Granulopoiesis in patients with congenital neutropenia

Reduction of CFU-GM and circulating hematopoietic progenitors in a subgroup of children with chronic neutropenia associated with severe infections and delayed recovery

Myelopoiesis was evaluated in 66 pediatric patients with chronic neutropenia who were positive for anti-neutrophil antibodies (median age at diagnosis: 11 months, median neutrophil count at diagnosis: 419/μl). Other causes of neutropenia were excluded. Bone marrow morphology, clonogenic tests and/or the peripheral blood CD 34+ cell count, and apoptotic rate were evaluated in 61 patients with neutropenia lasting > 12 months or severe infections. The peripheral blood CD 34+ cell count and apoptotic rate were evaluated in five patients with shorter neutropenia. The median follow-up time was 29 months (range 7-180 months). Forty-seven patients (71.2%) had a spontaneous recovery after 7-180 months (median 29 months). The group of patients younger than 24 months at diagnosis (n = 50) had a higher probability of recovery (40/50 vs. 7/16 χ2 p<0.01) with a shorter period of neutropenia (median 26 versus 47 months, Kaplan-Meier analysis p = 0.001). The colony-forming units-granulocyte-macrophage (CFU-GM) were significantly decreased in 26/35 patients (74%) evaluated for clonogenic tests. All patients with normal CFU-GM recovered (9/9 patients); whereas, neutropenia persisted in 12/26 patients with reduced CFU-GM (46%, Pearson χ2 p = 0.02). In 36/55 (65%) patients evaluated by flow cytometry we observed reduced circulating CD34+ cells compared with controls of the same age. An increase in the circulating CD34+ cell apoptotic rate was observed in 28/55 patients (51%). Infections requiring hospitalization were observed in 9/18 (50%; Pearson χ2, p = 0.03) patients with both decreased circulating CD34+ cells and increased CD34+ apoptotic rates. In the group aged < 24 months, we observed a significant correlation between the persistence of neutropenia and decreased circulating CD34+ cells (Pearson χ2 p = 0.008). In conclusion, reduced CFU-GM and circulating hematopoietic progenitors were observed in a subgroup of children with chronic neutropenia who were positive for anti-neutrophil antibodies and had a higher incidence of severe infections and delayed spontaneous remission.

Cross-regulation of JAK and Src kinases

Members of the Janus kinase (JAK) family, JAK1, JAK2, JAK3 and Tyk2 are intimately involved in the signalling events initiated by cytokines activating cell surface receptors. They are responsible for phosphorylating these receptors, which create docking sites for downstream molecules such as the signal transducer and activator of transcription family members. In addition, cytokine receptors associate with members of the Src family kinase (SFK). JAKs and SFK work in concert to activate many of the signalling molecules, with both kinase families required for optimal transmission of intracellular signals. JAKs and SFK are also required for the activation and recruitment of negative regulators of cytokine signalling, e.g., protein tyrosine phosphatases (PTPs) and suppressors of cytokine signalling. Aberrant activity of the JAK-Src kinase duet can result in hemopoietic abnormalities including leukaemia. Additionally, the recent identification of a somatic JAK2 mutation as the cause of polycythema vera, further highlights the clinical importance of these molecules.

A Novel Mutation in the Juxtamembrane Intracellular Sequence of the Granulocyte Colony-Stimulating Factor (G-CSF) Receptor Gene in a Patient with Severe Congenital Neutropenia Augments G-CSF Proliferation Activity but Not through the MAP Kinase Cascade

