Longitudinal dynamics of clonal hematopoiesis identifies gene-specific fitness effects

Microbial metabolite drives ageing-related clonal haematopoiesis via ALPK1

Clonal haematopoiesis of indeterminate potential (CHIP) involves the gradual expansion of mutant pre-leukaemic haematopoietic cells, which increases with age and confers a risk for multiple diseases, including leukaemia and immune-related conditions1. Although the absolute risk of leukaemic transformation in individuals with CHIP is very low, the strongest predictor of progression is the accumulation of mutant haematopoietic cells2. Despite the known associations between CHIP and increased all-cause mortality, our understanding of environmental and regulatory factors that underlie this process during ageing remains rudimentary. Here we show that intestinal alterations, which can occur with age, lead to systemic dissemination of a microbial metabolite that promotes pre-leukaemic cell expansion. Specifically, ADP-D-glycero-β-D-manno-heptose (ADP-heptose), a biosynthetic bi-product specific to Gram-negative bacteria3-5, is uniquely found in the circulation of older individuals and favours the expansion of pre-leukaemic cells. ADP-heptose is also associated with increased inflammation and cardiovascular risk in CHIP. Mechanistically, ADP-heptose binds to its receptor, ALPK1, triggering transcriptional reprogramming and NF-κB activation that endows pre-leukaemic cells with a competitive advantage due to excessive clonal proliferation. Collectively, we identify that the accumulation of ADP-heptose represents a direct link between ageing and expansion of rare pre-leukaemic cells, suggesting that the ADP-heptose-ALPK1 axis is a promising therapeutic target to prevent progression of CHIP to overt leukaemia and immune-related conditions.

Evolution of myeloproliferative neoplasms from normal blood stem cells

Over the course of the last decade, genomic studies in the context of normal human hematopoiesis have provided new insights into the early pathogenesis of myeloproliferative neoplasms (MPN). A preclinical phase of MPN, termed clonal hematopoiesis was identified and subsequent lineage tracing studies revealed a multi-decade long time interval from acquisition of an MPN phenotypic driver mutation in a hematopoietic stem cell to the development of overt MPN. Multiple germline variants associated with MPN risk have been identified through genome-wide association studies and in some cases functional interrogation of the impact of the variant has uncovered new insights into hematopoietic stem cell biology and MPN development. Increasingly sophisticated methods to study clonal contributions to human hematopoiesis and measure hematopoietic stem cell fitness have helped to discern the biology underlying the tremendous clinical heterogeneity observed in MPN. Despite these advances, significant knowledge gaps remain, particularly with respect to germline genetic contributors to both MPN pathogenesis and phenotypic diversity, as well as limitations in the ability to prospectively quantify rates of clonal expansion in individual MPN patients. Ultimately, we envisage a personalized approach to MPN care in the future, in which an individualized genetic assessment can predict MPN trajectory and this information will be used to inform and guide therapy. MPN is particularly amenable to precision medicine strategies and our increased understanding of the evolution of MPN from normal blood stem cells provides a unique opportunity for early therapeutic intervention approaches and potentially MPN prevention strategies.

A genotype-first approach identifies high incidence of NF1 pathogenic variants with distinct disease associations

Loss of function variants in the NF1 gene cause neurofibromatosis type 1, a genetic disorder characterized by complete penetrance, characteristic physical exam findings, and a substantially increased risk for malignancy. However, our understanding of the disorder is based on patients ascertained through phenotype-first approaches, which estimate prevalence at 1 in 3000. Leveraging a genotype-first approach in multiple large patient cohorts including over one million individuals, we demonstrate an unexpectedly high prevalence (1 in 1,286) of NF1 pathogenic variants. Half are identified in individuals lacking clinical features of NF1, with many appearing to have post-zygotic mosaicism for the identified variant. Incidentally discovered variants are not associated with classic neurofibromatosis features but are associated with an increased incidence of malignancy compared to control populations. Our findings suggest that NF1 pathogenic variants are substantially more common than previously thought, often characterized by somatic mosaicism and reduced penetrance, and are important contributors to cancer risk in the general population.

Inherited resilience to clonal hematopoiesis by modifying stem cell RNA regulation

Somatic mutations that increase hematopoietic stem cell (HSC) fitness drive their expansion in clonal hematopoiesis (CH) and predispose to blood cancers. Although CH frequently occurs with aging, it rarely progresses to overt malignancy. Population variation in the growth rate and potential of mutant clones suggests the presence of genetic factors protecting against CH, but these remain largely undefined. Here, we identify a non-coding regulatory variant, rs17834140-T, that significantly protects against CH and myeloid malignancies by downregulating HSC-selective expression and function of the RNA-binding protein MSI2. By modeling variant effects and mapping MSI2 binding targets, we uncover an RNA network that maintains human HSCs and influences CH risk. Importantly, rs17834140-T is associated with slower CH expansion rates in humans, and stem cell MSI2 levels modify ASXL1-mutant HSC clonal dominance in experimental models. These findings leverage natural resilience to highlight a key role for post-transcriptional regulation in human HSCs, and offer genetic evidence supporting inhibition of MSI2 or its downstream targets as rational strategies for blood cancer prevention.

Clinical progression of clonal hematopoiesis is determined by a combination of mutation timing, fitness, and clonal structure

Clonal hematopoiesis (CH) is characterized by expanding blood cell clones carrying somatic mutations in healthy aged individuals and is associated with various age-related diseases and all-cause mortality. While CH mutations affect diverse genes associated with myeloid malignancies, their mechanisms of expansion and disease associations remain poorly understood. We investigate the relationship between clonal fitness and clinical outcomes by integrating data from three longitudinal aging cohorts (n=713, observations=2,341). We demonstrate pathway-specific fitness advantage and clonal composition influence clonal dynamics. Further, the timing of mutation acquisition is necessary to determine the extent of clonal expansion reached during the host individual's lifetime. We introduce MACS120, a metric combining mutation context, timing, and variant fitness to predict future clonal growth, outperforming traditional variant allele frequency measurements in predicting clinical outcomes. Our unified analytical framework enables standardized clonal dynamics inference across cohorts, advancing our ability to predict and potentially intervene in CH-related pathologies.

Clonal hematopoiesis of indeterminate potential: the root cause of, and fertile ground for, hematological malignancies

Clonal hematopoiesis (CH) of indeterminate potential (CHIP), characterized by propagation of blood cell clones carrying somatic mutations in specific driver genes, is increasingly recognized as a critical factor in the development of hematological malignancies. This phenomenon, which often emerges with age, underscores the complex interplay between genetic predisposition and environmental influences in cancer initiation and progression. Recent years have witnessed significant advances in our understanding of the link between CHIP and hematological diseases. In this review, we provide a comprehensive overview of the features of CHIP and explore its role in promoting tumorigenesis and influencing treatment outcomes for blood cancers. Finally, we summarize current available tools for risk stratification and discuss management strategies for patients with CHIP.

