To understand why this matters, it helps to grasp the mechanics of the modification itself. m⁶A is deposited on adenosine bases within mRNA by a set of enzymes collectively called writers, the best characterized of which is the methyltransferase complex built around METTL3. Those marks can then be removed by erasers, chiefly the demethylases FTO and ALKBH5, and interpreted by readers, most notably proteins of the YTH domain family such as YTHDF1, that dictate whether a given transcript is stabilized, degraded, exported, or translated. Through this Writers–Erasers–Readers network, a cell can rapidly reprogram its entire protein output without changing a single letter of DNA sequence. The review emphasizes that this system is exquisitely sensitive to the conditions inside a tumor, responding to inflammatory signals, hypoxia, and metabolic stress, and that its output can swing the immune response in either direction.

The first direction is the one oncologists want: amplification of anti-tumor immunity. When the m⁶A machinery is configured favorably, it promotes type I interferon signaling, the chemical alarm system that alerts neighboring cells to danger. It also supports the maturation of dendritic cells, the sentinels that capture tumor antigens and present them to T cells, and it enhances antigen presentation itself, making cancer cells more visible to immune surveillance. The review highlights that reader proteins such as YTHDF1 can boost the translation of immune-related transcripts, while proper m⁶A deposition encourages macrophages to polarize toward the M1-like state, the pro-inflammatory, tumor-killing flavor of these scavenger cells. In these settings, m⁶A effectively turns up the volume on the innate immune system, priming the adaptive response that immune checkpoint blockade therapies are designed to unleash.

The second direction is far darker. Tumors have learned to hijack the very same machinery for their own protection. The review documents how cancer cells manipulate m⁶A regulators to suppress the cGAS-STING pathway, the intracellular sensor that normally detects leaked tumor DNA and triggers interferon production. They also dampen RIG-I and MDA5, the cytoplasmic receptors that recognize viral-like double-stranded RNA, and they promote the degradation of antigen transcripts, effectively erasing the molecular fingerprints that would otherwise expose them to cytotoxic T cells. Perhaps most strikingly, tumor-hijacked m⁶A enzymes silence viral mimicry, the process by which endogenous retroviruses and other repetitive elements in the genome are reactivated to produce double-stranded RNAs that fool the cell into thinking it is infected. When that ancient alarm is muffled, tumors shed one of their most potent endogenous triggers of immune attack.

The consequences ripple outward into the tumor immune microenvironment. The review describes how altered m⁶A signaling skews macrophage polarization away from the M1 state and toward the M2 phenotype, which suppresses inflammation and supports tumor growth. It also drives what the authors call immunosuppressive myeloid remodeling, expanding populations of myeloid-derived suppressor cells and other innate cells that actively paralyze T cells. In parallel, m⁶A regulation extends into non-coding RNA networks, including competing endogenous RNA circuits, that modulate how much interferon and inflammatory signaling a tumor cell generates. The net effect is a microenvironment in which the innate arm of immunity, which should be the first line of defense, has been co-opted into an accomplice of the cancer.

This mechanistic picture leads the authors to a conceptual proposal that may prove to be the review’s most influential contribution: an m⁶A-driven immunophenotyping framework. Rather than treating all tumors as a single immunological entity, the framework stratifies cancers into three mechanistically distinct categories. The first comprises dendritic cell-dysfunctional so-called cold tumors, in which antigen presentation and T cell priming fail at the very first step. The second consists of innate-sensing-silent tumors, in which cGAS-STING and RIG-I/MDA5 pathways have been shut down so that no interferon alarm sounds even when tumor DNA and RNA are abundant. The third encompasses myeloid-suppressed hot tumors, which may look inflamed on paper but are flooded with suppressive myeloid cells that neutralize any T cell response that does arise. Each category, the authors argue, reflects a different pattern of m⁶A dysregulation and therefore demands a different therapeutic approach.

The therapeutic implications are concrete. For tumors in which the reader protein YTHDF1 drives immune evasion, inhibiting that reader could restore antigen presentation and dendritic cell function. For tumors relying on the erasers FTO or ALKBH5 to keep interferon signaling suppressed, pharmacological demethylase inhibition could reactivate viral mimicry and innate sensing, converting a cold tumor into a hot one. Conversely, in contexts where METTL3 activity itself fuels immunosuppressive myeloid remodeling, blocking the writer becomes the rational move. The review stresses that these interventions should be phenotype-specific and guided by precise biomarkers, since applying the wrong m⁶A-targeting strategy to the wrong tumor type could plausibly worsen immune suppression rather than relieve it. This mechanism-based stratification, the authors suggest, offers a path to overcoming the resistance that so frequently defeats T cell-centered immune checkpoint blockade.

