Efprezimod Alfa (CD24Fc, MK-7110) for the Prevention of Acute Graft Versus Host Disease (GVHD) Following Myeloablative Hematopoietic Stem Cell Transplantation (HSCT) (MK-7110-005)

1. A prospective participant for allogeneic HCT for a malignant hematologic disorder.

2. The donor and recipient must have a human leukocyte antigen (HLA)-8/8 allelic match at the HLA-A, -B, -C, and - DRB1 loci. High-resolution typing is required for all alleles for unmatched donors. Only matched unrelated donors are acceptable for this trial.

3. The following diagnoses are to be included:

1. Acute Myeloid Leukemia (AML) or Acute Lymphoblastic Leukemia (ALL) in first or second remission. Remission is defined as the absence of blasts in the peripheral circulation at the time of enrollment, \< 5% blasts in the bone marrow and absence of extramedullary disease including CNS involvement.

2. Myelodysplastic syndrome (MDS) with intermediate or high-risk International Prognostic Scoring System (IPSS) or equivalent Revised International Prognostic Scoring System (IPSS-R) score with \< 10% blasts in the bone marrow.

4. Males or non-pregnant, non-lactating females, ≥ 18 years of age. Note there is no defined upper age limited, so long as deemed appropriate candidate for myeloablative conditioning.

5. Karnofsky Performance Status \>70%.

6. Participants must have normal or near normal organ function as defined by their treating institutions bone marrow transplant (BMT) program clinical practice guidelines. In addition, for purposes of this protocol minimum organ function criteria within 30 days of beginning conditioning include: Eligibility According to Pre HCT Organ Function:

1. Total bilirubin ≤2.5 mg% (unless from Gilbert's disease or disease-related);

2. Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase (SGOT))/ alanine aminotransferase (ALT) (serum glutamic-pyruvic transaminase (SGPT)) \<5.0 X institutional upper limit of normal;

3. Estimated or actual glomerular filtration rate (GFR)\>50 mL/min/1.73 m2 for participants with creatinine levels above institutional normal (GFR should be corrected for BSA);

4. Pulmonary Function Tests include diffusing capacity of the lungs for carbon monoxide (DLCO), forced expiratory volume in one second (FEV1), forced vital capacity (FVC)\> 50% DLCO should be corrected for hemoglobin;

5. Ejection Fraction \>50%;

6. Hematopoietic Cell Transplantation-Specific Comorbidity Index (HCT-CI) ≤ 5.

Item d and e may be assessed up to 10 weeks prior to the start of conditioning therapy.

7. Ability to understand and the willingness to sign a written informed consent document.

8. Women of child bearing potential and men must agree to use contraception prior to study entry and through day 100 post HCT (hormonal or barrier method of birth control; abstinence). Should a woman become pregnant or suspect she is pregnant while she or her partner is on treatment in this study, she should inform her study physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study until day 100 post HCT.

What this study is about