In recent years, new immunosuppressive drugs have made considerable improvements to the success of transplantation procedure and the treatment of autoimmune diseases. Despite these successes, the side effects of long-term drug treatment invariably decrease patients’ quality of life and cause generalized suppression of the immune system. To develop a more direct approach for these therapies, efforts are now focused on a particular aspect of the immune system that controls the response. T regulatory (Tr) cells are a subset of white blood cells that have the ability to suppress undesired immune responses, while leaving other aspects of the normal immune system intact. A gene named FoxP3 has been identified as the master controller for development of a subset of Tr cells that can provide protection against some types of autoimmune diseases and promote acceptance of foreign tissue in a transplant setting. FoxP3 plays an essential role in maintaining normal immune function, but the exact mechanisms by which this gene operates in Tr cells are not known. Due to the high potential for using Tr cells for immunomodulatory therapies, Sarah Allan is investigating the role of FoxP3 in human cells. Her research will increase our understanding of how Tr cells arise naturally, the mechanisms by which they suppress immune responses and how they differ from other types of T cells at the molecular and genetic level. This work will contribute to the development of novel therapies for autoimmune diseases, transplantation, and other pathologies of the immune system.