NINJA: an inducible genetic model for creating neoantigens in vivo

Mouse models with inducible neoantigens have been historically difficult to generate because of leaky expression of antigens in the thymus, which causes central tolerance in developing CD8 and CD4 T cells. Attempts to resolve this problem using existing genetic tools have been unsuccessful. We developed the iNversion INducible Joined neoAntigen (NINJA) mouse model that uses RNA splicing, DNA recombination, and three levels of regulation to prevent neoantigen leakiness and allow tight control over the induction of neoantigen expression. We describe the development of these genetic tools and their use for obtaining tumor cell lines with inducible neoantigen expression. Moreover, we show that the genetic regulation in NINJA mice bypasses central and peripheral tolerance mechanisms and allows for robust endogenous CD8 and CD4 T cells responses upon neoantigen induction in peripheral tissues. Thus, NINJA fills a long-standing gap in the field and will enable studies of how T cells respond to defined neoantigens in the context of peripheral tolerance, autoimmune diseases, and developing tumors.