Donor type and post-transplant outcomes in anti-thymocyte globulin based allogeneic transplantation for myelodysplastic syndromes

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only curative treatment for myelodysplastic neoplasms (MDS). While matched sibling donors (MSD) have traditionally been preferred, the impact of donor type on transplant outcomes under anti-thymocyte globulin (ATG)-based graft-versus-host disease (GVHD) prophylaxis remains unclear. We analyzed 391 adult MDS patients receiving allo-HSCT with fludarabine–busulfan conditioning and ATG between 2009 and 2019. Donors included MSD (n = 155), unrelated donors (UD; n = 134), and haploidentical donors (HID; n = 102). At a median follow-up of 108 months, the 5-year overall survival (OS) and relapse-free survival (RFS) rates were 63.0% and 58.4%. While OS and non-relapse mortality (NRM) did not significantly differ by donor type, MSD recipients had a higher cumulative incidence of relapse compared to UD and HID recipients (34.3% vs. 16.4% and 16.8% at 5 years, p < 0.001), with a trend toward inferior RFS. In multivariate analysis, MSD was independently associated with increased relapse risk and a lower incidence of GVHD, which may reflect a reduced graft-versus-leukemia effect. In this single-center large cohort, MSD transplants were associated with higher relapse risk compared with alternative donors under ATG-based prophylaxis.