Level of RUNX1 activity is critical for leukemic predisposition but not for thrombocytopenia

Organoids for Cancer Research: Advances and Challenges

As 3D culture technology advances, new avenues have opened for the development of physiological human cancer models. These preclinical models provide efficient ways to translate basic cancer research into clinical tumor therapies. Recently, cancer organoids have emerged as a model to dissect the more complex tumor microenvironment. Incorporating cancer organoids into preclinical programs have the potential to increase the success rate of oncology drug development and recapitulate the most efficacious treatment regimens for cancer patients. In this review, four main types of cancer organoids are introduced, their applications, advantages, limitations, and prospects are discussed, as well as the recent application of single-cell RNA-sequencing (scRNA-seq) in exploring cancer organoids to advance this field.

Haploinsufficient Transcription Factors in Myeloid Neoplasms

Many transcription factors (TFs) function as tumor suppressor genes with heterozygous phenotypes, yet haploinsufficiency generally has an underappreciated role in neoplasia. This is no less true in myeloid cells, which are normally regulated by a delicately balanced and interconnected transcriptional network. Detailed understanding of TF dose in this circuitry sheds light on the leukemic transcriptome. In this review, we discuss the emerging features of haploinsufficient transcription factors (HITFs). We posit that: (a) monoallelic and biallelic losses can have distinct cellular outcomes; (b) the activity of a TF exists in a greater range than the traditional Mendelian genetic doses; and (c) how a TF is deleted or mutated impacts the cellular phenotype. The net effect of a HITF is a myeloid differentiation block and increased intercellular heterogeneity in the course of myeloid neoplasia.

Runx1-R188Q germ line mutation induces inflammation and predisposition to hematologic malignancies in mice

Germ line mutations in the RUNX1 gene cause familial platelet disorder (FPD), an inherited disease associated with lifetime risk to hematopoietic malignancies (HM). Patients with FPD frequently show clonal expansion of premalignant cells preceding HM onset. Despite the extensive studies on the role of RUNX1 in hematopoiesis, its function in the premalignant bone marrow (BM) is not well-understood. Here, we characterized the hematopoietic progenitor compartments using a mouse strain carrying an FPD-associated mutation, Runx1R188Q. Immunophenotypic analysis showed an increase in the number of hematopoietic stem and progenitor cells (HSPCs) in the Runx1R188Q/+ mice. However, the comparison of Sca-1 and CD86 markers suggested that Sca-1 expression may result from systemic inflammation. Cytokine profiling confirmed the dysregulation of interferon-response cytokines in the BM. Furthermore, the expression of CD48, another inflammation-response protein, was also increased in Runx1R188Q/+ HSPCs. The DNA-damage response activity of Runx1R188Q/+ hematopoietic progenitor cells was defective in vitro, suggesting that Runx1R188Q may promote genomic instability. The differentiation of long-term repopulating HSCs was reduced in Runx1R188Q/+ recipient mice. Furthermore, we found that Runx1R188Q/+ HSPCs outcompete their wild-type counterparts in bidirectional repopulation assays, and that the genetic makeup of recipient mice did not significantly affect the clonal dynamics under this setting. Finally, we demonstrate that Runx1R188Q predisposes to HM in cooperation with somatic mutations found in FPDHM, using 3 mouse models. These studies establish a novel murine FPDHM model and demonstrate that germ line Runx1 mutations induce a premalignant phenotype marked by BM inflammation, selective expansion capacity, defective DNA-damage response, and predisposition to HM.

Applications of Innovation Technologies for Personalized Cancer Medicine: Stem Cells and Gene-Editing Tools

Personalized medicine is a new approach toward safer and even cheaper treatments with minimal side effects and toxicity. Planning a therapy based on individual properties causes an effective result in a patient's treatment, especially in a complex disease such as cancer. The benefits of personalized medicine include not only early diagnosis with high accuracy but also a more appropriate and effective therapeutic approach based on the unique clinical, genetic, and epigenetic features and biomarker profiles of a specific patient's disease. In order to achieve personalized cancer therapy, understanding cancer biology plays an important role. One of the crucial applications of personalized medicine that has gained consideration more recently due to its capability in developing disease therapy is related to the field of stem cells. We review various applications of pluripotent, somatic, and cancer stem cells in personalized medicine, including targeted cancer therapy, cancer modeling, diagnostics, and drug screening. CRISPR-Cas gene-editing technology is then discussed as a state-of-the-art biotechnological advance with substantial impacts on medical and therapeutic applications. As part of this section, the role of CRISPR-Cas genome editing in recent cancer studies is reviewed as a further example of personalized medicine application.

Ataluren prevented bone loss induced by ovariectomy and aging in mice through the BMP-SMAD signaling pathway

Both estrogen deficiency and aging may lead to osteoporosis. Developing novel drugs for treating osteoporosis is a popular research direction. We screened several potential therapeutic agents through a new deep learning-based efficacy prediction system (DLEPS) using transcriptional profiles for osteoporosis. DLEPS screening led to a potential novel drug examinee, ataluren, for treating osteoporosis. Ataluren significantly reversed bone loss in ovariectomized mice. Next, ataluren significantly increased human bone marrow-derived mesenchymal stem cell (hBMMSC) osteogenic differentiation without cytotoxicity, indicated by the high expression index of osteogenic differentiation genes (OCN , BGLAP, ALP, COL1A, BMP2, RUNX2). Mechanistically, ataluren exerted its function through the BMP-SMAD pathway. Furthermore, it activated SMAD phosphorylation but osteogenic differentiation was attenuated by BMP2-SMAD inhibitors or small interfering RNA of BMP2. Finally, ataluren significantly reversed bone loss in aged mice. In summary, our findings suggest that the DLEPS-screened ataluren may be a therapeutic agent against osteoporosis by aiding hBMMSC osteogenic differentiation.

RUNX1 mutations mitigate quiescence to promote transformation of hematopoietic progenitors in Fanconi anemia

Many inherited bone marrow failure syndromes (IBMFSs) present a high risk of transformation to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). During transformation of IBMFSs, hematopoietic stem and progenitor cells (HSPCs) with poor fitness gain ectopic, dysregulated self-renewal secondary to somatic mutations via undefined mechanisms. Here, in the context of the prototypical IBMFS Fanconi anemia (FA), we performed multiplexed gene editing of mutational hotspots in MDS-associated genes in human induced pluripotent stem cells (iPSCs) followed by hematopoietic differentiation. We observed aberrant self-renewal and impaired differentiation of HSPCs with enrichment of RUNX1 insertions and deletions (indels), generating a model of IBMFS-associated MDS. We observed that compared to the failure state, FA MDS cells show mutant RUNX1-mediated blunting of the G1/S cell cycle checkpoint that is normally activated in FA in response to DNA damage. RUNX1 indels also lead to activation of innate immune signaling, which stabilizes the homologous recombination (HR) effector BRCA1, and this pathway can be targeted to abrogate viability and restore sensitivity to genotoxins in FA MDS. Together, these studies develop a paradigm for modeling clonal evolution in IBMFSs, provide basic understanding of the pathogenesis of MDS, and uncover a therapeutic target in FA-associated MDS.

