Abnormal T lymphocyte (T cell) function, including tumor formation in T cells, can lead to a wide variety of diseases. Over 100 million people worldwide suffer from T cell autoimmune disorders of varying severity, such as lupus and graft-versus-host disease, and the incidence of T cell-mediated cancers, including lymphomas and leukemias, has risen over the past decade. These diseases can be deadly, and not all patients respond to standard therapies.