The impact of age and number of mutations on the size of clonal hematopoiesis

Clonal hematopoiesis of indeterminate potential: recent developments and perspectives

PURPOSE OF REVIEW

This review encompasses the recently published information on clonal hematopoiesis of indeterminate potential (CHIP) and discusses its future prospects. By announcing advances in the research of CHIP risk factors and related diseases, with the purpose of offering new insights to treat both hematologic and nonhematologic disorders.

RECENT FINDINGS

The majority of studies have shown that CHIP is a common biological condition associated with aging and the incidence of clonal hematopoiesis increases with age. The pathophysiology of blood diseases is projected to be significantly influenced by CHIP. Nevertheless, increasing studies have expanded the application of CHIP to cover nonhematologic diseases such as cardiovascular, renal, liver, and pulmonary diseases. Furthermore, with the fast advancement of genetic testing technology and preventive medicine, the involvement of CHIP in a variety of disorders shows promise as an essential target for preventing disease onset and progression.

SUMMARY

CHIP is linked to a variety of illnesses and has a significant influence on an individual's health outlook. Thus, identifying and managing CHIP is critical for improving the clinical results of the individuals concerned.

Indoleamine 2,3-dioxygenase 1 alters the proportions of B cell subpopulations in the microenvironment of acute myeloid leukemia

Acute myeloid leukemia (AML), the most common leukemia in adults, exhibits immune escape characteristics like solid tumors. The expression of indoleamine 2,3-dioxygenase 1 (IDO1), a well-recognized immune checkpoint, has been detected in AML blast cells and is associated with poor clinical outcome. Although an imbalance of B cell subpopulations exists in AML patients' bone marrow microenvironment, the role of B cells and their interaction with IDO1 in AML have yet to be elucidated. Herein, with bioinformatic analysis, we found the close correlations between IDO1 expression and survival and B cell subpopulation proportions in AML patients. Further, our investigation into IDO1 expression and activity, B cell subpopulation proportions and immunosuppressive interleukin-10 (IL-10) level in AML cells and clinical samples revealed significant findings. Using a co-culture system of healthy human PBMCs and AML cell lines, we demonstrated that high IDO1 expression in AML cells could alter the proportions of total B, regulatory B and memory B cells, and increased the level of IL-10. Finally, with the IDO1 inhibitor RY103 designed by our laboratory, we found that IDO1 inhibition had good anti-leukemic effect and restored the abnormal proportions of B cell subpopulations in AML mice. Our study is the first to reveal the modulation of IDO1 on B cell subpopulations in AML, making a significant breakthrough in understanding the immune escape mechanisms of AML. Application of IDO1 inhibitor, such as RY103, targeting the imbalance of B cell subpopulations can lead to innovative treatments for AML.

Clonal hematopoiesis: elements associated with clonal expansion and diseases

Clonal hematopoiesis (CH), characterized by the expansion of hematopoietic stem and progenitor cells harboring somatic mutations, has emerged as a significant age-related phenomenon with profound implications for human health. While initially recognized in the 1960s, recent technological advances have revealed its complex nature and widespread prevalence, affecting up to 84% of individuals aged ≥ 70 years. The clinical significance of CH extends beyond its well-established role as a precursor to hematological malignancies, encompassing its association with cardiovascular diseases, chronic kidney disease, and other non-malignant disorders. This comprehensive review synthesizes the current understanding of CH, focusing on recent advances in genetic and molecular mechanisms, particularly the roles of commonly mutated genes such as DNMT3A, TET2, and ASXL1. We address the emerging distinction between myeloid and lymphoid CH, their differential impacts on disease progression, and the complex interplay between CH and inflammation. Special attention is given to newly identified genetic determinants of clonal expansion rates and their implications for disease progression. The review also examines the revolutionary concept of passenger-approximated clonal expansion rate and its utility in understanding CH dynamics. Furthermore, we discuss therapeutic strategies targeting inflammatory pathways and their potential in mitigating CH-associated complications. By integrating recent findings from genetic, molecular, and clinical studies, this review provides a framework for understanding CH as a systemic condition and highlights promising directions for therapeutic interventions.

Clonal Hematopoiesis of Indeterminate Potential as a Predictor of Colorectal Cancer Risk: Insights from the UK Biobank Cohort

BACKGROUND

Clonal hematopoiesis of indeterminate potential (CHIP) has been shown to be associated with the occurrence of solid tumors, but its relationship with colorectal cancer still needs to be studied.

