O-Glycosylation Signatures Shape the Tumour Immune Microenvironment and Associate with Genomic Stability, Drug...

Background/Objectives: The tumour immune microenvironment (TIME) critically influences colorectal cancer (CRC) progression and therapeutic response, yet mechanisms shaping immune phenotypes remain unclear. Mucin-type O-glycosylation regulates tumour-immune interactions at the cell surface. Methods: We analysed O-glycosylation activity in 988 colorectal cancer (CRC) tumours derived from three independent cohorts: The Cancer Genome Atlas (TCGA-CRC, n = 534), the Clinical Proteomic Tumour Analysis Consortium (CPTAC2-CRC, n = 106), and the Sidra-Leiden University Medical Center (Sidra-LUMC, n = 348). O-glycosylation activity was quantified using a transcriptomic gene signature and single-sample gene set enrichment analysis (ssGSEA). Tumours were stratified into high and low O-glycosylation groups based on the median score, and associations with immune phenotypes, genomic alterations, and tumour functional states were assessed. Results: High O-glycosylation tumours exhibited an immune-desert phenotype with reduced immune-inflamed (p = 3.65 × 10^-10) and immune-excluded (p = 0.0070) signatures alongside increased immune-desert scores (p = 0.0049) and reduced Siglec signalling (p = 8.14 × 10^-5). O-glycosylation was associated with genomic stability, including lower TP53 mutation frequency (p = 0.0056), reduced aneuploidy (p = 0.0116), and decreased fraction of genome altered (p = 0.0309). High O-glycosylation tumours also showed upregulation of multidrug resistance programmes and reduced epithelial-mesenchymal transition (p = 0.0141) and proliferation (p = 0.0294). Conclusions: O-glycosylation defines a CRC subtype characterised by immune exclusion, genomic stability, and multidrug resistance, highlighting its potential as a biomarker and therapeutic target.