Inclusion Criteria:

Arm A: Model-based ATG dosing CD34-selection (PRAISE-IR population)

• Patients who participated in the PRAISE-IR single center phase II study
• Patient age at transplant: ≥ 1 year and < 66 years
• HLA 8/8 MRD or MUD
• Conditioning intensity: myeloablative
• Conditioning regimens: Model-based ATG with TBI/Thiotepa/Cyclophospamide (TBI/Thio/Cy) or Busulfan/Melphalan/Fludarabine (Bu/Mel/Flu).
• Morphologic complete remission at the time of alloHCT Arm B: Standard ATG dosing CD34-selection (CIBMTR population)
• First AlloHCT in the US between 2021-2023
• Patient age at transplant: ≥ 1 year and < 66 years
• Disease: Patients with AML, MDS, and ALL
• HLA 8/8 MRD or MUD
• Peripheral blood stem cell allograft
• Conditioning intensity: myeloablative conditioning
• Conditioning regimens: standard dose ATG (2.5 mg/kg/day given on Day -4 and Day -3)
• GVHD prophylaxis: ex vivo CD34 selection
• Morphologic complete remission at the time of alloHCT Arm B*:Standard ATG dosing CD34-selection (BMT CTN 1301 population)
• Patients in BMT CTN 1301, who received the CD34-selected graft
• Patient age at transplant: ≥ 1 year and < 66 years
• Disease:Patients with AML, MDS, and ALL
• HLA 8/8 MRD or MUD
• Peripheral blood stem cell allograft
• Conditioning intensity: myeloablative conditioning
• Conditoning regmens: TBI/Thiotepa/Cyclophospamide (TBI/Thio/Cy) or Busulfan/Melphalan/Fludarabine (Bu/Mel/Flu) and standard dose ATG (2.5 mg/kg/day given on Day -4 and Day -3)
• GVHD prophylaxis: ex vivo CD34 selection
• Morphologic complete remission at the time of alloHCT Arm C: Control CIBMTR population
• First AlloHCT in the US between 2021-2023
• Patient age at transplant: ≥ 1 year and < 66 years
• Disease:Patients with AML, MDS, and ALL
• HLA 8/8 MRD or MUD
• Peripheral blood stem cell
• Conditioning intensity: myeloablative conditioning
• Conditioning regimens: Busulfan/Cyclophosphamide (Bu/Cy), Busulfan/Fludaranbine (Bu/Flu), Cyclophosphamide/TBI (Cy/TBI), TBI/Etopsoside
• GVHD prophyalxis: / CNI or PTCy-based
• CNI-based: CNI (tacrolimus or ciclosporin) plus MTX
• PTCy-based: Cyclophosphamide on day +3 and +4 (50 mg/kg/d) combined with CNI and mycophenolate mofetil (MMF)

Exclusion Criteria:

Patients will be entered into this trial only if they meet none of the following criteria:

Arm A: Model-based ATG dosing CD34-selection (PRAISE-IR population)

• HLA <8/8 MRD or MUD Arm B: Standard ATG dosing CD34-selection (CIBMTR population)
• Patients who participated in the PRAISE-IR study
• Patients who did not sign consent for research
• Patient transplanted at a center that does not meet CIBMTR data quality standards
• Use of CNI-(Tac/MTX) or PTCy-based GVHD prophylaxis Arm B*:Standard ATG dosing CD34-selection (BMT CTN 1301 population)
• Patients who did not sign consent for research
• Patient transplanted at a center that does not meet CIBMTR data quality standards
• Use of CNI- or PTCy-based GVHD prophylaxis Arm C: Control CIBMTR population
• Patients who did not sign consent for research
• Patient transplanted at a center that does not meet CIBMTR data quality standards
• Use of ATG and/or alemtuzumab
• Patients who received PTCy with sirolimus (and not a CNI)
• Use of ex vivo CD34 selection