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T-Cell Responses To Immunodominant Listeria Epitopes Limit Vaccine-Directed Responses To The Colorectal Cancer Antigen, Guanylyl Cyclase C, John C. Flickinger, Jagmohan Singh, Yanki Yarman, Robert D Carlson, Joshua Barton, Scott A Waldman, Adam E. Snook

Department of Pharmacology and Experimental Therapeutics Faculty Papers

The Gram-positive bacterium Listeria monocytogenes (Lm) is an emerging platform for cancer immunotherapy. To date, over 30 clinical trials have been initiated testing Lm cancer vaccines across a wide variety of cancers, including lung, cervical, colorectal, and pancreatic. Here, we assessed the immunogenicity of an Lm vaccine against the colorectal tumor antigen GUCY2C (Lm-GUCY2C). Surprisingly, Lm-GUCY2C vaccination did not prime naïve GUCY2C-specific CD8+ T-cell responses towards the dominant H-2Kd-restricted epitope, GUCY2C254-262. However, Lm-GUCY2C produced robust CD8+ T-cell responses towards Lm-derived peptides suggesting that GUCY2C254-262 peptide may be subdominant to Lm-derived peptides. Indeed, incorporating immunogenic Lm peptides into an adenovirus-based GUCY2C …