Inclusion Criteria:
1. Male or female ages ≥18 and ≤ 65 years.
2. Before the start of the trial, the subject or his/her guardian is sufficient to understand and voluntarily sign the written informed consent form (ICF).
3. Subjects have a hematologic malignancy as defined below and are considered candidates for haplo-SCT:
1. Acute leukemia with morphologic complete remission (acute myelogenous leukemia \[AML\] or acute lymphoblastic leukemia \[ALL\]);
2. Myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia (CMML), or myeloproliferative neoplasm (MPN) with \< 10% blasts in the bone marrow.
4. Organ function tolerated for transplantation:
1. Cardiac function: Left ventricular ejection fraction at rest ≥ 45%;
2. Liver function: Total bilirubin \< 1.5 × upper limit of normal (ULN); alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \< 2.5 × ULN. Subjects who have been diagnosed with Gilbert's syndrome or malignant disease involvement are allowed to have a total bilirubin value \> 1.5 × ULN;
3. Serum creatine \< 2 mg/dL or estimated creatinine clearance \> 50 mL/min calculated using the Cockcroft-Gault equation；
4. Pulmonary function tests (PFTs): diffusing capacity of the lung for carbon monoxide (DLCO) (corrected for hemoglobin) and/or forced expiratory volume in 1 second (FEV1) ≥ 50%.
5. Subject is suitable for myeloablative haplotype related donor transplant.
6. Subject is suitable for receiving first alloHSCT.
7. The transplant donor must meet the following criteria:
1. Donor ages \> 30 years; If the donor ages is equal to or less than 30 years, the donor should be female for male subject;
2. High-resolution typing of human leukocyte antigen (HLA)-A, -B, -C, DR, and DQ are matched at least 5/10;
3. Meet the criteria for peripheral blood stem cell (PBSC) donation;
4. Donor's specific antibodies are negative, \<2,000 MFI.
8. Source of allografts: using G-CSF as the mobilizing agent to mobilize PBSC transplant; bone marrow or cord blood is not allowed.
9. Karnofsky Performance Status (KPS) score ≥ 60 points.
10. Is a Candidate for anti-GvHD prophylaxis, including ATG, calcineurin inhibitor (CsA or tacrolimus \[FK 506\]) in combination with MTX and MMF.
11. Female subjects of childbearing potential must have a negative serum pregnancy test prior to enrollment and must have agreed to use a double barrier method of contraception from the time of signing the ICF to 90 days after the last dose of investigational drug.
12. Male subjects must agree to use effective contraception from the time of signing the ICF to 90 days after the last dose of investigational drug.
Exclusion Criteria:
Any subjects who meet any of the following criteria will be excluded from study entry:
1. Has had any other prior organ transplantation.
2. Planned use of any additional or alternative drugs for GvHD prophylaxis than listed in the inclusion criteria.
3. Has had received an investigational drug within 4 half-lives or within 14 days prior to HSCT, whichever is longer; or plans to participate in another clinical study prior to completion of all scheduled evaluations in this clinical study.
4. Has other malignancies that are not controlled.
5. Has evidence of active central nervous system (CNS) disease.
6. Patients with uncontrolled active bacterial, viral, or fungal infections.
7. Known history of human immunodeficiency virus (HIV) or positive HIV antibody test.
8. Hepatitis B virus surface antigen (HBsAg) or hepatitis B virus core antibody (HBcAb) is positive, and the hepatitis B virus (HBV) DNA in peripheral blood is above the limit of quantification; or hepatitis C virus (HCV) antibody and peripheral HCV RNA are positive; or the syphilis TRUST test is positive.
9. Pregnant or lactating females.
10. Has undergone major surgery within 1 month prior to the first dose of investigational drug.
11. In the opinion of the investigator, the subject has any other medical condition that renders the subject unsuitable for participation in the study.
12. Has a history of uncontrolled autoimmune disease or on active treatment.
13. Vaccinated with live or attenuated vaccine within 4 weeks prior to the first dose of investigational drug.
14. History of myocardial infarction, unstable angina, acute coronary syndrome, congestive heart failure (New York Heart Society classification ≥ class Ⅲ), or clinically significant arrhythmia within 6 months prior to receiving the investigational drug.
15. Plan to use prophylaxis donor lymphocyte infusion (DLI) therapy.
16. The transplant donor is the subject's mother or collateral relative.