That resistance problem is the clinical backdrop against which the entire review is written. Immune checkpoint inhibitors have transformed outcomes in melanoma, lung cancer, and several other malignancies, yet a large fraction of patients either never respond or relapse after an initial benefit. The review’s framing of innate immunity as a double-edged sword helps explain why: the same pathways that suppress tumorigenesis early can, under chronic inflammatory conditions, sculpt an immunosuppressive microenvironment that shields the tumor from T cells. Because m⁶A regulates both faces of that sword, it represents a uniquely powerful lever. Modulating it does not simply add another drug to the arsenal; it potentially reprograms the fundamental immunological character of the tumor, shifting the balance from suppression to activation.

Significant obstacles remain before this vision reaches the clinic. The review is candid that tumor-selective delivery of m⁶A-targeting agents is an unsolved problem, since the Writers–Erasers–Readers network operates in every cell of the body and indiscriminate interference could unleash inflammatory toxicity or impair normal immune function. Safety evaluation will need to establish that manipulating m⁶A in tumors does not destabilize the delicate equilibrium of innate immunity elsewhere. Biomarker development is equally critical, because the proposed phenotyping framework depends on reliably identifying which m⁶A-driven state a given patient’s tumor occupies, likely through transcriptomic signatures and computational methods of the kind the field has begun to apply.

Even so, the synthesis offered by Chen, Zhu, Liu, and their colleagues marks a shift in how scientists think about the interface between RNA chemistry and cancer immunology. A modification once studied as a curiosity of mRNA metabolism now emerges as a master regulator of innate immune signaling, a sculptor of the tumor microenvironment, and a plausible explanation for why some tumors hide in plain sight from the immune system. If the framework holds up under experimental and clinical scrutiny, the humble methyl group on adenosine may become one of the most consequential targets in the next generation of cancer immunotherapy, turning the epitranscriptome from a subject of basic research into a battlefield where the war against immune-resistant tumors is fought.

Subject of Research: m6A RNA modification regulation of innate immune signaling and the tumor immune microenvironment

Article Title: N⁶-methyladenosine modification regulates innate immune signaling and reshapes the tumor immune microenvironment: a review

Article References: Chen, L., Wang, Y., Zhang, M., Shen, Y., Li, J., Hu, X., Fan, Z., Zhang, Y., Qin, Y., Zhu, Y., & Liu, X. (2026). N⁶-methyladenosine modification regulates innate immune signaling and reshapes the tumor immune microenvironment: a review. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09045-6

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09045-6

Keywords: m6A modification, epitranscriptomics, innate immunity, cGAS-STING, RIG-I, tumor immune microenvironment, immune checkpoint blockade, dendritic cells, macrophage polarization, viral mimicry, YTHDF1, FTO

LINE-1 elements are the only autonomously active retrotransposons in the human genome, and although the vast majority of copies are silenced by epigenetic mechanisms, they can be reawakened in cancer. When that happens, LINE-1 open reading frame proteins, particularly ORF1p, are produced at high levels, and retrotransposition activity generates new insertions, DNA double-strand breaks, and cytoplasmic DNA fragments. These products are recognized by the cell as signs of danger. In many tumor types, LINE-1 overexpression has been linked to a phenomenon sometimes described as viral mimicry, in which the cell behaves as though it were infected by a pathogen, switching on innate immune signaling pathways that include interferon responses and inflammatory gene programs.

Homologous recombination deficiency, or HRD, is another hallmark of genomic chaos. Cells with HRD cannot accurately repair double-strand breaks through the template-based homologous recombination pathway, forcing them to rely on error-prone alternatives such as non-homologous end joining. The result is an accumulating burden of mutations, structural rearrangements, and scars in the genome, including characteristic patterns of loss of heterozygosity and telomeric allelic imbalance that can be scored as an HRD signature. HRD is well established as a predictive biomarker in ovarian, breast, pancreatic, and prostate cancers, where it predicts sensitivity to platinum chemotherapy and PARP inhibitors, but its role in gastric cancer—particularly in combination with retrotransposon activity—has been far less explored.

The new research set out to determine whether gastric cancers with high LINE-1 expression and HRD represent a distinct biological subgroup with heightened immune activation. Drawing on genomic and transcriptomic data from gastric cancer cohorts, the investigators stratified tumors according to LINE-1 retrotransposon overexpression and the presence of homologous recombination deficiency signatures, then compared immune pathway activity, immune cell infiltration, and clinically relevant molecular features across the resulting groups. The analysis integrated somatic mutation patterns, copy number alterations, mutational signatures, and expression of immune checkpoint molecules to build a comprehensive picture of the tumor microenvironment in each subgroup.

