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The cell surface markers used for identification and purification of human HSCs by fluorescence-activated cell sorting (FACS) analysis incorporate a number of cluster of differentiation (CD) markers(see Table 3.1). The most primitive human HSC is identified as CD34þCD90þLin_ (Baum et al., 1992). Some other groups have identified human primitive HSC asCD34þCD38_/lo (Bhatia et al., 1997; Kondo etal., 2003). Absent expression of CD45RA has also been used in combination with the above markers for the identification of primitive HSCs, that is, 34þCD38_CD90þCD45RA_ (Majeti et al., 2007). Humanmultipotent progenitor cells are identified as Lin_CD34þCD38_CD90_
c-kitloflt3loCD133þCD45RA_ in FACS analysis. CLP and CMP cell phenotypes are 4þCD38þCD10þ and Lin_ CD34þCD38þ CD45RA_, respectively.The cellular constituents of BM include hematopoieticislands, adipocytic cells, stromal cells, and vascular tissue (endothelial cells and smooth muscle cells) (Travlos, 2006)
In humans, hematopoiesisoccurs in the shaft (diaphyseal) as well as the epiphyseal regions of the long appendicular bones and in the ribs. In older people, hematopoiesis is observed mainly in the vertebral bones.
The BM isa specialized soft and spongy tissue that fills the cavity of the cancellous bone. The cellular constituents of BM include hematopoietic islands, adipocytic cells, stromal cells, and vascular tissue(endothelial cells and smooth muscle cells)
The inner lining of the cavities in the marrow region, the endosteum, contains osteoblasts (OBs) and osteoclasts which actively remodel bone throughoutlife. Blood vessels in the marrow are sinusoidal in nature—that is, they have fenestrated endothelium that allows increased permeability to both proteins and cells. They traverse the center of trabecularspaces. Cellular constituents of the marrow are embedded in an ECM that contains collagen fibers, matrix proteins, glycoproteins, and proteoglycans. At the endosteal surface, bone-forming cells...