A truncation mutant of Csf3r cooperates with PML-RARα to induce acute myeloid leukemia in mice

Chronic neutrophilic leukemia and atypical chronic myeloid leukemia: 2024 update on diagnosis, genetics, risk stratification, and management

Chronic neutrophilic leukemia (CNL) is a rare BCR::ABL1-negative myeloproliferative neoplasm (MPN) defined by persistent mature neutrophilic leukocytosis and bone marrow granulocyte hyperplasia. Atypical chronic myeloid leukemia (aCML) (myelodysplastic "[MDS]/MPN with neutrophilia" per World Health Organization [WHO]) is a MDS/MPN overlap disorder featuring dysplastic neutrophilia and circulating myeloid precursors. Both manifest with frequent hepatosplenomegaly and less commonly, bleeding, with high rates of leukemic transformation and death. The 2022 revised WHO classification conserved CNL diagnostic criteria of leukocytosis ≥25 × 109/L, neutrophils ≥80% with <10% circulating precursors, absence of dysplasia, and presence of an activating CSF3R mutation. ICC criteria are harmonized with those of other myeloid entities, with a key distinction being lower leukocytosis threshold (≥13 × 109/L) for cases CSF3R-mutated. Criteria for aCML include leukocytosis ≥13 × 109/L, dysgranulopoiesis, circulating myeloid precursors ≥10%, and at least one cytopenia for MDS-thresholds (ICC). In both classifications ASXL1 and SETBP1 (ICC), or SETBP1 ± ETNK1 (WHO) mutations can be used to support the diagnosis. Both diseases show hypercellular bone marrow due to a granulocytic proliferation, aCML distinguished by dysplasia in granulocytes ± other lineages. Absence of monocytosis, rare/no basophilia, or eosinophilia, <20% blasts, and exclusion of other MPN, MDS/MPN, and tyrosine kinase fusions, are mandated. Cytogenetic abnormalities are identified in ~1/3 of CNL and ~15-40% of aCML patients. The molecular signature of CNL is a driver mutation in colony-stimulating factor 3 receptor-classically T618I, documented in >80% of cases. Atypical CML harbors a complex genomic backdrop with high rates of recurrent somatic mutations in ASXL1, SETBP1, TET2, SRSF2, EZH2, and less frequently in ETNK1. Leukemic transformation rates are ~10-25% and 30-40% for CNL and aCML, respectively. Overall survival is poor: 15-31 months in CNL and 12-20 months in aCML. The Mayo Clinic CNL risk model for survival stratifies patients according to platelets <160 × 109/L (2 points), leukocytes >60 × 109/L (1 point), and ASXL1 mutation (1 point); distinguishing low- (0-1 points) versus high-risk (2-4 points) categories. The Mayo Clinic aCML risk model attributes 1 point each for: age >67 years, hemoglobin <10 g/dL, and TET2 mutation, delineating low- (0-1 risk factor) and high-risk (≥2 risk factors) subgroups. Management is risk-driven and symptom-directed, with no current standard of care. Most commonly used agents include hydroxyurea, interferon, Janus kinase inhibitors, and hypomethylating agents, though none are disease-modifying. Hematopoietic stem cell transplant is the only potentially curative modality and should be considered in eligible patients. Recent genetic profiling has disclosed CBL, CEBPA, EZH2, NRAS, TET2, and U2AF1 to represent high-risk mutations in both entities. Actionable mutations (NRAS/KRAS, ETNK1) have also been identified, supporting novel agents targeting involved pathways. Preclinical and clinical studies evaluating new drugs (e.g., fedratinib, phase 2) and combinations are detailed.

Leukemia-associated truncation of granulocyte colony-stimulating factor receptor impacts granulopoiesis throughout the life-course

Introduction

The granulocyte colony-stimulating factor receptor (G-CSFR), encoded by the CSF3R gene, is involved in the production and function of neutrophilic granulocytes. Somatic mutations in CSF3R leading to truncated G-CSFR forms are observed in acute myeloid leukemia (AML), particularly those subsequent to severe chronic neutropenia (SCN), as well as in a subset of patients with other leukemias.

Methods

This investigation introduced equivalent mutations into the zebrafish csf3r gene via genome editing and used a range of molecular and cellular techniques to understand the impact of these mutations on immune cells across the lifespan.

Results

Zebrafish harboring truncated G-CSFRs showed significantly enhanced neutrophil production throughout successive waves of embryonic hematopoiesis and a neutrophil maturation defect in adults, with the mutations acting in a partially dominant manner.

Discussion

This study has elucidated new insights into the impact of G-CSFR truncations throughout the life-course and created a bone fide zebrafish model for further investigation.

