CpG Island Hypermethylation Mediated by DNMT3A Is a Consequence of AML Progression.

DNMT3A mutations occur in ∼25% of acute myeloid leukemia (AML) patients. The most common mutation, DNMT3AR882H, has dominant negative activity that reduces DNA methylation activity by ∼80% in vitro. To understand the contribution of DNMT3A-dependent methylation to leukemogenesis, we performed whole-genome bisulfite sequencing of primary leukemic and non-leukemic cells in patients with or without DNMT3AR882 mutations. Non-leukemic hematopoietic cells with DNMT3AR882H displayed focal methylation loss, suggesting that hypomethylation antedates AML. Although virtually all AMLs with wild-type DNMT3A displayed CpG island hypermethylation, this change was not associated with gene silencing and was essentially absent in AMLs with DNMT3AR882 mutations. Primary hematopoietic stem cells expanded with cytokines were hypermethylated in a DNMT3A-dependent manner, suggesting that hypermethylation may be a response to, rather than a cause of, cellular proliferation. Our findings suggest that hypomethylation is an initiating phenotype in AMLs with DNMT3AR882, while DNMT3A-dependent CpG island hypermethylation is a consequence of AML progression.

The origin and evolution of mutations in acute myeloid leukemia.

Most mutations in cancer genomes are thought to be acquired after the initiating event, which may cause genomic instability and drive clonal evolution. However, for acute myeloid leukemia (AML), normal karyotypes are common, and genomic instability is unusual. To better understand clonal evolution in AML, we sequenced the genomes of M3-AML samples with a known initiating event (PML-RARA) versus the genomes of normal karyotype M1-AML samples and the exomes of hematopoietic stem/progenitor cells (HSPCs) from healthy people. Collectively, the data suggest that most of the mutations found in AML genomes are actually random events that occurred in HSPCs before they acquired the initiating mutation; the mutational history of that cell is "captured" as the clone expands. In many cases, only one or two additional, cooperating mutations are needed to generate the malignant founding clone. Cells from the founding clone can acquire additional cooperating mutations, yielding subclones that can contribute to disease progression and/or relapse.

Genome Sequencing as an Alternative to Cytogenetic Analysis in Myeloid Cancers.

BACKGROUND: Genomic analysis is essential for risk stratification in patients with acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS). Whole-genome sequencing is a potential replacement for conventional cytogenetic and sequencing approaches, but its accuracy, feasibility, and clinical utility have not been demonstrated. METHODS: We used a streamlined whole-genome sequencing approach to obtain genomic profiles for 263 patients with myeloid cancers, including 235 patients who had undergone successful cytogenetic analysis. We adapted sample preparation, sequencing, and analysis to detect mutations for risk stratification using existing European Leukemia Network (ELN) guidelines and to minimize turnaround time. We analyzed the performance of whole-genome sequencing by comparing our results with findings from cytogenetic analysis and targeted sequencing. RESULTS: Whole-genome sequencing detected all 40 recurrent translocations and 91 copy-number alterations that had been identified by cytogenetic analysis. In addition, we identified new clinically reportable genomic events in 40 of 235 patients (17.0%). Prospective sequencing of samples obtained from 117 consecutive patients was performed in a median of 5 days and provided new genetic information in 29 patients (24.8%), which changed the risk category for 19 patients (16.2%). Standard AML risk groups, as defined by sequencing results instead of cytogenetic analysis, correlated with clinical outcomes. Whole-genome sequencing was also used to stratify patients who had inconclusive results by cytogenetic analysis into risk groups in which clinical outcomes were measurably different. CONCLUSIONS: In our study, we found that whole-genome sequencing provided rapid and accurate genomic profiling in patients with AML or MDS. Such sequencing also provided a greater diagnostic yield than conventional cytogenetic analysis and more efficient risk stratification on the basis of standard risk categories. (Funded by the Siteman Cancer Research Fund and others.).

IL-1ß expression in bone marrow dendritic cells is induced by TLR2 agonists and regulates HSC function.

