Acute megakaryoblastic leukaemia (AMKL) and transient myeloproliferative disorder (TMD) in Down syndrome: a multi-step model of myeloid leukaemogenesis

The hematopoietic microenvironment of the fetal liver and transient abnormal myelopoiesis associated with Down syndrome: A review

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome is a distinct form of leukemia or preleukemia that mirrors the hematological features of acute megakaryoblastic leukemia. However, it typically resolves spontaneously in the early stages. TAM originates from fetal liver (FL) hematopoietic precursor cells and emerges due to somatic mutations in GATA1 in utero. In TAM, progenitor cells proliferate and differentiate into mature megakaryocytes and granulocytes. This process occurs both in vitro, aided by hematopoietic growth factors (HGFs) produced in the FL, and in vivo, particularly in specific anatomical sites like the FL and blood vessels. The FL's hematopoietic microenvironment plays a crucial role in TAM's pathogenesis and may contribute to its spontaneous regression. This review presents an overview of current knowledge regarding the unique features of TAM in relation to the FL hematopoietic microenvironment, focusing on the functions of HGFs and the pathological features of TAM.

RUN(X) out of blood: emerging RUNX1 functions beyond hematopoiesis and links to Down syndrome

BACKGROUND

RUNX1 is a transcription factor and a master regulator for the specification of the hematopoietic lineage during embryogenesis and postnatal megakaryopoiesis. Mutations and rearrangements on RUNX1 are key drivers of hematological malignancies. In humans, this gene is localized to the 'Down syndrome critical region' of chromosome 21, triplication of which is necessary and sufficient for most phenotypes that characterize Trisomy 21.

MAIN BODY

Individuals with Down syndrome show a higher predisposition to leukemias. Hence, RUNX1 overexpression was initially proposed as a critical player on Down syndrome-associated leukemogenesis. Less is known about the functions of RUNX1 in other tissues and organs, although growing reports show important implications in development or homeostasis of neural tissues, muscle, heart, bone, ovary, or the endothelium, among others. Even less is understood about the consequences on these tissues of RUNX1 gene dosage alterations in the context of Down syndrome. In this review, we summarize the current knowledge on RUNX1 activities outside blood/leukemia, while suggesting for the first time their potential relation to specific Trisomy 21 co-occurring conditions.

CONCLUSION

Our concise review on the emerging RUNX1 roles in different tissues outside the hematopoietic context provides a number of well-funded hypotheses that will open new research avenues toward a better understanding of RUNX1-mediated transcription in health and disease, contributing to novel potential diagnostic and therapeutic strategies for Down syndrome-associated conditions.

Fetal vs adult megakaryopoiesis

Fetal and neonatal megakaryocyte progenitors are hyperproliferative compared with adult progenitors and generate a large number of small, low-ploidy megakaryocytes. Historically, these developmental differences have been interpreted as "immaturity." However, more recent studies have demonstrated that the small, low-ploidy fetal and neonatal megakaryocytes have all the characteristics of adult polyploid megakaryocytes, including the presence of granules, a well-developed demarcation membrane system, and proplatelet formation. Thus, rather than immaturity, the features of fetal and neonatal megakaryopoiesis reflect a developmentally unique uncoupling of proliferation, polyploidization, and cytoplasmic maturation, which allows fetuses and neonates to populate their rapidly expanding bone marrow and blood volume. At the molecular level, the features of fetal and neonatal megakaryopoiesis are the result of a complex interplay of developmentally regulated pathways and environmental signals from the different hematopoietic niches. Over the past few years, studies have challenged traditional paradigms about the origin of the megakaryocyte lineage in both fetal and adult life, and the application of single-cell RNA sequencing has led to a better characterization of embryonic, fetal, and adult megakaryocytes. In particular, a growing body of data suggests that at all stages of development, the various functions of megakaryocytes are not fulfilled by the megakaryocyte population as a whole, but rather by distinct megakaryocyte subpopulations with dedicated roles. Finally, recent studies have provided novel insights into the mechanisms underlying developmental disorders of megakaryopoiesis, which either uniquely affect fetuses and neonates or have different clinical presentations in neonatal compared with adult life.

The megakaryocytic transcription factor ARID3A suppresses leukemia pathogenesis

Given the plasticity of hematopoietic stem and progenitor cells, multiple routes of differentiation must be blocked in the the pathogenesis of acute myeloid leukemia, the molecular basis of which is incompletely understood. We report that posttranscriptional repression of the transcription factor ARID3A by miR-125b is a key event in the pathogenesis of acute megakaryoblastic leukemia (AMKL). AMKL is frequently associated with trisomy 21 and GATA1 mutations (GATA1s), and children with Down syndrome are at a high risk of developing the disease. The results of our study showed that chromosome 21-encoded miR-125b synergizes with Gata1s to drive leukemogenesis in this context. Leveraging forward and reverse genetics, we uncovered Arid3a as the main miR-125b target behind this synergy. We demonstrated that, during normal hematopoiesis, this transcription factor promotes megakaryocytic differentiation in concert with GATA1 and mediates TGFβ-induced apoptosis and cell cycle arrest in complex with SMAD2/3. Although Gata1s mutations perturb erythroid differentiation and induce hyperproliferation of megakaryocytic progenitors, intact ARID3A expression assures their megakaryocytic differentiation and growth restriction. Upon knockdown, these tumor suppressive functions are revoked, causing a blockade of dual megakaryocytic/erythroid differentiation and subsequently of AMKL. Inversely, restoring ARID3A expression relieves the arrest of megakaryocytic differentiation in AMKL patient-derived xenografts. This work illustrates how mutations in lineage-determining transcription factors and perturbation of posttranscriptional gene regulation can interact to block multiple routes of hematopoietic differentiation and cause leukemia. In AMKL, surmounting this differentiation blockade through restoration of the tumor suppressor ARID3A represents a promising strategy for treating this lethal pediatric disease.

