Alemtuzumab, Busulfan, and Cyclophosphamide Followed By a Donor Stem Cell Transplant in Treating Patients With Hematologic Cancer

DISEASE CHARACTERISTICS: * Confirmed diagnosis of one of the following: * Primary acute myeloid leukemia (AML) meeting any of the following criteria: * First complete remission (CR; defined as \< 5% blasts in marrow) with high-risk features as defined by failure to achieve remission by day 21 after induction chemotherapy, or the presence of chromosomal abnormalities involving any of the following: * -5/del(5q) * -7/del(7q) * Inversion 3q * Abnormalities of 11q23, 20q, 21q, del(9q), * Translocation 6;9 * Translocation 9;22 * Abnormalities of 17p * Complex karyotype with ≥ 3 abnormalities * Second CR or subsequent in remission * Refractory or relapsed disease * Secondary AML in remission or relapse * Chronic myelogenous leukemia (CML) in accelerated or blast phase meeting the following criteria: * Accelerated phase is defined by any one of the following: * Blasts 10% to 19% of peripheral blood white cells or bone marrow cells * Peripheral blood basophils ≥ 20% * Persistent thrombocytopenia (\< 100,000/mm³) unrelated to therapy, or persistent thrombocytosis (\> 1,000,000/mm³) unresponsive to therapy * Increasing spleen size and increasing WBC count unresponsive to therapy * Cytogenetic evidence of clonal evolution (i.e., the appearance of an additional genetic abnormality that was not present in the initial specimen at the time of diagnosis of chronic phase CML) * Blast phase is defined by any of the following: * Blasts ≥ 20% of peripheral blood white cells or bone marrow cells * Extramedullary blast proliferation * Large foci or clusters of blasts in bone marrow biopsy * Primary myelodysplastic syndromes (MDS) with an IPSS score \> 1.5 * Secondary MDS with any IPSS score * Primary acute lymphoblastic leukemia meeting any of the following criteria: * First CR (\< 5% blasts in marrow) with high-risk features as defined by 1 of the following: * Failure to achieve remission after first induction chemotherapy * Presence of chromosomal abnormalities including hypodiploidy or abnormalities of 11q23 or translocation 9;22 * Second CR or subsequent in remission * Refractory or relapsed disease * No patients for whom a suitable HLA genotypically identical sibling or fully matched HLA-A, -B, -C, and -DRB1 unrelated donor is available * No active CNS involvement with disease * Donors must meet the following criteria: * Unrelated volunteer donors who are mismatched for more than one HLA-class I alleles or antigens or for one HLA-class I antigen, but matched by high-resolution typing at HLA-DRB1 and -DQB1, OR who are mismatched for one or more HLA-class II alleles or antigens, but matched by high-resolution typing at HLA-A, -B, and -C * No two-antigen mismatch at a single HLA-A, -B, or -C locus * No mismatching of class I and class II HLA * Matching must be based on results of high-resolution typing at HLA-A, -B, -C, - DRB1, and -DQB1 PATIENT CHARACTERISTICS: * Karnofsky performance status 50-100% * No symptomatic coronary artery disease or symptomatic congestive heart failure * No hepatic disease with transaminases or bilirubin \> 2 times upper limit of normal except for isolated hyperbilirubinemia attributed to Gilbert's syndrome * No severe hypoxemia with room air P\_AO\_2 \< 70, supplemental oxygen-dependence, or DLCO \< 60% predicted * No impaired renal function with creatinine \> 2 times upper limit of normal or creatinine clearance \< 50% normal * Not HIV seropositive * Not pregnant or breast-feeding * Fertile patients must use effective contraception * No active infections that are untreated or failing to respond to appropriate therapy PRIOR CONCURRENT THERAPY: Inclusion criteria: * See Disease Characteristics Exclusion criteria: * Prior allogeneic or autologous bone marrow, peripheral blood stem cell, or umbilical cord blood transplantation using a high-dose total-body irradiation regimen