Hematopoietic stem/progenitor cells (HSPCs) reside in localized microenvironments, or niches, in the bone marrow that provide key signals regulating their activity. A fundamental property of hematopoiesis is the ability to respond to environmental cues such as inflammation. How these cues are transmitted to HSPCs within hematopoietic niches is not well established. Here, we show that perivascular bone marrow dendritic cells (DCs) express a high basal level of Toll-like receptor-1 (TLR1) and TLR2. Systemic treatment with a TLR1/2 agonist induces HSPC expansion and mobilization. It also induces marked alterations in the bone marrow microenvironment, including a decrease in osteoblast activity and sinusoidal endothelial cell numbers. TLR1/2 agonist treatment of mice in which Myd88 is deleted specifically in DCs using Zbtb46-Cre show that the TLR1/2-induced expansion of multipotent HPSCs, but not HSPC mobilization or alterations in the bone marrow microenvironment, is dependent on TLR1/2 signaling in DCs. Interleukin-1ß (IL-1ß) is constitutively expressed in both murine and human DCs and is further induced after TLR1/2 stimulation. Systemic TLR1/2 agonist treatment of Il1r1-/- mice show that TLR1/2-induced HSPC expansion is dependent on IL-1ß signaling. Single-cell RNA-sequencing of low-risk myelodysplastic syndrome bone marrow revealed that IL1B and TLR1 expression is increased in DCs. Collectively, these data suggest a model in which TLR1/2 stimulation of DCs induces secretion of IL-1ß and other inflammatory cytokines into the perivascular niche, which in turn, regulates multipotent HSPCs. Increased DC TLR1/2 signaling may contribute to altered HSPC function in myelodysplastic syndrome by increasing local IL-1ß expression.

Immunosuppression and outcomes in adult patients with de novo acute myeloid leukemia with normal karyotypes.

Acute myeloid leukemia (AML) patients rarely have long first remissions (LFRs; >5 y) after standard-of-care chemotherapy, unless classified as favorable risk at presentation. Identification of the mechanisms responsible for long vs. more typical, standard remissions may help to define prognostic determinants for chemotherapy responses. Using exome sequencing, RNA-sequencing, and functional immunologic studies, we characterized 28 normal karyotype (NK)-AML patients with >5 y first remissions after chemotherapy (LFRs) and compared them to a well-matched group of 31 NK-AML patients who relapsed within 2 y (standard first remissions [SFRs]). Our combined analyses indicated that genetic-risk profiling at presentation (as defined by European LeukemiaNet [ELN] 2017 criteria) was not sufficient to explain the outcomes of many SFR cases. Single-cell RNA-sequencing studies of 15 AML samples showed that SFR AML cells differentially expressed many genes associated with immune suppression. The bone marrow of SFR cases had significantly fewer CD4+ Th1 cells; these T cells expressed an exhaustion signature and were resistant to activation by T cell receptor stimulation in the presence of autologous AML cells. T cell activation could be restored by removing the AML cells or blocking the inhibitory major histocompatibility complex class II receptor, LAG3. Most LFR cases did not display these features, suggesting that their AML cells were not as immunosuppressive. These findings were confirmed and extended in an independent set of 50 AML cases representing all ELN 2017 risk groups. AML cell-mediated suppression of CD4+ T cell activation at presentation is strongly associated with unfavorable outcomes in AML patients treated with standard chemotherapy.

Immune Escape of Relapsed AML Cells after Allogeneic Transplantation.

