Graft-Versus-Leukemia Effect after Haplo-Identical Stem Cell Transplantation with Post-Transplant Cyclophosphamide in Patients with AML- No Association with Graft-Versus-Host Disease (GVHD): A Study on Behalf of the Acute Leukemia Working Party of EBMT.

Introduction Allogeneic stem-cell transplantation (SCT) is curative therapy in AML by providing intensive chemotherapy and enhancing a graft-versus-leukemia (GVL) effect. The GVL effect is usually closely associated with GVHD. The use of haploidentical SCT (haploSCT) is rapidly increasing due to the introduction of non-T depleted methods, in particular with post-transplant cyclophosphamide (PTCy), with similar outcomes as following other donor sources. There is no data whether GVL after haploSCT is associated with GVHD as in matched donor SCT. Methods We assessed the impact of acute and chronic GVHD on SCT outcomes following non-T depleted haploSCT with PTCy, by using a series of landmark analyses. Results The study included 605 patients with AML in CR1 (73%) or CR2 (27%) after haploSCT with PTCy, given during the years 2009-2016. The median age was 53 years (18-76). The overall rate of acute GVHD grade II-IV and III-IV was 28.4% and 8.0%, respectively. The rates of chronic GVHD all grades and extensive were 32.7% and 12.3%, respectively. The 2-year leukemia-free survival (LFS) was 59.9%. 509 patients were alive and leukemia-free 100 days after SCT; 366 had no prior acute GVHD at this landmark, 107 had acute GVHD grade II and 36 had grade III-IV. The subsequent relapse rate was 20.3%, 18.3% and 11.9%, respectively (P=0.60). The subsequent non-relapse mortality (NRM) rate was 10.3%, 19.0% and 35.7%, respectively (P Conclusions Acute and chronic GVHD of any grade were not associated with subsequent relapse. Acute GVHD grade III-IV and extensive chronic GVHD were associated with higher NRM and lower LFS. GVL is thus not closely associated with GVHD after non T-depleted haploSCT with PTCy. Future novel strategies for prevention of significant GVHD are warranted.