The medication being tested in the START trial is antithymocyte globulin (e.g., Thymoglobulin®), a mixture of specialized proteins called antibodies. ATG attaches itself to white blood cells known as T cells, some of which are responsible for the immune system's attack on beta cells that occurs in T1DM. ATG can change how T cells work, and can eliminate a large proportion of the T cells from the bloodstream temporarily. Treatment of new onset T1DM with ATG is therefore expected to alter the behavior of the T cells to halt their attack, and also reduce T cell numbers, so that new T cells that grow in their place will learn to accept the beta cells, rather than attacking them.