JAK2-V617F mutation analysis of granulocytes and platelets from patients with chronic myeloproliferative disorders: advantage of studying platelets

miR-203 and miR-221 regulate SOCS1 and SOCS3 in essential thrombocythemia

The biological basis of essential thrombocythemia (ET) patients lacking known mutations is still unknown. MicroRNAs (miRNA) regulate hematopoietic differentiation and are deregulated in several hematopoietic malignancies. However, miRNA expression in ET patients has been poorly explored. We performed miRNA profiling in platelets from 19 ET patients and 10 healthy controls. Hierarchical cluster analysis showed two well-separated clusters between patients and controls, indicating that ET platelets had a characteristic 70-miRNA signature (P<0.0001), 68 of which were downregulated. According to the mutational status, three differentially expressed miRNAs, miR-15a (P=0.045), miR-150 (P=0.001) and miR-519a (P=0.036), were identified. A 40-miRNA signature was identified characterizing JAK2V617F-positive ET patients. Eight genes, whose interaction with the miRNAs could activate the JAK/STAT pathway were identified. An inverse correlation was observed between miRNAs expression and their target genes for SOCS1 and miR-221, SOCS3 and miR-221, SOCS3 and miR-203, and PTPN11 and miR-23a. All three miRNAs were upregulated in JAK2V617F-negative ET patients. SOCS1 and SOCS3 were validated as targets of miR-221 and miR-203, respectively. In summary, our study shows that platelets from JAK2V617F-negative ET patients harbor a specific miRNA signature that can participate in the modulation of the JAK/STAT pathway through regulation of key genes as SOCS1 and SOCS3.

Validation of reference genes for the determination of platelet transcript level in healthy individuals and in patients with the history of myocardial infarction

RT-qPCR is the standard method for studying changes in relative transcript level in different experimental and clinical conditions and in different tissues. No validated reference genes have been reported for the normalization of transcript level in platelets. The very low level of platelet RNA and the elimination of leukocyte contamination represented special methodological difficulties. Our aims were to apply a simple technique to separate platelets for transcript level studies, and select the most stable reference genes for platelets from healthy individuals and from patients with the history of myocardial infarction. We developed a simple, straightforward method of platelet separation for RNA isolation. Platelet activation was inhibited by using acid-citrate-dextrose for anticoagulation and by prostaglandin E1. Leukocyte contamination was eliminated by three consecutive centrifugations. Samples prepared by this method were free of leukocytes, showed no inhibition in PCR reaction and no RNA degradation. The assay demands low blood volume, which complies with the requirements of everyday laboratory routine. Seventeen potential reference genes were investigated, but eight of them were excluded during optimization. The stability of the remaining genes, EEF2, EAR, ACTB, GAPDH, ANAPC5, OAZ1, HDGF, GNAS, and CFL1, were determined by four different descriptive statistics. GAPDH, GNAS, and ACTB were shown to be the most stable genes in platelets of healthy individuals, while HDGF, GNAS, and ACTB were the most stable in platelets of patients with the history of myocardial infarction. The results confirm that data normalization needs assessment of appropriate reference genes for a particular sample set.

Differences in the JAK2 and MPL mutation status in the cell lineages of the bcr/abl-negative chronic myeloproliferative neoplasm subtypes

OBJECTIVE

While the somatic mutation of Janus Kinase 2 (JAK2) and the thrombopoietin receptor (c-MPL) gene are thought to affect the pathogenesis of bcr/abl negative chronic myeloproliferative neoplasm (MPN), the relationship between the mutation and the clinical features remain obscure.

METHODS

The mutation status of these genes in granulocytes, platelets, T-cells, and erythroid colonies (BFU-E) was obtained from 115 MPN patients, and then the clinical features of the MPN subtypes were compared.

RESULTS

The JAK2-V617F mutation was observed in three lineages of granulocytes, platelets, and BFU-E in almost all polycythemia vera (PV) and primary myelofibrosis (PMF) patients. In contrast, 68% of essential thrombocythemia (ET) patients have the JAK2-V617F mutation in at least one of the lineages, of which 70% of these patients have the JAK2-V617F mutation in three lineages; the remaining ET patients with the JAK2-V617F mutation only exhibited the mutation in one or two lineages. Further, the ET patients that exhibited the JAK2-V617F mutation in three lineages had higher WBC and granulocyte counts as compared to the ET patients that did not have the JAK2-V617F mutation or only had the mutation in one or two lineages. Concerning the MPL gene, two ET patients had the MPL-W515L gene mutation in their platelets, although the lineage of the JAK2-V617F mutation involved differed from case to case.

CONCLUSION

The progenitor cells that are involved with the JAK2-V617F mutation in MPNs are different in each subtype and this difference may also affect the clinical features of MPNs.

Prognostic utility of spontaneous erythroid colony formation and JAK2 mutational analysis for thrombotic events in essential thrombocythaemia

BACKGROUND

Thrombotic events in essential thrombocythaemia (ET) are difficult to predict with current risk stratification based on age and prior history of thrombosis.