Chronic neutrophilic leukemia: 2022 update on diagnosis, genomic landscape, prognosis, and management

DISEASE OVERVIEW

Chronic neutrophilic leukemia (CNL) is a rare, often aggressive myeloproliferative neoplasm (MPN) defined by persistent mature neutrophilic leukocytosis, bone marrow granulocyte hyperplasia, and frequent hepatosplenomegaly. The 2013 seminal discovery of oncogenic driver mutations in colony-stimulating factor 3 receptor (CSF3R) in the majority of patients with CNL not only established its molecular pathogenesis but provided a diagnostic biomarker and rationale for pharmacological targeting.

DIAGNOSIS

In 2016, the World Health Organization (WHO) recognized activating CSF3R mutations as a central diagnostic feature of CNL. Other criteria include leukocytosis of ≥25 × 10⁹ /L comprising >80% neutrophils with <10% circulating precursors and rare blasts, and absence of dysplasia or monocytosis, while not fulfilling criteria for other MPN.

MANAGEMENT

There is currently no standard of care for management of CNL, due in large part to the rarity of disease and dearth of formal clinical trials. Most commonly used therapeutic agents include conventional oral chemotherapy (e.g., hydroxyurea), interferon, and Janus kinase (JAK) inhibitors, while hematopoietic stem cell transplant remains the only potentially curative modality.

DISEASE UPDATES

Increasingly comprehensive genetic profiling in CNL, including new data on clonal evolution, has disclosed a complex genomic landscape with additional mutations and combinations thereof driving disease progression and drug resistance. Although accurate prognostic stratification and therapeutic decision-making remain challenging in CNL, emerging data on molecular biomarkers and the addition of newer agents, such as JAK inhibitors, to the therapeutic arsenal, are paving the way toward greater standardization and improvement of patient care.

Mechanisms of leukemic transformation in congenital neutropenia

PURPOSE OF REVIEW

The development of a myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) in patients with congenital neutropenia is now the major cause of mortality. Treatment options are limited and there are no effective prevention strategies. This review focuses on mechanisms of leukemic transformation in severe congenital neutropenia (SCN) and Shwachman-Diamond syndrome (SDS), the two most common types of congenital neutropenia.

RECENT FINDINGS

AML/MDS that develops in the setting of congenital neutropenia has distinct molecular features. Clonal hematopoiesis because of TP53 mutations is seen in nearly 50% of patients with SDS, but is not seen in patients with SCN. Accordingly, there is a very high frequency of TP53 mutations in AML/MDS arising in the setting of SDS but not SCN. The rate of mutation accumulation in hematopoietic stem cells (HSCs) from patients with congenital neutropenia is not increased.

SUMMARY

Both HSC cell-intrinsic and noncell-intrinsic changes contribute to the development of clonal hematopoiesis in congenital neutropenia and likely accounts for the high rate of leukemic transformation. In SCN, the persistently high levels of granulocyte colony-stimulating factor drive expansion of HSCs carrying truncation mutations of CSF3R. In SDS, impaired ribosome biogenesis induces p53-mediated growth inhibition and drives expansion of HSCs carrying TP53 mutations.

Chronic neutrophilic leukemia: 2020 update on diagnosis, molecular genetics, prognosis, and management

DISEASE OVERVIEW

Chronic neutrophilic leukemia (CNL) is a rare, often aggressive myeloproliferative neoplasm (MPN) defined by persistent mature neutrophilic leukocytosis, bone marrow granulocyte hyperplasia, and frequent hepatosplenomegaly. The seminal discovery of oncogenic driver mutations in colony-stimulating factor 3 receptor (CSF3R) in the majority of patients with CNL in 2013 anchored a new scientific framework, deepening our understanding of its molecular pathogenesis, providing a diagnostic biomarker, and rationalizing the use of pharmacological targeting.

DIAGNOSTIC CRITERIA

In 2016, the World Health Organization (WHO) included the presence of activating CSF3R mutations as a central diagnostic feature of CNL. Other criteria include leukocytosis of ≥25 × 10⁹ /L comprising >80% neutrophils with <10% circulating precursors and rare blasts, and absence of dysplasia or monocytosis, while not fulfilling criteria for other MPN.

DISEASE UPDATES

Increasingly comprehensive genetic profiling of CNL has disclosed a complex genomic landscape and additional prognostically relevant mutational combinations. Though prognostic determination and therapeutic decision-making remain challenging, emerging data on prognostic markers and the use of newer therapeutic agents, such as JAK inhibitors, are helping to define state-of-the-art management in CNL.

