Rabbit ATG Plus Cyclophosphamide with or without Fludarabine Is Superior Conditioning Regimen for Patients with Severe Aplastic Anemia Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Objective: To compare rabbit antithymocyte globulin (ATG) containing conditioning regimen (group A) with horse antilymphocyte globulin (ALG)-based regimen (group B) for sibling allogeneic hematopoietic stem cell transplant (HSCT) outcome, disease free survival, rejection and complications in severe aplastic anemia patients.

Methods: We analysed 205 aplastic anemia patients undergoing allogeneic HSCT from HLA matched sibling donors from July 2001 to April 2016. Group A (n=169) received conditioning with ATG plus Cyclophosphamide (CY) 200 mg/Kg with Fludarabine (Flu) 120mg/m2 (n=100) or without Flu (n=69), whereas group B comprised of CY plus ALG (n=36). The stem cell source was bone marrow (43.9%); PBSC (8.3%) and bone marrow plus PBSC (47.8%). Cyclosporin (CsA) was given as GVHD prophylaxis in 129 patients, while methotrexate (MTX) was added to CsA in 76 cases. Chi-square test was used to compare categorical variables. Kaplan Meier survival curves with log rank test was applied to compare the groups for survival analysis.

Results: Overall survival was 78.7% in Group A compared to 69.4% in group B (p=0.23). Patients in group A had significantly better disease free survival (DFS) (75.1%) than group B (55.6%) (p=0.018). The incidence of acute GVHD was 18.3% in Group A compared to 22.2% in Group 2 (p=0.64), while chronic GVHD was significantly higher in Group 2 (22.2%) as compared to Group A (9.5%) (p= 0.04). Likewise frequency of Mucositis was high in Group B (30.5%) compared to Group A (10.7%) (p = 0.006). Moreover, patients receiving ALG-based conditioning had more frequent infections (86%) compared to ATG-based group (67.4%) (p=0.03). There was no significant difference within group A with respect to use of fludarabine as part of conditioning.

Conclusion: Rabbit ATG containing conditioning regimen is associated with less complications and better survival in patients with severe aplastic anemia undergoing allogeneic HSCT.