275. Optimization of IL13Rα2-Specific CAR T Cells for Clinical Development Using Orthotopic Human Glioblastoma Models in NSG Mice
Authors: Brenda Aguilar, Aniee Sarkissian, Alfonso Brito, Renate Starr, Brenda Chang, Yubo Zhai, Lihong Weng, Michael Barish, Behnam Badie, Stephen Forman, Christine Brown
Journal: Molecular Therapy (2016)

Standard-of-care therapies for glioblastoma (GBM), the most aggressive and common type of glioma, are inadequate, resulting in an unacceptably poor median overall survival of approximately 15 months following primary diagnosis. Immunotherapeutic targeting of brain tumors offers the opportunity to redirect the potency and specificity of the immune system to improve therapeutic outcomes. Our research program has developed a CAR T cell immunotherapy for GBM targeting IL-13 receptor α2 (IL13Rα2), a cell surface receptor over-expressed by the majority of high-grade gliomas. We have optimized second-generation IL13Rα2-specific CAR T cells, incorporating enhancements in CAR design and T cell engineering to improve T cell persistence and antitumor potency. These include a second-generation CAR containing the 41BB (CD137) costimulatory signaling domain (IL13BBζ-CAR), and a manufacturing strategy using an enriched central memory T cell (TCM) population for genetic engineering. In order to optimize clinical parameters for translating this therapy to patients, we have used orthotopic human GBM models in NSG mice. For these studies we have utilized the IL13Rα2-expressing primary low-passage GBM tumor sphere line PBT030-2, which has been engineered to express both EGFP and firefly luciferase (ffLuc) reporter genes (PBT030-2 EGFP:ffLuc). We first compared the route of delivery, intravenous (i.v.) or intracranial (i.c.), for mediating optimal antitumor activity against invasive TS-initiated PBT030-2. We found that i.c. delivery of the therapeutic CAR T cells elicited superior antitumor efficacy as compared to i.v. administration, which provided no therapeutic benefit. In a multifocal disease model, we also establish that CAR T cells that were injected i.c. at one tumor site were able to traffic to a second tumor site in the contralateral hemisphere. Performing CAR T cell titration studies, we estimate that approximately one CAR T cell is required for every two IL13Rα2 tumor cells based on volumetric analysis of day 8 PBT030-2 tumors. Further, we evaluated whether CAR positivity impacted therapeutic efficacy, as our product release criteria for the clinical trial requires the therapeutic product to be at least 10% CAR positive. Indeed, we found equivalent efficacy for i.c. delivered T cells of either 10% versus 100% CAR positivity when cell doses were standardized by CAR, suggesting that unengineered T cells do not negatively impact the therapeutic potency of the CAR T cells. Finally, we evaluated the impact of corticosteroid, given its frequent use in clinical management of GBM, and demonstrate that low dose dexamethasone does not diminish T cell antitumor activity in vivo. These findings provide the rational for initiating a first-in-human clinical trial with intracranial administration of IL13Rα2-specific CD4+ CD8+ IL13BBζ-CAR T cells for the treatment of GBM.