Mixed chimaerism is associated with poorer long-term failure-free survival among aplastic anaemia patients receiving HLA-matched donor transplantation

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The aim of this study was to evaluate the adverse effects of mixed chimaerism (MC) on survival outcomes and to assess the ability of different factors to predict MC in severe aplastic anaemia (SAA) patients after HLA-matched donor transplantation. A retrospective study was conducted in 103 consecutive SAA patients who received matched related (MRD) or unrelated donor (MUD) transplantation. The cumulative incidences of mixed chimaerism were 17.8 ± 0.2% and 25.0 ± 0.8% in the MRD and MUD cohorts, respectively ( P = 0.432). Patients with mixed chimaerism had significantly poorer 10-year failure-free survival (FFS) than those with donor chimaerism (35.0% vs. 87.0%, P < 0.001). A multivariable model identified independent adverse predictors of mixed chimaerism, including patient age and ferritin level at transplantation. The incidences of mixed chimaerism were 62.5%, 30.8% and 5.4% in the high- (2 factors), intermediate- (1 factor) and low-risk (0 factor) groups, respectively ( P < 0.001). The corresponding FFS rates were 37.5%, 75.3% and 83.6%, respectively ( P = 0.018), at the final follow-up. Therefore, patients with mixed chimaerism suffered poorer long-term FFS, and patients with high-risk scores will be more likely to develop mixed chimaerism. Thus, more intensive conditioning might be recommended for these high-risk patients.