Central role of tumour necrosis factor, GM-CSF, and interleukin 1 in the pathogenesis of juvenile chronic myelogenous leukaemia

Transmembrane TNF-TNFR2 signaling as a critical immunoregulatory node in pancreatic cancer

Pancreatic cancer is characterized by extreme therapeutic resistance. In pancreatic cancers harboring high-risk genomes, we describe that cancer cell-neutrophil signaling circuitry provokes neutrophil-derived transmembrane (tm)TNF-TNFR2 interactions that dictate inflammatory polarization in cancer-associated fibroblasts and T-cell dysfunction - two hallmarks of therapeutic resistance. Targeting tmTNF-TNFR2 signaling may sensitize pancreatic cancer to chemo±immunotherapy.

Phenotypic profiling of CD34+ cells by advanced flow cytometry improves diagnosis of juvenile myelomonocytic leukemia

Diagnostic criteria for juvenile myelomonocytic leukemia (JMML) are currently well defined, however in some patients diagnosis still remains a challenge. Flow cytometry is a well established tool for diagnosis and follow-up of hematological malignancies, nevertheless it is not routinely used for JMML diagnosis. Herewith, we characterized the CD34+ hematopoietic precursor cells collected from 31 children with JMML using a combination of standardized EuroFlow antibody panels to assess the ability to discriminate JMML cells from normal/reactive bone marrow cell as controls (n=29) or from cells of children with other hematological diseases mimicking JMML (n=9). CD34+ precursors in JMML showed markedly reduced B-cell and erythroid-committed precursors compared to controls, whereas monocytic and CD7+ lymphoid precursors were significantly expanded. Moreover, aberrant immunophenotypes were consistently present in CD34+ precursors in JMML, while they were virtually absent in controls. Multivariate logistic regression analysis showed that combined assessment of the number of CD34+CD7+ lymphoid precursors and CD34+ aberrant precursors or erythroid precursors had a great potential in discriminating JMMLs versus controls. Importantly our scoring model allowed highly efficient discrimination of truly JMML versus patients with JMML-like diseases. In conclusion, we show for the first time that CD34+ precursors from JMML patients display a unique immunophenotypic profile which might contribute to a fast and accurate diagnosis of JMML worldwide by applying an easy to standardize single eight-color antibody combination.

Modeling (not so) rare developmental disorders associated with mutations in the protein-tyrosine phosphatase SHP2

Src homology region 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2) is a highly conserved protein tyrosine phosphatase (PTP), which is encoded by PTPN11 and is indispensable during embryonic development. Mutations in PTPN11 in human patients cause aberrant signaling of SHP2, resulting in multiple rare hereditary diseases, including Noonan Syndrome (NS), Noonan Syndrome with Multiple Lentigines (NSML), Juvenile Myelomonocytic Leukemia (JMML) and Metachondromatosis (MC). Somatic mutations in PTPN11 have been found to cause cancer. Here, we focus on the role of SHP2 variants in rare diseases and advances in the understanding of its pathogenesis using model systems.

Inflammatory response in hematopoietic stem and progenitor cells triggered by activating SHP2 mutations evokes blood defects

Gain-of-function mutations in the protein-tyrosine phosphatase SHP2 are the most frequently occurring mutations in sporadic juvenile myelomonocytic leukemia (JMML) and JMML-like myeloproliferative neoplasm (MPN) associated with Noonan syndrome (NS). Hematopoietic stem and progenitor cells (HSPCs) are the disease propagating cells of JMML. Here, we explored transcriptomes of HSPCs with SHP2 mutations derived from JMML patients and a novel NS zebrafish model. In addition to major NS traits, CRISPR/Cas9 knock-in Shp2D61G mutant zebrafish recapitulated a JMML-like MPN phenotype, including myeloid lineage hyperproliferation, ex vivo growth of myeloid colonies, and in vivo transplantability of HSPCs. Single-cell mRNA sequencing of HSPCs from Shp2D61G zebrafish embryos and bulk sequencing of HSPCs from JMML patients revealed an overlapping inflammatory gene expression pattern. Strikingly, an anti-inflammatory agent rescued JMML-like MPN in Shp2D61G zebrafish embryos. Our results indicate that a common inflammatory response was triggered in the HSPCs from sporadic JMML patients and syndromic NS zebrafish, which potentiated MPN and may represent a future target for JMML therapies.

Induced Pluripotent Stem Cells to Model Juvenile Myelomonocytic Leukemia: New Perspectives for Preclinical Research

Juvenile myelomonocytic leukemia (JMML) is a malignant myeloproliferative disorder arising in infants and young children. The origin of this neoplasm is attributed to an early deregulation of the Ras signaling pathway in multipotent hematopoietic stem/progenitor cells. Since JMML is notoriously refractory to conventional cytostatic therapy, allogeneic hematopoietic stem cell transplantation remains the mainstay of curative therapy for most cases. However, alternative therapeutic approaches with small epigenetic molecules have recently entered the stage and show surprising efficacy at least in specific subsets of patients. Hence, the establishment of preclinical models to test novel agents is a priority. Induced pluripotent stem cells (IPSCs) offer an opportunity to imitate JMML ex vivo, after attempts to generate immortalized cell lines from primary JMML material have largely failed in the past. Several research groups have previously generated patient-derived JMML IPSCs and successfully differentiated these into myeloid cells with extensive phenotypic similarities to primary JMML cells. With infinite self-renewal and the capability to differentiate into multiple cell types, JMML IPSCs are a promising resource to advance the development of treatment modalities targeting specific vulnerabilities. This review discusses current reprogramming techniques for JMML stem/progenitor cells, related clinical applications, and the challenges involved.

TNF in the era of immune checkpoint inhibitors: friend or foe?

Immune checkpoint inhibitors (ICIs) are effective in the treatment of patients with advanced cancer and have emerged as a pillar of standard cancer care. However, their use is complicated by adverse effects known as immune-related adverse events (irAEs), including ICI-induced inflammatory arthritis. ICI-induced inflammatory arthritis is distinguished from other irAEs by its persistence and requirement for long-term treatment. TNF inhibitors are commonly used to treat inflammatory diseases such as rheumatoid arthritis, spondyloarthropathies and inflammatory bowel disease, and have also been adopted as second-line agents to treat irAEs refractory to glucocorticoid treatment. Experiencing an irAE is associated with a better antitumour response after ICI treatment. However, whether TNF inhibition can be safely used to treat irAEs without promoting cancer progression, either by compromising ICI therapy efficacy or via another route, remains an open question. In this Review, we discuss clinical and preclinical studies that address the relationship between TNF, TNF inhibition and cancer. The bulk of the evidence suggests that at least short courses of TNF inhibitors are safe for the treatment of irAEs in patients with cancer undergoing ICI therapy. Data from preclinical studies hint that TNF inhibition might augment the antitumour effect of ICI therapy while simultaneously ameliorating irAEs.

