Mutational analysis in BCR-ABL-negative classic myeloproliferative neoplasms: impact on prognosis and therapeutic choices

Bleeding diathesis in mice lacking JAK2 in platelets

The tyrosine kinase JAK2 is a critical component of intracellular JAK/STAT cytokine signaling cascades that is prevalent in hematopoietic cells, such as hematopoietic stem cells and megakaryocytes (MKs). Individuals expressing the somatic JAK2 V617F mutation commonly develop myeloproliferative neoplasms (MPNs) associated with venous and arterial thrombosis, a leading cause of mortality. The role of JAK2 in hemostasis remains unclear. We investigated the role of JAK2 in platelet hemostatic function using Jak2fl/fl Pf4-Cre (Jak2Plt-/-) mice lacking JAK2 in platelets and MKs. Jak2Plt-/- mice developed MK hyperplasia and splenomegaly associated with severe thrombocytosis and bleeding. This notion was supported by failure to occlude in a ferric chloride carotid artery injury model and by a cremaster muscle laser-induced injury assay, in which Jak2Plt-/- platelets failed to form stable thrombi. Jak2Plt-/- platelets formed thrombi poorly after adhesion to type 1 collagen under arterial shear rates. Jak2Plt-/- platelets spread poorly on collagen under static conditions or on fibrinogen in response to the collagen receptor GPVI-specific agonist, collagen-related peptide (CRP). After activation with collagen, CRP, or the CLEC-2 agonist rhodocytin, Jak2Plt-/- platelets displayed decreased α-granule secretion and integrin αIIbβ3 activation or aggregation, but showed normal responses to thrombin. Jak2Plt-/- platelets had impaired intracellular signaling when activated via GPVI, as assessed by tyrosine phosphorylation. Together, the results show that JAK2 deletion impairs platelet immunoreceptor tyrosine-based activation motif signaling and hemostatic function in mice and suggest that aberrant JAK2 signaling in patients with MPNs affects GPVI signaling, leading to hemostatic platelet function.

[CALR gene mutation detection and clinical observation of 150 essential thrombocythemia patients]

目的

研究原发性血小板增多症（ET)患者CALR基因突变情况，比较其与JAK2 V617F、MPL W515K突变及三种突变阴性患者部分临床参数的差异。

方法

采用基因组DNA-PCR扩增产物直接测序法检测150例ET患者CALR基因9号外显子及MPL W515K突变；采用等位基因特异性PCR检测JAK2 V617F突变检出情况。

结果

①150例ET患者中共检出CALR突变38例（25.3%)，Ⅰ型（c.1092_1143del52bp) 17例，Ⅱ型（c.1154_1155insTTGTC) 16例，Ⅲ型（c.1094_1139del46bp) 4例，Ⅳ型（c.1103_1136del34bp) 1例。②JAK2 V617F和MPL W515K的突变检出率分别为61.3% (92/150)和2.7% (4/150)；54例JAK2 V617F及MPL W515K突变阴性患者中CALR突变检出率为70.4% (38/54)，未检测到任何两种基因突变共存。③CALR突变组的外周血白细胞和血红蛋白水平低于JAK2 V617F突变组(P<0.05)，中位年龄为59 (29~89)岁，高于三种突变阴性组的29.5 (16~67)岁(P<0.01)；147例患者有染色体核型分析结果，其中4例存在核型异常，异常核型与正常核型患者中CALR基因突变检出率分别为75.0% (3/4)、24.5% (35/143)，差异有统计学意义(P=0.019)。

结论

CALR突变在JAK2 V617F及MPL W515K突变阴性的ET患者中有较高的检出率，并与异常核型相关；CALR突变组外周血白细胞和血红蛋白水平低于JAK2 V617F突变组。

Does the level of WT1 expression predict the outcome in Philadelphia-negative myeloproliferative neoplasms?

