Abstract LB-107: Repurposing endogenous immune pathways to improve chimeric antigen receptor T-cells potency

CAR T-cell therapies hold great promise for treating a range of liquid malignancies but are however challenged to access and eradicate solid tumors. To overcome this hurdle, CAR T-cell were engineered to secrete different cytokines known to improve T-cell antitumor activity, prevent T-cell anergy and reduce activation induced cell death. While cytokine-expressing CAR T-cell were shown to be be highly active against solid tumor in in vivo models, they have also led to toxicity associated with the systemic release of cytokine. Therefore, new engineering strategies enabling the fine tuning of cytokine secretion by CAR T-cell are warranted. We sought to explore one of these engineering strategies by integrating an IL-12 chimeric heterodimer expression cassette under the control of the endogenous promoters regulating PD1 or CD25. Because both genes are known to be activated upon tumor engagement by CAR T-cells, they could be repurposed to secrete cytokine only in the vicinity of a given tumor. This approach would reduce the potential side effects induced by their systemic secretion while maintaining their capacity to improve antitumor activity. By combining TALEN® technology with AAV6 repair vectors delivering the CAR to the TRAC locus and the IL-12 to the CD25 or PD1 loci, we have engineered CAR and IL-12 expressions under the respective control of TCR and CD25 or PD1 regulatory elements. This double targeted insertion led to the disruption of PD1 and TRAC genes, to the expression of a tool CAR and to the conditional secretion of IL-12 in the media. Such secretion was found to be transient, dependent on tumor engagement and to follow the regulation patterns of CD25 or PD1 genes, commonly observed upon T-cell activation. In addition, it was also found to enhance the antitumor activity and the proliferative capacities of CAR T-cells. Similar results were obtained when IL-15 was substituted for IL-12. This proof of concept paves the way for seamless multi-repurposing of immune pathways to generate smarter CAR T-cells able to sense and react to their environment in a highly regulated and specific manner. Citation Format: Mohit Sachdeva, Brian Busser, Sonal Temburni, Alexandre Juillerat, Laurent Poirot, Philippe Duchateau, Julien Valton. Repurposing endogenous immune pathways to improve chimeric antigen receptor T-cells potency [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 LB-107.