Program Description/Abstract Metabolism is the core process underlying essentially all biological functions. The goal of our research program is to discover the mechanisms linking the metabolic state of immune cells with tissue homeostasis and antitumor immunity, and to use these insights for development of better cancer treatments. We approach these questions by integrating hypothesis-driven and systems immunology approaches, and our work has produced innovation in three main areas. First, we revealed the principle of metabolic reprogramming for T cell fate, state and tolerance. Our earlier findings in metabolic control of T cell fate and state, including T cell subset-specific requirement of Warburg metabolism and mTOR signaling, contributed to the foundation and rapid growth of the immunometabolism field. More recently, we identified metabolic heterogeneity in vivo that underlies T cell fate between stemness and terminal differentiation in tumor microenvironment and inflammation, and the cycle of metabolic quiescence and quiescence exit in immune development and function. Second, we defined mechanisms of nutrient and immune signaling. We identified how nutrient and autophagic signals serve as potent regulators of cellular metabolism, and how dendritic cell-derived immune and metabolic signals are integrated by T cells. Third, we combined the traditional hypothesis-driven or ‘reductionist’ approach with systems biology principles, including in-house development of network algorithm NetBID, pooled in vivo CRISPR screening and systems proteomics, which led to the identification of new concepts and ‘hidden drivers’ in immunometabolism that cannot be surmised from simpler systems. More importantly, these approaches enabled the discovery of novel immuno-oncology targets with a clear path to clinical translation into innovative therapeutics for pediatric cancers. Our systems immunology strategies provide functionally- relevant discovery platforms to support future research in metabolic control of immunity and cancer. Specifically, the future research program will address three fundamental questions in immunometabolism and antitumor immunity, by testing the central hypothesis that immunometabolic pathways are inextricably connected to the mechanisms of adaptive immune responses and antitumor immunity; by understanding these connections, we gain new targets for the treatment of cancer: 1) How are nutrient signals sensed and integrated by immune cells? 2) How can immunometabolism be rewired to improve antitumor immunity? 3) Can we break metabolic barriers to cancer immunity and therapy, especially in therapeutically-resistant cancers? We will focus on T cells, the cornerstone for cancer immunotherapy, to gain in-depth insights, but we anticipate the findings can be tested and extended into other immune cells. Our experience in the application of multidisciplinary approaches, combined with our new development and use of novel preclinical and human diseas...