The RUNX Family of Proteins, DNA Repair, and Cancer

The RUNX family of transcription factors, including RUNX1, RUNX2, and RUNX3, are key regulators of development and can function as either tumor suppressors or oncogenes in cancer. Emerging evidence suggests that the dysregulation of RUNX genes can promote genomic instability in both leukemia and solid cancers by impairing DNA repair mechanisms. RUNX proteins control the cellular response to DNA damage by regulating the p53, Fanconi anemia, and oxidative stress repair pathways through transcriptional or non-transcriptional mechanisms. This review highlights the importance of RUNX-dependent DNA repair regulation in human cancers.

Hematopoietic Cell Autonomous Disruption of Hematopoiesis in a Germline Loss-of-function Mouse Model of RUNX1-FPD

RUNX1 familial platelet disorder (RUNX1-FPD) is a hematopoietic disorder caused by germline loss-of-function mutations in the RUNX1 gene and characterized by thrombocytopathy, thrombocytopenia, and an increased risk of developing hematologic malignancies, mostly of myeloid origin. Disease pathophysiology has remained incompletely understood, in part because of a shortage of in vivo models recapitulating the germline RUNX1 loss of function found in humans, precluding the study of potential contributions of non-hematopoietic cells to disease pathogenesis. Here, we studied mice harboring a germline hypomorphic mutation of one Runx1 allele with a loss-of-function mutation in the other Runx1 allele (Runx1 L148A/- mice), which display many hematologic characteristics found in human RUNX1-FPD patients. Runx1 L148A/- mice displayed robust and pronounced thrombocytopenia and myeloid-biased hematopoiesis, associated with an HSC intrinsic reconstitution defect in lymphopoiesis and expansion of myeloid progenitor cell pools. We demonstrate that specific deletion of Runx1 from bone marrow stromal cells in Prrx1-cre;Runx1 fl/fl mice did not recapitulate these abnormalities, indicating that the hematopoietic abnormalities are intrinsic to the hematopoietic lineage, and arguing against a driving role of the bone marrow microenvironment. In conclusion, we report a RUNX1-FPD mouse model faithfully recapitulating key characteristics of human disease. Findings do not support a driving role of ancillary, non-hematopoietic cells in the disruption of hematopoiesis under homeostatic conditions.

A RUNX1-FPDMM rhesus macaque model reproduces the human phenotype and predicts challenges to curative gene therapies

Germ line loss-of-function heterozygous mutations in the RUNX1 gene cause familial platelet disorder with associated myeloid malignancies (FPDMM) characterized by thrombocytopenia and a life-long risk of hematological malignancies. Although gene therapies are being considered as promising therapeutic options, current preclinical models do not recapitulate the human phenotype and are unable to elucidate the relative fitness of mutation-corrected and RUNX1-heterozygous mutant hematopoietic stem and progenitor cells (HSPCs) in vivo long term. We generated a rhesus macaque with an FPDMM competitive repopulation model using CRISPR/Cas9 nonhomologous end joining editing in the RUNX1 gene and the AAVS1 safe-harbor control locus. We transplanted mixed populations of edited autologous HSPCs and tracked mutated allele frequencies in blood cells. In both animals, RUNX1-edited cells expanded over time compared with AAVS1-edited cells. Platelet counts remained below the normal range in the long term. Bone marrows developed megakaryocytic dysplasia similar to human FPDMM, and CD34+ HSPCs showed impaired in vitro megakaryocytic differentiation, with a striking defect in polyploidization. In conclusion, the lack of a competitive advantage for wildtype or control-edited HSPCs over RUNX1 heterozygous-mutated HSPCs long term in our preclinical model suggests that gene correction approaches for FPDMM will be challenging, particularly to reverse myelodysplastic syndrome/ acute myeloid leukemia predisposition and thrombopoietic defects.

RUNX1-deficient human megakaryocytes demonstrate thrombopoietic and platelet half-life and functional defects

Heterozygous defects in runt-related transcription factor 1 (RUNX1) are causative of a familial platelet disorder with associated myeloid malignancy (FPDMM). Because RUNX1-deficient animal models do not mimic bleeding disorder or leukemic risk associated with FPDMM, development of a proper model system is critical to understanding the underlying mechanisms of the observed phenotype and to identifying therapeutic interventions. We previously reported an in vitro megakaryopoiesis system comprising human CD34+ hematopoietic stem and progenitor cells that recapitulated the FPDMM quantitative megakaryocyte defect through a decrease in RUNX1 expression via a lentiviral short hairpin RNA strategy. We now show that shRX-megakaryocytes have a marked reduction in agonist responsiveness. We then infused shRX-megakaryocytes into immunocompromised NOD scid gamma (NSG) mice and demonstrated that these megakaryocytes released fewer platelets than megakaryocytes transfected with a nontargeting shRNA, and these platelets had a diminished half-life. The platelets were also poorly responsive to agonists, unable to correct thrombus formation in NSG mice homozygous for a R1326H mutation in von Willebrand Factor (VWFR1326H), which switches the species-binding specificity of the VWF from mouse to human glycoprotein Ibα. A small-molecule inhibitor RepSox, which blocks the transforming growth factor β1 (TGFβ1) pathway and rescued defective megakaryopoiesis in vitro, corrected the thrombopoietic defect, defects in thrombus formation and platelet half-life, and agonist response in NSG/VWFR1326H mice. Thus, this model recapitulates the defects in FPDMM megakaryocytes and platelets, identifies previously unrecognized defects in thrombopoiesis and platelet half-life, and demonstrates for the first time, reversal of RUNX1 deficiency-induced hemostatic defects by a drug.

Molecular Basis of Hematological Disease Caused by Inherited or Acquired RUNX1 Mutations

The transcription factor RUNX1 is essential for correct hematopoietic development; in its absence in the germ line, blood stem cells are not formed. RUNX1 orchestrates dramatic changes in the chromatin landscape at the onset of stem cell formation, which set the stage for both stem self-renewal and further differentiation. However, once blood stem cells are formed, the mutation of the RUNX1 gene is not lethal but can lead to various hematopoietic defects and a predisposition to cancer. Here we summarize the current literature on inherited and acquired RUNX1 mutations, with a particular emphasis on mutations that alter the structure of the RUNX1 protein itself, and place these changes in the context of what is known about RUNX1 function. We also summarize which mutant RUNX1 proteins are actually expressed in cells and discuss the molecular mechanism underlying how such variants reprogram the epigenome setting stem cells on the path to malignancy.

Myeloid neoplasms and clonal hematopoiesis from the RUNX1 perspective

RUNX1 is a critical transcription factor for the emergence of definitive hematopoiesis and the precise regulation of adult hematopoiesis. Dysregulation of its regulatory network causes aberrant hematopoiesis. Recurrent genetic alterations in RUNX1, including chromosomal translocations and mutations, have been identified in both inherited and sporadic diseases. Recent genomic studies have revealed a vast mutational landscape surrounding genetic alterations in RUNX1. Accumulating pieces of evidence also indicate the leukemogenic role of wild-type RUNX1 in certain situations. Based on these efforts, part of the molecular mechanisms of disease development as a consequence of dysregulated RUNX1-regulatory networks have become increasingly evident. This review highlights the recent advances in the field of RUNX1 research and discusses the critical roles of RUNX1 in hematopoiesis and the pathobiological function of its alterations in the context of disease, particularly myeloid neoplasms, and clonal hematopoiesis.

