Novel point mutation in the extracellular domain of the granulocyte colony-stimulating factor (G-CSF) receptor in a case of severe congenital neutropenia hyporesponsive to G-CSF treatment

Germ line variants in patients with acute myeloid leukemia without a suspicion of hereditary hematologic malignancy syndrome

Germ line predisposition in acute myeloid leukemia (AML) has gained attention in recent years because of a nonnegligible frequency and an impact on management of patients and their relatives. Risk alleles for AML development may be present in patients without a clinical suspicion of hereditary hematologic malignancy syndrome. In this study we investigated the presence of germ line variants (GVs) in 288 genes related to cancer predisposition in 47 patients with available paired, tumor-normal material, namely bone marrow stroma cells (n = 29), postremission bone marrow (n = 17), and saliva (n = 1). These patients correspond to 2 broad AML categories with heterogeneous genetic background (AML myelodysplasia related and AML defined by differentiation) and none of them had phenotypic abnormalities, previous history of cytopenia, or strong cancer aggregation. We found 11 pathogenic or likely pathogenic variants, 6 affecting genes related to autosomal dominant cancer predisposition syndromes (ATM, DDX41, and CHEK2) and 5 related to autosomal recessive bone marrow failure syndromes (FANCA, FANCM, SBDS, DNAJC21, and CSF3R). We did not find differences in clinical characteristics nor outcome between carriers of GVs vs noncarriers. Further studies in unselected AML cohorts are needed to determine GV incidence and penetrance and, in particular, to clarify the role of ATM nonsense mutations in AML predisposition.

A congenital CSF3R mutation in chronic neutropenia reveals a vital role for a cytokine receptor extracellular hinge motif in the response to granulocyte colony-stimulating factor

We describe a patient with congenital neutropenia (CN) with a homozygous germline mutation in the colony-stimulating factor 3 receptor gene (CSF3R). The patient's bone marrow shows lagging neutrophil development with subtle left shift and unresponsiveness to CSF3 in in vitro colony assays. This patient illustrates that the di-proline hinge motif in the extracellular cytokine receptor homology domain of CSF3R is critical for adequate neutrophil production, but dispensable for in vivo terminal neutrophil maturation. This report underscores that CN patients with inherited CSF3R mutations should be marked as a separate clinical entity, characterized by a failure to respond to CSF3.

A Focused Review of Ras Guanine Nucleotide-Releasing Protein 1 in Immune Cells and Cancer

Four Ras guanine nucleotide-releasing proteins (RasGRP1 through 4) belong to the family of guanine nucleotide exchange factors (GEFs). RasGRPs catalyze the release of GDP from small GTPases Ras and Rap and facilitate their transition from an inactive GDP-bound to an active GTP-bound state. Thus, they regulate critical cellular responses via many downstream GTPase effectors. Similar to other RasGRPs, the catalytic module of RasGRP1 is composed of the Ras exchange motif (REM) and Cdc25 domain, and the EF hands and C1 domain contribute to its cellular localization and regulation. RasGRP1 can be activated by a diacylglycerol (DAG)-mediated membrane recruitment and protein kinase C (PKC)-mediated phosphorylation. RasGRP1 acts downstream of the T cell receptor (TCR), B cell receptors (BCR), and pre-TCR, and plays an important role in the thymocyte maturation and function of peripheral T cells, B cells, NK cells, mast cells, and neutrophils. The dysregulation of RasGRP1 is known to contribute to numerous disorders that range from autoimmune and inflammatory diseases and schizophrenia to neoplasia. Given its position at the crossroad of cell development, inflammation, and cancer, RASGRP1 has garnered interest from numerous disciplines. In this review, we outline the structure, function, and regulation of RasGRP1 and focus on the existing knowledge of the role of RasGRP1 in leukemia and other cancers.

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.

G-CSF, the guardian of granulopoiesis

A considerable amount of continuous proliferation and differentiation is required to produce daily a billion new neutrophils in an adult human. Of the few cytokines and factors known to control neutrophil production, G-CSF is the guardian of granulopoiesis. G-CSF/CSF3R signaling involves the recruitment of non-receptor protein tyrosine kinases and their dependent signaling pathways of serine/threonine kinases, tyrosine phosphatases, and lipid second messengers. These pathways converge to activate the families of STAT and C/EBP transcription factors. CSF3R mutations are associated with human disorders of neutrophil production, including severe congenital neutropenia, neutrophilia, and myeloid malignancies. More than three decades after their identification, cloning, and characterization of G-CSF and G-CSF receptor, fundamental questions remain about their physiology.

A fresh look to the phenotype in mono-allelic likely pathogenic variants of the leptin and the leptin receptor gene

Leptin (LEP) and leptin receptor (LEPR) play a major role in energy homeostasis, metabolism, and reproductive function. While effects of biallelic likely pathogenic variants (-/-) on the phenotype are well characterized, effects of mono-allelic likely pathogenic variants (wt/-) in the LEP and LEPR gene on the phenotype compared to wild-type homozygosity (wt/wt) have not been systematically investigated. We identified in our systematic review 44 animal studies (15 on Lep, 29 on Lepr) and 39 studies in humans reporting on 130 mono-allelic likely pathogenic variant carriers with 20 distinct LEP variants and 108 heterozygous mono-allelic likely pathogenic variant carriers with 35 distinct LEPR variants. We found indications for a higher weight status in carriers of mono-allelic likely pathogenic variant in the leptin and in the leptin receptor gene compared to wt/wt, in both animal and human studies. In addition, animal studies showed higher body fat percentage in Lep and Lepr wt/- vs wt/wt. Animal studies provided indications for lower leptin levels in Lep wt/- vs. wt/wt and indications for higher leptin levels in Lepr wt/- vs wt/wt. Data on leptin levels in human studies was limited. Evidence for an impaired metabolism in mono-allelic likely pathogenic variants of the leptin and in leptin receptor gene was not conclusive (animal and human studies). Mono-allelic likely pathogenic variants in the leptin and in leptin receptor gene have phenotypic effects disposing to increased body weight and fat accumulation.

