Clonal hematopoiesis in patients with rheumatoid arthritis

Association Between Rheumatoid Arthritis and Clonal Hematopoiesis: A Mendelian Randomization Study

Immunity activation and inflammation are the main characteristics of rheumatoid arthritis and clonal hematopoiesis. However, it remains unclear whether rheumatoid arthritis increase the risk of clonal hematopoiesis. Here, a Mendelian randomization (MR) analysis was conduct to explore the causal effects of rheumatoid arthritis on clonal hematopoiesis. Summary statistics data of rheumatoid arthritis (13,838 cases and 33,742 controls) and clonal hematopoiesis (10,203 cases and 173,918 controls) derived from a genomewide association study were selected to analyze. We selected inverse-variance weighted, MR-Egger, weighted median, simple mode, and weighted mode to evaluate the causal effect of rheumatoid arthritis on clonal hematopoiesis. The two-sample MR analysis suggested a strong causal relationship between rheumatoid arthritis and clonal hematopoiesis by inverse-variance weighted (OR = 1.002311673, 95% CI [1.000110757, 1.004517433], p = .039706) and weighted median (OR = 1.002311673, 95% CI [1.000110757, 1.004517433], p = .039518447) methods. No significant pleiotropy or heterogeneity was found in the sensitivity analysis. These results supported a potentially causal relationship between rheumatoid arthritis and clonal hematopoiesis, and the exposure of rheumatoid arthritis increased the risks of clonal hematopoiesis. Our findings highlight the importance of how chronic inflammation and immune activation induced rheumatoid arthritis enhances the risks of clonal hematopoiesis, and that early intervention with rheumatoid arthritis patients might reduce the clonal hematopoiesis risks in rheumatoid arthritis patients. Moreover, our study provides clues for prediction of risk factors and potential mechanisms of clonal hematopoiesis.

Clonal hematopoiesis driven by mutated DNMT3A promotes inflammatory bone loss

Clonal hematopoiesis of indeterminate potential (CHIP) arises from aging-associated acquired mutations in hematopoietic progenitors, which display clonal expansion and produce phenotypically altered leukocytes. We associated CHIP-DNMT3A mutations with a higher prevalence of periodontitis and gingival inflammation among 4,946 community-dwelling adults. To model DNMT3A-driven CHIP, we used mice with the heterozygous loss-of-function mutation R878H, equivalent to the human hotspot mutation R882H. Partial transplantation with Dnmt3aR878H/+ bone marrow (BM) cells resulted in clonal expansion of mutant cells into both myeloid and lymphoid lineages and an elevated abundance of osteoclast precursors in the BM and osteoclastogenic macrophages in the periphery. DNMT3A-driven clonal hematopoiesis in recipient mice promoted naturally occurring periodontitis and aggravated experimentally induced periodontitis and arthritis, associated with enhanced osteoclastogenesis, IL-17-dependent inflammation and neutrophil responses, and impaired regulatory T cell immunosuppressive activity. DNMT3A-driven clonal hematopoiesis and, subsequently, periodontitis were suppressed by rapamycin treatment. DNMT3A-driven CHIP represents a treatable state of maladaptive hematopoiesis promoting inflammatory bone loss.

Clonal expansion in normal tissues

Cancer originates from a single ancestral cell that acquires a driver mutation, which confers a growth or survival advantage, followed by the acquisition of additional driver mutations by descendant cells. Recently, it has become evident that somatic cell mutations accumulate in normal tissues with aging and exposure to environmental factors, such as alcohol, smoking, and UV rays, increases the mutation rate. Clones harboring driver mutations expand with age, leading to tissue remodeling. Lineage analysis of myeloproliferative neoplasms and der(1;16)-positive breast cancer revealed that driver mutations were acquired early in our lives and that the development of cancer takes decades, unveiling the previously unknown early process of cancer development. Evidence that clonal hematopoiesis affects various diseases, including nonneoplastic diseases, highlights the potential role of the identification and functional analysis of mutated clones in unraveling unknown pathologies. In this review, we summarize the recent updates on clonal expansion in normal tissues and the natural history of cancer revealed through lineage analysis of noncancerous and cancerous tissues.

Genetic Approaches to Study Rheumatic Diseases and Its Implications in Clinical Practice

Patients with rare and complex rheumatic diseases (RDs) present with immense clinical variability inherent to all immunologic diseases. In addition to systemic and organ-specific inflammation, patients may display features of immunodeficiency or allergy, which may represent major diagnostic and therapeutic challenges. The person's genetic architecture has been a well-established risk factor for patients with RDs, albeit to variable degrees. Patients with early-onset diseases and/or positive family history (FH) have a strong genetic component, whereas patients with late-onset RDs demonstrate a more complex interplay of genetic and environmental risk factors. Overall, the genetic studies in patients with RDs have been instrumental to our understanding of innate and adaptive immunity in human health and disease. The elucidation of the molecular causes underlying rare diseases has played a major role in the identification of genes that are critical in the regulation of inflammatory responses. In addition, studies of patients with rare disorders may help determine the mechanisms of more complex autoimmune diseases by identifying variants with small effect sizes in the same genes. In contrast, studies of patients with common RDs are conducted in cohorts of patients with well-established phenotypes and ancestry-matched controls, and they aim to discover disease-related pathways that can inform the development of novel targeted therapies. Knowing the genetic cause of a disease has helped patients and families understand the disease progression and outcome. Here, we discuss the current understanding of genetic heritability and challenges in the diagnosis of RDs in patients and how this field may develop in the future.