Harnessing the Power of Induced Pluripotent Stem Cells and Gene Editing Technology: Therapeutic Implications in Hematological Malignancies

In vitro modeling of hematological malignancies not only provides insights into the influence of genetic aberrations on cellular and molecular mechanisms involved in disease progression but also aids development and evaluation of therapeutic agents. Owing to their self-renewal and differentiation capacity, induced pluripotent stem cells (iPSCs) have emerged as a potential source of short in supply disease-specific human cells of the hematopoietic lineage. Patient-derived iPSCs can recapitulate the disease severity and spectrum of prognosis dictated by the genetic variation among patients and can be used for drug screening and studying clonal evolution. However, this approach lacks the ability to model the early phases of the disease leading to cancer. The advent of genetic editing technology has promoted the generation of precise isogenic iPSC disease models to address questions regarding the underlying genetic mechanism of disease initiation and progression. In this review, we discuss the use of iPSC disease modeling in hematological diseases, where there is lack of patient sample availability and/or difficulty of engraftment to generate animal models. Furthermore, we describe the power of combining iPSC and precise gene editing to elucidate the underlying mechanism of initiation and progression of various hematological malignancies. Finally, we discuss the power of iPSC disease modeling in developing and testing novel therapies in a high throughput setting.

Modeling genetic platelet disorders with human pluripotent stem cells: mega-progress but wanting more on our plate(let)

PURPOSE OF REVIEW

Megakaryocytes are rare hematopoietic cells that play an instrumental role in hemostasis, and other important biological processes such as immunity and wound healing. With the advent of cell reprogramming technologies and advances in differentiation protocols, it is now possible to obtain megakaryocytes from any pluripotent stem cell (PSC) via hematopoietic induction. Here, we review recent advances in PSC-derived megakaryocyte (iMK) technology, focusing on platform validation, disease modeling and current limitations.

RECENT FINDINGS

A comprehensive study confirmed that iMK can recapitulate many transcriptional and functional aspects of megakaryocyte and platelet biology, including variables associated with complex genetic traits such as sex and race. These findings were corroborated by several pathological models in which iMKs revealed molecular mechanisms behind inherited platelet disorders and assessed the efficacy of novel pharmacological interventions. However, current differentiation protocols generate primarily embryonic iMK, limiting the clinical and translational potential of this system.

SUMMARY

iMK are strong candidates to model pathologic mutations involved in platelet defects and develop innovative therapeutic strategies. Future efforts on generating definitive hematopoietic progenitors would improve current platelet generation protocols and expand our capacity to model neonatal and adult megakaryocyte disorders.

Characterization of the Platelet Phenotype Caused by a Germline RUNX1 Variant in a CRISPR/Cas9-Generated Murine Model

RUNX1-related disorder (RUNX1-RD) is caused by germline variants affecting the RUNX1 gene. This rare, heterogeneous disorder has no specific clinical or laboratory phenotype, making genetic diagnosis necessary. Although international recommendations have been established to classify the pathogenicity of variants, identifying the causative alteration remains a challenge in RUNX1-RD. Murine models may be useful not only for definitively settling the controversy about the pathogenicity of certain RUNX1 variants, but also for elucidating the mechanisms of molecular pathogenesis. Therefore, we developed a knock-in murine model, using the CRISPR/Cas9 system, carrying the RUNX1 p.Leu43Ser variant (mimicking human p.Leu56Ser) to study its pathogenic potential and mechanisms of platelet dysfunction. A total number of 75 mice were generated; 25 per genotype (RUNX1WT/WT, RUNX1WT/L43S, and RUNX1L43S/L43S). Platelet phenotype was assessed by flow cytometry and confocal microscopy. On average, RUNX1L43S/L43S and RUNX1WT/L43S mice had a significantly longer tail-bleeding time than RUNX1WT/WT mice, indicating the variant's involvement in hemostasis. However, only homozygous mice displayed mild thrombocytopenia. RUNX1L43S/L43S and RUNX1WT/L43S displayed impaired agonist-induced spreading and α-granule release, with no differences in δ-granule secretion. Levels of integrin αIIbβ3 activation, fibrinogen binding, and aggregation were significantly lower in platelets from RUNX1L43S/L43S and RUNX1WT/L43S using phorbol 12-myristate 13-acetate (PMA), adenosine diphosphate (ADP), and high thrombin doses. Lower levels of PKC phosphorylation in RUNX1L43S/L43S and RUNX1WT/L43S suggested that the PKC-signaling pathway was impaired. Overall, we demonstrated the deleterious effect of the RUNX1 p.Leu56Ser variant in mice via the impairment of integrin αIIbβ3 activation, aggregation, α-granule secretion, and platelet spreading, mimicking the phenotype associated with RUNX1 variants in the clinical setting.

Transcription Factors, R-Loops and Deubiquitinating Enzymes: Emerging Targets in Myelodysplastic Syndromes and Acute Myeloid Leukemia

Simple Summary

The advent of DNA massive sequencing technologies has allowed for the first time an extensive look into the heterogeneous spectrum of genes and mutations underpinning myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML). In this review, we wish to explore the most recent advances and the rationale for the potential therapeutic interest of three main actors in myelo-leukemic transformation: transcription factors that govern myeloid differentiation; RNA splicing factors, which ensure proper mRNA maturation and whose mutations increase R-loops formation; and deubiquitinating enzymes, which contribute to genome stability in hematopoietic stem cells (HSCs).

Abstract

Myeloid neoplasms encompass a very heterogeneous family of diseases characterized by the failure of the molecular mechanisms that ensure a balanced equilibrium between hematopoietic stem cells (HSCs) self-renewal and the proper production of differentiated cells. The origin of the driver mutations leading to preleukemia can be traced back to HSC/progenitor cells. Many properties typical to normal HSCs are exploited by leukemic stem cells (LSCs) to their advantage, leading to the emergence of a clonal population that can eventually progress to leukemia with variable latency and evolution. In fact, different subclones might in turn develop from the original malignant clone through accumulation of additional mutations, increasing their competitive fitness. This process ultimately leads to a complex cancer architecture where a mosaic of cellular clones—each carrying a unique set of mutations—coexists. The repertoire of genes whose mutations contribute to the progression toward leukemogenesis is broad. It encompasses genes involved in different cellular processes, including transcriptional regulation, epigenetics (DNA and histones modifications), DNA damage signaling and repair, chromosome segregation and replication (cohesin complex), RNA splicing, and signal transduction. Among these many players, transcription factors, RNA splicing proteins, and deubiquitinating enzymes are emerging as potential targets for therapeutic intervention.