We analyzed the structure of the granulocyte colony-stimulating factor (G-CSF) receptor gene in a 6-year-old female patient with severe congenital neutropenia (SCN) who experienced severe recurrent infections since 1 month of age. There is no family history of any similar disease. When the patient was 4 months old, she began receiving treatment with recombinant human G-CSF that resulted in a small increase in the neutrophil count sufficient for the prevention and treatment of bacterial infection. An analysis of complementary DNA for the patient's G-CSF receptor revealed a 3-base pair deletion in the juxtamembrane intracellular sequence. This deletion at the beginning of exon 16 was thought to be caused by alternative splicing; analysis of the DNA revealed a G-to-A point mutation of the final nucleotide of intron 15. To evaluate the functional activity of the G-CSF receptor with this 3-base pair deletion of the juxtamembrane region, we transfected this G-CSF receptor mutant into an interleukin 3-dependent cell line, BAF/3. BAF/3 cells expressing the mutant G-CSF receptor showed augmented proliferation activity in response to G-CSF compared with cells having the wild-type G-CSF receptor. Although the proliferation signal of G-CSF in normal hematopoiesis is transduced through the activation of MAP kinases, this G-CSF receptor mutant showed decreased activation of ERKI/2 in response to G-CSF compared with the wild type, but the transduced sig-nal for Stat3 activation by G-CSF was of the same magnitude as that of the wild-type G-CSF receptor. This result means that the augmented proliferation activity in response to G-CSF that we observed in cells having the G-CSF receptor gene with the 3-base pair deletion is transduced through an intracellular signaling pathway other than MAP kinase. Because SCN patients with a mutation in the G-CSF receptor frequently develop leukemia, this 3-base pair deletion in the juxtamembrane sequence of the G-CSF receptor gene in this patient may be one step in the course of leukemic transformation.

Dysregulation of transcriptions in primary granule constituents during myeloid proliferation and differentiation in patients with severe congenital neutropenia

We examined the expression of granule constituent genes in myeloid progenitor cells during proliferation and differentiation in patients with severe congenital neutropenia (SCN). The heterozygous mutation of the neutrophil elastase gene was identified in two of four patients. The CD34+/granulocyte-colony stimulating factor receptor (G-CSFR)+ cells of SCN patients showed defective responsiveness to G-CSF in serum-deprived culture. The CD34+/G-CSFR+ cells expressed low levels of the granule constituent mRNAs. The transcription levels of primary granule enzyme genes in CD34+/G-CSFR+ cells were gradually enhanced and then decreased when cells were induced toward myeloid lineage with G-CSF in normal subjects. However, the primary up-regulation and the following down-regulation of these enzyme transcriptions were not clearly observed in SCN patients. No differences in expressions of the lactoferrin gene were seen between normal subjects and patients with SCN. We hypothesize that the abnormal regulation of the transcription in primary granule constituents might involve the defective proliferation and differentiation of myeloid cells in patients with SCN.

Abnormalities of primitive myeloid progenitor cells expressing granulocyte colony-stimulating factor receptor in patients with severe congenital neutropenia

To define the basis for faulty granulopoiesis in patients with severe congenital neutropenia (SCN), the expression of granulocyte colony-stimulating factor receptor (G-CSFR) in primitive myeloid progenitor cells and their responsiveness to hematopoietic factors were studied. Flow cytometric analysis of bone marrow cells based on the expression of CD34, Kit receptor, and G-CSFR demonstrated a reduced frequency of CD34+/Kit+/ G-CSFR+cells in patients with SCN. The granulocyte-macrophage colony formation of CD34+/Kit+/G-CSFR+ cells in patients was markedly decreased in response to G-CSF alone and to the combination of stem cell factor, the ligand for flk2/flt3, and IL-3 with or without G-CSF in serum-deprived semisolid culture. In contrast, no difference in the responsiveness of CD34+/Kit+/G-CSFR− cells was noted between patients with SCN and subjects without SCN. These results demonstrate that the presence of qualitative and quantitative abnormalities of primitive myeloid progenitor cells expressing G-CSFR may play an important role in the impairment of granulopoiesis in patients with SCN.

