An acquired G-CSF receptor mutation results in increased proliferation of CMML cells from a patient with severe congenital neutropenia

Discerning clinicopathological features of congenital neutropenia syndromes: an approach to diagnostically challenging differential diagnoses

The congenital neutropenia syndromes are rare haematological conditions defined by impaired myeloid precursor differentiation or function. Patients are prone to severe infections with high mortality rates in early life. While some patients benefit from granulocyte colony-stimulating factor treatment, they may still face an increased risk of bone marrow failure, myelodysplastic syndrome and acute leukaemia. Accurate diagnosis is crucial for improved outcomes; however, diagnosis depends on familiarity with a heterogeneous group of rare disorders that remain incompletely characterised. The clinical and pathological overlap between reactive conditions, primary and congenital neutropenias, bone marrow failure, and myelodysplastic syndromes further clouds diagnostic clarity.We review the diagnostically useful clinicopathological and morphological features of reactive causes of neutropenia and the most common primary neutropenia disorders: constitutional/benign ethnic neutropenia, chronic idiopathic neutropenia, cyclic neutropenia, severe congenital neutropenia (due to mutations in ELANE, GFI1, HAX1, G6PC3, VPS45, JAGN1, CSF3R, SRP54, CLPB and WAS), GATA2 deficiency, Warts, hypogammaglobulinaemia, infections and myelokathexis syndrome, Shwachman-Diamond Syndrome, the lysosomal storage disorders with neutropenia: Chediak-Higashi, Hermansky-Pudlak, and Griscelli syndromes, Cohen, and Barth syndromes. We also detail characteristic cytogenetic and molecular factors at diagnosis and in progression to myelodysplastic syndrome/leukaemia.

The enigma of monosomy 7

Since a report of some 50 years ago describing refractory anemia associated with group C monosomy, monosomy 7 (-7) and interstitial deletions of chromosome 7 (del(7q)) have been established as one of the most frequent chromosomal aberrations found in essentially all types of myeloid tumors regardless of patient age and disease etiology. In the last century, researchers sought recessive myeloid tumor-suppressor genes by attempting to determine commonly deleted regions (CDRs) in del(7q) patients. However, these efforts were not successful. Today, tumor suppressors located in 7q are believed to act in a haploinsufficient fashion, and powerful new technologies such as microarray comparative genomic hybridization and high-throughput sequencing allow comprehensive searches throughout the genes encoded on 7q. Among those proposed as promising candidates, 4 have been validated by gene targeting in mouse models. SAMD9 (sterile α motif domain 9) and SAMD9L (SAMD9-like) encode related endosomal proteins, mutations of which cause hereditary diseases with strong propensity to infantile myelodysplastic syndrome (MDS) harboring monosomy 7. Because MDS develops in SAMD9L-deficient mice over their lifetime, SAMD9/SAMD9L are likely responsible for sporadic MDS with -7/del(7q) as the sole anomaly. EZH2 (enhancer of zeste homolog 2) and MLL3 (mixed lineage leukemia 3) encode histone-modifying enzymes; loss-of-function mutations of these are detected in some myeloid tumors at high frequencies. In contrast to SAMD9/SAMD9L, loss of EZH2 or MLL3 likely contributes to myeloid tumorigenesis in cooperation with additional specific gene alterations such as of TET2 or genes involved in the p53/Ras pathway, respectively. Distinctive roles with different significance of the loss of multiple responsible genes render the complex nature of myeloid tumors carrying -7/del(7q).

Severe congenital neutropenias

Severe congenital neutropenias are a heterogeneous group of rare haematological diseases characterized by impaired maturation of neutrophil granulocytes. Patients with severe congenital neutropenia are prone to recurrent, often life-threatening infections beginning in their first months of life. The most frequent pathogenic defects are autosomal dominant mutations in ELANE, which encodes neutrophil elastase, and autosomal recessive mutations in HAX1, whose product contributes to the activation of the granulocyte colony-stimulating factor (G-CSF) signalling pathway. The pathophysiological mechanisms of these conditions are the object of extensive research and are not fully understood. Furthermore, severe congenital neutropenias may predispose to myelodysplastic syndromes or acute myeloid leukaemia. Molecular events in the malignant progression include acquired mutations in CSF3R (encoding G-CSF receptor) and subsequently in other leukaemia-associated genes (such as RUNX1) in a majority of patients. Diagnosis is based on clinical manifestations, blood neutrophil count, bone marrow examination and genetic and immunological analyses. Daily subcutaneous G-CSF administration is the treatment of choice and leads to a substantial increase in blood neutrophil count, reduction of infections and drastic improvement of quality of life. Haematopoietic stem cell transplantation is the alternative treatment. Regular clinical assessments (including yearly bone marrow examinations) to monitor treatment course and detect chromosomal abnormalities (for example, monosomy 7 and trisomy 21) as well as somatic pre-leukaemic mutations are recommended.

