Quality assurance of hematopoietic stem cells by macrophages determines stem cell clonality.

Tissue-specific stem cells persist for a lifetime and can differentiate to maintain homeostasis or transform to initiate cancer. Despite their importance, there are no described quality assurance mechanisms for newly formed stem cells. We observed intimate and specific interactions between macrophages and nascent blood stem cells in zebrafish embryos. Macrophage interactions frequently led to either removal of cytoplasmic material and stem cell division or complete engulfment and stem cell death. Stressed stem cells were marked by surface Calreticulin, which stimulated macrophage interactions. Using cellular barcoding, we found that Calreticulin knock-down or embryonic macrophage depletion reduced the number of stem cell clones that established adult hematopoiesis. Our work supports a model in which embryonic macrophages determine hematopoietic clonality by monitoring stem cell quality.

Clonal Hematopoiesis Is Associated With Higher Risk of Stroke.

BACKGROUND AND PURPOSE: Clonal hematopoiesis of indeterminate potential (CHIP) is a novel age-related risk factor for cardiovascular disease-related morbidity and mortality. The association of CHIP with risk of incident ischemic stroke was reported previously in an exploratory analysis including a small number of incident stroke cases without replication and lack of stroke subphenotyping. The purpose of this study was to discover whether CHIP is a risk factor for ischemic or hemorrhagic stroke. METHODS: We utilized plasma genome sequence data of blood DNA to identify CHIP in 78 752 individuals from 8 prospective cohorts and biobanks. We then assessed the association of CHIP and commonly mutated individual CHIP driver genes (DNMT3A, TET2, and ASXL1) with any stroke, ischemic stroke, and hemorrhagic stroke. RESULTS: CHIP was associated with an increased risk of total stroke (hazard ratio, 1.14 [95% CI, 1.03-1.27]; P=0.01) after adjustment for age, sex, and race. We observed associations with CHIP with risk of hemorrhagic stroke (hazard ratio, 1.24 [95% CI, 1.01-1.51]; P=0.04) and with small vessel ischemic stroke subtypes. In gene-specific association results, TET2 showed the strongest association with total stroke and ischemic stroke, whereas DMNT3A and TET2 were each associated with increased risk of hemorrhagic stroke. CONCLUSIONS: CHIP is associated with an increased risk of stroke, particularly with hemorrhagic and small vessel ischemic stroke. Future studies clarifying the relationship between CHIP and subtypes of stroke are needed.

Distinction of lymphoid and myeloid clonal hematopoiesis.

Clonal hematopoiesis (CH) results from somatic genomic alterations that drive clonal expansion of blood cells. Somatic gene mutations associated with hematologic malignancies detected in hematopoietic cells of healthy individuals, referred to as CH of indeterminate potential (CHIP), have been associated with myeloid malignancies, while mosaic chromosomal alterations (mCAs) have been associated with lymphoid malignancies. Here, we analyzed CHIP in 55,383 individuals and autosomal mCAs in 420,969 individuals with no history of hematologic malignancies in the UK Biobank and Mass General Brigham Biobank. We distinguished myeloid and lymphoid somatic gene mutations, as well as myeloid and lymphoid mCAs, and found both to be associated with risk of lineage-specific hematologic malignancies. Further, we performed an integrated analysis of somatic alterations with peripheral blood count parameters to stratify the risk of incident myeloid and lymphoid malignancies. These genetic alterations can be readily detected in clinical sequencing panels and used with blood count parameters to identify individuals at high risk of developing hematologic malignancies.

Dnmt3a-mutated clonal hematopoiesis promotes osteoporosis.

Osteoporosis is caused by an imbalance of osteoclasts and osteoblasts, occurring in close proximity to hematopoietic cells in the bone marrow. Recurrent somatic mutations that lead to an expanded population of mutant blood cells is termed clonal hematopoiesis of indeterminate potential (CHIP). Analyzing exome sequencing data from the UK Biobank, we found CHIP to be associated with increased incident osteoporosis diagnoses and decreased bone mineral density. In murine models, hematopoietic-specific mutations in Dnmt3a, the most commonly mutated gene in CHIP, decreased bone mass via increased osteoclastogenesis. Dnmt3a-/- demethylation opened chromatin and altered activity of inflammatory transcription factors. Bone loss was driven by proinflammatory cytokines, including Irf3-NF-κB-mediated IL-20 expression from Dnmt3a mutant macrophages. Increased osteoclastogenesis due to the Dnmt3a mutations was ameliorated by alendronate or IL-20 neutralization. These results demonstrate a novel source of osteoporosis-inducing inflammation.

