Blood stem cells are crucial for producing the billions of blood cells circulating daily, maintaining a finely balanced ecosystem that ensures the immune system’s vitality and the ability to respond to environmental stressors. However, researchers have long faced a significant obstacle in directly monitoring the behavior of thousands of individual stem cells over a lifespan, as genetic modification techniques suitable for model organisms cannot ethically or practically be applied to humans. The novel approach, detailed in this study, circumvents these challenges by exploiting naturally occurring epigenetic modifications called DNA methylation marks.

DNA methylation involves the addition of chemical tags to DNA at specific genomic sites, regulating gene expression without altering the underlying genetic code. These methylation patterns are faithfully copied during cell division and serve as a natural “barcode” reflecting each cell’s lineage history. By reading these binary on-off methylation states in individual cells, researchers crafted an epigenetic family tree of hematopoietic cells, providing unprecedented insights into clonal dynamics throughout aging.

The researchers developed a pioneering technique termed EPI-Clone, which modifies an existing single-cell sequencing platform to decode these methylation barcodes at remarkable resolution. Using EPI-Clone, they traced the lineage trajectories of tens of thousands of blood stem cells from both mice and human donors aged between 35 and 70 years. Their analyses revealed a striking age-associated shift from a richly diverse stem cell pool in youth to dominance by fewer, larger clones by age 50, a trend that becomes nearly universal after age 60.

This clonal dominance is accompanied by a preference of these prolific clones to produce myeloid cells—immune cells implicated in chronic inflammation—while other stem cells fade from the active compartment. The loss of stem cell diversity destabilizes the blood system’s adaptability, making it more vulnerable to physiological stress and reducing its ability to mount robust immune responses. Such changes provide a plausible biological underpinning for inflammaging, the persistent low-grade inflammation that characterizes aging and predisposes individuals to cancer, cardiovascular diseases, and autoimmunity.

Interestingly, while some of the dominant clones harbored mutations typically linked to clonal hematopoiesis (CH)—a condition associated with increased risks of leukemia and cardiovascular events—a substantial fraction lacked known mutations entirely. This finding challenges the current paradigm that clonal expansion is largely driven by oncogenic mutations, indicating that the aging blood system may naturally favor clonal selection mechanisms independent of mutation status. Thus, clonal expansion appears to be an intrinsic feature of hematopoietic aging rather than solely a herald of malignancy.

By precisely mapping the decline in stem cell diversity and identifying problematic clones before clinical symptoms emerge, this research paves the way for revolutionary diagnostic tools. Clinicians could employ epigenetic barcoding to monitor blood stem cell dynamics as early biomarkers of unhealthy aging and disease risk. Such early warnings would enable timely preventative interventions, revolutionizing precision medicine approaches to age-related blood disorders and immune dysfunction.

Moreover, the study’s detailed insights are crucial for evaluating the potential of rejuvenation therapies, which aim to restore youthful cellular profiles and immune function. While experimental approaches in mice have demonstrated that selectively removing myeloid-biased stem cells can revitalize the blood system, similar strategies in humans have been hindered by the inability to accurately identify and track clonal behaviors. EPI-Clone’s reliance on natural epigenetic barcodes, rather than artificial genetic labels, makes it uniquely suitable for clinical research, bypassing ethical and technical roadblocks.

This innovative technology and the resulting biological insights represent a significant leap forward for the field of hematology and aging research. As Dr. Lars Velten from the Centre for Genomic Regulation (CRG) explains, blood stem cells compete dynamically for survival, producing a rich ecosystem in youth that deteriorates with age as some clones dominate while others are lost. This loss of diversity undermines the hematopoietic system’s robustness, highlighting how stem cell ecology shifts detrimentally over time.

Further development and refinement of EPI-Clone hold immense promise for expanding clinical research capabilities. By enabling longitudinal studies of blood stem cell populations in living humans, it offers a window into the fundamental mechanisms driving blood aging and the potential to develop targeted therapies to combat age-associated diseases. The approach heralds a new era wherein we can “see” and measure healthy versus unhealthy aging at the cellular lineage level, bridging the gap between molecular biology and translational medicine.

In conclusion, this study elegantly demonstrates that the aging of the blood system is marked not simply by random decline but by orderly, clock-like clonal evolution governed by epigenetic changes. The discovery that clonal expansion is a natural aging feature, rather than only a cancer precursor, reframes understanding of hematopoiesis and opens realistic pathways for intervention. With tools like EPI-Clone, the prospect of precision healthcare strategies tailored to an individual’s unique stem cell dynamics is rapidly approaching reality, offering hope for healthier aging and enhanced resilience against disease.

Subject of Research: Animals

Article Title: Clonal tracing with somatic epimutations reveals dynamics of blood ageing

News Publication Date: 21-May-2025

Web References: http://dx.doi.org/10.1038/s41586-025-09041-8

Image Credits: Joe Bowness/Centro de Regulación Genómica

Keywords: Cancer, Blood, Molecular biology

At the core of this innovation is the design of a targeted methylation panel focusing on 448 CpG sites known to exhibit variable methylation either between or within blood progenitor populations. This high-resolution panel allows for a precise capture of epimutations—heritable, somatic changes in DNA methylation patterns—that act as natural barcodes for tracing cellular lineage. Complementing this, the inclusion of 147 genomic regions frequently mutated in clonal hematopoiesis and 20 regions targeting the Y chromosome offers a robust ground truth against which the epigenetic clones identified with EPI-Clone can be validated.

