Preleukemic State Research Articles

Recent advances in the understanding of transient abnormal myelopoiesis in Down syndrome.

Neonates with Down syndrome (DS) have a propensity to develop the unique myeloproliferative disorder, transient abnormal myelopoiesis (TAM). TAM usually resolves spontaneously in ≤3 months, but approximately 10% of patients with TAM die from hepatic or multi-organ failure. After remission, 20% of patients with TAM develop acute myeloid leukemia associated with Down syndrome (ML-DS). Blasts in both TAM and ML-DS have trisomy 21 and GATA binding protein 1 (GATA1) mutations. Recent studies have shown that infants with DS and no clinical signs of TAM or increases in peripheral blood blasts can have minor clones carrying GATA1 mutations, referred to as silent TAM. Low-dose cytarabine can improve the outcomes of patients with TAM and high white blood cell count. A number of studies using fetal liver cells, mouse models, or induced pluripotent stem cells have elucidated the roles of trisomy 21 and GATA1 mutations in the development of TAM. Next-generation sequencing of TAM and ML-DS patient samples identified additional mutations in genes involved in epigenetic regulation. Xenograft models of TAM demonstrate the genetic heterogeneity of TAM blasts and mimic the process of clonal selection and expansion of TAM clones that leads to ML-DS. DNA methylation analysis suggests that epigenetic dysregulation may be involved in the progression from TAM to ML-DS. Unraveling the mechanisms underlying leukemogenesis and identification of factors that predict progression to leukemia could assist in development of strategies to prevent progression to ML-DS. Investigation of TAM, a unique pre-leukemic condition, will continue to strongly influence basic and clinical research into the development of hematological malignancies.

Clonal Hematopoiesis with Oncogenic Potential (CHOP): Separation from CHIP and Roads to AML.

The development of leukemia is a step-wise process that is associated with molecular diversification and clonal selection of neoplastic stem cells. Depending on the number and combinations of lesions, one or more sub-clones expand/s after a variable latency period. Initial stages may develop early in life or later in adulthood and include premalignant (indolent) stages and the malignant phase, defined by an acute leukemia. We recently proposed a cancer model in which the earliest somatic lesions are often age-related early mutations detectable in apparently healthy individuals and where additional oncogenic mutations will lead to the development of an overt neoplasm that is usually a preleukemic condition such as a myelodysplastic syndrome. These neoplasms may or may not transform to overt acute leukemia over time. Thus, depending on the type and number of somatic mutations, clonal hematopoiesis (CH) can be divided into CH with indeterminate potential (CHIP) and CH with oncogenic potential (CHOP). Whereas CHIP mutations per se usually create the molecular background of a neoplastic process, CHOP mutations are disease-related or even disease-specific lesions that trigger differentiation and/or proliferation of neoplastic cells. Over time, the acquisition of additional oncogenic events converts preleukemic neoplasms into secondary acute myeloid leukemia (sAML). In the present article, recent developments in the field are discussed with a focus on CHOP mutations that lead to distinct myeloid neoplasms, their role in disease evolution, and the impact of additional lesions that can drive a preleukemic neoplasm into sAML.

Downregulation of Morrbid in Tet2-Deficient Preleukemic Cells Overcomes Resistance to Inflammatory Stress and Mitigates Clonal Hematopoiesis

Myeloid malignancies including AML, CMML, MPN and MDS are considered clonal blood disorders. Hematopoietic stem and progenitor cells (HSPCs) with mutation(s) in AML-related genes such as TET2 or DNMT3A represent what are commonly defined as preleukemic HSPCs. The selection and expansion of preleukemic-HSPC clones precedes the development of AML. Additionally, preleukemic-HSPCs can transform through serial acquisition of additional somatic mutations over time and contribute to the development of full-blown AML. What is unclear is the nature of environmental signals that might contribute to the “switch” from a preleukemic state to a leukemic state in these cells. In this context, inflammation has been hypothesized to play an essential role, but precisely how inflammatory signals influence the growth, survival, differentiation and the overall engraftment potential of preleukemic-HSPCs is yet to be determined. Mouse models carrying loss of function alleles in Tet2 or Dnmt3a manifest an expanded HSPC pool, including a hematopoietic stem cell (HSC)-enriched fraction defined by cell surface markers Lineage-/Sca-1+/c-Kit+ (LSK). Some of these genetically modified mice go on to develop CMML or MPN with modest penetration when aged. Majority of pre-leukemic mutations on their own are insufficient to cause AML in mice, suggesting that a single mutation among the above-described mutations define a pre-leukemic state and perhaps additional cooperating mutations are necessary to provide a more effective selection advantage for preleukemic-HSPC leading to the development of full-blown leukemia. Inflammation has been linked to tumor induction and transformation in solid tissues. Inflammation caused by environmental exposure, infection, autoimmunity, or ageing may result in mutations and genomic instability in somatic cells as well as in reprogramming of the tumor microenvironment (i.e. through regulating angiogenesis and expression of cytokines and chemokines). Considering that both innate and adaptive immune cells are generated from HSPCs and are involved in regulating local as well as whole-body inflammatory processes, the relationship between inflammation and hematopoietic malignancies is likely to be complex. While the influence of inflammatory stress on normal HSPCs has recently gained significant attention, little is known about how preleukemic HSPCs respond to inflammation. Because HSPCs reside in the bone marrow and are surrounded by mature immune cells, the inflammatory microenvironment is likely to influence the growth and self-renewal of these cells in part by producing pro-inflammatory cytokines and chemokines. In support of this hypothesis are epidemiologic findings demonstrating that infection may act as a trigger for AML development in humans. In the present study, we asked whether Tet2-deficient HSPCs maintain growth and survival advantage during pathological stress by examining how Tet2-KO preleukemic-HSPCs respond to acute and chronic inflammation. We show a rapid increase in the frequency and absolute number of Tet2-deficient mature myeloid cells and HSPCs in response to acute inflammatory stress, which results in enhanced production of inflammatory cytokines, including IL-6, and resistance to apoptosis. Functionally, Tet2-deficient preleukemic-HSPCs showed resistance to inflammation-induced damage and apoptosis relative to controls. IL-6 induces hyperactivation of the Shp2-Stat3 signaling axis, resulting in increased expression of a novel anti-apoptotic lncRNA Morrbid in Tet2-KO myeloid cells and HSPCs. Expression of activated Shp2 in HSPCs phenocopies Tet2 loss, with regard to hyperactivation of Stat3 and Morrbid. In vivo, pharmacologic inhibition of Shp2 or Stat3 or genetic loss of Morrbid in Tet2-deficient mice rescues inflammatory stress-induced abnormalities in HSPCs and mature myeloid cells including clonal hematopoiesis. Our results suggest that the anti-inflammatory drugs E3330 and SHP099, which suppress the hyper-activation of Morrbid, could be of clinical benefit for TET2 mutations-induced clonal hematopoiesis and leukemogenesis. Our results provide insight into the selection advantage that might render Tet2-deficient HSPCs susceptible to transformation and suggest that anti-inflammation therapy could be of clinical benefit for individuals carrying TET2 mutations. DisclosuresKelley:Apexian Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties. Mohseni:Novartis Institutes of Biomedical Research: Employment.