Harnessing Tumor Necrosis Factor Alpha to Achieve Effective Cancer Immunotherapy

Tumor necrosis factor alpha (TNFα) is a pleiotropic cytokine known to have contradictory roles in oncoimmunology. Indeed, TNFα has a central role in the onset of the immune response, inducing both activation and the effector function of macrophages, dendritic cells, natural killer (NK) cells, and B and T lymphocytes. Within the tumor microenvironment, however, TNFα is one of the main mediators of cancer-related inflammation. It is involved in the recruitment and differentiation of immune suppressor cells, leading to evasion of tumor immune surveillance. These characteristics turn TNFα into an attractive target to overcome therapy resistance and tackle cancer. This review focuses on the diverse molecular mechanisms that place TNFα as a source of resistance to immunotherapy such as monoclonal antibodies against cancer cells or immune checkpoints and adoptive cell therapy. We also expose the benefits of TNFα blocking strategies in combination with immunotherapy to improve the antitumor effect and prevent or treat adverse immune-related effects.

Understanding of the crosstalk between normal residual hematopoietic stem cells and the leukemic niche in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease, yet clinically most patients present with pancytopenia resulting from bone marrow failure, predisposing them to life-threatening infections and bleeding. The mechanisms by which AML mediates hematopoietic suppression is not well known. Indeed, much effort has so far been focused on how AML remodels the bone marrow niche to make it a more permissive environment, with less focus on how the remodeled niche affects normal hematopoietic cells. In this perspective, we present evidence of the key role of the bone marrow niche in suppressing hematopoietic stem cells (HSCs) during leukemic progression and provide perspectives on how future research on this topic may be exploited to provide treatments for one of the key complications of AML.

Despite mutation acquisition in hematopoietic stem cells, JMML-propagating cells are not always restricted to this compartment

Juvenile myelomonocytic leukemia (JMML) is a rare aggressive myelodysplastic/myeloproliferative neoplasm of early childhood, initiated by RAS-activating mutations. Genomic analyses have recently described JMML mutational landscape; however, the nature of JMML-propagating cells (JMML-PCs) and the clonal architecture of the disease remained until now elusive. Combining genomic (exome, RNA-seq), Colony forming assay and xenograft studies, we detect the presence of JMML-PCs that faithfully reproduce JMML features including the complex/nonlinear organization of dominant/minor clones, both at diagnosis and relapse. Further integrated analysis also reveals that although the mutations are acquired in hematopoietic stem cells, JMML-PCs are not always restricted to this compartment, highlighting the heterogeneity of the disease during the initiation steps. We show that the hematopoietic stem/progenitor cell phenotype is globally maintained in JMML despite overexpression of CD90/THY-1 in a subset of patients. This study shed new lights into the ontogeny of JMML, and the identity of JMML-PCs, and provides robust models to monitor the disease and test novel therapeutic approaches.

Oncogenic KrasG12D causes myeloproliferation via NLRP3 inflammasome activation

Oncogenic Ras mutations occur in various leukemias. It was unclear if, besides the direct transforming effect via constant RAS/MEK/ERK signaling, an inflammation-related effect of KRAS contributes to the disease. Here, we identify a functional link between oncogenic KrasG12D and NLRP3 inflammasome activation in murine and human cells. Mice expressing active KrasG12D in the hematopoietic system developed myeloproliferation and cytopenia, which is reversed in KrasG12D mice lacking NLRP3 in the hematopoietic system. Therapeutic IL-1-receptor blockade or NLRP3-inhibition reduces myeloproliferation and improves hematopoiesis. Mechanistically, KrasG12D-RAC1 activation induces reactive oxygen species (ROS) production causing NLRP3 inflammasome-activation. In agreement with our observations in mice, patient-derived myeloid leukemia cells exhibit KRAS/RAC1/ROS/NLRP3/IL-1β axis activity. Our findings indicate that oncogenic KRAS not only act via its canonical oncogenic driver function, but also enhances the activation of the pro-inflammatory RAC1/ROS/NLRP3/IL-1β axis. This paves the way for a therapeutic approach based on immune modulation via NLRP3 blockade in KRAS-mutant myeloid malignancies.

Concurrent juvenile myelomonocytic leukemia with thalassemia in a case with Plasmodium knowlesi infection from Sabah, Malaysian Borneo

A 3-year-old male child was presented with worsening abdominal pain, abdominal distension, lethargy, pallor and hepatosplenomegaly. The patient had multiple outpatient visits in the past and was treated with oral antibiotics, oral anthelmintic agents, albeit with minimal benefit. The patient also had non-neutropenic pyrexia spikes and oral ulcers. The patient was an adopted child; hence details about his biological parents’ previous history were unclear. Differential diagnosis of Chronic Myelomonocytic Leukemia (CMML), Juvenile Myelomonocytic Leukemia (JMML), Gaucher’s disease, Thalassemia and discrete pancreatic pathology was considered. Hemoglobin electrophoresis was indicative of thalassemia. Also, molecular detection method by polymerase chain reaction confirms a concurrent infection with Plasmodium knowlesi malaria. The BCR-ABL fusion gene was found to be negative. Correlating with peripheral monocytosis, bone marrow aspiration and trephine biopsy with blasts only 3-4% and hepatosplenomegaly, a diagnosis of JMML was established. We present a rare phenomenon with an overlap of signs and symptoms between JMML, underlying thalassemia, and Plasmodium knowlesi, posing a diagnostic challenge to physicians.

Juvenile myelomonocytic leukemia: who's the driver at the wheel?

Juvenile myelomonocytic leukemia (JMML) is a unique clonal hematopoietic disorder of early childhood. It is classified as an overlap myeloproliferative/myelodysplastic neoplasm by the World Health Organization and shares some features with chronic myelomonocytic leukemia in adults. JMML pathobiology is characterized by constitutive activation of the Ras signal transduction pathway. About 90% of patients harbor molecular alterations in 1 of 5 genes (PTPN11, NRAS, KRAS, NF1, or CBL), which define genetically and clinically distinct subtypes. Three of these subtypes, PTPN11-, NRAS-, and KRAS-mutated JMML, are characterized by heterozygous somatic gain-of-function mutations in nonsyndromic children, whereas 2 subtypes, JMML in neurofibromatosis type 1 and JMML in children with CBL syndrome, are defined by germline Ras disease and acquired biallelic inactivation of the respective genes in hematopoietic cells. The clinical course of the disease varies widely and can in part be predicted by age, level of hemoglobin F, and platelet count. The majority of children require allogeneic hematopoietic stem cell transplantation for long-term leukemia-free survival, but the disease will eventually resolve spontaneously in ∼15% of patients, rendering the prospective identification of these cases a clinical necessity. Most recently, genome-wide DNA methylation profiles identified distinct methylation signatures correlating with clinical and genetic features and highly predictive for outcome. Understanding the genomic and epigenomic basis of JMML will not only greatly improve precise decision making but also be fundamental for drug development and future collaborative trials.

