PROJECT SUMMARY/ABSTRACT Chimeric antigen receptor T-cells (CART) have revolutionized cancer therapy. However, CART cause two common and severe toxicities: Cytokine Release Syndrome (CRS) and Immune Effector Cell Associated Neurotoxicity Syndrome (ICANS). CRS and ICANS are overlapping phenomena that occur with a spectrum of severity from mild to life threatening. Effective therapies for CRS currently exist but severe refractory cases still occur. Effective therapies for ICANS are lacking. The pathophysiology of CRS and ICANS have not yet been fully defined, precluding development and translation of novel therapies. In particular, the role of the host innate immune system in these conditions is poorly understood. The specific objective of this project is to identify the cellular and cytokine initiators of CRS and the role of complement and the inflammasome in the biology of ICANS. In Specific Aim 1, the candidate will determine the number and transcriptional activation state of different monocyte and non-monocyte populations associated with CRS using single cell RNA sequencing (scRNAseq) and test the role of novel monocyte produced cytokines in the priming and initiation of CRS. In Specific Aim 2, the candidate will dissect the role of the inflammasome and complement dysregulation in the development of ICANS, and test individual and combined approaches for inflammasome and complement blockade in preventing and treating ICANS. The candidate is a pediatric oncologist committed to understanding immune dysregulation disorders that occur as a consequence of cancer immunotherapy. The proposed training plan and research project will be conducted at the Children's Hospital of Philadelphia (CHOP) and the University of Pennsylvania (UPENN). CHOP and UPENN are leaders in cellular immunotherapies and basic and clinical immunology and will provide an outstanding environment in which to conduct the proposed research. Throughout the period of the award the candidate will be mentored by Dr. David Teachey and a very strong advisory committee including Drs. Ed Behrens, Marcela Maus, Wenchao Song and Stephan Grupp. The long-term goal of the candidate is to develop a research program devoted to understanding the role of the innate immune system in immune dysregulation related to cancer immunotherapies, and improving the health of patients by facilitating translation of less toxic, more effective immunotherapies. Completion of the proposed research project and the complementary training plan will provide a robust foundation to achieve this goal.