Delayed Hematologic Recovery in AML Patients after Induction Chemotherapy Is Associated with Inferior Relapse-Free Survival and Persistence of Preleukemic Mutations

Introduction:Induction chemotherapy debulks the leukemic burden in AML patients. Blood count recovery usually occurs during the fourth week of starting chemotherapy in patients who achieve a morphologic remission in bone marrow. However, a subset of patients experience significantly delayed recovery. The relevance of delayed recovery on long-term clinical outcomes and its contributing factors have not been well studied. Specifically, the association between recurrent mutations in AML and hematologic recovery is unknown.Methods:We studied a total of 262 newly diagnosed adult AML patients treated between September 2014 and December 2017 at Princess Margaret Cancer Centre who achieved a complete remission (CR) or CR with incomplete count recovery (CRi) after one cycle of induction chemotherapy. The regimens consisted of 3+7 (N=194) and FLAG-IDA (N=68). We collected information on disease characteristics and blood count results at baseline and during chemotherapy. Mutation profiling of diagnostic samples was performed using a 54-gene next generation sequencing panel (TruSight Myeloid Sequencing Panel, Illumina). Detection of persistent mutations in remission samples was performed using a custom 37-gene duplex sequencing platform with a lower detection limit of ~0.05% variant allele frequency (VAF).Results:Of the cohort of 262 patients, 256 patients (97.7%) achieved neutrophil recovery (defined as > 1x109/L), with time to recovery ranging from 17 to 84 days. Two hundred forty-four (93.1%) patients achieved platelet recovery (defined as > 100x109/L); time to recovery ranged from 17 to 117 days. The percentage of patients who achieved neutrophil and platelet count recovery before day 35 was 82.4% and 84.0% respectively (Fig. 1).To evaluate the prognostic significance of delayed recovery, we categorized patients who achieved CR into two groups, “normal” or “delayed” recovery, according to whether they achieved recovery before or after day 35, respectively. Relapse-free survival (RFS) of patients with delayed recovery was significantly worse than those with normal recovery and only marginally better than those with CRi (P=0.02; Fig. 2). Analysis restricted to 3+7 treated patients showed the same trend (P=0.02), excluding the possibility that the inferior outcome was due to treatment of higher risk patients with more intensive regimens.To study the factors associated with delayed recovery, we performed multivariable Cox regression analysis that included clinical factors and mutations identified at the time of diagnosis as covariates. Four factors were found to be independently correlated with delayed recovery: treatment with FLAG-IDA, truncating ASXL1mutations, SRSF2mutations, and DNMT3AR882 mutations (Table 1). Because FLAG-IDA is the preferred frontline regimen for higher risk patients at our institution, we performed a secondary analysis restricted to patients treated with 3+7 to exclude chemotherapy regimen as a potential confounding variable. This analysis identified six independent factors: AML with myelodysplasia-related changes, lower hemoglobin levels at presentation, truncating ASXL1mutations, TET2mutations, CEBPAmutations, and DNMT3AR882 mutations (Table 1).Somatic mutations in DNMT3A, TET2, ASXL1, and SRSF2(DTAS) mutations are associated with preleukemic conditions, such as myelodysplastic syndrome and age-related clonal hematopoiesis, and frequently persist in remission. These mutations are acquired in hematopoietic stem cells resulting in their propagation to progenitors and terminally differentiated blood cells. We hypothesized that the persistence of DTAS mutations in progenitors might compromise their capacity for reconstitution of normal hematopoiesis resulting in delayed recovery. To test this hypothesis, we performed duplex sequencing on peripheral blood DNA samples collected from a random subset of 43 patients during remission. The detection of DTAS mutations in remission above a VAF of 2% was strongly associated with delayed recovery (P=0.0004; Fig. 3).Conclusion:Delayed hematologic recovery in AML patients after induction chemotherapy is associated with inferior RFS and persistence of preleukemic mutations (i.e., DTAS mutations). Our results support a model in which progenitors harboring DTAS mutations have reduced repopulation capacity leading to delayed hematologic recovery after induction chemotherapy. DisclosuresGupta:Incyte: Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Schimmer:Otsuka Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Medivir AB: Research Funding. Yee:Agensys, Astex, GSK, Onconova, Genentech/Roche: Research Funding; Celgene, Novartis, Otsuka: Membership on an entity's Board of Directors or advisory committees. Maze:Novartis: Consultancy, Honoraria. Bratman:Roche: Other: SVB is a co-inventor on a patent describing methods for circulating tumor DNA analysis, which has been licensed to Roche Molecular Diagnostics.. Schuh:Shire: Consultancy; Jazz: Consultancy; Novartis: Consultancy; Otsuka: Consultancy; Teva: Consultancy; Pfizer: Consultancy; Celgene: Consultancy; Amgen Inc.: Consultancy.