Clonal hematopoiesis and autoimmunity

Clonal hematopoiesis (CH) has been associated with aging, occurring in about 10% of individuals aged >70 years, and immune dysfunction. Aged hematopoietic stem and progenitor cells exhibit pathological changes in immune function and activation of inflammatory pathways. CH clones commonly harbor a loss of function mutation in DNMT3A or TET2, which causes increased expression of inflammatory signaling genes, a proposed mechanism connected to CH and the development of age-related diseases. Additionally, inflammation may stress the hematopoietic compartment, driving the expansion of mutant clones. While the epidemiologic overlap between CH, hematologic malignancies, and atherosclerotic cardiovascular diseases has been reported, the mechanisms linking these concepts are largely unknown and merit much further investigation. Here, we review studies highlighting the interplay between CH, inflamm-aging, the immune system, and the prevalence of CH in autoimmune diseases.

Clonal Hematopoiesis, Inflammation, and Hematologic Malignancy

Somatic or acquired mutations are postzygotic genetic variations that can occur within any tissue. These mutations accumulate during aging and have classically been linked to malignant processes. Tremendous advancements over the past years have led to a deeper understanding of the role of somatic mutations in benign and malignant age-related diseases. Here, we review the somatic mutations that accumulate in the blood and their connection to disease states, with a particular focus on inflammatory diseases and myelodysplastic syndrome. We include a definition of clonal hematopoiesis (CH) and an overview of the origins and implications of these mutations. In addition, we emphasize somatic disorders with overlapping inflammation and hematologic disease beyond CH, including paroxysmal nocturnal hemoglobinuria and aplastic anemia, focusing on VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome. Finally, we provide a practical view of the implications of somatic mutations in clinical hematology, pathology, and beyond.

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.

Molecular and clinical aspects relevant for counseling individuals with clonal hematopoiesis of indeterminate potential

Clonal hematopoiesis of indeterminate potential (CHIP) has fascinated the medical community for some time. Discovered about a decade ago, this phenomenon links age-related alterations in hematopoiesis not only to the later development of hematological malignancies but also to an increased risk of early-onset cardiovascular disease and some other disorders. CHIP is detected in the blood and is characterized by clonally expanded somatic mutations in cancer-associated genes, predisposing to the development of hematologic neoplasms such as MDS and AML. CHIP-associated mutations often involve DNA damage repair genes and are frequently observed following prior cytotoxic cancer therapy. Genetic predisposition seems to be a contributing factor. It came as a surprise that CHIP significantly elevates the risk of myocardial infarction and stroke, and also contributes to heart failure and pulmonary hypertension. Meanwhile, evidence of mutant clonal macrophages in vessel walls and organ parenchyma helps to explain the pathophysiology. Besides aging, there are some risk factors promoting the appearance of CHIP, such as smoking, chronic inflammation, chronic sleep deprivation, and high birth weight. This article describes fundamental aspects of CHIP and explains its association with hematologic malignancies, cardiovascular disorders, and other medical conditions, while also exploring potential progress in the clinical management of affected individuals. While it is important to diagnose conditions that can lead to adverse, but potentially preventable, effects, it is equally important not to stress patients by confronting them with disconcerting findings that cannot be remedied. Individuals with diagnosed or suspected CHIP should receive counseling in a specialized outpatient clinic, where professionals from relevant medical specialties may help them to avoid the development of CHIP-related health problems. Unfortunately, useful treatments and clinical guidelines for managing CHIP are still largely lacking. However, there are some promising approaches regarding the management of cardiovascular disease risk. In the future, strategies aimed at restoration of gene function or inhibition of inflammatory mediators may become an option.

Philadelphia chromosome-negative myeloproliferative chronic neoplasms: is clonal hematopoiesis the main determinant of autoimmune and cardio-vascular manifestations?

In this article, we reviewed the possible mechanisms linking the clonal hematopoiesis of indeterminate potential (CHIP) to chronic myeloproliferative neoplasms (MPNs), autoimmune diseases (ADs), and cardiovascular diseases (CADs). CHIP is characterized by the presence of clonal mutations with an allelic frequency >2% in the peripheral blood without dysplasia, overt hematological neoplasms, or abnormalities in blood cell count. The prevalence may reach 20% of elderly healthy individuals and is considered a risk factor for myelodysplastic neoplasms and acute leukemia. In MPNs, CHIP is often associated with mutations such as JAK2V617F or DNMT3A, TET2, or ASXL1, which exhibit a 12.1- and 1.7-2-fold increase in CADs. Specifically, JAK2-mutated cells produce excessive cytokines and reactive oxygen species, leading to proinflammatory modifications in the bone marrow microenvironment. Consequently, the likelihood of experiencing thrombosis is influenced by the variant allele frequency (VAF) of the JAK2V617F mutation, which also appears to be correlated with anti-endothelial cell antibodies that sustain thrombosis. However, DNMT3A mutations induce pro-inflammatory T-cell polarization and activate the inflammasome complex, while TET2 downregulation leads to endothelial cell autophagy and inflammatory factor upregulation. As a result, in patients with TET2 and DNMT3A-related CHIP, the inflammasome hyperactivation represents a potential cause of CADs. CHIP also occurs in patients with large and small vessel vasculitis, while ADs are more frequently associated with MPNs. In these diseases, monocytes and neutrophils play a key role in the formation of neutrophil extracellular trap (NET) as well as anti-endothelial cell antibodies, resulting in a final procoagulant effect. ADs, such as systemic lupus erythematosus, psoriasis, and arthritis, are also characterized by an overexpression of the Rho-associated coiled-coil containing protein kinase 2 (ROCK2), a serine/threonine kinase that can hyperactivate the JAK-STAT pathway. Interestingly, hyperactivation of ROCK2 has also been observed in myeloid malignancies, where it promotes the growth and survival of leukemic cells. In summary, the presence of CHIP, with or without neoplasia, can be associated with autoimmune manifestations and thrombosis. In the presence of these manifestations, it is necessary to consider a "disease-modifying therapy" that may either reduce the clonal burden or inhibit the clonally activated JAK pathway.

