In vitro development of hematopoietic system from mouse embryonic stem cells: a new approach for embryonic hematopoiesis.

We developed an efficient differentiation induction system (OP9 system) from mouse embryonic stem (ES) cell to blood cells by coculture on a novel stromal cell line, OP9. This stromal cell line does not produce functional macrophage colony-stimulating factor (M-CSF) and presumably the deficiency of M-CSF production of OP9 cells might induce preferential differentiation of ES cells into hematopoietic cells other than the monocyte-macrophage lineage. ES cells gave rise to embryonic primitive erythrocytes, and then adult type definitive erythrocytes, myeloid and B lineage cells. The OP9 system should facilitate to elucidate the molecular mechanisms of hematopoietic system development and hematopoietic cell differentiation.