Clonal hematopoiesis of indeterminate potential (CHIP): Linking somatic mutations, hematopoiesis, chronic inflammation and cardiovascular disease.

Clonal hematopoiesis of indeterminate potential (CHIP) is the presence of a clonally expanded hematopoietic stem cell caused by a leukemogenic mutation in individuals without evidence of hematologic malignancy, dysplasia, or cytopenia. CHIP is associated with a 0.5-1.0% risk per year of leukemia. Remarkably, it confers a two-fold increase in cardiovascular risk independent of traditional risk factors. Roughly 80% of patients with CHIP have mutations in epigenetic regulators DNMT3A, TET2, ASXL1, DNA damage repair genes PPM1D, TP53, the regulatory tyrosine kinase JAK2, or mRNA spliceosome components SF3B1, and SRSF2. CHIP is associated with a pro-inflammatory state that has been linked to coronary artery disease, myocardial infarction, and venous thromboembolic disease, as well as prognosis among those with aortic stenosis and heart failure. Heritable and acquired risk factors are associated with increased CHIP prevalence, including germline variation, age, unhealthy lifestyle behaviors (i.e. smoking, obesity), inflammatory conditions, premature menopause, HIV and exposure to cancer therapies. This review aims to summarize emerging research on CHIP, the mechanisms underlying its important role in propagating inflammation and accelerating cardiovascular disease, and new studies detailing the role of associated risk factors and co-morbidities that increase CHIP prevalence.

Association of Diet Quality With Prevalence of Clonal Hematopoiesis and Adverse Cardiovascular Events.

Importance: Clonal hematopoiesis of indeterminate potential (CHIP), the expansion of somatic leukemogenic variations in hematopoietic stem cells, has been associated with atherosclerotic cardiovascular disease. Because the inherited risk of developing CHIP is low, lifestyle elements such as dietary factors may be associated with the development and outcomes of CHIP. Objective: To examine whether there is an association between diet quality and the prevalence of CHIP. Design, Setting, and Participants: This retrospective cohort study used data from participants in the UK Biobank, an ongoing population-based study in the United Kingdom that examines whole-exome sequencing data and survey-based information on health-associated behaviors. Individuals from the UK Biobank were recruited between 2006 and 2010 and followed up prospectively with linkage to health data records through May 2020. The present study included 44 111 participants in the UK Biobank who were age 40 to 70 years, had data available from whole-exome sequencing of blood DNA, and were free of coronary artery disease (CAD) or hematologic cancer at baseline. Exposures: Diet quality was categorized as unhealthy if the intake of healthy elements (fruits and vegetables) was lower than the median of all survey responses, and the intake of unhealthy elements (red meat, processed food, and added salt) was higher than the median. Diets were classified as healthy if the intake of healthy elements was higher than the median, and the intake of unhealthy elements was lower than the median. The presence of CHIP was detected by data from whole-exome sequencing of blood DNA. Main Outcomes and Measures: The primary outcome was CHIP prevalence. Multivariable logistic regression analysis was used to examine the association between diet quality and the presence of CHIP. Multivariable Cox proportional hazards models were used to assess the association of incident events (acute coronary syndromes, coronary revascularization, or death) in each diet quality category stratified by the presence of CHIP. Results: Among 44 111 participants (mean [SD] age at time of blood sample collection, 56.3 [8.0] years; 24 507 women [55.6%]), 2271 individuals (5.1%) had an unhealthy diet, 38 552 individuals (87.4%) had an intermediate diet, and 3288 individuals (7.5%) had a healthy diet. A total of 2507 individuals (5.7%) had CHIP, and the prevalence of CHIP decreased as diet quality improved from unhealthy (162 of 2271 participants [7.1%]) to intermediate (2177 of 38 552 participants [5.7%]) to healthy (168 of 3288 participants [5.1%]; P = .003 for trend). Compared with individuals without CHIP who had an intermediate diet, the rates of incident cardiovascular events progressively decreased among those with CHIP who had an unhealthy diet (hazard ratio [HR], 1.52; 95% CI, 1.04-2.22) and those with CHIP who had a healthy diet (HR, 0.99; 95% CI, 0.62-1.58) over a median of 10.0 years (interquartile range, 9.6-10.4 years) of follow-up. Conclusions and Relevance: This cohort study suggests that an unhealthy diet quality may be associated with a higher prevalence of CHIP and higher rates of adverse cardiovascular events and death independent of CHIP status.

