Inclusion Criteria:

   1. Age < 18 years and > 1 month (< 1 month upon approval by Sponsor)

   2. Life expectancy > 10 weeks

   3. Patients deemed clinically eligible for allogeneic stem cell transplantation.

   4. Patients may have failed prior allograft

   5. Patients with life-threatening acute leukemia (high-risk ALL in 1st CR, ALL in 2nd CR,
   high-risk AML in 1st CR, AML in 2nd CR.) or myelodysplastic syndromes. Morphological
   CR must be documented and minimal residual disease measurement before transplantation
   is recommended.

   6. Non-malignant disorders deemed curable by allogeneic transplantation: (a) primary
   immune deficiencies, (b) severe aplastic anemia not responding to immune suppressive
   therapy, (c) osteopetrosis, (d) selected cases of erythroid disorders such as β0 β0
   thalassemia major, sickle cell disease, Diamond-Blackfan anemia, (e)
   congenital/hereditary cytopenia, including Fanconi Anemia before any clonal malignant
   evolution (MDS, AML).

   Note: Subjects will be eligible if they meet either item 5 OR item 6.

   7. Lack of suitable conventional donor (HLA identical sibling or HLA phenotypically
   identical relative or 10/10 unrelated donor evaluated using high resolution molecular
   typing) or presence of rapidly progressive disease not permitting time to identify an
   unrelated donor

   8. A minimum genotypic identical match of 5/10 is required.

   9. The donor and recipient must be identical, as determined by high resolution typing, on
   at least one allele of each of the following genetic loci: HLA-A, HLA-B, HLA-Cw, HLA-
   DRB1 and HLA-DQB1.

10. Lansky/Karnofsky score > 50

11. Signed informed consent by the patient or the patient's parent or guardian for
   patients who are minors

Exclusion Criteria:

   1. Greater than active Grade II acute GvHD or chronic extensive GvHD due to a previous
   allograft at the time of screening

   2. Patient receiving an immunosuppressive treatment for GvHD treatment due to a previous
   allograft at the time of screening

   3. Dysfunction of liver (ALT/AST > 5 times normal value, or bilirubin > 3 times normal
   value), or of renal function (creatinine clearance <30ml/min/1.73m2)

   4. Severe cardiovascular disease (arrhythmias requiring chronic treatment, congestive
   heart failure or left ventricular ejection fraction < 40%)

   5. Current clinically active infectious disease (including positive HIV serology or viral
   RNA)

   6. Serious concurrent uncontrolled medical disorder

   7. Pregnant or breast feeding female patient

   8. Lack of parents'/guardian's informed consent for children who are minors.