Somatic KRAS mutations associated with a human non-malignant syndrome of autoimmunity and abnormal leukocyte homeostasis (47.4)

Abstract Autoimmune lymphoproliferative syndrome (ALPS) is a non-malignant disease characterized by early-onset chronic lymphadenopathy, splenomegaly, multilineage cytopenias, polyclonal hypergammaglobulinemia, expansion of circulating TCRαβ+B220+CD4-CD8- T (αβ+-DNT) lymphocytes, and an increased risk of B-cell lymphoma. Most ALPS patients have germline or somatic TNFRSF6 (FAS) mutations, and a small minority of patients have germline mutations in FAS ligand and caspase 10. We recently reported that an ALPS-like phenotype can be caused by a somatic NRAS mutation (G13D) resulting in the defective lymphocyte apoptosis. Here we demonstrate that somatic mutations in the related KRAS gene can also be associated with a non-malignant syndrome of autoimmunity and breakdown of leukocyte homeostasis. The activating KRAS mutation (G13C) impaired cytokine-withdrawal induced T cell apoptosis through the suppression of the pro-apoptotic protein BIM and facilitated proliferation through p27kip1 downregulation. These defects could be corrected by MEK1 or PI3K inhibition in vitro. We suggest the use of the term RAS-associated autoimmune leukoproliferative disease (RALD) to differentiate this disorder from ALPS. In the hematopoietic system, somatic KRAS and NRAS mutations are commonly observed in aggressive tumors such as multiple myeloma or juvenile myelomonocytic leukemia (JMML). From our reports, we think patients with somatic KRAS and NRAS mutations can follow a more benign clinical course.