SF3B1: from core splicing factor to oncogenic driver

Highly recurrent somatic mutations in the gene encoding the core splicing factor SF3B1 are drivers of multiple cancer types. SF3B1 is a scaffold protein that orchestrates multivalent protein-protein interactions within the spliceosome that are essential for recognizing the branchsite (BS) and selecting the 3' splice site during the earliest stage of pre-mRNA splicing. In this review, we first describe the molecular mechanism by which multiple oncogenic SF3B1 mutations disrupt splicing. This involves perturbation of an early spliceosomal trimeric protein complex necessary for accurate BS recognition in a subset of introns, which leads to activation of upstream branchpoints and selection of cryptic 3' splice sites. We next discuss how specific transcripts affected by aberrant splicing in SF3B1-mutant cells contribute to the initiation and progression of cancer. Finally, we highlight the prognostic value and disease phenotypes of different cancer-associated SF3B1 mutations, which is critical for developing new targeted therapeutics against SF3B1-mutant cancers still lacking in the clinic.

Single-cell DNA sequencing reveals pervasive positive selection throughout preleukemic evolution

The representation of driver mutations in preleukemic hematopoietic stem cells (pHSCs) provides a window into the somatic evolution that precedes acute myeloid leukemia (AML). Here, we isolate pHSCs from the bone marrow of 16 patients diagnosed with AML and perform single-cell DNA sequencing on thousands of cells to reconstruct phylogenetic trees of the major driver clones in each patient. We develop a computational framework that can infer levels of positive selection operating during preleukemic evolution from the statistical properties of these phylogenetic trees. Combining these data with 67 previously published phylogenetic trees, we find that the highly variable structures of preleukemic trees emerge naturally from a simple model of somatic evolution with pervasive positive selection typically in the range of 9%-24% per year. At these levels of positive selection, we show that the identification of early multiple-mutant clones could be used to identify individuals at risk of future AML.

Genomic instability and genetic heterogeneity in aging: insights from clonal hematopoiesis (CHIP), monoclonal gammopathy (MGUS), and monoclonal B-cell lymphocytosis (MBL)

Aging is a multifaceted process characterized by a gradual decline in physiological function and increased susceptibility to a range of chronic diseases. Among the molecular and cellular mechanisms driving aging, genomic instability is a fundamental hallmark, contributing to increased mutation load and genetic heterogeneity within cellular populations. This review explores the role of genomic instability and genetic heterogeneity in aging in the hematopoietic system, with a particular focus on clonal hematopoiesis of indeterminate potential (CHIP), monoclonal gammopathy of undetermined significance (MGUS), and monoclonal B-cell lymphocytosis (MBL) as biomarkers. CHIP involves the clonal expansion of hematopoietic stem cells with somatic mutations. In contrast, MGUS is characterized by the presence of clonal plasma cells producing monoclonal immunoglobulins, while MBL is characterized by clonal proliferation of B cells. These conditions are prevalent in the aging population and serve as measurable indicators of underlying genomic instability. Studying these entities offers valuable insights into the mechanisms by which somatic mutations accumulate and drive clonal evolution in the hematopoietic system, providing a deeper understanding of how aging impacts cellular and tissue homeostasis. In summary, the hematopoietic system serves as a powerful model for investigating the interplay between genomic instability and aging. Incorporating age-related hematological conditions into aging research, alongside other biomarkers such as epigenetic clocks, can enhance the precision and predictive power of biological age assessments. These biomarkers provide a comprehensive view of the aging process, facilitating the early detection of age-related diseases and hopefully enabling personalized healthcare strategies.

Clonal Hematopoiesis of Indeterminate Potential and Long-term Outcomes in Heart Transplantation

BACKGROUND

Clonal hematopoiesis of indeterminate potential (CHIP) mutations, a trait of aging, has been associated with the progression of cardiovascular disease and the development of malignancy. Uncertainty prevails regarding a robust association between CHIP and heart-transplantation (HT) outcomes.

OBJECTIVES

To determine the prevalence of CHIP mutations in HT and their association with long-term outcomes, including cardiac allograft vasculopathy (CAV), graft failure, malignancy, and all-cause mortality.

METHODS

We conducted a mixed retrospective-prospective observational study of HT recipients with targeted sequencing for CHIP mutations (variant allele frequency [VAF] of ≥ 2%). The primary composite outcome was the first occurrence of CAV grade ≥ 2, graft failure, malignancy, cardiac retransplantation, or all-cause death. Secondary outcomes were the individual components of the composite primary outcome. Sensitivity analyses with base-case and extreme scenarios were performed.

RESULTS

Among 95 HT recipients, 30 had CHIP mutations (31.6%). DNMT3A mutations were most common (44.7%), followed by PPM1D (13.2%), SF3B1 (10.5%), TET2 (7.9%), and TP53 (7.9%). The only significant independent predictor of CHIP was age at enrollment or age at transplantation. After multivariable adjustment, CHIP mutations were not associated with the primary outcome, which occurred in 44 (46.3%) patients (HR = 0.487; 95% CI:0.197-1.204; P = 0.119), nor were they associated with mlalignancy alone, or death.

CONCLUSION

We demonstrated no association between CHIP mutations and post-transplant outcomes, including CAV, graft failure, malignancy, and all-cause mortality. In line with previously published data, our analysis provides additional evidence about the lack of clinical value of using CHIP mutations as a biomarker for surveillance in outcomes after HT.

Correlates and Consequences of Clonal Hematopoiesis Expansion Rate: A 15-Year Longitudinal Study of 6,986 Women

Clonal hematopoiesis of indeterminate potential (CHIP) is associated with increased mortality and malignancy risk, yet the determinants of clonal expansion remain poorly understood. We performed sequencing at >4,000x depth of coverage for CHIP mutations in 6,986 postmenopausal women from the Women's Health Initiative at two timepoints approximately 15 years apart. Among 3,685 mutations detected at baseline (VAF ≥ 0.5%), 50% progressed to CHIP (VAF ≥ 2%) at follow-up. We confirmed that clonal expansion is highly dependent on initial clone size and CHIP driver gene, with SF3B1 and JAK2 mutations exhibiting the fastest growth rate. We identified germline variants in TERT , IL6R , TCL1A , and MSI2 that modulate clonal expansion rate. Measured baseline leukocyte telomere length showed differential effects on incident CHIP risk, with shorter baseline leukocyte telomere length predisposing to incident PPM1D mutations and longer baseline leukocyte telomere length favoring incident DNMT3A mutations. We discovered that the IL6R missense variant p.Asp358Ala specifically impairs TET2 clonal expansion, supported by direct measurements of soluble interleukin-6 receptor and interleukin-6. Faster clonal growth rate was associated with increased risk of cytopenia, leukemia, and all-cause mortality. Notably, CHIP clonal expansion rate mediated 34.4% and 43.7% of the Clonal Hematopoiesis Risk Score's predictive value for leukemia and all-cause mortality, respectively. These findings reveal key biological determinants of CHIP progression and suggest that incorporating growth rate measurements could enhance risk stratification.

