Fetal liver transplantation in the dog. II. Repopulation of the granulocyte-macrophage progenitor cell compartment by fetal liver cells from DLA-identical siblings.

The restoration of the granulocyte-macrophage progenitor cell (CFU-GM) compartments in blood and bone marrow, and the recovery of blood monocytes were followed for up to one year in ten beagles that had been exposed to fractionated (3 X 6 Gy) total-body irradiation before being transfused with cryopreserved fetal liver cells (FLC) from sibling donors that were genotypically matched for dog leukocyte antigens. Grafts contained 0.2-1.6 X 10(8) mononuclear cells and 0.9-19.8 X 10(4) CFU-GM/kg body weight. Numbers of circulating monocytes rose parallel to granulocyte numbers after day 6 and became normal by day 18 posttransplant. In bone marrow aspirates, low numbers of CFU-GM were detected on day 3 and their incidence per 10(5) mononuclear cells was normal after day 14. Circulating CFU-GM were present in significant numbers by day 7 and their elevated concentration per milliliter of blood after day 14 continued for one year. Dextran sulfate injection mobilized normal numbers of CFU-GM into the blood early after transplantation, and spontaneously circulating CFU-GM in a later phase did not differ from blood progenitors of normal animals with respect to radiation sensitivity and sedimentation velocity. Thus, FLC transplantation effected a rapid restoration of granulopoiesis and monocytopoiesis, which was reflected at both the level of mature blood cells and the compartments of CFU-GM in blood and bone marrow, underlining the high repopulating capacity of fetal liver stem cells.