The impact of adding Anti-thymocyte globulin to post-transplant cyclophosphamide in haploidentical stem cell transplantation.

Abstract Background Graft versus host disease (GvHD) is a major cause of mortality post allogeneic stem cell transplant. Post-transplant cyclophosphamide (PT/CY) has become standard prophylaxis of GvHD in T-replete haploidentical-transplantation. The question is whether adding anti-thymocyte globulin (ATG) to PT/CY may further reduce the incidence of GvHD compared to PT/CY only. Methods We have retrospectively studied 268 patients undergoing a myeloablative haploidentical-transplantation with Thiotepa-busulfan-fludarabine (TBF) conditioning. 69 patients (26%) received ATG. Results In the ATG group 3% died due to GvHD versus 8% in the no ATG group. The 100 day and 1-year NRM was 0% and 19% respectively in the whole cohort. On univariate analysis the one-year NRM was 8% vs 23% in patients receiving ATG and no ATG respectively (p=0.005). The no ATG group had a higher incidence of aGvHD at 12 months compared to the ATG group (22% vs 12% respectively, p=0.029). The ATG group had better OS at 12 months compared to the no ATG group (79% vs 69%, p=0.029). On multivariate analysis, adding ATG to PT/CY had no significant impact on any of the outcomes. A low disease risk index was associated with better OS and lower NRM, while HCT-CI score ≥3 was associated with higher NRM. Conclusion ATG can be safely used as part of the pre-transplantation conditioning and does not increase the incidence of relapse or complications post-transplant.