Abstract
A previous study demonstrated that treatment with a combination of recombinant human thrombopoietin (TPO) + interleukin-3 (IL-3) + stem cell factor (SCF) just slightly protected megakaryocytic progenitor cells (CD34+ colony-forming unit-megakaryocyte, [CFU-Meg]) from carbon-ion beams. In addition, the combination of TPO + IL-3 effectively stimulated the differentiation of the CD34+ CFU-Meg to megakaryocytes and platelets. However, each combination alone was insufficient to allow the CD34+ CFU-Meg to recover from heavy ion beam-induced damages. The effects of 2-step culture using the combinations of TPO + IL-3 + SCF and TPO + IL-3 on carbon-ion beam-irradiated CD34+ CFU-Meg isolated from the human placental/umbilical cord blood were evaluated to determine a more effective culture system for heavy ion beam-irradiated hematopoietic stem/progenitor cells. The CD34+ cells were exposed to carbon-ion beams (LET = 50 KeV/μm) at 2 Gy and then were cultured in IMDM-based medium supplemented with a combination of TPO + IL-3 + SCF for one day or 7 days. The medium was changed to a medium including the combination of TPO + IL-3 and these cultures were continued until analyses. The megakaryocytes and platelets numbers were assessed using a flow cytometer at 14 or 21 days after irradiation. However, the efficacy of each 2-step culture was equal to that of a 1-step culture using TPO + IL-3 + SCF combination alone and the 2-step culture could not protect hematopoietic stem/progenitor cells from high LET-radiation like carbon-ion beams. Therefore, additional cytokines and/or hematopoietic promoting compounds might be required to overcome damage to hematopoietic cells by heavy ion beams.