The Use of Stem Cell-Derived Organoids in Disease Modeling: An Update

Organoids represent one of the most important advancements in the field of stem cells during the past decade. They are three-dimensional in vitro culturing models that originate from self-organizing stem cells and can mimic the in vivo structural and functional specificities of body organs. Organoids have been established from multiple adult tissues as well as pluripotent stem cells and have recently become a powerful tool for studying development and diseases in vitro, drug screening, and host-microbe interaction. The use of stem cells-that have self-renewal capacity to proliferate and differentiate into specialized cell types-for organoids culturing represents a major advancement in biomedical research. Indeed, this new technology has a great potential to be used in a multitude of fields, including cancer research, hereditary and infectious diseases. Nevertheless, organoid culturing is still rife with many challenges, not limited to being costly and time consuming, having variable rates of efficiency in generation and maintenance, genetic stability, and clinical applications. In this review, we aim to provide a synopsis of pluripotent stem cell-derived organoids and their use for disease modeling and other clinical applications.

A novel RUNX1 mutation with ANKRD26 dysregulation is related to thrombocytopenia in a sporadic form of myelodysplastic syndrome

Aging is associated with a higher risk of developing malignant diseases, including myelodysplastic syndromes, clonal disorders characterised by chronic cytopenias (anaemia, neutropenia and thrombocytopenia) and abnormal cellular maturation. Myelodysplastic syndromes arising in older subjects are influenced by combinations of acquired somatic genetic lesions driving evolution from clonal haematopoiesis to myelodysplastic syndromes and from myelodysplastic syndromes to acute leukaemia. A different pattern of mutations has been identified in a small subset of myelodysplastic syndromes arising in young patients with familial syndromes. In particular, dysregulation of ANKRD26, RUNX1 and ETV6 genes plays a role in familial thrombocytopenia with predisposition to myelodysplastic syndromes and acute leukaemia. Whether these genes affect thrombopoiesis in sporadic myelodysplastic syndrome with thrombocytopenia is still undefined. Thirty-one myelodysplastic syndromes subjects and 27 controls subjects were investigated. Genomic DNA was used for mutation screening (ETV6, RUNX1, 5'UTR ANKRD26 genes). Functional studies were performed in the MEG-01-akaryoblastic cell line. We found four novel variants of RUNX1 gene, all in elderly myelodysplastic syndromes subjects with thrombocytopenia. Functional studies of the variant p.Pro103Arg showed no changes in RUNX1 expression, but the variant was associated with deregulated high transcriptional activity of ANKRD26 in MEG-01 cells. RUNX1 variant p.Pro103Arg was also associated with increased viability and reduced apoptosis of MEG-01, as well as impaired platelet production. Our findings are consistent with dysregulation of ANKRD26 in RUNX1 haploinsufficiency. Lack of repression of ANKRD26 expression may contribute to thrombocytopenia of subjects with sporadic myelodysplastic syndromes.

Short Time-Series Expression Transcriptome Data Reveal the Gene Expression Patterns of Dairy Cow Mammary Gland as Milk Yield Decreased Process

The existing research on dairy cow mammary gland genes is extensive, but there have been few reports about dynamic changes in dairy cow mammary gland genes as milk yield decrease. For the first time, transcriptome analysis based on short time-series expression miner (STEM) and histological observations were performed using the Holstein dairy cow mammary gland to explore gene expression patterns in this process of decrease (at peak, mid-, and late lactation). Histological observations suggested that the number of mammary acinous cells at peak/mid-lactation was significantly higher than that at mid-/late lactation, and the lipid droplets area secreted by dairy cows was almost unaltered across the three stages of lactation (p > 0.05). Totals of 882 and 1439 genes were differentially expressed at mid- and late lactation, respectively, compared to peak lactation. Function analysis showed that differentially expressed genes (DEGs) were mainly related to apoptosis and energy metabolism (fold change ≥ 2 or fold change ≤ 0.5, p-value ≤ 0.05). Transcriptome analysis based on STEM identified 16 profiles of differential gene expression patterns, including 5 significant profiles (false discovery rate, FDR ≤ 0.05). Function analysis revealed DEGs involved in milk fat synthesis were downregulated in Profile 0 and DEGs in Profile 12 associated with protein synthesis. These findings provide a foundation for future studies on the molecular mechanisms underlying mammary gland development in dairy cows.

Induced Pluripotent Stem Cells Enable Disease Modeling and Drug Screening in Calreticulin del52 and ins5 Myeloproliferative Neoplasms

Mutations in the calreticulin (CALR) gene are seen in about 30% of essential thrombocythemia and primary myelofibrosis patients. To address the contribution of the human CALR mutants to the pathogenesis of myeloproliferative neoplasms (MPNs) in an endogenous context, we modeled the CALRdel52 and CALRins5 mutants by induced pluripotent stem cell (iPSC) technology using CD34⁺ progenitors from 4 patients. We describe here the generation of several clones of iPSC carrying heterozygous CALRdel52 or CALRins5 mutations. We showed that CALRdel52 induces a stronger increase in progenitors than CALRins5 and that both CALRdel52 and CALRins5 mutants favor an expansion of the megakaryocytic lineage. Moreover, we found that both CALRdel52 and CALRins5 mutants rendered colony forming unit–megakaryocyte (CFU-MK) independent from thrombopoietin (TPO), and promoted a mild constitutive activation level of signal transducer and activator of transcription 3 in megakaryocytes. Unexpectedly, a mild increase in the sensitivity of colony forming unit-granulocyte (CFU-G) to granulocyte-colony stimulating factor was also observed in iPSC CALRdel52 and CALRins5 compared with control iPSC. Moreover, CALRdel52-induced megakaryocytic spontaneous growth is more dependent on Janus kinase 2/phosphoinositide 3-kinase/extracellular signal-regulated kinase than TPO-mediated growth and opens a therapeutic window for treatments in CALR-mutated MPN. The iPSC models described here represent an interesting platform for testing newly developed inhibitors. Altogether, this study shows that CALR-mutated iPSC recapitulate MPN phenotypes in vitro and may be used for drug screening.

Study of inherited thrombocytopenia resulting from mutations in ETV6 or RUNX1 using a human pluripotent stem cell model

Inherited thrombocytopenia results in low platelet counts and increased bleeding. Subsets of these patients have monoallelic germline mutations in ETV6 or RUNX1 and a heightened risk of developing hematologic malignancies. Utilizing CRISPR-Cas9, we compared the in vitro phenotype of hematopoietic progenitor cells and megakaryocytes derived from induced pluripotent stem cell (iPSC) lines harboring mutations in either ETV6 or RUNX1. Both mutant lines display phenotypes consistent with a platelet-bleeding disorder. Surprisingly, these cellular phenotypes were largely distinct. The ETV6-mutant iPSCs yield more hematopoietic progenitor cells and megakaryocytes, but the megakaryocytes are immature and less responsive to agonist stimulation. On the contrary, RUNX1-mutant iPSCs yield fewer hematopoietic progenitor cells and megakaryocytes, but the megakaryocytes are more responsive to agonist stimulation. However, both mutant iPSC lines display defects in proplatelet formation. Our work highlights that, while patients harboring germline ETV6 or RUNX1 mutations have similar clinical phenotypes, the molecular mechanisms may be distinct.

