Increased Haemopoietic Cell Survival in Vitro Induced by a Human Marrow Fibroblast Factor

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Abstract
Summary. Human marrow fibroblasts were grown in vitro and examined for effects on human and mouse haemopoietic cells. When human marrow cells were incubated with fibroblasts or with fibroblast‐conditioned medium for 1 week and then assayed for committed granulocyte/monocyte (CFU‐c) and erythroid (BFU‐e) progenitor cells, the numbers of CFU‐c and BFU‐e were considerably increased compared with controls. In contrast, human marrow‐fibroblast‐conditioned medium, when added directly to CFU‐c or BFU‐e assay cultures, had no effect on colony formation by these progenitor cells. As these results suggest that the fibroblast‐derived factor may be acting on a relatively primitive progenitor cell, possibly a pluripotent haemopoietic stem cell, the effect of this factor on mouse pluripotent haemopoietic stem cells (CFU‐s) was examined. Human marrow‐fibroblast‐conditioned medium considerably enhanced CFU‐s survival after a 24 h incubation and increased the proportion of CFU‐s in cell‐cycle. The increase in CFU‐s survival depended on the concentration of the fibroblast‐conditioned medium but not on the age of the fibroblast culture. The evidence suggests therefore that human marrow fibroblasts produce a factor that acts on a human myeloid progenitor cell more primitive than BFU‐e and CFU‐c, possibly the pluripotent haemopoietic stem cell.