Abstract 5018: Dissecting antigen-specific T-cell response in a novel mouse model of colon cancer

Abstract

Abstract Immune checkpoint blockade therapies, which unleash the immune system’s ability to recognize and eliminate cancer cells, are currently among the most promising treatments for cancer. Antibodies that block the immune inhibitory receptors CTLA4 and PD1 have shown clinical success, with objective response rates over 20% and some durable responses exceeding 10 years. However, some cancers, such as colorectal cancer (CRC), have proven particularly refractory to immunotherapy. Although it is appreciated that the colon is an immunosuppressive environment, the mechanism and extent of immune suppression remains unclear. Studies of human CRC tumors have shown that T cell infiltration is an important predictor of clinical outcome, yet current mouse models of CRC are not particularly well suited to the mechanistic study of T cell responses against tumor-specific antigens. Syngeneic cell line transplants, by far the most widely used models to study adaptive immune response in CRC, are characterized by a highly complex tumor antigen landscape, and have not employed orthotopic transplant into the colon. In order to track highly specific T cell responses in CRC, we have employed a novel colon organoid-based system, in which transformed organoids expressing model antigens are orthotopically transplanted into the wall of the colon via colonscopy-guided injection, a method pioneered in the lab of Omer Yilmaz. Organoids were harvested from VillinCreER; Apcfl/fl mice and grown in the presence of Wnt ligand; addition of tamoxifen and removal of Wnt from the media facilitated expression of the colon-specifc Cre, deletion of Apc, and selection of transformed organoids capable of growing in the absence of Wnt. To induce expression of model antigens, organoids were infected with a lentiviral vector that, in addition to the fluorescent reporter FusionRed, expressed the T cell antigens SIYRYYGL and two antigens from ovalbumin - SIINFEKL and OVA323-339 - fused to the C-terminus of luciferase (FRLucOS), enabling us to monitor antigen expression in vivo. Organoids were then sorted and injected into the wall of the colon. Previous work by Michael DuPage, in which he expressed the LucOS construct in an autochthonous lung cancer and sarcoma mouse model, provided key insights into the dynamic nature of T cell response against cancer cells. The novel model system described here provides a powerful new tool to dissect antitumor T cell responses in the poorly understood context of CRC. Citation Format: Mary C. Beytagh, Peter M. Westcott, Olivia C. Smith, Jatin Roper, Omer Yilmaz, Tyler E. Jacks. Dissecting antigen-specific T-cell response in a novel mouse model of colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5018. doi:10.1158/1538-7445.AM2017-5018