Timing of donor lymphocyte infusion after relapse following allogeneic hematopoietic cell transplantation: a retrospective single-center analysis.

Donor lymphocyte infusions (DLI) are an important strategy for managing relapse after allogeneic hematopoietic stem cell transplantation (allo-HCT), yet data on the impact of surveillance frequency and DLI timing remain limited. We retrospectively analyzed 83 adults with acute leukemia or MDS who received DLI after relapse between 2010 and 2022. Monthly molecular monitoring with donor chimerism and genetic markers enabled classification of preemptive DLI at molecular relapse and therapeutic DLI at overt hematologic relapse. Overall survival (OS) was assessed using Kaplan-Meier estimates and Cox regression. Therapeutic DLI was associated with inferior OS compared with preemptive DLI (HR = 0.15 in multivariable analysis, p < 0.001); median OS was 0.47 years in the therapeutic group, while it was not reached after preemptive DLI. GvHD after DLI was associated with better OS (HR = 0.28), consistent with graft-versus-leukemia effects. A longer interval between allo-HCT and relapse also predicted improved survival (HR = 0.78). Delivering DLI at molecular rather than hematologic relapse improved survival, suggesting that close MRD-based surveillance enables earlier detection, timely immunologic intervention, and may improve post-relapse outcomes.