Clinical outcomes with low dose anti-thymocyte globulin in patients undergoing matched unrelated donor allogeneic hematopoietic cell transplantation.

Anti-thymocyte globulin (ATG) has been associated with decreased rates graft versus host disease (GVHD) but with a potential risk of increasing risk of infection and relapse. We retrospectively studied the impact of single dose low dose (2.5 mg/kg) ATG in patients undergoing allogenic hematopoietic cell transplantation (HCT) from 8/8 matched unrelated donors (MUD). Of the total 209 patients identified, 129 received ATG. At baseline, the ATG group had more intermediate and high disease risk index (DRI) (64.6% vs. 54.3%) (28.3% vs. 23.7%) p < .001, respectively, and who received reduced intensity or non-myeloablative conditioning (RIC) (69.0% vs. 47.5%, p .003). There was no significant difference in the overall survival (OS) HR = 1.3, 95% CI [0.99, 1.0], p = .350 or relapse-free survival (RFS) HR = 1.2, 95% CI [0.74, 1.8], p = .526 between the two groups. Patients receiving ATG had a lower incidence of chronic GVHD (cGVHD) (10.1% vs. 25%, p = .007) and less moderate to severe cGVHD (8.5% vs. 25%, p = .002). ATG was associated with a reduced incidence of moderate to severe cGVHD OR = 0.28, 95% CI [0.12, 0.61], p < .01. There was no difference in the incidence of Epstein-Barr Virus (EBV) or cytomegalovirus (CMV) reactivation, CMV disease, invasive fungal infection, or grade III-IV acute GVHD (aGVHD). Our study shows that low dose ATG results in similar OS and RFS with lower rates of cGVHD. Additional prospective studies are needed to confirm these findings.