Inclusion Criteria:  Have undergone first allogeneic hematopoietic stem cell transplantation (allo-HSCT) from any donor source using bone marrow, peripheral blood stem cells, or cord blood for hematologic malignancies. Recipients of nonmyeloablative and myeloablative conditioning regimens are eligible. Clinically suspected Grades II to IV acute GVHD according to NCCN guidelines 2020 V2.0, occurring after allo-HSCT with any conditioning regimen and any anti-GVHD prophylactic program. Subjects with steroid-refractory acute GVHD, defined as any of the following:  Subjects with progressive GVHD (ie, increase in stage in any organ system or any new organ involvement) after 3-5 days of primary treatment with methylprednisolone ≥ 2 mg/kg per day (or equivalent) ± Calcineurin inhibitors（CNI）；Subjects with GVHD that has not improved (ie, decrease in stage in at least 1 involved organ system) after 5-7 days of primary treatment with methylprednisolone ≥ 2 mg/kg per day (or equivalent) ± Calcineurin inhibitors（CNI）；Subjects who Corticosteroid dependence（ie, begin corticosteroids at 2.0 mg/kg per day, demonstrate response, but progress before decrease from the initial starting dose of corticosteroids is achieved）.  ECOG: 0-2； Life expectancy > 4 weeks； Ability for oral drug intake； Willingness to comply with all study visits and procedures.  Exclusion Criteria:  Has received more than 2 allo-HSCT. Acute GvHD occurring after non-scheduled donor leukocyte infusion (DLI) administered. Has received more than 1 systemic treatment in addition to corticosteroids for acute GVHD. Presence of an active uncontrolled infection. Serum creatinine > 1.5 ULN or creatinine clearance < 30 mL/min calculated by Cockroft-Gault equation. Known allergies, hypersensitivity, or intolerance to any of the study medications, excipients, or similar compounds.