Distinct genetic pathways define pre-malignant versus compensatory clonal hematopoiesis in Shwachman-Diamond syndrome.

To understand the mechanisms that mediate germline genetic leukemia predisposition, we studied the inherited ribosomopathy Shwachman-Diamond syndrome (SDS), a bone marrow failure disorder with high risk of myeloid malignancies at an early age. To define the mechanistic basis of clonal hematopoiesis in SDS, we investigate somatic mutations acquired by patients with SDS followed longitudinally. Here we report that multiple independent somatic hematopoietic clones arise early in life, most commonly harboring heterozygous mutations in EIF6 or TP53. We show that germline SBDS deficiency establishes a fitness constraint that drives selection of somatic clones via two distinct mechanisms with different clinical consequences. EIF6 inactivation mediates a compensatory pathway with limited leukemic potential by ameliorating the underlying SDS ribosome defect and enhancing clone fitness. TP53 mutations define a maladaptive pathway with enhanced leukemic potential by inactivating tumor suppressor checkpoints without correcting the ribosome defect. Subsequent development of leukemia was associated with acquisition of biallelic TP53 alterations. These results mechanistically link leukemia predisposition to germline genetic constraints on cellular fitness, and provide a rational framework for clinical surveillance strategies.

Healthy Lifestyle and Clonal Hematopoiesis of Indeterminate Potential: Results From the Women's Health Initiative.

Background Presence of clonal hematopoiesis of indeterminate potential (CHIP) is associated with a higher risk of atherosclerotic cardiovascular disease, cancer, and mortality. The relationship between a healthy lifestyle and CHIP is unknown. Methods and Results This analysis included 8709 postmenopausal women (mean age, 66.5 years) enrolled in the WHI (Women's Health Initiative), free of cancer or cardiovascular disease, with deep-coverage whole genome sequencing data available. Information on lifestyle factors (body mass index, smoking, physical activity, and diet quality) was obtained, and a healthy lifestyle score was created on the basis of healthy criteria met (0 point [least healthy] to 4 points [most healthy]). CHIP was derived on the basis of a prespecified list of leukemogenic driver mutations. The prevalence of CHIP was 8.6%. A higher healthy lifestyle score was not associated with CHIP (multivariable-adjusted odds ratio [OR] [95% CI], 0.99 [0.80-1.23] and 1.13 [0.93-1.37]) for the upper (3 or 4 points) and middle category (2 points), respectively, versus referent (0 or 1 point). Across score components, a normal and overweight body mass index compared with obese was significantly associated with a lower odds for CHIP (OR, 0.71 [95% CI, 0.57-0.88] and 0.83 [95% CI, 0.68-1.01], respectively; P-trend 0.0015). Having never smoked compared with being a current smoker tended to be associated with lower odds for CHIP. Conclusions A healthy lifestyle, based on a composite score, was not related to CHIP among postmenopausal women. However, across individual lifestyle factors, having a normal body mass index was strongly associated with a lower prevalence of CHIP. These findings support the idea that certain healthy lifestyle factors are associated with a lower frequency of CHIP.

Premature Menopause, Clonal Hematopoiesis, and Coronary Artery Disease in Postmenopausal Women.

