Comparing the Outcomes of Matched and Mismatched Unrelated Allogeneic Hematopoietic Stem Cell Transplantation with Different Anti-Thymocyte Globulin Formulations: A Retrospective, Double-Centre Experience on Behalf of the Polish Adult Leukemia Group.

Despite notable advancements in immunotherapy in the past decades, allogeneic hematopoietic stem cell transplantation (allo-HCT) remains a promising, potentially curative treatment modality. Only a limited number of studies have performed a direct comparison of two prevalent rabbit anti-thymocyte globulin (r-ATG) formulations-specifically, Thymoglobuline (ATG-T, formerly Genzyme) and Grafalon (ATG-G, formerly Fresenius). The primary objective of our retrospective analysis was to compare the outcomes of adult patients undergoing matched or mismatched unrelated donor (MUD/MMUD) allo-HCT, with a graft-versus-host disease (GvHD) prophylaxis based on either ATG-T or ATG-G. A total of 87 patients who had undergone allo-HCT between 2012 and 2022 were included. We observed no significant differences between ATG-T and ATG-G concerning the occurrence of acute graft-versus-host disease (aGvHD), regardless of its severity. Conversely, chronic graft-versus-host disease (cGvHD) occurred less frequently in the ATG-T group compared to the ATG-G group (7.5% vs. 38.3%, p = 0.001). The negative impact of ATG-G on cGvHD was confirmed by multivariate analysis (HR 8.12, 95% CI 2.06-32.0, p = 0.003). Patients treated with ATG-T manifested a higher incidence of cytomegalovirus (CMV) reactivations (70% vs. 31.9%, p < 0.001), with a shorter time between transplant and CMV (<61 days, 77.8% vs. 33.3%, p = 0.008) and a higher median CMV copy number (1000 vs. 0, p = 0.004). Notably, despite a higher occurrence of CMV reactivations in the ATG-T cohort, most patients were asymptomatic compared to ATG-G (85.7% vs. 43.8%, p = 0.005). By multivariate analysis, only aGvHD had an influence on CMV reactivations (HR 0.18, 95% CI 0.04-0.75, p = 0.019). Finally, we observed no significant differences in terms of 5-year overall survival (OS) and 3-year relapse-free survival (RFS) while comparing ATG-T and ATG-G (32.0% vs. 40.3%, p = 0.423; 66.7% vs. 60.4%, p = 0.544, respectively).