Ablation of proliferating marrow with 5-fluorouracil allows partial purification of mesenchymal stem cells

The ability to identify and maintain mesenchymal stem cells in vitro is a prerequisite for the ex vivo expansion of cells capable of effecting mesenchymal tissue regeneration. The aim of this investigation was to develop an assay to enrich and ultimately purify mesenchymal stem cells. To enrich the population of mesenchymal stem cell-like cells, rats or mice were administered 5-fluorouracil (5-FU) in vivo. Limiting dilution analysis demonstrated that 5-FU-treated bone marrow had the potential to form colony-forming units-fibroblastic (CFU-F) at a 10-fold or sixfold enrichment compared to normal bone marrow in rats or mice, respectively. In vivo and in vitro differentiation assays supported the enrichment and purification effects. In vitro, bone marrow cultures from 5-FU-treated bone marrow demonstrated lineage-specific gene expression in lineage-specific medium conditions in contrast to the multilineage gene expression of control bone marrow cultures. In vivo implantation of 5-FU-treated cells that were not expanded in culture generated ossicles containing an intact bone cortex and mature hematopoietic components, whereas non-5-FU-treated bone marrow only formed fibrous tissues. Our results demonstrate that enrichment of a quiescent cell population in the bone marrow by in vivo treatment of 5-FU spares those undifferentiated mesenchymal stem cells and influences the differentiation of bone marrow stromal cells in vitro and in vivo. This prospective identification of a population of mesenchymal cells from the marrow that maintain their multilineage potential should lead to more focused studies on the characterization of a true mesenchymal stem cell.