Abnormalities of primitive myeloid progenitor cells expressing granulocyte colony-stimulating factor receptor in patients with severe congenital neutropenia

To define the basis for faulty granulopoiesis in patients with severe congenital neutropenia (SCN), the expression of granulocyte colony-stimulating factor receptor (G-CSFR) in primitive myeloid progenitor cells and their responsiveness to hematopoietic factors were studied. Flow cytometric analysis of bone marrow cells based on the expression of CD34, Kit receptor, and G-CSFR demonstrated a reduced frequency of CD34+/Kit+/ G-CSFR+cells in patients with SCN. The granulocyte-macrophage colony formation of CD34+/Kit+/G-CSFR+ cells in patients was markedly decreased in response to G-CSF alone and to the combination of stem cell factor, the ligand for flk2/flt3, and IL-3 with or without G-CSF in serum-deprived semisolid culture. In contrast, no difference in the responsiveness of CD34+/Kit+/G-CSFR− cells was noted between patients with SCN and subjects without SCN. These results demonstrate that the presence of qualitative and quantitative abnormalities of primitive myeloid progenitor cells expressing G-CSFR may play an important role in the impairment of granulopoiesis in patients with SCN.

Combined corticosteroid/granulocyte colony-stimulating factor (G-CSF) therapy in the treatment of severe congenital neutropenia unresponsive to G-CSF: Activated glucocorticoid receptors synergize with G-CSF signals

More than 90% of patients with severe congenital neutropenia (SCN) respond to granulocyte colony-stimulating factor (G-CSF) therapy. The basis for the refractory state in the remaining patients is unknown. To address this issue, we studied a child with SCN who was totally unresponsive to G-CSF and had a novel point mutation in the extracellular domain of the G-CSF receptor (GCSF-R). Marrow stromal support of granulopoiesis was evaluated by plating CD34(+) cells on preformed stromal layers. Nonadherent cells were harvested and assayed in clonogenic assays for granulocytic colony production. The in vitro effect of G-CSF and corticosteroids on granulopoiesis was evaluated in clonogenic assays of marrow mononuclear cells, by proliferation studies of the murine myeloid cell line 32D expressing the patient's mutated G-CSFR, and by measuring STAT5 activation in nuclear extracts from stimulated cells.Patient's stroma supported granulopoiesis derived from control marrow CD34(+) cells in a normal manner. Normal stroma, however, failed to induce granulopoiesis from patient's CD34(+) cells. Clonogenic assays of the patient's marrow mononuclear cells incorporating either G-CSF or hydrocortisone produced little neutrophil growth. In contrast, inclusion of both G-CSF and hydrocortisone in the cytokine "cocktail" markedly increased the neutrophil numbers. Proliferation of 32D cells expressing the mutated receptor and STAT5 activation were improved by a combination of G-CSF and dexamethasone. When small daily doses of oral prednisone were then administered to the patient with conventional doses of subcutaneous G-CSF, the patient responded with increased neutrophil numbers and with a complete reversal of the infectious problems. These data provide insight into SCN unresponsive to standard G-CSF treatment and to the potential corrective action of combined treatment with G-CSF and corticosteroids through synergistic activation of STAT5.

Defective Proliferation of Primitive Myeloid Progenitor Cells in Patients With Severe Congenital Neutropenia

Although several mechanisms have been proposed to explain the pathophysiology of severe congenital neutropenia (SCN), the precise defect responsible for SCN remains unknown. We studied the responsiveness of primitive myeloid progenitor cells to hematopoietic factors in 4 patients with SCN. The number of granulocyte-macrophage (GM) colonies formed in patients was decreased in response to granulocyte colony-stimulating factor (G-CSF) in both serum-supplemented and serum-deprived culture. The polymerase chain reaction–single-strand conformational polymorphism analysis of the G-CSF receptor gene showed no variance in structure conformation between the 4 patients and the normal subjects. In patients with SCN, the nonadherent light density bone marrow cells and cells that were purified on the basis of the expression of CD34 and Kit receptor (CD34+/Kit+ cells) showed the reduced response to the combination of steel factor (SF), the ligand for flk2/flt3 (FL), and interleukin-3 (IL-3) with or without G-CSF in serum-deprived culture. Furthermore, when individual CD34+/Kit+ cells from patients were cultured in the presence of SF, FL, and IL-3, with or without G-CSF for 10 days, the number of clones proliferated and the number of cells per each proliferating clone was significantly less than those in normal subjects. These results suggest that primitive myeloid progenitor cells of patients with SCN have defective responsiveness to not only G-CSF, but also the early- or intermediate-acting hematopoietic factors, SF, FL, and IL-3.

