This study aims to compare individualized anti-thymocyte globulin (ATG) dosing versus conventional fixed-dose regimens in unrelated donor peripheral blood stem cell transplantation (URD-PBSCT).

This study notes that URD-HSCT is a key treatment for malignant hematologic diseases and severe bone marrow failure, with rapid expansion in China. However, this study identifies post-transplant CMV infection as a major challenge, adversely affecting survival and quality of life. This study finds that CMV infection compromises immunity and causes multi-organ complications. Given the high costs, long treatment cycles, and limited efficacy of current interventions, this study considers optimizing CMV prevention to be of greater value than expanding treatment options. This study asserts that effective prevention can reduce infection rates and improve overall survival (OS) and long-term prognosis.

This study recognizes that ATG is widely used in URD-HSCT to prevent graft-versus-host disease (GVHD), but its dosage is significantly linked to CMV risk. This study indicates that inadequate ATG exposure increases GVHD risk, while excessive exposure raises viral reactivation (e.g., CMV, EBV) and may cause relapse. This study thus identifies balancing GVHD prevention and infection control as a key clinical goal. This study cites Remberger et al. (2004), who compared ATG doses (4-10 mg/kg) in 162 URD-HSCT patients, finding lower doses increased acute GVHD (aGVHD) and 10 mg/kg raised infection-related mortality, suggesting 6-8 mg/kg as a balanced range. This study also references Bacigalupo et al. (2001), who found no survival differences across doses but noted higher doses reduced severe aGVHD at the cost of increased infection. Therefore, this study concludes that optimal ATG dosing requires balancing GVHD, infection, and relapse.

This study acknowledges that ATG pharmacokinetics (PK) are complex, influenced by dose, body weight, and absolute lymphocyte count (ALC). This study points out that even with fixed dosing, internal exposure (active ATG-AUC) varies greatly among individuals, indicating that fixed dosing is suboptimal and individualized strategies are needed. This study notes that Admiraal et al. developed an ALC-based individualized ATG model, improving immune reconstitution, reducing viral infections, and enhancing OS. However, this study observes that this model was designed for non-myeloablative conditioning and is not applicable to myeloablative conditioning (MAC), which is standard in China.

To address this, this study states that our team initiated ATG PK studies in 2019. This study explains that under MAC, ALC is nearly eliminated, making traditional models unsuitable. By monitoring active ATG-AUC in 106 haploidentical HSCT (haplo-HSCT) patients and using machine learning, this study identified an optimal exposure window of 100-148.5 UE·day/mL. This study found that patients within this window had lower CMV/EBV reactivation without increased GVHD. This study developed a protocol adjusting doses on days -3 and -2 based on ATG concentrations measured on days -5 and -4. This study confirmed through a prospective single-arm study in haplo-HSCT that this regimen reduces CMV/EBV infection and improves disease-free survival (DFS) and OS while maintaining GVHD control.

Given the consistency between URD-PBSCT and haplo-PBSCT in conditioning, GVHD prophylaxis, and CMV prevention-and that CMV infection rates in Chinese URD-PBSCT patients reach 65%-70%-this study extends the individualized ATG protocol to URD-PBSCT to validate its universality across donor sources.

In summary, building on prior haploidentical transplant research, this study applies individualized ATG dosing to URD-PBSCT. This study aims to precisely regulate ATG exposure to reduce CMV infection while maintaining GVHD prophylaxis. This study seeks to improve patient survival and outcomes, laying the foundation for a population PK model and advancing HSCT toward precision medicine.

Inclusion Criteria:

1. Patients with indications for allogeneic hematopoietic stem cell transplantation, with malignant hematologic diseases in CR1 or CR2 before transplantation.
2. Have an HLA-matched sibling, unrelated, or haploidentical donor.
3. Age ≥ 14 years and ≤ 65 years.
4. Liver function: ALT and AST ≤ 2.5 × upper limit of normal, bilirubin ≤ 2 × upper limit of normal.
5. Renal function: creatinine ≤ upper limit of normal.
6. No uncontrolled infection or severe mental or psychological disorders.
7. ECOG performance status score of 0-2.
8. Signed informed consent.

Exclusion Criteria:

- 1.No HLA-matched donor. 2.Malignant hematologic disease in CR3 or higher disease stage, or refractory/relapsed status.

3.Patient age < 14 years or > 65 years. 4.Pregnancy of either the donor or the recipient. 5.Presence of mental illness or other conditions that preclude compliance with the protocol.