“…Definite hematopoiesis then ensues in the aorta-gonad-mesonephros (AGM), placenta, fetal liver, spleen, and finally in the bone marrow, the primary site of hematopoiesis for adults [9, 16]. During adult hematopoiesis, HSCs are found primarily in the bone marrow HSC niches, where various cellular components (e.g., osteolineage cells, vascular endothelial cells, neurons, macrophages), extracellular proteins (e.g., fibronectin, laminin, collagen, proteoglycans), and secreted or immobilized biomolecules and growth factors (e.g., SCF, TPO, Ang-1, Flt3L, CXCL-12, G-CSF, IL-3, IL-6, IL-11) comprise the functional microenvironments with local gradients in cellular and extracellular content [2, 19, 14, 24–28]. Several discrete anatomical localizations within the marrow have been described for HSC niches (e.g., endosteal, perivascular and, more specifically, sinusoidal and arteriolar niches) [19, 24, 27, 29, 30].…”