Defective Proliferation of Primitive Myeloid Progenitor Cells in Patients With Severe Congenital Neutropenia

Although several mechanisms have been proposed to explain the pathophysiology of severe congenital neutropenia (SCN), the precise defect responsible for SCN remains unknown. We studied the responsiveness of primitive myeloid progenitor cells to hematopoietic factors in 4 patients with SCN. The number of granulocyte-macrophage (GM) colonies formed in patients was decreased in response to granulocyte colony-stimulating factor (G-CSF) in both serum-supplemented and serum-deprived culture. The polymerase chain reaction–single-strand conformational polymorphism analysis of the G-CSF receptor gene showed no variance in structure conformation between the 4 patients and the normal subjects. In patients with SCN, the nonadherent light density bone marrow cells and cells that were purified on the basis of the expression of CD34 and Kit receptor (CD34+/Kit+ cells) showed the reduced response to the combination of steel factor (SF), the ligand for flk2/flt3 (FL), and interleukin-3 (IL-3) with or without G-CSF in serum-deprived culture. Furthermore, when individual CD34+/Kit+ cells from patients were cultured in the presence of SF, FL, and IL-3, with or without G-CSF for 10 days, the number of clones proliferated and the number of cells per each proliferating clone was significantly less than those in normal subjects. These results suggest that primitive myeloid progenitor cells of patients with SCN have defective responsiveness to not only G-CSF, but also the early- or intermediate-acting hematopoietic factors, SF, FL, and IL-3.

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

Severe congenital neutropenia (SCN) is a heterogeneous condition characterized by a drastic reduction in circulating neutrophils and a maturation arrest of myeloid progenitor cells in the bone marrow. Usually this condition can be successfully treated with granulocyte colony-stimulating factor (G-CSF). Here we describe the identification of a novel point mutation in the extracellular domain of the G-CSF receptor (G-CSF-R) in an SCN patient who failed to respond to G-CSF treatment. When this mutant G-CSF-R was expressed in myeloid cells, it was defective in both proliferation and survival signaling. This correlated with diminished activation of the receptor complex as determined by signal transducer and activator of transcription (STAT) activation, although activation of STAT5 was more affected than STAT3. Interestingly, the mutant receptor showed normal affinity for ligand, but a reduced number of ligand binding sites compared with the wild-type receptor. This suggests that the mutation in the extracellular domain affects ligand-receptor complex formation with severe consequences for intracellular signal transduction. Together these data add to our understanding of the mechanisms of cytokine receptor signaling, emphasize the role of GCSFR mutations in the etiology of SCN, and implicate such mutations in G-CSF hyporesponsiveness.

Structural abnormalities in the G-CSF receptor in severe congenital neutropenia

Structural abnormalities in the cytoplasmic region of the G-CSF receptor (G-CSF-R) or defects in signal transduction pathways triggered by the G-CSF-R or both have been implicated in the development of neutropenia and increased prediposition to leukemia in patients with severe congenital neutropenia (SCN). To assess the structural integrity of the G-CSF-R in SCN patients, the transmembrane and cytoplasmic regions of the G-CSF-R from 5 SCN patients were cloned and sequenced. DNA mutations (point, deletion, frame-shift, and silent) were observed in 3 patients. In 2 of these, the DNA mutations resulted in altered G-CSF-R protein sequences, including additions of novel C-terminal sequences. Three of the 5 mutant receptor clones lacked 115-121 amino acids in the cytoplasmic region, and 2 showed complete loss of the transmembrane and cytoplasmic regions. Neutrophils from 1 patient expressing these mutant receptors showed normal binding of radiolabeled G-CSF. G-CSF-R in 2 other patients with SCN showed no mutations. Our results indicate that structural abnormalities in the G-CSF-R may be present in some SCN patients. They may not affect the binding of G-CSF to the receptor but may contribute to the pathogenesis of SCN through impaired signal transduction pathways of the mutant G-CSF-R.

