Single-cell multi-omics of human clonal hematopoiesis reveals that DNMT3A R882 mutations perturb early progenitor states through selective hypomethylation

Somatic mutations in cancer genes have been ubiquitously detected in clonal expansions across healthy human tissue, including in clonal hematopoiesis. However, mutated and wildtype cells are morphologically and phenotypically similar, limiting the ability to link genotypes with cellular phenotypes. To overcome this limitation, we leveraged multi-modality single-cell sequencing, capturing the mutation with transcriptomes and methylomes in stem and progenitors from individuals with DNMT3A R882 mutated clonal hematopoiesis. DNMT3A mutations resulted in myeloid over lymphoid bias, and in expansion of immature myeloid progenitors primed toward megakaryocytic-erythroid fate. We observed dysregulated expression of lineage and leukemia stem cell markers. DNMT3A R882 led to preferential hypomethylation of polycomb repressive complex 2 targets and a specific sequence motif. Notably, the hypomethylation motif is enriched in binding motifs of key hematopoietic transcription factors, serving as a potential mechanistic link between DNMT3A R882 mutations and aberrant transcriptional phenotypes. Thus, single-cell multi-omics pave the road to defining the downstream consequences of mutations that drive human clonal mosaicism.

Inflammatory signals from fatty bone marrow supports the early stages of DNMT3a driven clonal hematopoiesis

Age related cancer is not only due to the random accumulation of mutations, but also how phenotypes are selected by the aging environment. While fatty bone marrow (FBM), is one of the hallmarks of bone marrow ageing, it is unknown whether FBM can modify the evolution of the early stages of leukemia and clonal hematopoiesis (CH). To address this question, we established FBM mice models and transplanted both human and mice preleukemic hematopoietic stem cells (PreL-HSCs) carrying DNMT3A mutations. We demonstrate that castration which models age related andropenia result in FBM. A significant increase in self-renewal was found when DNMT3AMut-preL-HSPCs were exposed to FBM. To better understand the mechanisms of the FBM-preL-HSPCs interaction, we performed single cell RNA-sequencing on HSPCs three days after FBM exposure. A 20-50 fold increase in DNMT3AMut-preL-HSCs was observed under FBM conditions in comparison to other conditions. PreL-HSPCs exposed to FBM exhibited an activated inflammatory signaling (IL-6 and INFγ). Cytokine analysis of BM fluid demonstrated increased IL-6 levels under FBM conditions. Anti-IL-6 neutralizing antibodies significantly reduced the selective advantage of DNMT3AMut-preL-HSPCs exposed to FBM. Overall, age related paracrine FBM inflammatory signals promote DNMT3A-driven clonal hematopoiesis, which can be inhibited by blocking the IL-6 receptor.

Increased prevalence of clonal hematopoiesis of indeterminate potential amongst people living with HIV

People living with human immunodeficiency virus (PLWH) have significantly increased risk for cardiovascular disease in part due to inflammation and immune dysregulation. Clonal hematopoiesis of indeterminate potential (CHIP), the age-related acquisition and expansion of hematopoietic stem cells due to leukemogenic driver mutations, increases risk for both hematologic malignancy and coronary artery disease (CAD). Since increased inflammation is hypothesized to be both a cause and consequence of CHIP, we hypothesized that PLWH have a greater prevalence of CHIP. We searched for CHIP in multi-ethnic cases from the Swiss HIV Cohort Study (SHCS, n = 600) and controls from the Atherosclerosis Risk in the Communities study (ARIC, n = 8111) from blood DNA-derived exome sequences. We observed that HIV is associated with a twofold increase in CHIP prevalence, both in the whole study population and in a subset of 230 cases and 1002 matched controls selected by propensity matching to control for demographic imbalances (SHCS 7%, ARIC 3%, p = 0.005). We also observed that ASXL1 is the most commonly mutated CHIP-associated gene in PLWH. Our results suggest that CHIP may contribute to the excess cardiovascular risk observed in PLWH.

Somatic Mutations in Cardiovascular Disease

Advances in population-scale genomic sequencing have greatly expanded the understanding of the inherited basis of cardiovascular disease (CVD). Reanalysis of these genomic datasets identified an unexpected risk factor for CVD, somatically acquired DNA mutations. In this review, we provide an overview of somatic mutations and their contributions to CVD. We focus on the most common and well-described manifestation, clonal hematopoiesis of indeterminate potential. We also review the currently available data regarding how somatic mutations lead to tissue mosaicism in various forms of CVD, including atrial fibrillation and aortic aneurism associated with Marfan Syndrome. Finally, we highlight future research directions given current knowledge gaps and consider how technological advances will enhance the discovery of somatic mutations in CVD and management of patients with somatic mutations.

Genome-wide analyses of 200,453 individuals yields new insights into the causes and consequences of clonal hematopoiesis

Clonal hematopoiesis (CH) is one of the most extensively studied somatic mutational phenomena, yet its causes and consequences remain poorly understood. We identify 10,924 individuals with CH amongst 200,453 whole-exome sequenced UK Biobank participants and use their linked genome-wide DNA genotypes to map the landscape of inherited predisposition to CH at unprecedented scale. We increase the number of European-ancestry genome-wide significant (P<5x10-8) germline associations with CH from four to 14 and identify one new transcriptome-wide significant (P<3.2x10-6) association. Genes at new loci implicate DNA damage repair (PARP1, ATM, and CHEK2), hematopoietic stem cell migration/homing (CD164), and myeloid oncogenesis (SETBP1) in CH development. Several associations were CH-subtype specific and, strikingly, variants at TCL1A and CD164 had opposite associations with DNMT3A- versus TET2-mutant CH, mirroring recently reported differences in lifelong behavior of these two most common CH subtypes and proposing important roles for these loci in CH pathogenesis. Using Mendelian randomization, we show, amongst other findings, that smoking and longer leukocyte telomere length are causal risk factors for CH and demonstrate that genetic predisposition to CH increases risks of myeloproliferative neoplasia, several non-hematological malignancies, atrial fibrillation, and blood epigenetic age acceleration.

Exome sequencing of 628,388 individuals identifies common and rare variant associations with clonal hematopoiesis phenotypes

Clonal hematopoiesis (CH) refers to the expansion of certain blood cell lineages and has been associated with aging and adverse health outcomes. Here, we use exome sequence data on 628,388 individuals to identify 40,208 carriers of clonal hematopoiesis of indeterminate potential (CHIP). Using genome-wide and exome-wide association analyses, we identify 27 loci (24 novel) where germline genetic variation influences CH/CHIP predisposition, including missense variants in the DNA-repair gene PARP1 and the lymphocytic antigen coding gene LY75 that are associated with reduced incidence of CH/CHIP. Analysis of 5,194 health traits from the UK Biobank (UKB) found relationships between CHIP and severe COVID outcomes, cardiovascular disease, hematologic traits, malignancy, smoking, obesity, infection, and all-cause mortality. Longitudinal analyses revealed that one of the CHIP subtypes, DNMT3A-CHIP, is associated with the subsequent development of myeloid but not lymphoid leukemias, and with solid cancers including prostate and lung. Additionally, contrary to previous findings from the initial 50,000 UKB exomes, our results in the full sample do not support a role for IL-6 inhibition in reducing the risk of cardiovascular disease among CHIP carriers. Our findings demonstrate that CHIP represents a complex set of heterogenous phenotypes with shared and unique germline genetic causes and varied clinical implications.