Transplantation of chromosomally marked syngeneic marrow cells into mice not subjected to hematopoietic stem cell depletion.

The percentage of donor-host chimerism was determined 4-6 weeks or six months after injection of normal bone marrow cells into normal syngeneic or coisogeneic recipient mice. Donor-recipient pairs had chromosome markers that provided easy identification of metaphase cells. The percentage of donor cells in marrow or spleen ranged from 0 to 16% and this percentage was independent of the age of recipient or attempts to stimulate hematopoiesis in donor and/or host mice. In adult C57BL/6 mice there was a roughly linear dose-response relationship between cell dose and percentage of chimerism. There was no apparent dose-response relationship for AKR mice. The percentage of donor cells in the spleen was correlated to that seen in the marrow of recipients. Neonatal mice given the same intraperitoneal marrow cell dose as weanlings, but a larger number of cells relative to their own marrow mass, did not show a larger percentage of chimerism than weanlings. Similarly, weanlings given the same intravenous dose as adults showed no greater degree of chimerism than adults. Temporary anemia, induced by bleeding donors prior to cell collection, or more chronic hemopoietic stimulus (produced by injecting recipients with phenylhydrazine prior to cell injection with subsequent bleeding at intervals) did not result in an increased percentage of chimerism. These results indicate that there are "empty" sites in bone marrow of normal mice in which injected hematopoietic stem cells can lodge and grow.