The study, led by Assistant Professor Priya Dipta of Nagoya University’s Institute for Glyco-Core Research in Japan and Professor Morten Thaysen-Andersen of Macquarie University in Australia, with collaborators including Daisuke Kasugai, Hironoshin Onizuka and colleagues at Nagoya University Graduate School of Medicine, was published in the Proceedings of the National Academy of Sciences of the United States of America. The team’s findings center on a layer of the cell surface that has long been overlooked in cancer immunology: the glycocalyx, a dense coating of proteins and lipids studded with sugar chains that mediates how cells communicate with one another and with their surroundings.

The sugar chains of the glycocalyx are frequently capped with sialic acid, a negatively charged sugar that influences everything from cell adhesion to immune recognition. Sialic acids attach to underlying glycans through two main linkage types, designated α2,3 and α2,6. Altered sialylation is already known to help cancer cells evade immune surveillance, but how these linkages change as macrophages shift between pro-inflammatory and anti-inflammatory states had remained unclear. To answer that question, the researchers isolated monocytes from healthy donors and differentiated them in the laboratory into tumor-fighting, pro-inflammatory macrophages and tumor-promoting, anti-inflammatory macrophages, then compared the sialic acid linkages displayed on their surfaces.

The contrast was dramatic. Using mass spectrometry and glycan-specific protein staining, the team found that tumor-fighting macrophages carried predominantly α2,3-linked sialic acids on their surface N-glycans. In tumor-promoting macrophages, the situation was nearly reversed: roughly ninety percent of their sialic acids were attached through the α2,6 linkage. This linkage switch, the researchers concluded, is a hallmark of the macrophage transition from a state that attacks tumors to one that tolerates and even supports them.

Perhaps the most visually striking discovery came from fluorescence microscopy. The tumor-promoting macrophages extended long, branching protrusions coated with α2,6-linked sialic acid, which the researchers named sialo-protrusions. These structures reached up to 800 micrometers from the cell body, an extraordinary distance for cellular extensions, and formed mesh-like networks by connecting neighboring cells. Tumor-fighting macrophages displayed far fewer of these structures. Intriguingly, the sialo-protrusions showed no evidence of actin, the protein that typically forms cellular extensions such as filopodia and lamellipodia. Instead, they carried α2,6-sialylated glycoproteins on their surface, suggesting they represent a previously unrecognized class of cellular projections distinct from known actin-based structures.

The search for the molecular switch behind this remodeling led the team to an enzyme called ST6GAL1, which catalyzes the addition of sialic acid in the α2,6 configuration. Only the tumor-promoting macrophages expressed high levels of ST6GAL1, making it a prime suspect in the linkage switch. When the researchers silenced the enzyme using siRNA, the effects were immediate and widespread. The sialo-protrusions broke apart and shortened, the macrophages moved less, and they interacted less with one another, indicating that these sugar-coated extensions are functionally important for macrophage motility and communication rather than mere decoration.

The consequences extended to the cancer cells themselves. With ST6GAL1 suppressed, the tumor-promoting macrophages made less contact with colorectal cancer cells in laboratory co-cultures, and the cancer cells grew much more slowly. This suggests that sialo-protrusions help macrophages migrate, communicate with cancer cells, and support tumor growth through those physical contacts. Removing the enzyme that builds the α2,6 linkages appears to sever a critical line of communication between immunosuppressive macrophages and the tumor.

Even more remarkably, suppressing ST6GAL1 did more than disable the protrusions. The treated tumor-promoting macrophages began to resemble their tumor-fighting counterparts in shape, in the cytokines they expressed, and in their phagocytic ability, the capacity to engulf targets. In other words, targeting a single enzyme appeared to shift the cells’ overall state back toward the pro-inflammatory, tumor-attacking program. The finding raises the possibility that glycocalyx remodeling could become a therapeutic lever for reprogramming the immune microenvironment of tumors rather than simply blocking one interaction at a time.

To confirm that the laboratory observations reflected biology in real patients, the team examined tumor tissue from patients with advanced colorectal cancer. The same pattern held: tumor-promoting TAMs carried more α2,6-linked sialic acid, while tumor-fighting TAMs displayed more α2,3 linkages, mirroring the results from the donor-derived cells. This consistency between controlled experiments and patient samples strengthens the case that the sialyl linkage switch is a genuine feature of the tumor immune landscape rather than an artifact of cell culture. Dipta noted that the findings provide a new perspective on how remodeling of the immune cell glycocalyx may influence the tumor microenvironment.