BACKGROUND: Premature menopause is an independent risk factor for cardiovascular disease in women, but mechanisms underlying this association remain unclear. Clonal hematopoiesis of indeterminate potential (CHIP), the age-related expansion of hematopoietic cells with leukemogenic mutations without detectable malignancy, is associated with accelerated atherosclerosis. Whether premature menopause is associated with CHIP is unknown. METHODS: We included postmenopausal women from the UK Biobank (n=11 495) aged 40 to 70 years with whole exome sequences and from the Women's Health Initiative (n=8111) aged 50 to 79 years with whole genome sequences. Premature menopause was defined as natural or surgical menopause occurring before age 40 years. Co-primary outcomes were the presence of any CHIP and CHIP with variant allele frequency >0.1. Logistic regression tested the association of premature menopause with CHIP, adjusted for age, race, the first 10 principal components of ancestry, smoking, diabetes, and hormone therapy use. Secondary analyses considered natural versus surgical premature menopause and gene-specific CHIP subtypes. Multivariable-adjusted Cox models tested the association between CHIP and incident coronary artery disease. RESULTS: The sample included 19 606 women, including 418 (2.1%) with natural premature menopause and 887 (4.5%) with surgical premature menopause. Across cohorts, CHIP prevalence in postmenopausal women with versus without a history of premature menopause was 8.8% versus 5.5% (P<0.001), respectively. After multivariable adjustment, premature menopause was independently associated with CHIP (all CHIP: odds ratio, 1.36 [95% 1.10-1.68]; P=0.004; CHIP with variant allele frequency >0.1: odds ratio, 1.40 [95% CI, 1.10-1.79]; P=0.007). Associations were larger for natural premature menopause (all CHIP: odds ratio, 1.73 [95% CI, 1.23-2.44]; P=0.001; CHIP with variant allele frequency >0.1: odds ratio, 1.91 [95% CI, 1.30-2.80]; P<0.001) but smaller and nonsignificant for surgical premature menopause. In gene-specific analyses, only DNMT3A CHIP was significantly associated with premature menopause. Among postmenopausal middle-aged women, CHIP was independently associated with incident coronary artery disease (hazard ratio associated with all CHIP: 1.36 [95% CI, 1.07-1.73]; P=0.012; hazard ratio associated with CHIP with variant allele frequency >0.1: 1.48 [95% CI, 1.13-1.94]; P=0.005). CONCLUSIONS: Premature menopause, especially natural premature menopause, is independently associated with CHIP among postmenopausal women. Natural premature menopause may serve as a risk signal for predilection to develop CHIP and CHIP-associated cardiovascular disease.

Clonal Hematopoiesis Before, During, and After Human Spaceflight.

Clonal hematopoiesis (CH) occurs when blood cells harboring an advantageous mutation propagate faster than others. These mutations confer a risk for hematological cancers and cardiovascular disease. Here, we analyze CH in blood samples from a pair of twin astronauts over 4 years in bulk and fractionated cell populations using a targeted CH panel, linked-read whole-genome sequencing, and deep RNA sequencing. We show CH with distinct mutational profiles and increasing allelic fraction that includes a high-risk, TET2 clone in one subject and two DNMT3A mutations on distinct alleles in the other twin. These astronauts exhibit CH almost two decades prior to the mean age at which it is typically detected and show larger shifts in clone size than age-matched controls or radiotherapy patients, based on a longitudinal cohort of 157 cancer patients. As such, longitudinal monitoring of CH may serve as an important metric for overall cancer and cardiovascular risk in astronauts.

In vivo clonal analysis of aging hematopoietic stem cells.

Hematopoietic stem cells (HSCs) are characterized by two key features: Self-renewal ability and multilineage differentiation potential (multipotentiality). With aging, these key features gradually change. This is thought to be related to hematological diseases. However, clonal in vivo analysis assessing the potential of HSCs to differentiate along erythroid and platelet lineages ("five-lineage tracing") has not been performed in the aged bone marrow. By contrast, in young HSCs clonal in vivo analysis combined with five-lineage tracing has provided us with novel insights into HSC biology. Understanding HSC aging at the clonal level will help us to elucidate aging mechanisms and disease progression. We review recent progress towards understanding HSC aging at the clonal cell level in the transplantation setting.

Interplay between Clonal Hematopoiesis of Indeterminate Potential and Metabolism.

Clonal hematopoiesis of indeterminate potential (CHIP), defined as a clone of hematopoietic cells consisting of a single acquired mutation during a lifetime, has recently been discovered to be a major risk factor for atherosclerotic cardiovascular disease (CVD). As such, this phenomenon has sparked interest into the role that these single mutations may play in CVD. Atherosclerotic CVD is a complex disease and we have previously shown that atherosclerosis can be accelerated by metabolic- or autoimmune-related risk factors such as diabetes, obesity, and rheumatoid arthritis. In this review, we discuss the role of CHIP, the interplay between CHIP and metabolic diseases, as well as how metabolism of hematopoietic stem cells (HSCs) could regulate CHIP-related HSC fate.