A Leukemic Progression Model of Severe Congenital Neutropenia Uncovers a Novel Mechanism of AML Development Involving Elevated Inflammatory Responses, Mutation of CXXC4 and Decreased TET2 Levels

Introduction: Severe congenital neutropenia (SCN) patients receive life-long treatment with CSF3/G-CSF to alleviate neutropenia and have a high risk to develop MDS or AML. The appearance of hematopoietic clones with CSF3 receptor (CSF3R) mutations represents a first step in MDS/AML progression, which is followed by mutations in RUNX1 shortly before MDS/AML becomes clinically overt. How intracellular signaling pathways are affected by the combination of CSF3 therapy, CSF3R and RUNX1 mutations, and how deregulation of these pathways contributes to MDS/AML development is unknown. Also, it has remained unclear how defects in epigenetic regulators such as ASXL1 or SUZ12, which are recurrently but less frequently mutated in SCN/AML, contribute to full malignant transformation.Aims: (i) To elucidate how CSF3R and RUNX1 mutations in conjunction with CSF3 treatment contribute to leukemic progression in an in vivo serial transplantation mouse model (ii) To determine whether additional mutations, specifically in epigenetic regulators, are needed for full malignant transformation and (iii) To validate the relevance of the findings for clinical SCN and AML.Mouse model and patient samples: Bone marrow (BM) cells from Csf3r-d715 mice, copying the most frequent CSF3R truncation mutant in SCN patients, were transduced with RUNX1 mutant D171N or empty vector control lentivirus and serially transplanted. Recipient mice were treated 3x a week with CSF3 or PBS (solvent control). Transcriptome analysis (RNA-sequencing + GSEA) and whole exome sequencing (WES) on FACS purified Lineage- cKit+ (LK) populations were done to identify molecular pathways associated with leukemic progression. Sequential CD34+ cell samples from a SCN/AML patient with identical CSF3R and RUNX1 mutations (Beekman, Blood 2012) and whole genome sequencing data from diagnostic AML samples were used for clinical comparisons.Results: CSF3 treatment of primary recipients of Csf3r-RUNX1 mutant BM cells resulted in sustained (30+ weeks) presence of LK cells (16.5% ± 7), which we morphologically and functionally identified as myeloblasts, in the peripheral blood (PB). None of the mice succumbed to symptoms of AML, suggesting that the elevated PB myeloblast counts reflected a pre-leukemic state. Upon transplantation in secondary and tertiary recipients, mice developed a Csf3r-RUNX1 mutant AML that no longer depended on CSF3 administration. Transcriptome profiles of purified progenitor cells at the sequential steps of transformation in the mouse model and an SCN/AML patient with identical mutations shared striking similarities in deregulation of signaling mechanisms, particularly showing progressive upregulation of TNFα-, interferon- and interleukin-6-driven inflammatory responses during leukemic progression.WES on the myeloblasts from these stages revealed a single additional clonal mutation in Cxxc4, an Internal tandem duplication (ITD) resulting in the in-frame insertion of two glycines at a.a. position 157 of the protein. This heterozygous mutation appeared in a subclone in the primary recipient (VAF: 0.27) and expanded in secondary and tertiary recipients, in which all AML cells harbored the Csf3r, RUNX1 and Cxxc4 mutations (VAF 0.52±0.06). The mutation resulted in a 10.8 fold (± 2.3) higher expression of a CXXC4 isoform. CXXC4 was shown to inhibit TET2 protein levels (Ko, Nature 2013). In agreement with this, TET2 levels were strongly (6.03 fold ± 0.78) reduced in the CXXC4 overexpressing leukemic samples.Intriguingly, CXXC4 mutations have also been detected in human AML cases (n=13), including the homologous ITD mutations identified in our mouse model. We are currently investigating the frequencies and co-occurrence of CXXC4 mutations in RUNX1 mutant and other molecular subtypes of AML. Also, studies are in progress to determine how the CXXC4-ITD alters CXXC4 and TET2 protein expression.Conclusion: By studying the leukemic progression of SCN, driven by CSF3 treatment and mutations in CSF3R and RUNX1, we have identified a mechanism of AML development that involves activation of multiple inflammatory pathways, mutation of CXXC4 and reduction of TET2 expression. These findings corroborate a recent study showing that inflammatory responses drive pre-leukemic myeloproliferation in Tet2 deficient mice (Meisel, Nature 2018). DisclosuresHaferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.

Loss-of-Function Mutation in tet2 in Zebrafish Leads to Early MDS like Phenotype

Myelodysplastic syndrome (MDS) is a pre-leukemic state characterized by the failure of the bone marrow to produce mature and functional blood cells. Nearly one-third of MDS patients progress to acute myeloid leukemia (AML). AML is the most common form of acute leukemia in adults and accounts for a high level of mortality in pediatric leukemia.Loss-of-function mutations in the Ten-11 Translocation 2 (TET2) gene are implicated in MDS and AML, but evidence that TET2 mutations are also found in healthy individuals as a result of clonal hematopoiesis calls into question the contribution of TET2 to leukemogenesis. Many studies have tried to mutate the DNA binding domain in TET2 both in mouse and zebrafish, but the blood phenotypes observed have been inconsistent.We created a tet2 zebrafish mutant using CRISPR-Cas9 technology, where we deleted 2.1 kb from exon 2, confirmed by cDNA analysis. A recent publication suggests the importance of Ser99 in the stability of the TET2 protein (Wu et al., 2018) and this conserved serine residue is contained in the region of deletion in our zebrafish tet2 mutant.These tet2 mutant fish were incrossed to create a maternal-zygotic mutant with no tet2 expression. Importantly, quantitative PCR demonstrated that there was no compensatory effect from tet1 and tet3 in the context of tet2 loss.Whole mount in situ hybridization performed on 24-48h tet2 mutant zebrafish embryos provided evidence of a significant reduction of early and mature myeloid and erythroid cells through staining for spi1/pu.1 (myeloid), gata1 (erythroid) myeloperoxidase (mpx; neutrophils), carboxypeptidase A5 (cpa5; mast cells) and l-plastin (lcp1; macrophages). The stem cell compartment was not impacted, as shown by wild-type runx1/c-myb expression. Further, o-dianisidine staining revealed low hemoglobin content in tet2 mutants compared with control embryos. Overall, the early embryos elucidate a refractory anemia like phenotype.Flow cytometry analysis of kidney marrow from 3-month-old adult tet2 mutant fish similarly demonstrated a decrease in the myeloid and erythroid compartments, in keeping with characteristics typical of low stage MDS. We are currently employing RNAseq and MeDIP analysis on blood cell populations from tet2 mutants to determine the genetic and epigenetic signatures associated with this mutation.This zebrafish model of tet2 loss uniquely provides with a dynamic phenotype that starts with refractory anemia with progression through low stage MDS. Thus this model will be beneficial in elucidating the mechanisms underlying how tet2 contributes to MDS and AML and provide a preclinical platform to screen for therapeutic interventions. DisclosuresNo relevant conflicts of interest to declare.

