Characterization of a cycling murine pluripotent stem cell population

In the present report we describe the properties of pluripotent stem cells isolated with elutriation and Percoll density gradient centrifugation techniques from spleens of recovering thiamphenicol pretreated anemic mice. Cells with a diameter between 7.2 and 8.4 microns and sedimenting at a density of 1.065 g/ml had a high capacity to repopulate lethally irradiated mice with all the hemopoietic precursor cells. The spleen colonies formed on day 8 and day 12 after inoculation in irradiated recipients showed no morphological differences in mixed and lineage-specific composition. Day 12 colonies were much larger than day 8 colonies. Pluripotent stem cells isolated from regenerating spleens were very susceptible to 3'-thymidine; 65% of the cells were killed. Only 2% kill was found in stem cells present in vivo 4 days earlier in the bone marrow. The purified stem cells were probably all in cycle and possibly partly synchronized.