The galectin family: 15 glycan readers reshaping cancer biology
They bind sugar. They talk to tumours. And they may be the next frontier in cancer immunotherapy.
Every cell in your body is coated in a dense forest of sugar chains — glycans. These structures are not decoration. They are read, constantly, by a class of proteins called lectins. Among them, the galectins stand out: a family of 15 human genes whose products specifically recognise β-galactoside motifs and translate glycan patterns into cellular decisions about growth, survival, and immune response.
In the language of glycobiology, galectins are glycan readers — they do not build or break sugar chains (that is the job of glycosyltransferase writers and glycosidase erasers), but they interpret them. And increasingly, it is clear that what they read in tumours spells trouble for the immune system.
The family tree: three structural archetypes
All 15 members share a conserved carbohydrate recognition domain (CRD), but differ in how many CRDs they carry and how those domains are arranged. This gives rise to three structural subtypes:
- LGALS1
- LGALS2
- LGALS7
- LGALS7B
- LGALS10
- LGALS13
- LGALS14
- LGALS16
Single CRD; non-covalent homodimers; bivalent glycan binding
- LGALS3
Single CRD + N-terminal proline/glycine-rich tail enabling oligomerisation
- LGALS4
- LGALS8
- LGALS9
- LGALS9B
- LGALS9C
- LGALS12
Two CRDs joined by a peptide linker; can crosslink glycan ligands
What galectins actually do
Galectins act both outside and inside cells. Extracellularly they bind glycan ligands on the cell surface and in the extracellular matrix, crosslinking receptors and remodelling how cells sense their environment. Intracellularly several members interact with signalling proteins to influence cell cycle, apoptosis, and mRNA splicing.
Their most studied functions converge on four themes:
Several galectins induce apoptosis in activated effector T cells, reducing immune pressure on tumour cells. LGALS1, LGALS3, and LGALS9 are the best-characterised players here.
Galectins expressed in tumour endothelium promote new vessel growth, ensuring tumours are supplied with oxygen and nutrients — and a route for metastatic spread.
By bridging glycoproteins in the matrix, galectins stiffen the tumour stroma, physically excluding immune cells from reaching tumour nodules.
Inside the cell, galectins interact with Ras, integrins, and laminins, amplifying proliferation and survival signals even without glycan binding.
The spotlight genes in cancer research
LGALS1 — the immunosuppressive workhorse
Galectin-1 is upregulated across many cancer types and correlates with advanced disease. It binds CD45 on T cells and triggers their apoptosis, directly disarming the anti-tumour immune response. In prostate cancer, elevated LGALS1 is associated with poor immunotherapy outcomes, and blocking Gal-1 has been shown to increase cytotoxic CD8+ T cell infiltration.
LGALS3 — checkpoint therapy interference
The only chimera-type galectin, Gal-3 is highly enriched in aggressive tumour microenvironments and is a key hypoxia-associated gene in pancreatic cancer. Strikingly, Gal-3 appears to physically enhance the PD-1/PD-L1 interaction — potentially explaining why some tumours respond poorly to pembrolizumab and atezolizumab. GB1211, a Gal-3 small-molecule inhibitor, is now in clinical trials.
LGALS9 — a rising immunotherapy target
Galectin-9 modulates regulatory T cell activity and is being targeted by LYT-200, an anti-LGALS9 humanised antibody currently in clinical trials for pancreatic cancer. Early data suggest blocking Gal-9 can reduce Treg-driven immune suppression and slow tumour progression.
LGALS8 — danger receptor and infection sensor
Beyond cancer, Gal-8 plays a fascinating role in innate immunity: it recognises glycans exposed on damaged vacuolar membranes during bacterial invasion, acting as a danger receptor that triggers antibacterial autophagy. In cancer it promotes tumour cell survival and metastasis, making it an emerging therapeutic target in its own right.
The galectin family sits at the intersection of glycobiology, immunology, and oncology. Their expression patterns across tissues, tumour types, and patient subgroups are now accessible for exploration — no coding required — in platforms like R2, where thousands of public datasets spanning TCGA, GTEx, and disease-specific cohorts can reveal which galectin is relevant in which context.
Why this family matters now
Immune checkpoint inhibitors have transformed oncology, but a substantial fraction of patients do not respond. Galectins are emerging as a key reason why: by remodelling the tumour stroma, inducing T cell death, and amplifying checkpoint signals, they create immune-excluded and immune-suppressed tumours that existing therapies cannot penetrate.
Combining galectin inhibition with checkpoint blockade (anti-PD-1, CAR-T, cancer vaccines) is the strategy now being tested in early clinical trials. The results will determine whether the LGALS family joins CTLA-4 and PD-L1 in the immunotherapy toolkit.
For researchers, the immediate opportunity is expression profiling — understanding which galectins are upregulated in which tumours, at which stage, in which patient subgroups. That is the question that open genomics platforms are built to answer.
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