Diagnosis and management of chronic neutropenia during childhood

The approach to the diagnostic evaluation of a patient with neutropenia can be guided largely by clinical history and physical examination and does not always require an extensive laboratory evaluation. Based on the history and bone marrow morphology, most children with chronic neutropenia can be classified and managed. Most patients with chronic neutropenia are free of infections and are able to maintain a normal lifestyle with no or minimal medical intervention. On the other hand, for patients with recurrent or severe infections, careful follow-up and institution of treatment are mandatory. The Food and Drug Administration has approved the use of rhG-CSF in patients with chronic neutropenia. As mentioned previously, the use of colony-stimulating factors has dramatically improved the outcome for many patients with the more severe neutropenia; however, this cytokine is expensive, so treatment should be reserved for more severely affected patients and not given just because the ANC is low. Although concerns exist regarding leukemogenic effects or eventual loss of the progenitor cell compartment driven by the continuous stimulation of rhG-CSF, at this moment, the long-term data available suggest that the chronic administration of rhG-CSF is safe.

Kostmann's disease, recombinant HuG-CSF, monosomy 7 and MDS/AML

Monosomy 7 (Mo7) and leukaemia predisposition are associated with Kostmann's disease (KD). The recent introduction of long-term recombinant HuG-CSF treatment in patients with KD, whilst showing significant reductions in infectious complications and improved quality of life, might also be associated with an increased risk of developing karyotypic abnormalities, myelodysplasia (MDS) and acute myeloid leukaemia (AML). We describe a case of an identical twin with probable autosomal dominant KD who developed anaemia, Mo7/MDS and AML at 18, 30 and 50 months respectively from starting r-metHuG-CSF (filgrastim) treatment. Further patient analyses are required to establish the natural history of KD and to determine what role, if any, filgrastim plays in altering the pathobiology of this disorder.

Mutations in the gene for the granulocyte colony-stimulating-factor receptor in patients with acute myeloid leukemia preceded by severe congenital neutropenia

BACKGROUND

In severe congenital neutropenia the maturation of myeloid progenitor cells is arrested. The myelodysplastic syndrome and acute myeloid leukemia develop in some patients with severe congenital neutropenia. Abnormalities in the signal-transduction pathways for granulocyte colony-stimulating factor (G-CSF) may play a part in the progression to acute myeloid leukemia.

METHODS

We isolated genomic DNA and RNA from hematopoietic cells obtained from two patients with acute myeloid leukemia and histories of severe congenital neutropenia. The nucleotide sequences encoding the cytoplasmic domain of the G-CSF receptor were amplified by means of the polymerase chain reaction and sequenced. Murine myeloid 32D.C10 cells were transfected with complementary DNA encoding the wild-type or mutant G-CSF receptors and tested for their responses to G-CSF.

RESULTS

Point mutations in the gene for the G-CSF receptor were identified in both patients. The mutations, a substitution of thymine for cytosine at the codon for glutamine at position 718 (Gln718) in one patient and at the codon for glutamine at position 731(Gln731) in the other, caused a truncation of the C-terminal cytoplasmic region of the receptor. Both mutant and wild-type genes for the G-CSF receptor were present in leukemic cells from the two patients. In one patient, the mutation was also found in the neutropenic stage, before the progression to acute myeloid leukemia. The 32D.C10 cells expressing mutant receptors had abnormally high proliferative responses but failed to mature when cultured in G-CSF. The mutant G-CSF receptors also interfered with terminal maturation mediated by the wild-type G-CSF receptor in the 32D.C10 cells that coexpressed the wild-type and mutant receptors.

CONCLUSIONS

Mutations in the gene for the G-CSF receptor that interrupt signals required for the maturation of myeloid cells are involved in the pathogenesis of severe congenital neutropenia and associated with the progression to acute myeloid leukemia.