The Mutational Landscape of Myeloid Leukaemia in Down Syndrome

Children with Down syndrome (DS) are particularly prone to haematopoietic disorders. Paediatric myeloid malignancies in DS occur at an unusually high frequency and generally follow a well-defined stepwise clinical evolution. First, the acquisition of mutations in the GATA1 transcription factor gives rise to a transient myeloproliferative disorder (TMD) in DS newborns. While this condition spontaneously resolves in most cases, some clones can acquire additional mutations, which trigger myeloid leukaemia of Down syndrome (ML-DS). These secondary mutations are predominantly found in chromatin and epigenetic regulators-such as cohesin, CTCF or EZH2-and in signalling mediators of the JAK/STAT and RAS pathways. Most of them are also found in non-DS myeloid malignancies, albeit at extremely different frequencies. Intriguingly, mutations in proteins involved in the three-dimensional organization of the genome are found in nearly 50% of cases. How the resulting mutant proteins cooperate with trisomy 21 and mutant GATA1 to promote ML-DS is not fully understood. In this review, we summarize and discuss current knowledge about the sequential acquisition of genomic alterations in ML-DS.

Clinical impact of genomic characterization of 15 patients with acute megakaryoblastic leukemia-related malignancies

Acute megakaryoblastic leukemia (AMKL) is a rare subtype of acute myeloid leukemia but is approximately 500 times more likely to develop in children with Down syndrome (DS) through transformation of transient abnormal myelopoiesis (TAM). This study investigates the clinical significance of genomic heterogeneity of AMKL in children with and without DS and in children with TAM. Genomic evaluation of nine patients with DS-related TAM or AMKL, and six patients with non-DS AMKL, included conventional cytogenetics and a comprehensive next-generation sequencing panel for single-nucleotide variants/indels and copy-number variants in 118 genes and fusions involving 110 genes. Recurrent gene fusions were found in all patients with non-DS, including two individuals with complex genomes and either a NUP98–KDM5A or a KMT2A–MLLT6 fusion, and the remaining harbored a CBFA2T3–GLIS2 fusion, which arose from both typical and atypical cytogenetic mechanisms. These fusions guided treatment protocols and resulted in a change in diagnosis in two patients. The nine patients with DS had constitutional trisomy 21 and somatic GATA1 mutations, and those with DS-AMKL had two to four additional clinically significant somatic mutations. Comprehensive genomic characterization provides critical information for diagnosis, risk stratification, and treatment decisions for patients with AMKL. Continued genetic and clinical characterization of these rare cancers will aid in improving patient management.

The in vitro effects of hepatoblastoma cells on the growth and differentiation of blasts in transient abnormal myelopoiesis associated with Down syndrome

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome, which spontaneously resolves within several weeks or months after birth, may represent a special form of leukemia developing in the fetal liver (FL). To explore the role of hepatoblasts, one of the major constituents of the FL hematopoietic microenvironment, in the pathogenesis of TAM, we investigated the influence of a human hepatoblastoma cell line, HUH-6, on the in vitro growth and differentiation of TAM blasts. In a coculture system with membrane filters, which hinders cell-to-cell contact between TAM blasts and HUH-6 cells, the growth and megakaryocytic differentiation of TAM blast progenitors were increased in the presence of HUH-6 cells. The culture supernatant of HUH-6 cells contained hematopoietic growth factors, including stem cell factor (SCF) and thrombopoietin (TPO). The neutralizing antibody against SCF abrogated the growth-stimulating activity of the culture supernatant of HUH-6 cells, demonstrating that, among the growth factors produced by HUH-6 cells, SCF may be the major growth stimulator and that TPO may be involved in megakaryocytic differentiation, rather than growth, of TAM blasts. This suggests that hepatoblasts function in the regulation of the growth and differentiation of TAM blasts in the FL through the production of hematopoietic growth factors, including SCF and TPO, and are involved in the leukemogenesis of TAM.

Pluripotent stem cell model of early hematopoiesis in Down syndrome reveals quantitative effects of short-form GATA1 protein on lineage specification

Children with Down syndrome (DS) are susceptible to two blood disorders, transient abnormal myelopoiesis (TAM) and Down syndrome-associated acute megakaryocytic leukemia (DS-AMKL). Mutations in GATA binding protein 1 (GATA1) have been identified as the cause of these diseases, and the expression levels of the resulting protein, short-form GATA1 (GATA1s), are known to correlate with the severity of TAM. On the other hand, despite the presence of GATA1 mutations in almost all cases of DS-AMKL, the incidence of DS-AMKL in TAM patients is inversely correlated with the expression of GATA1s. This discovery has required the need to clarify the role of GATA1s in generating the cells of origin linked to the risk of both diseases. Focusing on this point, we examined the characteristics of GATA1 mutant trisomy-21 pluripotent stem cells transfected with a doxycycline (Dox)-inducible GATA1s expression cassette in a stepwise hematopoietic differentiation protocol. We found that higher GATA1s expression significantly reduced commitment into the megakaryocytic lineage at the early hematopoietic progenitor cell (HPC) stage, but once committed, the effect was reversed in progenitor cells and acted to maintain the progenitors. These differentiation stage-dependent reversal effects were in contrast to the results of myeloid lineage, where GATA1s simply sustained and increased the number of immature myeloid cells. These results suggest that although GATA1 mutant cells cause the increase in myeloid and megakaryocytic progenitors regardless of the intensity of GATA1s expression, the pathways vary with the expression level. This study provides experimental support for the paradoxical clinical features of GATA1 mutations in the two diseases.

