Separation of CFU-S from primitive cells responsible for reconstitution of the bone marrow hemopoietic stem cell compartment following irradiation: evidence for a pre-CFU-S cell.

We have studied the in vivo spleen colony-forming ability and marrow repopulating ability of murine bone marrow cells differing in mitochondrial activity. Following centrifugal elutriation the cells were sorted on the basis of rhodamine-123 fluorescence intensity within a predetermined light scatter window. It is shown that a class of hemopoietic stem cells exists that differs from the majority of day-12 spleen colony-forming units (CFU-S) in that it has low mitochondrial activity and a high capacity to generate in time new day-12 CFU-S and cells that rescue recipients from radiation-inflicted death. These data add direct evidence for the identity of pre-CFU-S and CFU-S by physical separation.