The study investigates the cellular sources of factors that maintain hematopoietic stem cells (HSCs) in the bone marrow. Using Scfflp knock-in mice, the authors found that Stem Cell Factor (SCF) is primarily expressed by perivascular cells, particularly endothelial cells and Leptin receptor (Lepr)-expressing perivascular stromal cells. Deletion of SCF from these cells significantly depleted HSCs in the bone marrow, suggesting that these cells are crucial for HSC maintenance. The findings indicate that HSCs reside in a perivascular niche, where multiple cell types, including endothelial and perivascular stromal cells, contribute to HSC maintenance through the production of SCF.The study investigates the cellular sources of factors that maintain hematopoietic stem cells (HSCs) in the bone marrow. Using Scfflp knock-in mice, the authors found that Stem Cell Factor (SCF) is primarily expressed by perivascular cells, particularly endothelial cells and Leptin receptor (Lepr)-expressing perivascular stromal cells. Deletion of SCF from these cells significantly depleted HSCs in the bone marrow, suggesting that these cells are crucial for HSC maintenance. The findings indicate that HSCs reside in a perivascular niche, where multiple cell types, including endothelial and perivascular stromal cells, contribute to HSC maintenance through the production of SCF.