Activation of CRLF2/IL7RA Signaling in Normal Human Cord Blood Hematopoietic Progenitors Induces Philadelphia-like B-Cell Precursor Pre-Leukemia and Leukemia In Vivo

Philadelphia-like (Ph-like) B-cell precursor acute lymphoblastic leukemia (BCP-ALL) is a subgroup of BCP-ALL with an expression pattern similar to BCR-ABL+ BCP-ALL that is associated with poor prognosis.Aberrant expression of CRLF2 in BCP-ALL constitutes the majority of Ph-like BCP-ALL cases. CRLF2 is a receptor subunit that together with the IL7RA subunit comprises the receptor of the proinflammatory cytokine TSLP. Though activation of the IL7R pathway is commonly associated with T-cell malignancies, we previously described IL7RA-activating mutations in BCP-ALL predominantly in the context of CRLF2 aberrant expression (Shochat C. et al. J. Exp. Med. 2011).Here we aimed to test the role of aberrations in CRLF2 and IL7RA in the development of Ph-Like BCP-ALL. Both CRLF2 and TSLP differ extensively between mice and human in amino acid sequence and in lineage expression pattern; loss-of-function germline mutations in IL7RA are associated with lack of B and T cells in mice but with lack of only T cells in humans. Hence, we chose to test the hypothesis that activation of CRLF2/IL7RA contributes to the development of Ph-like BCP-ALL in the context of human lymphopoiesis by using a human xenograft system.To aberrantly activate TSLP/IL7 signaling, we transduced cord-blood (CB) CD34+ hematopoietic progenitors with a set of lentiviral vectors carrying CRLF2 and/or IL7RA [(wild type (IL7RAwt) or IL7R bearing an activating mutation (IL7RAins)] under a B-cell promoter/enhancer (to accentuate B-cell lineage expression). The backbone vector (BB) expressing GFP was used as a control. Transduced CB cells were transplanted into NOD/LtSz-scid IL2Rγnull (NSG) mice and engrafted cells were analyzed 24-30 weeks after transplantation. To test for self-renewal capacity, BM cells from primary engrafted mice were serially transplanted into secondary recipients and the occurrence of human engraftment was tested 24-30 weeks after transplantation.Enforced expression of activated IL7RA with or without CRLF2 led to a significant block in B-cell development at the B-cell progenitor stage (CD19+CD10+sIgM-) in vivo resembling the differentiation stage of leukemic cells (figure Bi). Repertoire sequencing of CD10+CD19+-transduced cells that were sorted from BM of transplanted mice revealed a significantly higher population of DJ-rearranged cells in the CRLF2-IL7RAins-transduced population than in BB-transduced cells (mean ratio of DJ/total rearrangement: BB:0.35+/-0.024, CRLF2-IL7RAins:0.76+/- 0.07, p=0.039, n=3 paired cord blood), in agreement with the early differentiation block phenotype measured by immunophenotyping. These cells furthermore exhibited a Ph-like gene expression pattern when compared to BB-transduced cells in gene set enrichment analysis.Overexpression of IL7RA alone significantly enhanced the early-B fraction (CD19+CD10+CD34+) in the BM of transplanted mice (figure Bii). Additionally, aberrant expression of IL7RA enhanced self-renewal capacity as was evident by an increased ability of the transduced cells to engraft in secondary recipients (number of mice with detectable human engraftment out of secondary transplanted mice: BB:0/6, CRLF2-IL7RAwt:0/3, CRLF2-IL7RAinst:0/3, IL7RAwt-GFP:3/6, IL7RAins-GFP:5/8).Notably, in one case, secondary transplantation of IL7RAins-transduced CB triggered the development of acute BCP-ALL. The leukemic cells (CD19+CD10+CD34+sIgM-) were clonal as validated by V(D)J rearrangement (figure Cii), had the ability to further propagate in serial transplantations and gained secondary Ph-like BCP-ALL-characteristic chromosomal deletions in the short arm of chromosome 9 (in the region including the genes for CDKN2A/B, PAX5 and JAK2) and the short arm of chromosome 7 (the region including IKZF1) (figure Ciii).These results support the hypothesis that aberrant activation of the CRLF2/IL7RA pathway in human B-cell lineage progenitors creates a pre-leukemic state by arresting differentiation of B-cell progenitors, instating Ph-like expression pattern and inducing self-renewal. This is the first model of de novo Ph-like BCP-ALL development from normal human hematopoietic progenitors in vivo. Additionally, we present here a first direct in vivo demonstration of a role for IL7 in human B-cell development. DisclosuresNo relevant conflicts of interest to declare.

