Certain leukemia-initiating mutations drive expansion of hemopoietic clones specifically under the selection pressures that prevail in an aged microenvironment.
Clonal hemopoiesis driven by leukemia-associated gene mutations can occur without evidence of a blood disorder. To investigate this phenomenon, we interrogated 15 mutation hot spots in blood DNA from 4,219 individuals using ultra-deep sequencing. Using only the hot spots studied, we identified clonal hemopoiesis in 0.8% of individuals under 60, rising to 19.5% of those ≥90 years, thus predicting that clonal hemopoiesis is much more prevalent than previously realized. DNMT3A-R882 mutations were most common and, although their prevalence increased with age, were found in individuals as young as 25 years. By contrast, mutations affecting spliceosome genes SF3B1 and SRSF2, closely associated with the myelodysplastic syndromes, were identified only in those aged >70 years, with several individuals harboring more than one such mutation. This indicates that spliceosome gene mutations drive clonal expansion under selection pressures particular to the aging hemopoietic system and explains the high incidence of clonal disorders associated with these mutations in advanced old age.
Background: Acquisition of leukemia‐associated somatic mutations by one or more haematopoietic stem cells (HSCs) is inevitable in healthy individuals by the age of 50–60 years 1 . However, the consequences of mutation acquisition are highly variable, even amongst those with identical mutations, and range from long‐term clinically silent clonal haematopoiesis (CH) to leukemic progression. Aims: To investigate the role of the inherited genome in determining CH emergence and behaviour, by studying CH concordance patterns in monozygotic (MZ) and dizygotic (DZ) twin pairs. Methods: 154 individuals from the TwinsUK cohort were studied, comprising 52 MZ and 27 DZ twin pairs, aged 70–99 years 2 . Deep sequencing was performed on blood DNA, targeting 41 genes implicated in CH and myeloid malignancies (Agilent SureSelect, ELID 0735431). Somatic single nucleotide variants and small indels were called using the Shearwater algorithm (v.1.21.5) and verified using CaVEMan (v.1.11.2) and Pindel (v.2.2), and curation of variant oncogenicity was performed, as described previously 3 . Statistical analyses were performed in R (version 3.4.0). Fisher's Exact Test was used to assess twin concordance for CH. Null distributions of CH within the MZ and DZ groups were generated using random permutation (1000 iterations). Results: Using deep sequencing (mean 1650X) and sensitive variant‐calling, we identified CH (VAF≥0.5%) in 62% of individuals (95/154) (Figure 1A), with mutations in the epigenetic regulators DNMT3A and TET2 predominant (Figure 1B). The overall prevalence of CH was very similar among individuals belonging to the MZ and DZ groups (59% and 54% respectively; p = 0.70). We did not observe higher concordance for CH within MZ twin pairs as compared to DZ pairs (p = 0.59, Figure 1C). Furthermore, using random sample permutation to model the null distribution, we found no difference in the observed distribution of CH among either MZ or DZ twins as compared to that expected by chance (p = 1 for MZ; p = 0.86 for DZ; Figure 1C). Increased twin concordance was also not observed when separately considering CH with: (i) mutations in DNMT3A, (ii) mutations in TET2, and (iii) larger clones (VAF > 2%). Despite the overall lack of concordance for CH, we identified two MZ twin pairs in which both twins harbored identical rare somatic nonsense mutations, KDM6A Q692X (NM_021140:c.C2074T) in one pair and DNMT3A R598X (NM_175629:c.C1792T) in the other. Finally, in 4 MZ twin pairs, serial blood samples taken after an interval of 4–5 years showed significant inter‐twin variability in clonal trajectories, even for clones harboring mutations in the same genes. Summary/Conclusion: We find no evidence for a strong heritable predisposition to age‐related CH. The variability in clonal dynamics over time between twins in MZ pairs supports an important role for the non‐inherited environment in determining clonal behaviour. The sharing of identical somatic mutations by twins in two MZ pairs, in view of the rarity of these particular mutations in CH and myeloid malignancies, suggests that mutation acquisition probably occurred during embryogenesis, either prior to twinning or more likely in an HSC whose progeny reached both twins through shared circulation in utero. While the sharing of somatic mutations has been demonstrated in other settings, including pediatric leukemia, this would be the first description of possible acquisition of adult‐type CH driver mutations during embryogenesis. image
We report the case of a middle-aged man who died from multiorgan failure 3 weeks after orthotopic liver transplant for fulminant hepatic failure, associated with a rare, often fatal, hematologic condition that usually presents in childhood. We discuss the importance of its diagnosis, treatment, and implications for liver transplant.
Prognostic stratification is critical for making therapeutic decisions and maximizing survival of patients with acute myeloid leukemia. Advances in the genomics of acute myeloid leukemia have identified several recurrent gene mutations whose prognostic impact is being deciphered. We used HaloPlex target enrichment and Illumina-based next generation sequencing to study 24 recurrently mutated genes in 42 samples of acute myeloid leukemia with a normal karyotype. Read depth varied between and within genes for the same sample, but was predictable and highly consistent across samples. Consequently, we were able to detect copy number changes, such as an interstitial deletion of BCOR, three MLL partial tandem duplications, and a novel KRAS amplification. With regards to coding mutations, we identified likely oncogenic variants in 41 of 42 samples. NPM1 mutations were the most frequent, followed by FLT3, DNMT3A and TET2. NPM1 and FLT3 indels were reported with good efficiency. We also showed that DNMT3A mutations can persist post-chemotherapy and in 2 cases studied at diagnosis and relapse, we were able to delineate the dynamics of tumor evolution and give insights into order of acquisition of variants. HaloPlex is a quick and reliable target enrichment method that can aid diagnosis and prognostic stratification of acute myeloid leukemia patients.
Abstract Current therapies for myeloproliferative neoplasms (MPN) improve symptoms but have limited effect on tumor size. In preclinical studies, tamoxifen restored normal apoptosis in mutated hematopoietic stem and progenitor cells (HSPCs). TAMARIN is a Phase-II, multicenter, single-arm clinical trial assessing tamoxifen’s safety and activity in patients with stable MPNs, no prior thrombotic events and mutated JAK2V617F, CALRins5 or CALRdel52 peripheral blood allele burden ≥20%. The primary outcome (≥50% allele burden reduction at 24 weeks) was met by 3/38 patients; 5/38 additional patients showed ≥25% reductions. Tamoxifen was well tolerated. Baseline analysis of HSPC transcriptome segregated responders and non-responders, suggesting a predictive signature. In responder HSPCs, longitudinal analysis showed high baseline expression of JAK-STAT signaling and oxidative phosphorylation genes, which were downregulated by tamoxifen. In JAK2V617F+ cells, 4-hydroxytamoxifen inhibited mitochondrial complex-I, activating proapoptotic integrated stress response (ISR) and decreasing pathogenic JAK2 signaling. Therefore, tamoxifen inhibits mitochondrial respiration, modulates ISR and suppresses pathogenic JAK-STAT signaling in a subset of prospectively identifiable MPN patients.
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