miR-155 is associated with the leukemogenic potential of the class IV granulocyte colony-stimulating factor receptor in CD34⁺ progenitor cells

Granulocyte colony-stimulating factor (G-CSF) is a major regulator of granulopoiesis on engagement with the G-CSF receptor (G-CSFR). The truncated, alternatively spliced, class IV G-CSFR (G-CSFRIV) has been associated with defective differentiation and relapse risk in pediatric acute myeloid leukemia (AML) patients. However, the detailed biological properties of G-CSFRIV in human CD34(+) hematopoietic stem and progenitor cells (HSPCs) and the potential leukemogenic mechanism of this receptor remain poorly understood. In the present study, we observed that G-CSFRIV-overexpressing (G-CSFRIV(+)) HSPCs demonstrated an enhanced proliferative and survival capacity on G-CSF stimulation. Cell cycle analyses showed a higher frequency of G-CSFRIV(+) cells in the S and G2/M phase. Also, apoptosis rates were significantly lower in G-CSFRIV(+) HSPCs. These findings were shown to be associated with a sustained Stat5 activation and elevated miR-155 expression. In addition, G-CSF showed to further induce G-CSFRIV and miR-155 expression of peripheral blood mononuclear cells isolated from AML patients. A Stat5 pharmacological inhibitor or ribonucleic acid (RNA) interference-mediated silencing of the expression of miR-155 abrogated the aberrant proliferative capacity of the G-CSFRIV(+) HSPCs. Hence, the dysregulation of Stat5/miR-155 pathway in the G-CSFRIV(+) HSPCs supports their leukemogenic potential. Specific miRNA silencing or the inhibition of Stat5-associated pathways might contribute to preventing the risk of leukemogenesis in G-CSFRIV(+) HSPCs. This study may promote the development of a personalized effective antileukemia therapy, in particular for the patients exhibiting higher expression levels of G-CSFRIV, and further highlights the necessity of pre-screening the patients for G-CSFR isoforms expression patterns before G-CSF administration.

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.

Prevalence and impact of colony stimulating factor 3 receptor (CSF3R) mutations among Egyptian acute myeloid leukemia patients

Granulocyte-colony stimulating factor receptor (G-CSFR) mutations have been implicated in the progression of severe congenital neutropenia (SCN) to leukemia. This study aimed to investigate the prevalence of colony stimulating factor 3 receptor (CSF3R) mutations among Egyptian acute myeloid leukemia and their clinic-pathological impact. The study was conducted on 179 adult patients (156 de novo AML and 23 secondary AML on top of SCN). CSF3R mutations were analyzed by sequencing of the PCR products. CSF3R mutations were detected in 2 cases out of 156 de novo AML patients (1.2%) and eighteen cases out of 23 secondary AML patients (78.2%). It was noticed that most of the mutant cases are of younger age, have a high white blood cells count, high bone marrow blasts, bad performance status, and absence of extra medullary disease and with low rate induction remission. Also the overall survival of AML patient's secondary to CSF3R mutations was shorter as compared to those with wild type AML cases. In conclusion the frequency of CSF3R mutations is highly prevalent among AML patients secondary to SCN compared to de novo AML.

Alternatively spliced, truncated GCSF receptor promotes leukemogenic properties and sensitivity to JAK inhibition

Granulocyte colony-stimulating factor (GCSF) drives the production of myeloid progenitor and precursor cells toward neutrophils via the GCSF receptor (GCSFR, gene name CSF3R). Children with severe congenital neutropenia chronically receive pharmacologic doses of GCSF, and ∼30% will develop myelodysplasia/acute myeloid leukemia (AML) associated with GCSFR truncation mutations. In addition to mutations, multiple isoforms of CSF3R have also been reported. We found elevated expression of the alternatively spliced isoform, class IV CSF3R in adult myelodysplastic syndrome/AML patients. Aside from its association with monosomy 7 and higher rates of relapse in pediatric AML patients, little is known about the biology of the class IV isoform. We found developmental regulation of CSF3R isoforms with the class IV expression more representative of a progenitor cell stage. Striking differences were found in phosphoprotein signaling involving Janus kinase (JAK)-signal transducer and activator of transcription (STAT) and cell cycle gene expression. Enhanced proliferation by class IV GCSFR was associated with diminished STAT3 and STAT5 activation, yet showed sensitivity to JAK2 inhibitors. Alterations in the C-terminal domain of the GCSFR result in leukemic properties of enhanced growth, impaired differentiation and resistance to apoptosis, suggesting that they can behave as oncogenic drivers, sensitive to JAK2 inhibition.