Dyshematopoiesis in combined immune deficiency with congenital neutropenia

This report describes a patient with combined immune deficiency associated with congenital neutropenia (CID/CN) and reports a partial characterization of his hematopoietic abnormalities. The CID/CN syndrome described is characterized by neutropenia and by deficiencies in B-lymphoid and T-lymphoid cell number and function. Red cell and platelet counts were normal. In vitro assays indicate that the myeloid lineage was developmentally arrested at the level of the committed monocyte/granulocyte progenitor (CFU-GM), while precursors to the CFU-GM progenitor were normal. In vitro studies showed that the defect in myeloid development was not corrected with G-CSF or GM-CSF. However, combinations of cytokines present in conditioned media from the T-cell lines MO or C5MJ, or defined multiple cytokine combinations containing IL-1, IL-3, GM-CSF, kit ligand, IL-6, and IL-9, restored myelopoiesis in-vitro. In contrast, C5MJ-conditioned media did not correct deficiencies in immune function in the patient's lymphocytes and accessory cells. No abnormalities in the production of G-CSF, GM-CSF, M-CSF, or IL-1 from the patient could be identified to account for the defects in myelopoiesis orimmune function.

Terminal acute myelogenous leukemia in a patient with congenital agranulocytosis

Congenital agranulocytosis terminating in acute myelogenous leukemia has been previously reported in only two cases of adolescent males. We describe the clinical and laboratory features of a 13-year-old male with congenital agranulocytosis, treated with G-CSF with initial good neutrophil response, who subsequently developed acute myeloid leukemia. This rare complication may define a preleukemic subset of patients for whom G-CSF therapy is ineffective. The diagnostic challenges of this case are presented.

Effects of recombinant human granulocyte colony-stimulating factor on neutropenia in patients with congenital agranulocytosis

Congenital agranulocytosis is a disorder characterized by severe neutropenia and a profound deficiency of identifiable neutrophil progenitors in bone marrow. In an attempt to stimulate neutrophil production and thereby reduce the morbidity and mortality associated with this disease, we administered recombinant human granulocyte colony-stimulating factor (rhG-CSF) in doses of 3 to 60 micrograms per kilogram of body weight per day to five patients with congenital agranulocytosis. In all five patients, an increase in the number of neutrophils was noted eight to nine days after the initiation of the effective dosage (the dose at which the neutrophil count reached 1000 cells per microliter or more and the bone marrow showed granulocyte maturation beyond the myelocyte stage). The absolute neutrophil counts rose from less than 100 to between 1300 and 9500 cells per microliter. Marrow aspirates obtained after 14 days at the effective dosage showed maturation to the mature neutrophil stage. The side effects that were observed were medullary pain, splenomegaly, and an elevation of levels of leukocyte alkaline phosphatase. All five patients have had sustained neutrophil counts of 1000 cells per microliter or more for 9 to 13 months while receiving subcutaneous maintenance therapy. Preexisting chronic infections have resolved clinically, and the number of new infectious episodes and the requirement for intravenous antibiotics have decreased. We conclude that treatment with rhG-CSF can lead to a large increase in the numbers of functional neutrophils in patients with congenital agranulocytosis.

Granulopoietic differentiation in long-term bone marrow cultures from children with congenital neutropenia

The capacity of granulopoietic precursor cells (CFU-GM) to differentiate in vitro was evaluated in five children with congenital neutropenia using short-term colony assays and long-term marrow cultures. In all five children, methylcellulose assays revealed normal numbers of CFU-GM, which displayed an appropriate response to various sources of GM-CSF and differentiated up to the polymorphonuclear leukocyte state (PMN). In contrast, neutrophil PMN were not observed in long-term bone marrow cultures from three patients, despite a normal production of CFU-GM, myeloblasts, and promyelocytes during the 5-6 week culture period. Thus, in these patients, the characteristic "block" in granulocytic maturation observed in vivo was reproduced in vitro in long-term cultures. Granulocytic differentiation proceeded normally in long-term cultures from the two other patients, thus indicating heterogeneity in the expression of the defect. These results might indicate abnormal interactions between stromal and hematopoietic cells in long-term marrow cultures from some patients with congenital neutropenia. Furthermore, our results showed some correlation between the granulocytic defect in vitro and the clinical outcome in vivo.