Nonmyeloablative Conditioning Regimen Including Low-Dose Total Marrow/Lymphoid Irradiation Before Haploidentical Transplantation with Post-Transplantation Cyclophosphamide in Patients with Advanced Lymphoproliferative Diseases

Low-dose total body irradiation (TBI) has long been used in nonmyeloablative conditioning (NMAC) regimens before allogeneic stem cell transplantation from haploidentical donors (haplo-SCT). More recently, the use of total marrow lymphoid irradiation (TMLI) instead of TBI in conditioning is increasing. This study aimed to evaluate outcomes in a cohort of patients treated with low-dose TMLI in terms of engraftment, full donor chimerism status, graft-versus-host disease (GVHD), and extrahematologic toxicities, and to compare these outcomes with those in a cohort of patients receiving conventional TBI-containing conditioning. This retrospective single-center study included 100 patients with advanced hematologic malignancies who underwent haplo-SCT. Between 2009 and 2011, the NMAC regimen consisted of cyclophosphamide, fludarabine, and low-dose TBI (2 Gy), and after 2011, TBI was replaced with TMLI (2 Gy). Patients received post-transplantation cyclophosphamide, calcineurin inhibitor, and mycophenolate mofetil as GVHD prophylaxis. For all patients, the median time to absolute neutrophil count (ANC) recovery to >0.5 x 10(9) /L was 21 days (range, 15 to 49 days), the 30-day incidence of ANC recovery was 97% (95% confidence interval [CI], 89% to 99%), the median time to achieve an unsupported platelet count >20 x 10(9)/L was 26 days (range, 12 to 67 days), and the 60-day rate of platelet engraftment was 99% (95% CI, 89% to 100%). Cumulative incidence of full donor chimerism by day 100 was 88% (95% CI 79-90). Grade II-IV acute GVHD occurred in 35% of the patients (95% CI, 26% to 45%) at a median of 40 days (range, 23 to 166 days). The incidence of moderate to severe chronic GVHD was 5% (95% CI, 2% to 10%). No differences between the TBI and TMLI cohorts were seen in terms of engraftment, full donor chimerism, and GVHD. No organ toxicity was observed in the first months after transplantation in either cohort. The overall 2-year OS and PFS rates were 63%, and 54%, respectively, and were comparable in the 2 groups (P = .548). The strongest finding was that TBI can be safely replaced by TMLI in terms of engraftment, achievement of full donor chimerism status, GVHD incidence, and extrahematologic toxicities. (C) 2021 The American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc. All rights reserved.