Clonal hematopoiesis and measurable residual disease assessment in acute myeloid leukemia.

Current objectives regarding treatment of acute myeloid leukemia (AML) include achieving complete remission (CR) by clinicopathological criteria followed by interrogation for the presence of minimal/measurable residual disease (MRD) by molecular genetic and/or flow cytometric techniques. Although advances in molecular genetic technologies have enabled highly sensitive detection of AML-associated mutations and translocations, determination of MRD is complicated by the fact that many treated patients have persistent clonal hematopoiesis (CH) that may not reflect residual AML. CH detected in AML patients in CR includes true residual or early recurrent AML, myelodysplastic syndrome or CH that is ancestral to the AML, and independent or newly emerging clones of uncertain leukemogenic potential. Although the presence of AML-related mutations has been shown to be a harbinger of relapse in multiple studies, the significance of other types of CH is less well understood. In patients who undergo allogeneic hematopoietic cell transplantation (HCT), post-HCT clones can be donor-derived and in some cases engender a new myeloid neoplasm that is clonally unrelated to the recipient's original AML. In this article, we discuss the spectrum of CH that can be detected in treated AML patients, propose terminology to standardize nomenclature in this setting, and review clinical data and areas of uncertainty among the various types of posttreatment hematopoietic clones.

Clinical impact of clonal hematopoiesis in patients with lymphoma undergoing ASCT: a national population-based cohort study.

Clonal hematopoiesis of indeterminate potential (CHIP) is suspected of being a risk factor for patients with cancer. This study aimed to assess the clinical consequences of CHIP in patients with lymphoma intended for high-dose chemotherapy and autologous stem-cell transplantation (ASCT) in a population-based setting. We identified 892 lymphoma patients who had undergone stem cell harvest at all transplant centers in Denmark. A total of 565 patients had an available harvest sample, which was analysed for CHIP by next-generation sequencing, and the median follow-up was 9.1 years. Of the patients who were intended for immediate ASCT, 25.5% (112/440) carried at least one CHIP mutation. In contrast to previous single-center studies CHIP was not associated with inferior overall survival (OS) in multivariate analyses. However, patients with mutations in genes of the DNA repair pathway (PPM1D, TP53, RAD21, BRCC3) had a significant inferior OS (HR after 1 year of follow-up 2.79, 95% confidence interval 1.71-4.56; p < 0.0001), which also was evident in multivariate analysis (p = 0.00067). These patients had also increased rates of therapy-related leukemia and admission to intensive care. Furthermore, in patients who did not undergo immediate ASCT, a significant inferior OS of individuals with DNA repair mutations was also identified (p = 0.003).

Tet2-mediated clonal hematopoiesis in nonconditioned mice accelerates age-associated cardiac dysfunction.

Clonal hematopoiesis of indeterminate potential is prevalent in elderly individuals and associated with increased risks of all-cause mortality and cardiovascular disease. However, mouse models to study the dynamics of clonal hematopoiesis and its consequences on the cardiovascular system under homeostatic conditions are lacking. We developed a model of clonal hematopoiesis using adoptive transfer of unfractionated ten-eleven translocation 2-mutant (Tet2-mutant) bone marrow cells into nonirradiated mice. Consistent with age-related clonal hematopoiesis observed in humans, these mice displayed a progressive expansion of Tet2-deficient cells in multiple hematopoietic stem and progenitor cell fractions and blood cell lineages. The expansion of the Tet2-mutant fraction was also observed in bone marrow-derived CCR2+ myeloid cell populations within the heart, but there was a negligible impact on the yolk sac-derived CCR2- cardiac-resident macrophage population. Transcriptome profiling revealed an enhanced inflammatory signature in the donor-derived macrophages isolated from the heart. Mice receiving Tet2-deficient bone marrow cells spontaneously developed age-related cardiac dysfunction characterized by greater hypertrophy and fibrosis. Altogether, we show that Tet2-mediated hematopoiesis contributes to cardiac dysfunction in a nonconditioned setting that faithfully models human clonal hematopoiesis in unperturbed bone marrow. Our data support clinical findings that clonal hematopoiesis per se may contribute to diminished health span.