Complex N-Glycosylation in Anti-Tumor Immunity
Pancreatic ductal adenocarcinoma (PDAC) is currently the third leading cause of cancer-related death in the United States. The five-year survival rate of thirteen percent can be attributed to a difficulty in early detection and a lack of effective treatments. Tumor-associated glycans represent a potential anti-tumor target for two reasons: (i) protein glycosylation is known to play a role in tumor progression, and (ii) alternatively glycosylated proteins may function as tumor neoantigens. The glycosyltransferase Mgat5 catalyzes the formation of 1,6-N-acetylglucosamine branched glycans, and overexpression has been implicated in tumor growth and metastasis in multiple cancers. Using a panel of clonal cell lines that recapitulate the immune heterogeneity of PDAC, we found that knockout of Mgat5 led to a significant and replicable decrease in tumor growth. This occurred not only in immune hot, “T cell-inflamed” tumors, but also the immunosuppressive “non-T cell-inflamed” tumors. Within these Mgat5 knockout tumors, CD8+ T cell infiltration was increased, and the cytotoxicity of both CD4+ and CD8+ T cells as measured by TNF⍺, IFN?, and granzyme B content was increased in the draining lymph nodes of tumors. Clearance of the knockout tumors was found to be dependent upon functional CD4+ and CD8+ T cells as well as dendritic cells, with NK cells playing only an early role in immune clearance. Mechanistically, Mgat5 KO cells were found to have significantly increased sensitivity to cell death via the TNF⍺ or TRAIL pathway, with death proceeding through either the necroptotic or apoptotic pathways respectively. Taken together, these results are consistent with a model in which loss of Mgat5-mediated N-glycans increases the sensitivity of tumors to T cell killing through lowering the threshold for engagement of the extrinsic cell death pathway and allowing for the formation of a durable immune response. Finally, Mgat5 knockout tumors treated with immune checkpoint blockade had significantly decreased tumor size and increased survival over controls, suggesting Mgat5 has potential as a novel target for pancreatic cancer.
Medical Sciences, Biology, Immunology and Infectious Disease
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