RUNX-1 haploinsufficiency causes a marked deficiency of megakaryocyte-biased hematopoietic progenitor cells

Patients with familial platelet disorder with a predisposition to myeloid malignancy (FPDMM) harbor germline monoallelic mutations in a key hematopoietic transcription factor, RUNX-1. Previous studies of FPDMM have focused on megakaryocyte (Mk) differentiation and platelet production and signaling. However, the effects of RUNX-1 haploinsufficiency on hematopoietic progenitor cells (HPCs) and subsequent megakaryopoiesis remains incomplete. We studied induced pluripotent stem cell (iPSC)-derived HPCs (iHPCs) and Mks (iMks) from both patient-derived lines and a wild-type (WT) line modified to be RUNX-1 haploinsufficient (RUNX-1+/-), each compared with their isogenic WT control. All RUNX-1+/- lines showed decreased iMk yield and depletion of an Mk-biased iHPC subpopulation. To investigate global and local gene expression changes underlying this iHPC shift, single-cell RNA sequencing was performed on sorted FPDMM and control iHPCs. We defined several cell subpopulations in the Mk-biased iHPCs. Analyses of gene sets upregulated in FPDMM iHPCs indicated enrichment for response to stress, regulation of signal transduction, and immune signaling-related gene sets. Immunoblot analyses in FPDMM iMks were consistent with these findings, but also identified augmented baseline c-Jun N-terminal kinase (JNK) phosphorylation, known to be activated by transforming growth factor-β1 (TGF-β1) and cellular stressors. These findings were confirmed in adult human CD34+-derived stem and progenitor cells (HSPCs) transduced with lentiviral RUNX1 short hairpin RNA to mimic RUNX-1+/-. In both iHPCs and CD34+-derived HSPCs, targeted inhibitors of JNK and TGF-β1 pathways corrected the megakaryopoietic defect. We propose that such intervention may correct the thrombocytopenia in patients with FPDMM.

The Role of Megakaryocytes in Myelofibrosis

Megakaryocytes give rise to platelets, which have a wide variety of functions in coagulation, immune response, inflammation, and tissue repair. Dysregulation of megakaryocytes is a key feature of in the myeloproliferative neoplasms, especially myelofibrosis. Megakaryocytes are among the main drivers of myelofibrosis by promoting myeloproliferation and bone marrow fibrosis. In vivo targeting of megakaryocytes by genetic and pharmacologic approaches ameliorates the disease, underscoring the important role of megakaryocytes in myeloproliferative neoplasms. Here we review the current knowledge of the function of megakaryocytes in the JAK2, CALR, and MPL-mutant myeloproliferative neoplasms.

Secondary leukemia in patients with germline transcription factor mutations (RUNX1, GATA2, CEBPA)

Recognition that germline mutations can predispose individuals to blood cancers, often presenting as secondary leukemias, has largely been driven in the last 20 years by studies of families with inherited mutations in the myeloid transcription factors (TFs) RUNX1, GATA2, and CEBPA. As a result, in 2016, classification of myeloid neoplasms with germline predisposition for each of these and other genes was added to the World Health Organization guidelines. The incidence of germline mutation carriers in the general population or in various clinically presenting patient groups remains poorly defined for reasons including that somatic mutations in these genes are common in blood cancers, and our ability to distinguish germline (inherited or de novo) and somatic mutations is often limited by the laboratory analyses. Knowledge of the regulation of these TFs and their mutant alleles, their interaction with other genes and proteins and the environment, and how these alter the clinical presentation of patients and their leukemias is also incomplete. Outstanding questions that remain for patients with these germline mutations or their treating clinicians include: What is the natural course of the disease? What other symptoms may I develop and when? Can you predict them? Can I prevent them? and What is the best treatment? The resolution of many of the remaining clinical and biological questions and effective evidence-based treatment of patients with these inherited mutations will depend on worldwide partnerships among patients, clinicians, diagnosticians, and researchers to aggregate sufficient longitudinal clinical and laboratory data and integrate these data with model systems.

Studying leukemia stem cell properties and vulnerabilities with human iPSCs

The reprogramming of cancer cells into induced pluripotent stem cells (iPSCs) can capture entire cancer genomes, and thus create genetically faithful models of human cancers. By providing stringent genetically clonal conditions, iPSC modeling can also unveil non-genetic sources of cancer heterogeneity and provide a unique opportunity to study them separately from genetic sources, as we recently showed in an iPSC-based model of acute myeloid leukemia (AML). Genetically clonal iPSCs, derived from a patient with AML, reproduce, upon hematopoietic differentiation, phenotypic and functional heterogeneity with all the hallmarks of a leukemia stem cell (LSC) hierarchy. Here we discuss the lessons that can be learned about the LSC state, its plasticity, stability and genetic and epigenetic determinants from iPSC modeling. We also discuss the practical and translational implications of exploiting AML-iPSCs to prospectively isolate large numbers of iLSCs for large-scale experiments, such as screens, and for discovery of new therapeutic targets specific to AML LSCs.

Therapeutic Vulnerabilities of Transcription Factors in AML

Acute myeloid leukemia (AML) is characterized by impaired myeloid lineage differentiation, uncontrolled proliferation, and inhibition of proapoptotic pathways. In spite of a relatively homogeneous clinical disease presentation, risk of long-term survival in AML varies from 20% to 80% depending on molecular disease characteristics. In recognition of the molecular heterogeneity of AML, the European Leukemia Net (ELN) and WHO classification systems now incorporate cytogenetics and increasing numbers of gene mutations into AML prognostication. Several of the genomic AML subsets are characterized by unique transcription factor alterations that are highlighted in this review. There are many mechanisms of transcriptional deregulation in leukemia. We broadly classify transcription factors based on mechanisms of transcriptional deregulation including direct involvement of transcription factors in recurrent translocations, loss-of-function mutations, and intracellular relocalization. Transcription factors, due to their pleiotropic effects, have been attractive but elusive targets. Indirect targeting approaches include inhibition of upstream kinases such as TAK1 for suppression of NFκB signaling and downstream effectors such as FGF signaling in HOXA-upregulated leukemia. Other strategies include targeting scaffolding proteins like BrD4 in the case of MYC or coactivators such as menin to suppress HOX expression; disrupting critical protein interactions in the case of β-catenin:TCF/LEF, and preventing transcription factor binding to DNA as in the case of PU.1 or FOXM1. We comprehensively describe the mechanism of deregulation of transcription factors in genomic subsets of AML, consequent pathway addictions, and potential therapeutic strategies.

Induced pluripotent stem cells and hematological malignancies: A powerful tool for disease modeling and drug development

The derivation of human pluripotent stem cell (iPSC) lines by in vitro reprogramming of somatic cells revolutionized research: iPSCs have been used for disease modeling, drug screening and regenerative medicine for many disorders, especially when combined with cutting-edge genome editing technologies. In hematology, malignant transformation is often a multi-step process, that starts with either germline or acquired genetic alteration, followed by progressive acquisition of mutations combined with the selection of one or more pre-existing clones. iPSCs are an excellent model to study the cooperation between different genetic alterations and to test relevant therapeutic drugs. In this review, we will describe the use of iPSCs for pathophysiological studies and drug testing in inherited and acquired hematological malignancies.