Spectrum of clonal hematopoiesis in VEXAS syndrome

Vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic (VEXAS) syndrome is caused by somatic mutations in UBA1 (UBA1mut) and characterized by heterogenous systemic autoinflammation and progressive hematologic manifestations, meeting criteria for myelodysplastic syndrome (MDS) and plasma cell dyscrasias. The landscape of myeloid-related gene mutations leading to typical clonal hematopoiesis (CH) in these patients is unknown. Retrospectively, we screened 80 patients with VEXAS for CH in their peripheral blood (PB) and correlated the findings with clinical outcomes in 77 of them. UBA1mut were most common at hot spot p.M41 (median variant allele frequency [VAF] = 75%). Typical CH mutations cooccurred with UBA1mut in 60% of patients, mostly in DNMT3A and TET2, and were not associated with inflammatory or hematologic manifestations. In prospective single-cell proteogenomic sequencing (scDNA), UBA1mut was the dominant clone, present mostly in branched clonal trajectories. Based on integrated bulk and scDNA analyses, clonality in VEXAS followed 2 major patterns: with either typical CH preceding UBA1mut selection in a clone (pattern 1) or occurring as an UBA1mut subclone or in independent clones (pattern 2). VAF in the PB differed markedly between DNMT3A and TET2 clones (median VAF of 25% vs 1%). DNMT3A and TET2 clones associated with hierarchies representing patterns 1 and 2, respectively. Overall survival for all patients was 60% at 10 years. Transfusion-dependent anemia, moderate thrombocytopenia, and typical CH mutations, each correlated with poor outcome. In VEXAS, UBA1mut cells are the primary cause of systemic inflammation and marrow failure, being a new molecularly defined somatic entity associated with MDS. VEXAS-associated MDS is distinct from classical MDS in its presentation and clinical course.

Interplay between chronic inflammation and clonal haematopoiesis of indeterminate potential in Behçet's disease

BACKGROUND

Clonal haematopoiesis of indeterminate potential (CHIP) is a predisposition to haematological malignancy whose relationship with chronic inflammatory diseases, such as cardiovascular diseases, has been highlighted. Here, we aimed to investigate the CHIP emergence rate and its association with inflammatory markers in Behçet's disease (BD).

METHODS

We performed targeted next-generation sequencing to detect the presence of CHIP using peripheral blood cells from 117 BD patients and 5004 healthy controls between March 2009 and September 2021 and analysed the association between CHIP and inflammatory markers.

RESULTS

CHIP was detected in 13.9% of patients in the control group and 11.1% of patients in the BD group, indicating no significant intergroup difference. Among the BD patients of our cohort, five variants (DNMT3A, TET2, ASXL1, STAG2, and IDH2) were detected. DNMT3A mutations were the most common, followed by TET2 mutations. CHIP carriers with BD had a higher serum platelet count, erythrocyte sedimentation rate, and C-reactive protein level; older age; and lower serum albumin level at diagnosis than non-CHIP carriers with BD. However, the significant association between inflammatory markers and CHIP disappeared after the adjustment for various variables, including age. Moreover, CHIP was not an independent risk factor for poor clinical outcomes in patients with BD.

CONCLUSIONS

Although BD patients did not have higher CHIP emergence rates than the general population, older age and degree of inflammation in BD were associated with CHIP emergence.

CHIPing away the progression potential of CHIP: A new reality in the making

Over the past few years, we have gained a deeper understanding of clonal hematopoiesis of indeterminate potential (CHIP), especially with regard to the epidemiology, clinical sequelae, and mechanical aspects. However, interventional strategies to prevent or delay the potential negative consequences of CHIP remain underdeveloped. In this review, we highlight the latest updates on clonal hematopoiesis research, including molecular mechanisms and clinical implications, with a particular focus on the evolving strategies for the interventions that are being evaluated in ongoing observational and interventional trials. There remains an urgent need to formulate standardized and evidence-based recommendations and guidelines for evaluating and managing individuals with clonal hematopoiesis. In addition, patient-centric endpoints must be defined for clinical trials, which will enable us to continue the robust development of effective preventive strategies and improve clinical outcomes.

