Inclusion Criteria:

   - Any of the following hematologic malignancies:

      - Acute myeloid leukemia (AML) in first cytomorphological remission (with < 5%
      blasts in the bone marrow) with Disease Risk Index (DRI) intermediate or above,
      or in second or higher cytomorphological remission (with < 5% blasts in the bone
      marrow)

      - Acute lymphoblastic leukemia (ALL) in first or higher remission (with < 5% blasts
      in the bone marrow)

      - Myelodysplastic syndrome (MDS): transfusion-dependent (requiring at least one
      transfusion per month), or intermediate or higher Revised International
      Prognostic Scoring System (IPSS-R) risk group

   - Clinical justification of allogeneic stem cell transplantation where a suitable HLA
   matched sibling or unrelated donor is unavailable in a timely manner

   - Availability of a related haploidentical donor with one fully shared haplotype and 2
   to 4 mismatches at the HLA-A, -B, -C, and -DRB1 loci of the unshared haplotype, as
   determined by high resolution human leukocyte antigen (HLA)-typing

   - Karnofsky Performance Status (KPS) ≥ 70%

   - Male or female, age ≥ 18 years and ≤ 70 years. Patients aged ≥ 65 years must have a
   Sorror score ≤ 3

   - Patient weight ≥ 25 kg and ≤ 130 kg

   - Availability of a donor aged ≥ 16 years and ≤ 75 years who is eligible according to
   local requirements and regulations. Donors aged < 16 years are allowed if they are the
   only option for an HSCT, if they are permitted by local regulations, and if the
   IRB/IEC approves participation in the study.

   - For females of childbearing potential who are sexually active and males who have
   sexual contact with a female of childbearing potential: willingness to use of reliable
   methods of contraception (oral contraceptives, intrauterine device, hormone implants,
   contraceptive injection or abstinence) during study participation

   - Given written informed consent (patient and donor)

Exclusion Criteria:

   - Diagnosis of chronic myelomonocytic leukemia (CMML)

   - Availability of a suitable HLA-matched sibling or unrelated donor in a donor search

   - Prior allogeneic hematopoietic stem cell transplantation

   - Diffusing capacity for carbon monoxide (hemoglobin corrected DLCO) < 50% predicted

   - Left ventricular ejection fraction < 45% (evaluated by echocardiogram or MUGA scan)

   - Aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) > 2.5 × upper
   limit of normal (CTCAE grade 2)

   - Creatinine clearance < 50 ml/min (calculated or measured)

   - Positive pregnancy test or breastfeeding of patient or donor (women of childbearing
   age only)

   - Estimated probability of surviving less than 3 months

   - Known allergy to any of the components of ATIR101 (e.g., dimethyl sulfoxide)

   - Known hypersensitivity to cyclophosphamide or any of its metabolites

   - Any contraindication for GVHD prophylaxis with mycophenolate mofetil, cyclosporine A,
   or tacrolimus

   - Known presence of HLA antibodies against the non-shared donor haplotype

   - Positive viral test of the patient or donor for human immunodeficiency virus (HIV)-1,
   HIV-2, hepatitis B virus (HBV), hepatitis C virus (HCV), Treponema pallidum, human
   T-lymphotropic virus (HTLV)-1 (if tested), HTLV-2 (if tested), West Nile virus (WNV;
   if tested), or Zika virus (if tested)

   - Any other condition that, in the opinion of the investigator, makes the patient or
   donor ineligible for the study