Modeling cancer progression using human pluripotent stem cell-derived cells and organoids

Conventional cancer cell lines and animal models have been mainstays of cancer research. More recently, human pluripotent stem cells (hPSCs) and hPSC-derived organoid technologies, together with genome engineering approaches, have provided a complementary platform to model cancer progression. Here, we review the application of these technologies in cancer modeling with respect to the cell-of-origin, cancer propagation, and metastasis. We further discuss the benefits and challenges accompanying the use of hPSC models for cancer research and discuss their broad applicability in drug discovery, biomarker identification, decoding molecular mechanisms, and the deconstruction of clonal and intra-tumoral heterogeneity. In summary, hPSC-derived organoids provide powerful models to recapitulate the pathogenic states in cancer and to perform drug discovery.

ClinGen Myeloid Malignancy Variant Curation Expert Panel recommendations for germline RUNX1 variants

Standardized variant curation is essential for clinical care recommendations for patients with inherited disorders. Clinical Genome Resource (ClinGen) variant curation expert panels are developing disease-associated gene specifications using the 2015 American College of Medical Genetics and Genomics (ACMG) and Association for Molecular Pathology (AMP) guidelines to reduce curation discrepancies. The ClinGen Myeloid Malignancy Variant Curation Expert Panel (MM-VCEP) was created collaboratively between the American Society of Hematology and ClinGen to perform gene- and disease-specific modifications for inherited myeloid malignancies. The MM-VCEP began optimizing ACMG/AMP rules for RUNX1 because many germline variants have been described in patients with familial platelet disorder with a predisposition to acute myeloid leukemia, characterized by thrombocytopenia, platelet functional/ultrastructural defects, and a predisposition to hematologic malignancies. The 28 ACMG/AMP codes were tailored for RUNX1 variants by modifying gene/disease specifications, incorporating strength adjustments of existing rules, or both. Key specifications included calculation of minor allele frequency thresholds, formulating a semi-quantitative approach to counting multiple independent variant occurrences, identifying functional domains and mutational hotspots, establishing functional assay thresholds, and characterizing phenotype-specific guidelines. Preliminary rules were tested by using a pilot set of 52 variants; among these, 50 were previously classified as benign/likely benign, pathogenic/likely pathogenic, variant of unknown significance (VUS), or conflicting interpretations (CONF) in ClinVar. The application of RUNX1-specific criteria resulted in a reduction in CONF and VUS variants by 33%, emphasizing the benefit of gene-specific criteria and sharing internal laboratory data.

Runx1 promotes scar deposition and inhibits myocardial proliferation and survival during zebrafish heart regeneration

Runx1 is a transcription factor that plays a key role in determining the proliferative and differential state of multiple cell types, during both development and adulthood. Here, we report how Runx1 is specifically upregulated at the injury site during zebrafish heart regeneration, and that absence of runx1 results in increased myocardial survival and proliferation, and overall heart regeneration, accompanied by decreased fibrosis. Using single cell sequencing, we found that the wild-type injury site consists of Runx1-positive endocardial cells and thrombocytes that induce expression of smooth muscle and collagen genes. Both these populations cannot be identified in runx1 mutant wounds that contain less collagen and fibrin. The reduction in fibrin in the mutant is further explained by reduced myofibroblast formation and upregulation of components of the fibrin degradation pathway, including plasminogen receptor annexin 2A as well as downregulation of plasminogen activator inhibitor serpine1 in myocardium and endocardium, resulting in increased levels of plasminogen. Our findings suggest that Runx1 controls the regenerative response of multiple cardiac cell types and that targeting Runx1 is a novel therapeutic strategy for inducing endogenous heart repair.

Role of RUNX Family Transcription Factors in DNA Damage Response

Cells are constantly exposed to endogenous and exogenous stresses that can result in DNA damage. In response, they have evolved complex pathways to maintain genomic integrity. RUNX family transcription factors (RUNX1, RUNX2, and RUNX3 in mammals) are master regulators of development and differentiation, and are frequently dysregulated in cancer. A growing body of research also implicates RUNX proteins as regulators of the DNA damage response, often acting in conjunction with the p53 and Fanconi anemia pathways. In this review, we discuss the functional role and mechanisms involved in RUNX factor mediated response to DNA damage and other cellular stresses. We highlight the impact of these new findings on our understanding of cancer predisposition associated with RUNX factor dysregulation and their implications for designing novel approaches to prevent cancer formation in affected individuals.

RUNX1 Mutations in the Leukemic Progression of Severe Congenital Neutropenia

Somatic RUNX1 mutations are found in approximately 10% of patients with de novo acute myeloid leukemia (AML), but are more common in secondary forms of myelodysplastic syndrome (MDS) or AML. Particularly, this applies to MDS/AML developing from certain types of leukemia-prone inherited bone marrow failure syndromes. How these RUNX1 mutations contribute to the pathobiology of secondary MDS/AML is still unknown. This mini-review focusses on the role of RUNX1 mutations as the most common secondary leukemogenic hit in MDS/AML evolving from severe congenital neutropenia (SCN).

Modeling Leukemia with Human Induced Pluripotent Stem Cells

The reprogramming of human somatic cells into induced pluripotent stem cells (iPSCs) a little over a decade ago raised exciting prospects to transform the study and potentially also the therapy of human diseases. iPSC models have now been created for a multitude of hematologic diseases, including malignancies. Here we discuss practical aspects of iPSC modeling of malignant diseases, review recent studies, and discuss the new opportunities that iPSC models offer, as well as their current limitations and prospects for future development.

Analysis of 153 115 patients with hematological malignancies refines the spectrum of familial risk

Estimating familial cancer risks is clinically important in being able to discriminate between individuals in the population at differing risk for malignancy. To gain insight into the familial risk for the different hematological malignancies and their possible inter-relationship, we analyzed data on more than 16 million individuals from the Swedish Family-Cancer Database. After identifying 153 115 patients diagnosed with a primary hematological malignancy, we quantified familial relative risks (FRRs) by calculating standardized incident ratios (SIRs) in 391 131 of their first-degree relatives. The majority of hematological malignancies showed increased FRRs for the same tumor type, with the highest FRRs being observed for mixed cellularity Hodgkin lymphoma (SIR, 16.7), lymphoplasmacytic lymphoma (SIR, 15.8), and mantle cell lymphoma (SIR, 13.3). There was evidence for pleiotropic relationships; notably, chronic lymphocytic leukemia was associated with an elevated familial risk for other B-cell tumors and myeloproliferative neoplasms. Collectively, these data provide evidence for shared etiological factors for many hematological malignancies and provide information for identifying individuals at increased risk, as well as informing future gene discovery initiatives.

