Clonal analysis and hierarchy of human bone marrow mesenchymal stem and progenitor cells.

OBJECTIVE: This study was performed to assess adult human bone marrow mesenchymal stem/progenitor cells at a single-cell level and to determine a hierarchy based on proliferative potential.
MATERIALS AND METHODS: Adult bone marrow mesenchymal cells expressing the enhanced green fluorescent protein (EGFP) were sorted as single cells into 24-well plates, each well confirmed with single EGFP-positive cells by fluorescence microscopy, and counted every 3 days. Colonies derived from single cells were expanded then sorted and evaluated using established differentiation protocols for adipogenic, chondrogenic, and osteogenic lineages. Cells were further analyzed by real-time reverse transcription polymerase chain reaction (RT-PCR) (peroxisome proliferator-activated receptor[PPAR]-gamma2, LEP, LPL, LUM, COMP, BIG, RUNX2, IBSP, BGLAP) and immunocytochemistry (PPAR-gamma1/2, collagen II, bone sialoprotein II) specific for trilineage differentiation.
RESULTS: Bone marrow mesenchymal cells were found to contain high proliferative potential (HPP) mesenchymal colony-forming cells (MCFC) (7%), low proliferative potential (LPP) MCFC (29%), mesenchymal cell clusters (MCC, 26%), and mature mesenchymal cells (MMC, 38%). All LPP-MCFC, MCC, and MMC colonies reached senescence at the end of the evaluation period. However, HPP-MCFC continued to grow, showed differentiation toward all three lineages, and demonstrated the capacity to give rise to secondary HPP-MCFC upon replating at a clonal level.
CONCLUSION: These findings suggest that there is a low frequency of bone marrow-derived HPP-MCFC that can both self-renew at a single-cell level and differentiate toward multiple lineages of mesenchymal origin.