e13528 Background: Dendritic cells (DCs) are the most potent antigen presenting cells and are employed in cancer vaccination. Several receptors are being studied in order to identif strategies to increase DCs activating capacity. The C-type lectin macrophage galactose type C-type lectin (MGL), expressed by DCs, is a receptor involved in the recognition of GalNAc (Tn)-carrying antigens. In this study we investigated the possibility of stimulating MGL receptor to increase DC performance by using the MUC1 based glycoimmunogen Tn-MUC1 (MUC19Tn) and the anti-MGL antibody (MLD-1).

METHODS: DCs were derived from PBMCs of 10 healthy donors and were analyzed before and after MGL engagement using MUC19Tn and MLD-1, as stimulators. DC phenotype, endocytosis, migration and IL-10/IL-12 secretion were evaluated by cytofluorimetry. Allo T cell-stimulating capacity and IFNg and IL-2 T cell production were estimated by (3)H-thymidine uptake and ELISpot assay, respectively. DC intracellular signaling and MGL oligomerization were studied by Western Blot and confocal microscopy.

RESULTS: MGL engagement induces homo-trimers and homo-dimers on DC plasma membrane, promotes the phosphorylation of Erk 1/2 MAP kinases and triggers NFkB classical pathway. The activation of intracellular signals leads to DC phenotypic maturation, with a concomitant reduction of phagocytosis and an enhanced migration capacity (25-30%). After MGL activation, DCs induce a strong proliferation of allogeneic T cells and stimulate high levels of IFNg and IL-2 secretion by both CD8 and CD4 T cells.

CONCLUSIONS: These results demonstrate that MGL engagement profoundly affects DC plasticity inducing and directing a Th1 immune response. Moreover, MGL receptor expressed on human DC can be targeted by glycopeptide based vaccines with adjuvant activity and tumor specificity.