Clonal composition of human multipotent mesenchymal stromal cells.

Multipotent mesenchymal stromal cells (MMSCs) are a heterogeneous population consisting of cells with a distinct proliferative potential. The aim of this study was to define clonal composition in MMSCs and trace the dynamics of individual clones in MMSC subpopulations with different proliferative potentials during the process of cultivation. The investigation was performed at single-cell level using genetically marked cells. Specifically, human bone marrow MMSCs were infected with a lentiviral vector-bearing marker gene. Integration site analysis was performed for clones at each passage by ligation-mediated polymerase chain reaction and Southern blot hybridization. Sibling connections between clones and clonal composition of MMSC culture at each passage were revealed. The MMSC population contained multiple, different, mainly small, clones. It was found that large long-living clones with a high, but limited proliferative potential could be detected rarely in MMSCs population. These data suggest that the human MMSC population does not fit the "stem cell" criteria, however, MMSCs may contain a subpopulation of large clones with a high proliferative potential.