Clonal evolution in a chronic neutrophilic leukemia patient

Objectives and importance: Chronic neutrophilic leukemia (CNL) is a distinct myeloproliferative neoplasm with a high prevalence (>80%) of mutations in the colony-stimulating factor 3 receptor (CSF3R); these mutations activate the receptor, leading to the proliferation of neutrophils that are a hallmark of CNL. Clinical presentation: We present a male patient who presented peripheral blood leukocytosis. On the basis of his morphological appearances and molecular findings he was determined to have a diagnosis of chronic neutrophilic leukemia. At a follow-up at 7 months, in addition to the CSF3R c.2373G > A (p.W791*) truncated mutation, another CSF3R mutation appeared as c.1853C > T(p.T618I). Discussion and conclusion: We present the first patient with a diagnosis of chronic neutrophilic leukemia with a c.2373G > A (p.W791*) truncated mutation of CSF3R. These findings elucidate a novel paradigm of CNL pathogenesis and explain how mutations drive the development of the disease. The order of acquisition of CSF3R mutations relative to mutations in epigenetic modifiers and the spliceosome have been determined only in isolated case reports; thus, further work is needed to understand the impact of mutation chronology on the clonal evolution and progression of CNL.

Recent Progress in Chronic Neutrophilic Leukemia and Atypical Chronic Myeloid Leukemia

PURPOSE OF REVIEW

We reviewed recent diagnostic and therapeutic progress in chronic neutrophilic leukemia (CNL) and atypical chronic myeloid leukemia (aCML). We summarized recent genetic data that may guide future efforts towards implementing risk-adapted therapy based on mutational profile and improving disease control and survival of affected patients.

RECENT FINDINGS

Recent genetic data in CNL and aCML prompted modifications to the World Health Organization (WHO) diagnostic criteria, which have improved our understanding of how CNL and aCML are different diseases despite sharing common findings of peripheral granulocytosis and marrow myeloid hyperplasia. The overlap of recurrently mutated genes between aCML and CMML support considering CSF3R-T618I mutated cases as a distinct entity, either as CNL or CNL with dysplasia. Ongoing preclinical and clinical studies will help to further inform the therapeutic approach to these diseases. Our understanding of CNL and aCML has greatly advanced over the last few years. This will improve clarity for the diagnosis of these diseases, provide a strategy for risk stratification, and guide risk-adapted therapy.

Chronic neutrophilic leukemia: new science and new diagnostic criteria

Chronic neutrophilic leukemia (CNL) is a distinct myeloproliferative neoplasm defined by persistent, predominantly mature neutrophil proliferation, marrow granulocyte hyperplasia, and frequent splenomegaly. The seminal discovery of oncogenic driver mutations in CSF3R in the majority of patients with CNL in 2013 generated a new scientific framework for this disease as it deepened our understanding of its molecular pathogenesis, provided a biomarker for diagnosis, and rationalized management using novel targeted therapies. Consequently, in 2016, the World Health Organization (WHO) revised the diagnostic criteria for CNL to reflect such changes in its genomic landscape, now including the presence of disease-defining activating CSF3R mutations as a key diagnostic component of CNL. In this communication, we provide a background on the history of CNL, its clinical and hemopathologic features, and its molecular anatomy, including relevant additional genetic lesions and their significance. We also outline the recently updated WHO diagnostic criteria for CNL. Further, the natural history of the disease is reviewed as well as potential prognostic variables. Finally, we summarize and discuss current treatment options as well as prospective novel therapeutic targets in hopes that they will yield meaningful improvements in patient management and outcomes.

Somatic mutations and clonal hematopoiesis in congenital neutropenia

Severe congenital neutropenia (SCN) and Shwachman-Diamond syndrome (SDS) are congenital neutropenia syndromes with a high rate of leukemic transformation. Hematopoietic stressors may contribute to leukemic transformation by increasing the mutation rate in hematopoietic stem/progenitor cells (HSPCs) and/or by promoting clonal hematopoiesis. We sequenced the exome of individual hematopoietic colonies derived from 13 patients with congenital neutropenia to measure total mutation burden and performed error-corrected sequencing on a panel of 46 genes on 80 patients with congenital neutropenia to assess for clonal hematopoiesis. An average of 3.6 ± 1.2 somatic mutations per exome was identified in HSPCs from patients with SCN compared with 3.9 ± 0.4 for healthy controls (P = NS). Clonal hematopoiesis due to mutations in TP53 was present in 48% (13/27) of patients with SDS but was not seen in healthy controls (0/17, P < .001) or patients with SCN (0/40, P < .001). Our SDS cohort was young (median age 6.3 years), and many of the patients had multiple TP53 mutations. Conversely, clonal hematopoiesis due to mutations of CSF3R was present in patients with SCN but was not detected in healthy controls or patients with SDS. These data show that hematopoietic stress, including granulocyte colony-stimulating factor, do not increase the mutation burden in HSPCs in congenital neutropenia. Rather, distinct hematopoietic stressors result in the selective expansion of HSPCs carrying specific gene mutations. In particular, in SDS there is enormous selective pressure to expand TP53-mutated HSPCs, suggesting that acquisition of TP53 mutations is an early, likely initiating event, in the transformation to myelodysplastic syndrome/acute myeloid leukemia in patients with SDS.

