Reduced-toxicity conditioning regimen with low dose post-transplantation cyclophosphamide and low-dose anti-thymocyte globulin as graft-versus-host disease prophylaxis for haploidentical stem cell transplantation in older patients

Abstract

Abstract Reduced-toxicity conditioning (RIC) regimens are used for allogeneic hematopoietic stem cell transplantation (allo-HSCT) in older patients. However, successful outcomes are still hindered by graft-versus-host disease (GVHD), treatment-related mortality (TRM) and relapse, especially in the setting of haploidentical donor (HID) hematopoietic cell transplantation (HCT). The aim of this study was to evaluate the effectiveness of a RIC conditioning regimen that included a combination of lower doses of post-transplantation cyclophosphamide (PTCy) (40 mg/kg on day +3) and anti-thymocyte globulin (ATG) (7.5 mg/kg) as GVHD prophylaxis, followed by haplo stem cell transplantation (SCT) in older patients. Method: We retrospectively analyzed 55 patients ≥ 55 years of age with hematologic malignancies treated with fludarabine, Cytarabine, busulfan, and low dose cyclophosphamide as the conditioning regimen between January 1, 2019 and November 30, 2023. Results: Neutrophil engraftment was successful in all the patients within 28 days, with 54 (98.2%) patients achieving complete donor chimerism. The cumulative incidence of non-relapse mortality was 0 at 30 days, 7.5% at 100 days and 19% at 1-year. The cumulative incidence of grade II-IV aGVHD was 25% (95%CI,15%−38%), while grade III-IV aGVHD was 9.1% (95%CI,3.3%−19%). The cumulative incidence of extensive cGVHD at 1 year was 3.6% (95%CI,0.66%-11%). The cumulative incidence of relapse (CIR), overall survival (OS) and GVHD-free/relapse-free survival (GRFS) at 1-year were 9.0%, 71.6%, and 67.1%, respectively. Conclusions: These results suggested that a RIC conditioning regimen including a combination of lower PTCy/ATG as GVHD prophylaxis, followed by haplo-SCTmight be a promising option for appropriately selected older patients.