Molecular Mechanisms of the Genetic Predisposition to Acute Megakaryoblastic Leukemia in Infants With Down Syndrome

Individuals with Down syndrome are genetically predisposed to developing acute megakaryoblastic leukemia. This myeloid leukemia associated with Down syndrome (ML–DS) demonstrates a model of step-wise leukemogenesis with perturbed hematopoiesis already presenting in utero, facilitating the acquisition of additional driver mutations such as truncating GATA1 variants, which are pathognomonic to the disease. Consequently, the affected individuals suffer from a transient abnormal myelopoiesis (TAM)—a pre-leukemic state preceding the progression to ML–DS. In our review, we focus on the molecular mechanisms of the different steps of clonal evolution in Down syndrome leukemogenesis, and aim to provide a comprehensive view on the complex interplay between gene dosage imbalances, GATA1 mutations and somatic mutations affecting JAK-STAT signaling, the cohesin complex and epigenetic regulators.

Outcome and Prognostic Features in Pediatric Acute Megakaryoblastic Leukemia Without Down Syndrome: A Retrospective Study in China

BACKGROUND

Acute megakaryoblastic leukemia (AMKL) is a biologically heterogeneous subtype of acute myeloid leukemia that originates from megakaryocytes. Patients with AMKL with non-Down syndrome (DS) had a poorer prognosis. However, clear prognostic indicators and treatment recommendations for this subgroup remain controversial.

PATIENTS AND METHODS

Herein, we performed a retrospective study on 40 patients (age ≤ 18 years) with non-Down syndrome AMKL at our institution. We assessed the effect of different prognostic factors, such as their cytogenetic abnormalities, early treatment response, and the role of hematopoietic stem cell transplantation (HSCT) as post-remission treatment on the outcomes.

RESULTS

The complete remission (CR) rate of the patients was 57.9% and 81.1%, respectively, at the end of induction therapy 1 and 2. The overall survival (OS) and event-free survival rates at 2 years were 41% ± 13% and 41% ± 10%, respectively. An analysis of the cytogenetic features showed that patients with +21 or hyperdiploid (> 50 chromosomes) had significantly better OS than those in other cytogenetic subgroups (P_log-rank = .048 and P_log-rank = .040, respectively). Besides cytogenetics, an excellent early treatment response (CR and minimal residual disease < 1% after induction therapy 1) also provided a significant survival benefit in univariate analysis in our study. However, multivariate analysis indicated that allogeneic HSCT was the only independent prognostic marker (relative risk, 11.192; 95% confidence interval, 2.045-61.241; P = .005 for OS and relative risk, 5.400; 95% confidence interval, 1.635-17.832; P = .006 for event-free survival, respectively).

CONCLUSION

AMKL in patients with non-Down syndrome has a poor outcome. With poor OS but CR rates comparable with other acute myeloid leukemia subtypes, allogenic HSCT may be a better option for post-remission therapy than conventional chemotherapy, especially for those having a poor response to induction therapy.

Changes in megakaryopoiesis over ontogeny and their implications in health and disease

A growing body of research has made it increasingly clear that there are substantial biological differences between fetal/neonatal and adult megakaryopoiesis. Over the last decade, studies revealed a developmentally unique uncoupling of proliferation, polyploidization, and cytoplasmic maturation in neonatal MKs that results in the production of large numbers of small, low ploidy, but mature MKs during this period of development, and identified substantial molecular differences between fetal/neonatal and adult MKs. This review will summarize our current knowledge on the developmental differences between fetal/neonatal and adult MKs, and recent advances in our understanding of the underlying molecular mechanisms, including newly described developmentally regulated pathways and miRNAs. We will also discuss the implications of these findings on the ways MKs interact with the environment, the response of neonates to thrombocytopenia, the pathogenesis of Down syndrome-transient myeloproliferative disorder (TMD), and the developmental stage specific-manifestations of congenital amegakaryocytic thrombocytopenia.

Direct Comparison of Four Hematopoietic Differentiation Methods from Human Induced Pluripotent Stem Cells

Induced pluripotent stem cells (iPSCs) are an invaluable resource for the study of human disease. However, there are no standardized methods for differentiation into hematopoietic cells, and there is a lack of robust, direct comparisons of different methodologies. In the current study we improved a feeder-free, serum-free method for generation of hematopoietic cells from iPSCs, and directly compared this with three other commonly used strategies with respect to efficiency, repeatability, hands-on time, and cost. We also investigated their capability and sensitivity to model genetic hematopoietic disorders in cells derived from Down syndrome and β-thalassemia patients. Of these methods, a multistep monolayer-based method incorporating aryl hydrocarbon receptor hyperactivation (“2D-multistep”) was the most efficient, generating significantly higher numbers of CD34⁺ progenitor cells and functional hematopoietic progenitors, while being the most time- and cost-effective and most accurately recapitulating phenotypes of Down syndrome and β-thalassemia.

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Direct comparison of 4 serum & feeder-free iPSC hematopoietic differentiation methods

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Comparison: cost-benefit efficiency, sensitivity to model genetic blood diseases

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Presents an improved iPSC hematopoietic differentiation: 7× efficiency at 50% cost

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Improved method = most live cells, CD34⁺, CFU; lowest cost; greatest sensitivity

Neonatal vesiculopustular eruption in Down syndrome and transient myeloproliferative disorder: A case report and review of the literature

Transient myeloproliferative disorder (TMD) is a spontaneously resolving clonal myeloid proliferation characterized by circulating megakaryoblasts in the peripheral blood that is restricted to neonates with Down syndrome (DS) or those with trisomy 21 mosaicism. Cutaneous manifestations of TMD are observed in only 5% of affected neonates and present as a diffuse eruption of erythematous, crusted papules, papulovesicles, and pustules, often with prominent and initial facial involvement. We describe the case of a male infant with DS and TMD, associated with a vesiculopustular eruption, which appeared on day 36 of life, and review previous cases.

