Genomic studies in chronic myeloid malignancies, including myeloproliferative neoplasms (MPN), myelodysplastic syndromes (MDS), and MPN/MDS, have identified common mutations in genes encoding ...signaling, epigenetic, transcription, and splicing factors. In the present study, we interrogated the clonal architecture by mutation-specific discrimination analysis of single-cell–derived colonies in 28 patients with chronic myelomonocytic leukemias (CMML), the most frequent MPN/MDS. This analysis reveals a linear acquisition of the studied mutations with limited branching through loss of heterozygosity. Serial analysis of untreated and treated samples demonstrates a dynamic architecture on which most current therapeutic approaches have limited effects. The main disease characteristics are early clonal dominance, arising at the CD34+/CD38− stage of hematopoiesis, and granulomonocytic differentiation skewing of multipotent and common myeloid progenitors. Comparison of clonal expansions of TET2 mutations in MDS, MPN, and CMML, together with functional invalidation of TET2 in sorted progenitors, suggests a causative link between early clonal dominance and skewed granulomonocytic differentiation. Altogether, early clonal dominance may distinguish CMML from other chronic myeloid neoplasms with similar gene mutations.
•Early clonal dominance may distinguish chronic myelomonocytic leukemia from other chronic myeloid neoplasms with similar gene mutations.•Early dominance of TET2-mutated cells in the hematopoietic tissue promotes myeloid differentiation skewing toward the granulomonocytic line.
Editorial discusses the perspectives opened by the recently discovered IL‐34, its conservation across species in the biology of the cytokine CSF‐1, and identification of a new CSF‐1R ligand that ...could together account for the well‐known heterogeneity of monocytes.
•ASXL1 hotspot mutations around codon G646 are prevalent in myeloid diseases but are rarely identified in clonal hematopoiesis of indeterminate potential, suggesting that they are highly pathogenic ...and confer a higher risk of the development of myeloid diseases.•Although genetic studies conducted in mice suggest that they are loss-of-function and gain-of-new-function at the physiologic level, overexpression studies in transgenic mice and cell lines indicate that they are dominant-negative and gain-of-function. Additional rigorous investigations are needed to provide a definitive answer to this question.•ASXL1 mutations are associated with poor prognosis in all myeloid diseases, perhaps owing to the reduced response to the current treatment options.•We recently discovered that Asxl1 loss cooperates with oncogenic Nras in mice to reprogram the immune microenvironment and drive leukemic transformation. Our study provides a strong rationale to develop combined targeted therapy and immunotherapy for treating patients with leukemia with concurrent ASXL1 and NRAS mutations.
Next-generation sequencing technology, including whole-exome or whole-genome sequencing and target gene sequencing, has allowed the molecular characterization of somatic mutation spectrums in hematologic diseases. Mutations in Additional sex combs-like 1 (ASXL1), a chromatin regulator, are identified in clonal hematopoiesis of indeterminate potential (CHIP), indicating ASXL1 mutations as early events in leukemogenesis. Not surprisingly, they occur at high frequency in myeloid malignancies and are associated with poor prognosis. Therefore, understanding how mutant ASXL1 drives clonal expansion and leukemogenesis will serve as the basis for the future development of preventative and/or therapeutic strategies for myeloid diseases with ASXL1 mutations. Here, we discuss the biology of ASXL1 and its role in controlling normal and malignant hematopoiesis. In addition, we review the clinical relevance of ASXL1 mutations in CHIP and myeloid diseases.
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.
Megakaryopoiesis is a 2-step differentiation process, regulated by thrombopoietin (TPO), on binding to its cognate receptor myeloproliferative leukemia (MPL). This receptor associates with ...intracytoplasmic tyrosine kinases, essentially janus kinase 2 (JAK2), which regulates MPL stability and cell-surface expression, and mediates TPO-induced signal transduction. We demonstrate that JAK2 and MPL mediate TPO-induced proliferation arrest and megakaryocytic differentiation of the human megakaryoblastic leukemia cell line UT7-MPL. A decrease in JAK2 or MPL protein expression, and JAK2 chemical inhibition, suppress this antiproliferative action of TPO. The expression of JAK2 and MPL, which progressively increases along normal human megakaryopoiesis, is decreased in platelets of patients diagnosed with JAK2- or MPL-mutated essential thrombocytemia and primary myelofibrosis, 2 myeloproliferative neoplasms in which megakaryocytes (MKs) proliferate excessively. Finally, low doses of JAK2 chemical inhibitors are shown to induce a paradoxical increase in MK production, both in vitro and in vivo. We propose that JAK2 and MPL expression levels regulate megakaryocytic proliferation vs differentiation in both normal and pathological conditions, and that JAK2 chemical inhibitors could promote a paradoxical thrombocytosis when used at suboptimal doses.
•We propose that megakaryopoiesis is regulated by the expression levels of the TPO receptor MPL and the associated tyrosine kinase JAK2.•This model could explain why suboptimal doses of JAK2 inhibitors can induce a paradoxical increase in platelet production.
Mutations in chromatin regulator ASXL1 are frequently identified in myeloid malignancies, in particular ∼40% of patients with chronic myelomonocytic leukemia (CMML). ASXL1 mutations are associated ...with poor prognosis in CMML and significantly co-occur with NRAS mutations. Here, we show that concurrent ASXL1 and NRAS mutations defined a population of CMML patients who had shorter leukemia-free survival than those with ASXL1 mutation only. Corroborating this human data, Asxl1-/- accelerated CMML progression and promoted CMML transformation to acute myeloid leukemia (AML) in NrasG12D/+ mice. NrasG12D/+;Asxl1-/- (NA) leukemia cells displayed hyperactivation of MEK/ERK signaling, increased global levels of H3K27ac, upregulation of Flt3. Moreover, we find that NA-AML cells overexpressed all the major inhibitory immune checkpoint ligands: programmed death-ligand 1 (PD-L1)/PD-L2, CD155, and CD80/CD86. Among them, overexpression of PD-L1 and CD86 correlated with upregulation of AP-1 transcription factors (TFs) in NA-AML cells. An AP-1 inhibitor or short hairpin RNAs against AP-1 TF Jun decreased PD-L1 and CD86 expression in NA-AML cells. Once NA-AML cells were transplanted into syngeneic recipients, NA-derived T cells were not detectable. Host-derived wild-type T cells overexpressed programmed cell death protein 1 (PD-1) and T-cell immunoreceptor with immunoglobulin and ITIM domains (TIGIT) receptors, leading to a predominant exhausted T-cell phenotype. Combined inhibition of MEK and BET resulted in downregulation of Flt3 and AP-1 expression, partial restoration of the immune microenvironment, enhancement of CD8 T-cell cytotoxicity, and prolonged survival in NA-AML mice. Our study suggests that combined targeted therapy and immunotherapy may be beneficial for treating secondary AML with concurrent ASXL1 and NRAS mutations.
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