but was upregulated after culture for 3 d. PDGF also enhanced the development of adherent cells/clusters that expressed the endothelial markers VE-cadherin and CD31. These findings suggest that PDGF is an effective cytokine for the ex vivo expansion of early stem and progenitor cells. The mechanism could be mediated by PDGFR-beta on committed CD34+ progenitor cells and/or secondary to the stimulation of autologous, stromal feeder cells.