AIMS

We aimed to assess the predictive value of the JAK2 V617F mutation (JAK2) and spontaneous erythroid colony (SEC) growth for the development of thrombotic events post diagnosis in patients with ET.

METHODS

Consecutive patients with ET were retrospectively identified, and clinical and laboratory correlates were evaluated. Thrombotic events were categorized according to their occurrence at or prior to diagnosis (prior thrombosis), and any time post diagnosis of ET (subsequent thrombosis). JAK2 analysis was performed by allele-specific PCR on whole blood or bone marrow.

RESULTS

A total of 62 patients was identified, median age 63 years; 67% (41/61) JAK2-positive and 47% (25/53) SEC-positive. Median follow-up was 33 months (range, 1 to 137). JAK2-positive patients showed a trend to increased prior thrombosis (27% vs 5%, P= 0.08), and a significant increase in the development of subsequent thrombosis (5-year event rate 31% vs 6%, P= 0.04), which persisted when stratified for a history of prior thrombosis (P= 0.04). Survival was not affected by JAK2 status. The SEC assay predicted an increased rate of baseline thrombosis (16% vs 0%, P= 0.04), but was not found to be predictive of any subsequent thrombotic events.

CONCLUSIONS

Patients with ET who are JAK2-positive by whole blood allele-specific PCR appear to be at increased risk of thrombotic complications, which is independent of a prior history of thrombosis.

Quantitative assay for the detection of the V617F variant in the Janus kinase 2 (JAK2) gene using the Luminex xMAP technology

Background

The availability of clinically valid biomarkers contribute to improve the diagnosis and clinical management of diseases. A valine-to-phenylalanine substitution at position 617 (V617F) in the Janus kinase 2 (JAK2) gene has been recently associated with key signaling abnormalities in the transduction of haemopoietic growth-factor receptors and is now considered as a useful clinical marker of myeloproliferative neoplasms. Several methods have recently been reported to detect the JAK2 V617F point mutation and show variable sensitivity.

Methods

Using the Luminex xMAP technology, we developed a quantitative assay to detect the JAK2V617F variant. The method was based on polymerase chain reaction (PCR) followed by hybridization to specific probes coupled with internally dyed microspheres. The assay comprises 3 steps: genomic DNA extraction, end point PCR reaction, direct hybridization of PCR fragments and quantification. It has been tested with different sources of nucleic acid.

Results

Applied to whole blood samples, this quantitative assay showed a limit of detection of 2%. A highly sensitive allele-specific primer extension reaction performed in parallel allowed to validate the results and to identify the specimens with values below 2%.

Conclusion

Direct hybridization assay using the Luminex xMAP technology allows sensitive quantification of JAK2V617F from blood spots. It is simple and can be easily performed in a clinical setting.

Design and evaluation of a real-time PCR assay for quantification of JAK2 V617F and wild-type JAK2 transcript levels in the clinical laboratory

The somatic mutation JAK2 V617F is associated with BCR-ABL1-negative myeloproliferative neoplasms. Detection of this mutation aids diagnosis of these neoplasms, and quantification of JAK2 V617F may provide a method to monitor response to therapy. For these reasons, we designed a clinical assay that uses allele-specific PCR and real-time detection with hydrolysis probes for the quantification of JAK2 V617F, wild-type JAK2, and GAPDH transcripts. Mutant and wild-type JAK2 were quantified by using external plasmid standards that contain the relevant JAK2 V617F or JAK2 sequence, respectively. We tested 55 peripheral blood specimens from patients with suspected myeloproliferative neoplasms and 55 peripheral blood specimens from patients not known to have myeloproliferative neoplasms. Low-level, nonspecific amplification was detected in reactions containing a high copy number of plasmid standards and in specimens from patients not known to have myeloproliferative neoplasms, necessitating the use of a laboratory-established mutant to wild-type cutoff. The limit of detection established by using cell line dilutions is 0.1%, and this method identified three JAK2 V617F-positive patients who were not detected by a less sensitive method. The assay characteristics and our initial evaluation indicate this method can be used for the detection and quantification of JAK2 V617F, which should be useful for diagnosis of myeloproliferative neoplasms and potentially for monitoring minimal residual disease in future trials of therapies targeted to myeloproliferative neoplasms.

JAK2(V617F) allele burden discriminates essential thrombocythemia from a subset of prefibrotic-stage primary myelofibrosis

OBJECTIVE

Among Philadelphia chromosome-negative myeloproliferative neoplasms (Ph(-) MPN), essential thrombocythemia (ET) and the prefibrotic phase of primary myelofibrosis (PMF) represent two subtypes with considerable overlap.

MATERIALS AND METHODS

In this study, histopathological classification of 490 MPN cases was correlated with the allelic burden of JAK2(V617F) and MPL(W515L).