Epigenetic silencing of AKAP12 in juvenile myelomonocytic leukemia

A-kinase anchor protein 12 (AKAP12) is a regulator of protein kinase A and protein kinase C signaling, acting downstream of RAS. Epigenetic silencing of AKAP12 has been demonstrated in different cancer entities and this has been linked to the process of tumorigenesis. Here, we used quantitative high-resolution DNA methylation measurement by MassARRAY to investigate epigenetic regulation of all three AKAP12 promoters (i.e., α, β, and γ) within a large cohort of juvenile myelomonocytic leukemia (JMML) patient samples. The AKAP12α promoter shows DNA hypermethylation in JMML samples, which is associated with decreased AKAP12α expression. Promoter methylation of AKAP12α correlates with older age at diagnosis, elevated levels of fetal hemoglobin and poor prognosis. In silico screening for transcription factor binding motifs around the sites of most pronounced methylation changes in the AKAP12α promoter revealed highly significant scores for GATA-2/-1 sequence motifs. Both transcription factors are known to be involved in the haematopoietic differentiation process. Methylation of a reporter construct containing this region resulted in strong suppression of AKAP12 promoter activity, suggesting that DNA methylation might be involved in the aberrant silencing of the AKAP12 promoter in JMML. Exposure to DNMT- and HDAC-inhibitors reactivates AKAP12α expression in vitro, which could potentially be a mechanism underlying clinical treatment responses upon demethylating therapy. Together, these data provide evidence for epigenetic silencing of AKAP12α in JMML and further emphasize the importance of dysregulated RAS signaling in JMML pathogenesis.

Long-term serial xenotransplantation of juvenile myelomonocytic leukemia recapitulates human disease in Rag2-/-γc-/- mice

Juvenile myelomonocytic leukemia is a clonal malignant disease affecting young children. Current cure rates, even with allogeneic hematopoietic stem cell transplantation, are no better than 50%-60%. Pre-clinical research on juvenile myelomonocytic leukemia is urgently needed for the identification of novel therapies but is hampered by the unavailability of culture systems. Here we report a xenotransplantation model that allows long-term in vivo propagation of primary juvenile myelomonocytic leukemia cells. Persistent engraftment of leukemic cells was achieved by intrahepatic injection of 1×10(6) cells into newborn Rag2(-/-)γc(-/-) mice or intravenous injection of 5×10(6) cells into 5-week old mice. Key characteristics of juvenile myelomonocytic leukemia were reproduced, including cachexia and clonal expansion of myelomonocytic progenitor cells that infiltrated bone marrow, spleen, liver and, notably, lung. Xenografted leukemia cells led to reduced survival of recipient mice. The stem cell character of juvenile myelomonocytic leukemia was confirmed by successful serial transplantation that resulted in leukemia cell propagation for more than one year. Independence of exogenous cytokines, low donor cell number and slowly progressing leukemia are advantages of the model, which will serve as an important tool to research the pathophysiology of juvenile myelomonocytic leukemia and test novel pharmaceutical strategies such as DNA methyltransferase inhibition.

Tumor necrosis factor, tumor necrosis factor inhibition, and cancer risk

OBJECTIVE

Tumor necrosis factor (TNF) is a highly pleiotropic cytokine with multiple activities other than its originally discovered role of tumor necrosis in rodents. TNF is now understood to play a contextual role in driving either tumor elimination or promotion. Using both animal and human data, this review examines the role of TNF in cancer development and the effect of TNF and TNF inhibitors (TNFis) on malignancy risk.

RESEARCH DESIGN

A literature review was performed using relevant search terms for TNF and malignancy.

RESULTS

Although administration of TNF can cause tumor regression in specific rodent tumor models, human expression polymorphisms suggest that TNF can be a tumor-promoting cytokine, whereas blocking the TNF pathway in a variety of tumor models inhibits tumor growth. In addition to direct effects of TNF on tumors, TNF can variously affect immunity and the tumor microenvironment. Whereas TNF can promote immune surveillance designed to eliminate tumors, it can also drive chronic inflammation, autoimmunity, angiogenesis, and other processes that promote tumor initiation, growth, and spread. Key players in TNF signaling that shape this response include NF-κB and JNK, and malignant-inflammatory cell interactions, each of which may have different responses to TNF signaling. Focusing on rheumatoid arthritis (RA) patients, where clinical experience is most extensive, a review of the clinical literature shows no increased risk of overall malignancy or solid tumors such as breast and lung cancers with exposure to TNFis. Lymphoma rates are not increased with use of TNFis. Conflicting data exist regarding the risks of melanoma and nonmelanoma skin cancer. Data regarding the risk of recurrent malignancy are limited.

CONCLUSIONS

Overall, the available data indicate that elevated TNF is a risk factor for cancer, whereas its inhibition in RA patients is not generally associated with an increased cancer risk. In particular, TNF inhibition is not associated with cancers linked to immune suppression. A better understanding of the tumor microenvironment, molecular events underlying specific tumors, and epidemiologic studies of malignancies within specific disease indications should enable more focused pharmacovigilance studies and a better understanding of the potential risks of TNFis.

Molecular targets for the treatment of juvenile myelomonocytic leukemia

Significant advances in our understanding of the genetic defects and the pathogenesis of juvenile myelomonocytic leukemia (JMML) have been achieved in the last several years. The information gathered tremendously helps us in designing molecular targeted therapies for this otherwise fatal disease. Various approaches are being investigated to target defective pathways/molecules in this disease. However, effective therapy is still lacking. Development of specific target-based drugs for JMML remains a big challenge and represents a promising direction in this field.

The safety of etanercept for the treatment of plaque psoriasis

Effective treatment with etanercept results from a congregation of immunological signaling and modulating roles played by tumor necrosis factor-alpha (TNF-alpha), a pervasive member of the TNF super-family of cytokines participating in numerous immunologic and metabolic functions. Macrophages, lymphocytes and other cells produce TNF as part of the deregulated immune response resulting in psoriasis or other chronic inflammatory disorders. Tumor necrosis factor is also produced by macrophages and lymphocytes responding to foreign antigens as a primary response to potential infection. Interference with cytokine signaling by etanercept yields therapeutic response. At the same time, interference with cytokine signaling by etanercept exposes patients to potential adverse events. While the efficacy of etanercept for the treatment of psoriasis is evident, the risks of treatment continue to be defined. Of the potential serious adverse events, response to infection is the best characterized in terms of physiology, incidence, and management. Rare but serious events: activation of latent tuberculosis, multiple sclerosis, lymphoma, and others, have been observed but have questionable or yet to be defined association with therapeutic uses of etanercept. The safe use of etanercept for the treatment of psoriasis requires an appreciation of potential adverse events as well as screening and monitoring strategies designed to manage patient risk