Clonal hematopoiesis, somatic mosaicism, and age-associated disease

Somatic mosaicism, the occurrence of multiple genetically distinct cell clones within the same tissue, is an evitable consequence of human aging. The hematopoietic system is no exception to this, where studies have revealed the presence of expanded blood cell clones carrying mutations in preleukemic driver genes and/or genetic alterations in chromosomes. This phenomenon is referred to as clonal hematopoiesis and is remarkably prevalent in elderly individuals. While clonal hematopoiesis represents an early step toward a hematological malignancy, most individuals will never develop blood cancer. Somewhat unexpectedly, epidemiological studies have found that clonal hematopoiesis is associated with an increase in the risk of all-cause mortality and age-related disease, particularly in the cardiovascular system. Studies using murine models of clonal hematopoiesis have begun to shed light on this relationship, suggesting that driver mutations in mature blood cells can causally contribute to aging and disease by augmenting inflammatory processes. Here we provide an up-to-date review of clonal hematopoiesis within the context of somatic mosaicism and aging and describe recent epidemiological studies that have reported associations with age-related disease. We will also discuss the experimental studies that have provided important mechanistic insight into how driver mutations promote age-related disease and how this knowledge could be leveraged to treat individuals with clonal hematopoiesis.

[Importance of clonal hematopoiesis for hematologic neoplasms]

BACKGROUND

Clonal hematopoiesis of indeterminate potential (CHIP) is a fairly newly described phenomenon characterized by myeloid cancer-associated somatic mutations detectable in the peripheral blood of individuals without evidence of hematologic disease. Individuals with CHIP have a significantly increased risk of developing a hematologic malignancy, although the overall rate of transformation is low.

OBJECTIVE

We review the current state of knowledge on causes of clonal expansion of blood cells as well as identifiable risk factors for progression to overt hematologic malignancy.

RESULTS AND CONCLUSION

CHIP is considered a premalignant state and predisposes to the development of hematologic malignancy. Because the overall rate of transformation is low, clear identification and subsequent monitoring of those CHIP individuals at a higher risk is of paramount importance. In the future, prospective studies evaluating preventive and/or preemptive therapeutic strategies may aid in avoiding progression to blood cancer in individuals with CHIP.

Clonal hematopoiesis of indeterminate potential and cardiovascular disease

Age is the most important risk factor for cardiovascular disease and appears to be more than a marker of cumulative exposure to other risk factors such as dyslipidemia and hypertension. With aging, genetic mutations occur that are not present in our germline DNA, observed as somatic mosaicism. Hematopoietic stem cells have an increased chance of developing mosaicism because they are highly proliferative, and mutations with survival benefits can establish clonal populations. Age-related clonal hematopoiesis resulting from somatic mutations was first described ∼25 years ago. The subset of clonal hematopoiesis in which a driver mutation with variant allele frequency of at least 2% occurs in a gene implicated in hematologic malignancies but in the absence of known hematologic malignancy or other clonal disorder is termed clonal hematopoiesis of indeterminate potential (CHIP). Large-scale exome-sequencing projects have recently enabled the study of CHIP frequency, gene-specific analyses, and longitudinal clinical consequences of CHIP, including an observed increased risk for cardiovascular disease. Animal models provide insight into the mechanisms by which CHIP increases cardiovascular disease risk, and combined animal, clinical, and epidemiological data suggest therapeutic implications for CHIP in cardiovascular disease prevention.

Turning the clock forward: Inflammation accelerates the aging of hematopoietic stem cells

In the current issue of Cell Stem Cell, Bogeska et al. demonstrate that repeated exposures to inflammation cause indelible and specific functional compromise and accelerated aging of long-term hematopoietic stem cells (LT-HSCs). This study proposes the notion that the cumulative inflammatory events over the course of an organism's lifespan may irreversibly damage LT-HSCs.

Tet2 deficiency drives liver microbiome dysbiosis triggering Tc1 cell autoimmune hepatitis

The triggers that drive interferon-γ (IFNγ)-producing CD8 T cell (Tc1 cell)-mediated autoimmune hepatitis (AIH) remain obscure. Here, we show that lack of hematopoietic Tet methylcytosine dioxygenase 2 (Tet2), an epigenetic regulator associated with autoimmunity, results in the development of microbiota-dependent AIH-like pathology, accompanied by hepatic enrichment of aryl hydrocarbon receptor (AhR) ligand-producing pathobionts and rampant Tc1 cell immunity. We report that AIH-like disease development is dependent on both IFNγ and AhR signaling, as blocking either reverts ongoing AIH-like pathology. Illustrating the critical role of AhR-ligand-producing pathobionts in this condition, hepatic translocation of the AhR ligand indole-3-aldehyde (I3A)-releasing Lactobacillus reuteri is sufficient to trigger AIH-like pathology. Finally, we demonstrate that I3A is required for L. reuteri-induced Tc1 cell differentiation in vitro and AIH-like pathology in vivo, both of which are restrained by Tet2 within CD8 T cells. This AIH-disease model may contribute to the development of therapeutics to alleviate AIH.

