Cancer Associated Aberrant Protein O-Glycosylation Can Modify Antigen Processing and Immune Response

Abstract

Aberrant glycosylation of mucins and other extracellular proteins is an important event in carcinogenesis and the resulting cancer associated glycans have been suggested as targets in cancer immunotherapy. We assessed the role of O-linked GalNAc glycosylation on antigen uptake, processing, and presentation on MHC class I and II molecules. The effect of GalNAc O-glycosylation was monitored with a model system based on ovalbumin (OVA)-MUC1 fusion peptides (+/− glycosylation) loaded onto dendritic cells co-cultured with IL-2 secreting OVA peptide-specific T cell hybridomas. To evaluate the in vivo response to a cancer related tumor antigen, Balb/c or B6.Cg(CB)-Tg(HLA-A/H2-D)2Enge/J (HLA-A2 transgenic) mice were immunized with a non-glycosylated or GalNAc-glycosylated MUC1 derived peptide followed by comparison of T cell proliferation, IFN-γ release, and antibody induction. GalNAc-glycosylation promoted presentation of OVA-MUC1 fusion peptides by MHC class II molecules and the MUC1 antigen elicited specific Ab production and T cell proliferation in both Balb/c and HLA-A2 transgenic mice. In contrast, GalNAc-glycosylation inhibited the presentation of OVA-MUC1 fusion peptides by MHC class I and abolished MUC1 specific CD8+ T cell responses in HLA-A2 transgenic mice. GalNAc glycosylation of MUC1 antigen therefore facilitates uptake, MHC class II presentation, and antibody response but might block the antigen presentation to CD8+ T cells.

Microvesicle Cargo of Tumor-Associated MUC1 to Dendritic Cells Allows Cross-presentation and Specific Carbohydrate Processing

“…MGL receptor-mediated endocytosis of the Tn-MUC1 glycoform induced a significant increase of MUC1 accumulation in the endolysosomal compartment but no cross-processing in the HLA-I compartment was observed. These results are in agreement with other studies showing that the presence of Tn residues on the antigen increased antigen uptake by dendritic cells and activation of CD4 þ -mediated T-cell response, but it failed to induce CD8 þ T-cell-mediated response in animal models (35). Cross-processing of MUC1 in dendritic cells was observed only when small synthetic glycopeptides were employed, suggesting that the shortening of the size of the antigen could be a way to override the block in processing (2,36).…”

Global Mapping of O-Glycosylation of Varicella Zoster Virus, Human Cytomegalovirus, and Epstein-Barr Virus

“…In a similar way, O-glycans have also been suggested to shield immunodominant epitopes in herpesviruses (91,92). Nevertheless, there is limited information regarding the impact of individual O-glycans on shielding underlying peptide epitopes or the capacity of host immunity to present and recognize glycosylated antigens (93,94 (18), mouse immune sera were able to detect and neutralize virus produced in mammalian cells, suggesting either that the epitope recognition is not affected by adjacent glycosylation or that putative O-linked glycans only partly occupy and protect the epitopes. We also found O-glycans located within a neutralizing peptide epitope at the N terminus of HCMV gH (S31) (119) and a discontinuous neutralizing antibody epitope on VZV gH (Ser 177 and Thr 184 ) (120).…”

“…Because O-glycans may affect immunity by shielding protein epitopes or introducing glycopeptide epitopes (91)(92)(93), it is important to consider O-glycans in the context of vaccine design. It is also important to consider O-glycans for innate immune targeting ligands to augment immunity (33,94).…”

Oncogenic Epstein–Barr virus recruits Nm23-H1 to regulate chromatin modifiers

“…81,82 Early expression of glycosyl transferases in cancer can serve as potential markers as seen in breast cancer. 83 N -acetylgluco-saminyltransferase V (GnT-V), a glycosyl transferase, shown to be regulated by Nm23-H1, can also have an impact on the metastatic phenotypes in lung cancer cells.…”