Immunotherapy for Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Blast Phase Chronic Myelogenous Leukemia (BP CML), and Myelodysplastic Syndrome (MDS) Relapse After Allogeneic Transplantation

Inclusion Criteria: 1. Age \> 1 year. 2. Patients who have received an allogeneic transplant to treat AML, ALL, MDS, or CML and have relapse or progression of their AML, ALL, MDS, or CML are eligible to participate in the study. Relapse is defined as: reappearance of leukemic blasts as determined by morphologic analysis of the blood or marrow, reappearance of a phenotypic population of leukemia blasts by flow cytometric analysis of the blood or marrow, reappearance of a chromosome abnormality which is associated with the original leukemia as determined by chromosomal or fluorescence in situ hybridization (FISH) testing (ex: a translocation between chromosomes 9 and 22 for CML), reappearance of the molecular marker which is associated with the original leukemia as determined by polymerase chain reaction (PCR) (ex: breakpoint cluster region \[BCR\]-Abelson murine leukemia \[ABL\] for CML or ALL). \*Patients who received allogeneic transplantation to treat AML, ALL, MDS, or CML with detectable disease, and did not achieve remission of their leukemia after transplant are eligible. 3. Eastern Cooperative Oncology Group (ECOG) performance status \< 2 for adults, and Lansky status 60% for children. 4. Liver functions tests (aspartate transaminase \[AST\]/alanine aminotransferase \[ALT\]/bilirubin) \< 5x the upper limit of normal. 5. Creatinine \< 3x the upper limit of normal. 6. Lack of active grade 2-4 acute graft-versus-host disease (GVHD) 3 weeks after discontinuation of immunosuppression. 7. Patients with limited stage and extensive stage chronic GVHD of mild severity (lichenoid changes), or requiring \< prednisone 10 mg/m² daily will be included. 8. Recipients of grafts procured from related and unrelated donors with any level of human leukocyte antigen (HLA)-matching. Exclusion Criteria: 1. Pregnant patients are excluded due to unknown risk to the unborn fetus with cytokines. 2. Allergy to components of interferon-alpha-2b or GM-CSF. 3. Current uncontrolled infection. 4. Current grade 2-4 acute GVHD or chronic extensive GVHD of moderate to severe nature, requiring treatment with more than 10 mg/m² of prednisone daily. 5. Uncompensated heart failure, New York Heart Association (NYHA) class III-IV: * Class I: patients with no limitation of activities; they suffer no symptoms from ordinary activities; * Class II: patients with slight, mild limitation of activity; they are comfortable with rest or with mild exertion; * Class III: patients with marked limitation of activity; they are comfortable only at rest; * Class IV: patients who should be at complete rest, confined to bed or chair; any physical activity brings on discomfort and symptoms occur at rest. 6. Breast feeding, due to unknown risk to the infant. 7. Inability to give informed consent. 8. Children under 1 year of age.