Clinical Significance of Clonal Hematopoiesis of Indeterminate Potential in Hematology and Cardiovascular Disease

Liquid profiling uses circulating tumor DNA (ctDNA) for minimal invasive tumor mutational profiling from peripheral blood. The presence of somatic mutations in peripheral blood cells without further evidence of a hematologic neoplasm defines clonal hematopoiesis of indeterminate potential (CHIP). CHIP-mutations can be found in the cell-free DNA (cfDNA) of plasma, are a potential cause of false positive results in liquid profiling, and thus limit its usage in screening settings. Various strategies are in place to mitigate the effect of CHIP on the performance of ctDNA assays, but the detection of CHIP also represents a clinically significant incidental finding. The sequelae of CHIP comprise the risk of progression to a hematologic neoplasm including therapy-related myeloid neoplasms. While the hematological risk increases with the co-occurrence of unexplained blood count abnormalities, a number of non-hematologic diseases have independently been associated with CHIP. In particular, CHIP represents a major risk factor for cardiovascular disease such as atherosclerosis or heart failure. The management of CHIP requires an interdisciplinary setting and represents a new topic in the field of cardio-oncology. In the future, the information on CHIP may be taken into account for personalized therapy of cancer patients.

Myelodysplastic syndrome and autoimmune disorders: two sides of the same coin?

Systemic inflammatory and autoimmune diseases and myelodysplastic syndromes have been linked in individual patients and in larger case series for at least 25 years. These associations frequently include thyroid disease, neutrophilic dermatoses, polyarthritis, connective tissue diseases, vasculitis, and autoimmune cytopenias. Studies have found that autoimmune disease (or its therapy) is a risk factor for the development of myelodysplastic syndromes, but such syndromes might also be an instigator of autoimmune disease. Epidemiological studies examining disease risk in myelodysplastic syndromes with and without comorbid autoimmune illness have reached mixed conclusions. The pathophysiology of myelodysplastic syndromes is tightly linked to excessive inflammatory activity in the bone marrow microenvironment, which could promote systemic inflammatory and autoimmune diseases directly or by stimulation of the adaptive immune response. Alternatively, autoimmune diseases could promote clonal evolution and disordered bone marrow growth, promoting the development of myeloid malignancy. Additionally, therapy-related myeloid neoplasms-including myelodysplastic syndromes-have been diagnosed after treatment of autoimmune diseases with immunosuppressant therapies. These associations raise the following question: are myelodysplastic syndromes and systemic inflammatory and autoimmune diseases two sides of the same coin-that is, do they share an underlying disease state that can manifest as a myeloid neoplasm, an autoinflammatory illness, or both? VEXAS syndrome, which was first reported in 2020, is caused by a mutation that affects myeloid-restricted cells and manifests with both myelodysplasia and autoinflammation, and could give insight into this biological possibility. We note that systemic inflammatory and autoimmune diseases are often steroid-dependent; however, studies have also evaluated the roles of other immunomodulating therapies. In this Viewpoint, we critically appraise and review the literature on the epidemiology, pathophysiology, and management of systemic inflammatory and autoimmune diseases that are associated with myelodysplastic syndromes and related diseases.

Clonal hematopoiesis: Mutation-specific adaptation to environmental change

Clonal hematopoiesis of indeterminate potential (CHIP) describes a widespread expansion of genetically variant hematopoietic cells that increases exponentially with age and is associated with increased risks of cancers, cardiovascular disease, and other maladies. Here, we discuss how environmental contexts associated with CHIP, such as old age, infections, chemotherapy, or cigarette smoking, alter tissue microenvironments to facilitate the selection and expansion of specific CHIP mutant clones. Further, we consider major remaining gaps in knowledge, including intrinsic effects, clone size thresholds, and factors affecting clonal competition, that will determine future application of this field in transplant and preventive medicine.

Clonal Hematopoiesis at the Crossroads of Inflammatory Bowel Diseases and Hematological Malignancies: A Biological Link?

Inflammatory bowel diseases (IBDs) are a group of chronic conditions of the gastrointestinal tract in which nationwide studies have revealed a higher risk of hematological malignancies (HMs). Clonal hematopoiesis (CH) is a premalignant condition defined by the presence of an acquired somatic mutation characterized by a variant allele frequency (VAF) of ≥2%, in a gene frequently associated with HMs. A growing body of evidence suggests a correlation between inflammation and CH; its occurrence in the context of IBD has been previously demonstrated. With the aim to assess CH possible co-occurrence in patients with an IBD associated with HMs, we performed a targeted next-generation sequencing analysis in a cohort of thirteen patients who were referred to our center with IBD associated with HMs. Eleven (85%) patients showed one or more mutations in CH-associated genes; DNMT3A was the most frequently mutated gene, followed by ASXL1 and JAK2. These results may suggest that the mechanisms at the basis of the inflammatory environment could potentially select for the growth of hematopoietic clones harboring specific mutations. In this context, CH emergence may be boosted by the proinflammatory IBD environment, thus acting as a biological link between IBD and the HM onset. If these data are confirmed, IBD patients screened and positive for CH should undergo a hematologic follow-up to assess the risk of developing HM. Future study will clarify the relationship between these conditions.

Inflammation and myeloid malignancy: Quenching the flame

Chronic inflammation with aging ("inflammaging") plays a prominent role in the pathogenesis of myeloid malignancies. Aberrant inflammatory activity impacts many different cells in the marrow, including normal blood and stromal marrow elements and leukemic cells, in unique and distinct ways. Inflammation can promote selective clonal expansion through differential immune-mediated suppression of normal hematopoietic cells and malignant clones. We review these complex roles, how they can be understood by separating cell-intrinsic from extrinsic effects, and how this informs future clinical trials.