Increased c-Jun expression and reduced GATA2 expression promote aberrant monocytic differentiation induced by activating PTPN11 mutants

Juvenile myelomonocytic leukemia (JMML) is characterized by myelomonocytic cell overproduction and commonly bears activating mutations in PTPN11. Murine hematopoietic progenitors expressing activating Shp2 undergo myelomonocytic differentiation, despite being subjected to conditions that normally support only mast cells. Evaluation of hematopoietic-specific transcription factor expression indicates reduced GATA2 and elevated c-Jun in mutant Shp2-expressing progenitors. We hypothesized that mutant Shp2-induced Ras hyperactivation promotes c-Jun phosphorylation and constitutive c-Jun expression, permitting, as a coactivator of PU.1, excessive monocytic differentiation and reduced GATA2. Hematopoietic progenitors expressing activating Shp2 demonstrate enhanced macrophage CFU (CFU-M) compared to that of wild-type Shp2-expressing cells. Treatment with the JNK inhibitor SP600125 or cotransduction with GATA2 normalizes activating Shp2-generated CFU-M. However, cotransduction of DeltaGATA2 (lacking the C-terminal zinc finger, needed to bind PU.1) fails to normalize CFU-M. NIH 3T3 cells expressing Shp2E76K produce higher levels of luciferase expression directed by the macrophage colony-stimulating factor receptor (MCSFR) promoter, which utilizes c-Jun as a coactivator of PU.1. Coimmunoprecipitation demonstrates increased c-Jun-PU.1 complexes in mutant Shp2-expressing hematopoietic progenitors, while chromatin immunoprecipitation demonstrates increased c-Jun binding to the c-Jun promoter and an increased c-Jun-PU.1 complex at the Mcsfr promoter. Furthermore, JMML progenitors express higher levels of c-JUN than healthy controls, substantiating the disease relevance of these mechanistic findings.

Juvenile myelomonocytic leukemia: a report from the 2nd International JMML Symposium

Juvenile myelomonocytic leukemia (JMML) is an aggressive childhood myeloproliferative disorder characterized by the overproduction of myelomonocytic cells. JMML incidence approaches 1.2/million persons in the United States (Cancer Incidence and Survival Among Children and Adolescents: United States SEER Program 1975-1995). Although rare, JMML is innately informative as the molecular genetics of this disease implicates hyperactive Ras as an essential initiating event. Given that Ras is one of the most frequently mutated oncogenes in human cancer, findings from this disease are applicable to more genetically diverse and complex adult leukemias. The JMML Foundation (www.jmmlfoundation.org) was founded by parent advocates dedicated to finding a cure for this disease. They work to bring investigators together in a collaborative manner. This article summarizes key presentations from The Second International JMML Symposium, on 7-8 December 2007 in Atlanta, GA. A list of all participants is in Supplementary Table.

Tumor necrosis factor alpha and adiponectin in bone marrow interstitial fluid from patients with acute myeloid leukemia inhibit normal hematopoiesis

PURPOSE

Locally residing cytokines may inhibit bone marrow hematopoiesis in acute myeloid leukemia (AML). Using a novel method to isolate bone marrow interstitial fluid, we examined if this fluid from 10 adult AML patients could affect normal bone marrow hematopoiesis.

EXPERIMENTAL DESIGN

Bone marrow interstitial fluid was isolated by centrifugation of bone marrow biopsies obtained at time of diagnosis and 2 to 4 weeks after start of induction therapy. The isolated fluid was added to normal bone marrow CD34 hematopoietic progenitor cells sampled from five healthy subjects.

RESULTS

Unlike plasma, AML-derived bone marrow interstitial fluid clearly repressed hematopoietic progenitor cell growth as determined by an in vitro colony assay, an effect that was lost after successful induction treatment. Antibodies against tumor necrosis factor alpha (TNFalpha) and adiponectin abolished growth inhibition by bone marrow interstitial fluid, suggesting a mechanistic role of these cytokines in impairing normal hematopoiesis in AML. The plasma levels of adiponectin and TNFalpha were unaffected by therapy whereas bone marrow interstitial fluid levels of both cytokines fell significantly in patients entering remission. Transcripts for TNFalpha, but not for adiponectin, were found in AML blast cells. Neither the plasma levels nor the bone marrow interstitial fluid levels of the proangiogenic factors vascular endothelial growth factor or basic fibroblast growth factor were appreciably elevated in the patients nor did they change with treatment.

CONCLUSIONS

Specific analyses of bone marrow interstitial fluid may give novel information on normal and malignant hematopoietic activity and thus form the basis for mechanism-based therapy.

Clinical manifestations associated with the aberrant expression of the soluble granulocyte-macrophage colony-stimulating factor receptor in patients presenting with haematological malignancies

The receptor for granulocyte-macrophage colony-stimulating factor (GM-CSF) can exist as both transmembrane (tmGMRalpha) and soluble (solGMRalpha) isoforms, and the latter, is a normal constituent of human plasma. We investigated if aberrant solGMRalpha expression occurs in haematopoietic malignancies and whether or not solGMRalpha expression levels correlated with clinical presentation. Compared with the normal population, patients with acute lymphoblastic leukaemia (ALL) had low levels of solGMRalpha whereas clonal disorders of the myeloid lineage demonstrated higher levels of solGMRalpha. Patients with acute myelogenous leukaemia (AML) and high levels of solGMRalpha presented with a distinct clinical picture. These patients were older, predominantly belonged to the M4 and M5 French-American-British (FAB) subtypes, and they had higher white blood cell counts at presentation including myeloid precursors and myeloblasts. They often presented with either unexplained lung infiltrates or hypoxia and lower rates of microbiologically defined infections. Elevated solGMRalpha levels were not associated with decreased relapse-free and overall survival in the AML population. On multivariate analysis, the correlation between elevated solGMRalpha levels and age, M4 and M5 FAB subtypes and decreased numbers of infections persisted. Our study is the first to describe that distinct clinical presentations are associated with aberrant solGMRalpha levels in haematological malignancies.

Hyperactivation of protein kinase B and ERK have discrete effects on survival, proliferation, and cytokine expression in Nf1-deficient myeloid cells

The Nf1 tumor suppressor encodes a GTPase-activating protein for Ras. Previous work has implicated hyperactive Ras in the aberrant growth of Nf1-deficient cells; however, there are limited data on which effectors modulate specific phenotypes. To address this, we generated myeloid cell lines by infecting fetal liver cells with a retrovirus encoding a truncated allele of c-Myb. Granulocyte-macrophage colony stimulating factor (GM-CSF) promoted the survival of wild-type Myb cells in a dose-dependent manner. By contrast, Nf1-deficient myeloid cells deprived of growth factors, were resistant to apoptosis due to hyperactivation of the phosphoinositide-3-OH kinase/protein kinase B cascade. Nf1(-/-) cells also demonstrated growth factor-independent proliferation and upregulation of GM-CSF mRNA production that were dependent upon Raf/MEK/ERK signaling. These data link specific Ras effectors with discrete cellular phenotypes in Nf1-deficient cells.

