Platelet-derived Growth Factor Enhances Ex Vivo Expansion of Megakaryocytic Progenitors from Human Cord Blood

Infusion of ex vivo expanded megakaryocytic (MK) progenitor cells is a strategy for shortening the duration of thrombocytopenia after haematopoietic stem cell transplantation. The cell dose after expansion has emerged as a critical factor for achieving the desired clinical outcomes. This study aimed to establish efficient conditions for the expansion of the MK lineage from enriched CD34(+) cells of umbilical cord blood and to investigate the effect of platelet-derived growth factor (PDGF) in this system. Our results demonstrated that thrombopoietin (TPO) alone produced a high proportion of CD61(+)CD41(+) cells but a low total cell count and high cell death, resulting in an inferior expansion. The addition of interleukin-1 beta (IL-1 beta), Flt-3 ligand (Flt-3L) and to a lesser extent IL-3 improved the expansion outcome. The treatment groups with three to five cytokines produced efficient expansions of CFU-MK up to 400-fold with the highest yield observed in the presence of TPO, IL-1 beta, IL-3, IL-6 and Flt-3L. CD34(+) cells were expanded by five to 22-fold. PDGF improved the expansion of all cell types with CD61(+)CD41(+) cells, CFU-MK and CD34(+) cells increased by 101%, 134% and 70%, respectively. On day 14, the CD61(+) population consisted of diploid (86.5%), tetraploid (11.8%) and polyploid (8N--32N; 1.69%) cells. Their levels were not affected by PDGF. TPO, IL-1 beta, IL-3, IL-6, Flt-3L and PDGF represented an effective cytokine combination for expanding MK progenitors while maintaining a moderate increase of CD34(+) cells. This study showed, for the first time, that PDGF enhanced the ex vivo expansion of the MK lineage, without promoting their in vitro maturation. PDGF might be a suitable growth factor to improve the ex vivo expansion of MK progenitors for clinical applications.