Advances in understanding the molecular basis of clonal hematopoiesis

Hematopoietic stem cells (HSCs) are polyfunctional, regenerating all blood cells via hematopoiesis throughout life. Clonal hematopoiesis (CH) is said to occur when a substantial proportion of mature blood cells is derived from a single dominant HSC lineage, usually because these HSCs have somatic mutations that confer a fitness and expansion advantage. CH strongly associates with aging and enrichment in some diseases irrespective of age, emerging as an independent causal risk factor for hematologic malignancies, cardiovascular disease, adverse disease outcomes, and all-cause mortality. Defining the molecular mechanisms underlying CH will thus provide a framework to develop interventions for healthy aging and disease treatment. Here, we review the most recent advances in understanding the molecular basis of CH in health and disease.

Clonal hematopoiesis of indeterminate potential and cardiovascular events in systemic lupus erythematosus (HEMATOPLUS study)

OBJECTIVE

The detection of somatic mutations in genes of myeloid cells in asymptomatic patients - defining clonal hematopoiesis of indeterminate potential (CHIP) - predisposes to cardiovascular events (CVE) in the general population. We aimed to determine whether CHIP was associated with CVE in SLE patients.

METHODS

The study is an ancillary study of the randomized, double-blind, placebo-controlled, multicenter trial PLUS study conducted from June 2007 through August 2010 at 37 centers in France involving 573 SLE patients. The search for somatic mutations by high-throughput sequencing of 53 genes involved in clonal hematopoiesis was performed on genomic DNA collected at PLUS inclusion. The CHIP prevalence was assessed in SLE and in a retrospective cohort of 479 patients free of hematological malignancy. The primary outcome was the incident CVE in SLE.

RESULTS

Screening for CHIP was performed in 438 SLE patients (38 [29-47] years, 91·8% female). Overall, 63 somatic mutations were identified in 47 patients defining a CHIP prevalence of 10·7% in SLE. Most SLE patients (78·7%) carried a single mutation. Most variants (62·5%) were located in the DNMT3A gene. CHIP was associated with age, age at SLE diagnosis and a lower frequency of antiphospholipid antibodies. CHIP occurred more than 20-years earlier (p < 0·00001) in SLE than in controls. The detection of CHIP at inclusion was not associated with the occurrence of CVE during follow up (HR = 0·42 (0·06 - 3·21), p = 0·406).

CONCLUSION

The prevalence of CHIP is high in SLE with respect to age but was not associated with incident CVE.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, https://clinicaltrials.gov, NCT05146414.

Clonal hematopoiesis and vascular disease

Somatic mutations in hematopoietic stem cells are common with aging and can result in expansion of clones harboring mutations, termed clonal hematopoiesis. This results in an increased risk of blood cancers but has also been linked with chronic inflammatory disease states. In recent years, clonal hematopoiesis has been established to have a causative role in atherogenesis and cardiovascular disease. Additionally, as the effector cells have been identified to be immune cells, there is ongoing interest in assessing whether dysregulated immune function plays a role in other chronic inflammatory conditions such as rheumatologic disease. Here, we summarize current understanding of clonal hematopoiesis with a focus on cardiovascular disease and inflammation while outlining the potential, yet unexplored, relationship between clonal hematopoiesis and autoimmune disease. Hematopoietic stem cells (HSCs) continually regenerate blood cells. Acquisition of a somatic mutation that provides a selective advantage, a driver mutation, can result in clonal expansion. Clonal hematopoiesis of indeterminate potential, where somatic mutations in certain cancer-associated genes result in clonal expansion in the absence of overt malignancy, can result in atherosclerotic cardiovascular disease in multiple vascular beds, inflammation, and may also contribute to the pathogenesis of autoimmune disease. Many questions remain unanswered regarding the relationship between clonal hematopoiesis and inflammatory disorders.

Somatic Mutations in Rheumatologic Diseases: VEXAS Syndrome and Beyond

Discovery of the VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome demonstrates that somatic mutations in hematologic precursor cells can cause adult-onset, complex inflammatory disease. Unlike germline mutations, somatic mutations occur throughout the lifespan, are restricted to specific tissue types, and may play a causal role in non-heritable rheumatologic diseases, especially conditions that start in later life. Improvements in sequencing technology have enabled researchers and clinicians to detect somatic mutations in various tissue types, especially blood. Understanding the relationships between cell-specific acquired mutations and inflammation is likely to yield key insights into causal factors that underlie many rheumatologic diseases. The objective of this review is to detail how somatic mutations are likely to be relevant to clinicians who care for patients with rheumatologic diseases, with particular focus on the pathogenetic mechanisms of the VEXAS syndrome.

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.

Clinical and pathologic challenges of clonal cytopenia of undetermined significance

Unexplained blood cytopenias, in particular anemia, are often found in older individuals. The relationship between these cytopenias and myeloid neoplasms like myelodysplastic syndromes is currently poorly defined. Terminology used to describe patients with unexplained cytopenias and with clonally restricted hematopoiesis can be confusing and is evolving. This review uses a complex clinical case with borderline morphology and somatic mutations with high variant allele frequencies to illustrate a diagnostic approach to clonal cytopenias, and differentiation from myeloid neoplasms with a focus on appropriate ancillary testing. Testing for somatic mutations and variant allele frequency is helpful in assessing risk for progression to myeloid malignancy. The interpretation of mutation profiles in patients with cytopenia has been challenging, as some of these genes are commonly detected in elderly adults showing a normal blood count as well as in individuals with nonmalignant bone marrow failure syndromes. For patients with unexplained cytopenias, longitudinal follow-up including monitoring of blood counts may also be appropriate.

