Animal survival and chimerism of animals after bone marrow transplantation (BMT). Male mice were used as bone marrow donors. Female recipient mice were letally irradiated, and 3 million nucleated cells were injected intravenously. The mice were killed 2 months after the graft, and the cells from one leg were injected into a new irradiated female mouse. This process was repeated 7 times. (A) Cumulative survival after serial BMT. Each group included 10 mice. The donor marrow from one leg of the previous transplant was individually injected into a new recipient. There was no mortality during the first 3 transplantations. Results of the fourth to seventh transplantations are shown here. (B) Numbers of nucleated cells per leg. At each transplantation, one leg was harvested from each mouse and cells were enumerated; results shown are the means ± SD for the 2 groups after the fourth to the sixth transplantation. (C) Numbers of colony-forming cells (CFCs) per leg at the fourth to the sixth transplantation. (D) Percentage of donor cells observed in recipient mice after each transplantation. At each transplantation, bone marrow cells from recipient mice were cultured in methylcellulose. Twenty colonies per mouse were picked, and monitored by Y and neo PCR.