Busulfan and cyclophosphamide‐based conditioning regimen still holds the promise of being a safe and efficacious regimen for allogeneic transplantation in patients with transfusion‐dependent thalassemia, even in high risk

Abstract

Busulfan and cyclophosphamide (BuCy)-based regimen has been used as a standard myeloablative chemotherapy for haematopoietic stem cell transplantation in thalassemia. However, treosulfan-based conditioning regimen has emerged due to concerns of toxicities. We retrospectively analysed the safety and efficacy of fludrabine/Bu/Cy/antithymocyte globulin (ATG) versus treosulfan/thiotepa/fludrabine regimens for Hematopoietic Stem Cell Transplant (HSCT) in transfusion-dependent thalassemia (TDT) conducted at our institute (2013-2021). In 75 patients, 36 (48%) received Flu/Bu/Cy/ATG whereas 39 (52%) received Treo/Thio/Flu. Median age was 6 (1-12) and 9 (1-15) years, respectively. Number of patients with Classes I, II, and III were 14, 10, and 12 in Flu/Bu/Cy/ATG versus 2, 19, and 18 in Treo/Thio/Flu group, respectively. Graft was growth factor mobilized bone marrow in Flu/Bu/Cy/ATG versus peripheral blood stem cell in Treo/Thio/Flu group. Mean stem cell dose was 3.82 (2.2-9.1) versus 5 (1.65-8.01)106 /kg in Flu/Bu/Cy/ATG versus Treo/Thio/Flu group, respectively. Neutrophils and platelets engrafted at a median of 16 (14-21) and 16 (9-47) days in Flu/Bu/Cy/ATG and 15 (10-20) and 13 (9-41) days in Treo/Thio/Flu group. Median duration of follow-up was 28 (23-32.9) months. Five (6.6%) patients had rejection (all secondary). Venoocclusive disease was observed in 2 (5.7%) versus 4 (10.3%) patients (p=.047), respectively. Flu/Bu/Cy/ATG had 4 (11.4%) patients with acute GVHD versus 15 (38.5%) patients which had significant impact on survival (p=.038). We observed chronic GVHD in 4 (11.4%) and 11 (28.2%) patients, respectively, with significant impact on survival (p=.031). Four (5.1%) patients had TRM in Treo/Thio/Flu group, in contrast to none in Flu/Bu/Cy/ATG group. Mixed chimerism was common in Flu/Bu/Cy/ATG {20 (57.1%)} versus Treo/Thio/Flu group {12 (30.1%)}. Five-year Event Free Survival (EFS) and OS of entire cohort were 87% + 4% and 94% + 3%, respectively. Estimated TFS, EFS, OS of Flu/Bu/Cy/ATG versus Treo/Thio/Flu was 97.1% + 2.9% versus 89.2% + 5.1% (p=.251), 97 + 3% versus 80.7 + 6% (p=.041) and 100% versus 90.4 + 5% (p=.067), respectively. In our experience, Flu/Bu/Cy/ATG regimen is safe and effective even in high-risk TDT. However, one needs to be vigilant for mixed chimerism.