Zebrafish Granulocyte Colony-Stimulating Factor Receptor Maintains Neutrophil Number and Function throughout the Life Span

Granulocyte colony-stimulating factor receptor (G-CSFR), encoded by the CSF3R gene, represents a major regulator of neutrophil production and function in mammals, with inactivating extracellular mutations identified in a cohort of neutropenia patients unresponsive to G-CSF treatment. This study sought to elucidate the role of the zebrafish G-CSFR by generating mutants harboring these inactivating extracellular mutations using genome editing. Zebrafish csf3r mutants possessed significantly decreased numbers of neutrophils from embryonic to adult stages, which were also functionally compromised, did not respond to G-CSF, and displayed enhanced susceptibility to bacterial infection. The study has identified an important role for the zebrafish G-CSFR in maintaining the number and functionality of neutrophils throughout the life span and created a bona fide zebrafish model of nonresponsive neutropenia.

Peering through zebrafish to understand inherited bone marrow failure syndromes

Inherited bone marrow failure syndromes are experiments of nature characterized by impaired hematopoiesis with cancer and leukemia predisposition. The mutations associated with inherited bone marrow failure syndromes affect fundamental cellular pathways, such as DNA repair, telomere maintenance, or proteostasis. How these disturbed pathways fail to produce sufficient blood cells and lead to leukemogenesis are not understood. The rarity of inherited cytopenias, the paucity of affected primary human hematopoietic cells, and the sometime inadequacy of murine or induced pluripotential stem cell models mean it is difficult to acquire a greater understanding of them. Zebrafish offer a model organism to study gene functions. As vertebrates, zebrafish share with humans many orthologous genes involved in blood disorders. As a model organism, zebrafish provide advantages that include rapid development of transparent embryos, high fecundity (providing large numbers of mutant and normal siblings), and a large collection of mutant and transgenic lines useful for investigating the blood system and other tissues during development. Importantly, recent advances in genomic editing in zebrafish can speedily validate the new genes or novel variants discovered in clinical investigation as causes for marrow failure. Here we review zebrafish as a model organism that phenocopies Fanconi anemia, Diamond-Blackfan anemia, dyskeratosis congenita, Shwachman-Diamond syndrome, congenital amegakaryocytic thrombocytopenia, and severe congenital neutropenia. Two important insights, provided by modeling inherited cytopenias in zebrafish, widen understanding of ribosome biogenesis and TP53 in mediating marrow failure and non-hematologic defects. They suggest that TP53-independent pathways contribute to marrow failure. In addition, zebrafish provide an attractive model organism for drug development.

New monogenic disorders identify more pathways to neutropenia: from the clinic to next-generation sequencing

Neutrophils are the most common type of leukocyte in human circulating blood and constitute one of the chief mediators for innate immunity. Defined as a reduction from a normal distribution of values, neutropenia results from a number of congenital and acquired conditions. Neutropenia may be insignificant, temporary, or associated with a chronic condition with or without a vulnerability to life-threatening infections. As an inherited bone marrow failure syndrome, neutropenia may be associated with transformation to myeloid malignancy. Recognition of an inherited bone marrow failure syndrome may be delayed into adulthood. The list of monogenic neutropenia disorders is growing, heterogeneous, and bewildering. Furthermore, greater knowledge of immune-mediated and drug-related causes makes the diagnosis and management of neutropenia challenging. Recognition of syndromic presentations and especially the introduction of next-generation sequencing are improving the accuracy and expediency of diagnosis as well as their clinical management. Furthermore, identification of monogenic neutropenia disorders is shedding light on the molecular mechanisms of granulopoiesis and myeloid malignancies.

Granulocyte Colony-Stimulating Factor and Its Potential Application for Skeletal Muscle Repair and Regeneration

Granulocyte colony-stimulating factor (G-CSF) was originally discovered in the context of hematopoiesis. However, the identification of the G-CSF receptor (G-CSFR) being expressed outside the hematopoietic system has revealed wider roles for G-CSF, particularly in tissue repair and regeneration. Skeletal muscle damage, including that following strenuous exercise, induces an elevation in plasma G-CSF, implicating it as a potential mediator of skeletal muscle repair. This has been supported by preclinical studies and clinical trials investigating G-CSF as a potential therapeutic agent in relevant disease states. This review focuses on the growing literature associated with G-CSF and G-CSFR in skeletal muscle under healthy and disease conditions and highlights the current controversies.

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.

Towards Quantitative Systems Pharmacology Models of Chemotherapy-Induced Neutropenia

Neutropenia is a serious toxic complication of chemotherapeutic treatment. For years, mathematical models have been developed to better predict hematological outcomes during chemotherapy in both the traditional pharmaceutical sciences and mathematical biology disciplines. An increasing number of quantitative systems pharmacology (QSP) models that combine systems approaches, physiology, and pharmacokinetics/pharmacodynamics have been successfully developed. Here, I detail the shift towards QSP efforts, emphasizing the importance of incorporating systems-level physiological considerations in pharmacometrics.

