An open-label, randomized, controlled clinical trial to explore the efficacy and safety of iMSC in preventing the development of acute graft-versus-host disease of degree III-IV in patients after allogeneic hematopoietic stem cell transplantation.

This is an open-label, randomized, controlled study, enrolled subjects(patients at risk for aGVHD of degree III-IV after allogeneic hematopoietic stem cell transplantation) will be 1:1 randomized to experimental group or control group. Control group will receive conventional aGVHD prophylaxis and the experimental group will receive iMSC injection plus conventional aGVHD prophylaxis, with 28 cases in each group, for a total of 56 subjects.

Inclusion Criteria:

• Subjects with malignant or nonmalignant hematologic diseases 7-21 days after allogeneic hematopoietic stem cell transplantation;
• No gender restrictions and age between 14-70 years old；
• Patients received aGVHD prophylaxis regimen of a calcium-modulated phosphatase inhibitor combined with mycophenolate mofetil wtih or without short-course methotrexate and rabbit anti-human thymocyte globulin (CNI+MMF± short-course MTX +ATG)；
• Patients had a MAGIC algorithm probability (MAP) score ≥ 0.14 at +7d or +14d after allogeneic hematopoietic stem cell transplantation(HSCT) (if patients had a MAP< 0.14 at +7d, another test was performed at +14d)；
• Estimated survival≥ 24 weeks；
• Eastern Cooperative Oncology Group（ECOG）≤ 2 points and Hematopoietic Cell Transplantation Comorbidity Index (HCT-CI)≤ 3 points；
• Subjects were be treated within 5 days after enrollment；
• Informed consent and willingness to participate in the study.

Exclusion Criteria:

• Serious organ dysfunction such as organ failure after allogeneic HSCT;
• Received more than once HSCT (including autologous transplants);
• Positive for Hepatitis B Surface Antigen (HBsAg) or Hepatitis B Core Antibody (HBcAb) and have Hepatitis B Virus (HBV) DNA titers above the normal range ; positive for Hepatitis C Virus (HCV) antibodies and have positive peripheral blood HCV RNA; positive for Human Immunodeficiency Virus (HIV) antibodies; positive for syphilis;
• Subjects with severe hepatic veno-occlusive disease or sinus veno-occlusive syndrome;
• Primary malignant hematologic disease was not remission;
• Within 6 months prior to enrollment, subjects had other diseases or their physiological conditions may interfere the study results, or had life-threatening complications;
• Those who are suffering mental or neurological illnesses, unable to express will correctly;
• Those with active malignant solid tumors within 5 years prior to participation in this study, with the exception of radically treated cervical cancer, in situ limited prostate cancer, and nonmelanoma skin cancer;
• Subjects known to be potentially allergic or highly sensitized to the cell therapy in the study protocol;
• Have participated or are participating in another clinical trial within one month prior to enrollment;
• Those who are judged by the investigator to be unsuitable for participation in this clinical trial.