The researchers applied this panel to CD34⁺-enriched total bone marrow samples collected from seven human donors of diverse ages, spanning a spectrum from young adults to the elderly. Alongside this, an expanded set of CD34⁺ cells was assembled from multiple donors to strengthen the dataset. The meticulous profiling of 135,432 single cells using scTAM-seq—a single-cell targeted methylation sequencing technique—enabled comprehensive scrutiny of both genetic mutations and epigenetic states. The samples were concurrently characterized by staining with a battery of 45 antibodies targeting surface proteins, thereby enriching the phenotypic context of the epigenetic data.

Leveraging a statistical framework known as CHOIR (Clonal Hematopoiesis Outlier Identification in R), the study sifted through the heterogeneous single-cell data to detect expanded clones, carefully combining epigenetic signatures and surface marker expression to delineate cell types and differentiation states. This dual-layered analysis refined the identification of clones, ensuring that both dynamic CpGs—those changing during differentiation—and robust phenotypic markers scouted by the antibody panel contributed to clone definition.

Validation of this intricate approach came from the detection of canonical CH mutations and loss of Y chromosome (LoY) events, which served as internal clonal markers. Consistently, clones bearing these somatic mutations grouped tightly together in reduced-dimensionality embeddings based solely on static CpG methylation patterns. This concordance affirms the fidelity of epigenetic marks as reliable surrogates for underlying genetic clonal identity. Notably, clones identified by EPI-Clone aligned well with known CH clones in nearly all donors, barring one with considerably fewer sampled cells, underscoring the importance of adequate cellular representation for accurate clonal mapping.

Quantitative analyses revealed that clonal populations driven by CH mutations consisted predominantly of mutant cells—averaging about 78.8%—while wild-type dominated clones exhibited an average purity exceeding 95%. These values are conservative estimates given potential allelic dropout in mutation detection at the single-cell level. Importantly, the method proved more adept at discerning clones in older individuals, who typically harbor less diverse hematopoietic pools due to accumulated clonal expansions, suggesting that epigenetic tracing performs optimally amidst reduced clonal complexity seen in aging hematopoiesis.

Beyond uncovering clones with known CH drivers, EPI-Clone unveiled a broader spectrum of 67 additional clonal expansions across the cohort, revealing a hidden landscape of hematopoietic diversity untouched by previously characterized mutations. This observation hints at the presence of unknown or subclonal drivers contributing to hematopoietic architecture or reflects the stochastic nature of epigenetic drift within the blood system.

The analysis extended to different immune cell types, confirming that natural killer cells and immature B cells also segregate predictably by clonal identity in accordance with their methylation profiles. T cells and mature B cells formed distinct, lymphoid-dominant clusters that diverged from myeloid-origin clones, illustrating separate ontogenetic trajectories within hematopoiesis. Intriguingly, in one donor with a large CH clone, mutant T cells clustered tightly with other CH-derived cells, suggesting that some mutated clones contribute broadly across lineages, reinforcing the notion of clonal stability from hematopoietic stem cells through multiple lineages including myeloid, T cells, NK cells, and immature B cells.

By establishing a conservative lower bound for EPI-Clone’s sensitivity, the group identified the smallest detectable CH clone, harboring a DNMT3A(C666Y) mutation, comprising 145 cells and representing about 1% of the myeloid compartment in one donor. Furthermore, notable diversification within large CH clones, such as the DNMT3A(R659H) mutation carrier, manifested as bifurcated epigenetic subclones with distinct but related static CpG profiles. This insight suggests that epimutations accrue progressively over time, refining phylogenetic resolution and providing a longitudinal record of clonal evolution spanning decades.

Together, these findings underscore EPI-Clone’s capacity to chart the nuanced topography of hematopoietic clonal expansions in human bone marrow and blood. By integrating high-dimensional epigenetic and phenotypic data with somatic mutation analyses, the approach extends our ability to dissect blood aging at unparalleled detail. It offers promise for elucidating the role of clonal hematopoiesis in age-related diseases and potentially guiding precision interventions targeting aberrant clonal dynamics.

This pioneering work melds cutting-edge single-cell epigenomics with rigorous statistical modeling, capturing a snapshot of blood’s evolutionary history etched into the methylome. As the field advances, EPI-Clone could catalyze transformative insights into hematological health and disease, driving a new era of clonal blood biology with far-reaching implications for aging research, cancer biology, and regenerative medicine.

Subject of Research: Clonal dynamics of human hematopoietic stem and progenitor cells during aging, traced via somatic epimutations and mutational profiling.

Article Title: Clonal tracing with somatic epimutations reveals dynamics of blood ageing.

Article References:
Scherer, M., Singh, I., Braun, M.M. et al. Clonal tracing with somatic epimutations reveals dynamics of blood ageing. Nature (2025). https://doi.org/10.1038/s41586-025-09041-8

Image Credits: AI Generated