Game of clones: the genomic evolution of severe congenital neutropenia

Severe congenital neutropenia (SCN) is a genetically heterogeneous condition of bone marrow failure usually diagnosed in early childhood and characterized by a chronic and severe shortage of neutrophils. It is now well-established that mutations in HAX1 and ELANE (and more rarely in other genes) are the genetic cause of SCN. In contrast, it has remained unclear how these mutations affect neutrophil development. Innovative models based on induced pluripotent stem cell technology are being explored to address this issue. These days, most SCN patients receive life-long treatment with granulocyte colony-stimulating factor (G-CSF, CSF3). CSF3 therapy has greatly improved the life expectancy of SCN patients, but also unveiled a high frequency of progression toward myelodysplastic syndrome (MDS) and therapy refractory acute myeloid leukemia (AML). Expansion of hematopoietic clones with acquired mutations in the gene encoding the G-CSF receptor (CSF3R) is regularly seen in SCN patients and AML usually descends from one of these CSF3R mutant clones. These findings raised the questions how CSF3R mutations affect CSF3 responses of myeloid progenitors, how they contribute to the pre-leukemic state of SCN, and which additional events are responsible for progression to leukemia. The vast (sub)clonal heterogeneity of AML and the presence of AML-associated mutations in normally aged hematopoietic clones make it often difficult to determine which mutations are responsible for the leukemic process. Leukemia predisposition syndromes such as SCN are unique disease models to identify the sequential acquisition of these mutations and to interrogate how they contribute to clonal selection and leukemic evolution.

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.

Inherited biallelic CSF3R mutations in severe congenital neutropenia

Severe congenital neutropenia (SCN) is characterized by low numbers of peripheral neutrophil granulocytes and a predisposition to life-threatening bacterial infections. We describe a novel genetic SCN type in 2 unrelated families associated with recessively inherited loss-of-function mutations in CSF3R, encoding the granulocyte colony-stimulating factor (G-CSF) receptor. Family A, with 3 affected children, carried a homozygous missense mutation (NM_000760.3:c.922C>T, NP_000751.1:p.Arg308Cys), which resulted in perturbed N-glycosylation and aberrant localization to the cell surface. Family B, with 1 affected infant, carried compound heterozygous deletions provoking frameshifts and premature stop codons (NM_000760.3:c.948_963del, NP_000751.1:p.Gly316fsTer322 and NM_000760.3:c.1245del, NP_000751.1:p.Gly415fsTer432). Despite peripheral SCN, all patients had morphologic evidence of full myeloid cell maturation in bone marrow. None of the patients responded to treatment with recombinant human G-CSF. Our study highlights the genetic and morphologic SCN variability and provides evidence both for functional importance and redundancy of G-CSF receptor-mediated signaling in human granulopoiesis.

Epidemiology of congenital neutropenia

Epidemiologic investigations of congenital neutropenia aim to determine several important indicators related to the disease, such as incidence at birth, prevalence, and outcome in the population, including the rate of severe infections, leukemia, and survival. Genetic diagnosis is an important criterion for classifying patients and reliably determining the epidemiologic indicators. Patient registries were developed in the 1990s. The prevalence today is probably more than 10 cases per million inhabitants. The rate of infection and leukemia risk can now be calculated. Risk factors for leukemia seem to depend on both the genetic background and cumulative dose of granulocyte colony stimulating factor.

Neutropenia in primary immunodeficiency

PURPOSE OF REVIEW

Neutropenia is a feature of several primary immunodeficiency diseases (PIDDs). Because of the diverse pathophysiologies of the PIDDs and the rarity of each disorder, data are often lacking, leading to the necessity of empiric treatment. Recent developments in the understanding of neutropenia in several of the PIDDs make a review of the data timely.

RECENT FINDINGS

The category of severe congenital neutropenia continues to expand. Mutations in G6PC3 have been identified as the cause of neutropenia in a minority of previously molecularly undefined cases. Recent advances have broadened our understanding of the pathophysiology and the clinical expression of this disorder. A possible function of the C16orf57 gene has been hypothesized that may explain the clinical overlap between Clerucuzio-type poikiloderma with neutropenia and other marrow diseases. Plerixafor has been shown to be a potentially useful treatment in the warts, hypogammaglobulinemia, infection, and myelokathexis syndrome. Investigations of patients with adenosine deaminase deficient severe combined immunodeficiency have identified neutropenia, and particularly susceptibility to myelotoxins, as a feature of this disorder. Granulocyte-colony stimulating factor is the treatment of choice for neutropenia in PIDD, whereas hematopoietic cell transplantation is the only curative option.

SUMMARY

The number of PIDDs associated with neutropenia has increased, as has our understanding of the range of phenotypes. Additional data and hypotheses have been generated helping to explain the diversity of presentations of neutropenia in PIDDs.

How to approach neutropenia

Neutropenia is defined as the reduction in the absolute number of neutrophils in the blood circulation. Acute neutropenia is a relatively frequent finding, whereas disorders of production of neutrophils are quite rare. Acute neutropenia is often well tolerated and normalizes rapidly. Neutropenia arising as a result of underlying hematologic disorders is far more significant. Such a patient may be at risk for infectious complications and will likely require a thorough investigation. Acute neutropenia evolves over a few days and occurs when neutrophil use is rapid and production is impaired. Chronic neutropenia may last for 3 months or longer and is a result of reduced production, increased destruction, or excessive splenic sequestration of neutrophils. Neutropenia may be classified by whether it arises secondarily to causes extrinsic to BM myeloid cells, which is common; as an acquired disorder of myeloid progenitor cells, which is less frequent; or as an intrinsic defect arising from impaired proliferation and maturation of myeloid progenitor cells in the BM, which is rare. Severe neutropenia with absolute neutrophil counts below 500/μL increases susceptibility to bacterial or fungal infections. Multiple disorders of severe congenital neutropenia have been found by the discovery of genetic defects affecting differentiation, adhesion, and apoptosis of neutrophil precursors. Elucidation of the multiple genetic defects have provided insight into the biology of the cell involving membrane structures, secretory vesicles, mitochondrial metabolism, ribosome biogenesis, transcriptional regulation, and cytoskeletal dynamics, as well as the risk for myelodysplasia and acute myeloid leukemia.

