Graft-versus-host disease (GVHD) is a major factor affecting the efficacy and quality of life of alternative donor transplantation in thalassemia major (TM), severely limiting the clinical application of alternative donor transplantation in TM.The purpose of this clinical trial is to evaluate whether recombinant humanized anti-CD25 monoclonal antibody is effective in preventing GVHD and its safety after haploidentical/matched unrelated donor hematopoietic stem cell transplantation. The main questions it aims to answer are:

• Does recombinant humanized anti-CD25 monoclonal antibody reduce the incidence of GVHD disease after haploidentical/matched unrelated donor hematopoietic stem cell transplantation?
• What medical problems will participants experience when using the recombinant humanized anti-CD25 monoclonal antibody? What is the quality of life after 2 years follow-up? In this clinical trail, participants will be randomly assigned to the intervention group or the control group by researchers in a 2:1 ratio. The intervention group will be given recombinant humanized anti-CD25 monoclonal antibody (1mg/Kg) combined with the standard GVHD prophylaxis after transplantation, while the control group will only receive the standard GVHD prophylaxis. The incidence of GVHD after transplantation in the two groups will be observed. The main evaluation is the clinical efficacy of recombinant humanized anti-CD25 monoclonal antibody in preventing aGVHD.

Inclusion Criteria:

• patients with transfusion-dependent thalassemia;
• patients who are planning to receive matched unrelated donor hematopoietic stem cell transplantation (MUD-HSCT) or HLA haploidentical donor hematopoietic stem cell transplantation (HID-HSCT);
• physical condition score (Lansky/Karnofsky score) ≥ 70%;
• patients (or legal guardians) voluntarily participate in the study and sign the informed consent form

Exclusion Criteria:

• patients with HLA-matched hematopoietic stem cell donors and willing to receive HLA-matched hematopoietic stem cell transplantation;
• patients with known infectious diseases such as hepatitis B, hepatitis C, AIDS, syphilis, human T-lymphotropic virus, etc.;
• patients with serious active bacterial, viral, fungal, malaria or parasitic infections;
• patients with autoimmune deficiency diseases;
• patients with a history of malignant tumors or current malignant tumors;
• patients with important organ diseases or abnormal laboratory tests, including but not limited to: 1) patients with cirrhosis, liver fibrosis or active hepatitis, and/or abnormal liver function tests (alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≥2.5×ULN; alkaline phosphatase ≥2.5×ULN); 2) patients with heart disease, or left ventricular ejection fraction (LVEF) <60%, or severe iron deposition in the heart; 3) kidney disease, or blood creatinine ≥1.5×ULN with creatinine clearance <30% of normal level; 4) patients with endocrine dysfunction;
• patients with uncorrected bleeding disease;
• patients with severe mental illness (such as severe depression, schizophrenia, etc.) or cognitive dysfunction (dementia, delirium, etc.), which are unable to cooperate with the study;
• peripheral blood white blood cell (WBC) count <3×10^9/L or platelet count <100×10^9/L;
• patients having received thalidomide treatment within the past 3 months;
• patients having received any type of gene and/or cell therapy in the past;
• patients with severe allergies;
• female patients who are pregnant, breastfeeding, or planning to become pregnant within 1 year of participating in this trial;
• patients who are participating in other clinical trials;
• other situations that are not suitable for participation in this clinical trial as assessed by the investigator.

The researchers and the subjects wil aware of the grouping and the intervention they received. However, this trail will implement a blind method for the outcomes assessors, who objectively evaluated the outcome indicators without knowing the grouping of the subjects.