Methotrexate or Pentostatin for Graft-versus-host Disease Prophylaxis in Risk-adapted Allogeneic Bone Marrow Transplantation for Hematologic Malignancies

Inclusion Criteria:

\*Age less than or equal to 21 years old

High risk malignancy as follows:

* High-risk ALL in CR1. Examples include, but not limited to: Induction failure or \> 1% leukemic lymphoblasts in the bone marrow on remission date;\> 0.1% leukemic lymphoblasts in the bone marrow in week 7 of continuation treatment (i.e. before reinduction I); re-emergence of leukemic lymphoblasts by MRD (at any level) in patients previously MRD negative; persistently detectable MRD at lower levels;early T-cell precursor (ETP) ALL.
* High-risk ALL beyond CR1, or with refractory disease. "Beyond CR1" denotes any CR following CR1, or any relapsed state. "Refractory disease" includes induction failure.
* High-risk de novo AML in CR1.Examples include but are not limited to:evidence of a high-risk genetic abnormality or high-risk MRD features.
* AML beyond CR1, or with refractory disease. "Beyond CR1" denotes any CR following CR1, or any relapsed state. "Refractory disease" includes induction failure.
* Therapy-related AML.
* MDS, primary or secondary, at any stage.
* NK cell lymphoblastic leukemia in any CR
* Biphenotypic bilineage, or undifferentiated leukemia.
* CML in any phase
* Hodgkin lymphoma beyond CR1 or with refractory disease. "Beyond CR1" denotes any CR following CR1, or any relapsed state.
* Non-Hodgkin lymphoma beyond CR1 or with refractory disease. "Beyond CR1" denotes any CR following CR1, or any relapsed state.
* Juvenile Myelomonocytic Leukemia (JMML).
* All patients with prior evidence of CNS leukemia must be treated and be in CNS CR to be eligible for study.
* Has a suitable HLA matched sibling or unrelated volunteer donor available for stem cell donation.A "matched" donor is defined as allele matching at 7/8 to 8/8 HLA loci at A, B, C and DRB1.For the purpose of this study, the term "matched sibling" also refers to an HLA matched family member.
* Does not have any other active malignancy other than the one for which this transplant is indicated.
* Left ventricular ejection fraction \> 40%,or shortening fraction \> 26%.
* Forced vital capacity (FVC) greater than or equal to 50% of predicted value (corrected for hemoglobin), or if patient is unable to perform pulmonary function testing, pulse oximetry greater than or equal to 92% on room air.
* Creatinine clearance greater than or equal to 70 ml/min/1.73m2
* Karnofsky or Lansky (age-dependent) performance score of greater than or equal to 70.
* Bilirubin less than or equal to 2.5 mg/dL.
* Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase less than or equal to 5 times upper limit of normal
* Not pregnant as confirmed by negative serum or urine pregnancy test within 14 days prior to enrollment.
* Not lactating.
* Has not had a prior allogeneic HSCT.

Exclusion Criteria:

* Pregnant and lactating females are excluded from participation as the short and long-term effects of the protocol interventions and infusion on a fetus or a nursing child through breast milk are not entirely known at this time.