The in vitro effects of cytokines on expansion and migration of megakaryocyte progenitors

Increasing the number of megakaryocyte progenitors in stem cell transplants by ex vivo expansion culture may be an approach to accelerate platelet rec overy in patients undergoing high-dose chemotherapy. We evaluated the effec t of three different cytokine combinations on expansion, with special empha sis on the type of colony formation and migration of megakaryocytic cells. The number of clonogenic megakaryocyte progenitors (colony-forming units-me gakaryocyte; CFU-Mk) with high- (> 20 cells/colony) and low-proliferative c apacity (5-20 cells/colony) and the number of megakaryocytic (CD61(+)) cell s were significantly increased by including interleukin 3 (IL-3) or IL-3 IL-6 + IL-11 + Flt3-ligand to cultures containing megakaryocyte growth and development factor (MGDF) plus stem cell factor (SCF). No difference in the maturation of megakaryocytes from all three cytokine combinations to plate lets were observed, as demonstrated by electron microscopy. In chemotaxis e xperiments, the migration towards stromal cell-derived factor 1 (SDF-1) was shown to be reduced for CD61(+) cells and megakaryocyte progenitors cultur ed in other cytokines besides MGDF + SCF. The reduced migration was related to a lower expression of CXCR4, the receptor for SDF-1, on megakaryocytes from the proliferating cultures. These in vitro results demonstrate that ex pansion in IL-3 and other cytokines besides MGDF + SCF significantly impair the capacity of megakaryocytic cells to migrate.