Three phase 1-2 studies have evaluated the effects of short-term treatment with rHuIL-3 in MDS (72-74). These preliminary studies suggested that rHuIL-3 could increase neutrophil counts but not as prominently as rHuGM-CSF or rHuG-CSF. Furthermore, rHuIL-3 transiently improves thrombocytopenia in some patients, but ery-thropoiesis was rarely stimulated. A longer term study of 3-mo rHuIL-3 therapy elicited improvements in two of five patients with initial platelet counts < 50 x 109/L, without notable changes in the other lineages (75). The issue as to whether combination HGF support with rHuIL-3 and rHuEPO could augment erythroid responses was evaluated in 22 MDS patients (76). The combination increased reticulocyte counts in five patients, but only two patients experienced decreased red cell transfusion requirements. The erythroid response was comparable to that in studies of rHuEPO alone, but rHuIL-3 produced toxicity requiring dose reduction in most patients.

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