Hematopoietic stem cell (HSC) self renewal and lineage commitment depend on complex interactions with the microenvironment. The ability to maintain or expand HSCs for clinical applications or basic research has been substantially limited because these interactions are not well defined. Recent evidence suggests that HSCs reside in a low-perfusion, reduced-nutrient niche and that nutrient-sensing pathways contribute to HSC homeostasis. Here we report that suppression of the mTOR pathway, an established nutrient sensor, combined with activation of canonical Wnt–β-catenin signaling, allows for the ex vivo maintenance of human and mouse long-term HSCs under cytokine-free conditions. We also show that the combination of two clinically approved medications that together activate Wnt–β-catenin and inhibit mTOR signaling increases the number (but not the proportion) of long-term HSCs in vivo.
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We thank W. Tong, N. Speck, A. Bhandoola, A. Chi and H.-C. Huang for insightful comments and discussion. We also thank A. Bhandoola (University of Pennsylvania) for providing OP9 and OP9-DL1 cells. We thank J. Garskof, A. Christian and A. Mezochow for technical help and all members of the Klein lab for help and discussions. We specially thank A. Secreto and C. Keefer of the Stem Cell and Xenograft Core and Flow Cytometry and Cell Sorting Facility at the University of Pennsylvania for technical support. This study was supported by a grant from the Institute for Translational Medicine and Therapeutics (ITMAT) at the University of Pennsylvania and by grants from the US National Institutes of Health to P.S.K. (1R21HL107968-01 and 1R01HL110806-01). J.H. was supported by a Leukemia and Lymphoma Society Career Development Award and a K99 award from the US National Institutes of Health (1K99HL10774701). E.O.H. was supported by a grant from the US National Institutes of Health (1-K23-HL-093366-01A1). We also appreciate support from the Human Hematopoietic Stem Cell Center of Excellence (5P30DK090969-02) at the Children's Hospital of Philadelphia and the University of Pennsylvania.
The authors declare no competing financial interests.
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Huang, J., Nguyen-McCarty, M., Hexner, E. et al. Maintenance of hematopoietic stem cells through regulation of Wnt and mTOR pathways. Nat Med 18, 1778–1785 (2012). https://doi.org/10.1038/nm.2984
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