Inclusion Criteria:

- Patients age >= 55 years with AML OR patients age < 55 years with AML, who also
through pre-existing medical conditions or prior therapy are considered to be at high
risk for serious toxicities associated with a conventional, high-dose preparative
regimen

- Patients must be in morphologic leukemia-free state (marrow blasts < 5%) without
evidence of extramedullary disease within 21 days of HCT

- Only patients with Relapse Risk Score > 0 ("high risk") will be enrolled during Part
1; patients with all Relapse Risk Scores will be enrolled during Part 2

- HLA-identical related or HLA-matched unrelated donor available

- A signed informed consent form or minor assent form

- Patients treated at the Fred Hutchinson Cancer Research Center (FHCRC), with actual
body weight > 15 kg will be eligible for clofarabine pharmacokinetic studies;
participation in pharmacokinetic studies will be optional and will be offered to
patients at the time of enrollment

- DONOR: FHCRC matching allowed will be Grade 1.0 to 2.1: unrelated donors who are
prospectively: matched for HLA-A, B, C, DRB1 and DQB1 by high resolution typing; only
a single allele disparity will be allowed for HLA-A, B, or C as defined by high
resolution typing

- DONOR: A positive anti-donor cytotoxic crossmatch is an absolute donor exclusion;
donors are excluded when preexisting immunoreactivity is identified that would
jeopardize donor hematopoietic cell engraftment; this determination is based on the
standard practice of the individual institution; the recommended procedure for
patients with 10 of 10 HLA allele level (phenotypic) match is to obtain a panel
reactive antibody (PRA) screens to class I and class II antigens for all patients
before HCT; if the PRA shows > 10% activity, then flow cytometric or B and T cell
cytotoxic cross matches should be obtained; the donor should be excluded if any of
the cytotoxic cross match assays are positive; for those patients with an HLA Class I
allele mismatch, flow cytometric or B and T cell cytotoxic cross matches should be
obtained regardless of the PRA results

- DONOR: Patient and donor pairs homozygous at a mismatched allele are considered a
two-allele mismatch, i.e., the patient is A*0101 and the donor is A*0102, and this
type of mismatch is not allowed

- DONOR: Peripheral blood stem cells (PBSC) only will be permitted as a HSC source on
this protocol

Exclusion Criteria:

- AML French-American-British (FAB) M3 in first complete remission (CR1)

- Active AML involvement of the central nervous system (CNS) with disease refractory to
intrathecal chemotherapy

- Presence of circulating leukemic blasts in the peripheral blood detected by standard
morphology

- Patients who are human immunodeficiency virus (HIV)+ (HIV+ patients registered at
Fred Hutchinson Cancer Research Center [FHCRC] should be offered treatment on
Protocol 1410)

- Fertile men and women unwilling to use contraceptive techniques during and for 12
months following treatment

- Left ventricular ejection fraction < 35% (or, if unable to obtain ejection fraction,
shortening fraction of < 26%); ejection fraction is required if age > 50 years or
there is a history of anthracycline exposure or history of cardiac disease; patients
with a shortening fraction < 26% may be enrolled if approved by a cardiologist

- Diffusion capacity of the lung for carbon monoxide (DLCO) < 40% (corrected), total
lung capacity (TLC) < 40%, forced expiratory volume in one second (FEV1) < 40% and/or
receiving supplementary continuous oxygen

- The FHCRC Principal Investigator (PI) of the study must approve enrollment of all
patients with pulmonary nodules

- Patients with clinical or laboratory evidence of liver disease will be evaluated for
the cause of liver disease, its clinical severity in terms of liver function, and the
degree of portal hypertension; patients will be excluded if they are found to have
fulminant liver failure, cirrhosis of the liver with evidence of portal hypertension,
alcoholic hepatitis, esophageal varices, a history of bleeding esophageal varices,
hepatic encephalopathy, uncorrectable hepatic synthetic dysfunction evinced by
prolongation of the prothrombin time, ascites related to portal hypertension,
bridging fibrosis, bacterial or fungal liver abscess, biliary obstruction, chronic
viral hepatitis with total serum bilirubin > 3mg/dL, or symptomatic biliary disease

- Serum creatinine should be within normal limits as specified by institutional
guidelines; for patients with serum creatinine > upper limit of normal, a 24-hour
creatinine clearance will be performed and should be equal to or more than the lower
limit of normal

- Karnofsky score < 60 or Lansky Score < 50

- Patients with poorly controlled hypertension and on multiple antihypertensives

- Females who are pregnant or breastfeeding

- Patients with active non-hematologic malignancies (except non-melanoma skin cancers)
or those with non-hematologic malignancies (except non-melanoma skin cancers) who
have been rendered with no evidence of disease, but have a greater than 20% chance of
having disease recurrence within five years; this exclusion does not apply to
patients with non-hematologic malignancies that do not require therapy

- The addition of cytotoxic agents for "cytoreduction" with the exception of tyrosine
kinase inhibitors (such as imatinib mesylate), cytokine therapy, hydroxyurea, low
dose cytarabine, chlorambucil, or Rituxan will not be allowed within three weeks of
the initiation of conditioning

- Fungal infections with radiological progression after receipt of amphotericin B or
active triazole for greater than 1 month

- Patients with active bacterial or fungal infections unresponsive to medical therapy

- DONOR: Marrow donors

- DONOR: Donors who are HIV-positive and/or medical conditions that would result in
increased risk to the donor filgrastim (G-CSF) mobilization and PBSC collections

- DONOR: Identical twin

- DONOR: Any contraindication to the administration of subcutaneous G-CSF at a dose of
16 mg/kg/day for 5 consecutive days

- DONOR: Serious medical or psychological illness

- DONOR: Pregnant or lactating females

- DONOR: Prior malignancy within the preceding 5 years, with the exception of
non-melanoma skin cancers

- DONOR: Children < 12 years old