The type of interaction between tumor-associated antigens and specialized antigen-presenting cells such as dendritic cells (DCs) is critical for the type of immunity that will be generated. MUC1, a highly O-glycosylated mucin, is overexpressed and aberrantly glycosylated in several tumor histotypes. This results in the expression of tumor-associated glycoforms and in MUC1 carrying the tumor-specific glycan Tn (GalNAcα1-O-Ser/Thr). Glycopeptides corresponding to three tandem repeats of MUC1, enzymatically glycosylated with 9 or 15 mol of GalNAc, were shown to specifically bind and to be internalized by immature monocyte-derived DCs (iDCs). Binding required calcium and the GalNAc residue and was competed out by GalNAc polymer and Tn-MUC1 or Tn-MUC2 glycopeptides. The macrophage galactose-type C-type lectin (MGL) receptor expressed on iDCs was shown to be responsible for the binding. Confocal analysis and ELISA done on subcellular fractions of iDCs showed that the Tn-MUC1 glycopeptides colocalized with HLA class I and II compartments after internalization. Importantly, although Tn-MUC1 recombinant protein was bound and internalized by MGL, the glycoprotein entered the HLA class II compartment, but not the HLA class I pathway. These data indicate that MGL expressed on iDCs is an optimal receptor for the internalization of short GalNAcs carrying immunogens to be delivered into HLA class I and II compartments. Such glycopeptides therefore represent a new way of targeting the HLA class I and II pathways of DCs. These results have possible implications in designing cancer vaccines. [Cancer Res 2007;67(17):8358–67]

Purpose: Cancer stem cells represent an attractive therapeutic target for tumor eradication. The present study aimed to determine whether CD133 expression may identify cells with characteristics of cancer stem/progenitor cells in human endometrial tumors.

Dendritic cells (DCs) sense the microenvironment through several types of receptors recognizing pathogen‐associated molecular patterns. In particular, C‐type lectins, expressed by distinct subsets of DCs, recognize and internalize specific carbohydrate antigen in a Ca²⁺‐dependent manner. Targeting of these receptors is becoming an efficient strategy of delivering antigens in DC‐based anticancer immunotherapy. Here we investigated the role of the macrophage galactose type C‐lectin receptor (MGL), expressed by immature DCs (iDCs), as a molecular target for α‐N‐acetylgalactosamine (GalNAc or Tn)‐carrying tumor‐associated antigens to improve DC performance. MGL expressed by ex vivo‐generated iDCs from healthy donors was engaged by a 60‐mer MUC1_9Tn‐glycopeptide as a Tn‐carrying tumor‐associated antigen, and an anti‐MGL antibody, as a specific MGL binder. We demonstrated that MGL engagement induced homotrimers and homodimers, triggering the phosphorylation of extracellular signal‐regulated kinase 1,2 (ERK1,2) and nuclear factor‐κB activation. Analysis of DC phenotype and function demonstrated that MGL engagement improved DC performance as antigen‐presenting cells, promoting the upregulation of maturation markers, a decrease in phagocytosis, an enhancement of motility, and most importantly an increase in antigen‐specific CD8⁺ T‐cell activation. These results demonstrate that the targeting of MGL receptor on human DCs has an adjuvant effect and that this strategy can be used to design novel anticancer vaccines.

C-type lectin receptors (CLRs) on antigen-presenting cells (APCs) facilitate uptake of carbohydrate antigens for antigen presentation, modulating the immune response in infection, homeostasis, autoimmunity, allergy, and cancer. In this review, we focus on the role of the macrophage galactose type C-type lectin (MGL) in the immune response against self-antigens, pathogens, and tumor associated antigens (TAA). MGL is a CLR exclusively expressed by dendritic cells (DCs) and activated macrophages (MØs), able to recognize terminal GalNAc residues, including the sialylated and nonsialylated Tn antigens. We discuss the effects on DC function induced throughout the engagement of MGL, highlighting the importance of the antigen structure in the modulation of immune response. Indeed modifying Tn-density, the length, and steric structure of the Tn-antigens can result in generating immunogens that can efficiently bind to MGL, strongly activate DCs, mimic the effects of a danger signal, and achieve an efficient presentation in HLA classes I and II compartments.