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.
Highlights
Cancer vaccines hold great promise for long lasting therapeutic efficacy [1]
GalNAc-glycosylation Improves CD4+ T cell Responses We first investigated the role of GalNAc-glycosylation on peptide antigen processing and peptide presentation on MHC class II molecules (Figure 1)
The potent I-Ab binding OVA peptide was fused to a MUC1 derived sequence with and without GalNAc-glycosylation (Table 1) and was loaded on dendritic cell (DC) which were co-cultured with ovalbumin peptide/MHC class II complex specific T cell hybridomas
Summary
Current experimental cancer vaccines primarily aim to elicit cellular immunity through induction of specific CD8+ T cells [2,3,4,5]. Altered proteins presented on cancer cells are important tumor antigens, which can be targeted by vaccines and therapeutic antibodies. Most cell surface proteins are glycosylated, and malignant transformation of cells is always accompanied by alterations of posttranslational modifications of proteins [9]. Aberrant mucin-type O-glycosylation represents one of the most abundant posttranslational cancer associated changes creating a diverse set of molecular structures found on the surface of cancer cells, but not on normal cells [9,10]. The specific pattern of the cancer associated short glycan structures on cancer-associated proteins produces novel glycopeptide epitopes that can be targeted by the immune system [11,12]
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