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Inhibition of human bone marrow fibroblast colony formation by leukemic cells.

The number of bone marrow fibroblast colony formations decreases in most cases of acute leukemia before the initiation of chemotherapy. This study was undertaken to clarify the mechanism of suppression of fibroblast colony formation in leukemic patients. Titration of the number of bone marrow cells did not indicate a linear relationship between the number of bone marrow cells cultured and the number of fibroblast colony formations. The number of fibroblast colony formations recovered by removal of nonadherent leukemic cells following one day of incubation increased. The cloning efficiency of patient bone marrow still showed increases in colony formation at higher plating concentrations after the nonadherent cells were removed. When leukemic and normal bone marrow cells were cocultured, the suppressive effect of leukemic cells on normal marrow fibroblast colony formation was clearly observed. The suppressive effect disappeared at complete remission, and then reappeared at relapse. Heat-inactivated serum and bone marrow culture media from leukemic patients whose fibroblast colony formations were small in number suppressed fibroblast colony formation from normal bone marrow. From these results, it was concluded that the suppression of fibroblast colony formation in leukemic patients was through humoral factors produced by leukemic cells.