Cytokine release syndrome: grading, modeling, and new therapy

Genetically modified T cells that express a chimeric antigen receptor (CAR) are opening a new frontier in cancer immunotherapy. CAR T cells currently are in clinical trials for many cancer types. Cytokine release syndrome (CRS) and neurotoxicities (CAR-related encephalopathy syndrome, CRES) are major adverse events limiting wide deployment of the CAR T cell treatment. Major efforts are ongoing to characterize the pathogenesis and etiology of CRS and CRES. Mouse models have been established to facilitate the study of pathogenesis of the major toxicities of CAR T cells. Myeloid cells including macrophages and monocytes, not the CAR T cells, were found to be the major cells mediating CRS and CRES by releasing IL-1 and IL-6 among other cytokines. Blocking IL-1 or depletion of monocytes abolished both CRS and CRES, whereas IL-6 blocker can ameliorate CRS but not CRES. Therefore, both IL-1 and IL-6 are major cytokines for CRS, though IL-1 is responsible for CRES. It was also demonstrated in the mouse models that blocking CRS does not interfere with the CAR T cell antitumor functions. We summarized new developments in the grading, modeling, and possible new therapeutic approaches for CRS and CRES in this review.