CHIP & HIPs: Clonal Hematopoiesis is Common in Hip Arthroplasty Patients and Associates with Autoimmune Disease

Clonal hematopoiesis (CH) is an age-related condition predisposing to blood cancer and cardiovascular disease (CVD). Murine models demonstrate CH-mediated altered immune function and proinflammation. Low-grade inflammation has been implicated in the pathogenesis of osteoarthritis (OA), the main indication for total hip arthroplasty (THA). THA-derived hip bones serve as a major source of 'healthy' hematopoietic cells in experimental hematology. We prospectively investigated frequency and clinical associations of CH in 200 patients without known hematologic disease undergoing THA. Prevalence of CH was 50%, including 77 patients with CH of indeterminate potential (CHIP, defined as somatic variants with allele frequencies [VAF] ≥2%), and 23 patients harboring CH with lower mutation burden (VAF 1-2%). Most commonly mutated genes were DNMT3A (29.5%), TET2 (15.0%) and ASXL1 (3.5%). CHIP significantly associated with lower hemoglobin, higher mean corpuscular volume, prior/present malignant disease, and CVD. Strikingly, we observed a previously unreported association of CHIP with autoimmune diseases (AID; multivariate adjusted odds ratio, 6.6; 95% confidence interval [1.7, 30]; p=0.0081). These findings underscore the association between CH and inflammatory diseases. Our results have considerable relevance for management of patients with OA and AID or mild anemia, and question use of hip bone-derived cells as 'healthy' experimental controls.

Donor clonal hematopoiesis increases risk of acute graft versus host disease after matched sibling transplantation

Clonal hematopoiesis (CH) is associated with older age and an increased risk of myeloid malignancies and cardiovascular complications. We analyzed donor DNA samples in patients with AML/MDS who underwent first allogeneic stem cell transplant (SCT) to investigate the association between donor CH and transplant outcomes. We performed targeted deep sequencing of 300 genes on donor blood samples and identified CH with the minimum variant allele frequency of 2%. Among 363 donors, 65 (18%) had CH. The most frequently mutated genes were DNMT3A (31 of 65; 48%), TET2 (16 of 65; 25%), PPM1D (5 of 65, 8%), and ASXL1 (7 of 65; 11%). Transplant outcomes: time to neutrophil and platelet recovery, relapse incidence, transplant-related mortality and progression-free survival, were comparable by donor CH. However, risk of grade II-IV and III-IV acute graft versus host disease (aGvHD) at 6 months after transplant was higher with donor CH vs. without donor CH (hazard ratio (HR) = 2.4, 95% Confidence Interval (CI) = 1.6-3.6, p < 0.001 and HR = 3.8, 95% CI = 1.6-8.9, p = 0.003). In this homogenous population of AML/MDS patients, donor CH was associated with increased risk of grade II-IV and III-IV aGvHD. Further studies to investigate the mechanisms of increased aGvHD and therapeutic interventions to improve aGvHD in the context of donor CH are warranted.

Stem cell donors should be screened for CHIP

This article has a companion Counterpoint by Gibson and Lindsley.

Somatic Mutations and the Risk of Undifferentiated Autoinflammatory Disease in MDS: An Under-Recognized but Prognostically Important Complication

Objectives: We theorized that myelodysplastic syndrome (MDS) with somatic mutations and karyotype abnormalities are associated with autoinflammation, and that the presence of autoinflammatory disease affected prognosis in MDS. Methods: One hundred thirty-four MDS patients were assessed for the prevalence of autoinflammatory complications and its link with karyotypes and somatic mutation status. Autoinflammatory complications were described either as well-defined autoinflammatory diseases (AD) or undifferentiated "autoinflammatory disease" (UAD) (defined as CRP over 10.0 mg/L on five consecutive occasions, taken at separate times and not explained by infection). Several patient characteristics including demographic, clinical, laboratory, cytogenetics charts, and outcomes, were compared between different groups. Results: Sixty-two (46.3%) patients had an autoinflammatory complication manifesting as arthralgia (43.5% vs. 23.6%, p = 0.0146), arthritis (30.6% vs. 15.3%, p = 0.0340), skin rash (27.4% vs. 12.5%, p = 0.0301), pleuritis (14.5% vs. 4.2%, p = 0.0371) and unexplained fever (27.4% vs. 0%, p < 0.0001). AD were found in 7.4% of MDS patients (with polymyalgia rheumatic being the most frequently one). Classical autoimmune diseases were found only in 4 MDS patients (3.0%). Transcription factor pathway mutations (RUNX1, BCOR, WTI, TP53) (OR 2.20 [95%CI 1.02-4.75], p = 0.0451) and abnormal karyotypes (OR 2.76 [95%CI 1.22-6.26], p = 0.0153) were associated with autoinflammatory complications. Acute leukaemic transformation was more frequent in MDS patients with autoinflammatory features than those without (27.4% vs. 9.7%, p = 0.0080). Conclusions: Autoinflammatory complications are common in MDS. Somatic mutations of transcription factor pathways and abnormal karyotypes are associated with greater risk of autoinflammatory complications, which are themselves linked to malignant transformation and a worse prognosis.

