Abstract LB-187: New methods for controlling CAR T cell-mediated cytokine storms
Authors: Lee Yong Gu , Chu Haiyan , Low Philip S. 
Published: July 2017

Abstract
Use of chimeric antigen receptor (CAR) T cells to eliminate tumors has attracted considerable attention due to their ability to eradicate otherwise difficult to treat leukemias. For example, although remarkable success has been reported in CAR T cell treatment of ALL (e.g. up to 70-93% complete responses), the technology is still plagued by the common occurrence of a cytokine storm (a.k.a. cytokine release syndrome) that causes fever, nausea, chills, hypotension, tachycardia, asthenia, headache, rash, dyspnea and sometimes death. Indeed, this inability to control the rate and degree of cytokine release has forced the interruption of several CAR T cell clinical trials, emphasizing the need for development of a reliable method to regulate the activation state of these genetically engineered cells. We have recently designed several novel methods to control the rate and extent of CAR T cell activation by using a bispecific adaptor molecule to mediate engagement of the CAR T cell with the cancer cell. In this strategy, the CAR T cell is designed to contain the usual 4-1BB and/or CD28 insert in the cytoplasmic domain of CD3ζ, but with an scFv that binds fluorescein instead of a tumor-specific scFv in the exoplasmic domain. The resulting CAR T cell can then only bind and kill a cancer cell when the bispecific adaptor, formed by linking fluorescein to a tumor-specific ligand, can establish a bridge between the CAR T cell and the cancer cell. Using the adaptor, fluorescein-folate, which bridges between our anti-fluorescein CAR T cell and any folate receptor-expressing cancer cell, we explore several novel strategies for regulating a cytokine storm, including: 1) discontinuation of bi-specific adaptor administration, 2) injection of excess folate to block/compete for adaptor bridging of the CAR T cell to the cancer cell, 3) use of a very low or very high dose of adaptor, 4) or gradual escalation of bi-specific adaptor dose. We show here that all of the above strategies mitigate/eliminate a cytokine storm, but at very different rates and with very different potencies. Thus, simultaneous discontinuation of adaptor administration combined with injection of excess free folate (i.e. methods 1 & 2 concurrently) promote the most rapid decline in a cytokine storm, whereas either method by itself affords the same outcome at a slower rate. In contrast, metronomic administration of a low adaptor dose or gradual escalation of adaptor dose over several days can totally prevent a cytokine storm under conditions where it would otherwise be prominent. Because the circulation half-life of most bi-specific adaptors is ~30 min, these data demonstrate that unwanted toxicity from CAR T cell-induced cytokine storms can be either pre-emptively prevented or rapidly suppressed following their emergence by use of anti-FITC CAR T cells together with easily adjustable bi-specific adaptor molecules.
Citation Format: Yong Gu Lee, Haiyan Chu, Philip S. Low. New methods for controlling CAR T cell-mediated cytokine storms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-187. doi:10.1158/1538-7445.AM2017-LB-187