Several approaches for controlling hematopoietic stem and progenitor cell expansion, lineage commitment, and maturation have been investigated for improving clinical interventions. We report here that amino acid substitutions in a thrombopoietin receptor (Mpl)- containing cell growth switch (CGS) extending receptor stability improve the expansion capacity of human cord blood CD34+ cells in the absence of exogenous cytokines. Activation of this CGS with a chemical inducer of dimerization (CID) expands total cells 99-fold, eryth-rocytes 70-fold, megakaryocytes 0.5-fold, and CD34+ stem/progenitor cells 4.4-fold by 21 days of culture. Analysis of cells in these expanded populations identified a CID-dependent bipotent erythrocyte-megakaryocyte precursor (PEM) population, and a CID-independent macrophage population. The CD235a+/CD41a+ PEM population constitutes up to 13% of the expansion cultures, can differentiate into erythrocytes or megakaryocytes, exhibits very little expansion capacity, and exists at very low levels in unexpanded cord blood. The CD206+ macrophage population constitutes up to 15% of the expansion cultures, exhibits highexpansion capacity, and is physically associated with differentiating erythroblasts. Taken together, these studies describe a fundamental enhancement of the CGS expansion platform, identify a novel precursor population in the erythroid/megakaryocytic differentiation pathway of humans, and implicate an erythropoietin-independent, macrophage-associated pathway supporting terminal erythropoiesis in this expansion system.
CITATION STYLE
Belay, E., Miller, C. P., Kortum, A. N., Torok-Storb, B., Blau, C. A., & Emery, D. W. (2015). A hyperactive Mpl-based cell growth switch drives macrophage-associated erythropoiesis through an erythroid-megakaryocytic precursor. Blood, 125(6), 1025–1033. https://doi.org/10.1182/blood-2014-02-555318
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