This study will evaluate the safety, tolerability, and efficacy of engineered donor grafts ("OrcaGraft"/"Orca-Q") in participants undergoing allogeneic hematopoietic cell transplant (alloHCT) transplantation for hematologic malignancies.

Key Inclusion Criteria:

1. Age at the time of enrollment:

   1. For MAC with fully matched donor (Arm A with 8/8 donor and Arm C) and NMA/RIC: Age ≥ 12 and ≤ 78 years
   2. For MAC with mismatched donors (Arm A with 7/8 donor and Arm B): Age ≥ 12 and ≤ 65 years

2. Diagnosed acute myeloid, lymphoblastic or mixed phenotype leukemia, or high or very high risk myelodysplastic syndrome (MDS) either in complete remission (CR) or with ≤ 10 percent of blast cells in bone marrow (BM)

3. Indicated for allogeneic hematopoietic stem cell transplant (alloHCT)

4. Matched to a 8/8 or 7/8 related or unrelated donor, or to a related haploidentical donor

5. Estimated glomerular filtration rate (eGFR) > 50 mL/minute (MAC with tacrolimus) or > 30 mL/minute (NMA/RIC or MAC without tacrolimus)

6. Cardiac parameters: Cardiac ejection fraction ≥ 45 percent (MAC) or ≥ 40 percent (NMA/RIC)

7. Diffusing capacity of the lung for carbon monoxide (DLCO) (adjusted for hemoglobin) ≥ 50 percent for MAC or ≥ 40 percent for NMA/RIC

8. Liver function: Total bilirubin < 1.5 times upper limit of normal (ULN) (MAC) or < 3 times ULN (NMA/RIC); alanine transaminase (ALT)/aspartate transaminase (AST) < 3 times ULN (MAC) or < 5 times ULN (NMA/RIC)

9. Participants enrolling on NMA/RIC-alloHCT arms must be deemed unfit for a myeloablative alloHCT per assessment of the principal investigator (PI)

Key Exclusion Criteria:

1. Prior alloHCT
2. Currently receiving corticosteroids or other immunosuppressive therapy except for approved disease-specific therapy for the patient's underlying hematologic malignancy. Topical corticosteroids or oral systemic corticosteroid doses less than or equal to 10 mg/day are allowed
3. Planned donor lymphocyte infusion (DLI)
4. Planned pharmaceutical in vivo or ex vivo T cell depletion, e.g., post-transplant cyclophosphamide (Cy) or alemtuzumab
5. Positive anti-donor HLA antibodies against a mismatched allele in the selected donor
6. Low performance score: For MAC: Karnofsky Performance Score (KPS) < 70 percent, For NMA/RIC: <60 percent
7. High HCT-specific Comorbidity Index (HCT-CI): For MAC > 4, For NMA/RIC >6
8. Uncontrolled bacterial, viral or fungal infections (currently taking antimicrobial therapy and with progression or no clinical improvement) at time of enrollment
9. Seropositive for human immunodeficiency virus (HIV)-1 or -2, human T-lymphotropic virus (HTLV)-1 or -2 or Hepatitis B surface antigen (HbsAg) or anti-Hepatitis C virus (HCV) antibody (Ab)
10. Any uncontrolled autoimmune disease requiring active immunosuppressive treatment
11. Concurrent malignancies or active disease within 1 year, except non-melanoma skin cancers that have been curatively resected. Patients with concurrent indolent hematologic malignancies that do not require active treatment and are under active surveillance only (such as CLL, low-grade lymphomas, smoldering MM, MZL) may be included with the approval of Medical Monitor
12. History of idiopathic or secondary myelofibrosis
13. Women who are pregnant or breastfeeding