BACKGROUND: As consolidation therapy for acute myeloid leukemia (AML), allogeneic hematopoietic stem-cell transplantation provides a benefit in part by means of an immune-mediated graft-versus-leukemia effect. We hypothesized that the immune-mediated selective pressure imposed by allogeneic transplantation may cause distinct patterns of tumor evolution in relapsed disease. METHODS: We performed enhanced exome sequencing on paired samples obtained at initial presentation with AML and at relapse from 15 patients who had a relapse after hematopoietic stem-cell transplantation (with transplants from an HLA-matched sibling, HLA-matched unrelated donor, or HLA-mismatched unrelated donor) and from 20 patients who had a relapse after chemotherapy. We performed RNA sequencing and flow cytometry on a subgroup of these samples and on additional samples for validation. RESULTS: On exome sequencing, the spectrum of gained and lost mutations observed with relapse after transplantation was similar to the spectrum observed with relapse after chemotherapy. Specifically, relapse after transplantation was not associated with the acquisition of previously unknown AML-specific mutations or structural variations in immune-related genes. In contrast, RNA sequencing of samples obtained at relapse after transplantation revealed dysregulation of pathways involved in adaptive and innate immunity, including down-regulation of major histocompatibility complex (MHC) class II genes ( HLA-DPA1, HLA-DPB1, HLA-DQB1, and HLA-DRB1) to levels that were 3 to 12 times lower than the levels seen in paired samples obtained at presentation. Flow cytometry and immunohistochemical analysis confirmed decreased expression of MHC class II at relapse in 17 of 34 patients who had a relapse after transplantation. Evidence suggested that interferon-γ treatment could rapidly reverse this phenotype in AML blasts in vitro. CONCLUSIONS: AML relapse after transplantation was not associated with the acquisition of relapse-specific mutations in immune-related genes. However, it was associated with dysregulation of pathways that may influence immune function, including down-regulation of MHC class II genes, which are involved in antigen presentation. These epigenetic changes may be reversible with appropriate therapy. (Funded by the National Cancer Institute and others.).

Mutation Clearance after Transplantation for Myelodysplastic Syndrome.

BACKGROUND: Allogeneic hematopoietic stem-cell transplantation is the only curative treatment for patients with myelodysplastic syndrome (MDS). The molecular predictors of disease progression after transplantation are unclear. METHODS: We sequenced bone marrow and skin samples from 90 adults with MDS who underwent allogeneic hematopoietic stem-cell transplantation after a myeloablative or reduced-intensity conditioning regimen. We detected mutations before transplantation using enhanced exome sequencing, and we evaluated mutation clearance by using error-corrected sequencing to genotype mutations in bone marrow samples obtained 30 days after transplantation. In this exploratory study, we evaluated the association of a mutation detected after transplantation with disease progression and survival. RESULTS: Sequencing identified at least one validated somatic mutation before transplantation in 86 of 90 patients (96%); 32 of these patients (37%) had at least one mutation with a maximum variant allele frequency of at least 0.5% (equivalent to 1 heterozygous mutant cell in 100 cells) 30 days after transplantation. Patients with disease progression had mutations with a higher maximum variant allele frequency at 30 days than those who did not (median maximum variant allele frequency, 0.9% vs. 0%; P<0.001). The presence of at least one mutation with a variant allele frequency of at least 0.5% at day 30 was associated with a higher risk of progression (53.1% vs. 13.0%; conditioning regimen-adjusted hazard ratio, 3.86; 95% confidence interval [CI], 1.96 to 7.62; P<0.001) and a lower 1-year rate of progression-free survival than the absence of such a mutation (31.3% vs. 59.3%; conditioning regimen-adjusted hazard ratio for progression or death, 2.22; 95% CI, 1.32 to 3.73; P=0.005). The rate of progression-free survival was lower among patients who had received a reduced-intensity conditioning regimen and had at least one persistent mutation with a variant allele frequency of at least 0.5% at day 30 than among patients with other combinations of conditioning regimen and mutation status (P≤0.001). Multivariate analysis confirmed that patients who had a mutation with a variant allele frequency of at least 0.5% detected at day 30 had a higher risk of progression (hazard ratio, 4.48; 95% CI, 2.21 to 9.08; P<0.001) and a lower 1-year rate of progression-free survival than those who did not (hazard ratio for progression or death, 2.39; 95% CI, 1.40 to 4.09; P=0.002). CONCLUSIONS: The risk of disease progression was higher among patients with MDS in whom persistent disease-associated mutations were detected in the bone marrow 30 days after transplantation than among those in whom these mutations were not detected. (Funded by the Leukemia and Lymphoma Society and others.).