Epigenetic drug screen identifies the histone deacetylase inhibitor NSC3852 as a potential novel drug for the treatment of pediatric acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous disease regarding morphology, immunophenotyping, genetic abnormalities, and clinical behavior. The overall survival rate of pediatric AML is 60% to 70%, and has not significantly improved over the past two decades. Children with Down syndrome (DS) are at risk of developing acute megakaryoblastic leukemia (AMKL), which can be preceded by a transient myeloproliferative disorder during the neonatal period. Intensification of current treatment protocols is not feasible due to already high treatment-related morbidity and mortality. Instead, more targeted therapies with less severe side effects are highly needed.

PROCEDURE

To identify potential novel therapeutic targets for myeloid disorders in children, including DS-AMKL and non-DS-AML, we performed an unbiased compound screen of 80 small molecules targeting epigenetic regulators in three pediatric AML cell lines that are representative for different subtypes of pediatric AML. Three candidate compounds were validated and further evaluated in normal myeloid precursor cells during neutrophil differentiation and in (pre-)leukemic pediatric patient cells.

RESULTS

Candidate drugs LMK235, NSC3852, and bromosporine were effective in all tested pediatric AML cell lines with antiproliferative, proapoptotic, and differentiation effects. Out of these three compounds, the pan-histone deacetylase inhibitor NSC3852 specifically induced growth arrest and apoptosis in pediatric AML cells, without disrupting normal neutrophil differentiation.

CONCLUSION

NSC3852 is a potential candidate drug for further preclinical testing in pediatric AML and DS-AMKL.

Transient leukemia of Down syndrome

Childhood leukemia is mostly a "developmental accident" during fetal hematopoiesis and may require multiple prenatal and postnatal "hits". The World Health Organization defines transient leukemia of Down syndrome (DS) as increased peripheral blood blasts in neonates with DS and classifies this type of leukemia as a separate entity. Although it was shown that DS predisposes children to myeloid leukemia, neither the nature of the predisposition nor the associated genetic lesions have been defined. Acute myeloid leukemia of DS is a unique disease characterized by a long pre-leukemic, myelodysplastic phase, unusual chromosomal findings and a high cure rate. In the present manuscript, we present a comprehensive review of the literature about clinical and biological findings of transient leukemia of DS (TL-DS) and link them with the genetic discoveries in the field. We address the manuscript to the pediatric generalist and especially to the next generation of pediatric hematologists.

Molecular features, prognosis, and novel treatment options for pediatric acute megakaryoblastic leukemia

INTRODUCTION

Acute megakaryoblastic leukemia (AMegL) is a rare hematological neoplasm most often diagnosed in children and is commonly associated with Down's syndrome (DS). Although AMegLs are specifically characterized and typically diagnosed by megakaryoblastic expansion, recent advancements in molecular analysis have highlighted the heterogeneity of this disease, with specific cytogenic and genetic alterations characterizing different disease subtypes. Areas covered: This review will focus on describing recurrent molecular variations in both DS and non-DS pediatric AMegL, their role in promoting leukemogenesis, their association with different clinical aspects and prognosis, and finally, their influence on future treatment strategies with a number of specific drugs beyond conventional chemotherapy already under development. Expert opinion: Deep understanding of the genetic and molecular landscape of AMegL will lead to better and more precise disease classification in terms of diagnosis, prognosis, and possible targeted therapies. Development of new therapeutic approaches based on these molecular characteristics will hopefully improve AMegL patient outcomes.

The changing scenario of non-Down syndrome acute megakaryoblastic leukemia in children

Pediatric non-Down-syndrome acute megakaryoblastic leukemia (non-DS-AMKL) is a heterogeneous subtype of leukemia that has historically been associated with poor prognosis. Until the advent of large-scale genomic sequencing, the management of patients with non-DS-AMKL was very difficult due to the absence of reliable biological prognostic markers. The sequencing of large cohort of pediatric non-DS-AMKL samples led to the discovery of novel genetic aberrations, including high-frequency fusions, such as CBFA2T3-GLIS2 and NUP98-KDM5 A, as well as less frequent aberrations, such as HOX rearrangements. These new insights into the genetic landscape of pediatric non-DS-AMKL has allowed refining the risk-group stratification, leading to important changes in the prognostic scenario of these patients. This review summarizes the most important molecular pathogenic mechanisms of pediatric non-DS-AMKL. A critical discussion on how novel genetic abnormalities have refined the risk profile assessment and changed the management of these patients in clinical practice is also provided.

miR-155 expression in antitumor immunity: The higher the better?

MicroRNAs are small noncoding RNAs that modulate gene expression either directly, by impairing the stability and/or translation of transcripts that contain their specific target sequence, or indirectly through the targeting of transcripts that encode transcription factors, factors implicated in signal transduction pathways, or epigenetic regulators. Abnormal expression of micro-RNAs has been found in nearly all types of pathologies, including cancers. MiR-155 has been the first microRNA to be implicated in the regulation of the innate and adaptative immune responses, and its expression is either increased or decreased in a variety of liquid and solid malignancies. In this review, we examine the oncogenic and antitumor potentials of miR-155, with special emphasize on its dose-dependent effects. We describe the impact of miR-155 levels on antitumor activity of lymphocytes and myeloid cells. We discuss miR-155 dose-dependent effects in leukemias and analyze results showing that miR-155 intermediate levels tend to be detrimental, whereas high levels of miR-155 expression usually prove beneficial. We also examine the beneficial effects of high levels of miR-155 expression in solid tumors. We discuss the possible causal involvement of miR-155 in leukemias and dementia in individuals with Down's syndrome. We finally propose that increasing miR-155 levels in immune cells might increase the efficiency of newly developed cancer immunotherapies, due to miR-155 ability to target transcripts encoding immune checkpoints such as cytotoxic T lymphocyte antigen-4 or programmed death-ligand 1.

