Researchers at the University of Veterinary Medicine Hannover set out to disentangle two factors that had previously been confounded in studies of RSV G protein heterogeneity. Earlier work had shown that G proteins made in primary human airway epithelial cultures, including air-liquid interface systems, reach an apparent molecular weight of approximately 170 kilodaltons and are more heavily glycosylated than the 55 to 90 kilodalton species typical of transformed lines such as HEp-2 or A549. Other experiments had shown that, within a single complete medium, different continuous cell lines produce G proteins differing in electrophoretic mobility and in reactivity with G-specific monoclonal antibodies. But in those comparisons either the cell line varied while the medium was held constant, or both cell identity and medium changed together. By varying the medium within a single cell background, the new study isolates the contribution of the medium itself from that of the cell.

The rationale for suspecting such an effect is grounded in glycobiology. Culture medium composition can influence the availability of nucleotide sugar donors, the activated sugars that glycosyltransferases in the Golgi apparatus attach to nascent glycoproteins, and can modulate the activity of glycosylation pathways more broadly. Because G protein glycans are likely to shape antigenic masking and functional behaviour of the virus, medium-dependent metabolic effects were a plausible driver of the heterogeneity reported across systems. The question also matters for antibody-based interventions: approved therapeutic monoclonal antibodies against RSV, including palivizumab, nirsevimab and clesrovimab, are all directed at the fusion F protein, yet virion composition and glycoprotein organisation may influence antibody binding and neutralising activity.

To test the principle directly, the team first used a recombinant expression system. A soluble form of the RSV G ectodomain, tagged for purification, was produced in HEK293T cells maintained in three different commercial media, designated A, B and C, which had been selected from an initial screen of nine formulations to represent the extremes and midpoint of the observed range. Purified proteins were analysed by SDS-PAGE and Western blot. The apparent molecular weight of the soluble G protein differed substantially depending on the medium: protein produced in medium A was the smallest at roughly 60 to 90 kilodaltons, medium B yielded an intermediate species of about 100 kilodaltons, and medium C produced the largest form at approximately 100 to 130 kilodaltons.

The critical control came from glycosylation-deficient cells. When the same soluble G protein was expressed in HEK293T cells knocked out for the GALE and GALK1 genes, which are deficient in galactose metabolism, the medium-dependent size differences vanished entirely. In these knockout cells the protein appeared as a lower molecular weight cluster of roughly 15 to 25 kilodaltons, consistent with incompletely processed, non-galactosylated glycans that the knockout does not eliminate. This result demonstrated that the differences in apparent size were caused by glycosylation and that medium composition, not cell-type-specific differences in the glycosylation machinery, defined the extent of that glycosylation. Importantly, the same hierarchy of medium-dependent molecular weights was reproduced during authentic infection: when A549 cells were infected with a reporter RSV strain in the three media and lysed 24 hours later, Western blots showed the same pattern, albeit with smaller absolute differences.

The team then asked whether the medium affects the biological properties of virus preparations. A549 cells were infected with an EGFP-expressing RSV at a multiplicity of one in each medium, with Opti-MEM, the reduced-serum medium B commonly used for RSV propagation, serving as the reference condition. Virus spread kinetics, quantified by integrated GFP fluorescence over 120 hours with a live-cell imaging system, revealed pronounced medium-dependent differences, with spread significantly higher in medium C than in media A and B. More strikingly, when virus stocks produced in each medium were used to infect fresh A549 cells at equal infectious doses and the inoculum was replaced with Opti-MEM after adsorption, the differences persisted: medium C virus spread most, medium B virus showed an intermediate phenotype, and medium A virus remained markedly attenuated. Because the production medium was no longer present during the infection period, and because a difference confined to the initial inoculum would be expected to produce comparable spread curves with a delay rather than a sustained gap, the result points to a stock-intrinsic property that also affects subsequent rounds of infection.

Analyses of the virus stocks themselves added a further layer. When stocks were adjusted to equal total protein concentrations and probed by Western blot, the relative G protein signal normalised to the viral N protein was lower for virus produced in media A and B than for virus produced in medium C, while relative F protein signals did not differ significantly between preparations. The G protein with the highest apparent molecular weight, consistent with the most extensive glycosylation, was thus associated with the highest relative G to N ratio, an association consistent with a link between G protein maturation and its relative abundance in stocks, though the authors are careful to note that this does not establish causality. A comparison of RT-qPCR signals with infectious titres proved revealing: virus produced in medium A yielded higher Cq values than medium C virus, yet its infectious titre was approximately 100-fold lower, indicating that the ratio of infectious to RT-qPCR-detectable viral material differed between preparations.

