Proliferation of Human Bone Marrow Cells in Diffusion Chambers Implanted Into Normal or Irradiated Mice

Diffusion chambers containing normal, human bone marrow cells were implanted in the abdominal cavity of normal and irradiated mice. Granulocytic cells and macrophages proliferated in the chambers. The number of cells in the granulocytic series recovered from the chambers dropped to 60% after 1 day; during the next 7 days it varied between 40% and 60% of the inoculated number of granulocytes, with no difference between irradiated and non-irradiated animals. From day 9 the yield of cells in granulocytic series increased in chambers from irradiated animals, and a higher percentage of cells were in the proliferating pool of the granulocytic series. Simultaneously, the cell yield in chambers from normal animals dropped markedly and consisted mostly of mature granulocytes. In both groups the percentage of eosinophilic cells increased significantly during the last part of the culture period. The enhanced growth in the irradiated mice suggests an increased self-renewal of granulocytic stem cells, leading to a larger yield of differentiated granulocytic cells later in the culture period. A shortened generation time and/or increased cloning efficiency of stem cells may also contribute to the enhanced granulocyte production. The suppression of the immune reactivity by irradiation of the host animals may allow better proliferation by delaying production of cytotoxic antibodies against the xenogenic human cells. The number of macrophages increased gradually, and there was no significant difference between irradiated and nonirradiated animals. The lymphocyte number decreased after implantation and varied between 30% and 50% of the inoculated number. From day 11, the lymphocyte number dropped more in normal animals than in irradiated animals.