Locoregionally administered B7-H3-targeted CAR T cells for treatment of atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumors (ATRTs) typically arise in the central nervous system (CNS) of children under 3 years of age. Despite intensive multimodal therapy (surgery, chemotherapy and, if age permits, radiotherapy), median survival is 17 months 1 , 2 . We show that ATRTs robustly express B7-H3 / CD276 that does not result from the inactivating mutations in SMARCB1 (refs. 3 , 4 ), which drive oncogenesis in ATRT, but requires residual SWItch/Sucrose Non-Fermentable (SWI/SNF) activity mediated by BRG1 / SMARCA4 . Consistent with the embryonic origin of ATRT 5 , 6 , B7-H3 is highly expressed on the prenatal, but not postnatal, brain. B7-H3.BB.z-chimeric antigen receptor (CAR) T cells administered intracerebroventricularly or intratumorally mediate potent antitumor effects against cerebral ATRT xenografts in mice, with faster kinetics, greater potency and reduced systemic levels of inflammatory cytokines compared to CAR T cells administered intravenously. CAR T cells administered ICV also traffic from the CNS into the periphery; following clearance of ATRT xenografts, B7-H3.BB.z-CAR T cells administered intracerebroventricularly or intravenously mediate antigen-specific protection from tumor rechallenge, both in the brain and periphery. These results identify B7-H3 as a compelling therapeutic target for this largely incurable pediatric tumor and demonstrate important advantages of locoregional compared to systemic delivery of CAR T cells for the treatment of CNS malignancies.