The efficacy and safety of using low-dose cyclophosphamide, fludarabine and thymoglobulin in allogeneic hematopoietic stem cell transplantation for transfusion-dependent non-severe aplastic anemia：a retrospective study. Free

Abstract Objectives:This study aimed to analyse the efficacy of allogeneic hematopoietic stem transplantation(HSCT) for transfusion-dependent non-severe aplastic anemia (TD-NSAA).We investigated the effect of conditioning protocol consisting of low-dose cyclophosphamide(Cy)100-120 mg/kg,fludarabine and thymoglobulin(ATG).

Methods:Retrospective analysis of 31 patients with TD-NSAA from January 2018 to June 2025. The conditioning protocol consisting of fludarabine 30 mg/m²/d × 4d (- 8d- -5d), low-dose CTX 25-30 mg/kg/d × 4d (- 8d- -5d), ATG 7.5mg/kg(-5d- -2d).Evaluation indicators included adverse reactions related to conditioning protocol(cardiac and liver complications),hematopoiesis reconstitution(engraftment time),incidence of graft-versus-host disease (GVHD) and survival data.Regimen-related cardiac toxicity was graded according to Bearman criteria.Cardiac and liver complications that developed within 28 days after transplantation were considered regimen-related toxicities.

Results A total of 31 TD-NSAA patients were reviewed,including 21 males and 10 females aged 4-46 years with a median age of 10 years.A disease duration of more than 20 years were 3 patients,of 10-19 years were 7 patients,of 5-9 years were 9 patients,1-4 years were 7 patients and 5 patients with a medical history of less than 1 year. The median disease duration was 95 months. There were 18 cases of stem cell derived from bone marrow combined with peripheral blood stem cells, 13 cases of umbilical cord blood combined with peripheral blood stem cells. HSCT from HLA matched donors were 7 patients (5 patients of sibling donor, 2 patients of unrelated donor), and 24 patients of haploidentical donor.

All 31 patients engrafted successfully. The median time of neutrophil engraftment was 19 days after HSCT in the MSD group (range, 11–28 days) and 23 days in HID HSCT patients (range, 15–37 days).The median time in platelet engraftment was 11 days(7d–33d) of MSD and 20 days (12d–49d) of HID between the two groups. In the MSD group, the incidence of grade II-IV aGVHD was 28.6%(2/7) and 45.8%(11/24) in the HID cohort.No patients developed grade III or IV cardiac and liver toxicity. At 2 years post- transplant, the event- free survival(EFS) was 93% and overall survival(OS) was 95%.

Conclusions: Low dose cyclophosphamide did not cause fatal adverse cardiac and liver toxicity, and did not affect the effectiveness of hematopoietic engraftment .These data highlight allo-HSCT using low-dose Cy(100-120 mg/kg),fludarabine and thymoglobulin(ATG)regimen is safe and effective for TD-NSAA.

Keywords Transfusion-dependent non-severe aplastic anemia;Hematopoietic stem cell transplantation；Cyclophosphamide.