Epigenetics refers to chemical and structural changes that influence how genes are used without altering the underlying DNA sequence. One of the most extensively studied epigenetic marks is DNA methylation, in which small chemical groups called methyl groups are attached to DNA, often near regulatory regions that help control gene activity. These marks can change in response to age, immune stimulation, disease, medication and environmental exposures. Because methylation patterns vary across the genome, an epigenome-wide association study can survey hundreds of thousands of sites at once to identify regions associated with a biological state or change over time. In this study, the investigators used Infinium Methylation EPIC v2.0 arrays to profile methylation in PBMC DNA. The approach is designed to measure methylation at a large number of genomic locations, allowing researchers to compare patterns across repeated samples from transplant recipients and to identify regions that become differentially methylated during long-term follow-up.

Liver transplantation creates a distinctive biological setting in which several forces act simultaneously. The procedure replaces a failing organ, but recipients must also live with long-term immune-modulating treatment intended to prevent rejection of the donated liver. The transplanted organ, the recipient’s immune system and medications therefore remain in continuous interaction. Over years, these factors can influence immune-cell composition and function, inflammation and tissue maintenance. The study was designed to examine whether this prolonged period after transplantation was associated with measurable epigenetic changes related to aging. Rather than relying on a single sample, the researchers compared three time points: T0, the time of transplantation; T5, five years afterward; and T10, ten years afterward. This longitudinal structure is important because it allows molecular differences to be considered as changes within a long-term clinical course, rather than simply as differences between unrelated groups sampled at one moment.

The largest signal emerged in the comparison between five and ten years after transplantation. Across that period, 211 DMRs showed significant differences in methylation and were enriched in immune-related pathways. In genomic research, pathway enrichment means that the affected regions occur more frequently than expected within sets of genes or biological processes connected to a particular function. The finding does not mean that every gene in an immune pathway changed, nor does methylation alone establish that a gene’s activity increased or decreased. Instead, it points to coordinated molecular remodeling in genomic regions associated with immune biology. Such remodeling could reflect changes in the proportions of circulating immune-cell types, altered activity within those cells, cumulative exposure to immunosuppressive therapy or the physiological consequences of living with a transplanted organ. The reported results identify an immune-centered pattern, but they do not by themselves determine which of these mechanisms is responsible or whether the methylation changes directly affect clinical outcomes.

The investigators also examined epigenetic age acceleration, a measure that compares a person’s molecular age with expectations based on chronological age. Epigenetic clocks are statistical models trained on DNA-methylation patterns that change predictably across the lifespan. When a person’s estimated epigenetic age is higher or lower than expected, the difference can be described as age acceleration or deceleration. Researchers often distinguish intrinsic measures, which are intended to reflect aging-related changes within cells, from extrinsic measures that may be influenced by immune-cell composition and other blood-based factors. In the transplant cohort, the clock analyses showed no significant differences in biological age acceleration. This negative result is central to the study’s interpretation. It indicates that the observed methylation changes should not automatically be described as evidence that recipients were aging faster overall. Instead, the molecular shifts appeared more closely related to immune remodeling than to a detectable change in the global pace captured by the epigenetic clocks used in the analysis.

The distinction matters because transplantation can produce dramatic biological changes that are not necessarily equivalent to accelerated aging. A patient’s immune system may adapt to the presence of a graft, respond to chronic medication exposure and undergo shifts in circulating cell populations, all of which can alter blood-based methylation profiles. A clock designed to summarize broad age-related patterns may remain stable while particular immune-associated genomic regions change substantially. Conversely, a change in an epigenetic clock would not automatically reveal which biological system was responsible. By examining DMRs and age-acceleration measures together, the researchers were able to separate these possibilities more clearly. Their results support a model in which long-term liver transplant survival is associated with selective epigenetic adaptation, especially in immune pathways, without evidence in this analysis of accelerated global biological aging. The work therefore adds nuance to discussions of age in transplant medicine, where chronological age, organ health, immune function and molecular aging may not move in parallel.