The central finding is striking: gastric tumors that combine LINE-1 overexpression with HRD show significantly stronger activation of immune signaling pathways than tumors lacking either feature. Interferon-gamma and interferon-alpha response programs, antigen processing and presentation machinery, and cytotoxic T lymphocyte activity are all enriched in this double-positive subgroup. The tumors also display greater infiltration by CD8-positive T cells and other immune effector populations, along with elevated expression of immune checkpoint genes including PD-L1, the molecular target of a class of immunotherapy drugs already used in advanced gastric cancer. In contrast, tumors without LINE-1 activation or HRD tend to show comparatively cold immune profiles with less inflammatory signaling.

From a mechanistic standpoint, the convergence of these two sources of genomic instability makes biological sense. Retrotransposon reactivation floods the cytoplasm and nucleus with aberrant nucleic acids that engage DNA sensors such as cGAS and activate the STING pathway, a central conduit to type I interferon production. At the same time, defective homologous recombination allows DNA damage to persist and diversify, generating neoantigens from accumulated mutations and further amplifying danger signaling. Together, these processes can convert an otherwise self-contained genomic meltdown into a visible inflammatory signal that recruits and activates immune cells. The study’s data suggest that in gastric cancer, LINE-1 activity and HRD are not merely parallel markers of instability but may act synergistically to shape an inflamed, immune-responsive tumor microenvironment.

The clinical implications are considerable. Immune checkpoint inhibitors have transformed the treatment of several cancers, but in gastric cancer only a subset of patients derives durable benefit, and better biomarkers are urgently needed to identify responders. If the combination of LINE-1 overexpression and HRD reliably marks a hyperinflamed, checkpoint-sensitive tumor state, it could complement existing predictors such as microsatellite instability, Epstein-Barr virus status, PD-L1 expression scores, and tumor mutational burden. Notably, the LINE-1–HRD subgroup described in the study is molecularly distinct from microsatellite instability–high tumors, meaning it could flag immunotherapy candidates among patients who would otherwise be missed by standard testing.

The findings also open therapeutic avenues beyond checkpoint blockade. Tumors with homologous recombination deficiency are classically vulnerable to PARP inhibitors and platinum-based chemotherapy, agents that exploit the repair defect to push cancer cells past the point of viable DNA damage. Combining such DNA-damage-targeted strategies with immunotherapy is an area of intense investigation, on the rationale that DNA-damaging treatment can further increase neoantigen release and immune priming. Meanwhile, pharmacological reactivation of silenced retrotransposons—for example through epigenetic drugs such as DNA methyltransferase or histone deacetylase inhibitors—is being explored as a way to induce viral mimicry in tumors that lack endogenous immune activation. The new study raises the possibility that in gastric cancer, patients whose tumors already harbor LINE-1 activity and HRD may be primed for exactly these combination approaches, whereas patients with silent genomes might need epigenetic priming first.

The research also underscores how much of cancer biology is written by the repetitive, transposable elements that make up nearly half of the human genome. Long dismissed as junk DNA, these sequences are increasingly recognized as sensors and amplifiers of cellular stress. In colorectal, esophageal, and other gastrointestinal cancers, LINE-1 expression has been associated with aggressive disease and, in some contexts, with immune evasion through interferon-mediated upregulation of checkpoint ligands. The gastric cancer findings add nuance to this picture by showing that retrotransposon activation can coincide with, rather than simply undermine, productive antitumor immunity—particularly when it occurs against the backdrop of a broken DNA repair system.

Important questions remain before these observations can be translated into routine clinical practice. The study’s conclusions rest on retrospective analysis of existing cohorts, and prospective validation in independent patient populations will be essential to confirm that the LINE-1–HRD immune signature predicts immunotherapy response. Standardized assays for measuring LINE-1 expression, such as ORF1p immunohistochemistry or targeted RNA sequencing, and validated algorithms for scoring HRD in gastric cancer will need to be developed and harmonized across laboratories. It will also be important to determine whether the immune activation seen in this subgroup translates into longer survival or better response rates in patients treated with checkpoint inhibitors, and whether resistance mechanisms emerge through immune editing or further retrotransposon-driven evolution. Longitudinal studies tracking LINE-1 activity and HRD scores during treatment could reveal whether these features are stable biomarkers or dynamic players in the evolutionary arms race between tumor and immune system.

