Stem Cell Niche as a Parameter and Prognostic Factor in Leukemia.

Accumulating studies point the importance of bone marrow microenvironment regulating the behavior and cell fate decisions of normal and malignant hematopoietic cells. The microenvironmental regulation of normal hematopoietic stem cells (HSCs) mostly occurs in a specialized architecture of bone marrows (BM), referred to as the stem cell niche, where the majority of HSCs reside and regulated by niche cells. Studies have shown that two types of niche exist in the bone marrow, an endosteal osteoblastic and a vascular/peri-sinusoidal niche. These two niches, while geographically distinct, share common cellular composition mostly comprised of mesenchymal stromal cells with participation of sinus endothelial cells and other cellular components. The niche cells are engaged in cross-talk with normal HSCs primarily through CXCL-12/CXCR-4, Jagged-1/Notch and other signaling pathways (reviewed by Oh and Kwon, Stem Cells 2010, 28(7) 1243-9, doi: 10.1002/stem.453). HSCs are regulated for self-renewal, quiescence, survival and differentiation in the context of these microenvironmental regulation.