Behavior of bone marrow-derived cells following in vivo transplantation: differentiation into stromal cells with roles in organ maintenance.

After injection of green fluorescent protein-positive (GFP(+)) bone marrow (BM) cells into lethally irradiated wild-type mice, the organs of the recipient mice [BM transplantation (BMT) mice] were regenerated; however, irradiation of the cecum or spleen (only) blocked their regeneration with loss of injected BM cells. These results suggest that the donor cells first enter the BM and then migrate to the peripheral organs. The maintenance of epithelial structure and function is controlled by interactions between stromal cells and the epithelia; the organ is stable only if the stroma is functioning normally. In BMT mice, intestinal GFP(+) stromal cells were regenerated fairly rapidly although GFP(+) cells were observed only rarely in the intestinal epithelium even if it passes several weeks or months post BMT, indicating that BM-derived stromal cells play a pivotal role in epithelial renewal and are crucial for maintaining organ structure and function. BM-derived cells in the periphery possess a special key to return to the BM and then to migrate to various organs to become resident cells.