Marrow transfusions increase pluripotential stem cells in normal hosts

In earlier investigations of marrow transfusions into isogeneic, nonirradiated mice, the percentage of donor cells in the recipients' marrow and peripheral blood was found to vary between 16% and 40% following transfusion of 200 million marrow cells. The present experiments demonstrated that the hosts' pluripotential stem cells were elevated to an average of 132% of simultaneously assayed nontransfused controls. The elevation persisted for two months and then returned to normal. The similar magnitude of elevation of pluripotential stem cells and of the percentage of donor cells in the recipients indicates that the seeded stem cells did not replace the hosts' own, but were added to the existing complement of pluripotential cells. Implications for the regulation of stem cell numbers are discussed.