Granulocyte colony-stimulating factor receptor signaling in severe congenital neutropenia, chronic neutrophilic leukemia, and related malignancies

Granulocyte colony-stimulating factor is a hematopoietic cytokine that stimulates neutrophil production and hematopoietic stem cell mobilization by initiating the dimerization of homodimeric granulocyte colony-stimulating factor receptor. Different mutations of CSF3R have been linked to a unique spectrum of myeloid disorders and related malignancies. Myeloid disorders caused by the CSF3R mutations include severe congenital neutropenia, chronic neutrophilic leukemia, and atypical chronic myeloid leukemia. In this review, we provide an analysis of granulocyte colony-stimulating factor receptor, various mutations, and their roles in the severe congenital neutropenia, chronic neutrophilic leukemia, and malignant transformation, as well as the clinical implications and some perspective on approaches that could expand our knowledge with respect to the normal signaling mechanisms and those associated with mutations in the receptor.

Genomics of chronic neutrophilic leukemia

Chronic neutrophilic leukemia (CNL) is a distinct myeloproliferative neoplasm with a high prevalence (>80%) of mutations in the colony-stimulating factor 3 receptor (CSF3R). These mutations activate the receptor, leading to the proliferation of neutrophils that are a hallmark of CNL. Recently, the World Health Organization guidelines have been updated to include CSF3R mutations as part of the diagnostic criteria for CNL. Because of the high prevalence of CSF3R mutations in CNL, it is tempting to think of this disease as being solely driven by this genetic lesion. However, recent additional genomic characterization demonstrates that CNL has much in common with other chronic myeloid malignancies at the genetic level, such as the clinically related diagnosis atypical chronic myeloid leukemia. These commonalities include mutations in SETBP1, spliceosome proteins (SRSF2, U2AF1), and epigenetic modifiers (TET2, ASXL1). Some of these same mutations also have been characterized as frequent events in clonal hematopoiesis of indeterminate potential, suggesting a more complex disease evolution than was previously understood and raising the possibility that an age-related clonal process of preleukemic cells could precede the development of CNL. The order of acquisition of CSF3R mutations relative to mutations in SETBP1, epigenetic modifiers, or the spliceosome has been determined only in isolated case reports; thus, further work is needed to understand the impact of mutation chronology on the clonal evolution and progression of CNL. Understanding the complete landscape and chronology of genomic events in CNL will help in the development of improved therapeutic strategies for this patient population.

Aberrant regulation of FBW7 in cancer

FBW7 (F-box and WD repeat domain-containing 7) or Fbxw7 is a tumor suppressor, which promotes the ubiquitination and subsequent degradation of numerous oncoproteins including Mcl-1, Cyclin E, Notch, c- Jun, and c-Myc. In turn, FBW7 is regulated by multiple upstream factors including p53, C/EBP-δ, EBP2, Pin1, Hes-5 and Numb4 as well as by microRNAs such as miR-223, miR-27a, miR-25, and miR-129-5p. Given that the Fbw7 tumor suppressor is frequently inactivated or deleted in various human cancers, targeting FBW7 regulators is a promising anti-cancer therapeutic strategy.

Granulocyte colony-stimulating factor receptor mutations in myeloid malignancy

Granulocyte colony-stimulating factor is a cytokine able to stimulate both myelopoiesis and hematopoietic stem cell mobilization, which has seen it used extensively in the clinic to aid hematopoietic recovery. It acts specifically via the homodimeric granulocyte colony-stimulating factor receptor (G-CSFR), which is principally expressed on the surface of myeloid and hematopoietic progenitor cells. A number of pathogenic mutations have now been identified in CSF3R, the gene encoding G-CSFR. These fall into distinct classes, each of which is associated with a particular spectrum of myeloid disorders, including malignancy. This review details the various CSF3R mutations, their mechanisms of action, and contribution to disease, as well as discussing the clinical implications of such mutations.