Licensing and niche competition in spermatogenesis: mathematical models suggest complementary regulation of tissue maintenance

To maintain and regenerate adult tissues after injury, division and differentiation of tissue-resident stem cells must be precisely regulated. It remains elusive which regulatory strategies prevent exhaustion or overgrowth of the stem cell pool, whether there is coordination between multiple mechanisms, and how to detect them from snapshots. In Drosophila testes, somatic stem cells transition to a state that licenses them to differentiate, but remain capable of returning to the niche and resuming cell division. Here, we build stochastic mathematical models for the somatic stem cell population to investigate how licensing contributes to homeostasis. We find that licensing, in combination with differentiation occurring in pairs, is sufficient to maintain homeostasis and prevent stem cell extinction from stochastic fluctuations. Experimental data have shown that stem cells are competing for niche access, and our mathematical models demonstrate that this contributes to the reduction in the variability of stem cell numbers but does not prevent extinction. Hence, a combination of both regulation strategies, licensing with pairwise differentiation and competition for niche access, may be needed to reduce variability and prevent extinction simultaneously.

Editorial for the Special Issue 'Molecular Mechanisms of Leukemia'

Leukemia encompasses a diverse and intricate group of hematological malignancies that arise from hematopoietic stem and progenitors (HSPCs) in the bone marrow [...].

Stem cell graft dose and composition could impact on the expansion of donor-derived clones after allogeneic hematopoietic stem cell transplantation - a virtual clinical trial

Introduction

Hematopoietic stem cell transplantation is a potentially curative intervention for a broad range of diseases. However, there is evidence that malignant or pre-malignant clones contained in the transplant can expand in the recipient and trigger donor-derived malignancies. This observation has gained much attention in the context of clonal hematopoiesis, a medical condition where significant amounts of healthy blood cells are derived from a small number of hematopoietic stem cell clones. In many cases the dominating clones carry mutations conferring a growth advantage and thus could undergo malignant transformation in the recipient. Since clonal hematopoiesis exists in a significant proportion of potential stem cell donors, a more detailed understanding of its role for stem cell transplantation is required.

Methods

We propose mechanistic computational models and perform virtual clinical trials to investigate clonal dynamics during and after allogenic hematopoietic stem cell transplantation. Different mechanisms of clonal expansion are considered, including mutation-related changes of stem cell proliferation and self-renewal, aberrant response of mutated cells to systemic signals, and self-sustaining chronic inflammation triggered by the mutated cells.

Results

Model simulations suggest that an aberrant response of mutated cells to systemic signals is sufficient to explain the frequently observed quick expansion of the mutated clone shortly after transplantation which is followed by a stabilization of the mutated cell number at a constant value. In contrary, a mutation-related increase of self-renewal or self-sustaining chronic inflammation lead to ongoing clonal expansion. Our virtual clinical trials suggest that a low number of transplanted stem cells per kg of body weight increases the transplantation-related expansion of donor-derived clones, whereas the transplanted progenitor dose or growth factor support after transplantation have no impact on clonal dynamics. Furthermore, in our simulations the change of the donors' variant allele frequencies in the year before stem cell donation is associated with the expansion of donor-derived clones in the recipient.

Discussion

This in silico study provides insights in the mechanisms leading to clonal expansion and identifies questions that could be addressed in future clinical trials.

Developmental hematopoietic stem cell variation explains clonal hematopoiesis later in life

Clonal hematopoiesis becomes increasingly common with age, but its cause is enigmatic because driver mutations are often absent. Serial observations infer weak selection indicating variants are acquired much earlier in life with unexplained initial growth spurts. Here we use fluctuating CpG methylation as a lineage marker to track stem cell clonal dynamics of hematopoiesis. We show, via the shared prenatal circulation of monozygotic twins, that weak selection conferred by stem cell variation created before birth can reliably yield clonal hematopoiesis later in life. Theory indicates weak selection will lead to dominance given enough time and large enough population sizes. Human hematopoiesis satisfies both these conditions. Stochastic loss of weakly selected variants is naturally prevented by the expansion of stem cell lineages during development. The dominance of stem cell clones created before birth is supported by blood fluctuating CpG methylation patterns that exhibit low correlation between unrelated individuals but are highly correlated between many elderly monozygotic twins. Therefore, clonal hematopoiesis driven by weak selection in later life appears to reflect variation created before birth.

The emerging role of clonal haematopoiesis in the pathogenesis of dilated cardiomyopathy

The increased sensitivity of novel DNA sequencing techniques has made it possible to identify somatic mutations in small circulating clones of haematopoietic stem cells. When the mutation affects a 'driver' gene, the mutant clone gains a competitive advantage and has the potential to expand over time, a phenomenon referred to as clonal haematopoiesis (CH), which is emerging as a new risk factor for various non-haematological conditions, most notably cardiovascular disease (e.g. heart failure). Dilated cardiomyopathy (DCM) is a form of non-ischaemic heart failure that is characterized by a heterogeneous aetiology. The first evidence is arising that CH plays an important role in the disease course in patients with DCM, and a strong association of CH with multiple aetiologies of DCM has been described (e.g. inflammation, chemotherapy, and atrial fibrillation). The myocardial inflammation induced by CH may be an important trigger for DCM development for an already susceptible heart, e.g. in the presence of genetic variants, environmental triggers, and comorbidities. Studies investigating the role of CH in the pathogenesis of DCM are expected to increase rapidly. To move the field forward, it will be important to report the methodology and results in a standardized manner, so results can be combined and compared. The accurate measurement of CH in patients with DCM can provide guidance of specific (anti-inflammatory) therapies, as mutations in the CH driver genes prime the inflammasome pathway.

Unidirectional association of clonal hematopoiesis with atherosclerosis development

Clonal hematopoiesis, a condition in which acquired somatic mutations in hematopoietic stem cells lead to the outgrowth of a mutant hematopoietic clone, is associated with a higher risk of hematological cancer and a growing list of nonhematological disorders, most notably atherosclerosis and associated cardiovascular disease. However, whether accelerated atherosclerosis is a cause or a consequence of clonal hematopoiesis remains a matter of debate. Some studies support a direct contribution of certain clonal hematopoiesis-related mutations to atherosclerosis via exacerbation of inflammatory responses, whereas others suggest that clonal hematopoiesis is a symptom rather than a cause of atherosclerosis, as atherosclerosis or related traits may accelerate the expansion of mutant hematopoietic clones. Here we combine high-sensitivity DNA sequencing in blood and noninvasive vascular imaging to investigate the interplay between clonal hematopoiesis and atherosclerosis in a longitudinal cohort of healthy middle-aged individuals. We found that the presence of a clonal hematopoiesis-related mutation confers an increased risk of developing de novo femoral atherosclerosis over a 6-year period, whereas neither the presence nor the extent of atherosclerosis affects mutant cell expansion during this timeframe. These findings indicate that clonal hematopoiesis unidirectionally promotes atherosclerosis, which should help translate the growing understanding of this condition into strategies for the prevention of atherosclerotic cardiovascular disease in individuals exhibiting clonal hematopoiesis.

