Optimizing conditioning regimen with low-dose irradiation or busulfan enables the outcome of transplantation from a 6–7/8 HLA-matched donor comparable to that from an 8/8 HLA-matched unrelated donor in severe aplastic anemia patients under 40 years

With the dramatic improvements in outcomes following alternative donor hematopoietic stem cell transplantation (HSCT), interest in the use of alternative donors in severe aplastic anemia (SAA) is increasing. We conducted a multicenter prospective study to explore the efficiency and safety of upfront HSCT from a 6–8/8 HLA-matched unrelated donor (MUD) or 6–7/8 HLA-matched related donor (MRD) in acquired SAA patients under 40 years. Between August 2014 and July 2017, 115 patients were enrolled, including 48 (41.7%) patients receiving grafts from an 8/8 MUD, 25 (21.7%) from a 6–7/8 MRD, and 42 (36.5%) from a 6–7/8 MUD. The incidence of grade II–IV acute graft-versus-host disease (GVHD) was higher in the 6–7/8 MUD group than in the 8/8 MUD group (42.9% vs. 12.8%, P =0.001). The corresponding incidence in the 6–7/8 MRD group was comparable to that in the 8/8 MUD group (21.7% vs. 12.8%, P =0.332). There was no significant difference in the incidence of chronic GVHD (24.3%, 13.6%, and 17.9%, P =0.676), graft failure (2.4%, 8.0%, and 6.3%, P =0.551), overall survival (85.7%, 96.0%, and 87.5%, P =0.424), and failure-free survival (83.3%, 88.0%, and 83.3%, P =0.885) among the three groups (6–7/8 MUD, 6–7/8 MRD, and 8/8 MUD). In multivariate analysis, conditioning regimen without low-dose irradiation or busulfan was associated with an inferior failure-free survival (HR=2.973, P =0.042). In conclusion, after an intensified conditioning regimen with additional low-dose irradiation or busulfan, the outcome of HSCT from a 6–7/8 MRD or 6–7/8 MUD is comparable to that from an 8/8 MUD.