Influence of a marrow stromal factor on survival of hemopoietic stem cells in vitro

When mouse bone marrow or spleen cells were incubated for 24 hours in medium conditioned by marrow adherent cells, the survival of pluripotent hemopoietic stem cells (CFUs) was considerably greater than that of stem cells incubated in fresh or spleen-conditioned medium. Medium conditioned by endosteal cells also increased marrow CFUs survival. Survival of CFUs more than 24 hours was greater when fresh marrow was incubated directly with marrow adherent cells than with medium conditioned by these cells. Although marrow-conditioned medium greatly increased CFUs susceptibility to 3H-thymidine suicide, DNA synthesis inhibitors did not prevent the increased survival of CUFs in marrow-conditioned medium. These results indicate that marrow stromal cells produce a factor that increases CFUs survival in vitro independently of proliferation.