Antithymocyte globulin: An immunosuppressive agent that selectively destroys T lymphocytes. Antithymocyte globulin is the gamma globulin fraction of antiserum from animals that have been immunized against human thymocytes. It is a polyclonal antibody.

The uses of this drug include the prevention and treatment of transplant rejection, aplastic anemia, and other conditions in which immunosuppression may be indicated. Pretreatment with this drug quashes rogue T cells in the DiGeorge syndrome and permits a successful thymus transplant.

Antithymocyte globulin is abbreviated ATG. The brand name is Thymoglobulin. It is produced in rabbits.