Studies on the self-renewal ability of CFU-S which have been serially transferred in long-term culture or in vivo.

The progressive decline in the repopulating ability of bone marrow serially-transferred through a succession of recipients is well documented. A similar series of transfers onto successive long-term culture adherent layers has been carried out using as 'donor' cells both adherent layer cells and cells from the culture supernatant. For as long as the in vitro serial transfer regime can be maintained the decline in self-renewal ability ('quality') of the CFU-S parallels the similar decline observed in vivo and occurs irrespective of the quality of CFU-S transferred. In both the in vivo and in vitro transfer regimes there is little or no loss of quality of CFU-S as a result of one 'transfer' although there may be a reduction in the total numbers of CFU-S in the mouse. However, a second and third transfer in vivo or in vitro leads to a rapid decline in the quality (self-renewal ability) of the CFU-S. Furthermore, despite the fact that the cells are transferred in vitro to a new adherent layer there is no recovery of the quality lost in the second transfer of the CFU-S. This fact implies that self-renewal potential of the CFU-S is a property intrinsic to the cell. The data presented here appear to exclude mitotic history and proliferative stress as factors determining the loss of self-renewal in CFU-S. They also fail to implicate stromal involvement in the decline. It may be that the dilution of an accessory cell or simply the disaggregation of the marrow may be major factors. The work presented indicates that the loss of self-renewal and repopulating ability of haemopoietic stem cells as a result of marrow transplantation may be studied using the long-term marrow culture and yield results relevant to in vivo marrow transplantation.