Impact of MRD on clinical outcomes of unrelated hematopoietic stem cell transplantation in patients with Ph+ ALL: A retrospective nationwide study

Measurable residual disease (MRD) status before transplantation has been shown to be a strong prognostic factor in patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL). However, the outcomes of unrelated hematopoietic stem cell transplantation based on the MRD status have not been fully investigated. In this retrospective study, we compared the outcomes of 715 consecutive adults with Ph+ ALL in complete remission who underwent unrelated cord blood transplantation (UCBT) (single-unit UCBT, n = 232 [4/6, 5/6, and 6/6 HLA match]), HLA-matched unrelated bone marrow transplantation (UBMT; n = 292 [8/8 HLA match]), or HLA-mismatched UBMT (n = 191 [7/8 HLA match]). In the MRD+ cohort, adjusted 3-year leukemia-free survival rates were 59.8%, 38.3%, and 55.5% after UCBT, HLA-matched UBMT, and HLA-mismatched UBMT, respectively. In the MRD- cohort, the corresponding rates were 65.3%, 70.4%, and 69.7%, respectively. The MRD+ HLA-matched UBMT group had a significantly higher risk of relapse than the MRD+ HLA-mismatched UBMT group (hazard ratio [HR] in the MRD+ HLA-mismatched UBMT group, 0.33; 95% confidence interval [CI] 0.15-0.74) and the MRD+ UCBT group (HR in the MRD+ UCBT group, 0.38; 95% CI 0.18-0.83). Furthermore, HLA-matched UBMT had a significant effect of MRD on death (HR 1.87; 95% CI 1.19-2.94), relapse or death (HR 2.24; 95% CI 1.50-3.34), and relapse (HR 3.12; 95% CI 1.75-5.57), while UCBT and HLA-mismatched UBMT did not. In conclusion, our data indicate Ph+ ALL patients with positive MRD may benefit from undergoing UCBT or HLA-mismatched UBMT instead of HLA-matched UBMT to reduce leukemic relapse.