A Randomized Trial of Recombinant Humanized Anti-IL-2 Receptor Antibody (Daclizumab) Versus Antithymocyte Globulin (ATG) to Treat the Cytopenia of Myelodysplastic Syndrome (MDS)

This study will evaluate a new immunosupressive therapy, Daclizumab, and compare it with antithymocyte globulin (ATG) to treat cytopenia, that is, the deficiency of cellular elements of the blood, in myelodysplastic syndrome (MDS). Daclizumab is an anti-interleukin-2 receptor (IL-2) antibody. MDS, also known as myelodysplasia, is a disorder that can cause anemia, spontaneous bleeding, and greater risk of infections. Although the bone marrow can still produce some blood cells, very few reach the bloodstream. The cause of MDS is not known, although its behavior is. Many patients need transfusions of red blood cells. They may also develop leukemia, which is often quite resistant to treatment with chemotherapy. However, the progression of the disorder to leukemia is usually slow, taking many years. Patients 18 years of age and older who have MDS may be eligible for this study. Participants will undergo the following tests and procedures: * Medical history and physical examination. * Collection of blood for tests including blood counts, liver and kidney function, and antibodies against common viruses. * Chest x-ray. * Electrocardiogram. * Bone marrow sample to confirm the diagnosis. Participants will randomly receive either ATG or Daclizumab. If they are in the group to receive ATG, they will be admitted as inpatients to undergo the first 10 to 14 days of treatment. If they do not already have a catheter in one of the large veins of the neck, chest, or arm, one will be placed. ATG will be given through the catheter. Blood counts and other blood analysis will be monitored daily while the patients are treated. After about 10 days, they will be released, to be under the care of their referring physicians. Those participants who are in the group to receive Daclizumab will receive a total of five doses, one every 2 weeks, over 8 weeks, given through a vein as a 15-minute infusion. The first, third, and fifth dose will be given at the outpatient clinic. The second and fourt