Safety and Clinical Activity of Itolizumab in aGVHD

Inclusion Criteria: * Male or female subject at least 18 years of age. * Has received allogeneic hematopoietic stem cell transplantation (allo-HSCT). * Clinical diagnosis of Grade II-IV aGVHD per MAGIC guideline requiring systemic immune suppressive therapy. * Initiation of systemic steroids therapy ≤ 72 hours. * Negative result of serum HCG within 72 hours before enrollment for female with potential fertility. * Have a life expectancy of 10 weeks or more. * Able to understand and comply with the planned procedure as required by the protocol, and sign a written informed consent form (ICF). Exclusion Criteria: * Has received more than 1 allo-HSCT. * Presence of morphologic relapsed primary malignancy, treatment for relapse after alloHSCT was performed, or requirement for rapid immunosuppressive treatment withdrawal for early malignancy relapse. * Evidence of graft failure based on cytopenia(s), and as determined by the investigator. * Evidence of post-transplant lymphoproliferative disease. * Any prior therapy for acute GVHD, except for alloHSCT prophylaxis regimens or systemically administered corticosteroids. * aGVHD induced by donor lymphocyte infusion(DLI). * Clinically or suspected diagnosed of cGVHD or overlap syndrome. * Unresolved toxicity or complications due to allo-HSCT,other than aGVHD. * Any clinical or laboratory abnormalities that is likely to negatively affect the reliability of the study safety data, as determined by the investigator. * Presence of any uncontrolled active infections, which was defined as hemodynamic instability due to sepsis or worsening of new symptoms, signs, or imaging findings due to infection. * Presence of any uncontrolled and active infections. * Presence of active and uncontrolled viral infections at screening. * History of active tuberculosis within 6 months prior to screening or negative result of interferon-gamma release assay at screening. * History of class III or IV congestive heart failure per New York Heart Association, clinically significant or uncontrolled unstable angina or myocardial infarction, cerebrovascular accident, or pulmonary embolism within 6 months prior to screening. * Severe impaired renal function at screening (serum creatinine \> 1.5 ULN or creatinine clearance \< 30mL/min). * Presence of persistent bilirubin abnormalities induced by hepatic sinusoidal obstruction, hepatic veno-occlusive disease, non-GVHD or progressive organ dysfunction at screening. * Serum ALT and AST \> 4 ULN at screening. * Absolute lymphocyte count \< 0.5×109/L at screening. * Any major surgical procedures performed within 4 weeks prior to screening, that is likely to negatively affect the evaluation of the study safety data, as determined by the investigator. * Any malignant tumor other than the transplanted tumor within 5 years before screening. * Suspected allergic to the experimental drug product or any of its excipients. * Currently pregnant, breastfeeding,or planning to become pregnant or not using reliable method to avoid pregnancy during study and within 3 months after the last study treatment. * As determined by the investigator, any medical, psychiatric, or other condition or circumstance that is likely to negatively affect the reliability of the study data.