PROJECT SUMMARY Amplification of the oncogene MYCN drives high-risk progressive disease, resistance to therapy, and a poor overall survival rate below 45% for high-risk neuroblastoma (NB) patients. Further, more than half of all high-risk patients will relapse, and the post-relapse survival rate is only 10%. MYCN-driven NB tumors have poor immune responses due to a relatively low mutational load, low MHC-I expression, and reduced immune cell infiltration. As a result, NB is often immunologically quiescent, thus limiting immunotherapy approaches. MYCN amplification has a central role in orchestrating the metabolic reprogramming that favors NB growth and adaptation to its microenvironment. Tumor cells and immune cells exist in a complex environment where they share and compete for specific nutrients. Through unbiased transcriptomics, metabolomics, and immune profiling of TH-MYCN GEM and syngeneic mouse models of NB, we have identified cysteine metabolism as a selective vulnerability in MYCN-driven NB. We have also found that MYCN drives an immune suppressive tumor microenvironment (TME) during oncogenesis, and reprograms NB tumors to create a cysteine-poor TME. By lacking de novo biosynthetic enzymes, T cells are exquisitely vulnerable to cysteine starvation, while cysteine supplementation restores T-cell activation, expansion, and effector functions. Our central hypothesis is that MYCN-driven tumor intrinsic metabolism and recruitment of other cysteine-consuming cells (such as PMN-MDSCs) deplete extracellular cysteine, thus blocking T cell anti-tumor activity. This proposal aims to: (1) elucidate how oncogenic MYCN rewires the metabolic environment of NB to drive immune suppression; and (2) modulate the metabolic environment of NB to enhance immune-based approaches for high-risk MYCN-amplified disease.