Recipient Inclusion Criteria:

   - Acute leukemia, in morphologic complete remission, OR myelodysplasia with < 10% blasts
   in the marrow, and no circulating blasts that contain auer rods. Patients with chronic
   myelomonocytic leukemia (CMML) must have a WBC count ≤ 10,000 cells/μL and < 10%
   blasts in the marrow.

   - Planned myeloablative conditioning regimen at Stanford University Medical Center.

   - Karnofsky or Lansky Performance Score ≥ 70%.

   - Must have an HLA related donor as follows: onor must be an 8/8 match for HLA A, B and
   C at intermediate (or higher) resolution, and DRB1 at high resolution using DNA based
   typing. The donors must be willing to receive G CSF followed by collection of cells by
   apheresis, and must meet the Program's criteria for donation.

   - Cardiac function: Ejection fraction at rest ≥ 40%.

   - Serum creatinine value of < 1.5 mg/dL, or an estimated creatinine clearance greater
   than 50 mL/minute (using the Stanford calculator for eGFR available in EPIC)

   - Diffusing capacity of the lungs for carbon monoxide (DLCO) ≥ 50% (adjusted for Hgb)

   - Forced vital capacity (FVC) ≥ 50%.

   - Forced expiratory volume (FEV1) ≥ 50%.

   - Total bilirubin < 2 times the upper limit of normal (ULN) (unless the elevated
   bilirubin is attributed to Gilbert's Syndrome)

   - Alanine aminotransferase (ALT) < 2.5 x ULN

   - Aspartate aminotransferase (AST) < 2.5 x ULN

   - Total bilirubin < 2 times the upper limit of normal (unless elevated bilirubin is
   attributed to Gilbert's Syndrome)

   - Signed informed consent

Recipient Exclusion Criteria:

   - Prior autologous or allogeneic hematopoietic stem cell transplant

   - Prior malignancies, except resected non melanoma or treated cervical carcinoma in
   situ. Cancer treated with curative intent ≥ 5 years previously is allowed. Cancer
   treated with curative intent < 5 years previously will not be allowed unless approved
   by the Protocol Officer or one of the Protocol Chairs

   - Active central nervous system (CNS) involvement by malignant cells

   - Presence of fluid collection (ascites, pleural or pericardial effusion) that
   interferes with methotrexate clearance or makes methotrexate use contraindicated

   - Requirement for supplemental oxygen

   - Uncontrolled bacterial, viral or fungal infections (currently taking medication and
   with progression or no clinical improvement) at time of enrollment

   - History of uncontrolled autoimmune disease or on active treatment (defined as > 5 mg
   prednisone daily)

   - Seropositive for HIV 1 or 2

   - Seropositive for HTLV I or -II

   - Active Hepatitis B or C viral replication by polymerase chain reaction (PCR)

   - Documented allergy to iron dextran or murine proteins

   - Pregnant (positive serum or urine βHCG) or breastfeeding)

   - Females of childbearing potential (FCBP) or men who have sexual contact with FCBP
   unwilling to use an effective form of birth control or abstinence for one year after
   transplantation

   - Unable to comply with the treatment protocol, including appropriate supportive care,
   follow up and research tests.

   - Planned to receive post transplant maintenance therapy except for fms-like tyrosine
   kinase 3 (FLT3) inhibitors or BCR ABL tyrosine kinase inhibitors (TKIs).

Donor Inclusion Criteria:

   - HLA matched donor (matching at 8/8 antigens or alleles including HLA A, B, C, and
   -DRB1).

   - ≥ 18 years to < 66.0 years

   - State of general good health

   - Completed a donor evaluation with history, medical examination and standard blood
   tests within 60 days of starting the hematopoietic cell collection procedure. In order
   to fairly represent the interests of the donor, the donor evaluation and consent will
   be performed by a study team member other than the recipient's attending physician.

   - Hepatitis A, B and C, HIV 1 and 2, HTLV, VZV, EBV, HSV, West Nile virus, Syphilis
   Treponema, T cruzi (Chagas), CMV, and the MPX NAT IDT (HIV/HCV/HBV) will be tested as
   per national standard of care guidelines for transplant donors. Donors who are HIV
   positive will be excluded. Donors who are positive by serology for Hepatitis B or C
   are eligible as long as PCR for RNA/DNA is negative

   - White blood cell count > 3.5 x 109/L

   - Platelets > 150 x 109/L

   - Hematocrit > 35%

   - Capable of undergoing leukapheresis

   - Able to understand and sign informed consent

Donor Exclusion Criteria:

   - Psychological traits or psychological or medical conditions which make them unlikely
   to tolerate the procedure

   - Pregnant or lactating female