Long-term repopulation of irradiated mice with limiting numbers of purified hematopoietic stem cells: in vivo expansion of stem cell phenotype but not function

Hematopoietic stem cells were isolated from normal adult mouse bone marrow based on surface antigen expression (Thy-l.l'""Lin"~Ly-6A/E+) and further selectedfor low reten-tion of rhodamine 123. This population of cells (Rh-123'"") could mediate radioprotection and long-term (greater than 12 months) repopulation after transplantation of as few as 25 cells. Transfer of five genetically marked Rh-123" " cells in the presence of IO5 normal bone marrow cells resulted in reconstitution of peripheral blood by greater than 10 % donor cells in 64 % (30 of 47) of recipient mice. Of 46 animals surviv-ing after 24 weeks, 10 had over 50 % donor-derived cells in peripheral blood. Two general patterns of long-term recon-stitution were observed: one in which many donor-derived cells were observed 5 t o 6 weeks after reconstitution and another in which donor-derived cells were rare initially bu