A practical, comprehensive classification for pediatric myelodysplastic syndromes: the CCC system

PURPOSE

Pediatric myelodysplastic syndromes (MDS) are biologically diverse. The French-American-British (FAB) classification of adult forms of MDS is not always applicable because many pediatric patients do not fit into any of the categories. To circumvent the FAB schema and other flawed formats, the authors developed a practical classification system for childhood MDS.

PATIENTS AND METHODS

The authors analyzed 40 children with MDS diagnosed in Toronto between 1988 and 1998 to test the utility of the classification. Children were classified according to three main features: category, cytology, and cytogenetics.

RESULTS

Using this system the authors were able to classify all 40 patients; about half could not be classified by FAB. Patients could also be longitudinally classified by serial analysis to show progression of disease. Juvenile myelomonocytic leukemia was excluded because of its known myeloproliferative pathogenesis. Chronic myelomonocytic leukemia, which almost never occurs in children, was also omitted. Also excluded were other chronic myeloproliferative disorders and any cytopenias without malignant potential.

CONCLUSIONS

Based on these data, the CCC system appears to have prognostic potential; children with advanced class and cytogenetic abnormalities had a poorer outcome. The authors urge international adoption of this system for uniformity in clinical practice and reporting purposes.

Targeting Raf-1 gene expression by a DNA enzyme inhibits juvenile myelomonocytic leukemia cell growth

Juvenile myelomonocytic leukemia (JMML) is an aggressive childhood disorder with few therapeutic options. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor-alpha (TNF-alpha) promote JMML cell growth. A hyperactive function of the ras oncogene is a hallmark of JMML. We therefore targeted the protein kinase Raf-1 downstream of Ras using a DNA enzyme that degrades mRNA-Raf-1. Western blots of JMML cell lysates revealed phosphorylated Raf-1 protein, indicating constitutive activation. Addition of GM-CSF, but not TNF-alpha, increased phosphorylation of both Raf-1 and the mitogen-activated protein kinases (MAPKs) JNK-1 and ERK-1. Depletion of Raf-1 protein markedly impaired activation of MAPKs, induced substantial inhibition of JMML cell colony formation, and virtually abolished GM-CSF hypersensitivity in JMML cells. Exogenous TNF-alpha, but not GM-CSF, restored colony formation of JMML cells pretreated with the enzyme. We could not detect any effect of the enzyme on the proliferation of normal bone marrow cells, indicating its specificity and potential safety. When immunodeficient mice engrafted with JMML cells were treated continuously with the enzyme via a peritoneal osmotic mini-pump for 4 weeks, a profound reduction in the JMML cell numbers in the recipient murine bone marrows was found. We conclude that GM-CSF is a chief regulator of JMML growth and exerts its proleukemic effects primarily via the Ras/Raf-1 signaling cascade. TNF-alpha plays a permissive role, being dependent upon GM-CSF to induce JMML cell proliferation. The DNA enzyme efficiently catabolized mRNA-Raf-1 with subsequent inhibition of JMML cell growth, suggesting its potential as a mechanism-based therapy in this fatal leukemia.

A practical, comprehensive classification for pediatric myelodysplastic syndromes: the CCC system

PURPOSE

Pediatric myelodysplastic syndromes (MDS) are biologically diverse. The French-American-British (FAB) classification of adult forms of MDS is not always applicable because many pediatric patients do not fit into any of the categories. To circumvent the FAB schema and other flawed formats, the authors developed a practical classification system for childhood MDS.

PATIENTS AND METHODS

The authors analyzed 40 children with MDS diagnosed in Toronto between 1988 and 1998 to test the utility of the classification. Children were classified according to three main features: category, cytology, and cytogenetics.

RESULTS

Using this system the authors were able to classify all 40 patients; about half could not be unclassified by FAB. Patients could also be longitudinally classified by serial analysis to show progression of disease. Juvenile myelomonocytic leukemia was excluded because of its known myeloproliferative pathogenesis. Chronic myelomonocytic leukemia, which almost never occurs in children, was also omitted. Also excluded were other chronic myeloproliferative disorders and any cytopenias without malignant potential.

CONCLUSIONS

Based on these data, the CCC system appears to have prognostic potential; children with advanced class and cytogenetic abnormalities had a poorer outcome. The authors urge international adoption of this system for uniformity in clinical practice and reporting purposes.

Evolving concepts in myelodysplastic syndromes

Myelodysplastic syndromes continue to be "a riddle, wrapped in a mystery inside of an enigma". Clearly, MDS represent a heterogeneous group of disorders, and no uniform etiology or treatment can be prescribed for all patients. This further underscores the need for MDS patients to be seen at specialized centers and placed on experimental protocols if they need treatment. The important thing to remember is that ultimately, the patient must remain the measure of all things, and must be given all the therapeutic choices including that of waiting and watching with supportive care alone. Recent biologic insights have expanded the therapeutic options, but no curative therapies except stem cell transplants are available at this time. By dissecting the biology and focusing efforts towards understanding the etiology of the cytopenias, significant therapeutic advances are being made in this disease. The momentum built up so far must not be lost now.

Inhibitors of angiogenesis selectively reduce the malignant cell load in rodent models of human myeloid leukemias

Angiogenesis is essential for growth and metastasis of solid tumors and probably also for hematological malignancies. Angiogenic inhibitors, like endostatin (ES) and PI-88, retard cancer growth. We tested these in mice with juvenile myelomonocytic leukemia (JMML), and in rats with acute myeloid leukemia (BNML). Eight weeks after transplantation and with a continuous drug treatment for the last 4 weeks, the leukemic cell mass decreased from almost 90% of all bone marrow cells to about 15 and 45% with ES, to about 35 and 55% with PI-88, and to about 10 and 25% with ES + PI-88 in the leukemic mice and rats, respectively. The numbers of normal human bone marrow cells transplanted into mice were unchanged by the treatments. The microvessel density in leukemic animals given ES or PI-88 was 10-50% of that in untreated animals. Notably, simultaneous treatment with ES and PI-88 led to a reduction of about 95% in JMML mice and 85% in BNML rats. In vitro proliferation of either JMML or BNML cells was not significantly altered by either drug, demonstrating the selectivity of ES and PI-88 as angiogenic inhibitors. In conclusion, anti-angiogenic therapy may be a valuable adjunct to conventional treatment of leukemia.