Dynamically adjusted cell fate decisions and resilience to mutant invasion during steady-state hematopoiesis revealed by an experimentally parameterized mathematical model

A major next step in hematopoietic stem cell (HSC) biology is to enhance our quantitative understanding of cellular and evolutionary dynamics involved in undisturbed hematopoiesis. Mathematical models have been and continue to be key in this respect, and are most powerful when parameterized experimentally and containing sufficient biological complexity. In this paper, we use data from label propagation experiments in mice to parameterize a mathematical model of hematopoiesis that includes homeostatic control mechanisms as well as clonal evolution. We find that nonlinear feedback control can drastically change the interpretation of kinetic estimates at homeostasis. This suggests that short-term HSC and multipotent progenitors can dynamically adjust to sustain themselves temporarily in the absence of long-term HSCs, even if they differentiate more often than they self-renew in undisturbed homeostasis. Additionally, the presence of feedback control in the model renders the system resilient against mutant invasion. Invasion barriers, however, can be overcome by a combination of age-related changes in stem cell differentiation and evolutionary niche construction dynamics based on a mutant-associated inflammatory environment. This helps us understand the evolution of e.g., TET2 or DNMT3A mutants, and how to potentially reduce mutant burden.

Long-term longitudinal analysis of 4,187 participants reveals insights into determinants of clonal hematopoiesis

Clonal hematopoiesis of indeterminate potential (CHIP) is linked to diverse aging-related diseases, including hematologic malignancy and atherosclerotic cardiovascular disease (ASCVD). While CHIP is common among older adults, the underlying factors driving its development are largely unknown. To address this, we performed whole-exome sequencing on 8,374 blood DNA samples collected from 4,187 Atherosclerosis Risk in Communities Study (ARIC) participants over a median follow-up of 21 years. During this period, 735 participants developed incident CHIP. Splicing factor genes (SF3B1, SRSF2, U2AF1, and ZRSR2) and TET2 CHIP grow significantly faster than DNMT3A non-R882 clones. We find that age at baseline and sex significantly influence the incidence of CHIP, while ASCVD and other traditional ASCVD risk factors do not exhibit such associations. Additionally, baseline synonymous passenger mutations are strongly associated with CHIP status and are predictive of new CHIP clone acquisition and clonal growth over extended follow-up, providing valuable insights into clonal dynamics of aging hematopoietic stem and progenitor cells. This study also reveals associations between germline genetic variants and incident CHIP. Our comprehensive longitudinal assessment yields insights into cell-intrinsic and -extrinsic factors contributing to the development and progression of CHIP clones in older adults.

Clonal hematopoiesis of indeterminate potential and cardiovascular disease: Pathogenesis, clinical presentation, and future directions

Clonal hematopoiesis of indeterminate potential (CHIP) is a well-studied phenomenon in hematologic malignancies. With advancements in gene sampling and analysis and the use of large cohort studies, CHIP has recently been linked to cardiovascular disease (CVD). The relationship between CHIP and CVD appears to be bidirectional, with traditional risk factors for cardiovascular disease increasing the mutation burden in CHIP, and CHIP itself effecting the incidence or prognosis of a variety of CVD. The purpose of this review is to understand the epidemiology, risk factors, and pathogenesis of CHIP in the context of various CVD conditions.

Gain-of-function human UNC93B1 variants cause systemic lupus erythematosus and chilblain lupus

UNC93B1 is a transmembrane domain protein mediating the signaling of endosomal Toll-like receptors (TLRs). We report five families harboring rare missense substitutions (I317M, G325C, L330R, R466S, and R525P) in UNC93B1 causing systemic lupus erythematosus (SLE) or chilblain lupus (CBL) as either autosomal dominant or autosomal recessive traits. As for a D34A mutation causing murine lupus, we recorded a gain of TLR7 and, to a lesser extent, TLR8 activity with the I317M (in vitro) and G325C (in vitro and ex vivo) variants in the context of SLE. Contrastingly, in three families segregating CBL, the L330R, R466S, and R525P variants were isomorphic with respect to TLR7 activity in vitro and, for R525P, ex vivo. Rather, these variants demonstrated a gain of TLR8 activity. We observed enhanced interaction of the G325C, L330R, and R466S variants with TLR8, but not the R525P substitution, indicating different disease mechanisms. Overall, these observations suggest that UNC93B1 mutations cause monogenic SLE or CBL due to differentially enhanced TLR7 and TLR8 signaling.

Genetic variation across and within individuals

Germline variation and somatic mutation are intricately connected and together shape human traits and disease risks. Germline variants are present from conception, but they vary between individuals and accumulate over generations. By contrast, somatic mutations accumulate throughout life in a mosaic manner within an individual due to intrinsic and extrinsic sources of mutations and selection pressures acting on cells. Recent advancements, such as improved detection methods and increased resources for association studies, have drastically expanded our ability to investigate germline and somatic genetic variation and compare underlying mutational processes. A better understanding of the similarities and differences in the types, rates and patterns of germline and somatic variants, as well as their interplay, will help elucidate the mechanisms underlying their distinct yet interlinked roles in human health and biology.

Decoding Clonal Hematopoiesis: Emerging Themes and Novel Mechanistic Insights

Clonal hematopoiesis (CH), the relative expansion of mutant clones, is derived from hematopoietic stem cells (HSCs) with acquired somatic or cytogenetic alterations that improve cellular fitness. Individuals with CH have a higher risk for hematological and non-hematological diseases, such as cardiovascular disease, and have an overall higher mortality rate. Originally thought to be restricted to a small fraction of elderly people, recent advances in single-cell sequencing and bioinformatics have revealed that CH with multiple expanded mutant clones is universal in the elderly population. Just a few years ago, phylogenetic reconstruction across the human lifespan and novel sensitive sequencing techniques showed that CH can start earlier in life, decades before it was thought possible. These studies also suggest that environmental factors acting through aberrant inflammation might be a common theme promoting clonal expansion and disease progression. However, numerous aspects of this phenomenon remain to be elucidated and the precise mechanisms, context-specific drivers, and pathways of clonal expansion remain to be established. Here, we review our current understanding of the cellular mechanisms driving CH and specifically focus on how pro-inflammatory factors affect normal and mutant HSC fates to promote clonal selection.