The consequences extended to antibody recognition. Fluorescently labelled palivizumab, which binds both pre-fusion and post-fusion F, and the pre-F-specific antibodies nirsevimab and clesrovimab were used to stain infected cells cultured in the three media, with signals normalised to the GFP reporter. Binding of all three therapeutic antibodies was significantly lower in cells cultured in media B and C than in medium A, whereas a post-F-specific control antibody showed largely unchanged binding. Because relative F protein signals in the virus stocks did not differ, these binding differences were not accompanied by detectable differences in total F protein abundance, though the analysis did not distinguish F conformations. In neutralisation assays, palivizumab consistently showed the highest IC50 values at approximately 1.5 micrograms per millilitre, with nirsevimab and clesrovimab more potent, and no statistically significant differences in IC50 emerged between viruses produced in media B and C, indicating that the altered binding signals did not translate into measurable differences in neutralising potency under the conditions tested.

The authors conclude that the choice of culture medium is an important variable that should be considered whenever RSV preparations are produced for studies of the virus’s biological and immunological properties. Several caveats frame the findings: the precise compositions of the commercial media are proprietary, precluding identification of the responsible components; medium B is reduced-serum rather than serum-free, so its effects may partly reflect serum content and lower nutrient availability; the study used transformed cell lines and a single reporter virus strain, so whether similar effects occur in primary airway epithelial, air-liquid interface or organoid systems remains open. Notably, such advanced cultures are maintained in differentiation media that differ substantially from those used for continuous lines, raising the possibility that the heavier glycosylation of G reported in primary cultures reflects the medium as well as cell identity. Resolving the exact medium-dependent glycan patterns will require site-resolved glycoproteomics, and the F protein’s glycosylation and conformational distribution merit parallel investigation. For now, the message to the field is clear: two laboratories growing the same virus in the same cells but different media may not be studying the same virus at all.

Subject of Research: Effect of cell culture medium composition on respiratory syncytial virus G protein glycosylation and monoclonal antibody recognition

Article Title: Cell culture medium influences RSV G protein glycosylation and recognition by monoclonal antibodies

Article References: Engling, N., Knittler, M.-C., Tagore, R., Ludlow, M., Osterhaus, A. D., Rimmelzwaan, G. F., & Meineke, R. (2026). Cell culture medium influences RSV G protein glycosylation and recognition by monoclonal antibodies. Virology Journal, 23(1), Article 226. https://doi.org/10.1186/s12985-026-03318-8

Image Credits: AI Generated

DOI: 10.1186/s12985-026-03318-8

Keywords: respiratory syncytial virus, glycosylation, G glycoprotein, cell culture medium, monoclonal antibodies, palivizumab, nirsevimab, clesrovimab, glycobiology, viral infectivity, HEK293T cells, A549 cells

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

Glycans are carbohydrate chains attached to proteins and lipids, and they are far more than metabolic fuel. In animals ranging from sea urchins to humans, they serve as molecular identity tags, mediating cell-to-cell recognition, fertilization, immune defense, and tissue organization. Lectins, a diverse family of sugar-binding proteins, read these tags and translate them into biological action. In marine organisms, glycans have been implicated in mucosal immunity of embryos, cellular interactions during development, fertilization success, egg development, and embryogenesis itself. Yet despite the ecological importance of corals, almost nothing was known about the glycan landscape of a developing coral embryo until now.

The research team, led by Kanokpron Loeslakwiboon and Hsing-Hui Li of National Sun Yat-Sen University and the National Museum of Marine Biology and Aquarium, together with colleagues including Sujune Tsai, Zhi-Hong Wen and Chiahsin Lin, chose Galaxea fascicularis as their study organism. This reef-building stony coral has recently emerged as a promising model system for coral symbiosis research, and its embryos are relatively accessible for laboratory work. Spawning colonies were induced in the lab, embryos were collected at defined developmental stages, and the researchers set out to profile the sugars present at each stage of the journey from fertilized egg to late-stage embryo.

The analytical centerpiece of the study was a lectin array, a technique that exploits the exquisite specificity of lectins for particular sugar structures. Each lectin on the array recognizes a characteristic glycan signature, and when fluorescently labeled samples bind to the array, the pattern of binding reveals which glycans are present and in what relative abundance. The team used a Cy3 dye detection method, allowing them to quantify binding signals and construct a comparative glycan profile for each developmental stage. This approach, long used in mammalian glycobiology, had rarely been applied to the early life stages of a reef coral.

