A Study of Jaktinib for the Treatment of Steroid-Refractory Acute Graft-Versus-Host Disease.

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 Cockcroft-Gault equation. * Known allergies, hypersensitivity, or intolerance to any of the study medications, excipients, or similar compounds.