RESTORATIVE EFFECT OF IL-3 ON ADHERENCE OF CLONED HEMATOPOIETIC PROGENITOR-CELL TO STROMAL CELL

Mammalian hemopoiesis results from a complex interaction between hemopoietic progenitor cells, stromal cells and extracellular matrix components, orchestrated by specific glycoprotein growth factors. Recently, these growth factors have been shown to possess an important function, apart from stimulation of proliferation, and that is suppression of an active cellular process of programmed cell death, or apoptosis. Highly specific biochemical and morphologic changes have been shown to occur during apoptosis, but their reflections on cellular functions are poorly understood. Interleukin-3 (IL-3)-dependent FDCP-1 (factor-dependent cell lines cloned in Paterson Laboratories) cells were studied for their ability to adhere to hemopoietic stroma in a temporal fashion under conditions of apoptosis and following rescue from apoptosis with growth factor. It was found that cloned FDCP-1 cells always maintained, in the presence of a source of IL-3 (either WEHI conditioned medium or rm-IL-3), bound cloned hemopoietic stromal cell GBI/6 in a constant fashion for 20 hours, while cells starved of IL-3 experienced a 50% time-dependent decrement in binding. If IL-3 were added back to FDCP-1 that had been starved of growth factor for 8 hours, but not 12 hours, adherence to stroma was restored to that of control cells always in the presence of IL-3. Granulocyte/macrophage colony-stimulating factor (GM-CSF), Interleukin-6 (IL-6) and transforming growth factor-beta (TGF-beta) did not restore cytoadherence. By transmission electron microscopy, nucleus and cytoplasm of IL-3-replenished cells resembled that of control cells. These data indicate that at least some events related to apoptosis were reversible for a period up to 8 hours, but not 12 hours, in cells that had been rescued by readdition of IL-3. These findings offer important insight into a way in which bone marrow progenitor cells may be maintained in a condition that optimizes their ability to engraft stroma during transplantation.