Background: Notch ligands enhance ex vivo expansion of hematopoietic stem cells (HSCs). But to use Notch ligands in HSC therapies of human diseases, efforts are required to improve ex vivo expansion efficiency and in vivo transplant engraftment.
Design and methods: We designed and produced an endothelium-targeted soluble Notch ligand, the DSL domain of Delta-like 1 fused with a RGD motif (D1R), and examined the effects of this protein on HSCs ex vivo and in vivo.
Results: D1R efficiently promoted ex vivo expansion of both mouse bone marrow (BM) and human umbilical cord blood HSCs. HSCs expanded with D1R up-regulated many of the stemness-related genes, and showed high BM engraftment efficacy with long-term repopulation capacity after transplantation. Moreover, in vivo administration of D1R increased the number of BM HSCs in mice, and facilitated BM recovery of mice after irradiation. Injection of D1R significantly improved HSC engraftment and myeloid recovery after BM transplantation in irradiated mice. D1R enhanced HSC engraftment not only in BM, but also in the liver and spleen after BM transplantation in mice. D1R induced the formation of compact cell clusters containing the transplanted HSCs in close contact with endothelial cells, reminiscent of HSC niches, in the liver and spleen.
Conclusions: D1R might be applied in improving both HSC expansion ex vivo and HSC engraftment in vivo in transplantation.
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