The effect of granulocyte colony stimulating factor receptor gene missense single nucleotide polymorphisms on peripheral blood stem cell enrichment

Granulocyte-colony stimulating factor (G-CSF) has become the most effective agent supporting hematopoietic stem cell transplantation (HSCT). The cognate interaction between G-CSF and its specific receptor, G-CSFR, induces the mobilization of HSCs and increases their pool in the peripheral blood. G-CSFR has a highly conserved structure which may be functionally modulated by the presence of missense single nucleotide polymorphisms (SNPs). In this study, we asked whether the missense SNPs in G-CSFR could affect the response to G-CSF in HSCT patients and donors. Here, for the first time, G-CSFR missense SNPs were screened and minor allele frequencies were determined in a specific population with Turkish racial background. Five (rs3917991, rs3918001, rs3918018, rs3918019, and rs146617729) out of 16 missense SNPs screened were determined with minor allele frequencies lower than 0.04. Subsequent association analyses indicated potential impact of rs3918001, rs3918018, and rs3918019 minor alleles on peripheral blood CD34(+) cell enrichment. Although their frequency is rather low, certain missense SNPs, especially which are placed in the conserved regions of G-CSFR may possess the capacity to influence the response to G-CSF treatment.

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 in a multigenerational family with a novel neutrophil elastase (ELANE) mutation

We have analysed a family with nine congenital neutropenia patients in four generations, several of which we have studied in a long-term follow-up of over 25 years. The patients were mild to severe neutropenic and suffered from various recurrent bacterial infections. Mutations in the genes ELANE, CSF3R and GFI1 have been reported in patients with autosomal dominant congenital neutropenias. Using a small-scale linkage analysis with markers around the ELANE, CSF3R, CSF3 and GFI1 genes, we were able to determine that the disease segregated with markers around the ELANE gene. We identified a novel mutation in the ELANE gene in all of the affected family members that was not present in any of the healthy family members. The mutation leads to an A28S missense mutation in the mature protein. None of these patients developed leukaemia. This is the first truly multigenerational family with mutations in ELANE as unambiguous cause of severe congenital neutropenia SCN.

The transcription factor Gfi1 regulates G-CSF signaling and neutrophil development through the Ras activator RasGRP1

The transcription factor growth factor independence 1 (Gfi1) and the growth factor granulocyte colony-stimulating factor (G-CSF) are individually essential for neutrophil differentiation from myeloid progenitors. Here, we provide evidence that the functions of Gfi1 and G-CSF are linked in the regulation of granulopoiesis. We report that Gfi1 promotes the expression of Ras guanine nucleotide releasing protein 1 (RasGRP1), an exchange factor that activates Ras, and that RasGRP1 is required for G-CSF signaling through the Ras/mitogen-activated protein/extracellular signal-regulated kinase (MEK/Erk) pathway. Gfi1-null mice have reduced levels of RasGRP1 mRNA and protein in thymus, spleen, and bone marrow, and Gfi1 transduction in myeloid cells promotes RasGRP1 expression. When stimulated with G-CSF, Gfi1-null myeloid cells are selectively defective at activating Erk1/2, but not signal transducer and activator of transcription 1 (STAT1) or STAT3, and fail to differentiate into neutrophils. Expression of RasGRP1 in Gfi1-deficient cells rescues Erk1/2 activation by G-CSF and allows neutrophil maturation by G-CSF. These results uncover a previously unknown function of Gfi1 as a regulator of RasGRP1 and link Gfi1 transcriptional control to G-CSF signaling and regulation of granulopoiesis.

Immune depletion with cellular mobilization imparts immunoregulation and reverses autoimmune diabetes in nonobese diabetic mice

OBJECTIVE

The autoimmune destruction of beta-cells in type 1 diabetes results in a loss of insulin production and glucose homeostasis. As such, an immense interest exists for the development of therapies capable of attenuating this destructive process through restoration of proper immune recognition. Therefore, we investigated the ability of the immune-depleting agent antithymocyte globulin (ATG), as well as the mobilization agent granulocyte colony-stimulating factor (GCSF), to reverse overt hyperglycemia in the nonobese diabetic (NOD) mouse model of type 1 diabetes.

RESEARCH DESIGN AND METHODS

Effects of each therapy were tested in pre-diabetic and diabetic female NOD mice using measurements of glycemia, regulatory T-cell (CD4+CD25+Foxp3+) frequency, insulitis, and/or beta-cell area.

RESULTS

Here, we show that combination therapy of murine ATG and GCSF was remarkably effective at reversing new-onset diabetes in NOD mice and more efficacious than either agent alone. This combination also afforded durable reversal from disease (>180 days postonset) in animals having pronounced hyperglycemia (i.e., up to 500 mg/dl). Additionally, glucose control improved over time in mice subject to remission from type 1 diabetes. Mechanistically, this combination therapy resulted in both immunological (increases in CD4-to-CD8 ratios and splenic regulatory T-cell frequencies) and physiological (increase in the pancreatic beta-cell area, attenuation of pancreatic inflammation) benefits.

CONCLUSIONS

In addition to lending further credence to the notion that combination therapies can enhance efficacy in addressing autoimmune disease, these studies also support the concept for utilizing agents designed for other clinical applications as a means to expedite efforts involving therapeutic translation.

