Impact of anti-thymocyte globulin on results of allogeneic peripheral blood stem cell transplantation for patients with Philadelphia-positive acute lymphoblastic leukaemia: An analysis by the Acute Leukemia Working Party of the EBMT

Background:Anti-thymocyte globulin (ATG) is widely used to prevent graft-versus-host disease (GVHD) after allogeneic peripheral blood stem cell transplantation (al-loPBSCT). The goal of this study was to retrospectively assess the effect of ATG on outcomesin the setting of Philadelphia chromosome-positive acute lymphoblastic leukaemia(PhþALL).Methods:In the analysis, 1170 adult patients undergoing alloPBSCT from human leucocyteantigenematched sibling or unrelated donors in the first complete remission between 2007and 2016 were included. ATG was used in 429/575 (75%) and 121/595 (20%) patients trans-planted from unrelated or sibling donors, respectively.Results:The incidence of chronic GVHD was 35% for patients treated with ATG comparedwith 52% in those not receiving ATG (p<0.001), while the rate of extensive chronic GVHDwas 16% and 36%, respectively (p<0.001). The probability of survival free from GVHD andrelapse (GRFS) was 42% and 32%, respectively (pZ0.002). In a multivariate model, the useof ATG was associated with reduced riskof overall chronic GVHD (hazard ratio[HR]Z0.52,p<0.001) and extensive chronic GVHD (HRZ0.46,p<0.001). It was alsoassociated with better GRFS (HRZ0.77,pZ0.007), despite increased risk of relapse(HRZ1.41,pZ0.02). No significant effect was found with regard to the risk of non-relapse mortality and overall mortality.Conclusions:The use of ATG for patients with PhþALL undergoing alloPBSCT is associatedwithreducedriskofchronicGVHDwithoutimpact on survival and therefore, could beconsidered. However, increased risk of relapse suggests the need for strict monitoring of min-imal residual diseases and appropriate interventions after transplantation.