AIMS

Despite the clinical importance of the leukemic transformation of chronic myeloproliferative neoplasms (MPNs), very little is known about markers that predict leukemic transformation. We studied WT1 expression in 37 MPN patients diagnosed as bcr-abl negative and JAK2 (V617F) positive with a molecular genetic test, and 23 healthy controls.

RESULTS

WT1 expression is higher in MPN patients compared with normal controls (p=0.002). According to the WT1 expression levels, patients were divided into two groups: high (≥0.205) and low (0-0.205) WT1 expression. Two out of six patients with a high WT1 expression level transformed to myelodysplastic syndrome at a 42- and 46-month follow-up, respectively.

CONCLUSIONS

Our results suggest that the overexpression of WT1 may play an important role in the leukemic transformation of MPNs.

Interferon and the treatment of polycythemia vera, essential thrombocythemia and myelofibrosis

Recombinant IFN-α (rIFN-α) induces complete hematologic remissions in patients with myeloproliferative neoplasms (MPNs), but its use has been limited by side effects owing to the relatively high doses used. Now, low-dose rIFN-α is stressed, starting relatively early in the course of the MPNs. In polycythemia vera, this has resulted in a significant clinical, hematologic, morphologic and molecular response manifested by reduction in the JAK2(V617F) allele burden, sustained even after discontinuation of recombinant IFN. In essential thrombocythemia, platelet count reduction is prompt and durable without treatment for varying periods. In hypercellular primary myelofibrosis, rIFN-α has restored normal blood counts, reduced splenomegaly and induced morphologic marrow remissions. This article highlights our current use of rIFN-α in MPNs.

Role of TET2 mutations in myeloproliferative neoplasms

Recently, 5-hydroxymethylcytosine (5-hmC), the 6th base of DNA, was discovered as the product of the hydroxylation of 5-methylcytosine (5-mC) by the ten-eleven translocation (TET) oncogene family members. One of them, TET oncogene family member 2 (TET2), is mutated in a variety of myeloid malignancies, including in 15% of myeloproliferative neoplasms (MPNs). Recent studies tried to go further into the biological and epigenetic function of TET2 protein and 5-hmC marks in the pathogenesis of myeloid malignancies. Although its precise function remains partially unknown, TET2 appears to be an important regulator of hematopoietic stem cell biology. In both mouse and human cells, its inactivation leads to a dramatic deregulation of hematopoiesis that ultimately triggers blood malignancies. Understanding this leukemogenic process will provide tools to develop new epigenetic therapies against blood cancers.

Jak/STAT pathways in cytokine signaling and myeloproliferative disorders: approaches for targeted therapies

Hematopoiesis is the cumulative result of intricately regulated signaling pathways that are mediated by cytokines and their receptors. Studies conducted over the past 10 to 15 years have revealed that hematopoietic cytokine receptor signaling is largely mediated by a family of tyrosine kinases termed Janus kinases (JAKs) and their downstream transcription factors, termed STATs (signal transducers and activators of transcription). Aberrations in these pathways, such as those caused by the recently identified JAK2(V617F) mutation and translocations of the JAK2 gene, are underlying causes of leukemias and other myeloproliferative disorders. This review discusses the role of JAK/STAT signaling in normal hematopoiesis as well as genetic abnormalities associated with myeloproliferative and myelodisplastic syndromes. This review also summarizes the status of several small molecule JAK2 inhibitors that are currently at various stages of clinical development. Several of these compounds appear to improve the quality of life of patients with myeloproliferative disorders by palliation of disease-related symptoms. However, to date, these agents do not seem to significantly affect bone marrow fibrosis, alter marrow histopathology, reverse cytopenias, reduce red cell transfusion requirements, or significantly reduce allele burden. These results suggest the possibility that additional mutational events might be associated with the development of these neoplasms, and indicate the need for combination therapies as the nature and significance of these additional molecular events is better understood.