Erythromyeloid-Derived TREM2: A Major Determinant of Alzheimer's Disease Pathology in Down Syndrome

Background:

Down syndrome (DS; trisomy 21) individuals have a spectrum of hematopoietic and neuronal dysfunctions and by the time they reach the age of 40 years, almost all develop Alzheimer’s disease (AD) neuropathology which includes senile plaques and neurofibrillary tangles. Inflammation and innate immunity are key players in AD and DS. Triggering receptor expressed in myeloid cells-2 (TREM2) variants have been identified as risk factors for AD and other neurodegenerative diseases.

Objective:

To investigate the effects of TREM2 and the AD-associated R47H mutation on brain pathology and hematopoietic state in AD and DS.

Methods:

We analyzed peripheral blood, bone marrow, and brain tissue from DS, AD, and age-matched control subjects by immunohistochemistry and western blotting. TREM2-related phagocytosis was investigated using a human myeloid cell line.

Results:

TREM2 protein levels in brain and sera declined with age and disease progression in DS. We observed soluble TREM2 in brain parenchyma that may be carried by a subset of microglia, macrophages, or exosomes. Two DS cases had the AD-associated TREM2-R47H mutation, which manifested a morphologically extreme phenotype of megakaryocytes and erythrocytes in addition to impaired trafficking of TREM2 to the erythroid membrane. TREM2 was shown to be involved in phagocytosis of red blood cells. TREM2 was seen in early and late endosomes. Silencing TREM2 using siRNA in THP1 cells resulted in significant cell death.

Conclusion:

We provide evidence that peripheral TREM2 originating from erythromyeloid cells significantly determines AD neuropathology in DS subjects. Understanding the molecular signaling pathways mediated by TREM2 may reveal novel therapeutic targets.

Loss of Full-Length GATA1 Expression in Megakaryocytes Is a Sensitive and Specific Immunohistochemical Marker for the Diagnosis of Myeloid Proliferative Disorder Related to Down Syndrome

OBJECTIVES

Myeloid proliferative disorders associated with Down syndrome (MPD-DS), including transient abnormal myelopoiesis and myeloid leukemia associated with Down syndrome (DS), harbor mutations of GATA1, a transcription factor essential for erythroid and megakaryocytic development. These mutations result in a N-terminally truncated GATA1 (GATA1s) and prohibit the production of the full-length GATA1 (GATA1f). Here, we demonstrate the utility of immunohistochemical GATA1f reactivity in diagnosing MPD-DS.

METHODS

Immunohistochemical studies for GATA1f expression were performed on bone marrow biopsy specimens.

RESULTS

In all cases of MPD-DS, megakaryocytes lacked GATA1f expression. In contrast, GATA1f expression was detected in megakaryocytes in all specimen types from patients without DS (normal bone marrows, pediatric myelodysplastic syndrome, juvenile myelomonocytic leukemia, adult acute megakaryocytic leukemia [pediatric and adult; without trisomy 2]), as well as normal bone marrows from patients with DS.

CONCLUSIONS

The lack of GATA1f expression is a sensitive and specific immunohistochemical marker for MPD-DS.

Purification of leukemic blast cells from blood smears using laser microdissection

In treatment of acute myeloid leukemia (AML), prognostic factors, including gene mutation and abnormal gene expression, enable risk stratification of patients. However, in the case of a small proportion of leukemic blast cells, such as AML associated with Down syndrome (AML-DS), it is not possible to examine prognostic factors precisely due to the large proportion of normal cells. Here, we present a novel method for examining prognostic factors by making a smear on a membrane slide glass from a small amount of diagnostic specimen and collecting highly pure leukemic blast cells by laser microdissection (LMD). We verified the effectiveness of this method using 10% KPAM1 cell line suspension and peripheral blood containing 20% blast cells obtained from a patient with transient abnormal myelopoiesis (TAM). After making blood smears, approximately 100 cells were collected and analyzed by direct sequencing. Frameshift mutations (2 bp deletion and 17 bp duplication, respectively) in GATA-1 were detected in each sample, suggesting KPAM1 and TAM blast cells were accurately purified. This novel method enables us to precisely examine prognostic factors in many cases, even in cases with a small proportion of leukemic blast cells or small specimens to preserve.

GATA1 mutations in a cohort of Malaysian children with Down syndrome-associated myeloid disorder

INTRODUCTION

Children with Down syndrome (DS) are at increased risk of developing distinctive clonal myeloid disorders, including transient abnormal myelopoiesis (TAM) and myeloid leukaemia of DS (ML-DS). TAM connotes a spontaneously resolving congenital myeloproliferative state observed in 10%-20% of DS newborns. Following varying intervals of apparent remission, a proportion of children with TAM progress to develop ML-DS in early childhood. Therefore, TAM and ML-DS represent a biological continuum. Both disorders are characterised by recurring truncating somatic mutations of the GATA1 gene, which are considered key pathogenetic events.

METHODS

We herein report, to our knowledge, the first observation on the frequency and nature of GATA1 gene mutations in a cohort of Malaysian children with DS-associated TAM (n = 9) and ML-DS (n = 24) encountered successively over a period of five years at a national referral centre.

RESULTS

Of the 29 patients who underwent GATA1 analysis, GATA1 mutations were observed in 15 (51.7%) patients, including 6 (75.0%) out of 8 patients with TAM, and 9 (42.9%) of 21 patients with ML-DS. All identified mutations were located in exon 2 and the majority were sequence-terminating insertions or deletions (66.7%), including several hitherto unreported mutations (12 out of 15).

