Embryonic stem cells release potentially novel hematopoietic factors

We have observed that a severe decrease in the number of erythroid progenit or cells follows the long-term culture (LTC) of human primitive stem cells on an established mouse fibroblast feeder layer. This suggests that one, or several, factors necessary to support erythroid differentiation might be m issing in these culture conditions. To improve the erythroid differentiatio n and stem cell output of LTCs, we have examined the hypothesis that the fa ctors that regulate pluripotent stem cell proliferation and erythroid commi tment can be found in media conditioned by embryonic stem (ES) cells. We ha ve found that media conditioned by undifferentiated and differentiating ES cells can affect differentiation patterns in both short-term culture and LT C assays. Medium conditioned by undifferentiated ES cells increases the num bers of estimated LTC-initiating cells (est.LTC-IC) and potentiates granulo cytic differentiation. In contrast, medium conditioned by ES cells undergoi ng differentiation increases the number of est.LTC-IC and is a powerful pro moter of erythroid differentiation. In the presence of rh is medium, the nu mber of erythroid progenitors generated after 5 weeks of LTC was increased up to 100-fold as compared with controls, and the number of est.LTC-IC was amplified up to 140-fold. These results offer a new approach for the identi fication of factors implicated in stem cell proliferation, self-renewal and commitment. In addition, the improved LTC conditions for the expansion of stem cells without reduction of their in vitro differentiation potential sh ould be useful for a wide range of applications. copyright (C) 2000 S. Karg er AG. Basel.