Molecular Features in the Diagnosis of Myeloid Neoplasms in Down Syndrome Patients Less Than Four Years of Age: Experience from a Single Institution

Introduction:Patients with Down syndrome (DS) have an increased risk of hematological disorders, including transient abnormal myelopoiesis (TAM), acute lymphoblastic leukemia (ALL), myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Twenty percent of patients with TAM subsequently develop myeloid neoplasm in the first 4 years of life. MDS represents a clonal aberration thought to be a pre-leukemic condition characterized clinically by cytopenias and erythroid, myeloid and/or megakaryocytic dysplasia in the bone marrow with or without increase in blasts and harbors a concordant, clone-specific mutation of GATA1. WHO 2016 classification of hematopoietic neoplasms does not distinguish between MDS and AML, as their overall prognosis appears to be similar. However, due to the rarity of this disorder, limited clinical and laboratory data is available, contributing to difficulties in establishing the diagnosis. Here we describe our center's recent experience with the diagnosis and molecular findings of myeloid neoplasm associated with Down syndrome (MN-DS).Design/Method:Retrospective review of the patient's electronic medical record and review of the literature was conducted. Routine karyotype, fluorescent in-situ hybridization (FISH) and next generation sequencing (NGS) studies were reviewed where available.Results:Six patients with DS diagnosed with AML or MDS were identified over a 3-year period. Mean age of the cohort was 18.5 (range 12-24) months with a slight female predominance. Three patients had a history of TAM, all of which resolved without intervention. Three patients had asymptomatic thrombocytopenia after birth without blasts or GATA1 mutation confirmation. One of the three patients with a history of TAM presented with overt AML, while in the others diagnosis was challenging. By WHO 2008 classification of myeloid neoplasms, four patients had refractory anemia with excess blasts, one had refractory cytopenia with multilineage dysplasia, and one had AML. For two patients, in whom myeloid directed next generation sequencing was obtained, mutations were found in GATA1, EZH2, and NRAS. One of the patients in our series presented with AML with gain of MECOM, RPN1 loss and D5S23 deletion by FISH and succumbed to relapsed disease. All patients were treated per Children's Oncology Group AAML1531 arm A protocol that included 3 induction cycles and 2 intensification cycles, except for a single patient that received one cycle per AAML0431 and completed therapy per AAML1531 arm B high risk due to persistent disease following initial induction cycle. Two patients are currently receiving treatment, three have no evidence of disease recurrence on follow up ranging from 2 to 18 months, and one of the patients has died due to relapsed/refractory disease.Conclusions:We present six cases of MN-DS in patients less than four years of age. Our cohort is representative of the diversity encountered in this rare disease including patients with 1) isolated cytopenia in the absence of overt morphological findings, 2) myelodysplasia, and 3) AML. In our patient with overt AML there were karyotypic features such as gain of MECOM, which with specific translocation partners has previously been described to portend a poor prognosis. This and other cytogenetic features perhaps warrant further investigation given our patient's refractory disease. In the patient with refractory cytopenia without blasts, there was a subpopulation of cells identified by NGS panel showing mutations in GATA1, EZH2, and NRAS that led to a diagnosis of MDS/MN-DS. Four of the patients had aberrant myeloid populations and dysplasia fitting diagnostic criteria for MDS. Establishing the clonal nature of the disease either by karyotype/FISH or NGS may help with the identification, treatment and prognostication of this unique patient population, and may aid in the diagnosis of MN-DS, which may be challenging in patients with DS once they have recovered from TAM. DisclosuresNo relevant conflicts of interest to declare.

Cell-lineage level–targeted sequencing to identify acute myeloid leukemia with myelodysplasia-related changes

AbstractAcute myeloid leukemia (AML) is a clonal myeloid neoplasm that typically arises de novo; however, some cases evolve from a preleukemic state, such as myelodysplastic syndrome (MDS). Such secondary AMLs and those with typical MDS-related clinical features are known as AMLs with myelodysplasia-related changes (AML-MRC). Because patients with AML-MRC have poor prognosis, more accurate diagnostic approaches are required. In this study, we performed targeted sequencing of 54 genes in 3 cell populations (granulocyte, blast, and T-cell fractions) using samples from 13 patients with MDS, 16 patients with clinically diagnosed AML-MRC, 4 patients with suspected AML-MRC but clinically diagnosed as AML not otherwise specified (AML-NOS), and 11 patients with de novo AML. We found that overlapping mutations, defined as those shared at least by the blast and granulocyte fractions, were significantly enriched in patients with MDS and AML-MRC, including those with suspected AML-MRC, indicating a substantial history of clonal hematopoiesis. In contrast, blast-specific nonoverlapping mutations were significantly enriched in patients with de novo AML. Furthermore, the presence of overlapping mutations, excluding DNMT3A, TET2, and ASXL1, effectively segregated patients with MDS and AML-MRC or suspected AML-MRC from patients with de novo AML. Additionally, the presence of ≥3 mutations in the blast fraction was useful for distinguishing patients with AML-MRC from those with MDS. In conclusion, our approach is useful for classifying clinically diagnosable AML-MRC and identifying clinically diagnosed AML-NOS as latent AML-MRC. Additional prospective studies are needed to confirm the utility of this approach.

Alteration of Serum Free Fatty Acids are Indicators for Progression of Pre-leukaemia Diseases to Leukaemia

Acute Leukaemia (AL) is a neoplasm of WBCs (white blood cells). Being an important class of metabolites, alteration in free fatty acids (FFAs) levels play a key role in cancer development and progression. As they involve in cell signaling, maintain membrane integrity, regulate homeostasis and effect cell and tissue functions. Considering this fact, a comprehensive analysis of FFAs was conducted to monitor their alteration in AL, pre-leukaemic diseases and healthy control. Fifteen FFAs were analyzed in 179 serum samples of myelodysplastic syndrome (MDS), aplastic anemia (APA), acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML) and healthy control using gas chromatography-multiple reaction monitoring-mass spectrometry (GC-MRM-MS). A multivariate statistical method of random forest (RF) was employed for chemometric analysis. Serum level of two FFAs including C18:0 and C14:0 were found discriminative among all five groups, and between ALL and AML, respectively. Moreover, C14:0 was identified as differentiated FFAs for systematic progression of pre-leukaemic conditions towards AML. C16:0 came as discriminated FFAs between APA and MDS/AML. Over all it was identified that FFAs profile not only become altered in leukaemia but also in pre-leukaemic diseases.

