Outcomes of Haploidentical Transplants with PT-CY versus 10/10 MUD Transplants with ATG in Germany

• 5-year OS and DFS were significantly lower in PT-CY Haplo transplantation compared to 10/10 MUD transplantation with ATG in a German cohort

• 10/10 MUD transplantation with ATG provides higher GRFS, lower aGVHD, cGVHD and NRM than PT-CY Haplo in a German cohort

Allogeneic stem cell transplantation (alloHSCT) is the best curative treatment modality for many malignant haematological disorders. In the absence of a matched related donor (MRD), matched unrelated donors (MUD) and haploidentical donors (Haplo-Tx) are the most important sources of stem cells. However, multicenter real-life data which compare 10/10 MUD transplantations with Haplo-Tx is still limited. In this registry based retrospective study, we compared the outcomes of alloHSCTs from 10/10 MUD with anti-thymocyte globulin (ATG) based regimens (n=7050) versus Haplo-Tx using post-transplant cyclophosphamide (PT-CY Haplo) (n=487) in adult patients with haematological malignancies between 2010 and 2020. Cox proportional hazard models and competing risks regression models were formed to compare the outcomes of the groups. OS, DFS and GRFS were superior for 10/10 MUD (OS: HR 1.27, CI 1.10- 1.47, p=0.001, DFS: HR 1.17, CI 1.02-1.34, p=0.022, GRFS: HR 1.34, CI 1.19-1.50, p<0.001). Risk for aGVHD grade II-IV, aGVHD grade III-IV and cGVHD was higher in the PT-CY Haplo group compared to the 10/10 MUD group (aGVHD grade II-IV: HR 1.46, CI 1.25- 1.71, p<0.001; aGVHD grade III-IV: HR 1.74, CI 1.37- 2.20, p<0.001 and cGVHD: HR 1.30, CI 1.11-1.51, p=0.001). A lower incidence of relapse was observed in the PT-CY Haplo group (relapse: HR 0.83, CI 0.69-0.99, p=0.038). Unrelated 10/10 matched transplantation with ATG treatment leads to lower GvHD rates and improved survival rates when compared to PT-CY Haplo transplantation in Germany.