Important questions remain before the discovery can be translated into treatment. The researchers emphasize that future studies must test ST6GAL1 inhibition in living organisms to evaluate whether it produces meaningful antitumor effects in the complex setting of a real tumor, where macrophages interact with many other immune and stromal cell types. The team also aims to identify the proteins that form the sialo-protrusions and to clarify exactly how these unusual structures mediate communication between macrophages and cancer cells. If those efforts succeed, they could open a new strategy for cancer immunotherapy: not boosting immune cells with checkpoint blockers alone, but chemically re-sculpting the sugar coat that tells macrophages which side to fight for. For now, the study offers a compelling proof of concept that the fate of tumor-associated macrophages may hinge, quite literally, on the fine chemical details of the sugars they display.

Subject of Research: Glycocalyx sialylation and macrophage polarization in the colorectal tumor microenvironment

Article Title: Shifting immune cells back toward cancer-fighting mode

Article References: Shifting immune cells back toward cancer-fighting mode. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: macrophages, tumor-associated macrophages, glycocalyx, sialic acid, ST6GAL1, colorectal cancer, tumor microenvironment, sialo-protrusions, glycosylation, cancer immunotherapy, Nagoya University, PNAS

Sialic acids are a family of nine-carbon acidic sugars that terminate glycan chains on the outer surface of virtually all vertebrate cells. Two linkages dominate: the α2,3 linkage, in which sialic acid attaches to the third carbon of a galactose residue, and the α2,6 linkage, which attaches at the sixth carbon. On cancer cells, overabundant sialylation is well known to dampen antitumor immunity, engaging inhibitory Siglec receptors on immune cells and creating a protective glycocalyx. But whether the T cells doing the attacking carry functionally meaningful sialic acid patterns of their own has remained murky, largely because existing tools could not resolve which linkage was present on which individual cell, let alone connect that information to gene expression in the same cell.

To break through that limitation, the group led by Xing Chen and Qi Tang developed a strategy they call scCAST_3&6, short for single-cell correlative analysis of sialoglycans and transcriptomes. The method uses mutant glycosidases and chemoenzymatic labeling tools—refinements of the team’s earlier work on linkage-specific sialoglycan labeling—to tag α2,3- and α2,6-linked sialic acids on single cells with distinct detectable labels. Those labels are then read out alongside single-cell RNA sequencing, allowing the researchers to pair, for every individual tumor-infiltrating immune cell, a quantitative measurement of its two sialic acid linkages with a full transcriptional profile. Applying the method to immune cells isolated from murine melanoma and other tumor models, they found that α2,3- and α2,6-sialylation are regulated independently and in strikingly cell-type-specific patterns across the tumor immune landscape, from macrophages and dendritic cells to natural killer cells and T cell subsets.

The most consequential discovery emerged when the team focused on CD8+ T cells, the cytotoxic lymphocytes responsible for directly killing cancer cells. Within tumors, these cells exist along a spectrum from naive bystanders to exhausted but tumor-reactive fighters, and the field has struggled to distinguish the truly antigen-reactive cells from the merely present ones. The scCAST analysis revealed that exhausted CD8+ T cells split into subpopulations based on their α2,6-sialylation levels, and that cells with low α2,6-sialylation—a state the researchers denote Sia2,6^lo—were dramatically enriched for tumor-specific antigen reactivity. When the team stained cells with peptide–MHC tetramers presenting a known tumor antigen, the Sia2,6^lo PD-1-positive fraction contained far more tetramer-binding cells than their Sia2,6^hi counterparts, and flow cytometry confirmed that the low-sialylation cells expressed higher levels of the activation markers TIM-3, CD137, granzyme B and interleukin-2.

Avidity—the collective strength of the interaction between a T cell receptor and the peptide–MHC complexes presented on a target cell—is a key determinant of antitumor potency. The researchers showed that Sia2,6^lo status tracks with high-avidity tumor antigen reactivity: expanded T cell clones within the low-sialylation compartment, and these cells killed antigen-bearing tumor cells more efficiently in vitro across multiple tumor models, including B16 melanoma, E0771 breast cancer and MC38 colon cancer. Critically, α2,6-sialylation did not drop indiscriminately during T cell activation. Naive CD8+ T cells stimulated with antibody-based activation reagents, which bypass the T cell receptor in a linkage-agnostic way, maintained their sialylation, whereas cells encountering antigen at high avidity specifically suppressed the gene encoding β-galactoside α2,6-sialyltransferase 1, or St6gal1, the enzyme that installs α2,6-linked sialic acids.

