Regulation of bone marrow HSC numbers by soluble KITL. Specific conditional knockout (KO) of mKITL from endothelial cells (ECs) or the combined deletion in ECs and LEPR⁺ perivascular stromal cells results in a modest reduction in systemic sKITL levels with no significant impact on bone marrow HSCs. In contrast, the deletion of both sKITL and mKITL leads to severe hematopoietic defects. The figure was partly generated using Servier Medical Art, provided by Servier, licensed under a Creative Commons Attribution 3.0 unported license.