Comparing outcomes of a second allogeneic hematopoietic cell transplant using HLA-matched unrelated versus T-cell replete haploidentical donors in relapsed acute lymphoblastic leukemia: a study of the Acute Leukemia Working Party of EBMT.

Optimal donor choice for a second allogeneic hematopoietic cell transplant (allo-HCT) in relapsed acute lymphoblastic leukemia (ALL) remains undefined. We compared outcomes using HLA-matched unrelated donors (MUD) versus haploidentical donors in this population. Primary endpoint was overall survival (OS). The MUD allo-HCT group comprised 104 patients (male = 56, 54%), median age 36 years, mostly (76%) with B-cell phenotype in complete remission (CR) (CR2/CR3 + = 76, 73%). The 61 patients (male = 38, 62%) in the haploidentical group were younger, median age 30 years (p = 0.002), had mostly (79%) a B-cell phenotype and the majority were also in CR at time of the second allo-HCT (CR2/CR3 + = 40, 66%). Peripheral blood stem cells was the most common cell source in both, but a significantly higher number in the haploidentical group received bone marrow cells (26% vs. 4%, p < 0.0001). A haploidentical donor second allo-HCT had a 1.5-fold higher 2-year OS (49% vs. 31%), albeit not statistically significant (p = 0.13). A longer time from first allo-HCT to relapse was associated with improved OS, leukemia-free survival, graft-versus-host disease-free-relapse-free survival, and lower cumulative incidences of relapse and non-relapse mortality. Results suggest no major OS difference when choosing either a MUD or haploidentical donor for ALL patients needing a second allo-HCT.