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The developmental history of blood cancer begins with mutation acquisition and the resulting malignant clone expansion. The two most prevalent driver mutations found in myeloproliferative neoplasms- JAK2 V617F and CALR m -occur in hematopoietic stem cells, which are highly complex to observe in vivo. To circumvent this difficulty, we propose a method relying on mathematical modeling and statistical inference to determine disease initiation and dynamics. Our findings suggest that CALR m mutations tend to occur later in life than JAK2 V617F . Our results confirm the higher proliferative advantage of the CALR m malignant clone compared to JAK2 V617F . Furthermore, we illustrate how mathematical modeling and Bayesian inference can be used for setting up early screening strategies.

Myeloproliferative neoplasms (MPN) are mainly sporadic but inherited variants have been associated with higher risk development. Here, we identified an EPOR variant (EPOR P488S ) in a large family diagnosed with JAK2 V617F -positive polycythaemia vera (PV) or essential thrombocytosis (ET). We investigated its functional impact on JAK2 V617F clonal amplification in patients and found that the variant allele fraction (VAF) was low in PV progenitors but increase strongly in mature cells. Moreover, we observed that EPOR P488S alone induced a constitutive phosphorylation of STAT5 in cell lines or primary cells. Overall, this study points for searching inherited-risk alleles affecting the JAK2/STAT pathway in MPN., (© 2022 British Society for Haematology and John Wiley & Sons Ltd.)

The germline predisposition associated with the autosomal dominant inheritance of the 14q32 duplication implicating ATG2B/GSKIP genes is characterized by a wide clinical spectrum of myeloid neoplasms. We analyzed 12 asymptomatic carriers and 52 patients aged 18-74 years from six families, by targeted sequencing of 41 genes commonly mutated in myeloid malignancies. We found that 75% of healthy carriers displayed early clonal hematopoiesis mainly driven by TET2 mutations. Molecular landscapes of patients revealed two distinct routes of clonal expansion and leukemogenesis. The first route is characterized by the clonal dominance of myeloproliferative neoplasms (MPN)-driver events associated with TET2 mutations in half of cases and mutations affecting splicing and/or the RAS pathway in one-third of cases, leading to the early development of MPN, mostly essential thrombocythemia, with a high risk of transformation (50% after 10 years). The second route is distinguished by the absence of MPN-driver mutations and leads to AML without prior MPN. These patients mostly harbored a genomic landscape specific to acute myeloid leukemia secondary to myelodysplastic syndrome. An unexpected result was the total absence of DNMT3A mutations in this cohort. Our results suggest that the germline duplication constitutively mimics hematopoiesis aging by favoring TET2 clonal hematopoiesis., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Classical BCR-ABL-negative myeloproliferative neoplasms (MPNs) are clonal disorders of hematopoietic stem cells (HSCs) caused mainly by recurrent mutations in genes encoding JAK2 (JAK2), calreticulin (CALR), or the thrombopoietin receptor (MPL). Interferon α (IFNα) has demonstrated some efficacy in inducing molecular remission in MPNs. To determine factors that influence molecular response rate, we evaluated the long-term molecular efficacy of IFNα in patients with MPN by monitoring the fate of cells carrying driver mutations in a prospective observational and longitudinal study of 48 patients over more than 5 years. We measured the clonal architecture of early and late hematopoietic progenitors (84 845 measurements) and the global variant allele frequency in mature cells (409 measurements) several times per year. Using mathematical modeling and hierarchical Bayesian inference, we further inferred the dynamics of IFNα-targeted mutated HSCs. Our data support the hypothesis that IFNα targets JAK2V617F HSCs by inducing their exit from quiescence and differentiation into progenitors. Our observations indicate that treatment efficacy is higher in homozygous than heterozygous JAK2V617F HSCs and increases with high IFNα dose in heterozygous JAK2V617F HSCs. We also found that the molecular responses of CALRm HSCs to IFNα were heterogeneous, varying between type 1 and type 2 CALRm, and a high dose of IFNα correlates with worse outcomes. Our work indicates that the long-term molecular efficacy of IFNα implies an HSC exhaustion mechanism and depends on both the driver mutation type and IFNα dose., (© 2021 by The American Society of Hematology.)

Mutations of calreticulin (CALRm) define a subtype of myeloproliferative neoplasms (MPN). We studied the biological and genetic features of CALR-mutated essential thrombocythemia and myelofibrosis patients. In most cases, CALRm were found in granulocytes, monocytes, B and NK cells, but also in T cells. However, the type 1 CALRm spreads more easily than the type 2 CALRm in lymphoid cells. The CALRm were also associated with an early clonal dominance at the level of hematopoietic stem and progenitor cells (HSPC) with no significant increase during granulo/monocytic differentiation in most cases. Moreover, we found that half of type 2 CALRm patients harbors some homozygous progenitors. Those patients were associated with a higher clonal dominance during granulo/monocytic differentiation than patients with only heterozygous type 2 CALRm progenitors. When associated mutations were present, CALRm were the first genetic event suggesting that they are both the initiating and phenotypic event. In blood, type 1 CALRm led to a greater increased number of all types of progenitors compared with the type 2 CALRm. However, both types of CALRm induced an increase in megakaryocytic progenitors associated with a ruxolitinib-sensitive independent growth and with a mild constitutive signaling in megakaryocytes. At the transcriptional level, type 1 CALRm seems to deregulate more pathways than the type 2 CALRm in megakaryocytes. Altogether, our results show that CALRm modify both the HSPC and megakaryocyte biology with a stronger effect for type 1 than for type 2 CALRm.

During these past 5 years several studies have provided major genetic insights into the pathogenesis of the so-called classical myeloproliferative neoplasms (MPNs): polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). The discovery of the JAK2V617F mutation first, then of the JAK2 exon 12 and MPLW515 mutations, have modified the understanding of these diseases, their diagnosis, and management. Now it is established that almost 100% of PV patients present a JAK2 mutation. Nearly 60% of ET patients and 50% of patients with PMF have the JAK2V617F mutation. The MPLW515 mutations are also present in a small proportion of ET and PMF patients. These mutations are oncogenic events that cause these disorders; however, they do not explain the heterogeneity of the entities in which they occur. Genetic defects have not been yet identified in around 40% of ET and PMF. There are likely additional somatic genetic factors important for the MPN phenotype like the recently described TET2, ASXL1, and CBL mutations. Moreover, polymorphisms in the JAK2 gene have been recently described as associated with MPN. Additional studies of large cohorts are required to dissect the genetic events in MPNs and the mechanisms of these oncogenic cooperations.

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., (2009 Massachusetts Medical Society)