Making the in-vitro model closer to actual B lymphopoiesis in the bone marrow

After more than a decade since Whitlock and Witte established an in-vitro long-term culture of bone marrow B lineage cells, c-kit+IL-7-receptor(R)+B precursor cells in fresh bone marrow are now able to be grown under a fully defined culture condition containing only BSA, transferrin, IL-7 and the ligand for c-kit(Kit-ligand;KL) as protein components. On the other hand, previous studies indicated that the actual intramarrow B-cell-genesis is a complex process involving multiple stromal cell-derived molecules. Thus, the next step for the culture of B-cell genesis is to develop this simple culture into a new defined culture of B-cell-genesis that is closer to the actual process. In this article, we will describe how this defined culture condition has developed from the original Whitlock-Witte type culture, how the B precursors under this culture-condition are different from that in the bone marrow, and finally our biased view on the future direction to which this defined culture should develop.