Cooperativity of RUNX1 and CSF3R mutations in severe congenital neutropenia: a unique pathway in myeloid leukemogenesis

CN/AML patients have a high frequency of CSF3R and RUNX1 mutations. CSF3R and RUNX1 mutations induce elevated proliferation of CD34+ cells.

The CSF3R T618I mutation causes a lethal neutrophilic neoplasia in mice that is responsive to therapeutic JAK inhibition

We have recently identified targetable mutations in CSF3R (GCSFR) in 60% of chronic neutrophilic leukemia (CNL) and atypical (BCR-ABL-negative) chronic myeloid leukemia (aCML) patients. Here we demonstrate that the most prevalent, activating mutation, CSF3R T618I, is sufficient to drive a lethal myeloproliferative disorder in a murine bone marrow transplantation model. Mice transplanted with CSF3R T618I-expressing hematopoietic cells developed a myeloproliferative disorder characterized by overproduction of granulocytes and granulocytic infiltration of the spleen and liver, which was uniformly fatal. Treatment with the JAK1/2 inhibitor ruxolitinib lowered the white blood count and reduced spleen weight. This demonstrates that activating mutations in CSF3R are sufficient to drive a myeloproliferative disorder resembling aCML and CNL that is sensitive to pharmacologic JAK inhibition. This murine model is an excellent tool for the further study of neutrophilic myeloproliferative neoplasms and implicates the clinical use of JAK inhibitors for this disease.

Oncogenic CSF3R mutations in chronic neutrophilic leukemia and atypical CML

BACKGROUND

The molecular causes of many hematologic cancers remain unclear. Among these cancers are chronic neutrophilic leukemia (CNL) and atypical (BCR-ABL1-negative) chronic myeloid leukemia (CML), both of which are diagnosed on the basis of neoplastic expansion of granulocytic cells and exclusion of genetic drivers that are known to occur in other myeloproliferative neoplasms and myeloproliferative-myelodysplastic overlap neoplasms.

METHODS

To identify potential genetic drivers in these disorders, we used an integrated approach of deep sequencing coupled with the screening of primary leukemia cells obtained from patients with CNL or atypical CML against panels of tyrosine kinase-specific small interfering RNAs or small-molecule kinase inhibitors. We validated candidate oncogenes using in vitro transformation assays, and drug sensitivities were validated with the use of assays of primary-cell colonies.

RESULTS

We identified activating mutations in the gene encoding the receptor for colony-stimulating factor 3 (CSF3R) in 16 of 27 patients (59%) with CNL or atypical CML. These mutations segregate within two distinct regions of CSF3R and lead to preferential downstream kinase signaling through SRC family-TNK2 or JAK kinases and differential sensitivity to kinase inhibitors. A patient with CNL carrying a JAK-activating CSF3R mutation had marked clinical improvement after the administration of the JAK1/2 inhibitor ruxolitinib.

CONCLUSIONS

Mutations in CSF3R are common in patients with CNL or atypical CML and represent a potentially useful criterion for diagnosing these neoplasms. (Funded by the Leukemia and Lymphoma Society and others.).

CSF3R T618I is a highly prevalent and specific mutation in chronic neutrophilic leukemia

Truncation mutations of the receptor cytoplasmic domain for colony-stimulating factor 3 (CSF3R) are frequently seen in severe congenital neutropenia, whereas activating missense mutations affecting the extracellular domain (exon 14) have been described in hereditary neutrophilia and chronic neutrophilic leukemia (CNL). In order to clarify mutational frequency, specificity and phenotypic associations, we sequenced CSF3R exons 14-17 in 54 clinically suspected cases of CNL (n=35) or atypical chronic myeloid leukemia (aCML; n=19). Central review of these cases confirmed WHO-defined CNL in 12 patients, monoclonal gammopathy (MG)-associated CNL in 5 and WHO-defined aCML in 9. A total of 14 CSF3R mutations were detected in 13 patients, including 10 with CSF3RT618I (exon 14 mutation, sometimes annotated as CSF3R T595I). CSF3RT618I occurred exclusively in WHO-defined CNL with a mutational frequency of 83% (10 of 12 cases). CSF3R mutations were not seen in aCML or MG-associated CNL. CSF3RT618I was also absent among 170 patients with primary myelofibrosis (PMF; n=76) or chronic myelomonocytic leukemia (CMML; n=94). SETBP1 mutational frequencies in WHO-defined CNL, aCML, CMML and PMF were 33, 0, 7 and 3%, respectively. Four CSF3RT618I-mutated cases co-expressed SETBP1 mutations. We conclude that CSF3RT618I is a highly sensitive and specific molecular marker for CNL and should be incorporated into current diagnostic criteria.