TP53 and Decitabine in Acute Myeloid Leukemia and Myelodysplastic Syndromes.

BACKGROUND: The molecular determinants of clinical responses to decitabine therapy in patients with acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS) are unclear. METHODS: We enrolled 84 adult patients with AML or MDS in a single-institution trial of decitabine to identify somatic mutations and their relationships to clinical responses. Decitabine was administered at a dose of 20 mg per square meter of body-surface area per day for 10 consecutive days in monthly cycles. We performed enhanced exome or gene-panel sequencing in 67 of these patients and serial sequencing at multiple time points to evaluate patterns of mutation clearance in 54 patients. An extension cohort included 32 additional patients who received decitabine in different protocols. RESULTS: Of the 116 patients, 53 (46%) had bone marrow blast clearance (<5% blasts). Response rates were higher among patients with an unfavorable-risk cytogenetic profile than among patients with an intermediate-risk or favorable-risk cytogenetic profile (29 of 43 patients [67%] vs. 24 of 71 patients [34%], P<0.001) and among patients with TP53 mutations than among patients with wild-type TP53 (21 of 21 [100%] vs. 32 of 78 [41%], P<0.001). Previous studies have consistently shown that patients with an unfavorable-risk cytogenetic profile and TP53 mutations who receive conventional chemotherapy have poor outcomes. However, in this study of 10-day courses of decitabine, neither of these risk factors was associated with a lower rate of overall survival than the rate of survival among study patients with intermediate-risk cytogenetic profiles. CONCLUSIONS: Patients with AML and MDS who had cytogenetic abnormalities associated with unfavorable risk, TP53 mutations, or both had favorable clinical responses and robust (but incomplete) mutation clearance after receiving serial 10-day courses of decitabine. Although these responses were not durable, they resulted in rates of overall survival that were similar to those among patients with AML who had an intermediate-risk cytogenetic profile and who also received serial 10-day courses of decitabine. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT01687400 .).

Rapid expansion of preexisting nonleukemic hematopoietic clones frequently follows induction therapy for de novo AML.

There is interest in using leukemia-gene panels and next-generation sequencing to assess acute myelogenous leukemia (AML) response to induction chemotherapy. Studies have shown that patients with AML in morphologic remission may continue to have clonal hematopoiesis with populations closely related to the founding AML clone and that this confers an increased risk of relapse. However, it remains unknown how induction chemotherapy influences the clonal evolution of a patient's nonleukemic hematopoietic population. Here, we report that 5 of 15 patients with genetic clearance of their founding AML clone after induction chemotherapy had a concomitant expansion of a hematopoietic population unrelated to the initial AML. These populations frequently harbored somatic mutations in genes recurrently mutated in AML or myelodysplastic syndromes and were detectable at very low frequencies at the time of AML diagnosis. These results suggest that nonleukemic hematopoietic stem and progenitor cells, harboring specific aging-acquired mutations, may have a competitive fitness advantage after induction chemotherapy, expand, and persist long after the completion of chemotherapy. Although the clinical importance of these "rising" clones remains to be determined, it will be important to distinguish them from leukemia-related populations when assessing for molecular responses to induction chemotherapy.

Genomic and epigenomic landscapes of adult de novo acute myeloid leukemia.