Human herpesvirus 6 infection mimicking juvenile myelomonocytic leukemia in an infant

In vitro cell culture studies of bone marrow and peripheral blood progenitor cells from patients with juvenile myclomonocytic leukemia (JMML) consistently show spontaneous proliferation and selective hypersensitivity to granulocyte-macrophage colony-stimulating factor (GM-CSF). This GM-CSF hypersensitivity dose-response assay has become a component of the international diagnostic criteria for JMML. The authors report a 2-week-old boy with perinatal human herpesvirus 6 (HHV-6) infection in whom in vitro bone marrow culture studies suggested the diagnosis of JMML by showing increased spontaneous proliferation, inhibition of this growth by anti-GM-CSF antibodies, and hypersensitivity to GM-CSF. Polymerase chain reaction viral studies from whole blood DNA and the shell vial viral culture assay were both positive for HHV-6. The patient's condition improved with expectant treatment, with an eventual return to normal blood counts and resolution of hepatosplenomegaly. This case of perinatal HHV-6 infection shows that viruses can initially mimic the in vitro culture results found in patients with JMML. It also illustrates that patients suspected of having JMML should be observed if there are no signs of progressive disease and concurrent features suggestive of viral infection.

Serum beta-2-microglobulin, TNF-alpha and interleukins in myeloproliferative disorders

Whereas beta-2-microglobulin (beta2M) has mainly been used as a prognostic factor in patients with lymphoproliferative disorders, some studies have reported the value of beta2M in myeloproliferative disorders (MPD). In order to investigate a potential role in the pathogenesis of MPD and to find a possible value as indicators in monitoring the course of the disease, we measured beta2M, TNF-alpha, IL-1alpha, IL-1beta, IL-2, sIL-2R, IL-6 and IL-10 in 55 patients with MPD, at diagnosis and during the course of the disease. In progressive disease and particularly when transformation to acute leukemia occurred, high levels of beta2M, IL-2 and sIL-2R were found in all patients; the elevation was progressive, which suggests a potential prognostic usefulness in the individual patient.

Modulation of Granulocyte-Macrophage Colony-Stimulating Factor Gene Expression by a Tumor Necrosis Factor  Specific Ribozyme in Juvenile Myelomonocytic Leukemic Cells

The human cytokines tumor necrosis factor  (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) both promote growth and survival of malignant cells from children with juvenile myelomonocytic leukemia (JMML). It has been postulated that TNF stimulates GM-CSF gene expression in an autocrine manner. We found here that the specific inhibition of TNF gene expression by a catalytic RNA molecule (ribozyme) also downregulated the expression of GM-CSF in JMML cells. GM-CSF protein, GM-CSF–dependent colony formation, and viability of JMML cells were reduced. The observed effect was specific, because synthesis of interleukin-1β, another cytokine produced by JMML cells, was not affected by the ribozyme treatment. The stimulatory effect of TNF on GM-CSF gene expression in JMML cells probably takes place at the transcription level, because the ribozyme treatment decreased GM-CSF mRNA. No apparent toxicity of the ribozyme was detected in normal bone marrow progenitor cells. Thus, the inhibition of TNF gene expression in JMML cells by ribozymes may be a novel therapeutic approach for this disorder.

Modulation of Granulocyte-Macrophage Colony-Stimulating Factor Gene Expression by a Tumor Necrosis Factor  Specific Ribozyme in Juvenile Myelomonocytic Leukemic Cells

The human cytokines tumor necrosis factor  (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) both promote growth and survival of malignant cells from children with juvenile myelomonocytic leukemia (JMML). It has been postulated that TNF stimulates GM-CSF gene expression in an autocrine manner. We found here that the specific inhibition of TNF gene expression by a catalytic RNA molecule (ribozyme) also downregulated the expression of GM-CSF in JMML cells. GM-CSF protein, GM-CSF–dependent colony formation, and viability of JMML cells were reduced. The observed effect was specific, because synthesis of interleukin-1β, another cytokine produced by JMML cells, was not affected by the ribozyme treatment. The stimulatory effect of TNF on GM-CSF gene expression in JMML cells probably takes place at the transcription level, because the ribozyme treatment decreased GM-CSF mRNA. No apparent toxicity of the ribozyme was detected in normal bone marrow progenitor cells. Thus, the inhibition of TNF gene expression in JMML cells by ribozymes may be a novel therapeutic approach for this disorder.

Haemopoietic cell transplantation in children with juvenile myelomonocytic leukaemia

Seven children, 11 months to 5.9 years of age, with juvenile myelomonocytic leukaemia (JMML) underwent allogeneic haemopoietic cell transplantation (HCT) using related or unrelated donor bone marrow or umbilical cord blood. All patients had active disease at time of transplant despite chemotherapy in five patients and chemotherapy and splenectomy in one patient prior to HCT conditioning. All patients received cyclophosphamide and TBI, with the addition of busulphan in two cases. Engraftment was documented in all cases. Notably, six of seven patients relapsed after allogeneic HCT with one achieving a return to full donor chimaerism after cyclosporin A (CSA) withdrawal. Two patients are alive in remission, 23+ and 30+ months after transplant. The role of allogeneic HCT in patients with JMML is discussed. A cooperative multicentre trial is needed to establish the optimal therapy for these patients.

Thrombopoietin Enhances the Production of Myeloid Cells, but not Megakaryocytes, in Juvenile Chronic Myelogenous Leukemia

We previously reported the aberrant growth of granulocyte-macrophage (GM) progenitors induced by a combination of stem cell factor (SCF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in juvenile chronic myelogenous leukemia (JCML). We examined here the effects of thrombopoietin (TPO) on the proliferation and differentiation of hematopoietic progenitors in JCML. In serum-deprived single-cell cultures of normal bone marrow (BM) CD34+CD38high cells, the addition of TPO to the culture containing SCF + GM-CSF resulted in an increase in the number and size of GM colonies. In the JCML cultures, in contrast, the number of SCF + GM-CSF–dependent GM colonies was not increased by the addition of TPO. However, the TPO addition caused an enlargement of GM colonies in cultures from the JCML patients to a significantly greater extent compared with the normal controls. There was no difference in the type of the constituent cells of GM colonies with or without TPO grown by JCML BM cells. A flow cytometric analysis showed that the c-Mpl expression was found on CD13+ myeloid cells generated by CD34+CD38high BM cells from JCML patients, but was at an undetectable level in normal controls. The addition of TPO to the culture containing SCF or SCF + GM-CSF caused a significant increase in the production of GM colony-forming cells by JCML CD34+CD38neg/lowpopulation, indicating the stimulatory effects of TPO on JCML primitive hematopoietic progenitors. Normal BM cells yielded a significant number of megakaryocytes as well as myeloid cells in response to a combination of SCF, GM-CSF, and/or TPO. In contrast, megakaryocytic cells were barely produced by the JCML progenitors. Our results may provide a fundamental insight that the administration of TPO enhances the aberrant growth of GM progenitors rather than the recovery of megakaryocytopoiesis.

