Abstract PR04: Locoregionally administered B7H3-targeting CAR T cells mediate potent antitumor effects in atypical teratoid/rhabdoid tumor

Abstract

Abstract Atypical teratoid/rhabdoid tumors (ATRT) are highly malignant embryonal brain tumors, arising in very young children, and are associated with inactivation of SMARCB1. The prognosis is extremely poor. Hence new treatments are urgently needed. We show that 100% of ATRT express B7-H3 and residual SMARCA4 SWI/SNF activity drives B7-H3 expression. Further, we demonstrate that prenatal brain expresses high levels of B7-H3, but expression is absent on pediatric brain, suggesting that the cell of origin may conserve high B7-H3 expression. We recently created a 4-1BB second-generation CAR targeting B7-H3. To date, there are little data on the most efficacious route of administration of CAR T cells in malignant brain tumors. The goal of this study was to test the antitumor activity of the B7-H3 CAR in highly aggressive ATRT xenograft models and compare intracavitary (IT), intraventricular (ICV), and intravenous (IV) administration in terms of efficacy, toxicity, and persistence of CAR T cells. Locoregionally (IT and ICV) administered B7H3.BB.z-CAR T cells mediate potent antitumor effects against cerebral ATRT xenografts, with more rapid kinetics, greater potency, and diminished systemic levels of inflammatory cytokines compared to CAR T cells administered intravenously. ICV-administered CAR T cells also demonstrate robust trafficking from the CNS into the periphery, and following clearance of ATRT xenografts, ICV or IV administered B7H3.BB.z-CAR T cells mediate antigen specific protection from tumor rechallenge in the CNS or in the flank. In summary, B7H3 is a promising immune target for this largely incurable pediatric tumor. We demonstrate that CNS delivered CAR T cells cure ATRT xenografts and efficiently traffic from the CNS into the periphery and can mediate long-term immune protection from disease recurrence in the CNS or in peripheral tissues. This abstract is also being presented as Poster A12. Citation Format: Johanna Theruvath, Elena Sotillo, Claus Moritz Graef, Sabine Heitzeneder, Louai Labanieh, Robbie Majzner, Crystal Mackall. Locoregionally administered B7H3-targeting CAR T cells mediate potent antitumor effects in atypical teratoid/rhabdoid tumor [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr PR04.