To understand why METTL3 has attracted such intense scrutiny, it helps to start with the chemistry. N6-methyladenosine is the most abundant internal chemical modification found in messenger RNA across eukaryotic cells, and it is installed and removed dynamically by dedicated enzyme complexes. METTL3 functions as the chief catalytic subunit of the methyltransferase complex, working alongside METTL14, which provides structural support, and accessory factors such as WT1-associated protein, VIRMA/KIAA1429, RBM15 and ZC3H13, which help target the complex to specific RNA substrates. The review details METTL3’s modular architecture: a central methyltransferase domain that binds the universal methyl donor S-adenosylmethionine, a zinc finger domain and a leading helix that contribute to substrate recognition, and a nuclear localization signal that governs where in the cell the protein operates. This structural organization allows METTL3 to deposit methyl marks onto thousands of RNA transcripts, altering their stability, translation efficiency, splicing and export without changing the underlying genetic sequence.

Because m6A methylation acts post-transcriptionally, it gives cancer cells a rapid and reversible way to reprogram gene expression. The review documents how METTL3 expression is itself regulated by an array of upstream signals, including cigarette smoke condensate in lung cancers, lactylation of the histone mark H3K18 in pancreatic ductal adenocarcinoma, the transcription factor Yin-yang 1, the hepatitis B X-interacting protein in hepatoblastoma, and the peptidyl prolyl isomerase PIN1. Once elevated, METTL3 methylates transcripts encoding drivers of proliferation, invasion and metabolic adaptation in malignancies ranging from acute myeloid leukemia and chronic myeloid leukemia to pancreatic, colorectal, gastric and esophageal cancers, hepatocellular carcinoma, glioblastoma, bladder cancer, ovarian cancer, prostate cancer, osteosarcoma and lung adenocarcinoma. In leukemia in particular, pharmacological inhibition of METTL3 has emerged as an active therapeutic strategy, with experimental inhibitors demonstrating that the enzyme is a druggable target rather than an incidental marker.

The most consequential portion of the review, however, concerns tumor immune escape, the process by which malignant cells avoid recognition and destruction by cytotoxic T lymphocytes, natural killer cells and other immune effectors. The authors argue that METTL3 operates along two parallel routes. The first is intrinsic: within tumor cells, METTL3-mediated methylation of specific transcripts triggers metabolic reprogramming that changes what nutrients the tumor consumes and what metabolites it releases into its surroundings. In several cancer types, METTL3 upregulates glycolytic enzymes such as hexokinase 2, intensifying aerobic glycolysis and depleting glucose from the microenvironment while flooding it with lactate and other immunosuppressive metabolites. In hepatocellular carcinoma associated with non-alcoholic fatty liver disease, METTL3 has been linked through the SREBP cleavage activating protein to lipid metabolic shifts that further distort immune signaling. These metabolic alterations do more than feed the tumor; they create a biochemical landscape in which infiltrating lymphocytes struggle to maintain their effector functions.

The second route is extrinsic and centers on the functional remodeling of tumor-infiltrating immune cells themselves. The review synthesizes evidence that METTL3 activity in macrophages skews these cells toward a tumor-associated, pro-tumoral phenotype, in part by methylating transcripts tied to the complement receptor C5aR1 and other polarization regulators. In myeloid-derived suppressor cells, METTL3-dependent methylation enhances immunosuppressive output, including the catabolism that generates kynurenine, a metabolite that acts on the N-methyl-D-aspartate receptor and other targets to dampen T-cell responses. Dendritic cells, the professional antigen-presenting cells that ignite anti-tumor T-cell immunity, also fall under METTL3’s influence, with methylation of transcripts governing maturation and interferon signaling impairing their ability to present tumor-associated antigens. Even regulatory T cells, the immune system’s own brakes, appear subject to METTL3-controlled tuning, which can tilt the balance of the tumor immune microenvironment further toward suppression.

