Abstract 2567: Novel therapeutic interventions to alleviate CAR T cell-induced cytokine release syndrome

CD19 chimeric antigen receptor (CAR) therapy is highly effective for some refractory B cell malignancies. Its broad implementation is limited in part by the occurrence of cytokine release syndrome (CRS), which is characterized by fever, hypotension and respiratory insufficiency that may require intensive care to overcome. CRS is associated with elevated serum cytokines, including interleukin-6 (IL-6), the blockade of which abates CRS in some but not all patients. The biological mechanisms involved in the pathogenesis of CRS are currently unknown, including the specific role of CAR T cells, tumor cells and other host cells. The development of relevant animal models is imperative in order to study the biology of CRS, analyze the role of different cell populations and ultimately identify interventions that not only treat but prevent CRS without reducing the therapeutic efficacy of CAR T cells. Here we present a novel mouse model in which CD19 CAR-induced CRS is predictably and reproducibly elicited and mirrors the rapid onset and acuteness of clinical CRS. Symptoms present within 24 hours post CAR T cell administration, including rapid weight loss and eventual mortality. Survival correlates negatively with pro-inflammatory human (T cell-derived) and murine (host-derived) cytokine levels. A comparison between the cytokine fingerprint in patients with CRS and our mouse model revealed remarkable similarity between the two profiles. Importantly, IL-6 is elevated, as seen in patients receiving CAR therapy, but of mouse origin. In accordance with the demonstrated clinical benefit of tocilizumab, we demonstrate that CRS-associated mortality can be abrogated by murine IL-6 receptor blockade. We further show that CAR T cell - tumor interaction is required for the robust recruitment of myeloid cells to the tumor site, including neutrophils, eosinophils, macrophages, monocytes and dendritic cells. Cytokine measurements and the transcriptomic analysis of myeloid populations from multiple sites reveal that IL-6 is of myeloid cell origin, dependent on CAR T cell - myeloid proximity and interactions at the tumor site. Furthermore, we probe the impact of myeloid involvement by activating or suppressing macrophage functions to show that CRS outcomes are largely determined by macrophage engagement. Probing into the functions of macrophages led us to identify multiple therapeutic interventions that can ameliorate the toxicities of CRS. We have also designed a novel CAR construct that can prevent CRS-associated mortality while maintaining intact antitumor efficacy in a mouse model. Overall, our results suggest an indispensible role for the myeloid system in severe CRS, especially macrophages, representing a cellular compartment that has been largely overlooked in pre-clinical models to date. Moreover, our model should be useful to guide the rational design of novel CAR T cells that can autonomously ameliorate or prevent CRS. Citation Format: Theodoros Giavridis, Sjoukje J. van der Stegen, Justin Eyquem, Mohamad Hamieh, Michel Sadelain. Novel therapeutic interventions to alleviate CAR T cell-induced cytokine release syndrome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2567.