PAX5-ELN oncoprotein promotes multistep B-cell acute lymphoblastic leukemia in mice

PAX5 is a well-known haploinsufficient tumor suppressor gene in human B-cell precursor acute lymphoblastic leukemia (B-ALL) and is involved in various chromosomal translocations that fuse a part of PAX5 with other partners. However, the role of PAX5 fusion proteins in B-ALL initiation and transformation is ill-known. We previously reported a new recurrent t(7;9)(q11;p13) chromosomal translocation in human B-ALL that juxtaposed PAX5 to the coding sequence of elastin (ELN). To study the function of the resulting PAX5-ELN fusion protein in B-ALL development, we generated a knockin mouse model in which the PAX5-ELN transgene is expressed specifically in B cells. PAX5-ELN-expressing mice efficiently developed B-ALL with an incidence of 80%. Leukemic transformation was associated with recurrent secondary mutations on Ptpn11, Kras, Pax5, and Jak3 genes affecting key signaling pathways required for cell proliferation. Our functional studies demonstrate that PAX5-ELN affected B-cell development in vitro and in vivo featuring an aberrant expansion of the pro-B cell compartment at the preleukemic stage. Finally, our molecular and computational approaches identified PAX5-ELN-regulated gene candidates that establish the molecular bases of the preleukemic state to drive B-ALL initiation. Hence, our study provides a new in vivo model of human B-ALL and strongly implicates PAX5 fusion proteins as potent oncoproteins in leukemia development.

3147 - Loss-of-Function Mutation in TET2 in Zebrafish Leads to Early MDS Like Phenotype

Abstract Myelodysplastic syndrome (MDS) is a pre-leukemic state characterized by the failure of the bone marrow to produce mature and functional blood cells. Nearly one-third of MDS patients progress to acute myeloid leukemia (AML). AML is the most common form of acute leukemia in adults and accounts for a high level of mortality in pediatric leukemia. Loss-of-function mutations in the Ten-11 Translocation 2 (TET2) gene are implicated in MDS and AML, but evidence that TET2 mutations are also found in healthy individuals as a result of clonal hematopoiesis calls into question the contribution of TET2 to leukemogenesis. Many studies have tried to mutate the DNA binding domain in TET2 both in mouse and zebrafish, but the blood phenotypes observed have been inconsistent. We created a tet2 zebrafish mutant using CRISPR-Cas9 technology, where we deleted 2.1 kb from exon 2, confirmed by cDNA analysis. A recent publication suggests the importance of Ser99 in the stability of the TET2 protein (Wu et al., 2018) and this conserved serine residue is contained in the region of deletion in our zebrafish tet2 mutant. These tet2 mutant fish were incrossed to create a maternal-zygotic mutant with no tet2 expression. Importantly, quantitative PCR demonstrated that there was no compensatory effect from tet1 and tet3 in the context of tet2 loss. Whole mount in situ hybridization performed on 24-48h tet2 mutant zebrafish embryos provided evidence of a significant reduction of early and mature myeloid and erythroid cells through staining for spi1/pu.1 (myeloid), gata1 (erythroid) myeloperoxidase (mpx; neutrophils), carboxypeptidase A5 (cpa5; mast cells) and l-plastin (lcp1; macrophages). The stem cell compartment was not impacted, as shown by wild-type runx1/c-myb expression. Further, o-dianisidine staining revealed low hemoglobin content in tet2 mutants compared with control embryos. Overall, the early embryos elucidate a refractory anemia like phenotype. Flow cytometry analysis of kidney marrow from 3-month-old adult tet2 mutant fish similarly demonstrated a decrease in the myeloid and erythroid compartments, in keeping with characteristics typical of low stage MDS. We are currently employing RNAseq and MeDIP analysis on blood cell populations from tet2 mutants to determine the genetic and epigenetic signatures associated with this mutation. This zebrafish model of tet2 loss uniquely provides with a dynamic phenotype that starts with refractory anemia with progression through low stage MDS. Thus this model will be beneficial in elucidating the mechanisms underlying how tet2 contributes to MDS and AML and provide a preclinical platform to screen for therapeutic interventions. Disclosures No relevant conflicts of interest to declare.

Abstract 1229: Clonal hematopoiesis of indeterminate potential (CHIP), centenarians and age-related cardiovascular risk: Is TET2 the culprit

Abstract Background. Clonal hematopoiesis of indeterminate potential (CHIP) is an age-related hematological condition, that has been associated with an increased risk of hematological malignancies and of overall mortality. This excess mortality in subjects with CHIP seems to be related to an increased risk of cardiovascular atherosclerotic diseases (Jaiswal S, NEJM 2014). Our aim was to analyze the prevalence of CHIP in patients with Coronary Artery Disease (CAD) and in a group of selected ultra-centenarians ((age >105 years), since no data hasve been produced until now in such a peculiar population of “super-controls” (Garagnani P, Aging 2013). Methods. We performed whole-exome sequencing (WES) from peripheral-blood cells DNA in 99 patients with angiographically proven severe CAD from the Verona Heart Study (Girelli D, NEJM 2000;), and 79 semisupercentenarians (age >105 years). The mean coverage varied from 30x to 100x (higher in centenarians). We analyzed somatic mutations predicted to alter function in 6 key genes (TET2, ASXL1, DNMT3A, JAK2, PPM1D, TP53), selected as the most frequently detected in CHIP according to literature. Results. The prevalence of CHIP in CAD patients was 18.2%, similarly to the increased prevalence detected in other CAD populations (Jaiswal S, NEJM 2017). On the other hand, CHIP was rare in centenarians (prevalence of 2.5%), a result that contradicts the expected exponential increase of CHIP observed after the age of 70 years in previous studies. This result suggested a kind of “survival bias”, that indirectly supports the pathogenic role of age-related CHIP. An utterly fascinating finding was in the frequency of driver mutations in CAD subjects with CHIP: the majority (85%) of CAD patients presented mutations in TET2. Conclusions. Our outcomes add further insights to the nature of CHIP, which could be seen as a preleukemic condition that also leads to an intrinsic odd of cardiovascular events. The Our outcomes add further insights to the recent hypothesis that links CHIP to an increased risk of cardiovascular disease. The study results raise the question over a possible many-sided clinical and biological significance of CHIP that might depend on the driver mutation. In particular, we propose that TET2-driven CHIP is the most responsible for the higher cardiovascular risk, consistently with the pro-atherosclerotic role of this gene in mouse models (Fuster JJ, Science 2017, Jaiswal S, NEJM 2017). Citation Format: Luca Bertamini, Claudia Sala, Nicola Martinelli, Cristina Papayannidis, Cristina Giuliani, Giovanni Malerba, Paolo Garagnani, Maria Abbondanza Pantaleo, Michele Cavo, Oliviero Olivieri, Giovanni Martinelli, Claudio Franceschi, Domenico Girelli. Clonal hematopoiesis of indeterminate potential (CHIP), centenarians and age-related cardiovascular risk: Is TET2 the culprit [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1229.

