Expression of messenger RNA for GM-CSF by blood mononuclear cells after allogeneic bone marrow transplantation

We examined blood mononuclear cells from six recipients of HLA-identical sibling marrow transplants for their ability to express messenger (m) RNA for granulocyte-macrophage colony stimulating factor (GM-CSF). Cells were cultured for 48 hours with the stimulus of ionomycin and phorbol myristate acetate. mRNA specific for GM-CSF was detectable in stimulated cell cultures from all six patients. In two patients at days 31 and 40 post transplant respectively, mRNA for GM-CSF was just detectable; in a third at day 38 post transplant it was readily detectable, and in the three others at days 42, 165 and 185 respectively, it was easily detectable. These results indicate that maintenance of haemopoiesis post transplant may, at least in part, be due to the elaboration of GM-CSF by blood mononuclear cells.