The results delivered a clear headline finding: mannose was the most abundant glycan present in Galaxea fascicularis embryos at every stage examined. Mannose, a simple hexose sugar, is a cornerstone of many glycan structures in eukaryotic cells, and its dominance in coral embryos suggests it plays a central role in early development. The researchers propose that mannose may be significant for cell proliferation, because it can serve as an energy source to drive the demanding processes of embryonic development. Rapidly dividing embryos need both building materials and fuel, and an abundant, readily mobilized sugar could supply both.

Perhaps more intriguing than the abundance of mannose was the pattern of change over time. Across the early stages of development, the glycan profiles remained remarkably stable, with only minor shifts observed. This developmental conservatism suggests that the early embryo relies on a consistent molecular toolkit, one laid down in the egg and maintained through the initial rounds of cell division. The picture changed at later stages of embryogenesis. As embryos approached the point where they must produce well-formed structures, the researchers suggest, they may require more energy and may increase their intake of monosaccharides accordingly. In other words, the sugar economy of the embryo appears to shift as morphogenesis accelerates, moving from a stable maintenance phase toward a more energy-intensive construction phase.

The findings resonate with a broader body of work on the role of carbohydrates in animal development. Glycoprotein synthesis has long been recognized as essential to embryonic development across the animal kingdom, and studies in sea urchins have shown that carbohydrate interactions are involved in cellular adhesion during gastrulation and in the fertilization process itself. Cell surface carbohydrates and lectins are known to participate in early development in organisms from mice to marine invertebrates, and even the reassociation of dissociated animal cells depends on specific carbohydrate groups at the cell surface. What the new study adds is a temporal dimension: a stage-by-stage map of how these sugars wax and wane as a coral embryo matures.

The work also connects to the growing literature on glycans in coral biology more broadly. Previous studies have profiled the glycan composition of coral mucus, revealing that the carbohydrate makeup of the gel-forming mucus layer varies among species and even correlates with coral phylogeny. Others have characterized mannose-binding lectins from corals that can bind both pathogens and symbiotic algae, hinting at a dual role for sugar recognition in immunity and symbiosis establishment. Lectin-glycan interactions have been shown to mediate the recognition between coral hosts and their dinoflagellate symbionts, the photosynthetic partners that power reef ecosystems. By extending glycan analysis to the embryo, the Taiwanese team has filled a conspicuous gap in this picture, showing that sugar biology matters from the very first hours of a coral’s life.

Why does this matter beyond the laboratory? Coral reefs are under unprecedented pressure from warming waters, acidification, and pollution, and conservationists increasingly rely on assisted reproduction and coral culture techniques to restore damaged reefs. Understanding the biochemical requirements of embryos could improve hatchery protocols, larval rearing conditions, and cryopreservation methods. If mannose availability influences cell proliferation and energy supply during development, then culture media and rearing environments might be tuned to support embryos at the stages when their sugar demands change. The authors note that their findings may provide a benefit to coral culture and conservation efforts, and the study’s timing is significant given that Galaxea fascicularis is being positioned as a model organism for the field.

There are, of course, limits to what a first study can establish. The lectin array reveals which glycans are present and how their relative abundance changes, but it does not identify every glycan structure in molecular detail, nor does it pinpoint the genes and enzymes that regulate their synthesis. Future work combining glycomics with transcriptomics could link the observed sugar dynamics to the underlying developmental genetic program, much as earlier molecular studies have charted gene expression from fertilization to metamorphosis in reef-building corals. Still, the study marks a genuine first: a total glycan profile tracked across the embryonic development of a coral. As reefs worldwide struggle to regenerate, even the smallest molecular insights into how coral life begins may prove to be valuable currency for the scientists working to keep them alive.

Subject of Research: Glycan profile changes during embryonic development of the reef-building coral Galaxea fascicularis

Article Title: Glycan dynamics across embryonic development in the coral Galaxea fascicularis

Article References: Glycan dynamics across embryonic development in the coral Galaxea fascicularis. (n.d.). https://doi.org/10.1007/s00338-026-02955-3

Image Credits: AI Generated

DOI: 10.1007/s00338-026-02955-3

Keywords: glycans, coral, Galaxea fascicularis, embryogenesis, lectin array, mannose, glycobiology, coral reefs, marine biology, cell proliferation, coral conservation, Taiwan