CONCLUSION

The low frequency of GATA1 mutations in ML-DS patients is unusual and potentially indicates distinctive genomic events in our patient cohort.

A neonate with a unique non-Down syndrome transient proliferative megakaryoblastic disease

Transient myeloproliferative disorder (TMD) is a leukemia type that occurs typically in newborns. In Down syndrome, TMD is referred to as transient abnormal myelopoiesis (TAM).³² Recently, transientness has also been reported in acute myeloid leukemia patients with germline trisomy 21 mosaicism, and even in cases with somatic trisomy 21, with or without GATA1 mutations. TMD cases without trisomy 21 are rare, and recurrent genetic aberrations that aid in clinical decision-making are scarcely described. We describe here a TMD patient without trisomy 21 or GATA1 mutation in whom single-nucleotide polymorphism analysis of leukemic blasts revealed a novel combined submicroscopic deletion (5q31.1-5q31.3 and 8q23.2q24).

Down syndrome and the complexity of genome dosage imbalance

Down syndrome (also known as trisomy 21) is the model human phenotype for all genomic gain dosage imbalances, including microduplications. The functional genomic exploration of the post-sequencing years of chromosome 21, and the generation of numerous cellular and mouse models, have provided an unprecedented opportunity to decipher the molecular consequences of genome dosage imbalance. Studies of Down syndrome could provide knowledge far beyond the well-known characteristics of intellectual disability and dysmorphic features, as several other important features, including congenital heart defects, early ageing, Alzheimer disease and childhood leukaemia, are also part of the Down syndrome phenotypic spectrum. The elucidation of the molecular mechanisms that cause or modify the risk for different Down syndrome phenotypes could lead to the introduction of previously unimaginable therapeutic options.

Distinct GATA1 Point Mutations in Monozygotic Twins With Down Syndrome and Transient Abnormal Myelopoiesis From a Triplet Pregnancy: A Case Report and Review of Literature

OBJECTIVES

Down syndrome (DS)-associated transient abnormal myelopoiesis (TAM) or acute megakaryoblastic leukemia (AMKL) in monozygotic twins is exceedingly rare and has not been well characterized.

METHODS

We describe a unique case of monozygotic twins with simultaneous TAM from a triplet pregnancy at 34 weeks' gestation. Previously reported cases of TAM and DS-AMKL in monozygotic twins have been reviewed to compare with our cases. The current concept of a sequential multistep process in leukemogenesis and disease evolution of TAM into DS-AMKL through the collaboration among trisomy 21, GATA1, and other gene mutations is also reviewed.

RESULTS

Distinct GATA1 mutations are identified in our neonate twins with TAM from a triplet pregnancy, whereas precisely identical GATA1 mutations have been detected in all three monozygotic DS twins reported in the literature.

CONCLUSIONS

Identical GATA1 mutations in cases of monozygotic twins are likely derived from twin-twin transmission. Distinct GATA1 mutations identified in our neonate twins with TAM provide unequivocal evidence of independent intra-utero GATA1 mutations, a completely different mechanism of development of TAM in monozygotic twins from previously reported cases. Interaction of trisomy 21 and GATA1 mutation produces TAM, but additional gene mutations are required for TAM to transform into DS-AMKL.

Systematic Cellular Disease Models Reveal Synergistic Interaction of Trisomy 21 and GATA1 Mutations in Hematopoietic Abnormalities

Chromosomal aneuploidy and specific gene mutations are recognized early hallmarks of many oncogenic processes. However, the net effect of these abnormalities has generally not been explored. We focused on transient myeloproliferative disorder (TMD) in Down syndrome, which is characteristically associated with somatic mutations in GATA1. To better understand functional interplay between trisomy 21 and GATA1 mutations in hematopoiesis, we constructed cellular disease models using human induced pluripotent stem cells (iPSCs) and genome-editing technologies. Comparative analysis of these engineered iPSCs demonstrated that trisomy 21 perturbed hematopoietic development through the enhanced production of early hematopoietic progenitors and the upregulation of mutated GATA1, resulting in the accelerated production of aberrantly differentiated cells. These effects were mediated by dosage alterations of RUNX1, ETS2, and ERG, which are located in a critical 4-Mb region of chromosome 21. Our study provides insight into the genetic synergy that contributes to multi-step leukemogenesis.

Baicalein antagonizes acute megakaryoblastic leukemia in vitro and in vivo by inducing cell cycle arrest

BACKGROUND

The prognosis of acute megakaryoblastic leukemia (AMKL) is really dismal, which urges for development of novel treatment. Baicalein is one type of flavonoids extracted from Scutellaria baicalensis Georgi (Huang Qin). It inhibited cell proliferation and subcutaneous tumor formation of many tumor cell lines. However, whether baicalein possesses anti-AMKL activities has not been tested.

RESULTS

We found that baicalein potently inhibited proliferation of multiple AMKL cells including CMK, CMY, Y10, 6133, and 6133 MPL/W515L due to apoptosis and cell cycle arrest at G1 phase. Unexpectedly, caspase inhibitor z-VAD-fmk did not restore cell proliferation. In contrast, ectopic expression of Cyclin D1 efficiently antagonized the inhibitory effect of baicalein. In addition, baicalein induced differentiation of 6133 MPL/W515L cells. Finally, baicalein promoted mice survival and reduced disease burden in a mouse model of AMKL.

CONCLUSIONS

Baicalein possesses potent anti-AMKL activity in vitro and in vivo. Baicalein may be a potent reagent for AMKL therapy.