METHODS

We conducted a prospective matched case-control study using data from the UK Biobank, including 5,310 incident colorectal cancer cases and 26,550 controls matched for age, sex, and body mass index.

RESULTS

Analysis of the UK Biobank data revealed that the presence of CHIP was associated with an increased risk of colorectal cancer. The odds ratio (OR) for colorectal cancer in the presence of CHIP was 1.20 (P = 0.006). This association remained significant even after excluding participants with a family history of bowel cancer (multivariate OR, 1.19; P = 0.007). Subgroup analyses demonstrated that CHIP independently increased the risk of colorectal cancer in females (multivariate OR, 1.25; P = 0.018) and in individuals older than 60 years (multivariate OR, 1.17; P = 0.046). Gene-specific analyses revealed that mutations in TET2 and ATM were particularly significant in relation to colorectal cancer risk, with an OR of 1.62 (P = 0.002) for TET2 and 2.98 (P < 0.001) for ATM.

CONCLUSIONS

Our findings indicate that CHIP is associated with an increased risk of colorectal cancer, particularly in individuals more than 60 years of age or in females.

IMPACT

Screening for CHIP in the population may improve the early detection and diagnosis rates of colorectal cancer.

Neomorphic leukemia-derived mutations in the TET2 enzyme induce genome instability via a substrate shift from 5-methylcytosine to thymine

Ten-eleven translocation (TET) enzymes oxidize 5-methylcytosine (mC) in DNA, contributing to the regulation of gene transcription. Diverse mutations of TET2 are frequently found in various blood cancers, yet the full scope of their functional consequences has been unexplored. Here, we report that a subset of TET2 mutations identified in leukemia patients alter the substrate specificity of TET2 from acting on mC to thymine. This neomorphic activity results from substitutions at key residues involved in the interactions with the mC base, including Asn1387 and His1904. Recombinant human TET2 proteins harboring the mutation of these residues can catalyze the oxidation of thymine to 5-hydroxymethyluracil (hmU) and 5-formyluracil (fU). Exogenous expression of the mutant TET2 Asn1387Thr (N1387T) in HEK293T cells leads to hmU accumulation, with levels further increased in cells lacking the glycosylase SMUG1. Endogenous knock-in of N1300T, the murine equivalent of N1387T, in mouse embryonic stem cells induces hmU production, causing DNA lesions and transcriptional activation of DNA damage response genes. N1300T cells accumulate more additional mutations with extended culture and exhibit heightened sensitivity to ATR inhibition compared to Tet2 knockout cells. Our study reveals that certain patient-derived TET2 mutations can acquire unexpected gain-of-function activities beyond impairing mC oxidation, offering a fresh perspective on the diverse molecular etiology of mutant TET2-related leukemogenesis.

Implications of Clonal Hematopoiesis in Hematological and Non-Hematological Disorders

Clonal hematopoiesis (CH) is associated with an increased risk of developing myeloid neoplasms (MNs) such as myelodysplastic neoplasm (MDS) and acute myeloid leukemia (AML). In general, CH comprises clonal hematopoiesis of indeterminate potential (CHIP) and clonal cytopenia of undetermined significance (CCUS). It is an age-related phenomenon characterized by the presence of somatic mutations in hematopoietic stem cells (HSCs) and hematopoietic stem and progenitor cells (HSPCs) that acquire a fitness advantage under selection pressure. Individuals with CHIP have an absolute risk of 0.5-1.0% per year for progressing to MDS or AML. Inflammation, smoking, cytotoxic therapy, and radiation can promote the process of clonal expansion and leukemic transformation. Of note, exposure to chemotherapy or radiation for patients with solid tumors or lymphomas can increase the risk of therapy-related MN. Beyond hematological malignancies, CH also serves as an independent risk factor for heart disease, stroke, chronic obstructive pulmonary disease, and chronic kidney disease. Prognostic models such as the CH risk score and MN-prediction models can provide a framework for risk stratification and clinical management of CHIP/CCUS and identify high-risk individuals who may benefit from close surveillance. For CH or related disorders, therapeutic strategies targeting specific CH-associated mutations and specific selection pressure may have a potential role in the future.

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.

