LGL leukemia is characterized by clonal expansion of cytotoxic T cells. Prominent clinical features include neutropenia, anemia, and rheumatoid arthritis. The terminal effector memory phenotype (CD3+/CD8+/CD57+/CD45RA+/CD62L-) of leukemic LGL suggest a pivotal chronic antigen driven immune response. LGL survival is then promoted by PDGF and IL-15, resulting in global dysregulation of apoptosis and resistance to normal pathways of activation-induced death. These pathogenic features explain why treatment of LGL leukemia is based on immunosuppression therapy. However, no standard therapy has been established due to the absence of large prospective trials.