IL-3 elicits hematologic responses in a small proportion of AA patients, and they are generally transient in nature. In 15 patients with severe AA, nonsustained increases in white blood cell counts were observed in 7/9 patients and 2/6 patients at dose levels of 1-2 |g/kg/d and 4-16 |g/kg/d, respectively, administered as 21-d continuous iv infusions (148). Responses were not elicited in other blood lineages. In a phase 1-2 study of 21 AA and MDS patients evaluating rHuIL-3 dose levels of 0.5-10 |g/kg/d sc for 21 d, 2 AA patients experienced improvements in red cell transfusion requirements (74). Two additional small trials reported neutrophil and platelet responses in a few patients, but erythroid responses were not observed (73,149). Studies of both rHuIL-1 and rHuIL-6 in patients with refractory severe AA patients have not shown any efficacy (150,151). Nonhematologic side effects produced by rHuIL-6 included fever, headache, arthralgia, tachycardia, and hypertension. Hematologic toxicity included worsening of pre-existing anemia and thrombocytopenia. The study was discontinued early because of the toxicities attributed to rHuIL-6.

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