Fludarabine-Based Conditioning Chemotherapy for Allogeneic Hematopoietic Stem Cell Transplantation in Acquired Severe Aplastic Anemia

Thirty-eight patients who met the diagnostic criteria for severe aplastic anemia underwent allogeneic hematopoietic stem cell transplantation (HSCT). The median patient age was 20 years (range, 14-36 years). Twenty-four patients were treatment-naïve, 11 had failed one or more previous courses of immunosuppressive therapy, and 3 had failed a previous HSCT. The conditioning regimen included fludarabine 30 mg/m²/day for 3 days (days −9, −8, and −7) and cyclophosphamide 50 mg/kg/day for 4 days (days −5, −4, −3, and −2). Graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporine and short-course methotrexate. All patients underwent transplantation with unmanipulated bone marrow as the stem cell source. The median total nucleated cell (TNC) dose was 2.43 × 10⁸/kg (range, 0.60-6.7 × 10⁸/ kg). The conditioning regimen was well tolerated, with minimal treatment-related mortality. Engraftment was observed in all patients after transplantation; the median time to engraftment of neutrophils and platelets was 18 and 23 days, respectively. Twenty-five of the 27 patients with available chimeric studies at day 180 maintained donor chimerism. Acute GVHD grade ≥II was diagnosed in 4 patients (11%). Extensive chronic GVHD was observed in 8 patients (25%) who survived beyond day +100, at a median observation time of 43 months. Graft rejection with relapse of aplais was observed in one patient. The overall survival (OS) for the whole group was 79%. A trend toward improved OS was observed in the treatment-naïve patients (83% vs 71%), but this was statistically insignificant (P = .384). The fludarabine-based conditioning regimen used in this study with relatively young cohort of patients was well tolerated, with a low rate of rejection and treatment outcomes comparable to those seen in other, more intense and potentially more toxic conditioning regimens. Our results await validation in a larger study, optimally in a randomized controlled manner.

Key Words: Aplastic anemia, Transplantation, Fludarabine