BACKGROUND: Many mutations that contribute to the pathogenesis of acute myeloid leukemia (AML) are undefined. The relationships between patterns of mutations and epigenetic phenotypes are not yet clear. METHODS: We analyzed the genomes of 200 clinically annotated adult cases of de novo AML, using either whole-genome sequencing (50 cases) or whole-exome sequencing (150 cases), along with RNA and microRNA sequencing and DNA-methylation analysis. RESULTS: AML genomes have fewer mutations than most other adult cancers, with an average of only 13 mutations found in genes. Of these, an average of 5 are in genes that are recurrently mutated in AML. A total of 23 genes were significantly mutated, and another 237 were mutated in two or more samples. Nearly all samples had at least 1 nonsynonymous mutation in one of nine categories of genes that are almost certainly relevant for pathogenesis, including transcription-factor fusions (18% of cases), the gene encoding nucleophosmin (NPM1) (27%), tumor-suppressor genes (16%), DNA-methylation-related genes (44%), signaling genes (59%), chromatin-modifying genes (30%), myeloid transcription-factor genes (22%), cohesin-complex genes (13%), and spliceosome-complex genes (14%). Patterns of cooperation and mutual exclusivity suggested strong biologic relationships among several of the genes and categories. CONCLUSIONS: We identified at least one potential driver mutation in nearly all AML samples and found that a complex interplay of genetic events contributes to AML pathogenesis in individual patients. The databases from this study are widely available to serve as a foundation for further investigations of AML pathogenesis, classification, and risk stratification. (Funded by the National Institutes of Health.).

Association Between Mutation Clearance After Induction Therapy and Outcomes in Acute Myeloid Leukemia.

IMPORTANCE: Tests that predict outcomes for patients with acute myeloid leukemia (AML) are imprecise, especially for those with intermediate risk AML. OBJECTIVES: To determine whether genomic approaches can provide novel prognostic information for adult patients with de novo AML. DESIGN, SETTING, AND PARTICIPANTS: Whole-genome or exome sequencing was performed on samples obtained at disease presentation from 71 patients with AML (mean age, 50.8 years) treated with standard induction chemotherapy at a single site starting in March 2002, with follow-up through January 2015. In addition, deep digital sequencing was performed on paired diagnosis and remission samples from 50 patients (including 32 with intermediate-risk AML), approximately 30 days after successful induction therapy. Twenty-five of the 50 were from the cohort of 71 patients, and 25 were new, additional cases. EXPOSURES: Whole-genome or exome sequencing and targeted deep sequencing. Risk of identification based on genetic data. MAIN OUTCOMES AND MEASURES: Mutation patterns (including clearance of leukemia-associated variants after chemotherapy) and their association with event-free survival and overall survival. RESULTS: Analysis of comprehensive genomic data from the 71 patients did not improve outcome assessment over current standard-of-care metrics. In an analysis of 50 patients with both presentation and documented remission samples, 24 (48%) had persistent leukemia-associated mutations in at least 5% of bone marrow cells at remission. The 24 with persistent mutations had significantly reduced event-free and overall survival vs the 26 who cleared all mutations. Patients with intermediate cytogenetic risk profiles had similar findings. [table: see text]. CONCLUSIONS AND RELEVANCE: The detection of persistent leukemia-associated mutations in at least 5% of bone marrow cells in day 30 remission samples was associated with a significantly increased risk of relapse, and reduced overall survival. These data suggest that this genomic approach may improve risk stratification for patients with AML.

Melanoma in a patient with DNMT3A overgrowth syndrome.

Alterations in epigenetic regulators are increasingly recognized as early events in tumorigenesis; thus, patients with acquired or inherited variants in epigenetic regulators may be at increased risk for developing multiple types of cancer. DNMT3A overgrowth syndrome (DOS), caused by germline pathogenic variants in the DNA methyltransferase gene DNMT3A, has been associated with a predisposition toward development of hematopoietic and neuronal malignancies. DNMT3A deficiency has been described to promote keratinocyte proliferation in mice. Although altered DNA methylation patterns are well-recognized in melanoma, the role of DNA methyltransferases in melanoma pathogenesis is not clear. We report the case of an adult DOS patient with a germline DNMT3A loss-of-function mutation, who developed an early-onset melanoma with regional lymph node metastatic disease. Exome sequencing of the primary tumor identified an additional acquired, missense DNMT3A mutation in the dominant tumor clone, suggesting that the loss of DNMT3A function was relevant for the development of this tumor.

Genomic landscape of TP53-mutated myeloid malignancies.

