Rabbit-Derived Anti-Thymocyte Globulin (ATG) Rabbit-derived anti-thymocyte globulin (ATG) is a gamma globulin preparation obtained from hyperimmune serum of rabbits immunized with human thymocytes. ATG has been used predominately in solid organ transplant immunosuppressive regimens. ATG is a predominantly lymphocyte-specific immunosuppressive agent. It contains antibodies specific to the antigens commonly found on the surface of T cells. After binding to these surface molecules, ATG promotes the depletion of T cells from the circulation through mechanisms, which include opsonization and complement-assisted, antibody- dependent, cell-mediated cytotoxicity. The plasma half-life ranges from 1.5-12 days. ATG is administered intravenously at a dose of 0.5 mg/kg recipient body weight on day -6 and a dose of 1.0 mg/kg recipient body weight on days -5, -4, -3, -2 and -1. Unlike equine ATG, rabbit ATG does not require a pre-infusion skin test to check for hypersensitivity. Methylprednisolone 1 gram will be given before every dose of ATG. Additional medications such as diphenhydramine may be given at the discretion of the attending physician. Although rare, the major toxicity is anaphylaxis. Chills, fever, pruritus or serum sickness may occur.