Even at this early stage, the study offers a compelling reframing of genomic instability in gastric cancer. Rather than viewing retrotransposon activation and DNA repair deficiency solely as engines of tumor progression, the work positions them as potential Achilles’ heels—sources of the very molecular noise that the immune system can detect and attack. As biomarker panels for gastric cancer grow more sophisticated, the ancient jumping genes embedded in our chromosomes may earn a place alongside viral status and repair signatures as guides to treatment decisions. For patients facing an aggressive and often treatment-resistant disease, that shift could mean the difference between a tumor that hides from the immune system and one that announces itself loudly enough to be destroyed.

Subject of Research: Immune pathway activation in gastric cancers with LINE-1 retrotransposon overexpression and homologous recombination deficiency

Article Title: Immune pathway activation in gastric cancers with LINE-1 retrotransposon overexpression and homologous recombination deficiency

Article References: Kim, Y. J., Baek, I.-P., Eom, B. W., Seo, M.-J., Joo, H., Choi, Y. R., Park, M. K., Oh, J., Lee, B., Ham, S. M., Choi, N.-H., Hong, S.-P., Choi, J., Kim, S., Kong, S.-H., Lee, H.-J., Suh, Y.-S., Kong, J., Rhee, J.-K., … Yang, H. K. (2026). Immune pathway activation in gastric cancers with LINE-1 retrotransposon overexpression and homologous recombination deficiency. Experimental & Molecular Medicine. https://doi.org/10.1038/s12276-026-01846-5

Image Credits: AI Generated

DOI: 10.1038/s12276-026-01846-5

Keywords: gastric cancer, LINE-1 retrotransposon, homologous recombination deficiency, immune pathway activation, immunotherapy, biomarkers, genomic instability, PD-L1, interferon signaling, tumor microenvironment, PARP inhibitors, viral mimicry

Viral mimicry was formally described in 2015, when two landmark studies showed that inhibiting DNA methylation in cancer cells could trigger an interferon response without any actual virus being present. The trigger turned out to be endogenous double-stranded RNA derived from endogenous retroviruses and other repeats that had been derepressed by epigenetic drugs. Since then, a large body of work has mapped how this process works at the molecular level. Many transposable elements, including long interspersed nuclear elements such as LINE1 and short interspersed elements such as Alu, retain vestiges of their viral ancestry, including promoter sequences and the capacity to generate RNA species that form double-stranded structures. Pairs of oppositely oriented Alu elements, known as IR-Alus, can fold into intramolecular double-stranded RNA hairpins that are recognized by innate immune sensors such as MDA5, while PKR and ZBP1 provide additional surveillance routes for endogenous double-stranded RNA and Z-form nucleic acids.

The review emphasizes that viral mimicry is not an accidental by-product confined to drug treatment. Cancer-associated alterations in DNA methylation, histone modifications, splicing and RNA processing routinely generate immunogenic nucleic acids in precancerous cells. Global DNA hypomethylation, a common feature of tumour genomes, relaxes repression at repetitive loci; loss of histone marks such as H3K9me3, mediated by enzymes like SETDB1, or disruption of Polycomb repressive complexes derepresses endogenous retroviruses. Splicing defects, which are pervasive across cancer transcriptomes, can create retained introns and aberrant junctions that form double-stranded RNA or Z-RNA structures sensed by MDA5, PKR and ZBP1. Even mitochondrial double-stranded RNA and cytoplasmic RNA–DNA hybrids derived from R-loops can contribute to the endogenous pool of alarm signals. In this sense, the review argues, the pro-tumorigenic regulatory chaos of transformation is inseparable from the collateral production of viral-like nucleic acids.

Viewed through this lens, viral mimicry emerges as a tumour-suppressive mechanism that shapes tumour evolution from its earliest stages. Cells that activate these antiviral programmes can undergo apoptosis, necroptosis, pyroptosis or translational shutdown driven by PKR, or they can attract immune cells through type I interferon signalling that enhances antigen presentation and cytotoxic lymphocyte activity. Recent work describing viral mimicry as a bottleneck in early cancer evolution, including evidence that the pathway acts as a tumour suppressor in inflammatory contexts such as colitis, supports the idea that most cells attempting transformation are eliminated precisely because they cannot simultaneously disrupt their epigenome and silence the repeats that become exposed. Only clones that acquire effective escape mechanisms survive this selective filter, which is why the review frames viral mimicry escape as a prerequisite rather than an option for malignant cells.

