In the endosteal region, osteoblasts and other mesenchymal-derived stromal cells such as reticular cells, fibroblasts, and adipocytes constitute the osteoblastic niche that supports the maintenance of hematopoietic stem cells in a quiescent and undifferentiated state, by adhesion and humoral factors [32].We propose that the expression of MMP-2 is inhibited by bone marrow stromal cells, in a proces