Development of Hematopoietic Stem Cells in the Early Mammalian Embryo

Hematopoietic stem cells (HSCs) were the first stem cells discovered in humans. A. A. Maximov proposed an idea of blood stem cells that was confirmed later by McCulloch and Till experimentally. HSCs were the first type of stem cells to be used in clinics and ever since are being continually used. Indeed, a single HSC transplanted intravenously is capable of giving rise to all types of blood cells. In recent decades, human and animal HSC origin, development, hierarchy, and gene signature have been extensively investigated. Due to the constant need for donor blood and HSCs suitable for therapeutic transplants, the experimental possibility of obtaining HSCs in vitro by directed differentiation of pluripotent stem cells (PSCs) has been considered in recent years. However, despite all efforts, it is not yet possible to reproduce in vitro the ontogenesis of HSCs and obtain cells capable of long-term maintenance of hematopoiesis. The study of hematopoiesis in embryonic development facilitates the establishment and improvement of protocols for deriving blood cells from PCSs and allows a better understanding of the pathogenesis of various types of proliferative blood diseases, anemia, and immunodeficiency. This review focuses on the development of hematopoiesis in mammalian ontogenesis.

Bone Marrow Morphology Associated With Germline RUNX1 Mutations in Patients With Familial Platelet Disorder With Associated Myeloid Malignancy

Germline mutations in RUNX1 result in autosomal dominant familial platelet disorder with associated myeloid malignancy (FPDMM). To characterize the hematopathologic features associated with a germline RUNX1 mutation, we reviewed a total of 42 bone marrow aspirates from 14 FPDMM patients, including 24 cases with no cytogenetic clonal abnormalities, and 18 with clonal karyotypes or leukemia. We found that all aspirate smears had ≥10% atypical megakaryocytes, predominantly characterized by small forms with hypolobated and eccentric nuclei, and forms with high nuclear-to-cytoplasmic ratios. Core biopsies showed variable cellularity and variable numbers of megakaryocytes with similar features to those in the aspirates. Granulocytic and/or erythroid dysplasia (≥10% cells per lineage) were present infrequently. Megakaryocytes with separate nuclear lobes were increased in patients with myelodysplastic syndrome (MDS) and acute leukemia. Comparison to an immune thrombocytopenic purpura cohort confirms increased megakaryocytes with hypolobated eccentric nuclei in FPDMM patients. As such, patients with FPDMM often have atypical megakaryocytes with small hypolobated and eccentric nuclei even in the absence of clonal cytogenetic abnormalities; these findings are related to the underlying RUNX1 germline mutation and not diagnostic of MDS. Isolated megakaryocytic dysplasia in patients with unexplained thrombocytopenia should raise the possibility of an underlying germline RUNX1 mutation.

Inherited thrombocytopenia and platelet disorders with germline predisposition to myeloid neoplasia

Advances in molecular genetic sequencing techniques have contributed to the elucidation of previously unknown germline mutations responsible for inherited thrombocytopenia (IT). Regardless of age of presentation and severity of symptoms related to thrombocytopenia and/or platelet dysfunction, a subset of patients with IT are at increased risk of developing myeloid neoplasms during their life time, particularly those with germline autosomal dominant mutations in RUNX1, ANKRD26, and ETV6. Patients may present with isolated thrombocytopenia and megakaryocytic dysmorphia or atypia on baseline bone marrow evaluation, without constituting myelodysplasia (MDS). Bone marrow features may overlap with idiopathic thrombocytopenic purpura (ITP) or sporadic MDS leading to misdiagnosis. Progression to myelodysplastic syndrome/ acute myeloid leukemia (MDS/AML) may be accompanied by progressive bi- or pancytopenia, multilineage dysplasia, increased blasts, cytogenetic abnormalities, acquisition of bi-allelic mutations in the underlying gene with germline mutation, or additional somatic mutations in genes associated with myeloid malignancy. A subset of patients may present with MDS/AML at a young age, underscoring the growing concern for evaluating young patients with MDS/AML for germline mutations predisposing to myeloid neoplasm. Early recognition of germline mutation and predisposition to myeloid malignancy permits appropriate treatment, adequate monitoring for disease progression, proper donor selection for hematopoietic stem cell transplantation, as well as genetic counseling of the affected patients and their family members. Herein, we describe the clinical and diagnostic features of IT with germline mutations predisposing to myeloid neoplasms focusing on mutations involving RUNX1, ANKRD26, and ETV6.

Modeling blood diseases with human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are derived from somatic cells through a reprogramming process, which converts them to a pluripotent state, akin to that of embryonic stem cells. Over the past decade, iPSC models have found increasing applications in the study of human diseases, with blood disorders featuring prominently. Here, we discuss methodological aspects pertaining to iPSC generation, hematopoietic differentiation and gene editing, and provide an overview of uses of iPSCs in modeling the cell and gene therapy of inherited genetic blood disorders, as well as their more recent use as models of myeloid malignancies. We also discuss the strengths and limitations of iPSCs compared to model organisms and other cellular systems commonly used in hematology research.

Thermodynamic investigation of DNA-binding affinity of wild-type and mutant transcription factor RUNX1

Transcription factor RUNX1 and its binding partner CBFβ play a critical role in gene regulation for hematopoiesis. Mutations of RUNX1 cause ~10% of acute myeloid leukemia (AML) with a particularly poor prognosis. The current paradigm for the leukemogenesis is that insufficient activity of wild-type (WT) RUNX1 impairs hematopoietic differentiation. The majority of mutant RUNX1 proteins lose the DNA-binding affinity and inhibit WT RUNX1 by depletion of CBFβ. Here, isothermal titration calorimetry (ITC) was used to quantitatively study the interactions of WT and three clinical mutant RUNX1, CBFβ and DNA. Our data show that the binding of RUNX1 to DNA is enthalpy-driven, and the affinity decreases in the order of WT > S114L > R139Q >> K83E, which support previous observations and conclusion. To find potentially beneficial RUNX1 mutations that could increase the overall RUNX1 activity, K83R and H179K mutations of RUNX1 were designed, using structure-based computational modeling, and found to possess significantly higher DNA-binding affinities than does WT RUNX1. K83R and H179K mutant RUNX1 could therefore be protein-based RUNX1 activators.

Disease modeling of bone marrow failure syndromes using iPSC-derived hematopoietic stem progenitor cells

The plasticity of induced pluripotent stem cells (iPSCs) with the potential to differentiate into virtually any type of cells and the feasibility of generating hematopoietic stem progenitor cells (HSPCs) from patient-derived iPSCs (iPSC-HSPCs) has many potential applications in hematology. For example, iPSC-HSPCs are being used for leukemogenesis studies and their application in various cell replacement therapies is being evaluated. The use of iPSC-HSPCs can now provide an invaluable resource for the study of diseases associated with the destruction of HSPCs, such as bone marrow failure syndromes (BMFSs). Recent studies have shown that generating iPSC-HSPCs from patients with acquired aplastic anemia and other BMFSs is not only feasible, but is also a powerful tool for understanding the pathogenesis of these disorders. In this article, we highlight recent advances in the application of iPSCs for disease modeling of BMFSs and discuss the discoveries of these studies that provide new insights in the pathophysiology of these conditions.

