The in vitro stimulatory effect of rHuIL-6 on thrombopoiesis prompted its evaluation in a phase 1 study of 22 low-risk MDS patients with thrombocytopenia (77). Eight (36%) patients experienced a transient increase in platelet counts, but only three were classified as major responders. rHuIL-6 increased the frequency of higher ploidy megakaryocytes without increasing the number of megakaryocyte progenitors, consistent with its known maturation-inducing effect. Nondose-dependent anemia developed in most patients, and no neutrophil responses were documented. Constitutional symptoms and anemia were seen in most patients, precluding all but three patients from receiving maintenance therapy. The marginal activity and significant therapy-related toxicity of rHuIL-6 makes it of limited value as a thrombopoietic agent in MDS.

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