Cost-Effective and Scalable Clonal Hematopoiesis Assay Provides Insight into Clonal Dynamics

Clonal hematopoiesis of indeterminate potential (CHIP) is a common age-related phenomenon in which hematopoietic stem cells acquire mutations in a select set of genes commonly mutated in myeloid neoplasia which then expand clonally. Current sequencing assays to detect CHIP mutations are not optimized for the detection of these variants and can be cost-prohibitive when applied to large cohorts or to serial sequencing. In this study, an affordable (approximately US $8 per sample), accurate, and scalable sequencing assay for CHIP is introduced and validated. The efficacy of the assay was demonstrated by identifying CHIP mutations in a cohort of 456 individuals with DNA collected at multiple time points in Vanderbilt University's biobank and quantifying clonal expansion rates over time. A total of 101 individuals with CHIP/clonal cytopenia of undetermined significance were identified, and individual-level clonal expansion rate was calculated using the variant allele fraction at both time points. Differences in clonal expansion rate by driver gene were observed, but there was also significant individual-level heterogeneity, emphasizing the multifactorial nature of clonal expansion. Additionally, mutation co-occurrence and clonal competition between multiple driver mutations were explored.

Considering clonal hematopoiesis of indeterminate potential in space radiation risk analysis for hematologic cancers and cardiovascular disease

BACKGROUND

Expanding human presence in space through long-duration exploration missions and commercial space operations warrants improvements in approaches for quantifying crew space radiation health risks. Currently, risk assessment models for radiogenic cancer and cardiovascular disease consider age, sex, and tobacco use, but do not incorporate other modifiable (e.g., body weight, physical activity, diet, environment) and non-modifiable individual risk factors (e.g., genetics, medical history, race/ethnicity, family history) that may greatly influence crew health both in-mission and long-term. For example, clonal hematopoiesis of indeterminate potential (CHIP) is a relatively common age-related condition that is an emerging risk factor for a variety of diseases including cardiovascular disease and cancer. CHIP carrier status may therefore exacerbate health risks associated with space radiation exposure.

METHODS

In the present study, published CHIP hazard ratios were used to modify background hazard rates for coronary heart disease, stroke, and hematologic cancers in the National Aeronautics and Space Administration space radiation risk assessment model. The risk of radiation exposure-induced death for these endpoints was projected for a future Mars exploration mission scenario.

RESULTS

Here we show appreciable increases in the lifetime risk of exposure-induced death for hematologic malignancies, coronary heart disease, and stroke, which are observed as a function of age after radiation exposure for male and female crew members that are directly attributable to the elevated health risks for CHIP carriers.

CONCLUSIONS

We discuss the importance of evaluating individual risk factors such as CHIP as part of a comprehensive space radiation risk assessment strategy aimed at effective risk communication and disease surveillance for astronauts embarking on future exploration missions.

Solid Organ Transplant Recipients Exhibit More TET2-Mutant Clonal Hematopoiesis of Indeterminate Potential Not Driven by Increased Transplantation Risk

PURPOSE

Solid organ transplant recipients comprise a unique population of immunosuppressed patients with increased risk of malignancy, including hematologic neoplasms. Clonal hematopoiesis of indeterminate potential (CHIP) represents a known risk factor for hematologic malignancy and this study describes the prevalence and patterns of CHIP mutations across several types of solid organ transplants.

EXPERIMENTAL DESIGN

We use two national biobank cohorts comprised of >650,000 participants with linked genomic and longitudinal phenotypic data to describe the features of CHIP across 2,610 individuals who received kidney, liver, heart, or lung allografts.

RESULTS

We find individuals with an allograft before their biobank enrollment had an increased prevalence of TET2 mutations (OR, 1.90; P = 4.0e-4), but individuals who received transplants post-enrollment had a CHIP mutation spectrum similar to that of the general population, without enrichment of TET2. In addition, we do not observe an association between CHIP and risk of incident transplantation among the overall population (HR, 1.02; P = 0.91). And in an exploratory analysis, we do not find evidence for a strong association between CHIP and rates of transplant complications such as rejection or graft failure.

CONCLUSIONS

These results demonstrate that recipients of solid organ transplants display a unique pattern of clonal hematopoiesis with enrichment of TET2 driver mutations, the causes of which remain unclear and are deserving of further study.

Dynamics of clonal hematopoiesis under DNA-damaging treatment in patients with ovarian cancer

Clonal hematopoiesis (CH) driven by mutations in the DNA damage response (DDR) pathway is frequent in patients with cancer and is associated with a higher risk of therapy-related myeloid neoplasms (t-MNs). Here, we analyzed 423 serial whole blood and plasma samples from 103 patients with relapsed high-grade ovarian cancer receiving carboplatin, poly(ADP-ribose) polymerase inhibitor (PARPi) and heat shock protein 90 inhibitor (HSP90i) treatment within the phase II EUDARIO trial using error-corrected sequencing of 72 genes. DDR-driven CH was detected in 35% of patients and was associated with longer duration of prior PARPi treatment. TP53- and PPM1D-mutated clones exhibited substantially higher clonal expansion rates than DNMT3A- or TET2-mutated clones during treatment. Expansion of DDR clones correlated with HSP90i exposure across the three study arms and was partially abrogated by the presence of germline mutations related to homologous recombination deficiency. Single-cell DNA sequencing of selected samples revealed clonal exclusivity of DDR mutations, and identified DDR-mutated clones as the origin of t-MN in two investigated cases. Together, these results provide unique insights into the architecture and the preferential selection of DDR-mutated hematopoietic clones under intense DNA-damaging treatment. Specifically, PARPi and HSP90i therapies pose an independent risk for the expansion of DDR-CH in a dose-dependent manner.

Clonal hematopoiesis and its impact on the aging osteo-hematopoietic niche

Clonal hematopoiesis (CH) defines a premalignant state predominantly found in older persons that increases the risk of developing hematologic malignancies and age-related inflammatory diseases. However, the risk for malignant transformation or non-malignant disorders is variable and difficult to predict, and defining the clinical relevance of specific candidate driver mutations in individual carriers has proved to be challenging. In addition to the cell-intrinsic mechanisms, mutant cells rely on and alter cell-extrinsic factors from the bone marrow (BM) niche, which complicates the prediction of a mutant cell's fate in a shifting pre-malignant microenvironment. Therefore, identifying the insidious and potentially broad impact of driver mutations on supportive niches and immune function in CH aims to understand the subtle differences that enable driver mutations to yield different clinical outcomes. Here, we review the changes in the aging BM niche and the emerging evidence supporting the concept that CH can progressively alter components of the local BM microenvironment. These alterations may have profound implications for the functionality of the osteo-hematopoietic niche and overall bone health, consequently fostering a conducive environment for the continued development and progression of CH. We also provide an overview of the latest technology developments to study the spatiotemporal dependencies in the CH BM niche, ideally in the context of longitudinal studies following CH over time. Finally, we discuss aspects of CH carrier management in clinical practice, based on work from our group and others.

