Keiko Katayose

Development of ET, primary myelofibrosis and PV in mice expressing JAK2 V617F

An acquired JAK2 V617F mutation is found in most patients with polycythemia vera (PV), and about half of patients with essential thrombocythemia (ET) or primary myelofibrosis (PMF). Mice transplanted with bone marrow cells in which JAK2 V617F was retrovirally expressed developed PV-like features, but not ET or PMF. To address the contribution of this mutation to the pathogenesis of these three MPDs, we generated two lines of JAK2 V617F transgenic mice. One line showed granulocytosis after 4 months of age. Among 43 mice, 8 (19%) showed polycythemia and 15 (35%) showed thrombocythemia. The second line showed extreme leukocytosis and thromobocytosis. They showed anemia that means Hb value from 9 to 10 g per 100 ml when 1 month old. Myeloid cells and megakaryocytes were predominant in the bone marrow of these animals, and splenomegaly was observed. The expression of JAK2 V617F mRNA in bone marrow cells was 0.45 and 1.35 that of endogenous wild-type JAK2 in the two lines, respectively. In vitro analysis of bone marrow cells from both lines showed constitutive activation of ERK1/2, STAT5 and AKT, and augmentation of their phosphorylations by cytokine stimulation. We conclude that in vivo expression of JAK2 V617F results in ET-, PMF- and PV-like disease.

TET2 is essential for survival and hematopoietic stem cell homeostasis.

Ten-Eleven-Translocation 2 (TET2) is an enzyme that catalyzes the conversion of 5-methylcytosine into 5-hydroxymethylcytosine (5-hmC) and thereby alters the epigenetic state of DNA; somatic loss-of-function mutations of TET2 are frequently observed in patients with diverse myeloid malignancies. To study the function of TET2 in vivo, we analyzed Ayu17-449 (TET2trap) mice, in which a gene trap insertion in intron 2 of TET2 reduces TET2 mRNA levels to about 20% of that found in wild-type (WT) mice. TET2trap/trap mice were born at Mendelian frequency but died at a high rate by postnatal day 3, indicating the essential role of TET2 for survival. Loss of TET2 results in an increase in the number of hematopoietic stem cells (HSCs)/progenitors in the fetal liver, and TET2trap/trap HSCs exhibit an increased self-renewal ability in vivo. In competitive transplantation assays, TET2trap/trap HSCs possess a competitive growth advantage over WT HSCs. These data indicate that TET2 has a critical role in survival and HSC homeostasis.

Absence of gain-of-function JAK1 and JAK3 mutations in adult T cell leukemia/lymphoma

Janus kinase 1 (JAK1) and JAK3 plays a critical role in lymphocyte proliferation and differentiation. Somatic JAK1 mutations are found in 18% of adult precursor T acute lymphoblastic leukemias and somatic JAK3 mutations are found in 3.3% of cutaneous T cell lymphomas. Some of the mutations are confirmed as a gain-of-function mutation and are assumed to be involved in leukemogenesis. Adult T cell leukemia/lymphoma (ATLL) is a type of T cell neoplasm, and activation of JAK/STAT pathways is sometimes observed in them. We investigated JAK1 and JAK3 mutations in 20 ATLL patients. No JAK1 mutations were found, and five types of single nucleotide polymorphisms were observed in 12 cases, whose frequencies almost match those in Asian populations. As for JAK3, a synonymous mutation was found in one case. JAK1 and JAK3 mutations are unlikely involved in the leukemogenesis of ATLL.

CD3 and EBER double positive cells in bone marrow are a diagnostic aid for EBV-positive T-cell lymphoproliferative disorders of childhood

We describe a case of Epstein–Barr virus (EBV)-positive T-cell lymphoproliferative disorders (EBV+ T-cell LPD) of childhood. The patient presented with high fever, jaundice, hepatosplenomegaly, pancytopenia, and disseminated intravascular coagulation (DIC). On admission, liver biopsy could not be conducted due to DIC. The small but definitive number of abnormal lymphocytes in bone marrow (BM) was indicative of malignant lymphoma or related diseases. The diagnosis of EBV+ T-cell LPD of childhood was tentatively made on the basis of the presence of CD3 and EBER double positive cells in BM. We started chemotherapy, which promptly resolved the symptoms and DIC. Later the diagnosis was confirmed by the T-cell receptor rearrangement and a single band for the EBV terminal repeat region by Southern blot analysis of BM cells. The detection of EBER-positive CD3 cells in BM is a diagnostic aid for EBV+ T-cell LPD of childhood.