Tumour‐associated glycan modifications of antigen enhance MGL2 dependent uptake and MHC class I restricted CD8 T cell responses

Abstract

We recently showed that MGL2 specifically binds tumour-associated glycan N-acetylgalactosamine (GalNAc). We here demonstrate that modification of an antigen with tumour-associated glycan GalNAc, targets antigen specifically to the MGL2 on bone marrow derived (BM)-DCs and splenic DCs. Glycan-modification of antigen with GalNAc that mimics tumourassociated glycosylation, promoted antigen internalisation in DCs and presentation to CD4 T cells, as well as differentiation of IFN-c producing CD4 T cells. Furthermore, GalNAc modified antigen enhanced cross-presentation of both BM-DCs and primary splenic DCs resulting in enhanced antigen specific CD8 T cell responses. Using MyD88-TRIFF 2/2 BM-DCs we demonstrate that the enhanced cross-presentation of the GalNAc modified antigen is TLR independent. Our data strongly suggest that tumourassociated GalNAc modification of antigen targets MGL on DCs and greatly enhances both MHC class II and class I presentation in a TLR independent manner.Dendritic cells (DCs) are specialised antigen presenting cells (APC) well known for their capacity to induce MHC class I and MHC class II antigen presentation by stimulating antigen specific CD8 and CD4 T cells, respectively. Distinct classes of receptors are involved in processes that regulate recognition and uptake of antigen while others receptors induce DC maturation upon antigen recognition. The most commonly studied pattern (pathogen) recognition receptors (PRR) on DCs are the Toll like receptors (TLR) and C-type lectin receptors (CLR). TLR recognise microbial and endogenously conserved molecular patterns resulting in induction of intra-cellular signalling cascade. 1 Activation of TLR signalling cascade results in DC maturation and production of pro-inflammatory cytokines. On the other hand, CLR are endocytic receptors that recognise and internalise glycosylated pathogenic and self-antigens. Antigen internalisation facilitates the intra-cellular processing of antigen as well as loading on to MHC class II molecules and presentation to CD4 T cells leading for efficient T cell proliferation.2,3 Alternatively, CLR such as DEC-205, mannose receptor and CLEC9A have been shown to mediate antigen uptake leading to MHC class I loading and CD8 T cell priming, a process known as cross-presentation. 4-8 Crosspresentation is an important mechanism crucial for the induction of immune responses to viral infections and tumours. DCs are very efficient in cross-presenting antigens. In mice, splenic CD8a þ DCs are known to efficiently cross-present antigens to CD8 T cells. 10 The traditional view of cross-presentation states that antigen endocytosed by APC can be processed by at least 2 different mechanisms depending upon the nature of the antigen. Internalised antigen is exported from the phagosome into the cytoplasm for proteosomal processing, followed by TAP-dependent loading of antigen to MHC class I molecules in the endoplasmic reticulum or phagosomes. 11-13Alternatively, endocytosed antigen is cleaved in endocytic vesicles by proteases such as cat...

The Biology and Underlying Mechanisms of Cross-Presentation of Exogenous Antigens on MHC-I Molecules

“…LPS and Pam2Csk4). However, while the MyD88 pathway can enhance XPT in some cases, it is not required and may even be detrimental for antigens that are not associated with TLR agonists both in vitro and in vivo (123, 124) (Shen&Rock unpublished).…”

Regulatory Circuits Mediated by Lectin-Glycan Interactions in Autoimmunity and Cancer

“…Because these particular glycoforms are specifically recognized and internalized by CLRs on DCs, tumor antigens have been coupled to these glycans and used as vehicles for stimulating antitumor immunity. Illustrating this concept, GalNAc-modified tumor-associated antigens are selectively internalized by MGL, delivered to MHC II compartments for presentation to CD4 + T cells, and cross-presented to CD8 + T cells for stimulation of CTL responses (Napoletano et al, 2007;Singh et al, 2011a). Similarly, conjugation of ovalbumin with 3-sulfo-Lewis(A) or tri-GlcNAc specifically targets this antigen to MR that mediates internalization and cross-presentation to CD8 + T cells (Singh et al, 2011b).…”

Targeting of macrophage galactose‐type C‐type lectin (MGL) induces DC signaling and activation

“…The targeting of MGL expressed by dermal DCs induced a strong HLA class II-restricted T-cell response with a concomitant induction of a potent anti-Tn antibody response following the internalization of MAG:Tn3 glycoimmunogen, containing a viral CD4 + T-cell epitope [29]. Moreover, MGL enhanced both CD4 + and CD8 + -T lymphocyte activity in TLR independent manner when interacted with Tn-OVA (ovalbumin) antigen [30]. Tn-polyacrylamide polymers conjugated to streptavidin were efficiently internalized through MGL and primed streptavidin-specific CD4 + T cells [31].…”