TP53-mutated myeloid malignancies are associated with complex cytogenetics and extensive structural variants, which complicates detailed genomic analysis by conventional clinical techniques. We performed whole-genome sequencing (WGS) of 42 acute myeloid leukemia (AML)/myelodysplastic syndromes (MDS) cases with paired normal tissue to better characterize the genomic landscape of TP53-mutated AML/MDS. WGS accurately determines TP53 allele status, a key prognostic factor, resulting in the reclassification of 12% of cases from monoallelic to multihit. Although aneuploidy and chromothripsis are shared with most TP53-mutated cancers, the specific chromosome abnormalities are distinct to each cancer type, suggesting a dependence on the tissue of origin. ETV6 expression is reduced in nearly all cases of TP53-mutated AML/MDS, either through gene deletion or presumed epigenetic silencing. Within the AML cohort, mutations of NF1 are highly enriched, with deletions of 1 copy of NF1 present in 45% of cases and biallelic mutations in 17%. Telomere content is increased in TP53-mutated AMLs compared with other AML subtypes, and abnormal telomeric sequences were detected in the interstitial regions of chromosomes. These data highlight the unique features of TP53-mutated myeloid malignancies, including the high frequency of chromothripsis and structural variation, the frequent involvement of unique genes (including NF1 and ETV6) as cooperating events, and evidence for altered telomere maintenance.

Genomic landscape of TP53 -mutated myeloid malignancies.

TP53 -mutated myeloid malignancies are most frequently associated with complex cytogenetics. The presence of complex and extensive structural variants complicates detailed genomic analysis by conventional clinical techniques. We performed whole genome sequencing of 42 AML/MDS cases with paired normal tissue to characterize the genomic landscape of TP53 -mutated myeloid malignancies. The vast majority of cases had multi-hit involvement at the TP53 genetic locus (94%), as well as aneuploidy and chromothripsis. Chromosomal patterns of aneuploidy differed significantly from TP53 -mutated cancers arising in other tissues. Recurrent structural variants affected regions that include ETV6 on chr12p, RUNX1 on chr21, and NF1 on chr17q. Most notably for ETV6 , transcript expression was low in cases of TP53 -mutated myeloid malignancies both with and without structural rearrangements involving chromosome 12p. Telomeric content is increased in TP53 -mutated AML/MDS compared other AML subtypes, and telomeric content was detected adjacent to interstitial regions of chromosomes. The genomic landscape of TP53 -mutated myeloid malignancies reveals recurrent structural variants affecting key hematopoietic transcription factors and telomeric repeats that are generally not detected by panel sequencing or conventional cytogenetic analyses. Key Points: WGS comprehensively determines TP53 mutation status, resulting in the reclassification of 12% of cases from mono-allelic to multi-hit Chromothripsis is more frequent than previously appreciated, with a preference for specific chromosomes ETV6 is deleted in 45% of cases, with evidence for epigenetic suppression in non-deleted cases NF1 is mutated in 48% of cases, with multi-hit mutations in 17% of these cases TP53 -mutated AML/MDS is associated with altered telomere content compared with other AMLs.

Genetic and Transcriptional Contributions to Relapse in Normal Karyotype Acute Myeloid Leukemia.

To better understand clonal and transcriptional adaptations after relapse in patients with acute myeloid leukemia (AML), we collected presentation and relapse samples from six normal karyotype AML cases. We performed enhanced whole-genome sequencing to characterize clonal evolution, and deep-coverage single-cell RNA sequencing on the same samples, which yielded 142,642 high-quality cells for analysis. Identifying expressed mutations in individual cells enabled us to discriminate between normal and AML cells, to identify coordinated changes in the genome and transcriptome, and to identify subclone-specific cell states. We quantified the coevolution of genetic and transcriptional heterogeneity during AML progression, and found that transcriptional changes were significantly correlated with genetic changes. However, transcriptional adaptation sometimes occurred independently, suggesting that clonal evolution does not represent all relevant biological changes. In three cases, we identified cells at diagnosis that likely seeded the relapse. Finally, these data revealed a conserved relapse-enriched leukemic cell state bearing markers of stemness, quiescence, and adhesion. SIGNIFICANCE: These data enabled us to identify a relapse-enriched leukemic cell state with distinct transcriptional properties. Detailed case-by-case analyses elucidated the complex ways in which the AML genome, transcriptome, and immune microenvironment interact to evade chemotherapy. These analyses provide a blueprint for evaluating these factors in larger cohorts.This article is highlighted in the In This Issue feature, p. 1.

