PS1557 EARLY ENGRAFTMENT OF UNRELATED CORD BLOOD TRANSPLANTATION IN PATIENTS WITH ACQUIRED SEVERE APLASTIC ANEMIA USING CONDITIONING REGIMEN WITHOUT ANTI‐THYMOCYTE GLOBULIN
Authors: X. Wan, H. Liu, X. Zhu, B. Tang, K. Song, X. Zhang, W. Yao, Z. Sun
Journal: HemaSphere (2019)

Background: Previous studies show that the use of unrelated cord blood transplantation (UCBT) for severe aplastic anemia (SAA) has poor outcome because of high incidence of primary graft failure. Effective measures to completely prevent rejection in SAA remain to be identified, but higher cell dose, less HLA disparities and better conditioning regimen are known to improve the outcome. Aims: In this study we compare two conditioning regimens to determine which is better to facilitate early engraftment after UCBT. Methods: We retrospectively analyzed the outcomes of 35 Chinese patients with acquired SAA who received UCBT since September 2016. 18 patients (ATG group) used a conditioning regimen consisting of ATG (thymoglobulin) 2.5 mg/kg (D‐9 to D‐7) with fludarabine 30 mg/m 2 (D‐9 to D‐4), cyclophosphamide 60 mg/kg (D‐3 to D‐2) and total body irradiation (3 Gray) on D‐1. Median age at time of UCBT was 9 (4–37) years. The median total nucleated cell number and CD34‐positive cell number at infusion were 4.08 (1.74–9.36) × 10 7 /kg and 2.13 (0.67–4.29) × 10 5 /kg, respectively. Another group (No‐ATG) of 17 patients used a conditioning regimen without ATG consisting of fludarabine 40 mg/m 2 (D‐8 to D‐4), cyclophosphamide 60 mg/kg (D‐3 to D‐2) and total body irradiation (4 Gray) on D‐1. Median age at time of UCBT was 14 (4–52) years. The median total nucleated cell number and CD34‐positive cell number at infusion were 3.5 (1.07–7.87) × 10 7 /kg and 1.7 (0.69–5.27) × 10 5 /kg, respectively. Ciclosporin (CsA) and mycophenolate mofetil (MMF) was given to both groups as prophylaxis for graft versus host disease (GVHD) Results: Neutrophil recovery (&gt;0.5 × 10 9 /L) was observed in 11 patients of the ATG group and the median time to engraftment was 19 (13–35) days. The median time to platelet recovery (&gt;20 × 10 9 /L) was 40 (24–153) days. Primary graft failure was observed in seven patients. Only 1 out of 17 patients in the No‐ATG group had primary graft failure. The median time to neutrophil engraftment was 17 (13–36) days. The median time to platelet engraftment was 31 (17–65) days. During follow‐up, 7 patients died before 1 year due to non‐engraftment (n = 4), infection (n = 2) and encephalorrhagia (n = 1) in the ATG group. Four patients died in the No‐ATG group due to infection (n = 3) and IV grade acute GVHD in the skin and the intestinal tract (n = 1, induced by discontinuing medicine). Furthermore, conditioning regimen without ATG shows even more superiority in patients refractory to immunosuppressive therapy with ATG and/or CsA (n = 8), who had neutrophil engraftment completely within 20 days after cord blood infusion. Summary/Conclusion: UCBT after a FLU‐CY‐TBI conditioning regimen without ATG for SAA patients is better than that with ATG, especially for patients refractory to immunosuppressive therapy. Pediatric and adult SAA patients who are younger than 50 years old, lack of HLA‐matched sibling donor and refractory to immunosuppressive therapy should consider UCBT.