Abstract
Genetically-engineered mouse models (GEMMs) exist for most types of cancer in which autochthonous tumors develop into advanced disease in the presence of a fully functional immune system. These GEMMs would be ideal for investigating questions in cancer immunology, including those concerning the commonalities and differences between immune responses that target different cancers, and how the tumor microenvironments (TMEs) associated with different cancer types impact the functions of tumor-infiltrating immune cells. However, unlike human tumors, tumors in GEMMs have few somatic mutations and thus require exogenous neoantigens (neoAgs) to drive interactions with anti-tumor T cells. There are only a handful of mechanisms to program tumors to express neoAgs, and thus, GEMMs for most tumor types remain inaccessible for cancer immunology studies. Here, we describe the “iNversion INducible Joined neoAg” (NINJA) mouse, which can be used to program GEMM tumors with a common neoAg, and thus stimulate a common set of tumor-specific CD8 T cells. NINJA will be useful for addressing many key unanswered questions cancer immunology, including comparisons of immune responses across several cancer types and comparisons of anti-tumor T cell responses targeting de novo expressed neoAgs at different stages in tumor development. NINJA mice will also be invaluable as a preclinical platform for testing immunotherapeutics, and for investigating why certain immunotherapeutic regimens are more effective when treating some cancers and not others. NINJA is unique, because neoAgs are encoded within the genome, yet NINJA avoids central and peripheral tolerance, a common problem with other systems. This is achieved because the DNA sequences encoding the full-length neoAgs are discontinuous in the OFF state and, thus, neoAgs are silent. Induction of neoAgs is highly regulated, requiring a permanent inversion of a DNA element in NINJA, which allows production of the full-length NINJA neoAgs and GFP (a marker of neoAg expression). This inversion is regulated by Flippase (FlpO), which itself is highly regulated, requiring cells are exposed to Cre recombinase, and then doxycycline and tamoxifen. Therefore, NINJA is compatible with most Cre-inducible GEMMs of cancer. Activating NINJA with adenoviral infection results in a strong, NINJA-specific CD8 T cell response while, in contrast, activation in the setting of lung tumors leads to T cell dysfunction. Thus, NINJA is a powerful, highly versatile system for investigating T cell function in many settings, including cancer, immune tolerance, and autoimmunity.
Citation Format: Nikhil Joshi, Tyler Jacks. Investigating endogenous anti-tumor T cell responses in native tumor microenvironments. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr A85.