Background and objective: Thrombopoietin (TPO), the ligand for the c-mpl receptor, regulates in vivo platelet production and increases the number of colony-forming unit megakaryocytes (CFU-MK). Other cytokines including interleukin (IL) -3, IL-6, IL-11 and stem cell factor (SCF) can stimulate megakaryopoiesis. The aim of this study was to evaluate the effects of different combinations of cytokines involved in megakaryocytopoiesis on stroma-free liquid cultures of purified human CD34+ cells.
Design and methods: Peripheral blood cells were collected after mobilization with granulocyte colony-stimulating factor (G-CSF). Purified CD34+ cells were then cultured with different combinations of TPO, SCF, IL-3, IL-6 and IL-11.
Results: The addition of TPO and SCF alone generated a population positive for the antigens CD41 (5.5+/-2.9%) and CD61 (6. 1+/-2.2%) but induced a low amplification of cell number (8.1+/-0.9 fold expansion). The presence of IL-6 or IL-11 was associated with MK progenitor cell expansion, and up to 7-10% of cultured cells were found to be CD41 and CD61 positive by flow cytometry. Conversely, the addition of IL-3 to this cytokine combination was associated with a prominent expansion of the myeloid lineage (70+/-10% of CD33+ cells) but only 0.9% and 2% of cultured cells were positive for CD61 and CD41 respectively.
Interpretation and conclusions: Our study supports the idea that IL-6 and IL-11 play crucial roles in the proliferation of MK progenitors and the use of SCF, TPO, IL-6 and IL-11 for ex vivo expansion of this cell population.