A slowly proliferating subpopulation in human umbilical cord mesenchymal stem cells in culture.

In this report, a slow-growing subpopulation of human umbilical cord mesenchymal stromal cells (MSCs) was identified. These cells were around 5 μm in diameter and their relative gravity was between 1.031 and 1.043 g/ml. In sharp contrast to the parent MSCs, they expressed highly CD271 and poorly the receptor for platelet-derived growth factor. Quantitative PCR with the identification of the products by DNA sequencing proved that these cells expressed Nanog at a higher level than cells from the other subpopulation (approximately 30-fold), which was further confirmed by western blotting. Furthermore, they did not grow at clonal density and depletion of these cells from the population had little effect on the colony formation of the parent MSCs. The results here indicate that a subpopulation of cells with special biological features exist in human cord MSCs in culture.