Should Anti-thymocyte Globulin be Added in Post-transplant Cyclophosphamide Based Matched Unrelated Donor Peripheral Blood Stem Cell Transplantation for Acute Myeloid Leukemia? A Study on Behalf of the Acute Leukemia Working Party of the EBMT

Abstract

Background: Post-transplant cyclophosphamide (PTCY) is increasingly used for allogeneic peripheral blood stem cell transplantation (allo-PBSCT) from an HLA-matched unrelated donor (MUD) as an alternative to the standard anti-thymocyte globulin (ATG) graft-versus-host disease (GvHD) prophylaxis. Following the demonstration that the use of PBSC haploidentical grafts results in more GvHD than bone marrow grafts, groups have attempted to reduce GvHD in haploidentical-PBSCT by adding ATG to PTCY. The experience of combined PTCY+ATG in the MUD allo-PBSCT is minimal and whether ATG brings any added value when PTCY is used in this setting is still unclear. Methods: In this registry-based study, we compared outcomes of 421 patients with PTCY and 151 patients with PTCY+ATG who underwent a first MUD allo-PBSCT for acute myeloid leukemia (AML) in complete remission. Results: Characteristics of PTCY and PTCY+ATG patients were well balanced, including the number of additional immunosuppressive drugs, with the only significant difference between the two cohorts being the median year of transplant, and the follow-up period (19.6 versus 31.1 months, respectively, p<0.0001). Engraftment failure was low in both groups. Overall, two-year survival was 69.9% vs 67.1% in PTCY and PTCY+ATG, respectively, with deaths related to relapse (39% vs 43.5%), infection (21.9% vs 23.9%) or GvHD (17.1% vs 17.4%) not differing between groups. On univariate comparison, a significantly lower rate of extensive chronic GvHD was found when ATG was added (9.9% vs 21%, p=0.029), a finding which was not confirmed in the multivariate analysis. The Cox proportional-hazards model showed no difference between PTCY+ATG and PTCY alone with respect to acute and chronic GvHD of all grades. In univariate and multivariate analyses, no statistical differences were observed for non-relapse mortality, relapse, leukemia-free survival, overall survival, and GvHD-free, relapse-free survival between study cohorts. Conclusions: To date, the question of the best combination of GvHD-preventing drugs in the MUD-PBSCT setting remains unanswered. Our results highlight that in PTCY-based MUD-PBSCT for AML, the addition of ATG does not provide any extra benefit in terms of further GvHD reduction, better GRFS or better survival.