Single-Cell DNA Sequencing Reveals an Evolutionary Pattern of CHIP in Transplant Eligible Multiple Myeloma Patients

Clonal hematopoiesis of indeterminate potential (CHIP) refers to the phenomenon where a hematopoietic stem cell acquires fitness-increasing mutation(s), resulting in its clonal expansion. CHIP is frequently observed in multiple myeloma (MM) patients, and it is associated with a worse outcome. High-throughput amplicon-based single-cell DNA sequencing was performed on circulating CD34+ cells collected from twelve MM patients before autologous stem cell transplantation (ASCT). Moreover, in four MM patients, longitudinal samples either before or post-ASCT were collected. Single-cell sequencing and data analysis were assessed using the MissionBio Tapestri® platform, with a targeted panel of 20 leukemia-associated genes. We detected CHIP pathogenic mutations in 6/12 patients (50%) at the time of transplant. The most frequently mutated genes were TET2, EZH2, KIT, DNMT3A, and ASXL1. In two patients, we observed co-occurring mutations involving an epigenetic modifier (i.e., DNMT3A) and/or a gene involved in splicing machinery (i.e., SF3B1) and/or a tyrosine kinase receptor (i.e., KIT) in the same clone. Longitudinal analysis of paired samples revealed a positive selection of mutant high-fitness clones over time, regardless of their affinity with a major or minor sub-clone. Copy number analysis of the panel of all genes did not show any numerical alterations present in stem cell compartment. Moreover, we observed a tendency of CHIP-positive patients to achieve a suboptimal response to therapy compared to those without. A sub-clone dynamic of high-fitness mutations over time was confirmed.

The lifelong natural history of clonal hematopoiesis and its links to myeloid neoplasia

ABSTRACT

The study of somatic mutations and the associated clonal mosaicism across the human body has transformed our understanding of aging and its links to cancer. In proliferative human tissues, stem cells compete for dominance, and those with an advantage expand clonally to outgrow their peers. In the hematopoietic system, such expansion is termed clonal hematopoiesis (CH). The forces driving competition, namely heterogeneity of the hematopoietic stem cell (HSC) pool and attrition of their environment, become increasingly prominent with age. As a result, CH becomes progressively more common through life to the point of becoming essentially ubiquitous. We are beginning to unravel the specific intracellular and extracellular factors underpinning clonal behavior, with somatic mutations in specific driver genes, inflammation, telomere maintenance, extraneous exposures, and inherited genetic variation among the important players. The inevitability of CH with age combined with its unequivocal links to myeloid cancers poses a scientific and clinical challenge. Specifically, we need to decipher the factors determining clonal behavior and develop prognostic tools to identify those at high risk of malignant progression, for whom preventive interventions may be warranted. Here, we discuss how recent advances in our understanding of the natural history of CH have provided important insights into these processes and helped define future avenues of investigation.

High-sensitivity analysis of clonal hematopoiesis reveals increased clonal complexity of potential-driver mutations in severe COVID-19 patients

Whether Clonal Hematopoiesis (CH) represents a risk factor for severity of the COVID-19 disease remains a controversial issue. We report the first high- sensitivity analysis of CH in COVID-19 patients (threshold of detection at 0.5% vs 1 or 2% in previous studies). We analyzed 24 patients admitted to ICU for COVID-19 (COV-ICU) and 19 controls, including healthy subjects and asymptomatic SARS-CoV2-positive individuals. Despite the significantly higher numbers of CH mutations identified (80% mutations with <2% variant allele frequency, VAF), we did not find significant differences between COV-ICU patients and controls in the prevalence of CH or in the numbers, VAF or functional categories of the mutated genes, suggesting that CH is not overrepresented in patients with COVID-19. However, when considering potential drivers CH mutations (CH-PD), COV-ICU patients showed higher clonal complexity, in terms of both mutation numbers and VAF, and enrichment of variants reported in myeloid neoplasms. However, we did not score an impact of increased CH-PD on patient survival or clinical parameters associated with inflammation. These data suggest that COVID-19 influence the clonal composition of the peripheral blood and call for further investigations addressing the potential long-term clinical impact of CH on people experiencing severe COVID-19. We acknowledge that it will indispensable to perform further studies on larger patient cohorts in order to validate and generalize our conclusions. Moreover, we performed CH analysis at a single time point. It will be necessary to consider longitudinal approaches with long periods of follow-up in order to assess if the COVID-19 disease could have an impact on the evolution of CH and long-term consequences in patients that experienced severe COVID-19.

Regulators of clonal hematopoiesis and physiological consequences of this condition

Clonal hematopoiesis (CH) is a prevalent condition that results from somatic mutations in hematopoietic stem cells. When these mutations occur in "driver" genes, they can potentially confer fitness advantages to the affected cells, leading to a clonal expansion. While most clonal expansions of mutant cells are generally considered to be asymptomatic since they do not impact overall blood cell numbers, CH carriers face long-term risks of all-cause mortality and age-associated diseases, including cardiovascular disease and hematological malignancies. While considerable research has focused on understanding the association between CH and these diseases, less attention has been given to exploring the regulatory factors that contribute to the expansion of the driver gene clone. This review focuses on the association between environmental stressors and inherited genetic risk factors in the context of CH development. A better understanding of how these stressors impact CH development will facilitate mechanistic studies and potentially lead to new therapeutic avenues to treat individuals with this condition.

Causes and consequences of clonal hematopoiesis

ABSTRACT

Clonal hematopoiesis (CH) is described as the outsized contribution of expanded clones of hematopoietic stem and progenitor cells (HSPCs) to blood cell production. The prevalence of CH increases dramatically with age. CH can be caused by somatic mutations in individual genes or by gains and/or losses of larger chromosomal segments. CH is a premalignant state; the somatic mutations detected in CH are the initiating mutations for hematologic malignancies, and CH is a strong predictor of the development of blood cancers. Moreover, CH is associated with nonmalignant disorders and increased overall mortality. The somatic mutations that drive clonal expansion of HSPCs can alter the function of terminally differentiated blood cells, including the release of elevated levels of inflammatory cytokines. These cytokines may then contribute to a broad range of inflammatory disorders that increase in prevalence with age. Specific somatic mutations in the peripheral blood in coordination with blood count parameters can powerfully predict the development of hematologic malignancies and overall mortality in CH. In this review, we summarize the current understanding of CH nosology and origins. We provide an overview of available tools for risk stratification and discuss management strategies for patients with CH presenting to hematology clinics.

Preleukemic single-cell landscapes reveal mutation-specific mechanisms and gene programs predictive of AML patient outcomes

Acute myeloid leukemia (AML) and myeloid neoplasms develop through acquisition of somatic mutations that confer mutation-specific fitness advantages to hematopoietic stem and progenitor cells. However, our understanding of mutational effects remains limited to the resolution attainable within immunophenotypically and clinically accessible bulk cell populations. To decipher heterogeneous cellular fitness to preleukemic mutational perturbations, we performed single-cell RNA sequencing of eight different mouse models with driver mutations of myeloid malignancies, generating 269,048 single-cell profiles. Our analysis infers mutation-driven perturbations in cell abundance, cellular lineage fate, cellular metabolism, and gene expression at the continuous resolution, pinpointing cell populations with transcriptional alterations associated with differentiation bias. We further develop an 11-gene scoring system (Stem11) on the basis of preleukemic transcriptional signatures that predicts AML patient outcomes. Our results demonstrate that a single-cell-resolution deep characterization of preleukemic biology has the potential to enhance our understanding of AML heterogeneity and inform more effective risk stratification strategies.