RESULTS

Ph(-) MPN entities largely overlap with regard to JAK2(V617F) and MPL(W515L) allele burden, but ET displayed mutant allele burden <50%. PMF with different stages of myelofibrosis all yielded similar JAK2(V617F) allele burden. At initial presentation one-quarter of prefibrotic PMF cases exhibited an allele burden exceeding 50% (38% median JAK2(V617F) alleles, n=102). In ET, its main differential diagnosis, not a single case was found with >40% JAK2(V617F) alleles (median, 24% JAK2(V617F) alleles; n=90; p<0.001). Increase in JAK2(V617F) alleles during follow-up could not be linked to fibrosis or blastic progression but was related to polycythemic transformation in ET. MPL(W515L) was found in 3% of ET and 8% of PMF, with a significantly higher percentage of mutated alleles in fibrotic than prefibrotic PMF (median, 78% MPL(W515L) alleles; p<0.05).

CONCLUSION

Histopathological categories ET and prefibrotic PMF correlate with significant differences in mutant allelic burden of JAK2(V617F), but not of MPL(W515L) which, by contrast to JAK2(V617F), shows a higher percentage of mutated alleles in fibrotic than in prefibrotic cases. Thus, for Ph(-) MPN in which ET and prefibrotic PMF represent the most probable diagnoses, a JAK2(V617F) allele burden >50% favors a diagnosis of prefibrotic PMF.

Association of V617F Jak2 mutation with the risk of thrombosis among patients with essential thrombocythaemia or idiopathic myelofibrosis: a systematic review

INTRODUCTION

Many studies evaluated the association of V617F Jak-2 with the risk of thrombosis in patients with essential thrombocythaemia, but the results of these studies were inconsistent. Few studies evaluated the association of V617F Jak-2 mutation with the risk of thrombosis in patients with idiopathic myelofibrosis. Therefore, we performed a systematic review of the studies that assessed the risk of thrombosis associated with V617F Jak-2 in patients with ET or IM.

MATERIALS AND METHODS

We searched MEDLINE and EMBASE databases and reference lists of retrieved articles. Odds ratios (ORs) and 95% confidence intervals (CI) were calculated for each trial and pooled.

RESULTS

We included 21 studies involving patients with essential thrombocythaemia and 6 studies patients with idiopathic myelofibrosis. In essential thrombocythaemia patients, V617F Jak-2 was associated with a significant increased risk of thrombosis (OR 1.92, 95% CI 1.45-2.53), both of venous (OR 2.49, 95% CI 1.71-3.61) and arterial (OR 1.77, 95% CI 1.29-2.43) vessels. In idiopathic myelofibrosis patients, the risk of thrombosis associated with V617F Jak-2 tended to be increased (OR 1.76, 95% CI 0.91-3.41).

CONCLUSIONS

Our systematic review suggests that V617F Jak-2 increases the risk of thrombosis in essential thrombocythaemia patients by about two fold while its role in idiopathic myelofibrosis patients is uncertain.

High prevalence of arterial thrombosis in JAK2 mutated essential thrombocythaemia: independence of the V617F allele burden

Approximately half of the patients with essential thrombocythaemia (ET) harbor the JAK2 V617F mutation. Despite a phenotypic mimicry of JAK2 V617F positive ET and polycythaemia vera (PV), the data on thromboembolic risk and correlation to JAK2 mutation status are ambiguous. On a strictly WHO defined ET cohort we evaluated possible clinical correlations to the JAK2 mutation status including a history of previous thrombosis. We used a highly sensitive quantitative real-time PCR (qPCR) assay for JAK2 V617F detection and allele burden quantification in a single institution study of 55 patients. A significantly increased prevalence of arterial thrombosis was recorded in JAK2 positive ET (p=0.001). There was no association between the mutational load and thrombosis. As compared to their JAK2 V617F negative counterparts, the JAK2 V617F positive patients had PV-like biochemical characteristics such as higher haemoglobin levels (p=0.02), lower platelet counts (p=0.002) and lower plasma EPO levels (p=0.04). The JAK2 V617F mutation per se but not the mutational load in patients with ET is associated with a PV-like phenotype and a higher prevalence of previous arterial thrombosis. This study adds further support to the contention of the JAK2 V617F mutation as a marker of increased risk of thrombosis.

Is JAK2 V617F mutation more than a diagnostic index? A meta-analysis of clinical outcomes in essential thrombocythemia

A systematic review and meta-analysis was carried out to compare the frequency of clinically significant outcomes between JAK2 V617F positive and wild type patients with essential thrombocythemia (ET). JAK2 V617F positivity in patients with ET was associated with a clear increase in the odds of thrombosis [OR=1.83 (95% CI, 1.32-2.53), p<0.0001], and much higher odds of transformation to polycythemia vera [OR=7.67 (95% CI, 2.04-28.87), p=0.0009]. The mean difference of the white blood cell count between JAK2 positive and negative patients was associated with an increased odds ratio for thrombosis (p=0.02). The JAK2 V617F mutation in patients with ET is associated with an increased risk of adverse cardiovascular outcomes via an increase in the leukocyte count.