High Serum Level of Antithymocyte Globulin Immediately before Graft Infusion Is Associated with a Low Likelihood of Chronic, But Not Acute, Graft-versus-Host Disease

Rabbit antithymocyte globulin (ATG) is administered during transplant conditioning to decrease the risk of both acute graft-versus-host disease (aGVHD) and chronic graft-versus-host disease (cGVHD). Here we evaluated the relationship between the serum concentration of ATG (capable of binding to lymphocytes) immediately before graft infusion (day 0) or on day +7 or +28 post-transplantation and the development of aGVHD or cGVHD. We studied 180 patients whose conditioning included 4.5 mg/kg antithymocyte globulin (ATG; Thymoglobulin). For aGVHD, we found no association with ATG levels on day 0. Nevertheless, high day +7 and +28 ATG levels were associated with a low likelihood of aGVHD. For cGVHD, high ATG levels at all 3 time points (days 0, +7, and +28) were associated with a low likelihood of cGVHD. In conclusion, high-dose ATG administration at the time of graft infusion appears to inhibit the development of cGVHD, but not aGVHD; however, higher ATG levels on days +7 and +28 are associated with lower rates of both aGVHD and cGVHD.