Jean-Pierre Le Couedic

A unique clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera

Myeloproliferative disorders are clonal haematopoietic stem cell malignancies characterized by independency or hypersensitivity of haematopoietic progenitors to numerous cytokines. The molecular basis of most myeloproliferative disorders is unknown. On the basis of the model of chronic myeloid leukaemia, it is expected that a constitutive tyrosine kinase activity could be at the origin of these diseases. Polycythaemia vera is an acquired myeloproliferative disorder, characterized by the presence of polycythaemia diversely associated with thrombocytosis, leukocytosis and splenomegaly. Polycythaemia vera progenitors are hypersensitive to erythropoietin and other cytokines. Here, we describe a clonal and recurrent mutation in the JH2 pseudo-kinase domain of the Janus kinase 2 (JAK2) gene in most (> 80%) polycythaemia vera patients. The mutation, a valine-to-phenylalanine substitution at amino acid position 617, leads to constitutive tyrosine phosphorylation activity that promotes cytokine hypersensitivity and induces erythrocytosis in a mouse model. As this mutation is also found in other myeloproliferative disorders, this unique mutation will permit a new molecular classification of these disorders and novel therapeutical approaches.

Mutation in TET2 in Myeloid Cancers

BACKGROUND The myelodysplastic syndromes and myeloproliferative disorders are associated with deregulated production of myeloid cells. The mechanisms underlying these disorders are not well defined. METHODS We conducted a combination of molecular, cytogenetic, comparative-genomic-hybridization, and single-nucleotide-polymorphism analyses to identify a candidate tumor-suppressor gene common to patients with myelodysplastic syndromes, myeloproliferative disorders, and acute myeloid leukemia (AML). The coding sequence of this gene, TET2, was determined in 320 patients. We analyzed the consequences of deletions or mutations in TET2 with the use of in vitro clonal assays and transplantation of human tumor cells into mice. RESULTS We initially identified deletions or mutations in TET2 in three patients with myelodysplastic syndromes, in three of five patients with myeloproliferative disorders, in two patients with primary AML, and in one patient with secondary AML. We selected the six patients with myelodysplastic syndromes or AML because they carried acquired rearrangements on chromosome 4q24; we selected the five patients with myeloproliferative disorders because they carried a dominant clone in hematopoietic progenitor cells that was positive for the V617F mutation in the Janus kinase 2 (JAK2) gene. TET2 defects were observed in 15 of 81 patients with myelodysplastic syndromes (19%), in 24 of 198 patients with myeloproliferative disorders (12%) (with or without the JAK2 V617F mutation), in 5 of 21 patients with secondary AML (24%), and in 2 of 9 patients with chronic myelomonocytic leukemia (22%). TET2 defects were present in hematopoietic stem cells and preceded the JAK2 V617F mutation in the five samples from patients with myeloproliferative disorders that we analyzed. CONCLUSIONS Somatic mutations in TET2 occur in about 15% of patients with various myeloid cancers.

Inhibition of TET2-mediated conversion of 5-methylcytosine to 5-hydroxymethylcytosine disturbs erythroid and granulomonocytic differentiation of human hematopoietic progenitors

TET2 converts 5-methylcytosine to 5-hydroxymethylcytosine (5-hmC) in DNA and is frequently mutated in myeloid malignancies, including myeloproliferative neoplasms. Here we show that the level of 5-hmC is decreased in granulocyte DNA from myeloproliferative neoplasm patients with TET2 mutations compared with granulocyte DNA from healthy patients. Inhibition of TET2 by RNA interference decreases 5-hmC levels in both human leukemia cell lines and cord blood CD34(+) cells. These results confirm the enzymatic function of TET2 in human hematopoietic cells. Knockdown of TET2 in cord blood CD34(+) cells skews progenitor differentiation toward the granulomonocytic lineage at the expense of lymphoid and erythroid lineages. In addition, by monitoring in vitro granulomonocytic development we found a decreased granulocytic differentiation and an increase in monocytic cells. Our results indicate that TET2 disruption affects 5-hmC levels in human myeloid cells and participates in the pathogenesis of myeloid malignancies through the disturbance of myeloid differentiation.

An activating mutation in the CSF3R gene induces a hereditary chronic neutrophilia

We identify an autosomal mutation in the CSF3R gene in a family with a chronic neutrophilia. This T617N mutation energetically favors dimerization of the granulocyte colony-stimulating factor (G-CSF) receptor transmembrane domain, and thus, strongly promotes constitutive activation of the receptor and hypersensitivity to G-CSF for proliferation and differentiation, which ultimately leads to chronic neutrophilia. Mutant hematopoietic stem cells yield a myeloproliferative-like disorder in xenotransplantation and syngenic mouse bone marrow engraftment assays. The survey of 12 affected individuals during three generations indicates that only one patient had a myelodysplastic syndrome. Our data thus indicate that mutations in the CSF3R gene can be responsible for hereditary neutrophilia mimicking a myeloproliferative disorder.

Role of granulocyte-macrophage colony-stimulating factor, Interleukin-3 and Interleukin-5 in the eosinophilia associated with T cell lymphoma

Summary. We studied two patients with a leukaemic T cell lymphoma who presented with a marked increase in blood eosinophilia. To investigate the mechanism of the eosinophilia, supernatants of peripheral blood cells containing more than 80% lymphoma cells were tested by biological assays for the presence of colony stimulating factors (CSF). In one case supernatants stimulated the growth of granulocyte‐macrophage (GM), erythroid and eosinophil colonies. These effects were neutralized by anti‐GM‐CSF antibodies; anti‐IL5 antibodies slightly decreased eosinophil colony formation. Supernatants derived from the second patient cells stimulated the same lineages. Neutralizing experiments demonstrated that in addition to GM‐CSF it contained interleukin 3 (IL‐3) and interleukin 5 (IL‐5). In agreement with the biological data. RNA studies using the polymerase chain reaction showed that cells from the first patient expressed GM‐CSF transcripts; IL‐5 transcripts were also detected in very low amounts. GM‐CSF, IL‐3 and IL‐5 transcripts were detected in cells from the second patient. Thus eosinophilia associated with some T cell lymphoma is likely due to secretion of different combinations of cytokines by malignant cells.

Mutations in JAK2V617F homologous domain of JAK genes are uncommon in solid tumors.

Department of Medicine, Institut Gustave Roussy, Villejuif, FranceDear Sir,ThefamilyofJanuskinase(JAK)includes4kinasesthatsharesignificant structural homology with each other: JAK1, JAK2,JAK3andTyk2.Thesekinasesassociatewithdifferent cytokineand hormone receptors. Upon ligand binding, the JAK kinasesare activated and in turn activate receptor downstream signalingpathways. Many of the effects of this signaling are mediated bythe 7 members of the signal transducers and activators of tran-scription (STAT).