The emerging role of GATA transcription factors in development and disease

The GATA family of transcription factors consists of six proteins (GATA1-6) which are involved in a variety of physiological and pathological processes. GATA1/2/3 are required for differentiation of mesoderm and ectoderm-derived tissues, including the haematopoietic and central nervous system. GATA4/5/6 are implicated in development and differentiation of endoderm- and mesoderm-derived tissues such as induction of differentiation of embryonic stem cells, cardiovascular embryogenesis and guidance of epithelial cell differentiation in the adult.

Evolution of myeloid leukemia in children with Down syndrome

Children with Down syndrome (DS) have a markedly increased risk of leukemia. They are at particular risk of acute megakaryoblastic leukemia, known as myeloid leukemia associated with DS (ML-DS), the development of which is closely linked to a preceding temporary form of neonatal leukemia called transient abnormal myelopoiesis (TAM). Findings from recent clinical and laboratory studies suggest that constitutional trisomy 21 and GATA1 mutation(s) cause TAM, and that additional genetic alteration(s) including those in epigenetic regulators and signaling molecules are involved in the progression from TAM to ML-DS. Thus, this disease progression represents an important model of multi-step leukemogenesis. The present review focuses on the evolutionary process of TAM to ML-DS, and advances in the understanding of perturbed hematopoiesis in DS with respect to GATA1 mutation and recent findings, including cooperating genetic events, are discussed.

Down syndrome and leukemia: insights into leukemogenesis and translational targets

Children with Down syndrome (DS) have a significantly increased risk of childhood leukemia, in particular acute megakaryoblastic leukemia (AMKL) and acute lymphoblastic leukemia (DS-ALL). A pre-leukemia, called transient myeloproliferative disorder (TMD), characterised by a GATA binding protein 1 (GATA1) mutation, affects up to 30% of newborns with DS. In most cases, the pre-leukemia regresses spontaneously, however one-quarter of these children will go on to develop AMKL or myelodysplastic syndrome (MDS) . AMKL and MDS occurring in young children with DS and a GATA1 somatic mutation are collectively termed myeloid leukemia of Down syndrome (ML-DS). This model represents an important multi-step process of leukemogenesis, and further study is required to identify therapeutic targets to potentially prevent development of leukemia. DS-ALL is a high-risk leukemia and mutations in the JAK-STAT pathway are frequently observed. JAK inhibitors may improve outcome for this type of leukemia. Genetic and epigenetic studies have revealed likely candidate drivers involved in development of ML-DS and DS-ALL. Overall this review aims to identify potential impacts of new research on how we manage children with DS, pre-leukemia and leukemia.

Clinical characteristics and laboratory analyses of acute myeloid leukemia with t(16;21)(p11;q22)

The present study reviewed three patients with acute myeloid leukemia (AML) who had the specific genetic abnormality t(16;21)(p11;q22). To investigate the clinical and laboratory characteristics of AML with t(16;21)(p11;q22) translocation, the similarities and differences of clinical characteristics and laboratory examinations were compared, and a literature review was conducted. According to the French-American-British classification system, patient 1 was M4, patient 2 was M1 and patient 3 was M2. The cytogenetic aberrations were 46, XY, t(16;21)(p11;q22)/47, idem, +21 for patient 1 and 46, XX, t(16;21)(p11;q22) for patients 2 and 3. Cytophagocytosis and cluster of differentiation 56 antigen expression were found in all three cases. The prognosis was poor in all the cases. AML with t(16;21)(p11;q22) is a specific subtype of AML that exhibits unique characteristics of morphology, immunology, cytogenetics and clinical features, as well as a poor prognosis. Stem cell transplantation may be the first and only choice for treatment.

Fetal liver stromal cells support blast growth in transient abnormal myelopoiesis in Down syndrome through GM-CSF

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome, which spontaneously resolves within several weeks or months after birth, may represent a very special form of leukemia arising in the fetal liver (FL). To explore the role of the fetal hematopoietic microenvironment in the pathogenesis of TAM, we examined the in vitro influences of stromal cells of human FL and fetal bone marrow (FBM) on the growth of TAM blasts. Both FL and FBM stromal cells expressed mesenchymal cell antigens (vimentin, α-smooth muscle actin, CD146, and nestin), being consistent with perivascular cells/mesenchymal stem cells that support hematopoietic stem cells. In addition, a small fraction of the FL stromal cells expressed an epithelial marker, cytokeratin 8, indicating that they could be cells in epithelial-mesenchymal transition (EMT). In the coculture system, stromal cells of the FL, but not FBM, potently supported the growth of TAM blast progenitors, mainly through humoral factors. High concentrations of hematopoietic growth factors were detected in culture supernatants of the FL stromal cells and a neutralizing antibody against granulocyte-macrophage colony-stimulating factor (GM-CSF) almost completely inhibited the growth-supportive activity of the culture supernatants. These results indicate that FL stromal cells with unique characteristics of EMT cells provide a pivotal hematopoietic microenvironment for TAM blasts and that GM-CSF produced by FL stromal cells may play an important role in the pathogenesis of TAM.

Haematopoietic development and leukaemia in Down syndrome

Children with constitutional trisomy 21 (cT21, Down Syndrome, DS) are at a higher risk for both myeloid and B-lymphoid leukaemias. The myeloid leukaemias are often preceded by a transient neonatal pre-leukaemic syndrome, Transient Abnormal Myelopoiesis (TAM). TAM is caused by cooperation between cT21 and acquired somatic N-terminal truncating mutations in the key haematopoietic transcription factor GATA1. These mutations, which are not leukaemogenic in the absence of cT21, are found in almost one-third of neonates with DS. Analysis of primary human fetal liver haematopoietic cells and of human embryonic stem cells demonstrates that cT21 itself substantially alters human fetal haematopoietic development. Consequently, many haematopoietic developmental defects are observed in neonates with DS even in the absence of TAM. Although studies in mouse models have suggested a pathogenic role of deregulated expression of several chromosome 21-encoded genes, their role in human leukaemogenesis remains unclear. As cT21 exists in all embryonic cells, the molecular basis of cT21-associated leukaemias probably reflects a complex interaction between deregulated gene expression in haematopoietic cells and the fetal haematopoietic microenvironment in DS.

