Efficacy of a Modified Post-Transplant Cyclophosphamide Regimen for Unrelated Donor Hematopoietic Stem Cell Transplantation in Patients with Severe Aplastic Anemia: A Prospective Study

The aim of the present study was to examine the efficacy of the modified post-transplant cyclophosphamide (PTCy) regimen, which involved reducing the Cy dose to 40 mg on days +3 and +4 in patients with severe aplastic anemia (SAA) subjected to unrelated donor allogeneic hematopoietic stem cell transplantation (URD-HSCT). For this purpose, a prospective single-center trial was conducted and the clinical outcomes were collected from 30 patients with SAA treated with the modified PTCy regimen for URD-HSCT. The median time to neutrophil and platelet engraftment was 13 days (range, 11 to 16) and 12 days (range, 5 to 33), respectively. The cumulative incidence of neutrophil and platelet engraftment was 93.1% ± 0.3% and 96.6% ± 0.2%, respectively. The 2-year overall survival (OS) was 97% (95% confidence interval [CI]: 90%-100%] and 2-year graft-versus-host disease (GVHD) and rejection-free survival (GRFS) was 93% (95% CI: 85%-100%). The incidence rates of acute GVHD (aGVHD) and chronic GVHD (cGVHD) were 13.8 ± 0.4% and 10.3 ± 0.3%, respectively, and no patients developed grades III-IV aGVHD. However, only one patient developed a moderate extensive cGVHD. The incidence of reconstitution varies among different subsets of immune cells after URD-HSCT. Natural killer (NK) cells recover first, followed by CD8⁺ T and CD19⁺ B cells, and finally CD4⁺ T cells. In conclusion, the present study demonstrates that the modified PTCy regimen, with a reduced dose of 40 mg on days +3 and +4, may be an effective regimen for URD-HSCT in patients with SAA and reduce the occurrence of the GVHD.