That mechanistic insight—high-avidity T cell receptor signaling drives St6gal1 downregulation—explains why the sugar signature is such a faithful proxy for tumor reactivity. Only T cells that have engaged their cognate antigen through a strong, multivalent receptor interaction pay the metabolic and transcriptional cost of remodeling their α2,6-sialylation, whereas low-avidity encounters leave the glycocalyx untouched. The team corroborated this in engineered systems where T cells were activated with variant peptides of graded affinity, showing that only high-avidity ligands suppressed St6gal1 expression. Datasets from human colorectal and lung cancer patients independently revealed that exhausted intratumoral PD-1-positive CD8+ T cells express lower levels of ST6GAL1 than their PD-1-negative counterparts, suggesting the mouse findings reflect a conserved biology.

Here the story takes a darker turn. Removing α2,6-linked sialic acids from glycan chains exposes the underlying galactose residues, which are preferred ligands for galectin-1, a β-galactoside-binding lectin abundantly produced by many tumors. The researchers demonstrated that Sia2,6^lo CD8+ T cells bind significantly more galectin-1 within the tumor, and that galectin-1 binding promotes apoptosis of these cells—effectively converting the very sugar change that marks a T cell as tumor-specific into a homing beacon for its own destruction. In tumors lacking galectin-1, the low-sialylation T cells persisted, and genetic deletion of St6gal1 in T cells enhanced galectin-1 binding without altering exhaustion markers, pinning the death pathway specifically on the exposed galectin ligands. Galectin-1 has long been implicated in creating immune-privileged tumor niches, and this work supplies a precise molecular handshake by which the tumor exploits the activation state of its attackers.

The therapeutic implications cut in two directions. On one hand, the Sia2,6^lo surface phenotype offers a practical, linkage-specific marker for isolating the highest-avidity tumor-reactive T cells from patient tumors—an advance that could sharpen adoptive cell therapy and tumor-infiltrating lymphocyte products, where identifying the right cells to expand has been a persistent bottleneck. Existing markers such as PD-1, CD39 and CD103 capture tumor reactivity only imperfectly, and a glycan-based readout adds an orthogonal, functionally grounded dimension. On the other hand, the galectin-1 vulnerability suggests that blocking galectin-1, or glycoengineering T cells to retain α2,6-sialylation while preserving their reactivity, could protect the most valuable antitumor cells from apoptosis. Combined with the growing arsenal of glycan-targeting immunotherapies—from sialidase-fused T cell engagers to inhibitors of sialyltransferases—the study expands the design space for manipulating the immune glycocalyx in cancer.

Technically, the work represents a milestone in single-cell multiomics: the ability to measure a chemically defined, linkage-specific glycan feature and a transcriptome in the same single cell, at scale, in a clinically relevant tissue. The scCAST platform and its associated datasets have been deposited in public repositories, and the tools build on a broader chemoenzymatic toolkit for glycan analysis that the Chen laboratory has developed over the past decade. As glycobiology moves from bulk descriptions of glycosylation toward cell-resolved, mechanistic accounts of how sugars regulate immunity in disease, this study offers both a template and a target: a sugar linkage that tells the true killers from the bystanders, and a lectin-mediated trap that tumors use to eliminate them. Understanding—and eventually interrupting—that trap may prove to be one of the more elegant ways to tip the balance of cancer immunotherapy in the patient’s favor.

Subject of Research: Linkage-specific sialylation of tumor-infiltrating CD8+ T cells and its role in antitumor immunity

Article Title: α2,6-Sialoglycan-regulated antitumor immunity of tumor-infiltrating CD8+ T cells

Article References: Liang, S., Tang, Q., Guo, Y., Zhang, S., Song, Q., Dai, P., & Chen, X. (2026). α2,6-Sialoglycan-regulated antitumor immunity of tumor-infiltrating CD8+ T cells. Nature Chemical Biology. https://doi.org/10.1038/s41589-026-02299-7

Image Credits: AI Generated

DOI: 10.1038/s41589-026-02299-7

Keywords: sialoglycans, α2,6-sialylation, CD8+ T cells, tumor microenvironment, galectin-1, St6gal1, single-cell multiomics, T cell avidity, cancer immunotherapy, glycosylation, glycobiology, Sialoglycan-regulated