Focal disruption of DNA methylation dynamics at enhancers in IDH-mutant AML cells.

Recurrent mutations in IDH1 or IDH2 in acute myeloid leukemia (AML) are associated with increased DNA methylation, but the genome-wide patterns of this hypermethylation phenotype have not been comprehensively studied in AML samples. We analyzed whole-genome bisulfite sequencing data from 15 primary AML samples with IDH1 or IDH2 mutations, which identified ~4000 focal regions that were uniquely hypermethylated in IDHmut samples vs. normal CD34+ cells and other AMLs. These regions had modest hypermethylation in AMLs with biallelic TET2 mutations, and levels of 5-hydroxymethylation that were diminished in IDH and TET-mutant samples, indicating that this hypermethylation results from inhibition of TET-mediated demethylation. Focal hypermethylation in IDHmut AMLs occurred at regions with low methylation in CD34+ cells, implying that DNA methylation and demethylation are active at these loci. AML samples containing IDH and DNMT3AR882 mutations were significantly less hypermethylated, suggesting that IDHmut-associated hypermethylation is mediated by DNMT3A. IDHmut-specific hypermethylation was highly enriched for enhancers that form direct interactions with genes involved in normal hematopoiesis and AML, including MYC and ETV6. These results suggest that focal hypermethylation in IDH-mutant AML occurs by altering the balance between DNA methylation and demethylation, and that disruption of these pathways at enhancers may contribute to AML pathogenesis.

Convergent Clonal Evolution of Signaling Gene Mutations Is a Hallmark of Myelodysplastic Syndrome Progression.

Progression from myelodysplastic syndromes (MDS) to secondary acute myeloid leukemia (AML) is associated with the acquisition and expansion of subclones. Our understanding of subclone evolution during progression, including the frequency and preferred order of gene mutation acquisition, remains incomplete. Sequencing of 43 paired MDS and secondary AML samples identified at least one signaling gene mutation in 44% of MDS and 60% of secondary AML samples, often below the level of standard sequencing detection. In addition, 19% of MDS and 47% of secondary AML patients harbored more than one signaling gene mutation, almost always in separate, coexisting subclones. Signaling gene mutations demonstrated diverse patterns of clonal evolution during disease progression, including acquisition, expansion, persistence, and loss of mutations, with multiple patterns often coexisting in the same patient. Multivariate analysis revealed that MDS patients who had a signaling gene mutation had a higher risk of AML progression, potentially providing a biomarker for progression. SIGNIFICANCE: Subclone expansion is a hallmark of progression from MDS to secondary AML. Subclonal signaling gene mutations are common at MDS (often at low levels), show complex and convergent patterns of clonal evolution, and are associated with future progression to secondary AML. See related article by Guess et al., p. 316 (33). See related commentary by Romine and van Galen, p. 270. This article is highlighted in the In This Issue feature, p. 265.

Functional and epigenetic phenotypes of humans and mice with DNMT3A Overgrowth Syndrome.

Germline pathogenic variants in DNMT3A were recently described in patients with overgrowth, obesity, behavioral, and learning difficulties (DNMT3A Overgrowth Syndrome/DOS). Somatic mutations in the DNMT3A gene are also the most common cause of clonal hematopoiesis, and can initiate acute myeloid leukemia (AML). Using whole genome bisulfite sequencing, we studied DNA methylation in peripheral blood cells of 11 DOS patients and found a focal, canonical hypomethylation phenotype, which is most severe with the dominant negative DNMT3AR882H mutation. A germline mouse model expressing the homologous Dnmt3aR878H mutation phenocopies most aspects of the human DOS syndrome, including the methylation phenotype and an increased incidence of spontaneous hematopoietic malignancies, suggesting that all aspects of this syndrome are caused by this mutation.