Thrombopoietin Enhances the Production of Myeloid Cells, but not Megakaryocytes, in Juvenile Chronic Myelogenous Leukemia

We previously reported the aberrant growth of granulocyte-macrophage (GM) progenitors induced by a combination of stem cell factor (SCF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in juvenile chronic myelogenous leukemia (JCML). We examined here the effects of thrombopoietin (TPO) on the proliferation and differentiation of hematopoietic progenitors in JCML. In serum-deprived single-cell cultures of normal bone marrow (BM) CD34+CD38high cells, the addition of TPO to the culture containing SCF + GM-CSF resulted in an increase in the number and size of GM colonies. In the JCML cultures, in contrast, the number of SCF + GM-CSF–dependent GM colonies was not increased by the addition of TPO. However, the TPO addition caused an enlargement of GM colonies in cultures from the JCML patients to a significantly greater extent compared with the normal controls. There was no difference in the type of the constituent cells of GM colonies with or without TPO grown by JCML BM cells. A flow cytometric analysis showed that the c-Mpl expression was found on CD13+ myeloid cells generated by CD34+CD38high BM cells from JCML patients, but was at an undetectable level in normal controls. The addition of TPO to the culture containing SCF or SCF + GM-CSF caused a significant increase in the production of GM colony-forming cells by JCML CD34+CD38neg/lowpopulation, indicating the stimulatory effects of TPO on JCML primitive hematopoietic progenitors. Normal BM cells yielded a significant number of megakaryocytes as well as myeloid cells in response to a combination of SCF, GM-CSF, and/or TPO. In contrast, megakaryocytic cells were barely produced by the JCML progenitors. Our results may provide a fundamental insight that the administration of TPO enhances the aberrant growth of GM progenitors rather than the recovery of megakaryocytopoiesis.

Nf1 regulates hematopoietic progenitor cell growth and ras signaling in response to multiple cytokines

Neurofibromin, the protein encoded by the NF1 tumor-suppressor gene, negatively regulates the output of p21(ras) (Ras) proteins by accelerating the hydrolysis of active Ras-guanosine triphosphate to inactive Ras-guanosine diphosphate. Children with neurofibromatosis type 1 (NF1) are predisposed to juvenile chronic myelogenous leukemia (JCML) and other malignant myeloid disorders, and heterozygous Nf1 knockout mice spontaneously develop a myeloid disorder that resembles JCML. Both human and murine leukemias show loss of the normal allele. JCML cells and Nf1-/- hematopoietic cells isolated from fetal livers selectively form abnormally high numbers of colonies derived from granulocyte-macrophage progenitors in cultures supplemented with low concentrations of granulocyte-macrophage colony stimulating factor (GM-CSF). Taken together, these data suggest that neurofibromin is required to downregulate Ras activation in myeloid cells exposed to GM-CSF. We have investigated the growth and proliferation of purified populations of hematopoietic progenitor cells isolated from Nf1 knockout mice in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF), as well as to GM-CSF. We found abnormal proliferation of both immature and lineage-restricted progenitor populations, and we observed increased synergy between SCF and either IL-3 or GM-CSF in Nf1-/- progenitors. Nf1-/- fetal livers also showed an absolute increase in the numbers of immature progenitors. We further demonstrate constitutive activation of the Ras-Raf-MAP (mitogen-activated protein) kinase signaling pathway in primary c-kit+ Nf1-/- progenitors and hyperactivation of MAP kinase after growth factor stimulation. The results of these experiments in primary hematopoietic cells implicate Nf1 as playing a central role in regulating the proliferation and survival of primitive and lineage-restricted myeloid progenitors in response to multiple cytokines by modulating Ras output.

Granulocyte-macrophage colony-stimulating factor gene transcription is directly repressed by the vitamin D3 receptor. Implications for allosteric influences on nuclear receptor structure and function by a DNA element

The primary function of activated T lymphocytes is to produce various cytokines necessary to elicit an immune response; these cytokines include interleukin-2 (IL-2), interleukin-4, and granulocyte-macrophage colony-stimulating factor (GMCSF). Steroid hormones and vitamin A and D3 metabolites act to repress the expression of cytokines. 1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) down-modulates activated IL-2 expression at the level transcription, through direct antagonism of the transactivating complex NFAT-1/AP-1 by the vitamin D3 receptor (VDR). We report here that GMCSF transcription in Jurkat T cells is also directly repressed by 1, 25-(OH)2D3 and VDR. Among four NFAT/AP-1 elements in the GMCSF enhancer, we have focused on one such element that when multimerized, is sufficient in mediating both activation by NFAT-1 and AP-1 and repression in response to 1,25-(OH)2D3. Although this element does not contain any recognizable vitamin D response elements (VDREs), high affinity DNA binding by recombinant VDR is observed. In contrast to VDR interactions with positive VDREs, this binding is independent of VDR's heterodimeric partner, the retinoid X receptor. Moreover, VDR appears to bind the GMCSF element as an apparent monomer in vitro. Protease digestion patterns of bound VDR, and receptor mutations affecting DNA binding and dimerization, demonstrate that the receptor binds to the negative site in a distinct conformation relative to a positive VDRE, suggesting that the DNA element itself acts as an allosteric effector of VDR function. This altered conformation may account for VDR's action as a repressing rather than activating factor at this locus.

Inhibition of Granulocyte-Macrophage Colony-Stimulating Factor Prevents Dissemination and Induces Remission of Juvenile Myelomonocytic Leukemia in Engrafted Immunodeficient Mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF ) and tumor necrosis factor α (TNFα) have been implicated in the pathogenesis of the fatal childhood disease termed juvenile myelomonocytic leukemia (JMML). We used a severe combined immunodeficient/nonobese diabetic (SCID/NOD) mouse model of JMML and examined the effect of inhibiting these cytokines in vivo with the human GM-CSF antagonist and apoptotic agent E21R and the anti-TNFα monoclonal antibody (MoAb) cA2 on JMML cell growth and dissemination in vivo. We show here that JMML cells repopulated to high levels in the absence of exogeneous growth factors. Administration of E21R at the time of transplantation or 4 weeks after profoundly reduced JMML cell load in the mouse bone marrow. In contrast, MoAb cA2 had no effect on its own, but synergized with E21R in virtually eliminating JMML cells from the mouse bone marrow. In the spleen and peripheral blood, E21R eliminated JMML cells, while MoAb cA2 had no effect. Importantly, studies of mice engrafted simultaneously with cells from both normal donors and from JMML patients showed that E21R preferentially eliminated leukemic cells. This is the first time a specific GM-CSF inhibitor has been used in vivo, and the results suggest that GM-CSF plays a major role in the pathogenesis of JMML. E21R might offer a novel and specific approach for the treatment of this aggressive leukemia in man.

