Clinical Outcomes of Matched Unrelated Allogeneic Stem Cell Transplant Patients: Low Dose ATG Vs. No ATG

Abstract

Introduction Anti-thymocyte globulin (ATG) is an immunoglobulin directed to human T lymphocytes, and may decrease the risk of chronic graft versus host disease (cGVHD) in allogenic hematopoietic cell transplantation (HCT). ATG, especially at higher doses (≥ 7.5 mg/kg), has been associated with higher incidence of disease relapse and infection. Our institution utilizes low dose rabbit ATG 2.5 mg/kg. In this retrospective study, we evaluated outcomes of HCT patients (pts) receiving low dose ATG vs. not undergoing in-vivo T-cell depletion Patients and Methods Pts with 8/8 HLA Matched Unrelated Donors (MUD) undergoing HCT between 2007-2016 were included. Pts were divided into two cohorts: those receiving low dose ATG vs. those that did not. Both cohorts received standard GVHD prophylaxis. Primary outcome was overall survival (OS). Secondary outcomes included relapse free survival (RFS), EBV or CMV reactivation, CMV disease, invasive fungal infection, acute GVHD (aGVHD) grades III-IV, and moderate to severe cGVHD. A series of univariate and multivariant Cox proportional hazard regression models were conducted for outcomes of interest. A Kaplan-Meier survival curve was used to depict probability of survival by ATG cohort. Results We identified 209 patients,129 in ATG group and 80 in non-ATG group. There were no differences in the age, sex, ABO incompatibility, or performance status. The ATG cohort had fewer low disease risk index (DRI) and more pts with intermediate or high DRI (2.4%, 64.6%, 28.3% vs 18.4%, 51.3%, 23.7% respectively); these differences were statistically significant between the two groups (p = There was no significant difference in OS between the two groups at up to 5 years post-transplant (p=0.35; Fig. 1). The primary predictor of OS was DRI very high vs low [HR 6.0 (2-18) p Conclusions Our study shows no significant difference in survival or death from relapse for patients who receive ATG. Importantly, patients receiving ATG had a lower rate of cGVHD with no increased rates of infectious complications. Low dose ATG did not appear to increase the risk of relapse, even when considering only myeloid malignancies. These findings suggest that low dose ATG can improve cGVHD with no impact on survival, relapse, or infectious complications. Additional prospective trials using low dose ATG compared to no ATG are warranted.