Disrupted filamin A/αIIbβ3 interaction induces macrothrombocytopenia by increasing RhoA activity

Filamin A (FLNa) links the cell membrane with the cytoskeleton and is central in several cellular processes. Heterozygous mutations in the X-linked FLNA gene are associated with a large spectrum of conditions, including macrothrombocytopenia, called filaminopathies. Using an isogenic pluripotent stem cell model derived from patients, we show that the absence of the FLNa protein in megakaryocytes (MKs) leads to their incomplete maturation, particularly the inability to produce proplatelets. Reduction in proplatelet formation potential is associated with a defect in actomyosin contractility, which results from inappropriate RhoA activation. This dysregulated RhoA activation was observed when MKs were plated on fibrinogen but not on other matrices (fibronectin, vitronectin, collagen 1, and von Willebrand factor), strongly suggesting a role for FLNa/α_IIbβ₃ interaction in the downregulation of RhoA activity. This was confirmed by experiments based on the overexpression of FLNa mutants deleted in the α_IIbβ₃-binding domain and the RhoA-interacting domain, respectively. Finally, pharmacological inhibition of the RhoA-associated kinase ROCK1/2 restored a normal phenotype and proplatelet formation. Overall, this work suggests a new etiology for macrothrombocytopenia, in which increased RhoA activity is associated with disrupted FLNa/α_IIbβ₃ interaction.

Downregulation of TREM-like transcript-1 and collagen receptor α2 subunit, two novel RUNX1-targets, contributes to platelet dysfunction in familial platelet disorder with predisposition to acute myelogenous leukemia

Germline RUNX1 mutations lead to thrombocytopenia and platelet dysfunction in familial platelet disorder with predisposition to acute myelogenous leukemia (AML). Multiple aspects of platelet function are impaired in these patients, associated with altered expression of genes regulated by RUNX1. We aimed to identify RUNX1-targets involved in platelet function by combining transcriptome analysis of patient and shRUNX1-transduced megakaryocytes (MK). Down-regulated genes included TREM-like transcript (TLT)-1 (TREML1) and the integrin subunit alpha (α)-2 (ITGA2) of collagen receptor α2-beta (β)-1, which are involved in platelet aggregation and adhesion, respectively. RUNX1 binding to regions enriched for H3K27Ac marks was demonstrated for both genes using chromatin immunoprecipitation. Cloning of these regions upstream of the respective promoters in lentivirus allowing mCherry reporter expression showed that RUNX1 positively regulates TREML1 and ITGA2, and this regulation was abrogated after deletion of RUNX1 sites. TLT-1 content was reduced in patient MK and platelets. A blocking anti-TLT-1 antibody was able to block aggregation of normal but not patient platelets, whereas recombinant soluble TLT-1 potentiated fibrinogen binding to patient platelets, pointing to a role for TLT-1 deficiency in the platelet function defect. Low levels of α2 integrin subunit were demonstrated in patient platelets and MK, coupled with reduced platelet and MK adhesion to collagen, both under static and flow conditions. In conclusion, we show that gene expression profiling of RUNX1 knock-down or mutated MK provides a suitable approach to identify novel RUNX1 targets, among which downregulation of TREML1 and ITGA2 clearly contribute to the platelet phenotype of familial platelet disorder with predisposition to AML.

Modeling Hematological Diseases and Cancer With Patient-Specific Induced Pluripotent Stem Cells

The advent of induced pluripotent stem cells (iPSCs) together with recent advances in genome editing, microphysiological systems, tissue engineering and xenograft models present new opportunities for the investigation of hematological diseases and cancer in a patient-specific context. Here we review the progress in the field and discuss the advantages, limitations, and challenges of iPSC-based malignancy modeling. We will also discuss the use of iPSCs and its derivatives as cellular sources for drug target identification, drug development and evaluation of pharmacological responses.

Cancer in a dish: progress using stem cells as a platform for cancer research

Cancer models derived from patient specimens poorly reflect early-stage cancer development because cancer cells acquire numerous additional molecular alterations before the disease is clinically detectable. Earlier studies have used differentiated cells derived from induced pluripotent cancer cells (iPCCs) to partially mirror cancer disease phenotype, but the highly heterogeneous nature of cancer cells as well as difficulties with reprogramming cancer cells has limited the application of this technique. An alternative approach to modeling cancer in a dish entails reprogramming adult differentiated cells from patients with cancer syndromes to pluripotent stem cells (PSCs), followed by directed differentiation of those PSCs. A directed reprogramming and differentiation strategy has the potential to recapitulate cancer progression and capture the earliest molecular alterations that underlie cancer initiation. The reprogrammed cells share patient-specific genetic and epigenetic traits, offering a new platform to develop personalized therapy for cancer patients. In this review, we will provide an overview of available reprogramming methods of cancer cells and describe how cancer-derived stem cells have been used to characterize effects of defined molecular alterations in specific cell types. We also describe the "disease in a dish" model developed to study genetic cancer syndromes. These approaches highlight recent contributions of stem cell technology to the cancer biology realm.

Recommendations for Surveillance for Children with Leukemia-Predisposing Conditions

Leukemia, the most common childhood cancer, has long been recognized to occasionally run in families. The first clues about the genetic mechanisms underlying familial leukemia emerged in 1990 when Li-Fraumeni syndrome was linked to TP53 mutations. Since this discovery, many other genes associated with hereditary predisposition to leukemia have been identified. Although several of these disorders also predispose individuals to solid tumors, certain conditions exist in which individuals are specifically at increased risk to develop myelodysplastic syndrome (MDS) and/or acute leukemia. The increasing identification of affected individuals and families has raised questions around the efficacy, timing, and optimal methods of surveillance. As part of the AACR Childhood Cancer Predisposition Workshop, an expert panel met to review the spectrum of leukemia-predisposing conditions, with the aim to develop consensus recommendations for surveillance for pediatric patients. The panel recognized that for several conditions, routine monitoring with complete blood counts and bone marrow evaluations is essential to identify disease evolution and enable early intervention with allogeneic hematopoietic stem cell transplantation. However, for others, less intensive surveillance may be considered. Because few reports describing the efficacy of surveillance exist, the recommendations derived by this panel are based on opinion, and local experience and will need to be revised over time. The development of registries and clinical trials is urgently needed to enhance understanding of the natural history of the leukemia-predisposing conditions, such that these surveillance recommendations can be optimized to further enhance long-term outcomes. Clin Cancer Res; 23(11); e14-e22. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

Deletion of RUNX1 exons 1 and 2 associated with familial platelet disorder with propensity to acute myeloid leukemia

Familial platelet disorder with propensity to acute myeloid leukemia (FPD/AML) associated with RUNX1 mutations is an autosomal dominant disorder included in the group of the myeloid neoplasms with germ line predisposition. We describe two brothers who were diagnosed with hematological malignancies (one with AML and the other with T-cell lymphoblastic lymphoma). There was a history of leukemia in the paternal family and two of their siblings presented with low platelet counts and no history of significant bleeding. A microdeletion encompassing exons 1-2 of RUNX1 (outside the cluster region of the Runt Homology domain and the transactivation domain) was detected in six family members using array-CGH and MLPA validation. A low platelet count was not present in all deletion carriers and, therefore, it should not be used as an indication for screening in suspected families and family members.