Tumor-Associated Carbohydrate Antigen (TACA). STn is a sialylated form of the truncated O-glycosylated core determinant Tn with structure: Neu5Acα2-6GalNAcα-O-Ser/Thr. STn results from an early sialylation of the Tn antigen due to overexpression of the enzyme STn synthase (ST6GalNAc-I) and/or disruption of further glycan elongation processes. STn is negligibly expressed in healthy tissues but overexpressed in >80% of human carcinomas. As such, STn is implicated in tumour cell organotropic metastasis. Targeting immune responses to truncated variants of O-glycan chains expressed by tumour cells represents a promising approach for the development of antigen-specific therapeutic vaccines against cancers, and accumulated evidence has rendered STn a prime target for cancer immunotherapy.
