This trial employs a single-arm, single-center design, planning to enroll 25 patients diagnosed with grade II-IV aGVHD at one center. Patients meeting all inclusion criteria and no exclusion criteria will be enrolled. After enrollment, all patients will receive Gecacitinib combined with methylprednisolone sodium succinate for at least 28 days.
After 28 days of Gecacitinib treatment, patients evaluated by the investigator as achieving Complete Response (CR) or Partial Response (PR) may continue study treatment for up to 24 weeks. If patients experience intolerance, disease progression, or require new systemic therapy, treatment will be adjusted.