Persistent inflammatory and non-inflammatory mechanisms in refractory rheumatoid arthritis

Despite nearly three decades of advances in the management of rheumatoid arthritis (RA), a substantial minority of patients are exposed to multiple DMARDs without necessarily benefitting from them; a group of patients variously designated as having 'difficult to treat', 'treatment-resistant' or 'refractory' RA. This Review of refractory RA focuses on two types of patients: those for whom multiple targeted therapies lack efficacy and who have persistent inflammatory pathology, which we designate as persistent inflammatory refractory RA (PIRRA); and those with supposed refractory RA who have continued disease activity that is predominantly independent of objective evidence of inflammation, which we designate as non-inflammatory refractory RA (NIRRA). These two types of disease are not mutually exclusive, but identifying those individuals with predominant PIRRA or NIRRA is important, as it informs distinct treatment and management approaches. This Review outlines the clinical differences between PIRRA and NIRRA, the genetic and epigenetic mechanisms and immune pathways that might contribute to the immunopathogenesis of recalcitrant synovitis in PIRRA, and a possible basis for non-inflammatory symptomatology in NIRRA. Future approaches towards the definition of refractory RA and the application of single-cell and integrated omics technologies to the identification of refractory RA endotypes are also discussed.

Clonal hematopoiesis and nonhematologic disorders

Clonal expansions of mutated hematopoietic cells, termed clonal hematopoiesis, are common in aging humans. One expected consequence of mutation-associated clonal hematopoiesis is an increased risk of hematologic cancers, which has now been shown in several studies. However, the hematopoietic stem cells that acquire these somatic mutations also give rise to mutated immune effector cells, such as monocytes, granulocytes, and lymphocytes. These effector cells can potentially influence many disease states, especially those with a chronic inflammatory component. Indeed, several studies have now shown that clonal hematopoiesis associates with increased risk of atherosclerotic cardiovascular disease. Emerging data also associate clonal hematopoiesis with other nonhematologic diseases. Here, we will review recent studies linking clonal hematopoiesis to altered immune function, inflammation, and nonmalignant diseases of aging.

Clonal haematopoiesis is increased in early onset in systemic sclerosis

Objectives

SSc is an autoimmune disease characterized by fibrosis, microangiopathy and immune dysfunctions including dysregulation of proinflammatory cytokines. Clonal haematopoiesis of indeterminate potential (CHIP) is defined by the acquisition of somatic mutations in haematopoietic stem cells leading to detectable clones in the blood. Recent data have shown a higher risk of cardiovascular disease in patients with CHIP resulting from increased production of proinflammatory cytokines and accelerated atherosclerosis. Eventual links between CHIP and autoimmune diseases are undetermined. The aim of our study was to evaluate the prevalence of CHIP in SSc patients and its association with clinical phenotype.

Methods

Forty-one genes frequently mutated in myeloid malignancies were sequenced in peripheral blood mononuclear cells from 90 SSc patients and 44 healthy donors.

Results

A total of 15 somatic variants were detected in 13/90 SSc patients (14%) and four somatic variants in 4/44 (9%) healthy donors (HD) (P = 0.58). The prevalence of CHIP was significantly higher in younger SSc patients than in HD: 25% (6/24) vs 4% (1/26) (P = 0.045) under 50 years and 17% (7/42) vs 3% (1/38) (P = 0.065) under 60 years. The prevalence of CHIP in patients over 70 years was similar in SSc patients and healthy donors. The most common mutations occurred in DNMT3A (seven variants). No major clinical differences were observed between SSc patients with or without CHIP.

Conclusion

Whether CHIP increases the risk to develop SSc or is a consequence of a SSc-derived modified bone marrow micro-environment remains to be explored.

Clonal haematopoiesis and COVID-19: A possible deadly liaison

We provide evidence for a linear correlation between the frequency of clonal haematopoiesis and COVID‐19 mortality rate. We discuss the mechanistic explanations for this association mediated by a pathological inflammatory response. Our hypothesis can be tested in COVID‐19‐infected patients and eventually lead to new approaches to risk stratification and therapy.

Overview of the Associations Between Cancer and Rheumatic Disease

People living with rheumatic diseases frequently encounter cancer, either as a potential harm of antirheumatic therapies or as a comorbidity that alters the conversation about management. This article provides a general overview of the issues related to cancer and rheumatic disease and serves as a springboard for the remaining chapters in this issue. Several topics are reviewed, including epidemiology, bidirectional causal pathways, and issues related to medications. Although uncertainties remain, the issue of cancer is of great importance to patients with rheumatic diseases, and an individualized, person-centered approach to assessment and management is necessary.

The origin of leukemia: Genetic alterations and inflammatory factors in the development of premalignant clonal hematopoiesis

Clonal hematopoiesis of indetermined potential (CHIP) is increasingly common with age and identified in more than 1 in 10 healthy individuals at the age of 70. Mutations in epigenetic and splicing factors are recurrent genetic events in CHIP, and experimental data suggest that microbial and inflammatory factors may contribute to the selective expansion of hematopoietic stem cells carrying these mutations. In parallel, CHIP is associated with an increased incidence of cardiovascular disease and studies in mice support a causal relationship where mutated hematopoietic cells contribute to inflammation and atherosclerotic plaque formation. Collectively, current clinical and experimental data suggest a complex network where genetic alterations and inflammatory factors contribute to the development of the early stages of hematological malignancy.