Low-dose anti-thymocyte globulin combined with low-dose post-transplant cyclophosphamide: a novel approach to prevent graft-versus-host disease in haploidentical stem cell transplantation

Background: In haploidentical hematopoietic stem cell transplantation (haplo-HSCT), combining low-dose post-transplant cyclophosphamide (PTCy) with low-dose anti-thymocyte globulin (ATG) is increasingly recognized as a promising approach for graft-versus-host disease (GVHD) prevention.Methods: This study evaluated 33 patients undergoing haplo-HSCT for hematological disorders, divided into two groups: low-dose ATG/PTCy (n = 17) and PTCy-only (n = 16).Results: The incidence of grades I-II acute GVHD (aGVHD) was 11.8% in the low-dose ATG/PTCy group compared to 31.3% in the PTCy-only group (p = 0.42). No cases of severe aGVHD (grades III-IV) were reported in either cohort. Moderate chronic GVHD (cGVHD) occurred less frequently in the ATG/PTCy group (28.6%) compared to the PTCy group (100%, p = 0.028). Severe cGVHD was absent in both groups. Non-relapse mortality (NRM) was significantly lower in the ATG/PTCy group compared to the PTCy-only group (17.6% vs 56.3%, p = 0.021). One year overall survival and disease-free survival rates were at 70.6% and 64.7% for ATG/PTCy cohort, versus 56.3% and 50.0% for PTCy-only group. Cytomegalovirus reactivation and relapse were comparable between the groups.Conclusion: The combination of low-dose ATG and PTCy appears to significantly reduce moderate cGVHD and NRM in haplo-HSCT compared to PTCy alone. To the best of our knowledge, this is the first study directly comparing these two regimens.