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  • Title: Recombinant human c-Mpl ligand (thrombopoietin) not only acts on megakaryocyte progenitors, but also on erythroid and multipotential progenitors in vitro.
    Author: Tanimukai S, Kimura T, Sakabe H, Ohmizono Y, Kato T, Miyazaki H, Yamagishi H, Sonoda Y.
    Journal: Exp Hematol; 1997 Sep; 25(10):1025-33. PubMed ID: 9293899.
    Abstract:
    To determine the hematopoietic actions of recombinant human c-Mpl ligand (thrombopoietin [TPO]), we studied its effects on the proliferation and differentiation of highly purified CD34+ blood progenitors in plasma-containing and serum-free culture. TPO alone promoted the growth of small megakaryocyte colonies (CFU-Meg) in numbers two to three times greater than those produced by interleukin (IL)-3. The combination of TPO and stem cell factor (SCF) exerted a significant synergistic effect on CFU-Meg formation. In the presence of TPO and IL-3 or granulocyte/macrophage-colony stimulating factor (GM-CSF), a significant number of mixed colonies (CFU-Mix) were observed. The combination of TPO and Epo did not increase the number of CFU-Meg, but did support erythroid-burst (BFU-E) and CFU-Mix colony formation. Interestingly, the combination of TPO with cytokines known to have burst-promoting activity (BPA), including IL-3, GM-CSF, IL-9, and SCF, increased the number of BFU-E and CFU-Mix in the presence of Epo. The BPA of TPO was further investigated by delayed addition of Epo on day 6 after incubation with TPO from day 0. None of the BFU-E or CFU-Mix survived, indicating that TPO acted as a costimulant exclusively for Epo. Moreover, a neutralizing anti-human Mpl receptor polyclonal antibody completely abrogated the BPA of TPO, demonstrating that this effect was mediated through the Mpl receptor. Finally, experiments in single-cell clone sorting and serum-free culture clearly demonstrated that a combination of TPO and Epo directly supported BFU-E and CFU-Mix. These results suggest that TPO acts not only in megakaryocytopoiesis but also in the early stage of hematopoiesis.
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