The Tn antigen promotes lung tumor growth by fostering immunosuppression and angiogenesis via interaction with Macrophage Galactose-type lectin 2 (MGL2)

Tn is a tumor-associated carbohydrate antigen that constitutes both a diagnostic tool and an immunotherapeutic target. It originates from interruption of the mucin O-glycosylation pathway through defects involving, at least in part, alterations in core-1 synthase activity, which is highly dependent on Cosmc, a folding chaperone. Tn antigen is recognized by the Macrophage Galactose-type Lectin (MGL), a C-type lectin receptor present on dendritic cells and macrophages. Specific interactions between Tn and MGL shape anti-tumoral immune responses by regulating several innate and adaptive immune cell programs. In this work, we generated and characterized a variant of the lung cancer murine cell line LL/2 that expresses Tn by mutation of the Cosmc chaperone gene (Tn(+) LL/2). We confirmed Tn expression by lectin glycophenotyping and specific anti-Tn antibodies, verified abrogation of T-synthase activity in these cells, and confirmed its recognition by the murine MGL2 receptor. Interestingly, Tn+ LL/2 cells were more aggressive in vivo, resulting in larger and highly vascularized tumors than those generated from wild type Tn(-) LL/2 cells. In addition, Tn(+) tumors exhibited an increase in CD11c(+) F4/80(+) cells with high expression of MGL2, together with an augmented expression of IL-10 in infiltrating CD4(+) and CD8(+) T cells. Importantly, this immunosuppressive microenvironment was dependent on the presence of MGL2(+) cells, since depletion of these cells abrogated tumor growth, vascularization and recruitment of IL-10(+) T cells. Altogether, our results suggest that expression of Tn in tumor cells and its interaction with MGL2-expressing CD11c(+)F4/80(+) cells promote immunosuppression and angiogenesis, thus favoring tumor progression.