The study’s material also illustrates the value and limitations of using PBMCs to investigate transplant biology. These cells include several immune-cell populations found in peripheral blood, making them practical for repeated sampling and relevant to systemic immune responses. However, a PBMC methylation profile represents a mixture of cell types rather than a single uniform population. If the relative abundance of lymphocytes, monocytes or other blood cells changes over time, part of the apparent methylation difference may reflect altered cellular composition. The reported enrichment of immune pathways is consistent with such biology, but additional experiments would be needed to determine whether the signals arise from changing cell proportions, stable changes within particular cell types or both. The source report does not establish that the DMRs predict rejection, infection, graft dysfunction, cancer or survival for individual patients. Nor does it show that modifying any identified methylation mark would improve outcomes. These boundaries are essential when translating an association study into potential clinical meaning.

Even with those limitations, the findings create a basis for more detailed research into the long-term molecular course of liver transplantation. Future studies could track larger groups of recipients, integrate methylation data with gene-expression, immune-cell and medication records, and test whether particular epigenetic patterns are associated with specific clinical events. Analyses of purified immune-cell populations could help determine whether the 211 DMRs represent cell-composition changes or stable regulatory remodeling. Repeated sampling beyond ten years could also reveal whether the immune-associated pattern persists, intensifies or eventually stabilizes. For now, the study’s main message is that long-term post-transplant biology cannot be reduced to a single measure of molecular age. In these recipients, the clearest epigenetic changes were linked to immune-related pathways, while epigenetic clocks detected no significant acceleration of biological aging. That combination suggests adaptation and remodeling rather than a simple molecular replay of accelerated aging.

The study’s longitudinal design strengthens the interpretation of its methylation findings because the comparisons were anchored to successive stages in the same post-transplant trajectory. This approach can reduce some of the ambiguity that arises when molecular profiles from different people are compared at a single time point. It also makes the timing of the strongest signal informative: the major remodeling was detected later in follow-up rather than immediately around transplantation. That pattern is compatible with biological processes that accumulate or evolve over years, although the study cannot establish which exposure or event initiated the changes.

DNA methylation arrays provide broad coverage of the epigenome, but they measure a molecular mark rather than gene activity itself. A differentially methylated region may lie in a regulatory part of the genome, yet its functional consequence depends on its location, the surrounding regulatory architecture and the cell type carrying the mark. Linking the reported regions to transcriptional measurements would therefore be an important next step. Such work could clarify whether the immune-related enrichment corresponds to altered expression of immune genes, changes in cellular state, or both. Protein measurements and functional immune assays could further test whether the molecular pattern has observable effects on immune responses.

Interpretation also benefits from separating discovery from prediction. Identifying a set of regions that changes across follow-up can reveal biology relevant to transplant survivorship, but it does not make those regions ready for use as a clinical biomarker. A useful biomarker would need to show reproducible performance in independent transplant populations and demonstrate associations with outcomes that matter to care. The report’s open-access brief-report format and its statement that the article was being shared before replacement by a final version of record also mean that details may be refined in the final publication. Nonetheless, the central observation is sufficiently focused to guide subsequent work: post-transplant molecular aging research should examine immune-system remodeling alongside, rather than beneath, broader measures of epigenetic age.

Subject of Research: Long-term immune-related epigenetic remodeling after liver transplantation

Article Title: Epigenome-wide association study uncovers aging-related genes and enriched pathways in liver transplant recipients

Article References: Baciu, C., Hasjim, B. J., Pasini, E., Saracino, G., Asrani, S. K., & Bhat, M. (2026). Epigenome-wide association study uncovers aging-related genes and enriched pathways in liver transplant recipients. Epigenetics Communications. https://doi.org/10.1186/s43682-026-00050-w

Image Credits: AI Generated

DOI: 10.1186/s43682-026-00050-w

Keywords: liver transplantation, DNA methylation, epigenetics, biological aging, immune pathways, epigenetic clocks, PBMCs, differentially methylated regions, Epigenome-wide, association, uncovers, aging-related