Inhibition of Granulocyte-Macrophage Colony-Stimulating Factor Prevents Dissemination and Induces Remission of Juvenile Myelomonocytic Leukemia in Engrafted Immunodeficient Mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF ) and tumor necrosis factor α (TNFα) have been implicated in the pathogenesis of the fatal childhood disease termed juvenile myelomonocytic leukemia (JMML). We used a severe combined immunodeficient/nonobese diabetic (SCID/NOD) mouse model of JMML and examined the effect of inhibiting these cytokines in vivo with the human GM-CSF antagonist and apoptotic agent E21R and the anti-TNFα monoclonal antibody (MoAb) cA2 on JMML cell growth and dissemination in vivo. We show here that JMML cells repopulated to high levels in the absence of exogeneous growth factors. Administration of E21R at the time of transplantation or 4 weeks after profoundly reduced JMML cell load in the mouse bone marrow. In contrast, MoAb cA2 had no effect on its own, but synergized with E21R in virtually eliminating JMML cells from the mouse bone marrow. In the spleen and peripheral blood, E21R eliminated JMML cells, while MoAb cA2 had no effect. Importantly, studies of mice engrafted simultaneously with cells from both normal donors and from JMML patients showed that E21R preferentially eliminated leukemic cells. This is the first time a specific GM-CSF inhibitor has been used in vivo, and the results suggest that GM-CSF plays a major role in the pathogenesis of JMML. E21R might offer a novel and specific approach for the treatment of this aggressive leukemia in man.

Deoxyribonucleic acid triplex formation inhibits granulocyte macrophage colony-stimulating factor gene expression and suppresses growth in juvenile myelomonocytic leukemic cells

Juvenile myelomonocytic leukemia (JMML) is a severe childhood malignancy. The autocrine production of GMCSF is believed to be responsible for the spontaneous proliferation of JMML cells. A nuclear factor-kappaB (NF-kappaB)/Rel binding site within the GM-CSF gene promoter, termed the kappaB element, plays an important role in controlling transcription from the GM-CSF gene. We investigated the effect of an oligonucleotide GM3, directed to form a DNA triple helix across this kappaB element, on growth and GM-CSF production by JMML cells. Treatment of these cells, either unstimulated or induced by TNFalpha, with GM3 led to a significant and specific inhibition of both GM-CSF production and spontaneous colony formation. This constitutes the first report linking specific triplex-mediated inhibition of gene transcription with a functional outcome; i.e., cell growth. We observed the constitutive presence of NF-kappaB/Rel proteins in the nucleus of JMML cells. The constitutive and TNFalpha-induced NF-kappaB/Rel complexes were identical and were composed mainly of p50 and c-Rel proteins. Treatment of the cells with a neutralizing anti-TNFalpha monoclonal antibody completely abrogated constitutive nuclear expression of NF-kappaB/Rel proteins. These results indicate that the aberrant, constitutive GM-CSF gene activation in JMML is maintained by TNFalpha-mediated activation of NF-kappaB/Rel proteins. Our findings identify the molecular basis for the autocrine TNFalpha activation of the GM-CSF gene in JMML and suggest potential novel and specific approaches for the treatment of this aggressive childhood leukemia.

Clinical and biological aspects of Philadelphia-negative/BCR-negative chronic myeloid leukemia

The Philadelphia (Ph) chromosome was the first chromosomal abnormality associated with a specific leukemia, chronic myeloid leukemia (CML). This chromosome arises from the t(9;22)(q34;q11) translocation which results in the juxtaposition of the bcr gene and the abl proto-oncogene. This BCR/ABL fusion gene encodes for a hybrid protein with the capacity of oncogenic transformation of hematopoietic cells. Nonetheless, very few myeloproliferative disorders (about 10%) included under the generic term of CML have no Ph chromosome. Half of these Ph-negative CML have the BCR/ABL fusion gene (BCR-positive) and are considered equivalent to Ph-positive CML. In contrast, the patients without detectable BCR/ABL fusion (BCR-negative) fulfil the criteria for atypical CML (aCML) of the French-American-British (FAB) classification, despite considerable variability at the individual level. Due to the very small number of patients with precise cytological descriptions already published, cooperative studies focused on aCML are warranted to draw definitive conclusions and to provide some pointers on physiopathology.

Juvenile myelomonocytic leukemia: molecular understanding and prospects for therapy

Juvenile myelomonocytic leukemia is a rare but deadly myeloproliferative disorder of early childhood that infrequently progresses to acute leukemia. The pathogenesis of this leukemia has been linked to deregulated signal transduction, resulting in growth factor hypersensitivity. Several other myeloproliferative disorders appear to share growth factor hypersensitivity as a common pathophysiological mechanism and thus this leukemia serves as an important model. New treatment modalities, such as retinoid therapy, are emerging for juvenile myelomonocytic leukemia. Further understanding of deregulated signal transduction should pave the way for even more rationally designed therapy for this leukemia and related disorders.

Juvenile chronic myelogenous leukemia multilineage CD34+ cells: aberrant growth and differentiation properties

Juvenile chronic myelogenous leukemia (JCML) is a hematologic malignancy of monocyte-macrophage lineage in which leukemic progression is mediated in an autocrine manner by tumor necrosis factor (TNF-alpha), GM-CSF and possibly other growth factors. Cytogenetic data showing involvement of both erythroid and monocyte-macrophage lineages in the JCML leukemic clone, as well as an observed episode of B-lineage lymphoid blast crisis in JCML, has strengthened the thesis for a lympho-hematopoietic pluripotent stem cell origin for the disorder. To study this further, JCML CD34+ cells from bone marrow (BM) or spleen from six newly diagnosed patients were isolated and cultured in clonogenic assays with combinations of recombinant cytokines. Compared to control CD34+ cells, JCML cells from all patients showed an aberrant growth pattern restricted almost exclusively to the monocyte-macrophage lineage. Most of the clonogenic activity was seen in a subsorted population of CD34+, HLA-Dr- cells. Additionally, an exaggerated growth response to minute doses of GM-CSF that had no effect on control cells was observed with JCML CD34+ cells. Recloning ("self-renewal") of JCML CD34+ cells was also strongly promoted by GM-CSF. JCML colonies also formed spontaneously in the absence of exogenous cytokines but were augmented by GM-CSF, interleukin 1 and TNF-alpha, the latter feature not seen with control CD34+ cells from normal BM. The abnormal spontaneous growth pattern of CD34+ JCML cells could be suppressed directly in vitro by anti-TNF-alpha antibodies and anti-GM-CSF antibodies alone or in combination, and by soluble TNF-alpha receptors (sTNF-R:Fc), consistent with the notion that JCML CD34+ cells are stimulated by both cytokines in an autocrine manner. In malignant CD34+ cells from one patient, the cytogenetic marker monosomy 7 proved leukemic involvement of monocyte-macrophage, erythroid and B-lymphoid lineages. We conclude that CD34+ JCML cells of multilineage potential exhibit excessive and aberrant monocyte-macrophage colony formation, a property that was previously observed in JCML progenitors found in light density cell fractions. Thus, within the CD34+ cellular compartment is a subpopulation of JCML "stem" cells that accounts for the abnormal leukemic proliferative activity in this disease.