Allogeneic Transplantation for Pediatric Leukemias With Unrelated Donors

Inclusion Criteria:

* Ages 0-21
* AML in one of the following stages:

  * Having preceding myelodysplasia (MDS)
  * High Risk cytogenetics
  * Requiring \> 2 cycles chemotherapy to obtain complete remission
  * High allelic ratio FLT3/ITD+,
  * Standard risk cytogenetics with positive MRD at end of Induction
  * Second or greater CR
  * First relapse with \< 25% blasts in bone marrow
  * With therapy-related AML whose prior malignancy has been in remission for at least 12 months
* ALL in one of the following stages:
* High risk first remission, defined as:

  * Ph+ ALL; or,
  * MLL rearrangement with slow early response \[defined as having M2 (5-25% blasts) or M3 (\>25% blasts on bone marrow examination on Day 14 of induction therapy)\]; or,
  * Hypodiploidy (\< 44 chromosomes or DNA index \< 0.81); or,
  * End of induction M3 bone marrow; or,
  * End of induction M2 marrow or MRD\>1% with M2-3 marrow or MRD\>1% at Day 42.
  * High-risk infant ALL defined as age \<6 months at diagnosis with MLL (11q23) translocation.
* High risk second remission, defined as:

  * Bone marrow relapse \< 36 months from induction; or \>36 mths if a matched sibling donor is available
  * T-lineage relapse at any time; or,
  * Very early isolated CNS relapse (\<18 months from diagnosis); or,
  * Slow reinduction (M2-3 at Day 28) after relapse at any time.
* Any third or subsequent CR.
* Biphenotypic or undifferentiated leukemia in any CR or if in first relapse must have \< 25% blasts in bone marrow
* MDS at any stage; prior therapies allowed
* CML in chronic or accelerated phase; prior therapies allowed
* Patient also must have the following organ requirements:

  * Adequate renal function defined as serum creatinine \<2x normal, or creatinine clearance \> 40 ml/min/m\^2 or 70 ml/min.
  * Adequate liver function as defined by total bilirubin less than or equal to 2 times normal and AST and ALT less than or equal to 4 times normal.
  * Adequate cardiac function as defined by: shortening fraction \> 24% by echocardiogram, or ejection fraction \> 30% by radionuclide angiogram.
  * Adequate pulmonary function as defined by DLCO, FEV1/FVC \> 60% by pulmonary function tests. For children who are uncooperative for PFTs and have no evidence of dyspnea at rest or exercise intolerance, pulse oximetry \> 94% on room air is considered acceptable, with a normal chest xray.
  * Adequate venous access; a double lumen central vascular access device or its equivalent and an additional PICC line will be required for all patients.
* Women of childbearing potential and sexually active males should use effective contraception while on study.

Exclusion Criteria:

* Inability to give informed consent or assent
* Inability to obtain a suitable donor
* Patient who is HIV-positive
* Patient who has active Hepatitis B
* Patient who is pregnant
* Patient who is otherwise considered unsuitable for transplant at the discretion of the principal investigator.