DIRECT EVIDENCE FOR THE COMMITMENT OF HEMATOPOIETIC STEM-CELLS TO T-LINEAGE, B-LINEAGE AND MYELOID IN MURINE FETAL LIVER

We established an experimental system in vitro to examine the developm ental capacity of individual hematopoietic progenitors to generate T, B and myeloid (M) cells, By using this system we analyzed the process of lineage commitment of hematopoietic progenitors in murine fetal liv er (FL), It is known that small numbers of B and M cells, in addition to T cells, are generated in a co-culture of hematopoietic progenitors and a deoxyguanosine-treated fetal thymus (FT) lobe, We tried to enha nce the growth of B and M cells by the addition of IL-7, IL-3 and stem cell factor into the co-culture, This cytokine-supplemented FT organ culture was used to examine the developmental capacity of individual h ematopoietic progenitors in FL. Single cells of lineage marker (Lin)(- )c-kit(+)Sca(-)1(+) (Sca-(1+)) and Lin(-)c-kit(+)Sca-(1-) (Sca-(1-)) p opulations from the FL harvested at day 12 of gestation were cultured for 10 days, and the phenotypes of cells generated in each lobe were a nalyzed with a flow cytometer, All progenitors in the Sca-(1-) populat ion were shown to be committed to generate only T, B or NI cells, On t he other hand, multipotent progenitors, which are capable of generatin g T, B and M cells, as well as unipotent progenitors committed to the T, B or M lineage were found in the Sca-(1+) population, Bipotent prog enitors generating M and T cells and those generating M and B cells we re also found in the Sca-(1+) population, which probably represent pro genitors in the process of commitment, However, no bipotent progenitor s generating T and B cells were detected.