Favorable Effects of Low-Dose Anti-Thymocyte Globulin in a Partially-Mismatched HLA Group in an Unrelated Allogeneic Stem Cell Transplantation Setting

Background: The outcomes of unrelated stem cell transplantation (SCT) have improved with the use of anti-thymocyte globulin (ATG) to prevent graft-versus-host disease (GVHD) and graft rejection. Therefore, based on the HLA matching status classifications of well-matched (WM), partially-matched (PM), and mismatched (MM), the current study evaluated the role of ATG use among these 3 HLA groups in an unrelated SCT setting. Material/Methods: Data from a total of 92 patients who received allogeneic SCT from unrelated donors (65 peripheral blood and 27 bone marrow) were retrospectively analyzed. Results: Among the 92 patients, 19 were classified as WM, 42 as PM, and 31 as MM. Fifty-seven patients (61.9%) received ATG as GVHD prophylaxis. The overall survival (OS) rate was higher for the WM group (83%) when compared to the PM group (54%) and MM group (34%, p=0.076). For the PM group, the OS was significantly improved with ATG (83.3% vs. 38.6%, p=0.018). However, there was no difference in OS with or without ATG for the MM group (32.4% vs. 41.7%, p=0.215). The use of ATG lowered the cumulative incidence of grade 3-4 acute GVHD (10% vs. 40.2%, p=0.068) and severe chronic GVHD (21.2% vs. 52.2%, p=0.037). Conclusions: Use of ATG effectively improved the survival rate for the PM group in an unrelated SCT setting. However, this report has a major limitation in confirming the role of ATG for unrelated transplantation because the number of patients in each group was too small to compare therapy with ATG and without ATG, and a heterogeneous population was included in the current study. A larger study comparing different doses of ATG for unrelated PBSCT in a homogenous population will be needed to confirm the role of ATG.