Genetic and molecular diagnosis of severe congenital neutropenia

PURPOSE OF REVIEW

Severe congenital neutropenia has been a well known hematological condition for over 50 years. Over this long period of time, the variable genetic causes and associated sequelae of the disease have been ascertained, and successful treatment strategies developed. Over the past 2 years, however, new studies have added greatly to our understanding of the molecular basis of the disease, details of which are presented in this review.

RECENT FINDINGS

Recent studies have elucidated a role for the unfolded protein response in mediating the pathogenic effects of ELA2 mutations, the most common mutation in severe congenital neutropenia (SCN) as well as cyclic neutropenia. Genetic lesions in HAX1 have also been identified in the original Kostmann pedigree representing the autosomal recessive form of SCN. An emerging theme is the convergence of these and other genetic lesions underlying SCN in enhancing neutrophil apoptosis. Other studies have revealed the importance of multiple independent mutations in these and other genes in SCN. Finally, the key role for signal transducer and activator of transcription 5 in mediating the effects of granulocyte colony-stimulating factor receptor truncation mutations in the development of myelodysplastic syndrome/acute myeloid leukemia following SCN has been elucidated.

SUMMARY

As the full spectrum of molecular mutations causing neutropenia emerges, it is becoming possible to differentiate patients into subtypes with different prognoses, for whom tailored therapies are indicated.

Zebrafish granulocyte colony-stimulating factor receptor signaling promotes myelopoiesis and myeloid cell migration

Granulocyte colony-stimulating factor receptor (GCSFR) signaling participates in the production of neutrophilic granulocytes during normal hematopoietic development, with a particularly important role during emergency hematopoiesis. This study describes the characterization of the zebrafish gcsf and gcsfr genes, which showed broad conservation and similar regulation to their mammalian counterparts. Morpholino-mediated knockdown of gcsfr and overexpression of gcsf revealed the presence of an anterior population of myeloid cells during primitive hematopoiesis that was dependent on GCSF/GCSFR for development and migration. This contrasted with a posterior domain that was largely independent of this pathway. Definitive myelopoiesis was also partially dependent on a functional GCSF/GCSFR pathway. Injection of bacterial lipopolysaccharide elicited significant induction of gcsf expression and emergency production of myeloid cells, which was abrogated by gcsfr knockdown. Collectively, these data demonstrate GCSF/GCSFR to be a conserved signaling system for facilitating the production of multiple myeloid cell lineages in both homeostatic and emergency conditions, as well as for early myeloid cell migration, establishing a useful experimental platform for further dissection of this pathway.

Pharmacologic rationale for early G-CSF prophylaxis in cancer patients and role of pharmacogenetics in treatment optimization

The use of recombinant human granulocyte colony stimulating factors (G-CSF) has become an integral part of supportive care during cytotoxic chemotherapy. Current guidelines recommend the use of G-CSF in patients with substantial risk of febrile neutropenia. However, little consensus exists about optimal timing and tailoring of this therapy. Based on the known effects of chemotherapy and G-CSF on bone marrow compartments, we propose a model that supports the prophylactic rather than therapeutic use of G-CSF therapy. In addition, several genetic alterations in G-CSF signalling pathway have been described. These genetic variants may predict the risk of febrile neutropenia and response to G-CSF. Thus, future pharmacogenetic/omics studies in this field are warranted. Through the identification of patients at risk and the knowledge of biological basis for optimal timing, hopefully we should soon be able to improve the application of the existing guidelines for G-CSF therapy and patient's prognosis.

Functional interaction between mutations in the granulocyte colony-stimulating factor receptor in severe congenital neutropenia

Most severe congenital neutropenia (SCN) cases possess constitutive neutrophil elastase mutations; a smaller cohort has acquired mutations truncating the granulocyte colony-stimulating factor receptor (G-CSF-R). We have described a case with constitutive extracellular G-CSF-R mutation hyporesponsive to ligand. Here we report two independent acquired G-CSF-R truncation mutations and a novel constitutive neutrophil elastase mutation in this patient. Co-expression of a truncated receptor chain restored STAT5 signalling responses of the extracellular G-CSF-R mutant, while constitutively-active STAT5 enhanced its proliferative capacity. These data add to our knowledge of SCN and further highlight the importance of STAT5 in mediating proliferative responses to G-CSF.

Lessons from congenital neutropenia: 50 years of progress in understanding myelopoiesis

Severe congenital neutropenia (SCN) was first described just over 50 years ago. The progress in elucidating the clinical features and molecular pathophysiology of SCN closely parallels the progressive growth in our understanding of myelopoiesis. In this historical review, I have delineated this parallel progression in our understanding of the processes of granulocyte differentiation and the pathogenesis of congenital neutropenia. SCN is a heterogeneous disease that can serve as a model for the failure of myelopoiesis, and dissection of its pathogenesis has yielded important insights into the normal process of myeloid development.

A molecular classification of congenital neutropenia syndromes

Current knowledge on the molecular pathogenesis of severe congenital neutropenia indicates that the clinical diagnosis includes a heterogeneous group of disorders following different patterns of inheritance. Similarly, multifaceted syndromes associated with neutropenia can be classified molecularly, which in turn allows for a better understanding of the basis of the neutropenia. Many of the neutropenia disorders can be treated with G-CSF (filgrastim) to increase the neutrophil count, thereby reducing infection morbidity and mortality. In some instances hematopoietic stem cell transplantation remains the only curative treatment currently available. This review describes and classifies, on a molecular basis, both primary congenital neutropenia and multifaceted syndromes associated with neutropenia.

