Thrombopoietin activates the growth of megakaryoblasts in patients with chronic myeloproliferative disorders and myelodysplastic syndrome.

The effects of thrombopoietin (TPO) on cell proliferation and differentiation, and the relation between these effects and the expression of c-mpl on leukemia cells were studied in seven acute myelogeneous leukemia cell lines and seven myelogeneous blast cell preparations from patients with chronic myeloproliferative disorders (CMPDs) and myelodysplastic syndrome (MDS). Among the leukemia cells, five preparations of megakaryoblastic leukemia cells from patients and one megakaryoblastic cell line, CMK 11.5, proliferated in response to TPO in vitro. CMK 11.5 and the blastic cells from one patient diagnosed with MDS with myelofibrosis differentiated with increasing expression of CD41a in response to TPO. However, TPO had no effect on the cells lacking megakaryocytic characteristics. Some patients with CMPD and MDS develop acute transformation with blasts demonstrating megakaryocytic features, and some of these cells show growth in response to TPO. Therefore, in vivo administration of TPO should be considered carefully for patients with CMPD or MDS, since TPO may induce leukemic cell proliferation.