Reduced-Intensity Unrelated Cord Blood Transplantation for Adult Patients with Severe Aplastic Anemia

Although unrelated cord blood transplantation (UCBT) has become a viable therapeutic option widely applicable for adult patients with hematological diseases, UCBT for severe aplastic anemia (SAA) remains to be controversial due to higher incidence of graft failure (GF) relative to the other stem cell sources. To evaluate the feasibility of UCBT for SAA, we retrospectively analyzed results for 11 adult patients with SAA who received first UCBT after reduced-intensity conditioning regimen (RI-UCBT) in Toranomon Hospital. Median age was 49 years (range, 20–70). Nine of them were non-responders to intensive immunosuppressive therapy and were multiply transfused, and two patients were fulminant type with no neutrophils in peripheral blood at diagnosis. The conditioning regimen consisted of fludarabine 125mg/m², melphalan 80mg/m², and 4 Gy of total body irradiation. Graft-versus-host disease prophylaxis was composed of cyclosporine alone (n=2), tacrolimus alone (n=2), and tacrolimus plus mycophenolate mofetil (n=7). Median total nucleated cell number and median CD34+ cell number were 2.65 × 10⁷/kg (range, 1.83–4.39) and 0.70 × 10⁵/kg (range, 0.27–1.52), respectively. Serological HLA disparities were as follows; 6/6 (n=3), 5/6 (n=2), and 4/6 (n=6). Ten of the 11 patients achieved primary neutrophil and platelet engraftment. Median time to an absolute neutrophil count > 0.5×10⁹/liter and an unsupported platelet count > 20×10⁹/liter were 18 days (range, 12–28) and 42.5 days (range, 26–64) respectively. All patients who achieved engraftment resulted in complete hematological recovery with complete donor chimerism, except for one patient who developed late GF at three years after UCBT. All 2 who experienced GF (1: primary GF, 1: late GF) were rescued by second RI-UCBT. Two of the 11 patients died from IPS (n=2), and remaining 9 patients are alive, having survived for 18.7 months (range, 2–71 months). Six out of 7 patients who survived more than 6 months were free from immunosuppressant. The probabilities of overall survival and event-free survival at 2 years after UCBT were 77.8% and 68.2%, respectively. Our results here strongly indicated feasibility and effectiveness of RI-UCBT for adult SAA patients with high engraftment rate and low treatment-related mortality. RI-UCBT could be considered as a viable therapeutic option for those who lack suitable HLA-matched sibling donors and failed immunosuppressive therapy.