Comprehensive Serum Proteome Profiling of Cytokine Release Syndrome and Immune Effector Cell-Associated Neurotoxicity Syndrome Patients with B-Cell ALL Receiving CAR T19

Purpose: To study the biology and identify markers of severe cytokine release syndrome (CRS) and immune effector cell- associated neurotoxicity syndrome (ICANS) in children after chimeric antigen receptor T-cell (CAR T) treatment. Experimental Design: We used comprehensive proteomic pro-filing to measure over 1,400 serum proteins at multiple serial timepoints in a cohort of patients with B-cell acute lymphoblastic leukemia treated with the CD19-targeted CAR T CTL019 on two clinical trials. Results: We identified fms-like tyrosine kinase 3 (FLT3) and mast cell immunoglobulin-like receptor 1 (MILR1) as preinfusion predictive biomarkers of severe CRS. We demonstrated that CRS is an IFN gamma-driven process with a protein signature overlapping with hemophagocytic lymphohistiocytosis (HLH). We identified IL18 as a potentially targetable cytokine associated with the development of ICANS. Conclusions: We identified preinfusion biomarkers that can be used to predict severe CRS with a sensitivity, specificity, and accuracy superior to the current gold standard of disease burden. We demonstrated the fundamental role of the IFN gamma pathway in driving CRS, suggesting CRS and carHLH are overlapping rather than distinct phenomena, an observation with important treatment implications. We identified IL18 as a possible targetable cytokine in ICANS, providing rationale for IL18 blocking therapies to be translated into clinical trials in ICANS.