Large granular lymphocyte leukemia: a clonal disorder with autoimmune manifestations

Large granular lymphocyte (LGL) leukemia is a rare lymphoproliferative disorder characterized by an expansion of clonal T or natural killer lymphocytes. Neutropenia-related infections and anemia represent the main manifestations. LGL leukemia is frequently associated with autoimmune disorders such as rheumatoid arthritis, Sjögren's syndrome, autoimmune endocrinopathies, vasculitis, or autoimmune cytopenia. Recent advances in the phenotypic and molecular characterization of LGL clones have underscored the pivotal role of a chronic antigenic stimulation and a dysregulation of the Jak/STAT signaling pathway in the pathophysiology linking leukemic-cell expansion and autoimmunity. In more than half of patients, there is a somatic STAT3 mutation. The disease is characterized by an indolent course, but approximately half of all patients will eventually require therapy. The first-line treatment for LGL leukemia is historically based on immunosuppressive agents (methotrexate, cyclophosphamide, or cyclosporine). However, cytokines blocking molecules or Jak/STAT inhibitors represent a new conceptual therapeutic approach for LGL leukemia. In this review, we present an overview of the spectrum of LGL proliferations, potential links between LGL expansion and autoimmunity, and therapeutic approaches.