Hematopoietic stem cell transplantation for severe congenital neutropenia

PURPOSE OF REVIEW

Hematopoietic stem cell transplantation (HCT) is the only curative option for patients with severe congenital neutropenia (SCN). Transplant success is dependent on identifying at-risk patients and proceeding to transplant before the development of severe infections or malignant transformation. This review focuses on recent advancements in risk stratification of SCN patients, indications for HCT, and review of published transplant studies.

RECENT FINDINGS

Patients with poor neutrophil response despite high doses of granulocyte colony-stimulating factor (G-CSF) are at greatest risk for malignant transformation. Other studies demonstrate elevated risk with mutations in the G-CSF receptor gene and a specific mutation in the ELANE gene. These patients are at high-risk of sepsis or leukemia development and should proceed to transplant with best available donor. As recent published studies demonstrate, HCT is highly successful in patients without leukemia and, therefore, may be considered in selected low-risk patients given the life-long risk of malignancy and infection.

SUMMARY

The decision whether to proceed to HCT in healthy patients maintained on G-CSF is difficult. As transplant-related mortality continues to decrease, the role of transplant in SCN is likely to expand to more patients.

Severe congenital neutropenia

Congenital neutropenia (CN) is a genetically heterogeneous bone marrow failure syndrome characterized by a maturation arrest of myelopoiesis at the level of the promyelocyte/myelocyte stage with peripheral blood absolute neutrophil counts below 0.5 x 10(9)/L. From early infancy patients who have CN suffer from bacterial infections. Leukemias occur in both the autosomal dominant and recessive subtypes of CN. The individual risk for each genetic subtype needs to be evaluated further, because the number of patients tested for the underlying genetic defect is still limited. Acquired G-CSFR (CSF3R) mutations are detected in approximately 80% of patients who had CN and who developed acute myeloid leukemia, suggesting that these mutations are involved in leukemogenesis.

Clinical implications of ELA2-, HAX1-, and G-CSF-receptor (CSF3R) mutations in severe congenital neutropenia

Congenital Neutropenia (CN) is a heterogeneous bone marrow failure syndrome characterized by a maturation arrest of myelopoiesis at the level of the promyelocyte/myelocyte stage with peripheral blood absolute neutrophil counts below 0.5 x 10(9)/l. There are two major subtypes of CN as judged by inheritance: an autosomal dominant subtype, e.g. defined by neutrophil elastase mutations (approximately 60% of patients) and an autosomal recessive subtype (approximately 30% of patients), both presenting with the same clinical and morphological phenotype. Different mutations have been described (e.g. HAX1, p14 etc) in autosomal recessive CN, with HAX1 mutations in the majority of these patients. CN in common is considered as a preleukemic syndrome, since the cumulative incidence for leukemia is more than 25% after 20 years of observation. Leukemias occur in both, the autosomal dominant and recessive subtypes of CN. The individual risk for each genetic subtype needs to be further evaluated. Numbers of patients tested for the underlying genetic defect are still limited. Acquired G-CSFR (CSF3R) mutations are detected in approximately 80% of CN patients who developed acute myeloid leukemia independent of the ELA2 or HAX1 genetic subtype, suggesting that these mutations are involved in leukemogenesis. As the majority of patients benefit from G-CSF administration, HSCT should be restricted to non-responders and patients with leukaemic transformation.

Severe congenital neutropenia: inheritance and pathophysiology

PURPOSE OF REVIEW

Severe congenital neutropenia is a heterogeneous disorder of hematopoiesis characterized by a maturation arrest of granulopoiesis at the level of promyelocytes with peripheral blood absolute neutrophil counts below 0.5 x 10/l. In this review we summarize our current knowledge on inheritance and pathophysiolgy of congenital neutropenia.

RECENT FINDINGS

There are two major subtypes of congenital neutropenia as judged by inheritance: autosomal dominant trait defined by neutrophil elastase mutations consisting of 60% of patients and autosomal recessive trait comprising approximately 30% of patients. This genetic heterogeneity suggests that several pathologic mechanisms may lead to the same phenotype due to downregulation of common myeloid transcription factors. Lymphoid enhancer-binding factor 1 is the most promising candidate, as its abrogation together with downregulation of lymphoid enhancer-binding factor 1 target genes is compatible with this phenotype. Congenital neutropenia is considered as a preleukemic syndrome, since after 10 years of observation the cumulative incidence for leukemia is 21%. Acquired granulocyte colony-stimulating factor receptor mutations are detected in approximately 80% of congenital neutropenia patients who developed acute myeloid leukemia.

SUMMARY

Congenital neutropenia is a congenital disorder of hematopoiesis inherited by autosomal dominant or recessive traits. Downregulation of lymphoid enhancer-binding factor 1 is involved in the pathophysiology of all congenital neutropenia patients. Congenital neutropenia patients with acquired granulocyte colony-stimulating factor receptor mutations define a group with high risk for development of leukemia.