Immune checkpoint blockade, the class of therapies that includes antibodies against PD-1 and its ligand PD-L1, has transformed treatment for many cancers but fails in a majority of patients. The review makes the case that METTL3 is deeply entangled with this variability. In lung adenocarcinoma, METTL3-mediated methylation influences splicing factors such as serine-arginine protein kinase 1, affecting PD-L1 expression and thereby the tumor’s visibility to checkpoint inhibitors. In melanoma and other models, elevated METTL3 in tumor cells has been associated with reduced interferon-gamma responsiveness and diminished recruitment of cytotoxic T lymphocytes, whereas loss of METTL3 can restore inflammatory chemokine production and sensitize tumors to anti-PD-1 therapy. Conversely, METTL3 activity within T cells themselves regulates their differentiation, integrin beta 1-mediated trafficking, granzyme B production and persistence, meaning that the same enzyme can either undermine or support immunotherapy depending on which cell compartment is examined. This cell-type-specific duality, the authors emphasize, is precisely why a systems-level understanding of the METTL3 network is needed before the enzyme can be safely targeted in combination regimens.

The clinical dimension of the review extends to biomarker discovery. Across multiple tumor types, METTL3 expression profiles correlate with disease stage, immune infiltration patterns, immune checkpoint molecule abundance and patient survival, suggesting that METTL3 levels in tumor biopsies could one day help stratify patients for immunotherapy or identify those likely to experience hyperprogression. The authors also survey emerging therapeutic approaches beyond small-molecule catalytic inhibitors, including RNA-targeted strategies such as antisense oligonucleotides and targeted protein degradation, as well as rational combinations that pair METTL3 inhibition with immune checkpoint blockade, metabolic interventions or epigenetic drugs. The concept of topical immune modulation, in which RNA-modification biology is exploited to reprogram immune cells locally within the tumor, features among the forward-looking therapeutic ideas discussed.

Yet the review is equally candid about the gaps that remain. The complete molecular network connecting METTL3 to tumor immune escape has not been systematically mapped, and many of the individual methylated transcripts responsible for the phenotypes described above have been characterized only in isolation. It is not always clear whether METTL3’s effects on immunity are direct, mediated through methylation of immune-regulatory transcripts, or indirect, secondary to its influence on tumor metabolism and growth. Context dependence complicates the picture further: METTL3 appears to act as an oncogene in several cancers but has been reported to exert tumor-suppressive effects in others, and its activity in immune cells can either restrain or promote anti-tumor responses depending on the cell type and disease setting. Resolving these contradictions, the authors argue, will require single-cell multi-omics approaches that can trace m6A deposition, transcript output and immune phenotype simultaneously at cellular resolution in human tumors.

The overarching message is that METTL3 should be viewed as a critical molecular hub bridging the intrinsic properties of cancer cells and the immune responses of the surrounding microenvironment. As the most prevalent internal RNA modification in eukaryotes, m6A methylation offers tumors a fast, flexible and reversible layer of gene control, and METTL3 is the enzyme that wields it. Whether delivered as a standalone epitranscriptomic therapy or woven into combination strategies with checkpoint inhibitors and metabolic drugs, precise targeting of METTL3 represents a highly promising anti-tumor frontier. The authors caution that translating that promise into clinical benefit will depend on refined dissection of the regulatory network governing tumor immune escape and on the development of highly specific agents that can reach the right cells at the right time. For now, the review consolidates a rapidly growing literature into a coherent framework, positioning the RNA methyltransferase that was once studied as a matter of basic biochemistry at the center of the fight against cancer’s ability to hide.

Subject of Research: The role of the m6A RNA methyltransferase METTL3 in tumor immune escape and cancer treatment

Article Title: Methyltransferase-like 3: structure, biological function and role in tumor immune escape and treatment

Article References: Liu, G., Zhu, Y., Zhang, J., Wu, J., Liao, M., Zhao, J., Guo, M., & Xu, L. (2026). Methyltransferase-like 3: structure, biological function and role in tumor immune escape and treatment. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08960-y

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08960-y

Keywords: METTL3, m6A methylation, tumor immune escape, epitranscriptomics, RNA modification, tumor microenvironment, immune checkpoint blockade, metabolic reprogramming, immunotherapy, cancer epigenetics, tumor-associated macrophages, PD-L1