The STRO-1+ Marrow Cell Population Is Multipotential

Human marrow-derived STRO-1+ cells were tested for their ability to differentiate into multiple mesenchymal phenotypes. STRO-1+ cells were isolated from long-term cultures of human marrow cells by magnetic immunobeads linked to the antibody STRO-1. Stromal layers generated from STRO-1+ cells, when cocultured without exogenous cytokines for several weeks with CD34+/CD38+ and CD34+/CD38low cells, were able to induce a 10- to 20-fold increase in colony-forming units, and to sustain cobblestone area colony-forming cells with a distinct time course for the different hematopoietic precursors. A myofibroblastic and adipocytic phenotype was observed in hematopoiesis-supportive stromal cells, as shown by electron microscopy and staining of lipids with Nile red. The adipocytic potential of STRO-1+ cells was further demonstrated by flow cytometry of Nile red O-stained cells cultured in adipocyte-induced medium. The same population of STRO-1+ cells cultured in osteoblast-inducing medium was shown to have osteogenic potential, as demonstrated in vitro by the formation of mineral (von Kossa staining), and in vivo by the formation of bone tissue within porous calcium phosphate ceramics implanted into athymic mice. This population of STRO-1+ cells was also shown to have chondrogenic potential in aggregate cultures which displayed a morphologic appearance of cartilage and stained positively with antibodies specific to type II and type X collagens. These results show that the subset of marrow cells that express the STRO-1 antigen is capable of differentiating into multiple mesenchymal lineages including hematopoiesis-supportive stromal cells with a vascular smooth muscle-like phenotype, adipocytes, osteoblasts and chondrocytes.