Decline in colony‐forming ability of marrow cells subjected to serial transplantation into irradiated mice

It is concluded that colony-forming cells derived from normal marrow are not capable of indefinite proliferation when they are subjected to the pressure of repeated transplantation. Cells with colony-forming ability found within spleen colonies cannot be considered to be exact replications of their original colony-forming ancestors since they have reduced capacity for selfrenewal. This view is supported by the results of preliminary experiments designed to compare the radiation sensitivities of colony-forming cells before and after transplantation. It was found that the radiation sensitivity of colony-forming ability increases in cells subjected to serial transplantation, which again suggests that the self-renewal process does not necessarily result in an exact replication of the original colony-forming cells.