Cost-effective and scalable clonal hematopoiesis assay provides insight into clonal dynamics

Clonal hematopoiesis of indeterminate potential (CHIP) is a common age-related phenomenon that occurs when hematopoietic stem cells acquire mutations in a select set of genes commonly mutated in myeloid neoplasia which then expand clonally. Current sequencing assays to detect CHIP are not optimized for the detection of these variants and can be cost-prohibitive when applied to large cohorts or serial sequencing. Here, we present and validate a CHIP targeted sequencing assay that is affordable (∼$8/sample), accurate and highly scalable. To demonstrate the utility of this assay, we detected CHIP in a cohort of 456 individuals with DNA collected at multiple timepoints in the Vanderbilt BioVU biobank and quantified clonal expansion rates over time. A total of 101 individuals with CHIP were identified, and individual-level clonal expansion rate was calculated using the variant allele fraction (VAF) at both timepoints. Differences in clonal expansion rate by driver gene were observed, but there was also significant individual-level heterogeneity, emphasizing the multifactorial nature of clonal expansion. We further describe the mutation co-occurrence and clonal competition between multiple driver mutations.

Hematopoietic-specific heterozygous loss of Dnmt3a exacerbates colitis-associated colon cancer

Clonal hematopoiesis (CH) is defined as clonal expansion of mutant hematopoietic stem cells absent diagnosis of a hematologic malignancy. Presence of CH in solid tumor patients, including colon cancer, correlates with shorter survival. We hypothesized that bone marrow-derived cells with heterozygous loss-of-function mutations of DNMT3A, the most common genetic alteration in CH, contribute to the pathogenesis of colon cancer. In a mouse model that combines colitis-associated colon cancer (CAC) with experimental CH driven by Dnmt3a+/Δ, we found higher tumor penetrance and increased tumor burden compared with controls. Histopathological analysis revealed accentuated colonic epithelium injury, dysplasia, and adenocarcinoma formation. Transcriptome profiling of colon tumors identified enrichment of gene signatures associated with carcinogenesis, including angiogenesis. Treatment with the angiogenesis inhibitor axitinib eliminated the colon tumor-promoting effect of experimental CH driven by Dnmt3a haploinsufficiency and rebalanced hematopoiesis. This study provides conceptually novel insights into non-tumor-cell-autonomous effects of hematopoietic alterations on colon carcinogenesis and identifies potential therapeutic strategies.

U2AF1 pathogenic variants in myeloid neoplasms and precursor states: distribution of co-mutations and prognostic heterogeneity

We have previously recognized the genotypic and prognostic heterogeneity of U2AF1 mutations (MT) in myelofibrosis (MF) and myelodysplastic syndromes (MDS). In the current study, we considered 179 U2AF1-mutated patients with clonal cytopenia of undetermined significance (CCUS; n = 22), MDS (n = 108), MDS/acute myeloid leukemia (AML; n = 18) and AML (n = 31). U2AF1 variants included S34 (60%), Q157 (35%), and others (5%): corresponding mutational frequencies were 45%, 55%, and 0% in CCUS; 57%, 39%, and 4% in MDS; 61%, 33%, and 6% in MDS/AML; and 55%, 35% and 10% in AML (P = 0.17, 0.36 and 0.09), respectively. Concurrent mutations included ASXL1 (37%), BCOR (19%), RUNX1 (14%), TET2 (15%), DNMT3A (10%), NRAS/KRAS (8%), TP53 (8%), JAK2 (5.5%) and SETBP1 (5%). The two most frequent U2AF1 MT were S34F (n = 97) and Q157P (n = 46); concurrent MT were more likely to be seen with the latter (91% vs 74%; P = 0.01) and abnormal karyotype with the former (70% vs 62%; P = 0.05). U2AF1 S34F MT clustered with BCOR (P = 0.04) and Q157P MT with ASXL1 (P = 0.01) and TP53 (P = 0.03). The median overall survival (OS) in months was significantly worse in AML (14.2) vs MDS/AML (27.3) vs MDS (33.7; P = 0.001); the latter had similar OS with CCUS (30.0). In morphologically high-risk disease (n = 49), defined by ≥10% blood or bone marrow blasts (i.e., AML or MDS/AML), median OS was 14.2 with Q157P vs 37.1 months in the presence of S34F (P = 0.008); transplant-adjusted multivariable analysis confirmed the detrimental impact of Q157P (P = 0.01) on survival and also identified JAK2 MT as an additional risk factor (P = 0.02). OS was favorably affected by allogeneic hematopoietic stem cell transplantation (HR: 0.16, 95% CI; 0.04-0.61, P = 0.007). The current study defines the prevalence and co-mutational profiles of U2AF1 pathogenic variants in AML, MDS/AML, MDS, and CCUS, and suggests prognostic heterogeneity in patients with ≥10% blasts.

Long-term longitudinal analysis of 4,187 participants reveals new insights into determinants of incident clonal hematopoiesis

Clonal hematopoiesis (CH), characterized by blood cells predominantly originating from a single mutated hematopoietic stem cell, is linked to diverse aging-related diseases, including hematologic malignancy and atherosclerotic cardiovascular disease (ASCVD). While CH is common among older adults, the underlying factors driving its development are largely unknown. To address this, we performed whole-exome sequencing on 8,374 blood DNA samples collected from 4,187 Atherosclerosis Risk in Communities Study (ARIC) participants over a median follow-up of 21 years. During this period, 735 participants developed incident CH. We found that age at baseline, sex, and dyslipidemia significantly influence the incidence of CH, while ASCVD and other traditional risk factors for ASCVD did not exhibit such associations. Our study also revealed associations between germline genetic variants and incident CH, prioritizing genes in CH development. Our comprehensive longitudinal assessment yields novel insights into the factors contributing to incident CH in older adults.

Clonal haematopoiesis and dysregulation of the immune system

Age-related diseases are frequently linked to pathological immune dysfunction, including excessive inflammation, autoreactivity and immunodeficiency. Recent analyses of human genetic data have revealed that somatic mutations and mosaic chromosomal alterations in blood cells - a condition known as clonal haematopoiesis (CH) - are associated with ageing and pathological immune dysfunction. Indeed, large-scale epidemiological studies and experimental mouse models have demonstrated that CH can promote cardiovascular disease, chronic obstructive pulmonary disease, chronic liver disease, osteoporosis and gout. The genes most frequently mutated in CH, the epigenetic regulators TET2 and DNMT3A, implicate increased chemokine expression and inflammasome hyperactivation in myeloid cells as a possible mechanistic connection between CH and age-related diseases. In addition, TET2 and DNMT3A mutations in lymphoid cells have been shown to drive methylation-dependent alterations in differentiation and function. Here we review the observational and mechanistic studies describing the connection between CH and pathological immune dysfunction, the effects of CH-associated genetic alterations on the function of myeloid and lymphoid cells, and the clinical and therapeutic implications of CH as a target for immunomodulation.