Development of a highly sensitive method for detection of JAK2V617F

Background

Ph- myeloproliferative neoplasms (MPNs) represent a heterogeneous group of chronic diseases characterized by increased expansion of hematopoietic cells of the myeloid lineage. JAK2V617F, an activation mutation form of tyrosine kinase JAK2, is found in the majority of patients with MPNs. Studies have demonstrated that JAK2V617F can cause MPNs, and various methods have been developed to detect JAK2V617F for diagnostic purposes. However, a highly sensitive method is still needed for the earliest possible detection and for disease prevention and treatment.

Methods

In the present study, we developed a method dubbed restriction fragment nested allele-specific PCR (RFN-AS-PCR). The method consists of three steps: 1) initial amplification of DNA samples with PCR primers surrounding the JAK2V617F mutation site, 2) digestion of the PCR products with restriction enzyme BsaXI which only cleaves the wild type allele, and 3) detection of JAK2V617F by allele-specific PCR with nested primers.

Results

We tested the sensitivity of the method by using purified plasmid DNAs and blood cell DNAs containing known proportions of JAK2V617F. We were able to detect JAK2V617F with a sensitivity of 0.001%. We further analyzed blood cell DNA samples from 105 healthy donors with normal blood cell counts and found three JAK2V617F-positive cases, which would have remained undetected using a less sensitive method.

Conclusions

We have developed a highly sensitive method that will allow for detection of JAK2V617F at a very early stage. This method may have major implications in diagnosis and prevention of MPNs and related diseases.

Sensitive detection and quantification of the JAK2V617F allele by real-time PCR blocking wild-type amplification by using a peptide nucleic acid oligonucleotide

A single G-to-T missense mutation in the gene for the JAK2 tyrosine kinase, leading to a V617F amino acid substitution, is commonly found in several myeloproliferative neoplasms. Reliable quantification of this mutant allele is of increasing clinical and therapeutic interest in predicting and diagnosing this group of neoplasms. Because JAK2V617F is somatically acquired and may be followed by loss of heterozygosity, the percentage of mutant versus wild-type DNA in blood can vary between 0% and almost 100%. Therefore, we developed a real-time PCR assay for detection and quantification of the low-to-high range of the JAK2V617F allele burden. To allow the assay to meet these criteria, amplification of the wild-type JAK2 was blocked with a peptide nucleic acid oligonucleotide. JAK2V617F patient DNA diluted in JAK2 wild-type DNA could be amplified linearly from 0.05% to 100%, with acceptable reproducibility of quantification. The sensitivity of the assay was 0.05% (n = 3 of 3). In 9 of 100 healthy blood donors, a weak positive/background signal was observed in DNA isolated from blood, corresponding to approximately 0.01% JAK2V617F allele. In one healthy individual, we observed this signal in duplicate. The clinical relevance of this finding is not clear. By inhibiting amplification of the wild-type allele, we developed a sensitive and linear real-time PCR assay to detect and quantify JAK2V617F.

Novel multiplex bead-based assay with LNA-modified probes for detection of MPL exon 10 mutations

MPL exon 10 mutations were the second class of mutations shown to be associated with the pathogenesis of some Philadelphia chromosome - negative myeloproliferative neoplasms (MPNs). Recently, their identification gained wide recognition in the diagnostic work-up for suspected cases of JAK2 V617F negative MPNs. Various molecular approaches have been applied, yet universally accepted method is still lacking. We aimed at development and validation of a novel bead-based liquid assay using Locked nucleic acids (LNA)-modified oligonucleotide probes for multiplexed detection of the following MPL mutations: W515L/K/A/R. Testing on both artificial plasmid constructs and on clinical samples revealed that the method was comparable in terms of specificity to direct sequencing and had a much higher sensitivity of 1% mutant alleles. This method could be successfully implemented in the diagnostic work-up for MPNs. Furthermore, this system allows further multiplexing for single-tube identification of different mutations associated with MPNs.