Molecular and Spatial Factors Defining Tumor-specific CD8 T Cell States in Cold Tumors - PROJECT SUMMARY Solid tumors can be classified into two broad categories, T cell inflamed (hot) and non-T cell inflamed (cold) tumors. While hot tumors are characterized by a tumor microenvironment enriched in T cells, cold tumors of the immune dessert phenotype, (e.g. pancreatic and breast) lack T cell infiltration. Human cold tumors exhibit profound resistance to immune checkpoint blockade which represents a major therapeutic challenge. To design predictably effective immunotherapies for cold tumors, we must elucidate the mechanisms that control tumor- specific CD8 T cell (TST) dysfunctional states and therapeutic reprogramming. To fill this knowledge gap, I utilize clinically relevant autochthonous cold tumor models, including an oncogene-driven insulinoma model. Tracking TST differentiation longitudinally from cancer initiation to terminal endpoints, I find that TST reside in tumor draining lymph nodes (tdLN), but fail to infiltrate the pancreas, recapitulating the cold tumor immune phenotype of human insulinomas. TdLN TST express numerous inhibitory receptors (e.g. PD1, LAG3) and fail to produce effector cytokines (IFNγ, TNFα). Despite their exhausted phenotype, TST express high levels of transcription factors critical for T cell stemness and self-renewal. Strikingly, tdLN TST of do not generate differentiated progenies, which is in sharp contrast to observations in murine and human hot tumors. This poses the intriguing question whether the inability to differentiate in tdLN is a hallmark feature of TST in cold tumors. Interestingly, over the course of tumorigenesis, tdLN TST lose their ability to respond to immunotherapeutic strategies. My working hypothesis is that TST in tdLN of cold tumors fail to differentiate into effector-like TST, which is associated with the inability to egress the tdLN and infiltrate into tumors. In this application, I will leverage the power of autochthonous tumor mouse models as well as human samples, to identify the molecular and spatial factors that determine TST states in cold tumors and elucidate mechanisms of resistance and responsiveness to immunotherapeutic approaches.