Transcription factor Gfi-1 induced by G-CSF is a negative regulator of CXCR4 in myeloid cells

The mechanisms underlying granulocyte-colony stimulating factor (G-CSF)-induced mobilization of granulocytic lineage cells from the bone marrow to the peripheral blood remain elusive. We provide evidence that the transcriptional repressor growth factor independence-1 (Gfi-1) is involved in G-CSF-induced mobilization of granulocytic lineage cells from the bone marrow to the peripheral blood. We show that in vitro and in vivo G-CSF promotes expression of Gfi-1 and down-regulates expression of CXCR4, a chemokine receptor essential for the retention of hematopoietic stem cells and granulocytic cells in the bone marrow. Gfi-1 binds to DNA sequences upstream of the CXCR4 gene and represses CXCR4 expression in myeloid lineage cells. As a consequence, myeloid cell responses to the CXCR4 unique ligand SDF-1 are reduced. Thus, Gfi-1 not only regulates hematopoietic stem cell function and myeloid cell development but also probably promotes the release of granulocytic lineage cells from the bone marrow to the peripheral blood by reducing CXCR4 expression and function.

Cytokine receptor signaling through the Jak–Stat–Socs pathway in disease

The complexity of multicellular organisms is dependent on systems enabling cells to respond to specific stimuli. Cytokines and their receptors are one such system, whose perturbation can lead to a variety of disease states. This review represents an overview of our current understanding of the cytokine receptors, Janus kinases (Jaks), Signal transducers and activators of transcription (Stats) and Suppressors of cytokine signaling (Socs), focussing on their contribution to diseases of an immune or hematologic nature.

Neutrophil elastase in cyclic and severe congenital neutropenia

Mutations in ELA2 encoding the neutrophil granule protease, neutrophil elastase (NE), are the major cause of the 2 main forms of hereditary neutropenia, cyclic neutropenia and severe congenital neutropenia (SCN). Genetic evaluation of other forms of neutropenia in humans and model organisms has helped to illuminate the role of NE. A canine form of cyclic neutropenia corresponds to human Hermansky-Pudlak syndrome type 2 (HPS2) and results from mutations in AP3B1 encoding a subunit of a complex involved in the subcellular trafficking of vesicular cargo proteins (among which NE appears to be one). Rare cases of SCN are attributable to mutations in the transcriptional repressor Gfi1 (among whose regulatory targets also include ELA2). The ultimate biochemical consequences of the mutations are not yet known, however. Gene targeting of ELA2 has thus far failed to recapitulate neutropenia in mice. The cycling phenomenon and origins of leukemic transformation in SCN remain puzzling. Nevertheless, mutations in all 3 genes are capable of causing the mislocalization of NE and may also induce the unfolded protein response, suggesting that there might a convergent pathogenic mechanism focusing on NE.

Src family kinases are important negative regulators of G-CSF-dependent granulopoiesis

Granulocyte colony-stimulating factor (G-CSF) is the principal cytokine regulating granulopoiesis. Truncation mutations of the G-CSF receptor (G-CSFR) are associated with the development of acute myeloid leukemia in patients with severe congenital neutropenia. Although increased proliferative signaling by a representative G-CSFR truncation mutation (termed d715) has been documented, the molecular basis for this hyperproliferative phenotype has not been fully characterized. Given the accumulating evidence implicating Src family kinases in the transduction of cytokine receptor signals, the role of these kinases in the regulation of G-CSF signaling was examined. We show that Hck and Lyn, Src family kinases expressed in myeloid cells, are negative regulators of granulopoiesis that act at distinct stages of granulocytic differentiation. Whereas Hck regulates the G-CSF-induced proliferation of granulocytic precursors, Lyn regulates the production of myeloid progenitors. Interestingly, d715 G-CSFR myeloid progenitors were resistant to the growth-stimulating effect of treatment with a Src kinase inhibitor. Together, these data establish Lyn and Hck as key negative regulators of granulopoiesis and raise the possibility that loss of Src family kinase activation by the d715 G-CSFR may contribute to its hyperproliferative phenotype.

Development and validation of a sensitive ELISA for quantitation of Grastim® (rhG-CSF) in rat plasma: application to a pharmacokinetic study

Grastim is bacterially produced recombinant counterpart of human granulocyte colony stimulating factor (G-CSF). It has biological activity similar to that of endogenous G-CSF. In the present work a sensitive, accurate, precise and enzyme-linked immunosorbent assay (ELISA) for the quantitation of G-CSF in rat plasma was developed and validated. The ELISA method employed a technique in which anti-human-G-CSF was adsorbed onto 96-well maxisorp plates and used to capture the G-CSF in rat plasma samples. The captured G-CSF was then detected using streptavidin-HRP amplification system. Absolute recovery was >90% from rat plasma. The validation includes assessments of method accuracy and precision, range of reliable response, lower limit of quantitation (LLOQ), storage stability (30 days) in rat plasma and assay specificity. The standard curve for G-CSF was linear (R2 > 0.996) in the concentration range 4.88-625 pg/mL. The LLOQ was established at 4.88 pg/mL. The inter- and intra-day precisions in the measurement of quality control (QC) samples, 15, 250 and 500 pg/mL, were in the range 3.00-8.66% relative standard deviation (RSD) and 1.03-4.69% RSD, respectively. Accuracy in the measurement of QC samples was in the range 87.28-110.79% of the nominal values. The assay shows dilutional linearity and specificity. Stability of G-CSF was established for 30 days at -80 degrees C and through three freeze-thaw cycles. The validated assay was successfully employed for the assessment of pharmacokinetic disposition of G-CSF in rats.