Vesiculopustular eruption in neonatal transient myeloproliferative disorder

Transient myeloproliferative disorder (TMD) typically presents with pancytopenia, hepatosplenomegaly, and immature circulating white blood cells, and affects approximately 10 % of neonates with Down syndrome. The authors report a neonate with Down syndrome who developed acute widespread pustular eruptions as a sign of TMD. The white blood cell counts on the first day of life were markedly elevated, with blasts seen on examination of the peripheral blood smear. And the patient was noted to have a few erythematous papules and pustules especially on the face. On the following days pathergy positive crusted papules and pustules were increased and spread to trunk and extremities. Skin biopsy specimens showed pustular dermatitis, with subcorneal vesiculopustules and perivascular inflammation in superficial dermis. These lesions improved parallel with the hematologic improvement within two weeks. The authors aim to alert clinicians about this uncommon cause of vesiculopustular eruption with the present illustrative case and review the literature.

The prenatal origins of cancer

The concept that some childhood malignancies arise from postnatally persistent embryonal cells has a long history. Recent research has strengthened the links between driver mutations and embryonal and early postnatal development. This evidence, coupled with much greater detail on the cell of origin and the initial steps in embryonal cancer initiation, has identified important therapeutic targets and provided renewed interest in strategies for the early detection and prevention of childhood cancer.

Morphologic and GATA1 sequencing analysis of hematopoiesis in fetuses with trisomy 21

Trisomy 21 alters fetal liver hematopoiesis and, in combination with somatic globin transcription factor 1 (GATA1) mutations, leads to development of transient myeloproliferative disease in newborns. However, little is known about the morphological hematopoietic changes caused by trisomy 21 in the fetus, and to date, the exact onset of GATA1 mutations remains uncertain. Therefore, we analyzed fetal liver hematopoiesis from second trimester pregnancies in trisomy 21 and screened for GATA1 mutations. We examined 57 formalin-fixed and paraffin-embedded fetal liver specimens (49 harboring trisomy 21 and 8 controls) by immunohistochemistry for CD34, CD61, factor VIII, and glycophorin A. GATA1 exon 2 was sequenced in fetal livers and corresponding nonhematologic tissue. Cell counts of megakaryocytes (P = .022), megakaryocytic precursors (P = .021), and erythroid precursors were higher in trisomy 21 cases. CD34-positive hematopoietic blasts showed no statistically significant differences. No mutation was detected by GATA1 exon 2 sequencing in fetal livers from 12 to 25 weeks of gestation. Our results suggest that GATA1 exon 2 mutations occur late in trisomy 21 fetal hematopoiesis. However, trisomy 21 alone provides a proliferative stimulus of fetal megakaryopoiesis and erythropoiesis. CD34-positive precursor cells are not increased in trisomy 21 fetal livers.

The impact of trisomy 21 on foetal haematopoiesis

The high frequency of a unique neonatal preleukaemic syndrome, transient abnormal myelopoiesis (TAM), and subsequent acute myeloid leukaemia in early childhood in patients with trisomy 21 (Down syndrome) points to a specific role for trisomy 21 in transforming foetal haematopoietic cells. N-terminal truncating mutations in the key haematopoietic transcription factor GATA1 are acquired during foetal life in virtually every case. These mutations are not leukaemogenic in the absence of trisomy 21. In mouse models, deregulated expression of chromosome 21-encoded genes is implicated in leukaemic transformation, but does not recapitulate the effects of trisomy 21 in a human context. Recent work using primary human foetal liver and bone marrow cells, human embryonic stem cells and iPS cells shows that prior to acquisition of GATA1 mutations, trisomy 21 itself alters human foetal haematopoietic stem cell and progenitor cell biology causing multiple abnormalities in myelopoiesis and B-lymphopoiesis. The molecular basis by which trisomy 21 exerts these effects is likely to be extremely complex, to be tissue-specific and lineage-specific and to be dependent on ontogeny-related characteristics of the foetal microenvironment.

AKT collaborates with ERG and Gata1s to dysregulate megakaryopoiesis and promote AMKL

The requirement that leukemic GATA1 mutations be present in cells harboring trisomy 21 led to the discovery that overexpression of ERG drives aberrant megakaryopoiesis. Given that constitutive PI3K/AKT signaling is a frequent component of hematologic malignancies and the relationship between AKT and Notch in this lineage, we studied the cross talk between AKT signaling and ERG in megakaryopoiesis. We discovered that constitutive AKT signaling is associated with a dramatic increase in apoptosis of WT MKs, but that overexpression of ERG blocks AKT-induced death. We further found that Gata1 mutations protect megakaryocytes from activated AKT-induced apoptosis. As a consequence, however, the enhanced signaling inhibits differentiation of Gata1 mutant, but not WT, megakaryocytes. Gata1 mutant cells that overexpress ERG with hyperactive AKT are characterized by diminished FOXO1/3a expression and an increased dependency on the c-Jun pathway similar to that seen in AMKL cell lines, AML with knockdown of FOXO3a, or AML with expression of myrAKT. Additionally, we found that the AKT allosteric inhibitor MK2206 caused reduced cell viability and proliferation of AMKL cell lines. The contribution of aberrant AKT signaling during the ontogeny of DS-TMD/AMKL indicates that AKT is a therapeutic target in this form of AML.