The mechanisms cancer cells use to escape are diverse and, the authors argue, reveal a fundamental dependency. On the transcriptional side, tumours often impose compensatory epigenetic repression on repetitive elements, re-engaging DNA methyltransferases, SETDB1, the RB–EZH2 complex or KDM5B to re-silence retroelements. At the RNA level, the editing enzyme ADAR1 converts adenosine to inosine within double-stranded RNA, destabilizing the structures that immune sensors require and acting as a master regulator of viral mimicry escape; high ADAR1 activity is a hallmark of many tumours and is exploited in leukaemia relapse and other contexts. RNA modifications add another layer: N6-methyladenosine deposited by METTL3 and related machinery can reshape double-stranded RNA to prevent sensor recognition and control the fate of endogenous retroviruses. RNA decay enzymes provide a further escape route, with the exonuclease XRN1 degrading retroelement transcripts, while proteins such as DHX9 and the LINE1 ORF1 protein — which acts like a viral innate immune evasion factor — can chaperone or sequester problematic nucleic acids.

Beyond eliminating the trigger molecules themselves, tumours can dampen the downstream signalling that would translate them into an immune response. Sensor pathways can be epigenetically silenced, as has been described for STING and RIG-I–MAVS components in various cancers; interferon signalling itself can be attenuated through regulators such as USP18 and STAT2, or through negative feedback that blunts the antiviral state. Oncogenic drivers also contribute: mutant KRAS in colorectal cancer impairs DDX60-mediated double-stranded RNA accumulation and viral mimicry, converting immunologically hot tumours into cold ones, while p53 loss has been shown to create chronic viral mimicry pressure that selected clones must overcome. Chemotherapy-resistant breast cancers can switch epigenetic states to evade viral mimicry, illustrating that escape is a dynamic, evolving process throughout tumour progression rather than a one-time event.

The review also connects escape mechanisms to biomarkers and therapeutic vulnerabilities. LINE1 ORF1 protein circulating in the blood has been developed as an ultrasensitive multicancer biomarker, and genome-wide repeat landscapes measurable in cell-free DNA reflect the extent of repeat deregulation in individual tumours. Ratios of stemness to interferon signalling have been proposed as biomarkers of progression in myeloproliferative neoplasms. More importantly, every escape mechanism creates a dependency: tumours that rely on ADAR1, XRN1, DHX9, SETDB1 or m6A machinery to survive their own endogenous viral alarm are theoretically vulnerable to drugs that disable those factors. Pharmacological reactivation of viral mimicry — through DNA methyltransferase inhibitors, EZH2 inhibitors, LSD1 inhibitors, spliceosome-targeted therapies, PRMT inhibition or METTL3 blockade — has been shown in preclinical models to restore immunogenicity, and several such approaches are now entering clinical testing.

Combining viral mimicry induction with immunotherapy is a central translational theme. Because viral mimicry activation enhances antitumour immunity and sensitizes cells to immune checkpoint blockade, epigenetic priming with DNMT inhibitors followed by anti-PD1 therapy has shown promise, including in relapsed or refractory NK/T-cell lymphoma, where one of the first trials demonstrating that triggering viral mimicry could augment checkpoint immunotherapy has now been reported. Similar synergy has been observed with EZH2 inhibition in prostate cancer and glioblastoma models, with ZBP1-driven immunogenicity in HER2-directed combinations, and with strategies that restore cGAS–STING and RIG-I–MAVS signalling. Conversely, the review notes that sustained type I interferon signalling can also mediate resistance to some therapies, underscoring that timing, context and combination design matter when manipulating these pathways in patients.

By gathering this evidence into a single conceptual model, the authors propose a reframing of malignant transformation itself: cancer is not simply uncontrolled growth, but uncontrolled growth that has necessarily survived an internal antiviral insurgency of its own making. This unifying model explains why escape mechanisms are so consistently observed across tumour types, why they map onto established dependencies, and why deliberately reactivating viral mimicry represents a rational strategy to expose tumours to their own genome once again. If the framework holds up under experimental and clinical scrutiny, the ancient viral fossils scattered through human DNA may prove to be one of oncology’s most powerful untapped weapons — an alarm that every successful cancer has had to silence, and that medicine may now learn to ring.

Subject of Research: Viral mimicry escape mechanisms in malignant transformation and cancer immunotherapy

Article Title: Viral mimicry escape as a necessary feature of malignant transformation

Article References: Viral mimicry escape as a necessary feature of malignant transformation. (n.d.). https://doi.org/10.1038/s41568-026-00977-1

Image Credits: AI Generated

DOI: 10.1038/s41568-026-00977-1

Keywords: viral mimicry, transposable elements, malignant transformation, epigenetics, interferon signalling, endogenous retroviruses, ADAR1, immune checkpoint blockade, DNA methylation, cancer immunotherapy, innate immunity, double-stranded RNA