Incidence of CSF3R mutations in severe congenital neutropenia and relevance for leukemogenesis: Results of a long-term survey

Point mutations in the gene for the granulocyte colony-stimulating factor (G-CSF) receptor CSF3R have been implicated in the progression of severe congenital neutropenia (CN) to leukemia. In this study we present data on a total of 218 patients with chronic neutropenia, including 148 patients with CN (23/148 with secondary malignancies). We detected CSF3R nonsense mutations at 17 different nucleotide positions (thereof 10 new mutations) which lead to a loss of 1 to all 4 tyrosine residues in the intracellular domain of the receptor. Of 23 patients with CN with signs of malignant transformation, 18 (78%) were shown to harbor a CSF3R mutation, indicating that these mutations, although not a necessary condition, are highly predictive for malignant transformation even if detected in a low percentage of transcripts. In serial analyses of 50 patients with CSF3R mutations we were able to follow the clonal dynamics of mutated cells. We could demonstrate that even a highly clonal hematopoiesis did not inevitably show a rapid progression to leukemia. Our results strongly suggest that acquisition of a CSF3R mutation is an early event in leukemogenesis that has to be accompanied by cooperating molecular events, which remain to be defined.

Granulocyte colony-stimulating factor preferentially stimulates proliferation of monosomy 7 cells bearing the isoform IV receptor

Granulocyte colony-stimulating factor (GCSF) administration has been linked to the development of monosomy 7 in severe congenital neutropenia and aplastic anemia. We assessed the effect of pharmacologic doses of GCSF on monosomy 7 cells to determine whether this chromosomal abnormality developed de novo or arose as a result of favored expansion of a preexisting clone. Fluorescence in situ hybridization (FISH) of chromosome 7 was used to identify small populations of aneuploid cells. When bone marrow mononuclear cells from patients with monosomy 7 were cultured with 400 ng/ml GCSF, all samples showed significant increases in the proportion of monosomy 7 cells. In contrast, bone marrow from karyotypically normal aplastic anemia, myelodysplastic syndrome, or healthy individuals did not show an increase in monosomy 7 cells in culture. In bone marrow CD34 cells of patients with myelodysplastic syndrome and monosomy 7, GCSF receptor (GCSFR) protein was increased. Although no mutation was found in genomic GCSFR DNA, CD34 cells showed increased expression of the GCSFR class IV mRNA isoform, which is defective in signaling cellular differentiation. GCSFR signal transduction via the Jak/Stat system was abnormal in monosomy 7 CD34 cells, with increased phosphorylated signal transducer and activation of transcription protein, STAT1-P, and increased STAT5-P relative to STAT3-P. Our results suggest that pharmacologic doses of GCSF increase the proportion of preexisting monosomy 7 cells. The abnormal response of monosomy 7 cells to GCSF would be explained by the expansion of undifferentiated monosomy 7 clones expressing the class IV GCSFR, which is defective in signaling cell maturation.

Severe Congenital Neutropenia

Severe congenital neutropenia (CN) includes a variety of hematologic disorders characterized by severe neutropenia, with absolute neutrophil counts (ANC) below 0.5 x 10(9)/L, and associated with severe systemic bacterial infections from early infancy. One subtype of CN, Kostmann syndrome, is an autosomal recessive disorder, characterized histopathologically by early-stage maturation arrest of myeloid differentiation. CN with similar clinical features occurs as an autosomal dominant disorder and many sporadic cases also have been reported. This genetic heterogeneity suggests that several pathophysiological mechanisms may lead to this common clinical phenotype. Recent studies on the genetic bases of CN have detected inherited or spontaneous point mutations in the neutrophil elastase gene (ELA 2) in about 60% to 80% of patients and, less commonly, mutations in other genes. Acquisition of additional genetic defects during the course of the disease, for example, granulocyte colony-stimulating factor (G-CSF) receptor gene mutations and cytogenetic aberrations, indicates an underlying genetic instability as a common feature for all congenital neutropenia subtypes. Data on more than 600 patients with CN collected by the Severe Chronic Neutropenia International Registry (SCNIR) demonstrate that, regardless of the particular CN subtype, more than 95% of these patients respond to recombinant human (rHu)G-CSF with ANCs that can be maintained above 1.0 x 10(9)/L. Adverse events include mild splenomegaly, osteoporosis, and malignant transformation into myelodysplasia (MDS)/leukemia. If and how G-CSF treatment impacts on these adverse events is not fully understood. In recent analyses the influence of the G-CSF dose required to achieve neutrophil response (ANC >1,000/microL) in the risk of developing acute myeloid leukemia (AML) has been reported. Hematopoietic stem cell transplantation (HSCT) is still the only treatment available for patients who are refractory to G-CSF treatment.