Comparing Post-Transplant Cyclophosphamide As GVHD Prophylaxis to Standard of Care for Acute Leukemia Patients

Inclusion Criteria:

* Patients with Acute Leukemias (AML, ALL) in morphologic complete remission with or without hematologic recovery
* Patients must have a fully matched (8/8) related donor willing to donate peripheral blood stem cells and must meet institutional criteria for donation
* Planned Myeloablative conditioning regimen
* Cardiac function: ejection fraction at rest ≥ 50% by MUGA or TTE
* Estimated creatinine clearance greater than 50 mL/minute
* Pulmonary function: DLCO ≥ 50% (adjusted for hemoglobin), and FVC and FEV1 ≥ 50%
* Liver function: total bilirubin \< 2x the upper limit of normal (unless elevated bilirubin is attributed to Gilbert's Syndrome) and ALT/AST \< 2.5x the upper normal limit
* Signed informed consent

Exclusion Criteria:

* Karnofsky or Lansky Performance Score \< 70%.
* Active disease
* Patients with uncontrolled bacterial, viral, or fungal infections
* Presence of fluid collection (ascites, pleural or pericardial effusion) that interferes with methotrexate clearance or makes methotrexate use contraindicated
* Patients seropositive for HIV-1 or -2
* Patients seropositive for HTLV-I or -II
* Patients with active Hepatitis B or C viral replication by PCR
* Women who are pregnant (positive serum or urine βHCG) or breastfeeding
* Females with childbearing potential (FCBP) or men who have sexual contact with FCBP unwilling to use effective forms of birth control or abstinence for one year after transplantation
* History of uncontrolled autoimmune disease or on active treatment
* Patients with prior malignancies, except resected non-melanoma skin cancer or treated cervical carcinoma in situ; cancer treated with curative intent ≥ 5 years previously will be allowed; cancer treated with curative intent \< 5 years previously will not be allowed.