[Clinical characteristics and prognosis of patients with myelodysplastic syndrome with a bone marrow nucleated erythroid cell proportion of greater than or equal to 50]

Objective: To analyze the clinical characteristics and prognosis of patients with myelodysplastic syndrome (MDS) with a bone marrow nucleated erythroid cell proportion of greater than or equal to 50% (MDS-E) . Methods: The clinical characteristics and prognostic factors of patients with MDS-E were retrospectively analyzed by collecting the case data of 1 436 newly treated patients with MDS diagnosed in the Institute of Hematology and Blood Diseases Hospital, Chinese Academy of Medical Sciences from May 2014 to June 2023. Results: A total of 1 436 newly diagnosed patients with complete data were included in the study, of which 337 (23.5%) patients with MDS-E had a younger age of onset and lower neutrophil and platelet counts compared with those in patients with an erythroid cell proportion of less than 50% (MDS-NE) (all P<0.05). The proportion of MDS cases with ring sideroblasts (MDS-RS) was higher in the MDS-E group than in the MDS-NE group, and multi-hit TP53 mutations were more enriched in the MDS-E group than in the MDS-NE group (all P<0.05). Among patients with MDS-RS, the frequency of complex karyotypes and the TP53 mutation rate were significantly lower in the MDS-E group than in the MDS-NE group (0 vs 11.9%, P=0.048 and 2.4% vs 15.1%, P=0.053, respectively). Among patients with TP53 mutations, the frequencies of complex karyotypes and multi-hit TP53 mutations were significantly higher in the MDS-E group than in the MDS-NE group (87.5% vs 64.6%, P=0.003 and 84.0% vs 54.2%, P<0.001, respectively). Survival analysis of patients with MDS-RS found that the overall survival (OS) in the MDS-E group was better than that in the MDS-NE group [not reached vs 63 (95% CI 53.3-72.7) months, P=0.029]. Among patients with TP53 mutations and excess blasts, the OS in the MDS-E group was worse than that in the MDS-NE group [6 (95% CI 2.2-9.8) months vs 12 (95% CI 8.9-15.1) months, P=0.022]. Multivariate analysis showed that age of ≥65 years (HR=2.47, 95% CI 1.43-4.26, P=0.001), mean corpuscular volume (MCV) of ≤100 fl (HR=2.62, 95% CI 1.54-4.47, P<0.001), and TP53 mutation (HR=2.31, 95% CI 1.29-4.12, P=0.005) were poor prognostic factors independent of the Revised International Prognostic Scoring System (IPSS-R) prognosis stratification in patients with MDS-E. Conclusion: Among patients with MDS-RS, MDS-E was strongly associated with a lower proportion of complex karyotypes and TP53 mutations, and the OS in the MDS-E group was longer than that in the MDS-NE group. Among patients with TP53 mutations, MDS-E was strongly associated with complex karyotypes and multi-hit TP53 mutations, and among TP53-mutated patients with excess blasts, the OS in the MDS-E group was shorter than that in the MDS-NE group. Age of ≥65 years, MCV of ≤100 fl, and TP53 mutation were independent adverse prognostic factors affecting OS in patients with MDS-E.

Aging and comprehensive molecular profiling in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aging-related and heterogeneous hematopoietic malignancy. In this study, a total of 1,474 newly diagnosed AML patients with RNA sequencing data were enrolled, and targeted or whole exome sequencing data were obtained in 94% cases. The correlation of aging-related factors including age and clonal hematopoiesis (CH), gender, and genomic/transcriptomic profiles (gene fusions, genetic mutations, and gene expression networks or pathways) was systematically analyzed. Overall, AML patients aged 60 y and older showed an apparently dismal prognosis. Alongside age, the frequency of gene fusions defined in the World Health Organization classification decreased, while the positive rate of gene mutations, especially CH-related ones, increased. Additionally, the number of genetic mutations was higher in gene fusion-negative (GF-) patients than those with GF. Based on the status of CH- and myelodysplastic syndromes (MDS)-related mutations, three mutant subgroups were identified among the GF- AML cohort, namely, CH-AML, CH-MDS-AML, and other GF- AML. Notably, CH-MDS-AML demonstrated a predominance of elderly and male cases, cytopenia, and significantly adverse clinical outcomes. Besides, gene expression networks including HOXA/B, platelet factors, and inflammatory responses were most striking features associated with aging and poor prognosis in AML. Our work has thus unraveled the intricate regulatory circuitry of interactions among different age, gender, and molecular groups of AML.