Transfusion of circulating stem cells

Bone marrow collected from all species including man contains specific cells, putative pluripotential stem cells, capable of reestablishing hemopoiesis in a syngeneic or genetically identical member of the same species which has been treated with whole body irradiation. The question of whether similar pluripotential stem cells are present in the circulation in all animals is not yet resolved. In mice, reconstitution of hemopoiesis can be achieved by transfusion of peripheral blood cells only. The same result can be obtained in dogs and probably in baboons. In dogs, experiments with fresh and cryopreserved blood mononuclear cells have confirmed a dose-response relationship--below a certain number of mononuclear cells failure of hemopoietic reconstitution can be predicted. In man, isolated anecdotal case reports suggest that pluripotential stem cells in the circulation may or may not be valuable in repopulating a bone marrow defective as a result of primary disease or following chemotherapy. Indirect evidence from in vitro culture of circulating myeloid progenitor cells suggests but does not prove that pluripotential stem cells circulate in normal man. Pluripotential stem cell numbers are probably greatly increased in the circulation in patients with chronic granulocytic leukemia: such cells can be collected, cryopreserved, and used at a later date as "bone marrow autografts". Whether circulating stem cells can be collected and used in an analogous manner for patients with other leukemias or other neoplasms is not yet established.