GCNT1 is a glycosyltransferase that catalyzes transfer of N-acetylglucosamine in beta-1,6 linkage to mucin-type core 1 O-glycans, forming branched core 2 O-glycans that serve as scaffolds for selectin ligand display by myeloid cells. The enzyme also participates in glycolipid synthesis and SSEA-1 determinant formation. In prostate cancer, GCNT1 is consistently overexpressed and associated with altered O-glycosylation of PSA, MUC1, and PAP proteins 1. GCNT1 expression in diagnostic biopsy specimens independently predicts biochemical recurrence after radical prostatectomy and correlates with extraprostatic extension 2, making it a candidate biomarker for aggressive disease. Mechanistically, GCNT1-mediated core 2 O-glycosylation promotes tumor growth and modifies oncogenic pathways in prostate cancer models 3. Beyond oncology, GCNT1 expression is controlled by androgen receptor signaling in prostate cancer cells 4 and regulates T cell activation through Notch signaling-dependent core 2 O-glycosylation of CD43 5. Conversely, Gcnt1 deficiency in mice increases susceptibility to tuberculosis through excessive neutrophil recruitment 6. These findings position GCNT1 as a multifunctional regulator of immune homeostasis and cancer progression, with potential therapeutic implications in both malignancy and infectious disease.