STEM CELLS 2006;24: 386 -398

Background Hairy cell leukemia (HCL) is a well defined clinico-pathological entity whose underlying genetic lesion is still obscure. Methods We searched for HCL-associated mutations by massively parallel sequencing of the whole exome of leukemic and matched normal mononuclear cells purified from the peripheral blood of one patient with HCL. Results Whole exome sequencing identified 5 missense somatic clonal mutations that were confirmed at Sanger sequencing, including a heterozygous V600E mutation involving the BRAF gene. Since the BRAF V600E mutation is oncogenic in other tumors, further analyses were focused on this genetic lesion. Sanger sequencing detected mutated BRAF in 46/46 additional HCL patients (47/47 including the index case; 100%). None of the 193 peripheral B-cell lymphomas/leukemias other than HCL that were investigated carried the BRAF V600E mutation, including 36 cases of splenic marginal zone lymphomas and unclassifiable splenic lymphomas/leukemias. Immunohistological and Western blot studies showed that HCL cells express phospho-MEK and phospho-ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF-MEK-ERK mitogen-activated protein kinase pathway in HCL. In vitro incubation of BRAF-mutated primary leukemic cells from 5 HCL patients with PLX-4720, a specific inhibitor of active BRAF, led to marked decrease of phosphorylated ERK and MEK. Conclusions The BRAF V600E mutation was present in all HCL patients investigated. This finding may have relevant implications for the pathogenesis, diagnosis and targeted therapy of HCL (Funded by the Associazione Italiana Ricerca Cancro and others).

Distinct forms of tyrosine kinase domain (TKD), juxtamembrane domain, exon 8, and internal tandem duplication (ITD) mutations of c-KIT, were observed in about 46% of core binding factor leukemia (CBFL) patients. To evaluate their prognostic significance, 67 adult patients with CBFL were analyzed to ascertain the c-KIT mutation status. In acute myeloid leukemia (AML) with t(8;21), the presence of c-KIT TKD mutation at codon 816 (TKD 816 ) was associated with a high white blood cell count at diagnosis (median, 29.60 ؋ 10 9 /L) and a higher incidence (33%) of extramedullary leukemia (EML) during the course of the disease. Data also showed that the TKD 816 mutated patients (n ‫؍‬ 12) had a significantly higher incidence of relapse and a lower overall survival (OS) at 24 months, compared with the 17 c-KIT unmutated (c-KIT ؊ ) patients (90% vs 35.3%, P ‫؍‬ .002; 25% vs 76.5%, P ‫؍‬ .006, respectively). No difference in relapse incidence (P ‫؍‬ .126) and OS (P ‫؍‬ .474) was observed between the c-KIT mutated other than TKD 816 (n ‫؍‬ 7) and the c-KIT ؊ patients. These findings indicate that c-KIT TKD 816 mutation has a negative impact on the outcome of AML with

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Aberrant signal transduction contributes substantially to leukemogenesis. The Janus kinase 1 (JAK1) gene encodes a cytoplasmic tyrosine kinase that noncovalently associates with a variety of cytokine receptors and plays a nonredundant role in lymphoid cell precursor proliferation, survival, and differentiation. We report that somatic mutations in JAK1 occur in individuals with acute lymphoblastic leukemia (ALL). JAK1 mutations were more prevalent among adult subjects with the T cell precursor ALL, where they accounted for 18% of cases, and were associated with advanced age at diagnosis, poor response to therapy, and overall prognosis. All mutations were missense, and some were predicted to destabilize interdomain interactions controlling the activity of the kinase. Three mutations that were studied promoted JAK1 gain of function and conferred interleukin (IL)-3–independent growth in Ba/F3 cells and/or IL-9–independent resistance to dexamethasone-induced apoptosis in T cell lymphoma BW5147 cells. Such effects were associated with variably enhanced activation of multiple downstream signaling pathways. Leukemic cells with mutated JAK1 alleles shared a gene expression signature characterized by transcriptional up-regulation of genes positively controlled by JAK signaling. Our findings implicate dysregulated JAK1 function in ALL, particularly of T cell origin, and point to this kinase as a target for the development of novel antileukemic drugs.

B lymphocyte stimulator (BLyS) is a novel member of the TNF ligand superfamily that is important in B cell maturation and survival. We demonstrate that human neutrophils, after incubation with G-CSF or, less efficiently, IFNγ, express high levels of BLyS mRNA and release elevated amounts of biologically active BLyS. In contrast, surface expression of the membrane-bound BLyS was not detected in activated neutrophils. Indeed, in neutrophils, uniquely among other myeloid cells, soluble BLyS is processed intracellularly by a furin-type convertase. Worthy of note, the absolute capacity of G-CSF–stimulated neutrophils to release BLyS was similar to that of activated monocytes or dendritic cells, suggesting that neutrophils might represent an important source of BLyS. In this regard, we show that BLyS serum levels as well as neutrophil-associated BLyS are significantly enhanced after in vivo administration of G-CSF in patients. In addition, serum obtained from two of these patients induced a remarkable accumulation of neutrophil-associated BLyS in vitro. This effect was neutralized by anti–G-CSF antibodies, indicating that G-CSF, present in the serum, stimulated neutrophils to produce BLyS. Collectively, our findings suggest that neutrophils, through the production of BLyS, might play an unsuspected role in the regulation of B cell homeostasis.

A large panel of human CD4+ T helper (Th) cell clones with established Th1, Th2, or Th0 profiles of cytokine secretion were examined for the expression of CD30, a member of the tumor necrosis factor receptor superfamily. Th1 clones expressed poor or no CD30 mRNA, and showed low or undetectable expression of both membrane and soluble CD30 (sCD30) protein, whereas Th2 clones showed both CD30 mRNA and membrane CD30 and released substantial amounts of sCD30, Th0 clones exhibited an intermediate pattern of CD30 expression and release. When T cells from the same donor were stimulated with three different antigens (purified protein derivative, PPD; Toxocara canis excretory/secretory antigen, TES; Lalium perenne group I, Lol p I), production of high concentrations of IFN‐γ, but not expression of CD30 or production of IL‐4 and IL‐5, were observed at any time after stimulation with PPD. In contrast, both CD30 expression and production of IL‐4 and IL‐5. but not of IFN‐γ, were concomitantly detectable in TES‐ and Lol p I‐reactive T cells, suggesting a temporal relationship between CD30 expression and beginning of Th2‐typc cytokine production. Finally, CD4+CD30+ T cells specific for Lol p I and inducible to production of Th2‐type cytokines were sorted out from the circulation of grass‐sensitive patients in concomitance with the onset of allergic symptoms during the seasonal exposure to grass pollen. Thus, CD30 expression appears to be associated with the differentiation/activation pathway of human T cells producing Th2‐type cytokines.—Del Prete, G., De Carli, M., Almerigogna, F., Daniel, C. K., D'Elios, M. M., Zancuoghi, G., Virante, F., Pizzolo, G., Romagnani, S. Preferential expression of CD30 by human CD4+ T cells producing Th2‐type cytokines, FASEB J. 9, 81‐86 (1995)

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