Replication of pluripotent stem cells in granulocyte/macrophage colonies developed in methylcellulose culture of mouse bone marrow cells.

The existence of pluripotent hemopoietic stem cells in granulocyte/macrophage colonies was demonstrated in a culture of mouse bone marrow cells in semi-solid methylcellulose with spleen conditioned medium as colony-stimulating activity. When fresh growth medium containing the conditioned medium was supplemented to 1-week culture, the number of cells per colony increased significantly in the next week. The number of pluripotent stem cells also increased by a factor of 12 or more in the second week of the culture. The number of cell divisions in such a culture was calculated as 12-15 in 2 weeks. These results indicate that some of the granulocyte/macrophage colonies are derived from pluripotent stem cells, and that the stem cells can undergo 3-5 self-replications in such semi-solid culture.