Molecular interactions in stem cell homing and bone marrow transplantation therapy

The blood-forming or “hematopoietic” stem cells (HSCs) can develop into any of the three types of blood cells: red cells, white cells or platelets. In case of cancer and similar conditions, high-dose chemotherapy or radiation therapy results in massive cell death of cycling hematopoietic cells in the bone marrow, spleen and blood. The transplantation of blood-forming stem cells is an accepted treatment to restore the body’s ability to make blood and immune cells. Once transplanted the hematopoietic stem cells is found to actively cross the blood / bone marrow endothelium barrier and occupy in the bone marrow compartment by activation of adhesion interactions prior to their proliferation. The migration of hematopoietic stem cells through the blood across the endothelial vasculature to different organs and to their bone marrow (BM) niches, requires active navigation, a process termed homing. HSC therapy relies on the ability of such cells to successfully home to, and persist in, the marrow niche following delivery into the bloodstream. The molecular and cellular cues that account for the unique specificity and efficiency of HSPC homing to their niches in the BM are being unraveled due to the extensive research carried out now. This review is focused to elaborate the different molecular mechanisms behind the specificity of the wandering hematopoietic cells towards their home-the bone marrow.