STEM-CELL FACTOR ENHANCES THE GROWTH OF PRIMITIVE ERYTHROID PROGENITORS TO A GREATER EXTENT THAN INTERLEUKIN-3 IN PATIENTS WITH APLASTIC-ANEMIA

We examined the combined effects of stem cell factor (SCF), or interleukin-3 (IL-3) with erythropoietin on the development of haemopoietic progenitors in 19 patients with aplastic anaemia (AA) and eight normal controls by using an in vitro clonal assay. SCF significantly enhanced the growth of total erythroid colonies (erythroid bursts, mixed colonies) in 11 patients and all normal controls, whereas IL-3 did so in only three patients. The number of SCF- or IL-3-dependent erythroid colonies was substantially lower in AA patients than in the controls. Comparison of the capacity of SCF and IL-3 to increase total erythroid colony growth indicated that half of the AA patients responded more strongly to SCF than the normal controls, while few patients responded in such a manner to IL-3. These findings suggest that SCF in vivo will have a more dramatic effect than IL-3 in improving anaemia in patients with AA.