Homing efficiency and hematopoietic reconstitution of bone marrow-derived stroma cells expanded by recombinant human macrophage-colony stimulating factor in vitro

The increasing recognition of the properties of marrow stromal cells has spawned a major switch in our perception of their nature and the potential therapeutic applications that have been envisioned and implemented. Yet, several aspects of bone marrow stromal cell biology remain in question. This report describes the ability of recombinant human macrophage colony-stimulating factor (rhM-CSF) to maintain proliferation and differentiation of bone marrow stromal cells ex vivo. Our results demonstrated that M-CSF was essential for proliferation and differentiation of bone marrow-derived stromal cells and exerted its effects in a dose-dependent manner. The number of colony-forming unit (CFU) fibroblasts increased by 25% after incubation with rhM-CSF. In vitro expanded bone marrow stromal cells were easy to passage and differentiated to adipocyte and chondroblast cells under appropriate culture conditions. Furthermore, these expanded stromal cells to support CD34+ hematopoietic stem cells, as demonstrated by their ability to form CFU-Mix, burst-forming units-erythroid, and CFU-granulocyte macrophage colonies after 3 weeks of culture. The homing efficiency of in vitro expanded or fresh isolated bone marrow-derived stromal cells, which were labeled with carboxy fluorescein diacetate succinimidyl ester, to bone marrow was also investigated. Homing assays demonstrated that freshly isolated CD45+-depleted bone marrow cells were able to home to bone marrow in a dose-dependent manner, although some cells were found in the spleen, liver, and lung. However, their ability to home was dramatically reduced with culture time and was completely lost after five to seven passages in vitro. Animal studies showed that freshly isolated or rhM-CSF-induced bone marrow stromal cells promoted hematopoietic reconstitution in lethally irradiated mice. The ability to easily expand human stromal cells, which support survival and proliferation of CD34+ cells, has many important clinical applications for hematopoietic disorders.