Clofarabine, Cytarabine, and Thymoglobulin for Allogeneic Transplantation

Inclusion Criteria (Patient): 1. Myelodysplastic Syndrome (MDS), as defined by the World Health Organization criteria, OR Chronic Myelomonocytic Leukemia (CMML) as defined by the French American British classification OR Acute Myeloid Leukemia (AML) in complete remission \[excluding FAB-M3\] diagnosed by standard criteria and meet the criteria below: 1. Patients may be in any CR 2. No more than 2 cycles of consolidation. Any consolidation regimen may be used. 3. No more than 6 months from documented CR to transplant. 2. Age 18 years or older. 3. ECOG performance status \<=2 4. Identification of suitable donor 5. DLCO \>=40% with no symptomatic pulmonary disease 6. LVEF by MUGA \>= 30% 7. Serum creatinine \<=1.0 mg/dL; if serum creatinine \>1.0 mg/dL, then the estimated glomerular filtration rate (GFR) must be \>60 mL/min/1.73 m2 as calculated by the Modification of Diet in Renal Disease equation where Predicted GFR (ml/min/1.73 m2) = 186 x (Serum Creatinine)-1.154 x (age in years)-0.023 x (0.742 if patient is female) x (1.212 if patient is black). 8. Bilirubin \<=2 times the upper limit of normal 9. AST \<=3 times the upper limit of normal Donor criteria: 1. HLA-Matched Sibling: The donor must be an adequate HLA match as determined by serologic typing for class (A, B) and low resolution molecular typing for class II (DRB1) as defined by institutional standards. 2. Matched Unrelated Donor: An acceptable match per NMDP standards based on high resolution molecular typing. 3. The donor must be healthy and must be an acceptable donor as per institutional standards for stem cell collection. 4. The donor must have no significant cardiopulmonary, renal, endocrine, or hepatic disease. 5. There is no upper age restriction for donors, but they must be at least 18 years of age. 6. Syngeneic donors are not eligible. 7. No known HIV. Exclusion Criteria: 1. Pregnant or nursing. 2. Active systemic infection considered opportunistic, life threatening or clinically significant at the time of treatment. 3. Severe concurrent disease, including severe insulin-dependent diabetes, uncontrolled hypertension, transient ischemic attacks, uncontrolled symptomatic coronary artery disease, or symptomatic CNS involvement or psychiatric illness/social situations that would limit compliance with study requirements. 4. Known HIV disease. 5. History of other malignancy except for basal cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix or breast unless the subject has been off treatment and free from disease for \> 3 years. 6. Active disease at the time of transplant.