A mathematical model of hematopoiesis—I. Periodic chronic myelogenous leukemia

Periodic chronic myelogenous leukemia (PCML) is an interesting dynamical disease of the hematopoietic system in which oscillating levels of circulating leukocytes, platelets and/or reticulocytes are observed. Typically all of these three differentiated cell types have the same oscillation period, but the relation of the oscillation mean and amplitude to the normal levels is variable. Given the appearance of the abnormal Philadelphia chromosome in all of the nucleated progeny of the hematopoietic stem cells (HSCs), the most parsimonious conclusion is that chronic myelogenous leukemia, and its periodic variant, arise from derangements partially involving the dynamics of the stem cells. Here, we have synthesized several previous mathematical models of HSC dynamics, and models for the regulation of neutrophils, platelets and erythrocytes into a comprehensive model for the regulation of the hematopoietic system. Based on estimates of parameters for a typical normal human, we have systematically explored the changes in some of these parameters necessary to account for the quantitative data on leukocyte, platelet and reticulocyte cycling in 11 patients with PCML. Our results indicate that the critical model parameter changes required to simulate the PCML patient data are an increase in the amplification in the leukocyte line, an increase in the differentiation rate from the stem cell compartment into the leukocyte line, and the rate of apoptosis in the stem cell compartment. Our model system is particularly sensitive to changes in stem cell apoptosis rates, suggesting that changes in the numbers of proliferating stem cells may be important in generating PCML.

Congenital neutropenia: advances in diagnosis and treatment

PURPOSE OF REVIEW

A decade after the availability of hematopoietic growth factors, the long-term outcome of severe congenital neutropenia has dramatically changed. The prolonged survival of neutropenic patients receiving hematopoietic growth factors has drawn attention to the heterogeneity of this disease and to the complications of treatment. The dose of granulocyte colony stimulating factor that is required to obtain normal levels of circulating neutrophils and to prevent fever and infections is quite variable among patients, but is higher in children with severe congenital neutropenia than in those with other conditions of neutropenia. Moreover, leukemic transformation during treatment is not observed in all patients, but is more typical of severe congenital neutropenia and Shwachman-Diamond patients.

RECENT FINDINGS

In recent years, the converging efforts of hematologists, immunologists and geneticists have led to the discovery of the genetic and biochemical basis of severe congenital neutropenia; cyclic neutropenia; warts, hypogammaglobulinemia, immunodeficiency, myelokathexis or WHIM syndrome and other rarer conditions associated to neutropenia.

SUMMARY

Although the diagnosis of congenital neutropenia includes many disorders of distinct origin and variable prognosis, their treatment is still based on granulocyte colony stimulating factor administration. Understanding the pathogenesis of these forms of neutropenia and their evolution will focus future studies on the mechanisms of normal and pathological myelopoiesis and on the development of the most appropriate treatment for each type of neutropenia.

Novel mechanism of G-CSF refractoriness in patients with severe congenital neutropenia

Severe congenital neutropenia (SCN) is a rare disease diagnosed at or soon after birth, characterized by a myeloid maturation arrest in the bone marrow, ineffective neutrophil production, and recurrent infections. Most patients respond to treatment with granulocyte colony-stimulating factor (G-CSF), and the majority harbor mutations in the neutrophil elastase gene. In the subset of patients with SCN transforming to acute myeloid leukemia (AML), mutations that truncate the cytoplasmic tail of the G-CSF receptor (G-CSFR) have been detected. Here, we report a novel mutation in the extracellular portion of the G-CSFR within the WSXWS motif in a patient with SCN without AML who was refractory to G-CSF treatment. The mutation affected a single allele and introduced a premature stop codon that deletes the distal extracellular region and the entire transmembrane and cytoplasmic portions of the G-CSFR. Expression of the mutant receptor in either myeloid or lymphoid cells was shown to alter subcellular trafficking of the wild-type (WT) G-CSFR by constitutively heterodimerizing with it. WT/mutant G-CSFR heterodimers appeared to be retained in the endoplasmic reticulum and/or Golgi and accumulate intracellularly. These findings together with 2 previous case reports of extracellular mutations in the G-CSFR in patients with SCN unresponsive to G-CSF suggest a common mechanism underlying G-CSF refractoriness.

Congenital neutropenia

Congenital neutropenia is strictly defined as neutropenia present at birth. However, it is more generally used to describe neutropenia secondary to inherited genetic mutations. This review will discuss the presentation of such children and the various causes of congenital neutropenia. In particular, it will focus on severe congenital neutropenia (SCN) and the recent discovery of mutations in the gene encoding neutrophil elastase in the majority of cases of SCN. The potential mechanisms of pathogenesis and of transformation to leukaemia will be discussed. Shwachman-Diamond Syndrome and other less common causes of congenital neutropenia will also be reviewed. Finally, an approach to the child with potential congenital neutropenia will be presented.

Granulocyte colony-stimulating factor and its receptor in normal hematopoietic cell development and myeloid disease

Hematopoiesis, the process of blood cell formation, is orchestrated by cytokines and growth factors that stimulate the expansion of different progenitor cell subsets and regulate their survival and differentiation into mature blood cells. Granulocyte colony-stimulating factor (G-CSF) is the major hematopoietic growth factor involved in the control of neutrophil development. G-CSF is now applied on a routine basis in the clinic for treatment of congenital and acquired neutropenias. G-CSF activates a receptor of the hematopoietin receptor superfamily, the G-CSF receptor (G-CSF-R), which subsequently triggers multiple signaling mechanisms. Here we review how these mechanisms contribute to the specific responses of hematopoietic cells to G-CSF and how perturbations in the function of the G-CSF-R are implicated in various types of myeloid disease.

