Figure 2: Infused HSCs must home to their bone marrow niches before they can begin the process of hematopoiesis. After infusion of HSCs into the peripheral blood, shown as purple circles, HSCs begin the process of homing to the marrow. E- and P-selectins and VCAM1 on the vessel walls tether circulating HSCs and allow for rolling on the vessel wall to occur. This is followed by extravasation of the HSCs through the extracelluar matrix into the bone marrow. The release of SDF-1 from osteoblasts and epithelial tissues in the bone marrow binding to the HSCs CXCR4 receptors is important. After reaching the bone marrow, HSCs then migrate to the perivascular regions and begin the process of hematopoiesis.