Abstract: Objective To elucidate the effect of thrombopoietin (TPO) in vitro expansion of c-kit+Lin- cells from bone marrow . Methods c-kit+Lin- cells were isolated by using a high-gradient magnetic cell sorting system (MACS) , and expanded with combinations of stem cell factor(SCF), FLt-3 ligand (FL) ,leukemia inhibitor factor（LIF）and different concentration of thrombopoietin (TPO) for 7days in a liquid culture system. Totall cells and Annexin-V positive cells were studied by fluorescence-activated cell sorter ( FACS) . Results Each group could expand c-kit+Lin- cells effectively and rapidly,and the numbers of cells expanded were 4～7 times compared with the beginning's number. Added 50μg/L TPO into SCF+FL+LIF increased expasions of c-kit+Lin- and total cells by 7.07 and 40.19 times,which was more than the group that had no TPO。But when the concentration of TPO increased,the c-kit+Lin- cells decreased,and the apoptosis rate rised. Conclusion It showed TPO synergistic actions with SCF+FL+LIF to expand c-kit+Lin- cells but too much TPO could induce it differentiation and apoptosis．50μg/L TPO was the best concentration to expand c-kit+Lin- cells.

Key words: Thrombopoietin, c-kit+Lin-cells in bone marrow, hepatic stem cell, expand