MiR-143/145 differentially regulate hematopoietic stem and progenitor activity through suppression of canonical TGF\u03b2 signaling

Expression of miR-143 and miR-145 is reduced in hematopoietic stem/progenitor cells (HSPCs) of myelodysplastic syndrome patients with a deletion in the long arm of chromosome 5. Here we show that mice lacking miR-143/145 have impaired HSPC activity with depletion of functional hematopoietic stem cells (HSCs), but activation of progenitor cells (HPCs). We identify components of the transforming growth factor β (TGFβ) pathway as key targets of miR-143/145. Enforced expression of the TGFβ adaptor protein and miR-145 target, Disabled-2 (DAB2), recapitulates the HSC defect seen in miR-143/145−/− mice. Despite reduced HSC activity, older miR-143/145−/− and DAB2-expressing mice show elevated leukocyte counts associated with increased HPC activity. A subset of mice develop a serially transplantable myeloid malignancy, associated with expansion of HPC. Thus, miR-143/145 play a cell context-dependent role in HSPC function through regulation of TGFβ/DAB2 activation, and loss of these miRNAs creates a preleukemic state.

Loss of Pax5 Exploits Sca1-BCR-ABLp190 Susceptibility to Confer the Metabolic Shift Essential for pB-ALL.

Preleukemic clones carrying BCR-ABLp190 oncogenic lesions are found in neonatal cord blood, where the majority of preleukemic carriers do not convert into precursor B-cell acute lymphoblastic leukemia (pB-ALL). However, the critical question of how these preleukemic cells transform into pB-ALL remains undefined. Here, we model a BCR-ABLp190 preleukemic state and show that limiting BCR-ABLp190 expression to hematopoietic stem/progenitor cells (HS/PC) in mice (Sca1-BCR-ABLp190) causes pB-ALL at low penetrance, which resembles the human disease. pB-ALL blast cells were BCR-ABL-negative and transcriptionally similar to pro-B/pre-B cells, suggesting disease onset upon reduced Pax5 functionality. Consistent with this, double Sca1-BCR-ABLp190+Pax5+/- mice developed pB-ALL with shorter latencies, 90% incidence, and accumulation of genomic alterations in the remaining wild-type Pax5 allele. Mechanistically, the Pax5-deficient leukemic pro-B cells exhibited a metabolic switch toward increased glucose utilization and energy metabolism. Transcriptome analysis revealed that metabolic genes (IDH1, G6PC3, GAPDH, PGK1, MYC, ENO1, ACO1) were upregulated in Pax5-deficient leukemic cells, and a similar metabolic signature could be observed in human leukemia. Our studies unveil the first in vivo evidence that the combination between Sca1-BCR-ABLp190 and metabolic reprogramming imposed by reduced Pax5 expression is sufficient for pB-ALL development. These findings might help to prevent conversion of BCR-ABLp190 preleukemic cells.Significance: Loss of Pax5 drives metabolic reprogramming, which together with Sca1-restricted BCR-ABL expression enables leukemic transformation. Cancer Res; 78(10); 2669-79. ©2018 AACR.

Preleukemic and second-hit mutational events in an acute myeloid leukemia patient with a novel germline RUNX1 mutation

BackgroundGermline mutations in the RUNX1 transcription factor give rise to a rare autosomal dominant genetic condition classified under the entity: Familial Platelet Disorders with predisposition to Acute Myeloid Leukaemia (FPD/AML). While several studies have identified a myriad of germline RUNX1 mutations implicated in this disorder, second-hit mutational events are necessary for patients with hereditary thrombocytopenia to develop full-blown AML. The molecular picture behind this process remains unclear. We describe a patient of Malay descent with an unreported 7-bp germline RUNX1 frameshift deletion, who developed second-hit mutations that could have brought about the leukaemic transformation from a pre-leukaemic state. These mutations were charted through the course of the treatment and stem cell transplant, showing a clear correlation between her clinical presentation and the mutations present.Case presentationThe patient was a 27-year-old Malay woman who presented with AML on the background of hereditary thrombocytopenia affecting her father and 3 brothers. Initial molecular testing revealed the same novel RUNX1 mutation in all 5 individuals. The patient received standard induction, consolidation chemotherapy, and a haploidentical stem cell transplant from her mother with normal RUNX1 profile. Comprehensive genomic analyses were performed at diagnosis, post-chemotherapy and post-transplant. A total of 8 mutations (RUNX1, GATA2, DNMT3A, BCORL1, BCOR, 2 PHF6 and CDKN2A) were identified in the pre-induction sample, of which 5 remained (RUNX1, DNMT3A, BCORL1, BCOR and 1 out of 2 PHF6) in the post-treatment sample and none were present post-transplant. In brief, the 3 mutations which were lost along with the leukemic cells at complete morphological remission were most likely acquired leukemic driver mutations that were responsible for the AML transformation from a pre-leukemic germline RUNX1-mutated state. On the contrary, the 5 mutations that persisted post-treatment, including the germline RUNX1 mutation, were likely to be part of the preleukemic clone.ConclusionFurther studies are necessary to assess the prevalence of these preleukemic and secondary mutations in the larger FPD/AML patient cohort and establish their prognostic significance. Given the molecular heterogeneity of FPD/AML and other AML subtypes, a better understanding of mutational classes and their involvement in AML pathogenesis can improve risk stratification of patients for more effective and targeted therapy.

