This study aims to compare the incidence of graft-versus-host disease (GVHD) in haploidentical hematopoietic stem cell transplant recipients who receive varying doses of anti-T lymphocyte globulin (ATLG) for GVHD prophylaxis. Our primary objective is to determine the optimal dose of ATLG for preventing acute GVHD (aGVHD). Additionally, we plan to evaluate the impact of different doses of ATLG on post-transplant viral infections and other clinical outcomes.

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only therapeutic option for many hematological malignancies. Haploidentical related donor transplantation is now considered an important allo-HSCT. GVHD prevention has a crucial role in post-transplant outcomes by potentially interfering with the graft-versus-leukemia (GVL) effect and immune reconstitution. In vivo T cell depletion (TCD) modalities, including anti-T lymphocyte globulin (ATLG)-based protocols have been widely used worldwide for GVHD prophylaxis.

Several European studies have shown that a dose of 30mg/kg of ATLG can effectively prevent GVHD with acceptable safety. But, the most commonly reported dose among Chinese population is 20mg/kg. Additionally, the main type of allo-HSCT in China is haploidentical transplantation. The application experience of ATLG in Europe mainly focuses on sibling and unrelated donor transplants. There is still a lack of sufficient exploration on the optimal dose of ATLG in GVHD prevention in haploidentical transplantation.

In this prospective multiple-center randomized trial, we aim to compare the effects of different doses of ATLG on GVHD prevention, risk of viral infection, and patient survival after haploidentical transplantation.

Inclusion Criteria:

• 1，Age ≥ 16 and ≤ 65 years 2, Patients undergoing Haplo-identical hematopoietic stem cell transplantation 3, AML and ALL in complete cytologic response or MDS requiring allogeneic stem cell transplantation 4, ECOG performance status ≤ 2

Exclusion Criteria:

• 1，Pregnant or lactating females 2，Patients who have previously undergone allogeneic hematopoietic stem cell transplantation or organ transplantation 3, Patients with major organ abnormal including renal, liver, lung , heart and/or CNS diseases, where these diseases or others cannot be controlled by treatment and may affect the completion of this study 4, Uncontrolled infection 5, Seropositivity for HIV or HTLV-1 or active hepatitis B or C 6, Patients with any other complications that may affect this study or with a history of malignant diseases.