Deletional mutation of the external domain of the human granulocyte colony-stimulating factor receptor in a patient with severe chronic neutropenia refractory to granulocyte colony-stimulating factor

Severe chronic neutropenia (SCN) is characterized by a profound neutropenia, which mostly presents during the neonatal period. The precise genetic basis of SCN remains elusive. Acquired somatic mutations involving the carboxy-terminus of the G-CSF receptor (G-CSFR) have been found, often in association with myelodysplastic syndrome. The authors describe a girl with SCN who did not respond to pharmacologic doses of filgrastim. Genetic analysis of bone marrow and germline cells revealed a 182-bp deletion in the extracellular domain of the G-CSFR. Co-precipitation studies showed an association between the wild-type and mutant G-CSFR, confirmed by their co-localization by confocal microscopy. Coexpression of the mutant receptor inhibited the wild-type response in Ba/F3 cells. These findings establish a novel constitutional defect in the G-CSFR that supports a partial dominant negative mechanism for receptor dysfunction in SCN.

Oscillations in cyclical neutropenia: new evidence based on mathematical modeling

We present a dynamical model of the production and regulation of circulating blood neutrophil number. This model is derived from physiologically relevant features of the hematopoietic system, and is analysed using both analytic and numerical methods. Supercritical Hopf bifurcations and saddle-node bifurcations of limit cycles are shown to exist. We make the estimation of kinetic parameters for dogs and then apply the model to cyclical neutropenia (CN) in the grey collie, a rare disorder in which oscillations in all blood cell counts are found. We conclude that the major cause of the oscillations in CN is an increased rate of apoptosis of neutrophil precursors which leads to a destabilization of the hematopoietic stem cell compartment.

Impaired neutrophil maturation in truncated murine G-CSF receptor-transgenic mice

Severe congenital neutropenia (SCN) is a hematopoietic disorder characterized by neutropenia in peripheral blood and maturation arrest of neutrophil precursors in bone marrow. Patients with SCN may evolve to have myelodysplastic syndrome or acute myelocytic leukemia. In approximately 20% of SCN cases, a truncation mutation is found in the cytoplasmic region of the granulocyte colony-stimulating factor receptor (G-CSFR). We then generated mice carrying murine wild-type G-CSFR and its mutants equivalent to truncations at amino acids 718 and 731 in human G-CSFR, those were reported to be related to leukemic transformation of SCN. Although numbers of peripheral white blood cells, red blood cells, and platelets did not differ among mutant and wild-type G-CSFR transgenic (Tg) mice, both of the mutant receptor Tg mice had one third of peripheral neutrophil cell counts compared with wild-type receptor Tg mice. The mutant receptor Tg mice also showed impaired resistance to the infection with Staphylococcus aureus. Moreover, bone marrow of these Tg mice had an increased percentage of immature myeloid cells, a feature of SCN. This maturation arrest was also observed in in vitro cultures of bone marrow cells of truncated G-CSFR Tg mice under G-CSF stimulation. In addition, clonal culture of bone marrow cells of the truncated G-CSFR Tg mice showed the hypersensitivity to G-CSF in myeloid progenitors. Our Tg mice may be useful in the analysis of the role of truncated G-CSFR in SCN pathobiology.

Expression and functional analysis of granulocyte colony-stimulating factor receptors on CD34++ cells in patients with myelodysplastic syndrome (MDS) and MDS-acute myeloid leukaemia

CD34++ cells from 45 patients with myelodysplastic syndrome (MDS) and MDS-acute myeloid leukaemia (MDS-AML) were observed by flow cytometry for the expression of granulocyte colony-stimulating factor receptor (G-CSFR). Ten patients had a significantly reduced expression of G-CSFR. Late stages of disease showed a higher proportion of either high or low G-CSFR expression than earlier stages. In MDS refractory anaemia (RA), G-CSFR was inversely related to CD33 expression. Most patients (9/10) with low G-CSFR expression had neutropenia of the peripheral blood. Neutropenia was less common in the normal group, but also occurred in the high expression group. No neutrophil response was observed following G-CSF administration to MDS-AML patients (6/6) with low G-CSFR expression. In the high expression group, patients (3/3) showed a response to G-CSF while, in the normal group (1/2), the response was minor. In the normal- or high-receptor-expressing groups, the receptors were functionally active in terms of apoptosis but not proliferation and clonogenic growth, although no clear correlation to receptor expression was observed. The G-CSFR signal transduction pathway in the normal and high group was not deficient of messenger RNA for either janus kinases (Jaks) or signal transducers and activators of transcription (Stats). These findings suggest that the lowered expression of G-CSFR may cause neutropenia in MDS and MDS-AML patients and, therefore, may partially explain the neutropenia in myelodysplastic patients.

Paternal mosaicism proves the pathogenic nature of mutations in neutrophil elastase in severe congenital neutropenia

Heterozygous mutations in neutrophil elastase have been detected in many sporadic cases of congenital neutropenia. However, a convincing pathogenetic mechanism has not been established, and it is unclear whether the effects of the mutant enzyme occur within the cell of production or are paracrine in nature. The healthy father of a patient was demonstrated to be mosaic for his daughter's Cys42Arg elastase mutation. Using semiquantitative polymerase chain reaction, approximately half of his T cells were shown to carry the mutation in contrast to less than 10% of neutrophils. Individual hematopoietic colonies grown from peripheral blood were heterozygous for the mutation or were homozygous wild type. These results demonstrate that precursors containing the mutation are selectively lost during myelopoiesis or fail to develop into neutrophils. This is the first in vivo confirmation of the pathogenic nature of elastase mutations in humans. The normal neutrophil count in the father suggests that the mutant elastase does not have paracrine effects.