Progressive disruption of hematopoietic architecture from clonal hematopoiesis to MDS

Clonal hematopoiesis of indeterminate potential (CHIP) describes the age-related acquisition of somatic mutations in hematopoietic stem/progenitor cells (HSPC) leading to clonal blood cell expansion. Although CHIP mutations drive myeloid malignancies like myelodysplastic syndromes (MDS) it is unknown if clonal expansion is attributable to changes in cell type kinetics, or involves reorganization of the hematopoietic hierarchy. Using computational modeling we analyzed differentiation and proliferation kinetics of cultured hematopoietic stem cells (HSC) from 8 healthy individuals, 7 CHIP, and 10 MDS patients. While the standard hematopoietic hierarchy explained HSPC kinetics in healthy samples, 57% of CHIP and 70% of MDS samples were best described with alternative hierarchies. Deregulated kinetics were found at various HSPC compartments with high inter-individual heterogeneity in CHIP and MDS, while altered HSC rates were most relevant in MDS. Quantifying kinetic heterogeneity in detail, we show that reorganization of the HSPC compartment is already detectable in the premalignant CHIP state.

A genotype-first approach identifies high incidence of NF1 pathogenic variants with distinct disease associations

Loss of function variants in the NF1 gene cause neurofibromatosis type 1 (NF1), a genetic disorder characterized by complete penetrance, prevalence of 1 in 3,000, characteristic physical exam findings, and a substantially increased risk for malignancy. However, our understanding of the disorder is entirely based on patients ascertained through phenotype-first approaches. Leveraging a genotype-first approach in two large patient cohorts, we demonstrate unexpectedly high prevalence (1 in 450-750) of NF1 pathogenic variants. Half were identified in individuals lacking clinical features of NF1, with many appearing to have post-zygotic mosaicism for the identified variant. Incidentally discovered variants were not associated with classic NF1 features but were associated with an increased incidence of malignancy compared to a control population. Our findings suggest that NF1 pathogenic variants are substantially more common than previously thought, often characterized by somatic mosaicism and reduced penetrance, and are important contributors to cancer risk in the general population.

Clonal hematopoiesis and inflammation - the perpetual cycle

Acquired genetic or cytogenetic alterations in a blood stem cell that confer clonal fitness promote its relative expansion leading to clonal hematopoiesis (CH). Despite a largely intact hematopoietic output, CH is associated with a heightened risk of progression to hematologic malignancies and with non-hematologic health manifestations, including cardiovascular disease and overall mortality. We focus on the evidence for the role of inflammation in establishing, maintaining and reciprocally being affected by CH. We describe the known pro-inflammatory signals associated with CH and preclinical studies that elucidated the cellular mechanisms involved. We review the evolving literature on early-onset CH in germline predisposition conditions and the possible role of immune dysregulation in this context.

Clonal hematopoiesis of indeterminate potential and outcomes after heart transplantation: A multicenter study

Cardiac allograft vasculopathy (CAV) is a leading cause of late graft failure and mortality after heart transplantation (HT). Sharing some features with atherosclerosis, CAV results in diffuse narrowing of the epicardial coronaries and microvasculature, with consequent graft ischemia. Recently, clonal hematopoiesis of indeterminate potential (CHIP) has emerged as a risk factor for cardiovascular disease and mortality. We aimed to investigate the relationship between CHIP and posttransplant outcomes, including CAV. We analyzed 479 HT recipients with stored DNA samples at 2 high-volume transplant centers, Vanderbilt University Medical Center and Columbia University Irving Medical Center. We explored the association between the presence of CHIP mutations with CAV and mortality after HT. In this case-control analysis, carriers of CHIP mutations were not at increased risk of CAV or mortality after HT. In a large multicenter genomics study of the heart transplant population, the presence of CHIP mutations was not associated with an increased risk of CAV or posttransplant mortality.

Birth Weight Is Associated With Clonal Hematopoiesis of Indeterminate Potential and Cardiovascular Outcomes in Adulthood

Background High and low birth weight are independently associated with increased cardiovascular disease risk in adulthood. Clonal hematopoiesis of indeterminate potential (CHIP), the age-related clonal expansion of hematopoietic cells with preleukemic somatic mutations, predicts incident cardiovascular disease independent of traditional cardiovascular risk factors. Whether birth weight predicts development of CHIP later in life is unknown. Methods and Results A total of 221 047 adults enrolled in the UK Biobank with whole exome sequences and self-reported birth weight were analyzed. Of those, 22 030 (11.5%) had low (<2.5 kg) and 29 292 (14.7%) high birth weight (>4.0 kg). CHIP prevalence was higher among participants with low (6.0%, P=0.049) and high (6.3%, P<0.001) versus normal birth weight (5.7%, ref.). Multivariable-adjusted logistic regression analyses demonstrated that each 1-kg increase in birth weight was associated with a 3% increased risk of CHIP (odds ratio, 1.03 [95% CI, 1.00-1.06]; P=0.04), driven by a stronger association observed between birth weight and DNMT3A CHIP (odds ratio, 1.04 per 1-kg increase [95% CI, 1.01-1.08]; P=0.02). Mendelian randomization analyses supported a causal relationship of longer gestational age at delivery with DNMT3A CHIP. Multivariable Cox regression demonstrated that CHIP was independently and additively associated with incident cardiovascular disease or death across birth weight groups, with highest absolute risks in those with CHIP plus high or low birth weight. Conclusions Higher birth weight is associated with increased risk of developing CHIP in midlife, especially DNMT3A CHIP. These findings identify a novel risk factor for CHIP and provide insights into the relationships among early-life environment, CHIP, cancer, and cardiovascular disease.

Unraveling Heterogeneity in the Aging Hematopoietic Stem Cell Compartment: An Insight From Single-cell Approaches

Specific cell types and, therefore, organs respond differently during aging. This is also true for the hematopoietic system, where it has been demonstrated that hematopoietic stem cells alter a variety of features, such as their metabolism, and accumulate DNA damage, which can lead to clonal outgrowth over time. In addition, profound changes in the bone marrow microenvironment upon aging lead to senescence in certain cell types such as mesenchymal stem cells and result in increased inflammation. This heterogeneity makes it difficult to pinpoint the molecular drivers of organismal aging gained from bulk approaches, such as RNA sequencing. A better understanding of the heterogeneity underlying the aging process in the hematopoietic compartment is, therefore, needed. With the advances of single-cell technologies in recent years, it is now possible to address fundamental questions of aging. In this review, we discuss how single-cell approaches can and indeed are already being used to understand changes observed during aging in the hematopoietic compartment. We will touch on established and novel methods for flow cytometric detection, single-cell culture approaches, and single-cell omics.