LAUSR

Chimeric antigen receptor (CAR) T cells and bispecific T cell engagers have demonstrated clinical efficacy, however are often accompanied by severe toxicity including cytokine release syndrome (CRS), neurotoxicity or macrophage activation syndrome (MAS). Mechanistic understanding of the development of these toxicities and testing of therapeutic interventions is limited by a lack of suitable immunocompetent pre-clinical models. We have developed both human and murine versions of a bispecific molecule with specific activity against target expressing tumor cells in vitro and in vivo. These bispecific proteins are constructed from the extracellular portion of either mouse or human NKG2D receptor and target cells expressing the cognate ligands by redirecting T cells through their CD3 binding arm. Using the murine bispecific protein, mNKG2DxCD3, we have developed an immunocompetent mouse tumor model which exhibits treatment induced toxicity and recapitulates key features similar to those observed in human CRS. Toxicity was observed between the 2nd and 4th bispecific protein injections but was not observed following subsequent injections. Monitoring of toxicity kinetics showed transient symptoms peaking 3-4 hours following bispecific protein injection with complete resolution after 8 hours. Weight loss and elevated plasma cytokines including IFNγ, IL6, TNFα, IL2 and IL10 were also associated with toxicity. Pathology analysis showed a reduction in white pulp in the mouse spleens, however, other organs evaluated (brain, kidney, lung and heart) were normal. Using mouse genetic knockout models, we were able to show that T cells, IFNγ and Perforin were required for development of this toxicity. Additionally, In vivo depletion of either CD4+ or CD8+ T cells was sufficient to prevent the onset of toxicity. These findings highlight the importance of T cell activation and function and shed light on the mechanistic underpinnings of bispecific T cell engager protein induced toxicity. Citation Format: Claire Godbersen-Palmer, Tiffany Coupet, Zakaria Grada, Charles Sentman. Bispecific T cell engager-induced toxicity in an immunocompetent solid tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1542.