ATG is a purified serum that suppresses the immune system to allow the bone marrow time to recover. It is produced by injecting animals (horse or rabbit) with white blood cells called lymphocytes. The animal then makes antibodies which are collected and purified to produce globulin.

ATG can either be used ahead of a stem cell transplant (rabbit) or with ciclosporin as a stand-alone treatment to let the bone marrow recover.