Abnormal RNA splicing and genomic instability after induction of DNMT3A mutations by CRISPR/Cas9 gene editing

DNA methyltransferase 3A (DNMT3A) mediates de novo DNA methylation. Mutations in DNMT3A are associated with hematological malignancies, most frequently acute myeloid leukemia. DNMT3A mutations are hypothesized to establish a pre-leukemic state, rendering cells vulnerable to secondary oncogenic mutations and malignant transformation. However, the mechanisms by which DNMT3A mutations contribute to leukemogenesis are not well-defined. Here, we successfully created four DNMT3A-mutated K562 cell lines with frameshift mutations resulting in truncated DNMT3A proteins. DNMT3A-mutated cell lines exhibited significantly impaired growth and increased apoptotic activity compared to wild-type (WT) cells. Consistent with previous studies, DNMT3A-mutated cells displayed impaired differentiation capacity. RNA-seq was used to compare transcriptomes of DNMT3A-mutated and WT cells; DNMT3A ablation resulted in downregulation of genes involved in spliceosome function, causing dysfunction of RNA splicing. Unexpectedly, we observed DNMT3A-mutated cells to exhibit marked genomic instability and an impaired DNA damage response compared to WT. CRISPR/Cas9-mediated DNMT3A-mutated K562 cells may be used to model effects of DNMT3A mutations in human cells. Our findings implicate aberrant splicing and induction of genomic instability as potential mechanisms by which DNMT3A mutations might predispose to malignancy.

A Human IPS Model Implicates Embryonic B-Myeloid Fate Restriction as Developmental Susceptibility to B Acute Lymphoblastic Leukemia-Associated ETV6-RUNX1

SummaryETV6-RUNX1 is associated with childhood acute B-lymphoblastic leukemia (cALL) functioning as a first-hit mutation that initiates a clinically silent pre-leukemia in utero. Because lineage commitment hierarchies differ between embryo and adult, and the impact of oncogenes is cell-context dependent, we hypothesized that the childhood affiliation of ETV6-RUNX1 cALL reflects its origins in a progenitor unique to embryonic life. We characterize the first emerging B cells in first-trimester human embryos, identifying a developmentally restricted CD19−IL-7R+ progenitor compartment, which transitions from a myeloid to lymphoid program during ontogeny. This developmental series is recapitulated in differentiating human pluripotent stem cells (hPSCs), thereby providing a model for the initiation of cALL. Genome-engineered hPSCs expressing ETV6-RUNX1 from the endogenous ETV6 locus show expansion of the CD19−IL-7R+ compartment, show a partial block in B lineage commitment, and produce proB cells with aberrant myeloid gene expression signatures and potential: features (collectively) consistent with a pre-leukemic state.

A FOXO1-induced oncogenic network defines the AML1-ETO preleukemic program

AbstractUnderstanding and blocking the self-renewal pathway of preleukemia stem cells could prevent acute myeloid leukemia (AML) relapse. In this study, we show that increased FOXO1 represents a critical mechanism driving aberrant self-renewal in preleukemic cells expressing the t(8;21)-associated oncogene AML1-ETO (AE). Although generally considered as a tumor suppressor, FOXO1 is consistently upregulated in t(8;21) AML. Expression of FOXO1 in human CD34+ cells promotes a preleukemic state with enhanced self-renewal and dysregulated differentiation. The DNA binding domain of FOXO1 is essential for these functions. FOXO1 activates a stem cell molecular signature that is also present in AE preleukemia cells and preserved in t(8;21) patient samples. Genome-wide binding studies show that AE and FOXO1 share the majority of their binding sites, whereby FOXO1 binds to multiple crucial self-renewal genes and is required for their activation. In agreement with this observation, genetic and pharmacological ablation of FOXO1 inhibited the long-term proliferation and clonogenicity of AE cells and t(8;21) AML cell lines. Targeting of FOXO1 therefore provides a potential therapeutic strategy for elimination of stem cells at both preleukemic and leukemic stages.

SEMA3A partially reverses VEGF effects through binding to neuropilin-1

Cross-talk between hematopoietic stem cells (HSCs) and bone marrow stromal cells (BMSCs) is essential for HSCs regulation and leukemogenesis. Studying bone marrow of myelodysplasia patients, a pre-leukemic condition, we found mRNA overexpression of vascular endothelial growth factor A (VEGFA) in CD34+ HSCs and semaphorin 3A (SEMA3A) in BMSCs. To better understand the role of VEGFA and SEMA3A in leukemogenesis, we recruited 30 myelodysplastic syndrome (MDS) patients, 29 acute myeloid leukemia (6 secondary to MDS) patients and 12 controls. We found higher VEGFA expression in de novo AML patients (without prior MDS) group (p=0.0073) and higher SEMA3A expression in all BMSCs patient's samples compared to control group. We then overexpressed VEGFA in an acute myelogenous leukemia cell line, KG1 cells, and in normal CD34+ cells. This overexpression increased KG1 (p=0.045) and CD34+ cell (p=0.042) viability and KG1 (p=0.042) and CD34+ cell (p=0.047) proliferation. Moreover, KG1 and CD34+ cells overexpressing VEGFA also had increased proliferation when co-cultured with human marrow stromal HS5 cells (p=0.045 and p=0.02, respectively). However, co-culture of these transformed cells with HS5 cells overexpressing SEMA3A reduced KG1 (p=0.004) and CD34+ (p=0.009) proliferation. Co-culture of KG1 transformed cells with HS27 cells overexpressing SEMA3A reduced KG1 proliferation as well (p=0.01). To investigate whether the dominant SEMA3A effect over VEGFA could be due to competition for neuropilin1 receptor (NRP1), we performed immunoprecipitation with anti-NRP1 antibody of cell extracts of co-cultured KG1 and HS5 cells, induced or not by VEGFA and SEMA3A recombinant proteins. Results showed a preferential association of NRP1 with SEMA3A, suggesting that SEMA3A can partially reverse the effects caused by the VEGFA preventing its binding with the NRP1 receptor. Since both hematopoietic cells, leukemic and normal, showed similar behavior, we suppose that the attempt to reversion of VEGF effects by SEMA3A is a homeostatic phenomenon in the hematopoietic niche. Finally, we conclude that VEGFA overexpression confers AML cell advantages and SEMA3A may partially reverse this effect; thus, SEMA3A protein combined with VEGFA inhibitors could be beneficial for AML treatment.